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Photosynthesis Flashcards

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1
Q

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

A

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

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2
Q

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

A

Stroma

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3
Q

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

A

RuBP

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4
Q

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

A

G3P

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5
Q

What role do stomata play in photosynthesis?

A

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

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6
Q

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

A

Light Reactions

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7
Q

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

A

ATP

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8
Q

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

A

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

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9
Q

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

A

G3P

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10
Q

Which pigment is primarily responsible for absorbing light in photosynthesis?

A

Chlorophyll

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11
Q

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

A

Calvin Cycle

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12
Q

Which of the following best describes photophosphorylation?

A

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

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13
Q

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

A

NADPH

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14
Q

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

A

provides electrons by going through photolysis.

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15
Q

What is chemiosmosis in photosynthesis?

A

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

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16
Q

Why do plants appear green?

A

Chlorophyll reflects green light.

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17
Q

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

A

NADPH

18
Q

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

A

Rubisco

19
Q

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

A

Light Reactions

20
Q

What process generates the oxygen released during photosynthesis?

A

Splitting of water molecules during the light-dependent reactions

21
Q

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

A

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

22
Q

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

A

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

23
Q

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

A

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

24
Q

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

A

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

25
Q

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

A

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

26
Q

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

A

makes oxygen and replenish electrons lost by chlorophyll.

27
Q

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

A

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

28
Q

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

A

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

29
Q

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

A

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

30
Q

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

A

To ensure continuous carbon fixation

31
Q

Describe the characteristics of chloroplasts.

A
  • 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.
32
Q

What plant parts are involved in photosynthesis?

A
  • Endodermis
  • Stomata
  • Mesophyll cells
33
Q

Which colors of light have the most energy

A

Shorter wavelengths (violet and blue) have more energy.

34
Q

What colors are absorbed by chlorophyll?

A

Blue and red light, while green is reflected

35
Q

What are the two types of chlorophyll?

A

Chlorophyll a and b

36
Q

What is at the center of the porphyrin ring?

A

A magnesium ion (Mg²⁺)

37
Q

What is photoexcitation in the light reactions?

A

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

38
Q

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

A
  • Photosystem II: Z protein, Pq
  • Photosystem I: Pc
39
Q

What are the main products of the light reactions?

A

ATP, NADPH, O2

40
Q

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

A
  • 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.
41
Q

Which types of plants use C4 and CAM carbon fixation?

A

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

42
Q

How does C4 and CAM differ from C3?

A

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

Biology (3 decks)

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