Category: Curriculum Map

Chlorophyll Fluorescence

 

Chlorophyll Fluorescence

INTRODUCTION

When a pigment absorbs light, electrons of certain atoms in the pigment molecules are boosted to a higher energy level. The energy of an absorbed photon is converted to the potential energy of the electron that has been raised to an excited state. In most pigments, the excited electron drops back to its ground-state, or normal orbit, and releases the excess energy as heat. Some pigments, including chlorophyll, emit light as well as heat after absorbing photons.
In the chloroplast, these excited electrons jump from the chlorophyll molecule to a protein molecule in the thylakoid membrane, and are replaced by electrons from the splitting of water. The energy thus transferred, is used in carbohydrate production.
This release of light is called fluorescence. Chlorophyll will fluoresce in the red part of the spectrum, and also give off heat. In this lab, you will observe this fluorescence by separating the chlorophyll from the thylakoid membrane.

MATERIALS

 

Spinach leaves Flashlight or small lab light
Mortar and pestle Test tube
Acetone Filter paper
25-mL graduated cylinder Funnel
Ring stand or funnel rack Safety goggles

PROCEDURE

1. Grind the spinach leaves using a mortar and pestle.

2. Add acetone to the ground leaves, using enough acetone and spinach leaves to get between 10 and 15 mL of extract.

3. Set up your filtering apparatus, and using proper filtering technique, filter the extract to a test tube. NOTE: Use a small amount of acetone to wet the filter paper, to hold it into place, instead of water.

4. Shine a flashlight, or other similar light source, through the test tube and extract.

5. Observe the fluorescence of the chlorophyll at a 90 degree angle to the flashlight.

 

Chemistry Quiz

Name: 

Chemistry Quiz

 

True/False
Indicate whether the sentence or statement is true or false.
1.
The types of particles that are located in the nucleus of an atom are protons and neutrons, and the types of particles that are located in the energy levels surrounding the nucleus are electrons.
2.
The atomic number of carbon is 6, so it must contain 12 electrons.
3.
Most elements are stable if their outermost energy level contains an even number of electrons.
4.
Atoms in a gas move more rapidly than atoms in a liquid or a solid do.
5.
The products of an endergonic chemical reaction possess more energy than the reactants from which they are produced.
6.
The amount of energy needed to cause a chemical reaction to start is called activation energy.
7.
When an enzyme binds with its substrate, the activation energy needed for the chemical reaction to occur is raised.
8.
Enzymes speed up a chemical reaction by increasing the activation energy of the reaction.
9.
Free hydrogen ions can react with water molecules and form a positively charged ion, the hydronium ion.
10.
Buffers can neutralize acids, but they do not affect bases.
 

Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
11.
The smallest particle of matter that can retain the chemical properties of carbon is
a.
a carbon molecule.
c.
a carbon atom.
b.
a carbon macromolecule.
d.
an element.
12.
The bond formed when two atoms share a pair of electrons is called a
a.
hydrogen bond.
c.
covalent bond.
b.
nonpolar bond.
d.
water bond.
13.
Sharing of electrons in the outer energy levels of two atoms
a.
results in ion formation.
b.
occurs in covalent bonds.
c.
only occurs if both are atoms of the same element.
d.
is found only among carbon atoms.
14.
An atom that has gained or lost electrons is called a(n)
a.
molecule.
c.
ion.
b.
nucleon.
d.
element.
15.
Which of the following statements most accurately describes the difference between an ionic bond and a covalent bond?
a.
Atoms held together by ionic bonds separate when placed in water while atoms held together by covalent bonds do not separate in water.
b.
Ionic bonds hold together atoms of two different types, while covalent bonds hold together atoms of the same type.
c.
Electrons are exchanged between atoms held together by an ionic bond, but they are shared between atoms held together by a covalent bond.
d.
Ionic bonds form between atoms that carry opposite charges, while covalent bonds form between uncharged atoms.
16.
A reaction in which the products have less energy than the reactants is
a.
an endergonic reaction.
c.
a filamentous reaction.
b.
an exergonic reaction.
d.
impossible.
      chemistry_quiz_files/i0190000.jpg
17.
Refer to the graph above. Reaction “1” in the graph
a.
is an energy-storing reaction.
b.
requires a greater activation energy than Reaction “2.”
c.
may use the same initial reactant condition needed to form Product “B.”
d.
All of the above
18.
Refer to the graph above. Which of these statements is true regarding the graph?
a.
Reaction “2” occurs faster than Reaction “3” because Reaction “2” requires more energy than Reaction “3.”
b.
The difference in the graphs shown for Reaction “2” and Reaction “3” is due to a difference in the activation energy needed for these reactions.
c.
Reactant “A” contains more energy at the beginning of the reaction than Product “C” has after the reaction.
d.
All of the above
19.
Changing the course or pathway of a chemical reaction so that it requires less activation energy
a.
is a violation of the laws of nature.
b.
requires higher temperatures than those found within cells.
c.
occurs only when reactants are quickly added to the reaction mixture.
d.
is accomplished by the action of catalysts on reactants.
20.
Oxidation-reduction reactions are important in organisms because they
a.
allow the passage of energy from molecule to molecule.
b.
prevent nuclear reactions from occurring.
c.
allow the creation and destruction of energy.
d.
None of the above; oxidation-reduction reactions do not occur in living organisms.

 
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Chromatography Plant Pigments

 

Chromatography of Plant Pigments

INTRODUCTION:

Chlorophyll often hides the other pigments present in leaves. In Autumn, chlorophyll breaks down, allowing xanthophyll and carotene, and newly made anthocyanin, to show their colors.
The mix of pigments in a leaf may be separated into bands of color by the technique of paper chromatography. Chromatography involves the separation of mixtures into individual components. Chromatography means “color writing.” With this technique the components of a mixture in a liquid medium are separated. The separation takes place by absorption and capillarity. The paper holds the substances by absorption; capillarity pulls the substances up the paper at different rates. Pigments are separated on the paper and show up as colored streaks. The pattern of separated components on the paper is called a chromatogram.

PRELAB PREPARATION:

Gather leaves from several different plants. CAUTION: Avoid poisonous plants. Autumn leaves from deciduous trees are especially interesting. Sort the leaves by kind (maple, etc.) and color. Review a diagram of a plant cell . Find the grana and the chloroplasts of the cell.

MATERIALS:

Safety goggles
Chromatography solvent (92 parts Petroleum ether to 8 parts acetone)
Chromatography paper (or filter paper) about 1 cm x 15 cm
Ethyl alcohol
Fresh spinach
Test tube
Test tube rack
Scissors and Ruler
Fresh leaves of plants
Glass stirring rod
Paper clip
Cork (to fit test tube)
Mortar and pestle
Sand (optional)
10-ml Graduated cylinder

PROCEDURE:

Leaves should be grouped by kind (maple, etc.) and color. Work with a spinach leaf and with one or more other types. CAUTION: Chromatography solvents are flammable and toxic. Have no open flames; maintain good ventilation; avoid inhaling fumes.

1. Cut a strip of filter paper or chromatography paper so that it just fits inside a 15-cm (or larger) test tube. Cut a point at one end. Draw a faint pencil line as shown in figure 1. Bend a paper clip and attach it to a cork stopper. Attach the paper strip so that it hangs inside the tube, as shown. The sides of the strip should not touch the glass.

2. Tear a spinach leaf into pieces about the size of a postage stamp. Put them into a mortar along with a pinch or two of sand to help with grinding. Add about 5 ml ethyl alcohol to the leaf pieces. Crush leaves with the pestle, using a circular motion, until the mixture is finely ground. The liquid in which the leaf pigments are now for paper chromatography dissolved is called the pigment extract.

3. Use a glass rod to touch a drop of the pigment extract to the center of the pencil line on the paper strip. Let it dry. Repeat as many as 20 times, to build up the pigment spot. NOTE: You must let the dot dry after each drop is added. The drying keeps the pigment dot from spreading out too much.

