TONICITY
What is the tonicity of this solution?
What happens to the cell?
What is this called?
What is the tonicity of this solution?
What happens to the cell?
What is this called?
What is the tonicity of this solution?
What happens to the cell?
What is this called?
Animations by Terry Brown – http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm
Toothpick-ase: Introduction to Enzymes
Enzymes are used in all metabolic reactions to control the rate of reactions and decrease the amount of energy necessary for the reaction to take place. Enzymes are specific for each reaction and are reusable. Enzymes have an area called the active site to which a specific substrate will bond temporarily while the reaction is taking place. Enzymes are proteins that are used as catalysts in biochemical reactions. A catalyst is a factor that controls the rate of a reaction without itself being used up. In biological systems, enzymes are used to speed up the rate of a reaction. However, there are a number of factors that can affect the rate of an enzyme-facilitated reaction, in addition to the presence of the enzyme, amongst them are:
Here is a set of quick activities designed to simulate how substrate concentration and temperature affect enzyme function. In the activities that follow:
Materials:
100 toothpicks per team
bowl
clock/watch with a second hand
Pencil
Procedure:
Part A – rate of Product Formation in an Enzyme-Facilitated reaction
In this activity, the toothpicks represent a substrate and your thumbs and index fingers represent the enzyme, toothpick-ase. When you break a toothpick, the place where the toothpick fits between your fingers represents the active site of the enzyme.
1. Count out 100 unbroken toothpicks into a bowl on your desk.
2. Have one person in the group serve as the timer, have one person serve as the recorder, and have another person in your group act as the enzyme or toothpick-ase.
3. The person acting as the enzyme is to break toothpicks without looking at the bowl and all of its products (broken toothpicks). All broken toothpicks must remain in the bowl along with the unbroken toothpicks, & you cannot re-break a broken toothpick!.
4. The experiment is conducted in 10 second intervals.
5. WITHOUT LOOKING AT THE BOWL, break as many toothpicks as you can in 10 second intervals and record this on the data table. Broken toothpicks should be kept in the bowl with unbroken toothpicks because products & reactants mix in metabolic reactions. DO NOT BREAK TOOTHPICKS ALREADY BROKEN!
Remember when counting, two halves equal a whole broken toothpick!
6. Do another 10 seconds of breaking (total of 20 seconds now), and then count & record the number of toothpicks broken.
7. Do another 10 seconds (thirty seconds total now) more of breaking and count and record the number of toothpicks broken.
8. Continue breaking toothpicks for these total time intervals ( 60, 120, and 180 seconds). REMEMBER TO ALWAYS THROW BROKEN TOOTHPICKS BACK IN THE PILE (because products & reactants stay mixed in reactions), BUT DON’T RE-BREAK THEM (the enzyme has already acted on the substrate!
6. Graph the number of toothpicks broken as a function of time (10, 20, 30, 60, 120, & 180 seconds.) Be sure to title your graph and to label the x and y-axis.
Data Table:
| Total Time (seconds) | Number of toothpicks broken |
| 10 | |
| 20 (additional 10 seconds) |
|
| 30 (additional 10 seconds) |
|
| 60 (additional 30 seconds) |
|
| 120 (additional 60 seconds) |
|
| 180 (additional 60 seconds) |
Graph Title: ____________________________________________________________
Materials:
1 box toothpicks per team
100 paper clips
clock/watch with a second hand
Pencil
PART B: EFFECT OF SUBSTRATE CONCENTRATION ON REACTION RATE
Discussion & summary:
Data Table:
| Time (seconds) | Toothpick Concentration | Number of toothpicks broken |
| 20 | 10 | |
| 20 | 20 | |
| 20 | 30 | |
| 20 | 40 | |
| 20 | 50 | |
| 20 | 60 | |
| 20 | 70 | |
| 20 | 80 | |
| 20 | 90 | |
| 20 | 100 |
Graph Title: ____________________________________________________________
Materials:
10 toothpicks per team
ice & ice bucket
clock/watch with a second hand
Pencil
PART C: EFFECT OF TEMPERATURE SUBSTRATE CONCENTRATION ON REACTION RATE
Discussion & summary:
Analysis & conclusions:
1.What happens to the reaction rate as the supply of toothpicks runs out?
