Light reactions and calvin cycle

Biology-Assignments

10.1 Photosythesis_______________________________________________________

1A. Write the overall reaction (major reactants and major products) for photosysthesis:

sunlight + water + CO2 ( O2 and glucose

B. Where is each reactant used (light reactions or Calvin cycle?)

Sunlight= light reactions

Water= light reactions (when it is “split” the electrons in the bonds of water are used to replace the electrons lost from the P680 reaction center)

CO2= Calvin cycle

C. Where is each product produced (light reactions or Calvin cycle?)

O2= light reactions (when water is “split”)

Glucose= Calvin cycle

2. Compare and contrast Autotrophs and Heterotrophs.

Auto- make their own food

Hetero- rely on autotrophs for food

3. A. Where would you most likely find mesophyll cells in a tree?

Any photosynthetic part of the tree. Leaves are the main photosynthetic organs in the tree.

B. How many chloroplasts does a typical mesophyll cell hold? 30-40

C. What pigment gives a leaf its green color? chlorophyll

D. Where exactly is this pigment located? Within chloroplasts

E. How does carbon dioxide enter the leaf? Through stomata in the leaves

4. Chloroplast structure: Name all components of the chloroplast and describe their orientation relative to one another. Start at the outer membrane and end inside a thylakoid.

Outer membrane

Intermembrane space

Inner membrane

Stroma

Thylakoid membrane

Thylakoid space

5. Identify the two main stages of photosynthesis and where these stages occur respectively. Also describe how the two stages are dependent on one another.

Stage 1= Light reactions- in thylakoid membranes and thylakoid space, the main products of this stage are some the main reactants of the next stage

Stage 2= Calvin cycle- in stroma, some of the products of this stage are some of the main reactants for stage 1.

10.2 Light Rxns. Chemical Energy of Sun ( ATP and NADPH____________________

6. Green light is _____reflected______________ (reflected/absorbed) by a chloroplast, giving it its green color.

7. What wavelengths of light are most effective in driving photosynthesis?

Violet and red

Briefly describe the experiment (discussed in the chapter and powerpoint for this chapter) that identified these wavelengths of light.

The plants produced high levels of oxygen (one of the major products of photosynthesis) when exposed to violet and red light and produced little to no oxygen when exposed to other wavelengths of light. This makes sense. Think about the photosystem reaction centers in the thylakoid membranes of the chloroplast. P680 and P700, the letter “P” represents “photosystem” and the numbers refer to the wavelengths of light the photosystems absorb. Wavelengths 680 and 700 are both in the red range!

8. Describe what happens when chlorophyll absorbs light?

Electrons in chlorophyll absorb energy and are “jumped” to higher energy level.

9. Photosystems: What are they and where are they located?

Light harvesting complexes in thylakoid membranes of chloroplasts.

Identify the components of the photosystem reaction center.

Reaction center:

Light harvesting complexes

Chlorophyll Pigment molecules

Special chlorophyll a molecules

Primary electron acceptor

10. Describe the path of a photon of light starting outside the chloroplast through the photosystem reaction center to the primary electron acceptor. Light from sun ( outer membrane of chloroplast (inner membrane of chloroplast ( stroma ( light harvesting complex within thylakoid membrane (photosystem) ( chlorophyll pigment molecules within the photosystem( electrons of the special chlorophyll a molecules in the reaction center ( primary electron acceptor in the reaction center

11. In photosystem II why is it necessary to split water into Oxygen, hydrogen ions and electrons?

To replace electron “jumped” or lost from the special chlorophyll a molecules in the P680 reaction center of the photosystem. Electrons are jumped or lost to primary electron acceptor when a photon of light energizes the electrons in the special chlorophyll a molecules.

12. What is generated in photosystem II reactions? (2 products)

O2 and ATP

13, Where do the electrons that replace the electron lost from the special chlorophyll a molecules of photosystem I in the P700 reaction center come from?

PSII

14. What is generated in photosystem I reactions? (1 product)

NADPH

15. Where are the products of photosystem II and I used?

Calvin Cycle

16. Compare and contrast cell respiration in mitochondria and photosynthesis in chloroplasts in terms of…

A. Where the hydrogen ion gradient forms (where hydrogen ions are concentrated).

B. Chemiosmosis (movement of Hydrogen ions through the ATP synthase to generate ATP)

Mitochondria

A. H+ are pumped from matrix through the inner membrane to the intermembrane space by action of electron transport chain protein pumps. Hydrogen ion gradient forms in the intermembrane space.

B. Hydrogen ions move from the intermembrane space to the matrix through the ATP synthase, generating ATP in the stroma!

Chloroplast

A. H+ are pumped from the stroma through the thylakoid membrane to the thylakoid space by action of an electron transport chain protein pump.

