Photosynthesis and Cellular Respiration – Understanding the Basics of Bioenergetics and Biosynthesis1

This figure shows the processes that plant cells use to provide the energy needed for many of the activities of life.

First, photosynthesis uses the energy in sunlight to make glucose from carbon dioxide and water.

Then, cellular respiration uses glucose and oxygen as inputs for reactions that release energy, which is used to make ATP from ADP and P.

Finally, hydrolysis of ATP provides energy in the form needed for many biological processes.

1a. Cellular respiration produces carbon dioxide and water. These molecules are inputs for

__________________________________________.(cellular respiration / hydrolysis of ATP / photosynthesis)

1b. Photosynthesis produces glucose and oxygen, which are inputs for _________________________ .

1c. Notice that photosynthesis and cellular respiration make a cycle where the products of each process are input molecules for the other process. Draw an oval around the part of the figure that shows this cycle.

2a. Cellular respiration produces ATP and H2O. These molecules are the inputs for _________________

__________, which provides the energy for many biological processes.

2b. The hydrolysis of ATP produces ADP and P, which are inputs for ____________________________.

2c. Cellular respiration and hydrolysis of ATP make a cycle where the products of each process are inputs for the other process. Draw a rectangle around the part of the figure that shows this cycle.

3. This diagram summarizes the energy transformations and transfers that plant cells use to provide the energy needed for the activities of life. Label each arrow with the name of the process represented by the arrow:

cellular respiration hydrolysis of ATP photosynthesis.

1By Dr. Ingrid Waldron, Department of Biology, University of Pennsylvania, © 2017. Teachers are encouraged to copy this Student Handout for classroom use. This Student Handout and Teacher Notes with background information and instructional suggestions are available at http://serendipstudio.org/exchange/bioactivities/photocellrespir.

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To represent the overall chemical equations for photosynthesis and cellular respiration, you will use 16 rectangles. Divide a sheet of paper into 16 rectangles.

For photosynthesis, prepare: four rectangles, each with one of the following: C6H12O6, 6 CO2, 6 H2O, 6 O2;

write the name of the molecule represented by each chemical formula one rectangle with → to represent a chemical reaction two rectangles with + one rectangle with sunlight

For cellular respiration, you will need all of the photosynthesis rectangles except the last, plus: four rectangles, each with one of the following: ~29 ATP, ~29 ADP, ~29 P, ~29 H2O one additional rectangle with → two additional rectangles with + one rectangle with \/

\/

4. Arrange the eight rectangles for photosynthesis to show the overall chemical equation for photosynthesis. Copy this chemical equation into the top box in this chart.

5. Rearrange the photosynthesis rectangles (except for sunlight) to show one of the chemical equations for cellular respiration. Arrange the additional rectangles (except the last) to show the other chemical equation for cellular respiration. Use the rectangle with two \/ to connect the →s in these two equations; this represents energy transfer between the coupled reactions of cellular respiration. Copy these chemical equations into the bottom box in the above chart.

6. Draw two arrows to show how the products of photosynthesis can be used as the inputs for cellular respiration. Next, draw two arrows to show how two of the products of cellular respiration can be used as the inputs for photosynthesis.

7a. Why do plants need to carry out both photosynthesis and cellular respiration?

7b. Why do animals need to carry out cellular respiration, but not photosynthesis?

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Photosynthesis

Cellular Respiration

Some of the sugar molecules produced by photosynthesis are used to synthesize other organic molecules. For example, multiple glucose monomers are joined together to make polymers such as starch or cellulose.

8a. Circle one glucose monomer in each polymer in this figure.

8b. Put an * next to the location of each carbon atom in a glucose monomer in cellulose.

This figure shows the process that adds glucose monomers to a growing starch or cellulose polymer.

9. Explain why dehydration synthesis is a good name for this process.

10. Glucose produced by photosynthesis is also a precursor for the synthesis of other organic

molecules such as amino acids, which are the monomers in ________________ .

A plant is made up primarily of organic molecules (e.g. cellulose and proteins) plus water molecules. To grow, plants add more organic molecules and more water.

11. Explain how photosynthesis contributes to plant growth.

12. The sugars produced by photosynthesis are used for two different purposes: Some of the sugar molecules are used for cellular respiration to produce ________ which provides

energy for the processes of life. Some of the sugar molecules are used to synthesize _____________________________________.

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Plant Growth PuzzleBiomass is the weight of the organic molecules in an organism. For plants and many other organisms,

biomass = an organism’s weight - the weight of the water in the organism.

13a. ___________________________ can result in increased biomass for a plant. (Cellular respiration / Photosynthesis)

13b. What molecules are taken in by the plant and used to create organic molecules that become part of the plant's biomass?

14. When a seed sprouts and a seedling begins growing underground in the dark, the seedling cannot

carry out _____________________________ because there is no light. A seedling growing in the dark (cellular respiration / photosynthesis)

will only carry out _______________________________. Starch molecules stored in the seed are (cellular respiration / photosynthesis) broken down to glucose molecules which are used for cellular respiration to produce the ATP needed by the seedling. The carbon dioxide produced by cellular respiration is released to the air.

15. A seed sprouting underground loses biomass. Explain why.

An experimenter kept seeds in petri dishes under three different conditions (shown in the top row of the table below). At the beginning of the experiment each batch of seeds weighed 1.5 grams, which was almost all biomass, since the seeds had very little water.

After ten days, the seeds that were exposed to water had sprouted to produce plants. To determine the biomass of each batch of seeds/plants, they were dried in an oven overnight (to remove all the water) and then weighed.

16. For each condition in the table below, circle the predicted change in biomass after ten days. Explain why you predict a decrease (↓), no change (→), or increase (↑) in biomass.

Condition for each batch of seeds

Light, no water(seeds didn’tsprout)

Light, water(seedssprouted)

Water, no light(seedssprouted)

Predicted change in biomass ↓ → ↑ ↓ → ↑ ↓ → ↑

Reason for predicting decrease, no change, or increase in biomass

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17. Your teacher will tell you the results of the experiment. Enter the observed results in this table. For each condition, circle the observed change in biomass after 10 days. (1.46 grams of biomass is not significantly different from the 1.5 g of total mass in each initial batch of seeds.) If any of the observed results differ from your predictions in question 16, explain the biological reasons for the observed results.

Condition for each batch of seeds

1. Light, no water (seeds did not sprout)

2. Light, water (seeds sprouted to produce plants)

3. Water, no light (seeds sprouted to produce plants)

Observed biomass at 10 days (grams)Observed change in biomass ↓ → ↑ ↓ → ↑ ↓ → ↑

If any result did not match your prediction, explain a possible reason for the observed result.

This figure summarizes some paradoxical results observed after 10 days in each experimental condition. Notice that the experimental condition that resulted in the lowest total mass did not result in the lowest biomass.

18. Explain why the seeds in light with no water had less total mass, but more biomass than the plants that developed with water, but no light. (Hint: There is very little water in seeds, but more than three-quarters of the total mass of an actively growing plant is water.)

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LIGHT, NO WATERLOWEST VOLUME ANDLOWEST TOTAL MASS

WATER, NO LIGHTLOWEST BIOMASS