2. What would happen to the reaction rate if the toothpicks were spread out so that the “breaker” has to reach for them?
3. What would happen to the reaction rate if more toothpicks (substrate) were added?
4. What would happen to the reaction rate if there were two “breakers” (more enzymes)?
5. What happens if the breaker wears bulky gloves (active site affected) when picking up toothpicks?
6. Explain what would happen to an enzyme-facilitated reaction if temperature were increased. Be sure to include the effect if temperature were increased to 100°C.
7. What is the optimal temperature (°C) for enzymes functioning in the human body?
Transpiration
Introduction:
The amount of water needed daily by plants for the growth and maintenance of tissues is small in comparison to the amount that is lost through the process of transpiration and guttation. If this water is not replaced, the plant will wilt and may die. The transport up from the roots in the xylem is governed by differences in water potential ( the potential energy of water molecules). These differences account for water movement from cell to cell and over long distances in the plant. Gravity, pressure, and solute concentration all contribute to water potential and water always moves from an area of high water potential to an area of low water potential. The movement itself is facilitated by osmosis, root pressure, and adhesion and cohesion of water molecules.
The overall process: Minerals actively transported into the root accumulate in the xylem, increase solute concentration and decrease water potential. Water moves in by osmosis. As water enters the xylem, it forces fluid up the xylem due to hydrostatic root pressure. But this pressure can only move fluid a short distance. The most significant force moving the water and dissolved minerals in the xylem is upward pull as a result of transpiration, which creates a negative tension. The “pull” on the water from transpiration is increased as a result of cohesion and adhesion of water molecules.
The details: Transpiration begins with evaporation of water through the stomates (stomata), small openings in the leaf surface which open into air spaces that surround the mesophyll cells of the leaf. The moist air in these spaces has a higher water potential than the outside air, and water tends to evaporate from the leaf surface. The moisture in the air spaces is replaced by water from the adjacent mesophyll cells, lowering their water potential. Water will then move into the mesophyll cells by osmosis from surrounding cells with the higher water potentials including the xylem. As each water molecule moves into a mesophyll cell, it exerts a pull on the column of water molecules existing in the xylem all the way from the leaves to the roots. This transpirational pull is caused by (1) the cohesion of water molecules to one another due to hydrogen bond formation, (2) by adhesion of water molecules to the walls of the xylem cells which aids in offsetting the downward pull of gravity. The upward transpirational pull on the fluid in the xylem causes a tension (negative pressure) to form in the xylem, pulling the xylem walls inward. The tension also contributes to the lowering of the water potential in the xylem. This decrease in water potential, transmitted all the way from the leaf to the roots, causes water to move inward from the soil, across the cortex of the root, and into the xylem. Evaporation through the open stomates is a major route of water loss in the plant. However, the stomates must open to allow the entry of CO2 used in photosynthesis. Therefore, a balance must be maintained between the gain of CO2 and the loss of water by regulating the opening and closing of stomates on the leaf surface. Many environmental conditions influence the opening and closing of the stomates and also affect the rate of transpiration. Temperature, light intensity, air currents, and humidity are some of these factors. Different plants also vary in the rate of transpiration and in the regulation of stomatal opening.
Exercise 9A Transpiration
In this lab, you will measure transpiration under various laboratory conditions using a potometer. Four suggested plant species are Coleus, Oleander, Zebrina, and two week old bean seedlings.
Materials:
0.1 mL pipette, plant cutting, ring stand, clamps, clear plastic tubing, petroleum jelly, fan, lamp, spray bottle, and plastic bag.
Procedures:
Each lab group will expose one plant to one treatment.
1. Place the tip of a 0.1 mL pipette into a 16 -inch piece of clear plastic tubing.
2. Submerge the tubing and the pipette in a shallow tray of water. Draw water through the tubing until all the air bubbles are eliminated.
3. Carefully cut your plant stem under water. This step is very important, because no air bubbles must be introduced into the xylem.
4. While your plant and tubing are submerged, insert the freshly cut stem into the open end of the tubing.
5. Bend the tubing upward into a “U” and use the clamp on a ring stand to hold both the pipette and the tubing.
6. If necessary use petroleum jelly to make an airtight seal surrounding the stem after it has been inserted into the tube. Do not put petroleum jelly on the end of the stem.