4. Pour 5 ml chromatography solvent into the test tube. Fit the paper and cork assembly inside. Adjust it so that the paper point just touches the solvent (but not the sides of the tube). The pigment dot must be above the level of the solvent. Watch the solvent rise up the paper, carrying and separating the pigments as it goes. At the instant the solvent reaches the top, remove the paper and let it dry. Observe the bands of pigment. The order, from the top, should be carotenes (orange), xanthophylls (yellow), chlorophyll a (yellow-green), chlorophyll b (blue-green), and anthocyanin (red). Identify and label the pigment bands on the dry strip. Write the species of leaf on the strip as well.
Record the species, external color, and chromatogram pigments in the DATA TABLE of your report sheet.

5. Each pigment has an Rf value, the speed at which it moves over the paper compared with the speed of the solvent.

Rf = Distance moved by the pigment / Distance moved by the solvent

Measure the distance in cm from the starting point (pencil line) to the center of each pigment band. Then measure the entire distance traveled by the solvent. Remember, the starting point for the solvent is also the pencil line and the ending point for the solvent is the top edge of the paper. Do the required divisions and record your Rf values in the DATA TABLE of your report sheet.

6. Wash the mortar and pestle thoroughly, using a little alcohol to remove any remaining pigment.

7. Repeat steps 1 through 6 for each species.

DATA TABLE:

Chromatography Data
Leaf Type (species) External color Chromatogram Pigments
Colors from the Top Pigment Names Rf Values

 

DNA Quiz 2

Name: 

Mendel’s Genetics

 

 

True/False
Indicate whether the sentence or statement is true or false.
1.
The law of segregation states that two or more pairs of alleles separate independently of one
another during gamete formation.
2.
Cells that contain a single set of chromosomes are said to be haploid (N).
3.
Crosses involving a study of one gene are called monohybrid crosses.
4.
A dominant allele masks the effect of a recessive allele.
5.
Mendel concluded that the patterns of inheritance are determined entirely by the environment.
6.
A Punnett square represents the phenotype of an organism.
7.
The physical appearance of an individual organism, as determined by the genes it has inherited from its parents, is called its genotype.
8.
Individuals must exhibit a trait in order for it to appear in their offspring.
9.
In codominance, two alleles are expressed at the same time.
 

Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
10.
In fruit flies, the gene for long wings, L, is dominant to the gene for short wings, l.  A heterozygous long wing male and a short wing female produce many offspring. The possible genotype(s) among the long-winged offspring is (are)
a.
Ll only
c.
LL and Ll
b.
ll only
d.
Ll and ll.
11.
In drosophila, curled wing is recessive to straight wing. If a homozygous straight-winged fly is mated with a curled-wing fly, how many different phenotypes will be produced?
a.
1
c.
3
b.
2
d.
4
12.
If an organism has two identical alleles for a trait, it is
a.
homozygous.
c.
homozygous dominant.
b.
heterozygous.
d.
heterozygous recessive.
13.
Alleles for the same trait separate during
a.
fertilization.
c.
meiosis I.
b.
mitosis.
d.
meiosis II.
14.
The inheritance of genes that determine one trait (hair color) is not affected by the inheritance of genes that control another trait (tongue rolling).  Which of Mendel’s rules apply to the above statement?
a.
the rule of dominance
c.
the rule of independent assortment
b.
the rule of segregation
15.
In fruit flies, the gene for straight wings, C, is dominant to the gene for curly wings, c. Two flies, when bred, produced 98 straight-winged and 102 curly-winged offspring.  What was the genotype of the curly-winged offspring?
a.
CC
c.
cc
b.
Cc
d.
straight-winged
16.
All homozygous individuals have:
a.
the same genotype
c.
two alleles exactly alike
b.
the same phenotype
d.
a hybrid genotype.
17.
If a family has three daughters, the probability that the next child will be a girl is
a.
1/4.
c.
1/2.
b.
1/3.
d.
3/4.
18.
Mendel explained the reappearance of recessive traits in the F2 generation in his principle of
a.
independent assortment.
c.
dominance.
b.
segregation.
d.
blending inheritance.
19.
If any offspring from a test cross show a recessive phenotype, the parent with the unknown genotype is
a.
heterozygous dominant.
c.
heterozygous recessive.
b.
homozygous dominant.
d.
homozygous recessive.
20.
A homozygous black rabbit is mated with a heterozygous rabbit. If black is dominant over white, they should produce:
a.
all white rabbits
b.
all black rabbits
c.
half black and half white rabbits
d.
one pure dominant and heterozygous individual.
21.
Mendel’s finding that the inheritance of one trait had no effect on the inheritance of another became known as the
a.
law of dominance.
c.
law of segregation.
b.
law of universal inheritance.
d.
law of independent assortment.
22.
The phenotype of an organism
a.
represents its genetic composition.
b.
reflects all the traits that are actually expressed.
c.
occurs only in dominant pure organisms.
d.
cannot be seen.
23.
In humans the ability to taste PTC paper is dominant to non-tasting and hair color shows incomplete dominance (Dark hair x blond hair => brown hair).  A brown haired man who cannot taste PTC paper marries a woman with brown hair and who can taste PTC paper.  Their first child had brown hair and could not taste PTC paper. What are the chances that their next child will be a brown taster?
a.
1/4
c.
1/8
b.
1/2
d.
3/8
24.
Two long-furred cats were mated and produced 25 percent short-furred cats.  The parents were probably:
a.
pure recessive individuals
b.
pure dominant individuals
c.
heterozygous individuals
d.
one pure dominant and heterozygous individual.
25.
When certain types of black roosters are crossed with white hens, speckled chickens result. These chickens, which have a mixture of black and white feathers, show
a.
dominance.
c.
polygenes.
b.
codominance.
d.
recessive
26.
codominance : both traits are displayed::
a.
probability : crosses
c.
homozygous : alleles are same
b.
heterozygous : alleles are the same
d.
Punnett square : chromosomes combine
27.
A Punnett square is used to determine the
a.
probable outcome of a cross.
c.
result of segregation.
b.
actual outcome of a cross.
d.
result of meiosis I.
28.
If a family has four sons, the probability that the next child will be a boy is
a.
1/2.
c.
1/5.
b.
1/4.
d.
4/5.
29.
Suppose that on Mars green creatures are dominant over red creatures and that 3-eyes are recessive to 4-eyes.  Assume that inheritance of traits on Mars occurs the same way as on Earth.  A cross between 2 GgEe Martians would result in what fraction of the offspring being red-3-eyed Martians?
a.
1/16
c.
4/16
b.
2/16
d.
9/16
30.
The fact that a man and woman, both of whom have wavy hair, could have children with curly hair, wavy hair, or straight hair is best explained by the phenomenon called
a.
codominance.
b.
dominance.
c.
incomplete dominance.
d.
None of the above; this would be impossible.
31.
A Punnett square does not show the
a.
genetic makeup of the eggs.
c.
genetic makeup of the sperm.
b.
probable outcome of a cross.
d.
actual outcome of a cross.
32.
The “father” of genetics was
a.
T. A. Knight.
c.
Gregor Mendel.
b.
Dr. Judd.
d.
None of the above
33.
What is the probability that the offspring of a homozygous dominant individual and a  homozygous recessive individual will exhibit the dominant phenotype?
a.
0.25
c.
0.66
b.
0.5
d.
1.0
34.
Which of the following is the designation for Mendel’s original pure strains of plants?
a.
P
c.
F1
b.
P1
d.
F2
35.
F2 : F1 ::
a.
P : F1
c.
F1 : P
b.
F1 : F2
d.
dominant trait : recessive trait
36.
The passing of traits from parents to offspring is called
a.
genetics.
c.
development.
b.
heredity.
d.
maturation.
37.
homozygous : heterozygous ::
a.
heterozygous : Bb
c.
dominant : recessive
b.
probability : predicting chances
d.
homozygous : BB
38.
The phenotype of an organism
a.
represents its genetic composition.
b.
reflects all the traits that are actually expressed.
c.
occurs only in dominant pure organisms.
d.
cannot be seen.
39.
If an individual has two recessive alleles for the same trait, the individual is said to be
a.
homozygous for the trait.
c.
heterozygous for the trait.
b.
haploid for the trait.
d.
mutated.
40.
Tallness (T) is dominant to shortness (t) in pea plants. Which of the following represents a genotype of a pea plant that is heterozygous for tallness?
a.
T
c.
Tt
b.
TT
d.
tt
41.
How many different phenotypes can be produced by a pair of codominant alleles?
a.
1
c.
3
b.
2
d.
4
chp_9_web_tutorial_files/i0440000.jpg
42.
Refer to the illustration above. The genotype represented by the cell labeled “2” is
a.
GgIi.
c.
GI.
b.
GGIi.
d.
Gi.
In rabbits, black fur (B) is dominant to brown fur (b). Consider the following cross between two rabbits.
      chp_9_web_tutorial_files/i0460000.jpg
43.
Refer to the illustration above. Both of the parents in the cross are
a.
black.
c.
homozygous dominant.
b.
brown.
d.
homozygous recessive.
44.
Refer to the illustration above. The genotypic ratio of the F1 generation would be
a.
1:1.
c.
1:3.
b.
3:1.
d.
1:2:1.
45.
In pea plants, yellow seeds are dominant over green seeds. What would be the expected genotype ratio in a cross between a plant with green seeds and a plant that is heterozygous for seed color?
a.
1:3
c.
4:1
b.
1:2:1
d.
1:1

