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11 Photosynthesis-S - PDF worksheet with Answer key.

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Photosynthesis 1

Photosynthesis

How do light-dependent and light-independent reactions provide food for a plant?

Plants are the original solar panels. Through photosynthesis a plant is able to convert electromagnetic (light) energy into chemical energy. This energy is used not only to keep the plant alive, but also to sustain all creatures that rely on the plant for food and shelter. Plants and photosynthetic algae are also the source of all oxygen on Earth, allowing the inhabitants of Earth to benefit from our most plentiful renewable energy resource.

Model 1 – Chloroplast

6co 2 + 12h 2 o + sunlight energy ⎯→ c 6 h 12 o 6 + 6o 2 + 6h 2 o.

Outer membrane

Inner membrane

Stroma Site of the Calvin cycle, or light- independent reactions.

Thylakoid Site of the light-dependent reactions. Contains chlorophyll—a colored compound that absorbs light.

Glucose (C 6 H 12 O 6 )

• Consider the organelle illustrated in Model 1.

a. What is the name of this organelle?

b. Is this organelle more likely to be found in animal cells or plant cells?

• The structures inside the organelle in Model 1 are called thylakoids. What compound necessary for photosynthesis is contained in the thylakoids?

Chloroplast

Plant cells

Chlorophyll

2 POGIL™ Activities for AP* Biology

• Consider the chemical reaction in Model 1. This represents photosynthesis.

a. What substances are the reactants in photosynthesis? Include the name and chemical formula of each substance in your answer.

b. Where in the organelle are these molecules stored before they are used in photosynthesis?

c. Is photosynthesis an endergonic or exergonic reaction? Support your answer with evidence from Model 1.

d. What is the energy source for photosynthesis?

• Photosynthesis occurs in two parts—the light-dependent reactions and the light-independent reactions.

a. What is another name for the light-independent reactions?

b. In what part of the chloroplast do the light-dependent reactions occur?

c. In what part of the chloroplast do the light-independent reactions occur?

Considering your answers to Question 4, what compound is best able to absorb the light energy from the Sun and convert it into chemical energy?

What substances are produced during photosynthesis? Include the name and chemical formula of each substance in your answer.

Why is it necessary to have six CO 2 entering the chloroplast?

CO2 - carbon dioxide H2O - water

In the stroma.

Endergonic - larger molecules have been built from smaller ones.

Calvin Cycle

Thylakoid membrane

They occur in the stroma.

Chlorophyll is best able to absorb light energy.

C6H12O6 - glucose O2 - oxygen

Each carbon from CO2 is used to build glucose.

4 POGIL™ Activities for AP* Biology

The light-dependent reactions of photosynthesis include three major processes:

A. Excited electrons leave chlorophyll and reduce NADP+ into NADPH.

B. Excited electrons moving through the electron transport chain provide the free energy needed to pump hydrogen ions into the inner thylakoid.

C. Hydrogen ions flowing out of the thylakoid via a protein channel provide the free energy needed to convert ADP to ATP.

In Model 2, label the diagram with “A,” “B,” and “C” to indicate where the three steps in the Read This! box are occurring.

The light-dependent reactions include an electron transport chain system that works in a very similar fashion to the electron transport chain in respiration. Briefly describe how this system works and what job it performs in the light-dependent reactions. (Your answer should include a discussion about concentration gradient.)

Refer to Model 2.

a. Name the embedded protein complex found in the thylakoid membrane that uses excited electrons to reduce NADP+ into NADPH.

b. Name the embedded protein complex found in the thylakoid membrane that provides excited electrons to the electron transport chain.

c. Name the embedded protein complex found in the thylakoid membrane that converts ADP to ATP using free energy from a flow of hydrogen ions.

Electrons at high energy are passed between molecules. The cytochrome complex pumps H+ ions into the thylakoid space only to have them diffuse back out through ATP SYnthase. The whole process is powered by the high energy electrons as they seek lower potential energy.

NADPH reductase

Photosystem II

ATP synthase

Photosynthesis 5

• Once a chlorophyll molecule has released electrons it is no longer useful until those electrons are replaced.

a. According to Model 2, what is the source of replacement electrons for those released from photosystem I?

b. According to Model 2, what is the source of replacement electrons for those released from photosystem II?

Is carbon dioxide involved in the light-dependent reaction?

a. Write a chemical reaction that summarizes all of the chemical reactions in the light-dependent reactions of photosynthesis starting with two water molecules.

b. In the photosynthesis reaction in Model 1, twelve water molecules are shown as reactants, but six water molecules are shown as products. Are any of the twelve water molecules products of the light-dependent reactions?

c. Calculate the total number of oxygen, NADPH, and ATP molecules that are produced when twelve water molecules complete the light-dependent reactions.

• Where do the ATP and NADPH produced during the light-dependent reactions go when the process is complete?

Electrons from the ETC.

Electrons from H2O.

