Protein Synthesis Worksheet: Definition, Examples & Practice

Meta: Need to learn how protein synthesis works? We’ve got your complete guide to the process on our protein synthesis worksheet, including the difference between DNA and RNA, important misconceptions about mutations, and an explanation of the central dogma of biology. Plus, get practice exercises and quiz questions. 

 

What is Protein Synthesis?

 

Protein synthesis is the construction of proteins within living cells. The process consists of two parts; transcription and translation.

Proteins are an important organic compound that exists in every living organism. They are an essential part of the majority of cell functions. Specific proteins are needed for particular functions. Proteins are made up of long chains of amino acids which can be arranged in either a linear pattern or can be folded to form a more complex structure.

Proteins can be complex in structure and so are filtered into four categories – primary secondary, tertiary and quaternary.

Protein synthesis is a biological procedure which living cells perform to create new proteins. When studied in detail, the chemical synthesis of proteins process is extremely complex. The process begins with the production of new and different amino acids, some of which are collected from food sources.

The process requires ribonucleic acid (RNA), deoxyribonucleic acid (DNA), and a specific set of enzymes. All the different types of ribonucleic acids are needed for protein synthesis to work effectively. These are messenger ribonucleic acid (mRNA), transfer ribonucleic acid (tRNA), and ribosomal ribonucleic acid (rRNA).

 

 

Protein Synthesis: Definition, Examples, and Practice

Let’s check out a couple of important definitions to better understand protein synthesis.

Most protein synthesis worksheets will require a working understanding of the following definitions:

Central Dogma of Biology

A polypeptide encoded in a gene is expressed in a directional relationship called the central dogma of biology. It recognizes that information moves from the DNA to the RNA to the protein.

DNA

Deoxyribonucleic acid (otherwise known as DNA), is the carrier of genetic info found in almost every found living organism to date. It is present in the nucleus of cells and is self-replicating, meaning it’s integral to protein synthesis.

RNA

RNA is ribonucleic acid, and it’s present in every living cell discovered to date. It is a messenger and vitally involved in translating genetic code from DNA to the ribosomes so that amino acids can be created.

There are three kinds of RNA: messenger RNA (mRNA) transfers the genetic code from the DNA in the nucleus out to the ribosomes in the cytoplasm. Ribosomal RNA (rRNA) provides the structure for the ribosomes. Finally, transfer RNA (tRNA) works during translation to bring the amino acids to the ribosome so that a polypeptide (an amino acid chain) can be built.

Transcription

Transcription is the stage of manufacturing in which the DNA gene sequence is copied so that an RNA molecule can be made. We’ll explain more shortly.

Translation

The second stage of protein synthesis is translation. At this point in the process, a mRNA (messenger RNA) molecule is “read” and the information is used by the ribosome to build a polypeptide.

Polypeptide

A polypeptide is a chain made up of amino acids.

Codon

Three nucleotides form a codon. This codon is then used to create amino acids.

RNA vs. DNA

It’s tempting to confuse RNA with DNA, but they’re very different, and it’s important to understand these differences. They are both made up of nucleotides, which are the basic units of nucleic acids (like DNA and RNA). These nucleotides contain a phosphate group, a nitrogenous base, and a 5-carbon sugar ribose.

Instead of DNA’s ribose, however, RNA uses deoxyribose, a different kind of sugar. Also, RNA is most often a single strand, while DNA is famously double-stranded. Finally, DNA contains thymine, while RNA uses uracil instead.

Chromosomes

DNA is found by the meter inside even minuscule cells. During replication, the masses of coiled DNA called chromatin (shaped thanks to proteins called histones) organize into what are called chromosomes.

Different types of cells (eukaryotes) have chromosomes in varying amounts. Humans, as you probably know, have 46 chromosomes, while dogs, for example, have 78.

Transcription and Translation

To best understand your protein synthesis worksheet, let’s cover the complete protein synthesis process. It starts with transcription. Special enzymes in the nucleus arrive to gently pull apart the DNA code needed, and RNA begins to transcribe or rewrite the genetic material.

During translation, the mRNA connects with the ribosome and its information is decoded again so that the correct sequence of amino acids will connect to form a polypeptide. It’s important to note here that the ribosome doesn’t make protein nor does it make amino acids. It simply instructs already-made amino acids to form the correct sequence.

The amino acids’ sequence determines its protein’s shape, function, and properties and it can do so thanks to the RNA’s four bases (all of which are nucleotides): adenine (A), cytosine (C), guanine (G), and uracil (U). A codon, as we explained earlier, is a combination of three of these bases in a specific order: UUC, for example.

Some codons tell the ribosome to start or stop (UAA, UAG, and UGA indicate stop) and the rest indicate specific amino acids.

Understanding the Codon Table

codon table by cabal edu, protein synthesis worksheet

Image Source: sabal.uscb.edu

The heart of protein synthesis (and what you’ll most likely see on a protein synthesis worksheet) is the codon table. It helps us work through translation to understand the amino acids the mRNA is prescribing. For example, if you want to know what the codon CAA translates to, you’ll use the first letter of the codon (C) to locate the corresponding row on the left side of the chart.

Next, use the second letter of the codon (A) to identify the corresponding column on the top of the chart. The box indicated includes four codons that began with C and A; if you’d like, you can simply identify your codon there, or you can use the right side of the chart to identify the corresponding order of the third letter in the codon (A).

Either way, the single amino acid for CAA is Gln (glutamine).

Mutations

Mutations sound scary, but don’t worry–we’re not talking about superheroes with latent power and plans for world domination. Instead, we’re talking about what happens when there’s a mistake in the transcription or translation process.

Mutations come in three forms: silent, missense, and nonsense. A mutation that is silent means that the amino acid will not be impacted during translation. Missense mutations mean that the single amino acid has been changed and a nonsense mutation ends prematurely.

How are Mutations Caused?

There are several different reasons a mutation may occur. If at least one base is added to a DNA sequence, this is referred to as an insertion. A deletion, however, occurs when at least one base has been removed from the DNA sequence.

Similarly, when a change is made to the codons so that the reading frame of the sequence is changed, the resulting mutation is called a frameshift mutation. For example, a mRNA codon that reads AUG-AUA-CGG-AAU might experience an insertion of a T in the DNA sequence.

This frameshift mutation leads to a new codon: AUG-UAC-GGA-AU.

If we utilize the codon chart, we find that the polypeptide mutates from Met-Ile-Arg-Asn to Met-Tyr-Gly.

Common Misconceptions About Mutations

Something important to note is that sometimes the DNA sequence experiences an insertion or deletion of three nucleotides in a row. This doesn’t cause a frameshift mutation. Instead, it will just impact whether or not the deleted or inserted amino acids are added or not.

This can cause a dramatic change in the outcome of the polypeptide.

Another common misconception is that a mutation is always dramatic. While this is sometimes the case, mutations are common and provide the genetic variation we so appreciate in life. Many mutations have little to no impact on life, and some mutations even create good changes.

It’s a very limited number of mutations that survive to be problematic.

 

What Exactly Are Genes?

 

A gene is a short section of DNA that acts as an instruction manual for our bodies. DNA is found inside almost every cell in the body.

Genes contain the instructions that tell cells to create new proteins via protein synthesis. Every gene carries certain instructions which make up who you are such as eye color, height, and hair color. Genes come in many different types and versions for each feature. For example, one variant of a gene may contain instructions for blue eyes whereas another contains instructions for brown eyes. Genes are so small that there are around 20,000 inside each cell in the body. The entire sequence of your genes is named the genome.

 

How Do Genes Work?

 

Genes are responsible for telling each of your cells what to do and when to do it. They do this by making proteins. Why are proteins important? Well, our bodies are made up of proteins. Around 50% of a cell is some form of protein. Proteins are also responsible for many bodily functions such as digestion, immunity, circulation, motion, and communication between cells. These are made possible by the estimated 100,000 different proteins that are produced in the body.

Genes within your DNA don’t make proteins directly. Instead, enzymes read and copy the DNA code. The section of DNA that is to be copied gets unzipped by an enzyme which then uses that segment of DNA as a template to build a single-stranded molecule of ribonucleic acid. This ribonucleic acid then leaves the nucleus of the cell and enters the cytoplasm where ribosomes then translate the code to create the specific protein.

In certain genes, not all of the DNA sequence is used to make a protein. The section of DNA that is non-coding is known as introns. The coding sections of DNA are called exons.

 

The Structure of DNA

 

DNA is made up of pairs of nucleotides on a phosphate and sugar backbone. There are four different nucleotides: thymine, cytosine, guanine, and adenine. Each of the types of nucleotides only pairs with one other type. Hydrogen bonds connect to those nucleotide pairs. The sugar and phosphate backbone, along with the nucleotide pairs form a ladder-like structure that twists to form the double helix structure of DNA. Each side of this ladder shape is known as a strand of DNA.

 

Nucleotides consist of a base, a phosphate group, and five carbon atoms. Each of the different types of nucleotide has a base with a different structure, however, all the bases contain nitrogen. The four bases can be split into two groups. These are pyrimidine bases and purine bases. Pyrimidine bases are small and have one six-atom ring. Purine bases are larger and are made up of a six-atom ring plus a five-atom ring which are joined by two shared atoms. Thymine and cytosine are pyrimidine bases and adenine and guanine are purine bases.

 

Pyrimidine bases bond to purine bases because the shapes of these bases allow hydrogen bonds to form between them. The base pairing rules states that guanine pairs only with cytosine and adenine pairs only with thymine. This rule is known as complementary base pairing. Three hydrogen bonds form between a guanine and cytosine pair whereas only two hydrogen bonds form between an adenine and thymine base pair.