 
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Chromatography Lab

Chromatography Lab

Problem:  How do you separate the different pigments in a plant?

Materials:

Cone-type (size 4) coffee filter paper (or Whatman #1 chromatography paper)
large glass jars
acetone
distilled water
capillary tubes
fresh spinach
mortar and pestle
clean sand

Introduction:

In this activity you will be experimenting with a technique called chromatography which will allow you to visually demonstrate that the pigment in leaves is a combination of several different colored pigments.

This technique is useful in that it can separate and identify the various components of mixtures, such as those contained in plant pigments. A pigment is a substance that absorbs light at specific wavelengths, chlorophyll is one of these pigments. Its green-yellow in color is due to the absorption of red, orange, blue, and violet wavelengths and the reflection of the green and yellow wavelengths.   This occurs when white light (containing all of the light wavelengths, or the entire spectrum of colors) shines on the leaf surface, all of the wavelengths are absorbed except for the ones you see, which are green-yellow, those are the portions of the spectrum being reflected.

If the conditions are identical, the relative distance moved by a particular compound is the same from one mixture to another. This is why chromatography can be used to identify a compound. The actual identification requires a simple calculation as shown below:

Rf = distance moved by compound from original spot divided by the distance moved by solvent from original spot

It is important to remember that several factors can influence the reliability of the Rf value, these include humidity, temperature, solvent, pigment extract preparation, and the amounts of the material present.  Values are comparable only when the extracts are prepared in the same way and the chromatograms are prepared identically and developed together in the same container.

Acetone is flammable (even the amount found in nail polish remover), keep it away from sparks or open flames. Wear eye protection, especially if using pure acetone.

Procedure

1.   Each lab group (or individual if not working in groups) will need 4 strips of filter paper, approximately 6 inches long and 1 inch wide, 2 chromatography development containers (500 ml beakers or large fruit jars work well), 2 large rubber bands (able to stretch around the vessels from the mouth to the bottom of the vessel), 2 solvents, water and either pure acetone, or nail polish remover.