2 H2O + 2NADP + 3ADP + 3P; yields O2 + 2NADPH + 3ATP

2 H2O produces 3ATP 1 O 2 NADPH

6 H2O produces 9ATP 3 O 6 NADPH

To the light-independent reactions (Calvin Cycle)

Photosynthesis 7

• Ribulose biphosphate (RuBP) combines with carbon dioxide (CO 2 ) to form phosphoglycerate (PGA) during the carbon fixation phase of the Calvin cycle.

a. How many CO 2 molecules are used in one turn of the Calvin cycle?

b. How many PGA molecules are made in one turn of the Calvin cycle?

c. How many carbon atoms are in each PGA molecule?

d. Calculate the total number of carbon atoms represented in all of the PGA molecules used in one turn of the Calvin cycle.

Explain what happened to the carbon atoms from the carbon dioxide molecules that entered the Calvin cycle.

Consider the term “carbon fixation.” Think individually for a moment what this term might mean, then share ideas among the group. Record the group’s consensus definition for carbon fixation here.

Model 3 is a simplified version of the Calvin cycle. Each of the three phases in the cycle consist of multiple reactions that are catalyzed by enzymes specific to that reaction. These enzymes have names like RuBisCo, phosphoglycerate kinase, and PGAL hydrogenase.

• Refer to the reduction phase of the Calvin cycle in Model 3.

a. What molecule does the PGA molecule turn into during this phase of the Calvin cycle?

b. Describe specifically how the structures of the two molecules in part a are different.

c. Identify the types and numbers of molecules that provide the free energy necessary for the reduction of the PGA molecules.

d. Is the total number of carbon atoms present in the Calvin cycle changed during the reduction phase? Support your answer with evidence from Model 3.

3 molecules

6 molecules

3 carbon atoms

18 carbon atoms

They were used to create PGA.

Carbon fixation = extracting carbon from the air and sequestering it as a solid compound.

PGA = carboxyl group PGAL = carbonyl group

No, we start and end with 6 molecules of PGA/PGAL, both of which have 3 carbon atoms.

8 POGIL™ Activities for AP* Biology

• Water is a product of the reduction phase of the Calvin cycle. a. How many water molecules are produced?

b. Explain where the hydrogen and oxygen atoms in these water molecules originated.

• Refer to the regeneration phase of the Calvin cycle in Model 3. a. How many PGAL molecules continue on to the regeneration phase of the Calvin cycle?

b. Identify the types and numbers of molecules that provide the free energy necessary for the regeneration of these molecules.

c. How many total carbon atoms remain in the Calvin cycle at this point?

d. What molecule(s) are “regenerated” in this phase of the cycle?

e. How many total carbon atoms leave the Calvin cycle before the regeneration phase?

f. What happens to the PGAL molecule that does not continue on in the Calvin cycle?

As you have learned from your careful study of the Calvin cycle illustrated in Model 3, three atoms of car- bon enter the cycle as carbon dioxide and three carbon atoms leave the cycle as PGAL. It is easy to assume that the three atoms that leave are one and the same with the three that entered, but that is incorrect. It may be that none of the carbon atoms from the carbon dioxide become incorporated into a molecule of PGAL that leaves the cycle. Alternatively, it is also possible that one of the carbon atoms from the carbon dioxide will become part of a PGAL molecule that leaves the cycle. Eventually all of the carbon atoms that enter the cycle will leave as part of a PGAL molecule, but they must wait their turn.

6 water molecules are produced.

5 molecules

3 ATP molecules

15 carbon atoms

Used to produce glucose and other molecules.

10 POGIL™ Activities for AP* Biology

Extension Questions

Model 4 – the study of photosynthesis.

Carbon dioxide

Concentration RuBP of molecules

• When algae are undergoing photosynthesis, the concentrations of various molecules change with- in the cells. These concentrations can be monitored and graphed. In complete sentences, explain the shape of each line on the graph in Model 4.

carbon dioxide—

• Photosynthesis is typically represented by a simple equation.

6CO 2 + 6H 2 O + light ⎯→ C 6 H 12 O 6 + 6O 2

a. Compare and contrast this simplified equation with the one presented in Model 1.

b. Using the information from this activity explain why the equation above is a vastly oversim- plified representation of the actual process.

a reactant in photosynthesis and is used up in the Calvin Cycle.

produced in the light-dependent reactions by photosystem II

Ribulose bisphosphate levels decline and are regenerated through the Calvin Cycle.

This equation has 6 fewer H2O molecules on the reactant side and six fewer on the product side. Otherwise, it is the same.

Although H2O is an overall "input" to photosynthesis, in reality it is partially regenerated in the Calvin Cycle, which can be seen in Model 3. Therefore, the equation represents a "net" input of H2O without accounting for the 6 NADPH/9 ATP needed for one turn of the Calvin Cycle.

• Multiple Choice

Topic : Unit 3: Cellular Energetics

Subject : ap biology.

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