 

Protein Synthesis Worksheet Practice

It’s helpful to utilize practice protein synthesis worksheets. To help you, here’s a list of questions–and their answers–that you’re likely to find on tests, worksheets, and protein synthesis projects:

  1. During translation, which RNA carries amino acids to the ribosome? (transfer RNA or tRNA)
  2. Is DNA made with uracil or thymine? (thymine)
  3. In which part of the cell does transcription happen? (in the nucleus)
  4. Which RNA carries the genetic code to the ribosomes from the DNA? (messenger RNA or mRNA)
  5. What is the central dogma of biology? (DNA → RNA → protein)
  6. What are the building blocks of proteins? (amino acids)
  7. What are the three causes of mutations? (insertion, deletion, and frameshift)
  8. What is a codon? (three nucleotides)
  9. What are the three differences between DNA and RNA? (RNA uses deoxyribose instead of ribose, is single-stranded instead of double-stranded, and contains uracil instead of thymine)
  10. In what phase is tRNA molecules used? (translation)
  11. Does protein synthesis build protein? (no; protein synthesis builds amino acids)
  12. What are polypeptides? (chains of amino acids)
  13. What do codons do? (indicate the specific amino acid and in what order, and indicate when to stop and start the amino acid chain)
  14. Which leaves the nucleus: DNA or RNA? (RNA)
  15. What are the three kinds of mutations? (silent, missense, and nonsense)
  16. Which codons indicate stop? (refer to the codon chart for the answer; UAA, UAG, and UGA)
  17. What does chromatin organize into during replication? (chromosomes)

Practice with the Codon Chart

Another great way to increase your knowledge of protein synthesis and better prepare for protein synthesis worksheets is to practice with the codon chart. You can find the solutions in parenthesis after the example:

  1. CUU-CGU-AAU-UGG-AAG (leu-arg-asn-trp-lys)
  2. ACU-ACA-AGU-UGC-UUU (thr-thr-ser-cys-phe)
  3. AAC-AAG-GUC-GUC-AGG (asn-lys-val-ile-arg)

Protein synthesis is a complex, highly tuned process that enables life to flourish. Understanding it, from the DNA to the RNA to the amino acids, gives us a better appreciation for life itself. Use our protein synthesis worksheet practice questions to help you learn the ins and outs of protein synthesis and remember the informaion.

Dihybrid Cross Worksheet: Definition, Examples, Practice & More

Genetics plays a significant role in our understanding of how living organisms come to be as well as bettering our overall knowledge of Biology and cells. Learn more about a dihybrid cross worksheet and the role it plays in genetics. 

 

Dihybrid Cross Worksheet: Definition, Examples, and Practice

 

It’s incredible to think that genetics can play a role in how we look, feel, express, and even taste things and it can also play an integral part in what kind of apple grows on a tree, as well as the cells that multiply within us. Genetics is an essential part of understanding all living things and can help us to understand Biology better overall.

Like many aspects of science, genetics is not cut and dry. Often people think they have it all figured out and then become easily confused by another factor. Dihybrid cross is a standard experiment in genetics that students of Biology will study.

We will discuss what it is and help you understand it better, so you can express, explain, and answer any of the questions when your instructor hands you a dihybrid cross worksheet.

 

What Is A Dihybrid Cross Worksheet?

 

Dihybrid cross in the “mating experiment between two organisms that are identically hybrid for two characteristics.” What’s a hybrid organism? It’s one that is heterozygous (or monohybrid), which means that it has two different genes (or alleles) at a specific point (this point is often referred to as a locus).

A significant amount of organisms, who can sexually reproduce via the sperm and egg process, have two copies of each gene, which allows them to carry two different alleles. An organism that has parts from two different “true-breeding” lines is often referred to as a hybrid.

While machines or vehicles are not living things, we can easily form a comparison to hybrids; we can also consider this concept when thinking about mixed-breed dogs that have two purebred parents, such as a Puggle or Maltipoo.

The concept and name of the dihybrid cross comes from experimenting with and observing the generations that are produced after two “pure” lines reproduce. A dihybrid cross worksheet allows us to predict how likely an offspring is to inherit a particular single trait.

 

How to Set Up a Dihybrid Cross Worksheet

 

A dihybrid cross worksheet will help to predict and determine the genotype of an offspring. It does this by determining all the possible combinations of alleles in the gametes of each of the parents.

As an example, half of the gametes get a dominant S and a dominant Y allele. The other half get a recessive s and a recessive y allele. In this case, both parents are producing 25 percent of each of the following: SY, Sy, sY, and sy.

Since each of the parents, in this case, are producing four different combinations, we must draw a four by four punnett square. We must then list the gametes from one of the parents alone one edge of the punnett square, and the gametes for the other parent along another edge of the punnett square. We will then list in each square, the alleles for the first parent, followed by the addition of the alleles from the second parent. Each combination should contain a dominant-recessive allele. 

The final result will form a diagram of all of the possible combinations of genotypes for the offspring of these two parents.

Try out this method out on a dihybrid cross practice worksheet. 

 

What is Dominant and Recessive? 

 

The terms “dominant” and “recessive” refer to the inheritance patterns of certain characteristics. This describes how likely it is for a certain phenotype to be passed on from a parent to their offspring.

Beings that reproduce sexually via the sperm and egg process have two copies of each of their genes. Each of these copies, which are known as alleles, are slightly different and never identical. These differences can affect the rate and variation of proteins that are produced. As proteins affect traits, these differences can affect and produce different phenotypes.

Dominant alleles produce dominant phenotypes and dominant traits in people who have one copy of the allele, which comes from just one parent. In order for a recessive allele to produce a recessive phenotype, the being must have two copies, one from each of the parents. Someone that has a dominant and a recessive allele for a gene will have the dominant phenotype and not the recessive phenotype. This means that they are then considered “carriers” of the recessive allele. This is because the recessive allele is there, however, the recessive phenotype is not.

Dominant and recessive disorders can occur when a person has “broken” genes. This results in a broken code for a protein that doesn’t work properly. Since one regular copy of a gene can mask the effects of a broken gene, many disorders of this type are recessive in their single trait inheritance pattern. However, not all disease alleles are recessive.

 

Monohybrid Cross Example

 

A monohybrid cross is defined as a genetic cross mix between individuals who have homozygous genotypes, or genotypes which completely recessive, or completely dominant alleles. This results in opposite phenotypes for a particular genetic characteristic.

 

Following is an example of a monohybrid cross experiment performed by Gregor Mendel…

 

Mendel’s Dihybrid Cross Experiment

 

gregor mendel, dihybrid cross worksheet

 

Gregor Mendel is well known for his work in the field of genetics, and he performed various genetic experiments, including the dihybrid cross, on pea plants in the late 1800s. When he performed dihybrid crosses on plants, he discovered his Law of Independent Assortment.

You might already be familiar with this law of genetics and that it refers to when two or more characteristics are inherited through reproduction, individual hereditary factors independently assort (during gamete or egg production) and give different traits an equal opportunity to occur together.

Even though Mendel was famous for experimenting on pea plants (mostly because the seeds were cheap and readily available), we can consider the dihybrid cross experiment with every living organism from the food we grow to an expanding family.

 

Let’s observe how Mendel’s Dihybrid Cross experiment looks.

 

Crossing The P Generation

 

pea plant under sunlight, dihybrid cross worksheet

 

Mendel chose a pea plant that was homozygous and dominant for round (RR) yellow (YY) seeds. He crossed the plant with a pea plant that was homozygous and recessive for wrinkled (rr) green (yy) seeds. Remember, homozygous is a particular gene that has identical alleles.

The notation for crossing the two pea plants is RRYY x rryy. The organisms in this first cross are the parental generation or P generation, which should make sense since they are the “parental” organisms that will be reproducing.

The direct offspring from the P generation (RRYY x rryy cross) is known as the F1 generation. All of the plants from the P generations were heterozygous and had round yellow seeds; the genotype was RrYy.

 

Crossing The F1 Generation: Dihybrid Cross

 

The dihybrid cross didn’t occur until Mendel crossed two pea plants from the F1 generation and the notation was RrYy x RrYy. The result of the dihybrid cross gave Mendel the F2 generation and a ratio of 9:3:3:1. Here’s what the ratio means:

  • Nine pea plants with round, yellow seeds
  • Three pea plants with round, green seeds
  • Three pea plants with wrinkled, yellow seeds
  • One pea plant with wrinkled, green seeds

From his findings, Mendel deduced that certain pairs of traits in the P generation sorted independently from one another, from one generation and into the next, and that there is never an equal chance of trait occurrence.

 

Clarifying The Difference Between A Dihybrid and Monohybrid

 

Until you get a solid understanding of genetics and cells, dihybrid and monohybrid can be a little confusing, even after we’ve discussed Mendel’s experiment, so let’s clarify the two.

Remember, the dihybrid cross deals with two traits and as the name suggests, the monohybrid centers around a difference in just one trait. The parental organisms are both homozygous for the trait being studied (such as color) but have different alleles for that trait.

One parental organism is homozygous dominant, and the other is homozygous recessive. The F1 generation in a monohybrid is all heterozygous (like the dihybrid cross). F2 generation is typically three-fourths dominant phenotype and one-quarter recessive phenotype.

 

 

Applying The Dihybrid Cross Experiment

 

Mendel’s pea plant dihybrid cross experiment is groundbreaking and helped to form genetics as we know it today, but let’s observe a few other examples…

 

What Are Some Examples of a Dihybrid Cross Worksheet?