2.   Do the following with both fresh spinach leaves; tear leaf material and place in a glass container, cover with acetone (this should be done the day before the actual lab activity). An alternative pigment extraction technique is to use a
mortar and pestle. Place plant material the vessel, add a little clean sand, some acetone and then grind until a dark green liquid appears.    Both techniques yield very dark pigments with which to work. Be certain to keep the pigments apart throughout the entire activity.

3.   Place one of each solvents (water and acetone, or nail polish remover) in the chromatography vessels and stretch a rubber band length-wise around each vessel. The rubber band will be the mechanism for hanging the chromatography strips.

4.   Make a pencil mark on each of the 2 chromatography strips, in the center, directly above the point of the strip, about 1 inch from the tip of the paper. Using a capillary tube, or tooth pick, apply the plant pigment to each filter paper strip. This is done by touching the tooth pick or capillary tube which has been dipped in the pigment, to the pencil mark. Make an application, then wave the paper gently to dry it a little before the next application. Be patient, you will need 12 to 15 applications.

5.   By now you should have 2 strips with spinach pigment.  Suspend one of each in each of the chromatography development vessels. You can attach them with paper clips, or simply fold over a portion of the end and it should hang in place. The tip of each strip should just touch the solvent.

6.   Wait 20 to 30 minutes for the chromatograms to develop. Remove the chromatograms. Mark with a pencil (NOT a pen) where the solvent stopped as it moved up the chromatogram. This is called the solvent front. Mark also where each pigment stopped moving up the chromatogram. Using the equation below, determine a reference number for each pigment on the chromatograms. Depending on which chromatogram you are viewing, you should see greens, yellow/yellow orange, and red. All measurements should be in mm. (Any material which did not move from the
pencil dot is insoluble).

Rf = distance moved by compound from original spot divided by the
distance moved by solvent from original spot

Note: each pigment has a special name,
green = chlorophyll a or b
yellow/yellow orange = carotene
red = anthocyanin
brown = xanthophyll

The reference numbers for the chlorophylls in this activity are:
0.28 = chlorophyll a, 0.18 = chlorophyll b (spinach). You need these
numbers so that you can determine one chlorophyll from the other.
Calculate reference fronts for all of your pigments.

See if your calculations come close to those above for chlorophyll a and b.

Note:  You can use different solvents such as mixtures involving petroleum ether
to do this sort of paper chromatography.

To view notes and a graphic showing a separation of plant pigments involving
paper chromatography, click here.  Can you calculate the Rf values for the
pigments separated in this graphic?

Conclusion Questions

1.  What reference numbers (Rf) did you calculate for chlorophyll a and chlorophyll b?
2.  With what you have discovered about pigments, what conclusions can you
make regarding the changing color of leaves in autumn?
3.  What adaptive purpose do different colored pigments serve for a plant?
4.  Why do some pigments move farther up the chromatogram than others?
5.  What are some possible sources of error in this lab?

Paper chromatography is a technique used to separate a mixture into its component molecules. The molecules migrate, or move up the paper, at different rates because of differences in solubility, molecular mass, and hydrogen bonding with the paper.

For a simple, beautiful example of this technique, draw a large circle in the center of a piece of filter paper with a black water-soluble, felt-tip pen. Fold the paper into a cone and place the tip in a container of water. In just a few minutes you will have tie-dyed filter paper!

Separation of black ink pigments

The green, blue, red, and lavender colors that came from the black ink should help you to understand that what appears to be a single color may in fact be a material composed of many different pigments —and such is the case with chloroplasts.

chromatography setup

 

In paper chromatography the pigments are dissolved in a solvent that carries them up the paper. In the ink example, the solvent is water. To separate the pigments of the chloroplasts, you must use an organic solvent

 

 

pigment separation

 

pigment separation

 

Analysis of Results I

If you did a number of chromatographic separations, each for a different length of time, the pigments would migrate a different distance on each run. However, the migration of each pigment relative to the migration of the solvent would not change. This migration of pigment relative to migration of solvent is expressed as a constant, Rf (Reference front). It can be calculated by using the formula: