Photosynthesis

Question 1

What is the main purpose of the light reactions in photosynthesis?

Answer 1

To convert light energy into chemical energy in the form of ATP and NADPH

Question 2

In which part of the chloroplast does the Calvin Cycle occur?

Answer 2

Stroma

Question 3

During the Calvin Cycle, carbon dioxide is initially fixed to which molecule?

Answer 3

RuBP

Question 4

Which of the following molecules is a product of the Calvin Cycle that can eventually be used to form glucose?

Answer 4

G3P

Question 5

What role do stomata play in photosynthesis?

Answer 5

They regulate gas exchange, allowing CO₂ in and O₂ out.

Question 6

The process that splits water to release electrons, protons, and oxygen occurs in which phase?

Answer 6

Light Reactions

Question 7

Which molecule acts as an energy carrier between the light reactions and the Calvin Cycle?

Answer 7

ATP

Question 8

What happens to the electrons that are excited in chlorophyll during the light reactions?

Answer 8

They move through the Electron Transport Chain, helping to produce ATP and NADPH.

Question 9

What is the end product of the Calvin Cycle that is a precursor to glucose?

Answer 9

G3P

Question 10

Which pigment is primarily responsible for absorbing light in photosynthesis?

Answer 10

Chlorophyll

Question 11

Which phase of photosynthesis is also known as the “dark reactions”?

Answer 11

Calvin Cycle

Question 12

Which of the following best describes photophosphorylation?

Answer 12

The process of adding a phosphate group to ADP to form ATP during the light reactions.

Question 13

In non-cyclic electron flow, what is produced in addition to ATP?

Answer 13

NADPH

Question 14

What is the role of water in the light-dependent reactions?

Answer 14

provides electrons by going through photolysis.

Question 15

What is chemiosmosis in photosynthesis?

Answer 15

The movement of protons across the thylakoid membrane to make ATP.

Question 16

Why do plants appear green?

Answer 16

Chlorophyll reflects green light.

Question 17

What molecule carries electrons from the light reactions to the Calvin Cycle?

Answer 17

NADPH

Question 18

Which enzyme is essential in carbon fixation during the Calvin Cycle?

Answer 18

Rubisco

Question 19

The Calvin Cycle requires ATP and NADPH. Where are these molecules produced?

Answer 19

Light Reactions

Question 20

What process generates the oxygen released during photosynthesis?

Answer 20

Splitting of water molecules during the light-dependent reactions

Question 21

During the light-dependent reactions, what is the significance of the pigment P680 in Photosystem II?

Answer 21

Light energy excites electrons, which move through the electron transport chain.

Question 22

Why is the electron flow in photosynthesis described as “non-cyclic” in the light-dependent reactions?

Answer 22

Because electrons are lost from the system and end up in NADPH, not returning to the starting point.

Question 23

What is the function of the proton gradient across the thylakoid membrane?

Answer 23

It drives ATP synthesis through ATP synthase by allowing protons to flow back into the stroma.

Question 24

How does cyclic electron flow differ from non-cyclic electron flow in the light-dependent reactions?

Answer 24

Cyclic electron flow only involves Photosystem I and produces ATP but not NADPH.

Question 25

What role does the enzyme rubisco play in the Calvin Cycle, and why is it considered inefficient?

Answer 25

It fixes CO₂, but can also bind to O₂, leading to photorespiration and loss of efficiency.

Question 26

Which of the following best describes the purpose of photolysis in Photosystem II?

Answer 26

makes oxygen and replenish electrons lost by chlorophyll.

Question 27

How is the energy stored in ATP and NADPH used in the Calvin Cycle?

Answer 27

ATP provides energy for carbon fixation, while NADPH provides high-energy electrons to reduce CO₂.

Question 28

What effect does photorespiration have on the efficiency of photosynthesis in C3 plants?

Answer 28

It reduces efficiency by using ATP and releasing CO₂ without producing sugars.

Question 29

Why is the Calvin Cycle often referred to as “light-independent” when it still depends on products of the light reactions?

Answer 29

Because it does not directly use light energy but relies on ATP and NADPH produced in the light-dependent reactions.

Question 30

What is the primary purpose of regenerating RuBP at the end of the Calvin Cycle?

Answer 30

To ensure continuous carbon fixation

Question 31

Describe the characteristics of chloroplasts.

Answer 31

- Bean-shaped - contain their own DNA and ribosomes - self-replicating - thought to have originated from bacteria - have an inner and outer membrane with stroma fluid, contain thylakoid stacks - produce glucose using ATP, NADPH, and chlorophyll pigments.

Question 32

What plant parts are involved in photosynthesis?

Answer 32

- Endodermis - Stomata - Mesophyll cells

Question 33

Which colors of light have the most energy

Answer 33

Shorter wavelengths (violet and blue) have more energy.

Question 34

What colors are absorbed by chlorophyll?

Answer 34

Blue and red light, while green is reflected

Question 35

What are the two types of chlorophyll?

Answer 35

Chlorophyll a and b

Question 36

What is at the center of the porphyrin ring?

Answer 36

A magnesium ion (Mg²⁺)

Question 37

What is photoexcitation in the light reactions?

Answer 37

The process where light excites electrons in chlorophyll, starting the transfer of electrons through the photosystems.

Question 38

Name the proteins involved in photosystem II and photosystem I in the light reactions.

Answer 38

- Photosystem II: Z protein, Pq - Photosystem I: Pc

Question 39

What are the main products of the light reactions?

Answer 39

ATP, NADPH, O2

Question 40

What are the three phases of the Calvin cycle, and why are they important?

Answer 40

- Carbon fixation - CO₂ is fixed to produce a stable molecule - Reduction - ATP and NADPH reduce intermediates to form G3P - Regeneration - RuBP is regenerated to continue the cycle.

Question 41

Which types of plants use C4 and CAM carbon fixation?

Answer 41

C4 and CAM plants (eg pineapple) are adapted to hot, dry environments

Question 42

How does C4 and CAM differ from C3?

Answer 42

They reduce photorespiration by fixing CO₂ at different times or in different cells than C3 plants