 

Fruit Flies

 

fruit flies, dihybrid cross worksheet

 

If you were studying fruit flies and wanted to use the dihybrid cross experiment on them, where would you begin? Some may say that you should breed the hybrid flies together while others would recommend counting the number of each type of fruit fly you have.

The first step is to establish the lines of homozygotes. If you want your heterozygotes to breed, you have to ensure that the P generation is “true.”

In order to get a line of homozygotes, you would need to breed the lines repeatedly and select the flies that only show one allele for each characteristic in their offspring. It would be a lengthy process, but that’s the only way a dihybrid cross experiment could be successful.

 

Summer Squash

 

summer squash, dihybrid cross worksheet

 

Ready for another example that you might find on a dihybrid cross worksheet? Let’s take a look at this problem.

Find the phenotypic and genotypic ratios for the F1 and F2 generation of summer squash. The summer squash has white fruit color (W), which has dominance over yellow fruit color (w). The disk-shaped fruit (D) has dominance over the sphere-shaped fruit (d).

What results will we have if we cross a squash plant true-breeding for white, disk-shaped fruit with a squash plant true-breeding for yellow, sphere-shaped fruit? Remember, we’re looking for the ratios of F1 and F2 generations.

The P1 geno and phenotypes should be WWDD (white, disk-shaped fruit) x wwdd (yellow, sphere-shaped fruit). To figure out your results, you’ll enter your information into a Punnett Square (you can see how this should look when you click on the genetic cross worksheet that we have listed above).

The results for the F2 generation ratios will form the following:

1:2:2:1:4:2:1:2:1 genotypic ratio (look at the details below)

  • 1/16 will be homozygous dominant for both traits (WWDD)
  • 2/16 will be homozygous dominant for color and heterozygous for shape (WWDd)
  • 2/16 will be heterozygous for color and homozygous dominant for shape (WwDD)
  • 1/16 will be homozygous dominant for color and homozygous recessive for shape (WWdd)
  • 4/16 will be heterozygous for both traits  (WwDd)
  • 2/16 will be heterozygous for color and homozygous recessive gene for shape (Wwdd)
  • 1/16 will be homozygous recessive for color and homozygous dominant for shape (wwDD)
  • 2/16 will be homozygous recessive for color and heterozygous for shape (wwDd)
  • 1/16 will be homozygous recessive for both traits (wwdd)

9:3:3:1 phenotypic ratio (look at the details below)

  • 9/16 will have white, disk-shaped fruit
  • 3/16 will have white, sphere-shaped fruit
  • 3/16 will have yellow, disk-shaped fruit
  • 1/16 will have yellow, sphere-shaped fruit

The Offspring of Made-Up Creatures

 

Let’s take a look at one more example for variety (and practice).

Imagine a made-up creature that has yellow eyes and green fur. We can assume that both creatures are heterozygous for yellow eyes and green fur, let’s find out the genotype and phenotype of the creature’s offspring; Yellow eyes are E, and green fur is F. The recessive traits are red eyes (ee) and yellow fur (ff). What is the chance that the baby will have red eyes and yellow fur?

First, we need to find the genotype of the parents. Remember that they are heterozygous, which means the genotype is Ee for the eyes and Ff for the fur.

After you form your Punnet Square, you should list every possible combination: E-F, E-f, e-F, e-f. If you’ve filled out your square correctly, there’s a one in 16 chance that the creature’s baby will have red eyes and yellow fur because only one box equals the combination eeff.

As you can see the summer squash problem is a little more complex and time-consuming than Mendel’s pea plant (and the made-up creature is a little bit silly), but with practice and the right information, you can complete any problem on a dihybrid cross worksheet with relative ease and determine the likelihood that certain cells and traits will be produced in an offspring.

 

Practicing Dihybrid Cross Worksheets

 

A simple search in Google will bring up many different practice worksheets to help you build upon your skills of creating a dihybrid cross worksheet of your own. Many of these practice worksheets will include a dihybrid cross worksheet answer key so that you can practice yourself and be sure that you are doing them correctly. 

Practicing will ensure that you are ready to answer any questions that your college or university professor may have for you regarding a dihybrid cross worksheet.

Works Cited Page Example for MLA, APA, Chicago, and More

Whether you’re writing a research paper for Biology class or putting together a presentation, it’s important to do your research and cite your sources. Never know which works cited style to use? Learn more about MLA, APA, Chicago, and other helpful hints.

Works Cited Page Example for MLA, APA, Chicago, and More

opening a book

Research projects are a lot of work, but it’s worth all the hard work when your instructor gives you rave reviews, and you’ve earned top marks. You’re able to be successful on your research paper or presentation because you spent time reading dozens of articles and journals written by scholars and scientist.

Since they spent years of research to provide you with essential information, it only seems fair to give them credit, right? Citing your sources properly might be a little confusing, but we’ll discuss some of the different citation styles, share a works cited page example for each style, and give you all the information you need to give proper credit where it’s due.

Why Citing Is Important

Few people will argue with the fact that citing your sources is important, but you might be curious if it’s truly necessary. The answer is yes, and there are a few reasons why it’s so crucial. Not only does it give researchers, scholars, and other writers appropriate credit, but citing is a “must” for the following reasons:

  • Avoiding confusion or “alternative facts”
  • You won’t be accused of plagiarism
  • It shows your professors, classmates, and readers that you know how to conduct research
  • You learn more as a researcher
  • You become a better writer
  • It shows that you’re respectful and responsible

What To Cite and What Not To Cite

Depending on the citation style you use, there may be come different rules but if you’re wondering what should be cited in your work and what’s not necessary, here are some general rules.

DO Cite

  • Books and journal articles
  • Newspaper, magazines, brochures, and pamphlets
  • Film, television, ads
  • Websites and other electronic resources
  • Letter, email, forums
  • Personal interviews
  • Diagrams, charts, photos, and other graphics

You Shouldn’t Need To Cite (But Double-Check)

  • Your own collected data in a field study
  • Your notes
  • Your own journaling
  • Your opinions
  • When you use “common knowledge”
  • Well-known facts

An In-Depth Look At Citation Styles

Now that we’ve briefly discussed the importance of citing sources and the do’s and don’t, let’s take an in-depth look at some of the most common citation styles you may use throughout your academic career.

While you already know what a citation is, you may not understand what a citation style is or how one works. Citation style is the rules for formatting, how the information you cite in an article or project is ordered, and how to punctuate; each style has specific rules for citing information.

If you’re unsure of what type of citation style you should use, always ask your professor. It’s best to double-check rather than assuming. Citing information incorrectly can take up a lot of your valuable time, and it can also negatively affect your grade.

 

APA

APA is also known as the American Psychological Association, and this style is frequently used in the social sciences. Some general highlights of this style include an essay with a title page, abstract, main body, and references.

It should also be typed and double-spaced on standard 8.5 x 11” paper (with 1” margins on all sides). The recommended font is 12 pt. Times New Roman and page headers are a must.

When you create your works cited page, you should have References centered at the top, double-space the list, and the first line of your citation should be indented one half-inch from the left margin. The list should also be alphabetized. For more information on APA style and a works cited page example, click here.

 

MLA

MLA, also known as Modern Language Association, is a citation style commonly used by the Humanities. There are many similarities between APA and MLA, but rather than References and the end of your essay; you should have the words “Works Cited.”

A works cited page example will show you that you should have an alphabetized list and the second line of the citation should be indented.

 

Chicago

The Chicago Manual of Style (CMS) is a citation style that is used in the social sciences and the humanities. Rather than a works cited page, a note and bibliography or author-date is needed at the end of the paper. Notes and bibliography are often requested for arts, literature, and history while author-date style is better suited for science and social sciences..

As you explore CMS, you may also come across the Turabian Style, which is a variation of CMS and may be used in social or natural sciences and in the humanities.

Now that we’ve given you some of the most commonly used citation styles, let’s take a look at some other styles that you might be asked to use at some point in your academic or professional career.

If you continue to study the sciences, you may be asked to use the following citation styles:

  • American Chemical Society (ACS) for Chemistry
  • American Institute of Physics (AIP) for Physics
  • American Medical Association (AMA) for Medical Sciences
  • American Mathematical Society (AMS) for Mathematics
  • Council of Science Editors (CSE) for Biology
  • National Library of Medicine (NLM) for Medicine

If you study the social sciences or law, you may be asked to use the following styles:

  • Association of Legal Writing Directors (ALWD) for Legal Studies
  • American Political Science Association (APSA) for Political Science and International Studies
  • American Sociological Association (ASA) for Sociology
  • Bluebook for Legal Studies
  • Maroonbook for Legal Studies

Other citation styles include Harvard Business School, Associated Press (AP), and Linguistic Society of America (LSA).

Finding Citation Style Resources

eyeglass on top of a book

It would take a long time to explain each citation style in detail; thankfully, there are several resources available (and a majority of them are online). Depending on your coursework, you may have instructors that require you to purchase a citation style manual.

Even if it’s not a course requirement, it’s great to have on hand, and you may be surprised how often you use the manual. Although many people shy away from hard copy resources and would instead use the convenience of the internet, owning an official citation style guide may be more accurate and easier to use than finding all the information you need online.

While there are plenty of online resources that are legitimate, convenient, and helpful, don’t be afraid to utilize a writing or academic center if one is available; the people who work in these centers are knowledgeable in all citation styles and can help you make sure that you know which style to use.

If you don’t have a center nearby, head to your public library; a librarian should be able to assist you.

A writing or academic center can also be a great resource if you need someone to proofread an essay before you submit it to your professor. If you have any doubts about how your project or paper is formatted, you should get the feedback you need.

What About Citation Software?

software used in inserting citation

Making sure you cite your sources correctly is definitely important and some people will go so far as to use citation software. Citation management software is also known as bibliographic software, and it helps you organize, store, and retrieve information from the sources you use (like books, articles, journals, online resources, and websites).

Depending on the software you use, you might be able to import records or PDFs from databases and add abstracts and keywords to your paper or project. Once you’re ready to cite your sources, the software helps you create a bibliography.

While citation software can be a helpful tool, it should not be your “go to” solution for the proper citing of sources. The software is not flawless, and you still need to know the basic guidelines of the citation style that you’re using (such as MLA or APA).

Another option to try, when you need a little extra help with citing your sources, is an online citation builder. These are often free and can help you do citations quickly. Builders do not work the same as software.

Some Final Words On Citation Styles

As you can see, there are many different citation styles to choose from, and while some are specific, you might have a few style options (depending on your paper or project). If you’re unsure of what style to use, always ask.

If you use a couple of different citation styles on a regular basis, it’s a wise investment to purchase a hard-copy of the style guide; these are relatively inexpensive and easy to find. If you’re buying a used copy of a style guide, make sure that it has all the up-to-date information and if not, be sure to gather the right info to make it a current guide.

Citations are important, and while it may feel like an overwhelming part of writing a paper, it can be easy as long as you know the basics of the citation style and how to create the appropriate works cited page.

Using a Heart Model to Study for AP Biology – Explore On a Deeper Level

Students in AP Biology have more opportunities for in-depth and hands-on experiences in the classroom. Learn how using a heart model to study can be beneficial when taking AP Biology.

Using A Heart Model To Study For AP Biology

heart model 500x500px

Since Biology is the study of living organisms, it’s essential to learn about and understand how the heart works. Although the basic functions of the heart are often taught at an early age and in elementary school, AP Biology provides the perfect opportunity to explore the unique organ at a deeper level.

While there are typically many lab sessions where students have the chance to examine and dissect a real heart, it’s not always the ideal model when studying the heart. We’ll discuss some of the ways that using a heart model can enhance and improve the overall learning experience in AP Biology.

Taking A Look At Heart Models

Walk into any AP Biology lab or even a doctor’s office, and there’s a good chance that you’ll see a model of a human heart on display. As an AP Biology student, exploring a human heart model may be the closest, you’ll get to human heart unless you decide to advance in the sciences or attend medical school.

Have a big exam coming up or just want to gain a better understanding of how all of the parts of the heart works? A model of a heart is an excellent resource for studying. If your AP Biology teacher has a heart model, you are probably encouraged to take a look at it in the classroom, but what can you use when you’re studying outside of the classroom?

what can you use when you’re studying outside of the classroom?

Quick Study Illustrations

heart illustration model

Your Biology book may have some stunning and highly-detailed graphics of a human heart, but it may not showcase every part in detail. You can find a variety of “quick study” pamphlets online that give you multiple views of the human heart, and in great detail.

This type of resource is nice for studying while “on the go,” or when you want something lightweight and compact, but it is still very similar to looking at a model of the heart in your textbook. If you are a visual learner, this method may be enough to help you study, but if you’re a “hands-on” learner, you may have a harder time learning about the heart.

3D Model Apps

If you spend a lot of time at your computer or on your device while you study, it may be worthwhile to check out a 3D model of the heart. Depending on the 3D model you choose, you might be able to do virtual dissection, manipulate the heart rate, or see what happens to the heart during a heart attack.

While a 3D model that you can touch and manipulate with your own hands, may help you understand the heart better than an app, the app may be beneficial due to some of its features (such as a beating heart or blood flow).

3D “Hand On” Models

Human heart model

As we mentioned earlier, there might be a 3D model of the human heart in your AP Biology classroom, and you have access to it while you’re in class. 3D heart models typically have pieces that come apart and allow you to see all the parts of the heart, which is essential when learning about the complex organ.

 When you want a more “hands-on” approach to studying the human heart, it can be difficult to have access to a 3D model, particularly if you’re in a large classroom with other students who are also wanting to see the model of the heart.

Purchasing a heart model for yourself might make studying more convenient and help information “sink in” a little better. If you’ve already started to search around online for 3D heart models, you might be a little disheartened by the price.

Many life-sized 3D heart models cost hundreds of dollars, and it might not be in your budget as an AP student. The good news is that there are many smaller 3D models available online for under $50.

If you decide to purchase a 3D model, it’s important to read the reviews before buying and keep in mind that the model will not be life-sized. Ideally, the 3D model should have parts that can be removed or at least moved out of the way, so that you can see all the parts of the heart.

Purchasing a 3D model of a heart can be a wise financial investment, particularly if you’re planning on pursuing Biology or other Life Sciences further. Your 3D model can also be a great asset to a study group or when using a variety of resources like the quick study pamphlet or 3D app.

Do You Have To Use A Heart Model When Studying?

A girl holding a heart model

You might be wondering if you need to use a model of a heart when studying for AP Biology. Your teacher may strongly recommend using heart models as a study guide, but as we mentioned earlier, you might understand how the heart works without looking at a model.

Even though we mention quick study pamphlets and 3D model apps as good alternatives to studying the heart, research suggests that students are more likely to understand and retain information better when they are presented with 3D models rather than 2D.

In one study, a group of nursing students was tested after learning and studying with 2D models, and the other group was tested (with the same test) after learning and studying with 3D models. Overall, the group that had access to a 3D model performed better on the test.

The methods, which were compared included a dissection of a sheep heart and a PowerPoint presentation versus a 3D heart model; the 3D model resulted in higher test scores.

Isn’t Dissection The Best Option For Studying The Heart?

humna heart model sectioned

Many may argue that dissecting a heart is the best way to study the heart and gain a better understanding of how it works. In AP Biology, you may have the opportunity to dissect a sheep heart or another mammal heart, but you won’t be able to have an up close and personal interaction with a human heart.

While dissection is a fascinating and “must have” experience in every Biology course, it can also be challenging to understand and often it’s a hurried process with limited explanations. It can also be more challenging when more than one student is working on dissecting a heart at once (such as a group of two or three people).

Dissection takes practice and time, and even though many students would benefit from one-on-one help from their instructor, it’s not always feasible. Dissecting a heart can also be very difficult for some students and may make them feel nervous or uneasy, which can also affect the overall learning experience.

Another reason why dissection may not be the best option for studying is that you can’t carry the heart around with you. Depending on how many students are in the class or how many class sessions touch and examine a heart, it can become harder to work with or easily damaged.

Ideally, every student would have the opportunity to dissect a heart and learn enough from the experience to understand how the heart works and ace an exam on how the heart functions. Since a heart is such a unique and complex organ, it’s beneficial to explore a variety of resources to help better understand the heart.

Dissection is a great option, but it’s not the only option (nor should it be) when providing an in-depth look at the heart. Unless you have a photographic memory, most students benefit from seeing the parts of a heart multiple times, not just during the various steps of a dissection.

Using a 3D model allows you to take the heart apart and put it back together as many times as you want. If the model is made of high-quality materials and is handled carefully, it can withstand many study sessions and years of science courses.

Using Various Heart Models For Studying

The type of heart models you choose will most likely depend on your learning style and preferences. Since learning about the heart is not something that is easily done overnight, it’s best to utilize as many resources as you can when you study.

If a model of the human heart is not available to you on a regular basis or at home, consider the 3D model app and even some of the quick study guides.

Biome Map: Definition, Examples, And Why It Is Important

If you want to gain a better understanding of all living things, from plants to animals, it’s essential to learn about biomes and the role they play in Biology. Learn how to read a biome map and define each type of biome in the world.

Biome Map: Definition, Examples, And Practice

Biomes are an interesting and important part of Biology, and without understanding what a biome is and how it works, you don’t have a full understanding of Biology. Let’s take an in-depth look at biomes, so you can take a look at a biome map and understand it; learning about biomes can also better prepare you for if you’re ever tested on a map of biomes.

What Is A Biome?

While you might have learned a little about biomes when you were in elementary school, there’s a good chance that you don’t have a biome map memorized or know about all of the biomes. As we all know, the entire surface of the planet has some lifeform, but it varies depending on factors like vegetation, climate, water, and light. A biome is classified by the flora and fauna (dominant plants and animal life) that resides in that particular area; the plants and animals that live in a biome are also known as biota. While some biomes share some characteristics, each type is unique, and the smaller units in a biome are what we know best as a habitat.Biomes are often mistakenly referred to as ecosystems (and vice versa). An ecosystem is made up of living organisms and the relationship that they have in their nonliving environment. There are many examples of ecosystems but think about a dark cave in a secluded part of the world and all of the known (and unknown) living things that live in the cave.One of the reasons why ecosystems may be easily confused with biomes is that a biome may have many different ecosystems.

Exploring The Different Types Of Biomes

If you look at a biome map, you will notice that it is color-coded with a key that refers to different types of biomes. Depending on what map you look at and who is teaching you about biomes, you may only learn about five biomes, which include tundra, grassland, forest, desert, and aquatic; sometimes it’s six basic biomes be splitting the aquatic into marine and freshwater.As you might guess, these biomes are basic, have a broad definition, and may refer to many parts of the globe. In order to gain a better understanding of Biology as a whole, you may want to consider learning more about other biomes like the rainforest, temperate forest, chaparral, taiga, savanna, temperate grasslands, and freshwater or marine.Younger learners or individuals who just want some basic information on biomes may benefit from learning about the broad classifications, but taking the time to learn about other biomes (and their specialized classifications) can help understand the world as a whole.As you explore biomes, it’s not uncommon to see different biomes in the same area, and often there are no clear boundaries from one biome to the next. If you were to compare a map of biomes from thousands of years ago to today, you’d see a completely different map.Climate change plays a significant role in how biomes are defined and where they are located on a map. The major biomes typically correspond to the climatic zones, such as a tropical wet climate.

Tundra

Man and dogs in snowAs you might already imagine, the tundra biome is located in the northernmost regions on a map of biomes. A tundra is flat, cold, but still has plant life during the short growing season. A variety of birds call the tundra their home during the summer and migrate in the winter. Smaller mammals thrive in their habitats under the snow.

Grassland

grasslandThe grassland biome is often referred to as plains or prairie, due to the large areas of a variety of grasses. Grasslands typically receive minimal rain and are often at high risk for fires. Even though there is not a large variety of flora, the biome is home to large herding mammals. Grassland is found on every continent except for Antarctica.

Forests

forest with rocksThe forest biome makes up about one-third of the Earth’s land area, and as you might imagine, there are more classifications to the forest biome than “just trees.” The tropical rainforest has two seasons, 12-hour days, and has little variation in the climate. You’re most likely to find tropical rainforest countries near the equator like South America, Southeast Asia, and Southern Africa.forests with sunraysA temperate forest biome is most frequently found in eastern parts of North America, northeastern Asian, and western and central parts of Europe. Animals from small mammals (squirrels) to predators (black bears) call the biome their home. The boreal or taiga forest is similar to the temperate forest biome and is found in Siberia, Scandinavia, Alaska, and Canada. The taiga forest biome doesn’t have as long of growing seasons as the temperate forest, and the climate is cold and dry.

Deserts

desert with camelsIt’s not uncommon to see all types of desert biomes lumped into one broad desert biome and again, depending on the map you’re looking at or who is teaching information about biomes, the classifications may be different. Some people break down the desert biome even further to include hot and dry, semiarid, coastal and cold. If you live in the U.S., you may be most familiar with a hot and dry desert biome, as it includes four of the major deserts in North America. The seasons are very dry and warm year round.desertSemiarid desert biomes may be found in parts of the U.S., but are also found in Newfoundland, Greenland, Europe, and parts of Asia. There are more flora and fauna in semiarid biomes than the hot and dry.The coastal desert biome sees moderate rainfall and the cold desert biome experiences heavy snowfall; both have plants and animals that have adapted to the environment (much like every other biome on the map)

Aquatic

sea turtle underwaterWhen exploring a map of biomes, it’s important not to overlook the aquatic biome. While many people pay close attention to flora and fauna throughout the various biomes “on land,” there’s plenty to consider when we look at the bodies of water.The aquatic biome is typically divided into freshwater and saltwater (or marine) biomes. From there it might be broken down even more to ponds or lakes, rivers, oceans, and estuaries.sting ray underwaterIt’s essential to think about aquatic biomes because just like other biomes, climate change and other environmental factors affect these “off land” biomes, which over time will change the layout of a map of biomes.

Why Are Biome Maps Important?

world biomes mapImage Source: askabiologist.asu.eduNow that you have a better understanding of the different biomes and how one map could be different from another, you might be wondering why biome maps are so important. As we mentioned earlier, learning about biomes and understanding where they are in the world can help us understand all living organisms. Biome maps can help people learn about places they may never get to see; the map may open their eyes to a new species of animal or a unique variety of flora. Biome maps may be a basic resource for understanding Biology, but without the maps, we know very little about Biology, it’s past, and what might be in store for the future of our planet.Even though we may not see drastic changes to our environment in our lifetime, we can see small scales changes such as more prairie fires or decreasing populations of a specific bird.To some, these may not seem like that big of a deal when comparing it to the world at large, but it can give us some idea as to how biome maps will continue to evolve.

Making The Most Of A Biome Map

Not only are biome maps an important resource to use in a Biology course, but it can be used in a variety of fields such as Agriculture. The United States Department of Agriculture can utilize the map to learn more about soil distribution while conservation programs can strive to protect biomes that need it the most.

If your goal is to learn how to draw a map of biomes or memorize it for a class, you might want to consider the following tips.

  • Familiarize yourself with Geography; you can’t make a map without knowing where places are located.
  • Use the knowledge you already have. Think about living organisms and where they live. Can you guess what type of biome (or biomes) are in this area?
  • Get to know a climatic map. Remember climatic zones may correspond with specific biomes.
  • Practice, practice, practice. Make several copies of a blank world map.
  • Use a color-code and key that’s easy to read. Choose colors that stand out from one another.

Dimensional Analysis: Definition, Examples, And Practice

If you’ve heard the term “dimensional analysis,” you might find it a bit overwhelming. While there’s a lot to “unpack” when learning about dimensional analysis, it’s a lot easier than you might think. Learn more about the basics and a few examples of how to utilize the unique method of conversion.

Dimensional Analysis: Definition, Examples, and Practice

As a student of Biology or any of the sciences, you will have to use math of some kind, and there’s a good chance that you will find dimensional analysis (or unit analysis) to be helpful. Math equations and other conversions can be overwhelming for some, but dimensional analysis doesn’t have to be; once you learn it, it’s relatively easy to use and understand.

We’ll give you the basics and give you some easy-to-understand examples that you might find on a dimensional analysis worksheet so that you can have a general understanding about what it is and how to use the technique in all types of applications as you continue to take science courses.

What Is Dimensional Analysis?

As we mentioned, you may hear dimensional analysis referred to as unit analysis; it is often also known as factor-label method or the unit factor method. A formal definition of dimensional analysis refers to a method of analysis “in which physical quantities are expressed in terms of their fundamental dimensions that is often used.”

Most people might agree that this definition needs to be broken down a bit and simplified. It might be easier to understand this method of analysis if we look at it as a method of solving problems by looking converting one thing to another.

While dimensional analysis may seem like just another equation, one of the unique (and important) parts of the equation is that the unit of measurement always plays a role in the equation (not just the numbers).

We use conversions in everyday life (such as when following a recipe) and in math class or in a biology course. When we think about dimensional analysis, we’re looking at units of measurement, and this could be anything from miles per gallon or pieces of pie per person.

Many people may “freeze up” when they see a dimensional analysis worksheet or hear about it in class, but if you’re struggling with some of the concepts, just remember that it’s about units of measurements and conversion. Dimensional analysis is used in a variety of applications and is frequently used by chemists and other scientists.

The Conversion Factor in Dimensional Analysis

One important thing to consider when using dimensional analysis is the conversion factor. A conversion factor, which is always equal to 1, is a fraction or numerical ratio that can help you express the measurement from one unit to the next.

When using a conversion factor, the values must represent the same quantity. For example, one yard is the same as three feet or seven days is the same as one week. Let’s do a quick example of a conversion factor.

Imagine you have 20 ink pens and you multiply that by 1; you still have the same amount of pens. You might want to find out how many packages of pens that 20 pens equal and to figure this out, you need your conversion factor.

Now, imagine that you found the packaging for a set of ink pens and the label says that there are 10 pens to each package. Your conversion factor ends up being your conversion factor. The equation might look something like this:

20 ink pens x 1 package of pens/10 pens = 2 packages of ink pens. We’ve canceled out the pens (as a unit) and ended up with the package of pens.

While this is a basic scenario, and you probably wouldn’t need to use a conversion factor to figure out how many pens you have, it gives you an idea of what it does and how it works. As you can see, conversion factors work a lot like fractions (working with numerators and denominators)

Even though you’re more likely to work with more complex units of measurement while in chemistry, physics, or other science and math courses, you should have a better understanding of using the conversion factor in relation to the units of measurement.

Steps For Working Through A Problem Using Dimensional Analysis

Like many things, practice makes perfect and dimensional analysis is no exception. Before you tackle a dimensional analysis that your instructor hands to you, here are some tips to consider before you get started.

  • Read the problem carefully and take your time
  • Find out what unit should be your answer
  • Write down your problem in a way that you can understand
  • Consider a simple math equation and don’t forget the conversion factors
  • Remember, some of the units should cancel out, resulting in the unit you want
  • Double-check and retry if you have to
  • The answer you come up with should make sense to you

To help you understand the basic steps we are using an easy problem that you could probably figure out fairly quickly. The question is: How many seconds are in a day?

First, you need to read the question and determine the unit you want to end up with; in this case, you want to figure out “seconds in a day.” To turn this word problem into a math equation, you might decide to put seconds/day or sec/day.

The next step is to figure out what you already know. You know that there are 60 seconds to one minute and you also know that there are 24 hours in one day; all of these units work together, and you should be able to come up with your final unit of measurement. Again, it’s best to write down everything you know into an equation.

After you’ve done a little math, your starting factor might end up being 60 seconds/1 minute. Next, you will need to work your way into figuring out how many seconds per hour. This equation will be 60 seconds/1 minute x 60 minutes/1 hour. The minutes cancel themselves out, and you have seconds per hour.

Remember, you want to find out seconds per day so you’ll need to add another factor that will cancel out the hours. The equation should be 60 seconds/1 minute x 60 minutes/1 hour x 24 hours/1 day. All units but seconds per day should cancel out and if you’ve done your math correctly 86,400 seconds/1 day.

When doing a dimensional analysis problem, it’s more important to pay attention to the units and make sure you are canceling out the right ones to get the final product. Doing your math correctly important, but it’s easier to double-check than trying to backtrack and figure out how you ended up with the wrong unit.

Our example is relatively simple, and you probably had no problem getting the right answer or using the right units. As you work through your science courses, you will be faced with more difficult units to understand. While dimensional analysis will undoubtedly be more challenging, just keep your eye on the units, and you should be able to get through a problem just fine.

Why Use Dimensional Analysis?

As we’ve demonstrated, dimensional analysis can help you figure out problems that you may encounter in your everyday. While you’re likely to explore dimensional analysis a bit more as you take science courses, it can be particularly helpful for Biology students to learn more.

Some believe that dimensional analysis can help students in Biology have a “better feel for numbers” and help them transition more easily into courses like Organic Chemistry or even Physics (if you haven’t taken those courses yet).

Can you figure out a math equation or a word problem without dimensional analysis? Of course, and many people have their own ways of working through a problem. If you do it correctly, dimensional analysis can actually help you answer a problem more efficiently and accurately.

Ready To Test Your Dimensional Analysis Skills?

If you want to practice dimensional analysis, there are dozens of online dimensional analysis worksheets. While many of them are pretty basic or geared towards specific fields of study like Chemistry, we found a worksheet that has an interesting variety. Test out what we’ve talked about and check your answers when you’re done.

  • How many minutes are in 1 year?
  • Traveling at 65 miles/hour, how many minutes will it take to drive 125 miles to San Diego?
  • Convert 4.65 km to meters
  • Convert 9,474 mm to centimeters
  • Traveling at 65 miles/hour, how many feet can you travel in 22 minutes? (1 mile = 5280 feet)

Ready to check out your answers and see more questions? Click here.

Introduction to Biology Quiz

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Introduction to Biology
 

1. Ultimately, all scientific knowledge comes from:
experimentation
observation
textbooks
both experimentation & observation

2. A hypothesis must be:
proven correct
testable
observed
experimental

3. A scientist testing the affects of a chemical on apple yeild sprays an orchard with the chemical. A second orchard does not receive the chemical. In the fall, the number of apples harvested from each forest is counted. Which of the following is the independent variable in the experiment?
the chemical
the number of apples
the first orchard
the second orchard

4. The orchard sprayed with the chemical yeilds an average of 60 apples per tree, the other orchard yields an average of 40 apples per tree. Based on the data, the scientist would:
report his data
test the chemical on other plants
determine that the chemical increases apple yield
determine that the results were inconclusive

5. In order for the apple tree experiment to be valid scientifically, both orchards must:
receive the same amount of sunlight
receive the same amount of water
have the same species of apple tree
all of these

6. Theories help scientists to:
explain large bodies of data
prove hypotheses
determine truth from lies
propose new ideas about how the world works

7. If a theory is challenged by new evidence, which of the following could occur?
the theory could be altered
the theory is accepted, not the evidence
the evidence is wrong
a vote is taken on whether to accept the new evidence

8. All living things must:
move
have two parents
eat food
maintain homeostasis

9. The mechanism by which evolution occurs is called:
creationism
natural selection
interdependence
metabolism

10. The smallest unit capable of carrying out life functions is:
a cell
tissue
DNA
blood

Score =
Correct answers:

BACK TO BIOLOGY I HOME PAGE CHAPTER 8

 

CHAPTER 8,  CELL REPRODUCTIONSECTION 8-1, CHROMOSOMES

DNA is a long thin molecule that stores Genetic Information.  The DNA in a human cell is estimated to consist of six billion pairs of nucleotides.

OBJECTIVES:  Describe the structure of a chromosome.  Compare prokaryotic chromosomes with eukaryotic chromosomes.  Explain the differences between sex chromosomes and autosomes.  Give examples of diploid and haploid cells.

CHROMOSOME STRUCTURE

1. During Cell Division, the DNA (CHROMATIN) in an Eukaryotic Cell’s Nucleus is coiled into very tight compact structures called CHROMOSOMES.(Figure 8-1)

2. Chromosomes are Rod Shaped structures made of DNA and Proteins.

3. The Chromosomes of stained Eukaryotic cells undergoing cell division are visible as darkened structures inside the Nuclear Membrane.

4. The DNA in Eukaryotic cells wraps tightly around Proteins called HISTONES. They help to maintain the shape of Chromosomes and aid in the tight packing of DNA.

5. Proteins called NONHISTONE Proteins Do Not participate in packing of DNA, they are involved in Controlling the Activity of Specific Regions of the DNA.

6. When preparing for Cell Division, Chromosomes form Copies of themselves, Each half of the Chromosome is called a CHROMATID or SISTER CHROMATIDS. Chromatids form as the DNA makes copies of itself before cell division.  (Figure 8-2)

7. The constricted area of each Chromatid is called a CENTROMERE . The Centromere holds the Two Chromatids together until the separate during Cell Division.

8. Between Cell Division, DNA IS NOT so Tightly Coiled into Chromosomes.  The Less tightly coiled DNA-Protein complex is called CHROMATIN .

9. Chromosomes are simpler in prokaryotes.  The DNA of most Prokaryotes comprises only ONE Chromosome, which is attached to the inside of the Cell Membrane.

10. Prokaryotic Chromosomes consist of a circular DNA Molecule and associated Proteins.

CHROMOSOME NUMBERS

1. EACH HUMAN BODY CELL CONTAINS 46 CHROMOSOMES, (2n) OR TWO COMPLETE SETS.

2. ANY CELL THAT CONTAINS TWO COMPLETE SETS OF CHROMOSOMES IS CALLED A DIPLOID CELL. A Diploid Cell  is commonly abbreviated as 2n.

3.  THE NUMBER OF CHROMOSOMES IN A DIPLOID CELL IS CALLED THE DIPLOID NUMBER.  EVERY ORGANISM HAS A CHARACTERISTIC DIPLOID NUMBER (2n).

4.  EXAMPLES:  FRUIT FLIES – 8, LETTUCE – 14, GOLDFISH 94, AND HUMANS 46.

5.  A CELL WITH ONLY ONE COMPLETE SET OF CHROMOSOMES IS CALLED A HAPLOID CELL.
A Haploid Cell is abbreviated as 1n.

6.  GAMETES, EGGS AND SPERM CONTAIN ONLY ONE COMPLETE SET.  EACH HUMAN SPERM OR EGG (GAMETE) CONTAINS 23 CHROMOSOMES, THE HAPLOID NUMBER (1n) FOR ALL HUMANS.

7.  WHEN AN EGG AND A SPERM OF THE SAME TYPE OF ORGANISM JOIN TO PRODUCE A NEW INDIVIDUAL, THE PROCESS IS CALLED FERTILIZATION.

8.  THE SINGLE CELL THAT RESULTS FROM FERTILIZATION IS KNOWN AS A ZYGOTE. THE ZYGOTE CONTAINS TWO COMPLETE SETS OF CHROMOSOMES, ONE SET FROM EACH GAMETE, FORMING A DIPLOID CELL.  IN MOST MULTICELLULAR ORGANISMS, THE ZYGOTE IS THE FIRST CELL OF THE NEW INDIVIDUAL.

9.  The Chromosomes in the Zygote exist in PAIRS.  For every Chromosome that was in the egg, there is a matching Chromosome from the sperm.

10. Human and Animal Chromosomes are categorized as either SEX CHROMOSOMES or AUTOSOMES.

11. SEX CHROMOSOMES are Chromosomes that Determine the SEX of an Organism.

12. In Humans, Sex Chromosomes are either X or Y.  Females have TWO X Chromosomes and Males have an X and Y Chromosome.

13. All the Other Chromosomes in an Organism are called AUTOSOMES.

14. TWO of the 46 Human Chromosomes are Sex Chromosomes, while the reaming 44 are Autosomes.

15. MATCH SET OF AUTOSOMES IN A DIPLOID CELL ARE CALLED HOMOLOGOUS PAIRS.  BOTH CHROMOSOMES IN A HOMOLOGOUS PAIR CONTAIN INFORMATION THAT CODE THE SAME TRAIT (GENES).  Example Eye Color.

SECTION 8-2, CELL DIVISION

All cells are derived from preexisting cells.  Cell division is the process by which cells produce offspring cells.  Cell division differs in prokaryotes and eukaryotes.  In eukaryotes, cell division differs in different stages of an organisms life cycle.

OBJECTIVES:  Describe the events of binary fission.  Describe each phase of the cell cycle.  Summarize the phases of mitosis.  Compare cytokinesis in animal cells with cytokinesis in plant cells.

CELL DIVISION IN PROKARYOTES

1. BINARY FISSION is the Division of a Prokaryotic cell INTO TWO Offspring Cells.

2. Binary Fission consist of THREE General Stages: (Figure 8-4):

STAGE 1 – The Chromosome, which is attached to the Inside of the Cell Membrane, makes a COPY of Itself, Resulting in Two Identical Chromosomes Attached to the Inside of the Inner Cell Membrane.

STAGE 2 – The Cell continues to grow until it reaches approximately TWICE its Normal Size. Then a CELL WALL Begins forms between the Two Chromosomes.

STAGE 3 – The Cell SPLITS into TWO NEW CELLS.  Each New Cell contains on the Identical Chromosomes.

CELL DIVISION IN EUKARYOTES

1. The trillions of cells that make up your body came from just ONE ORIGINAL CALLED: A FERTILIZED EGG (Zygote).  The Cell Theory states “CELLS COME ONLY FROM THE REPRODUCTION OF EXISTING CELLS” Chapter 4.

2. Each time A Cell Reproduces, the NEW Cells that are formed contained all the ESSENTIAL CYTOPLASM, ORGANELLES, AND NUCLEIC ACIDS NEEDED TO SURVIVE AND FUNCTION.

3. A Cell typically goes through PHASES during its Life, performing life processes of GROWTH AND DEVELOPMENT before it divides into new cells.

4. THE PHASES OF LIFE OF A CELL ARE CALLED THE CELL CYCLE . THE CELL CYCLE CONSISTS OF THREE PHASES:
      A. INTERPHASE
        B. MITOSIS
        C. CYTOKINESIS.

5. The CELL CYCLE is the Repeating Events that make up the Life of a Cell. (Figure 8-5)

6. Cell Division is One Phase of the Cell Cycle.  Cell Division consists of MITOSIS AND CYTOKINESIS.

7. MITOSIS is a Series of PHASES in Cell Division during which the NUCLEUS of a Cell Divides into TWO NUCLEI WITH IDENTICAL GENETIC MATERIAL.  MITOSIS OCCURS ONLY IN EUKARYOTES.

INTERPHASE

1. INTERPHASE IS THE PORTION OF THE CELL CYCLE BETWEEN DIVISION.

2. Interphase is the LONGEST Phase in the Cell Cycle of a typical Cell.  Interphase used to be referred to as the “RESTING PHASE”.

3. During Interphase, calls carry on all their usual functions, such as respiration and enzyme production.  The Cell also GROWS and DEVELOPS into MATURE FUNCTIONING Cells while in Interphase.  It is the period of normal metabolic activity.

4. INTERPHASE CONSIST OF THREE PHASES:

A. G1 PHASE – PERIOD OF NORMAL METABOLIC CELLULAR ACTIVITIES: THE NUMBER OF ORGANELLES AND AMOUNT OF CYTOPLASM IN A CELL INCREASE. Offspring Cells Grow to Mature Size.

B. S PHASE – THE GENETIC MATERIAL (DNA) IS DUPLICATED (COPIED).  THE CHROMOSOMES OF THE CELL REPLICATE.

C. G2 PHASE – Structure directly involved with mitosis are formed.  The Cell makes the Organelles and substances it needs for Cell Division.  A time during which the Cell prepares to divide.

5. REPLICATION IS THE PROCESS OF COPYING GENETIC MATERIAL.

6. REPLICATION RESULTS IN TWO IDENTICAL COPIES OF A CHROMOSOME CALLED SISTER CHROMATIDS.

7. CHROMOSOMES MUST REPLICATE DURING INTERPHASE SO THERE WILL BE A COMPLETE COPY OF EACH CHROMOSOME IN EACH NEW CELL.

8. BECAUSE THE DNA CONTAINED IN CHROMOSOMES CONTROL GROWTH DEVELOPMENT, AND FUNCTION OF EVERY CELL, EACH NEW CELL MUST HAVE AN EXACT COPY OF THE ORIGINAL SET OF CHROMOSOMES.
CELL DIVISION

1. CELL DIVISION IS THE PROCESS BY WHICH ONE CELL PRODUCES TWO NEW IDENTICAL DAUGHTER CELLS.

2. CELL DIVISION INVOLVES TWO STEPS: CALLED MITOTIC CELL DIVISION.

A.  MITOSIS – FIRST STEP. A SERIES OF  PHASES IN CELL DIVISION DURING WHICH THE NUCLEUS OF A CELL DIVIDES INTO TWO NUCLEI WITH IDENTICAL GENETIC MATERIAL.

B. CYTOKINESIS – SECOND STEP. THE CYTOPLASM OF THE CELL DIVIDES INTO TWO NEW CELLS CALLED DAUGHTER CELLS.

3. DAUGHTER CELL NUCLEI ARE IDENTICAL TO THE PARENT CELL NUCLEUS IN EVERY WAY.  LIKE THEIR PARENT CELL, SOME DAUGHTER CELLS WILL PASS THROUGH THE CELL CYCLE OF GROWTH, DEVELOPMENT, AND CELL DIVISION.

4. MULTICELLULAR ORGANISMS GROW AS MORE CELLS REPEAT THE CYCLE OF CELL DIVISION AND GROWTH.

MITOSIS

1. Mitosis is the Division of the Nucleus, which occurs during Cell Division.

2. Biologist have named the Steps, or Phases, of Mitosis to help study the process.  The FOUR Phases of Mitosis are called PROPHASE, METAPHASE, ANAPHASE, AND TELOPHASE. (Figure 8-6)

3. THE ACTUALLY PROCESS OF MITOSIS IS CONTINUOUS.

4. MITOSIS IS THE PROCESS BY WHICH A NUCLEUS GIVES RISE TO TWO IDENTICAL NUCLEI.

5. INTERPHASE PRIOR TO MITOSIS, THE PERIOD OF NORMAL METABOLIC ACTIVITY. The Chromosomes REPLICATE and the CYTOPLASM Increases as he cell prepares to divide. Interphase includes G1, S, G2 Phases of the Cell Cycle.

FOUR PHASES OF MITOSIS

PHASE 1- PROPHASE  (Figure 8-6 (a))

1. Chromatin condenses into Chromosomes of TWO Sister Chromatids joined together by the CENTROMERE, and visible when viewed through a microscope.

2. THE NUCLEOLUS AND NUCLEAR MEMBRANE DISAPPEAR.

3. TWO Structures called CENTROSOMES appear next to the Disappearing Nucleus.  In Animal Cells, each Centrosome contains a pair of small, cylindrical bodies called CENTRIOLES. Plant Cells lack Centrioles.

4. In BOTH Animal and Plant Cells, the Centrosomes move toward opposite poles of the cell. As they Separate, SPINDLE FIBERS made of microtubules radiate from the Centrosomes in preparation for Mitosis.  The array of Spindle fibers is called the MITOTIC SPINDLE, which serves to Equally divides the Sister Chromatids between the Two Offspring Cells.

5. There are TWO Type of Spindle Fibers:

A. KINETOCHORE FIBERS – They Attached to the Centromere Region of each Sister Chromatids.

B. POLAR FIBERS – they extend across the dividing cell from Centrosome to Centrosome.

PHASE 2 – METAPHASE  (Figure 8-6 (b))

1. The Chromosomes are moved to the CENTER of the CELL (Equatorial Plane) by the Kinetochore Fibers attached to the Centromeres.

2. The Two Sister Chromatids of each Chromosome are attached to Kinetochore Fibers radiating from OPPOSITE ENDS OF THE CELL.

PHASE 3 – ANAPHASE  (Figure 8-6 (c))

1. The Centromeres of Each Chromosome are pulled by the Kinetochore Fibers toward the ends of the cell (OPPOSITE POLES).

2. THE SISTER CHROMATIDS ARE THUS SEPARATED FROM EACH OTHER.  They are now Considered to be Individual Chromosomes.

PHASE 4 – TELOPHASE (Figure 8-6 (d))

1. After the Chromosomes reach opposite ends of the Cell, the Spindle Fibers Disassemble.

2. The Chromosomes return to less tightly coiled Chromatin State.

3. New Nuclear Envelope begins to form around the Chromosomes at each end of the cell.

4. CYTOKINESIS BEGINS.

5.  THE PROCESS OF MITOSIS IS NOW COMPLETE.  THE CELL MEMBRANE BEGINS TO PINCH THE CELL IN TWO AS CYTOKINESIS BEGINS.

CYTOKINESIS

1. Following the last phase of Mitosis, Cytokinesis COMPLETES the process of Cell Division.

2. During Cytokinesis, the Cytoplasm of a cell and its ORGANELLES SEPARATE INTO TWO NEW DAUGHTER CELLS.

3. Cytokinesis proceeds differently in animal and plant cells.

4. CYTOKINESIS OF ANIMAL CELLS: The Cytoplasm Divides when a GROOVE called the CLEAVAGE FURROW forms through the Middle of the Parent Cell.  The Cleavage Furrow Deepens until the parent cell pinches into TWO New Identical Cells.  The New Cells are Now in INTERPHASE.

5. CYTOKINESIS OF PLANT CELLS: In a Plant Cell, the material for NEW CELL WALL CALLED THE CELL PLATE  AND MEMBRANES GATHER AND FUSE ALONG THE EQUATOR, OR MIDDLE OF THE CELL, BETWEEN TWO NUCLEI. Forming TWO New Identical Cells.

6. In Both Animal and Plant Cells, New Offspring Cells are approximately equal in Size.

SECTION 8-3, MEIOSIS

Meiosis is a process of nuclear division that Reduces the number of chromosomes in new cells to Half the number in the original cell. The Halving of the chromosome number counteracts a fusion of cells later in the life cycle of the organism.  For example, in humans, meiosis produces haploid reproductive cells called GAMETES. Human gametes are sperm and egg cells, each which contains 23(1n) chromosomes.  The fusion of sperm and egg results in a zygote that contains 46 (2n) chromosomes.

OBJECTIVES:  List and describe the phases of meiosis.  Compare the end products of mitosis with those of meiosis.  Explain crossing-over and how it contributes to the production of unique individuals.  Summarize the major characteristics of spermatogenesis and oogenesis.

1. Most organisms are capable of COMBINING CHROMOSOMES FROM TWO PARENTS TO PRODUCE OFFSPRING.

2. WHEN CHROMOSOMES OF TWO PARENTS COMBINE TO PRODUCE OFFSPRING, THE PROCESS IS KNOWN As SEXUAL REPRODUCTION.

3. THE CHROMOSOMES THAT COMBINE DURING SEXUAL REPRODUCTION ARE CONTAINED IN SPECIAL REPRODUCTIVE CELLS CALLED GAMETES.

4. IN MOST ORGANISMS, GAMETES CAN BE EITHER EGG OR SPERM .

5. EGGS are larger than sperm and contain a lot of Cytoplasm.  An egg is nonmotile.

6. SPERM Cells contain very little Cytoplasm, have Flagella, that helps them swim to the nonmotile egg.

7. The Chromosomes of Two Gametes are added together when they join.  The number of Chromosomes in the offspring DOES NOT DOUBLE WITH EACH GENERATION, BUT REMAINS THE SAME BECAUSE OF MEIOSIS.