7. Let the potometer equilibrate for 10 minutes before recording the time zero reading.
8. Expose the plant in the tubing to one of the following treatments( you will be assigned a treatment by your teacher):
a). Room conditions.
b). Floodlight (over head projector light).
c). Fan ( place at least 1 meter from the plant, on low speed, creating a gentle breeze).
d). Mist ( mist leaves with water and cover with a transparent plastic bag; leave the bottom of the bag open).
9. Read the level of water in the pipette at the beginning of your experiment(time zero) and record your finding in Table 9.1.
10. Continue to record the water level in the pipette every 3 minutes for 30 minutes and record the data in Table 9.1.
Table 9.1: Potometer Readings
| Time (min) | Beginning (0) | v3ss | fff6ff | 9 | 12 | 15 | 18 | 21 | 24 | 27 | 30 |
| Reading (mL) | 4nnnnnnn | 4nnnnnn | nnnn4 |
11. At the end of your experiment, cut the leaves off the plant and mass them. Remember to blot off all excess water before massing.
Mass of leaves ______________ grams.
Calculation of Leaf Surface Area
The total surface area of all the leaves can be calculated by using one of the following procedures.
__________________ = Leaf Surface Area (m2)
Leaf Trace Method:
After arranging all the cut-off leaves on the grid below, trace the edge pattern directly on to the grid. Count all of the grids that are completely within the tracing and estimate the number of grids that lie partially within the tracing. The grid has been constructed so that a square of four blocks equals 1 cm2. The total surface area can then be calculated by didvding the total number of blocks covered by 4. Record the value above.
Grid 9.1
Leaf Mass Method:
12. Water lost per square meter: To calculate the water loss per square meter of leaf surface, divide the water loss at each reading (Table 9.1) by the leaf surface area you calculated.
Table 9.2: Individual Water Loss in mL /m2
| Time Intervals ( minutes) | ||||||||||
| s | 0-3 | 3-6 | 6-9 | 9-12 | 12-15 | 15-18 | 18-21 | 21-24 | 24-27 | 27-30 |
| Water Loss (mL) | ||||||||||
| Water loss per m2 | ||||||||||
13. Record the averages of the class data for each treatment in Table 9.3.
Table 9.3: Class Average Cumulative Water Loss in mL /m2
| Time ( minutes) | |||||||||||
| Treatment | 0 | 3 | 6 | 9 | 12 | 15 | 18 | 21 | 24 | 27 | 30 |
| Room | 0 | ||||||||||
| Light | 0 | ||||||||||
| Fan | 0 | ||||||||||
| Mist | 0 | ||||||||||
14. For each treatment, graph the average of the class data for each time interval. You may need to convert data to scientific notation. All numbers must be reported to the same power of ten for graphing purposes.
Graph Title________________________________________
Graph 9.1
Analysis of Results:
1. Calculate the average rate of water loss per minute for each of the treatments:
Room: ______________________________________________________________________
Fan: _______________________________________________________________________
Light: _______________________________________________________________________
Mist: _______________________________________________________________________
2. Explain why each of the conditions causes an increase or decrease in transpiration compared to the control.
| Conditions | Effect | Reasons |
| Room | ||
| Fan | ||
| Light | ||
| Mist |
3. How did each condition affect the gradient of water potential from stem to leaf in the experimental plant?
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
4. What is the advantage to a plant of closed stomata when water is in short supply? What are the disadvantages?
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
5. Describe several adaptations that enable plants to reduce water loss from their leaves. Include both structural and physiological adaptations.