B. Hydrogen ions move from the thylaokid space to the stroma through the ATP synthase, generating ATP in the matrix!

17. Why is it that when the lights are turned off in a laboratory, the hydrogen ion gradient across the thylakoid membrane is abolished, but quickly restored when the light are turned back on?

Light drives the Light reactions. Light reactions produce gradient across the thylakoid membrane by flow of electrons through electron transport chain. With the energy absorbed from the electrons, the proteins of the electron transport chain pump H+ from the stroma through the thylakoid membrane to the thylakoid space creating a gradient across the membrane. Without light the electron transport chain ceases to function and the gradient is abolished

10.3 Calvin Cycle = ATP and NADPH ( Glucose_______________________________

18. In terms of USE and PRODUCTION of electron carriers* (NADPH* vs. NADH*) how is the Calvin cycle different from the citric acid cycle in cell respiration.

Calvin USES NADPH, citric acid cycle PRODUCES NADH

19. In what form does carbon (that will eventually be combined with other carbon atoms to form glucose) enter the Calvin cycle? CO2

20. What carbohydrate is produced directly from the Calvin cycle? G3P, a three carbon simple sugar.

How many times must this cycle take place to produce one molecule of glucose? Two turns to make one glucose molecule (BECAUSE GLUCOSE IS A 6 CARBON SUGAR)

21. The 3 main phases of the Calvin cycle are listed below. Describe the major events that occur in each phase.

Carbon Fixation-

A. How many CO2 molecules enter the Calvin cycle at one time? 3 CO2 molecules

B. What is the CO2 acceptor molecule (the one CO2 binds to)? RuBP

C. How many molecules of the CO2 acceptor are required? 3 RuBP, one for each CO2 molecule that enters the Calvin cycle at the same time.

D. Identify the enzyme that facilitates the attachment of a CO2 molecule to the CO2 acceptor molecule Ribisco enzyme

Reduction-

A. What does it mean for something to be “reduced” in terms of electrons? Electrons are negatively charged subatomic particles. When something is said to be “reduced” negative charges (electrons) are being added to that molecule. Where do the electrons come from to accomplish the reduction phase of the Calvin cycle? Of course, the electron carrier molecules made in the light reactions NADPH and ATP!

B. What two molecules (generated in the light reactions) are used in this phase?

NADPH and ATP

Regeneration of RuBP-

A. How many G3P molecules are produced with one turn of the Calvin cycle? 6

B. How many G3P molecules exit the Calvin cycle, thereby making it/them available for glucose production? 1

C. Why don’t all G3P molecules produced with one turn of the Calvin cycle exit the Calvin cycle, making them available for glucose production?

5 three carbon G3Ps are recycled, to regenerate 3 RuBP CO2 acceptor molecules so another turn of the Calvin cycle can occur

22. Explain why a poison that inhibits an enzyme of the Calvin cycle will also inhibit the light reactions.

ADP and NADP+ are required to make ATP and NADPH. Without these starting materials recycled from the Calvin cycle the light reactions could not proceed

23. 4. If you start with 12 molecules of CO2 at the beginning of the Calvin cycle, how many molecule of glucose could you make?

2 molecules of glucose can be produced.

3 CO2 enter the Calvin cycle at a time, resulting in one G3P (a 3-carbon molecule that can be used to make glucose). So the number of carbon atoms in the CO2 that enters the Calvin cycle (3 at a time) are made available for G3P production. Glucose is a 6-carbon molecule, so we need 2 G3Ps to make 1 glucose molecule. Therefore, 4 G3Ps are needed to make 2 glucose molecules. 3 CO2 are needed to make 1 G3P molecule, so 12 CO2 molecules would make 4 G3P molecules = 2 glucose molecules!

24. If you want to make 4 molecules of glucose, how many molecules of CO2 would you need?

Determine how many carbon atoms are in 4 molecules of glucose. Each glucose has 6 carbon molecules x 4 glucose molecules = 24 carbon atoms. So we would need 24 CO2 molecules to make 4 molecules of glucose.

25. In photosynthesis, the reduction of carbon dioxide to form glucose is carried out in a controlled series of reactions. In general, each step or reaction in the sequence requires the input of energy. The sun is the ultimate source of this energy.

Are the compounds listed here used, produced, or n/a (not applicable) in:

Light reactions

Photosystem II?

Light reactions

Photosystem I?

The Calvin cycle?

Glucose

n/a

n/a

produced

O2

produced

n/a

n/a

CO2

n/a

n/a

used

H2O

used

n/a

n/a

ATP

produced

n/a

used

ADP + P i

used

n/a

produced

NADPH

n/a

produced

used

NADP+

n/a

used

produced