8. MEIOSIS IS THE WAY MANY ORGANISMS PRODUCE GAMETES THROUGH A TYPE OF CELL REPRODUCTION.

9. MEIOSIS IS A TYPE OF NUCLEAR DIVISION IN WHICH THE CHROMOSOME NUMBER IS HALVED.  LIKE MITOSIS, MEIOSIS IS FOLLOWED BY CYTOKINESIS.

10. IN HUMANS SPECIALIZED REPRODUCTIVE CELLS WITH 46 CHROMOSOMES (2n) (DIPLOID CELL) UNDERGO MEIOSIS AND CYTOKINESIS TO GIVE RISE TO EGG OR SPERM THAT HAVE ONLY 23 CHROMOSOMES (1N) (HAPLOID CELL) EACH.

11. MEIOSIS ONLY OCCURS IN EUKARYOTIC CELLS IN PHASES SIMILAR TO THE PHASES OF MITOSIS.

12. MEIOSIS IS DIFFERENT FROM MITOSIS IN SOME VERY IMPORTANT WAYS.

A. The process of meiosis results in the production of Daughter Cells that have HALF THE NUMBER OF CHROMOSOMES OF THE PARENT CELL (HAPLOID CELL).

B. Daughter Cell produced by meiosis ARE NOT ALL ALIKE.  THE DAUGHTER CELLS     MAY HAVE DIFFERENT CHROMOSOMES FROM EACH OTHER.

C. The NUMBER OF CELLS PRODUCED BY MEIOSIS IS DIFFERENT.

(1) Mitosis – One Parent Cell PRODUCES TWO DIPLOID DAUGHTER CELLS.

(2) Meiosis – One Parent Cell PRODUCES FOUR HAPLOID DAUGHTER CELLS.

STAGES OF MEIOSIS

1. THE PROCESS OF MEIOSIS SEPARATES THE PAIRS OF CHROMOSOMES IN A DIPLOID CELL TO FORM HAPLOID CELLS.

2. ONE PARENT CELL DIVIDES TWICE TO PRODUCE FOUR HAPLOID DAUGHTER CELLS.

3. DURING MEIOSIS, THE NUMBER OF CHROMOSOMES IN EACH CELL IS REDUCED FROM DIPLOID TO HAPLOID BY SEPARATING HOMOLOGOUS PAIRS OF CHROMOSOMES.

4. MEIOSIS PROCEEDS IN TWO MAIN STAGES:

A. MEIOSIS I HOMOLOGOUS PAIRS ARE SEPARATED.

B. MEIOSIS II THE SISTER CHROMATIDS OF EACH CHROMOSOME ARE SEPARATED.

MEIOSIS I  (Figure 8-9)

1. AT THE START OF MEIOSIS I EACH CHROMOSOME CONSIST OF TWO STRANDS OF SISTER CHROMATIDS CONNECTED AT THE CENTROMERE.

2. HOMOLOGOUS PAIRS OF CHROMOSOMES COME TOGETHER BEFORE MEIOSIS BEGINS, AN EVENT THAT DOES NOT OCCUR IN MITOSIS. THIS EVENT IS CALLED SYNAPSIS .

3. Each Pair of Homologous Chromosomes is called a TETRAD .

PROPHASE I.

1. Chromosomes become thick and visible, the chromosomes of each homologous pair are tangled together.

2. Portions of Chromatids may Break Off and attach to Adjacent Chromatids on the homologous Chromosome – a process called CROSSING-OVER. (Figure 8-10)

3. Crossing-Over results in Genetic Recombination by producing a New Mixture of Genetic Material.

4. Each pair consists of FOUR CHROMATIDS, BECAUSE EACH CHROMOSOME IN THE PAIR HAD REPLICATED BEFORE MEIOSIS BEGAN.

5. The Nucleoli and the Nuclear Envelope disappear and the spindle fibers form.

METAPHASE I.  Homologous pairs (Tetrads) are still together and arrange in the middle of the cell.

ANAPHASE I.  The homologous pairs of chromosomes separate from each other, spindle fibers pull one member from each pair to opposite ends of the cell. The Random separation of the Homologous Chromosomes is called INDEPENDENT ASSORTMENT.

TELOPHASE I.  Cytokinesis takes place; each new cell is haploid, containing one chromosome
from each pair.

MEIOSIS II  (Figure 8-11)

1. CHROMOSOMES DO NOT REPLICATE BEFORE BEGINNING THE SECOND PHASE MEIOSIS II WILL DIVIDE CHROMOSOMES INTO HAPLOID CELLS CALLED GAMETES.

2. Each Diploid Cell from Meiosis I will go through a second division, forming the FOUR GAMETES HAPLOID CELL.  (Review Figure 8-11)

CROSSING-OVER

1. CHROMOSOMES OF ALL ORGANISMS CONTAIN REGIONS CALLED GENES .

2. EACH GENE CODES FOR ONE TRAIT, OR CHARACTERISTIC, OF THE ORGANISM.

3. ONE VERY IMPORTANT EVENT THAT CAN OCCUR DURING MEIOSIS I IS CROSSING- OVER.

4. CROSSING-OVER IS THE EXCHANGE OF GENES BETWEEN PAIR OF HOMOLOGOUS CHROMOSOMES.

5. CROSSING-OVER OCCURS ONLY DURING PROPHASE I (ONLY!) WHEN HOMOLOGOUS PAIRS ARE STILL JOINED TOGETHER.  THESE PAIRS CAN SOMETIMES BREAK WHERE THEY MEET AN EXCHANGE GENES. (Figure 8-10)

FORMATION OF GAMETES

1. In Animals, meiosis produces haploid reproductive cells called GAMETES.

2. Meiosis occurs within the Reproductive Organs, in the TESTES or OVARIES.

3. In the Testes, meiosis is involved in the production of Male Gametes known as Sperm Cells or Spermatozoa.

4. In the development of Sperm Cells, a Diploid Reproductive Cell divides Meiotically to form FOUR Haploid Cells called SPERMATIDS.

5. Each Spermatid then develops into a Mature Sperm Cell.

6. The production of Sperm Cells is called SPERMATOGENESIS . (Figure 8-12 (b))
7. OOGENESIS is the production of Mature Egg Cells or OVA.  (Figure 8-12 (c))

8. Notice that the Female only produces ONE EGG (OVUM) under normal circumstances.

9. Although creating 4 Haploid Cells through meiosis, only One Becomes the Egg, the other Three products of meiosis are called POLAR BODIES ,and Degenerate.  This is due to the unequal dividing of the cytoplasm during Cytokinesis I & II.

ASEXUAL AND SEXUAL REPRODUCTION

1. EVOLUTION IS THE PROCESS OF CHANGE IN LIVING POPULATIONS OVER TIME.

2. ASEXUAL REPRODUCTION is the production of Offspring from ONE PARENT.

3. Asexual reproduction DOES NOT Usually involve Meiosis or the Union of Gametes.

4. In Unicellular Organisms, such as bacteria, New Organisms are created by either BINARY FISSION or MITOSIS.

5. Asexual Reproduction in multicellular organisms results from BUDDING OFF a Portion of Their Bodies. (Plants)

6. The Offspring From Asexual Reproduction are Genetically Identical to the Parent.

7. SEXUAL REPRODUCTION is the Production of Offspring through Meiosis and the Union of a Sperm and an Egg.

8. MEIOSIS AND SEXUAL REPRODUCTION RESULTS IN NEW COMBINATIONS OF CHARACTERISTICS WITHIN A POPULATION.

9. ORGANISMS IN A POPULATION THAT REPRODUCE SEXUALLY ARE NOT ALL ALIKE.

10. DIFFERENCES AMONG MEMBERS OF A POPULATION ARE COLLECTIVELY CALLED VARIATION.  WHICH RESULTS FROM THE RECOMBINATION OF GENES DURING MEIOSIS AND FERTILIZATION.

11. MEIOSIS AND FERTILIZATION SHUFFLE THE GENES FROM PARENT ORGANISMS, PRODUCING NEW COMBINATIONS OF GENES IN THE OFFSPRING.

12. AN ORGANISMS CHARACTERISTICS ENABLE IT TO SURVIVE IN IT’S ENVIRONMENT. THE CONDITIONS OF THE ENVIRONMENT DETERMINE WHICH CHARACTERISTICS OR TRAITS BENEFIT THE SURVIVAL AND WHICH DO NOT.

13. THE ORGANISMS WITH THE TRAITS TO SURVIVE WILL THEN REPRODUCE TO PASS THOSE POSITIVE TRAITS ON TO THEIR OFFSPRING.

14. OVER TIME THIS PROCESS LEADS TO THE CHANGE IN THE POPULATIONS, BECAUSE ONLY THOSE WITH POSITIVE TRAITS TO PASS ON WILL REPRODUCE.  NATURAL SELECTION.

15. THE ACCUMULATION OF SUCH GENES AND TRAITS IN EACH GENERATION IS THE BASIS OF EVOLUTION.

16. SINCE ASEXUAL OFFSPRING HAVE THE EXACT SAME GENES AND TRAITS AS THE PARENT, GENETIC VARIATION RARELY OCCURS.

17. A CHANGE IN THE ENVIRONMENT THAT CAN DESTROY ONE INDIVIDUAL COULD DESTROY THE ENTIRE POPULATION.