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
6. Why did you need to calculate leaf surface area in tabulating your results?
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
Understanding Graphs
| Graph 1: Rabbits Over Time
a. The graph shows a __________ growth curve. |
|
| Graph 2: Average Toe Length
a. In 1800, about how many people surveyed had a 3 cm toe? _______ |
|
| Graph 3: Mexico and US
a. In Mexico, what percentage of the population is between 0-4 years of age? _______ In the US? ______
|
|
| Chart 4: Trapping Geese
In order to estimate the population of geese in Northern Wisconsin, ecologists marked 10 geese and then released them back into the population. Over a 6 year period, geese were trapped and their numbers recorded. a. Use the formula to calculate the estimated number of geese in the area studied? _____________
|
|
|||||||||||||||||||||
| Chart 5: Mushroom Plots
Another ecologist uses a different method to estimate the number of mushrooms in a forest. She plots a 10×10 area and randomly chooses 5 spots, where she counts the number of mushrooms in the plots and records them on the grid. a. Calculate the number of mushrooms in the forest based on the grid data: _________________ |
 |
| Chart 6: Snakes & Mice
The data shows populations of snake and mice found in an experimental field. a. During which year was the mouse population at zero population growth? ______ |
|
| Sucrose Hydrolysis Using Sucrase |  |
INTRODUCTION:
In this lab, you will demonstrate the production of the enzyme sucrase (invertase) by yeast. The enzyme sucrase catalyzes the hydrolysis of the disaccharide sucrose to invert sugar. Invert sugar is a mixture of glucose and fructose, which are both monosaccharides. Yeast cannot directly metabolize (ferment) sucrose. For the yeast to utilize sucrose as an energy source, it must first convert it to the fermentable monosaccharides glucose and fructose.
Benedict’s solution is a test reagent that reacts positively with simple reducing sugars. All monosaccharides and most disaccharides are reducing sugars, possessing a free carbonyl group (=C=O). Sucrose is an exception in that it is not a reducing sugar. A positive Benedict’s test is observed as the formation of a brownish-red cuprous oxide precipitate. A weaker positive test will be yellow to orange. Both glucose and fructose test positive with benedict’s solution, sucrose does not.
MATERIALS NEEDED:
*Yeast filtrate solution
one 7 gram package active dry yeast per 80 mL distilled water
Ring stand and ring to hold funnel
Filtering funnel
Filter paper (fast speed)
**5% sucrose solution
5 grams sucrose per 95 mL distilled water
***5% glucose (dextrose) solution
5 grams dextrose per 95 mL distilled water
Benedict’s qualitative solution
Distilled water
Five 10-mL graduated cylinders (one for each solution)
7 test tubes 18 x 150 mm
Test tube holder
Test tube rack
2 400-mL beakers
Hot plate
PRE-LAB:
* To prepare a yeast filtrate solution, mix one package of active dry yeast with 80 mL of distilled water. Let stand for 20 minutes, stirring occasionally. Filter the resulting suspension and save the filtrate solution. This is your invertase extract. Refrigerate the extract if held overnight. Approximately enough for 8 labs.
**To prepare a 5% sucrose solution, dissolve 5 grams of sucrose in 95 mL of distilled water. This should be prepared shortly before use. Approximately enough for 4 labs.
***To prepare a 5% glucose solution, dissolve 5 grams of dextrose (this is the name used when dry) in 95 mL of distilled water. This should be prepared shortly before use. Approximately enough for 9 labs.
PROCEDURE:
1. Label 3 test tubes A1, A2, and A3, and place in the test tube rack. Place into the test tubes as follows:
A1
10 mL
Into tube A2, place 10 mL of 5% sucrose solution and 4 mL of invertase extract.
Into tube A3, place 10 mL distilled water and 4 mL of invertase extract.
Thump the tubes to mix.
2. Put approximately 250 mL of 30 to 35 oC water into a 400-mL beaker. Incubate the three tubes in this warm water bath for 35 minutes.
3. Label 4 test tubes B1, B2, B3 and B4, and place in the test tube rack. Place 5 mL of Benedict’s qualitative solution into each tube. Now transfer to the B tubes as follows:
B1
A1
Into tube B2, transfer the contents of tube A2.
Into tube B3, transfer the contents of tube A3.
Into tube B4, place 10 mL of 5% glucose solution.
Thump the tubes to mix.
4. Place tubes B1, B2, B3, and B4 into a boiling water bath. CAUTION: do not let the bath boil hard. Keep it just at the boiling point. After 3 or 4 minutes, remove the tubes and note whither any change is evident.
QUESTIONS AND OBSERVATIONS:
1. Did tube B1 test positive or negative?
2. What does this show?
3. Did tube B2 test positive or negative?
4. What does this show?
5. Did tube B3 test positive or negative?
6. What does this show?
7. Did tube B4 test positive or negative?
8. What does this show?
