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Biology - Module 5 > Photosynthesis > Flashcards

Photosynthesis Flashcards

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1
Q

What is the purpose of the light-dependent reactions?

A

To make the 2 molecules needed for the next stage of photosynthesis: the energy storage molecule ATP and the reduced electron carrier NADPH.

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2
Q

Where do the light-dependent reactions take place?

A

The thylakoid membranes in chloroplasts.

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3
Q

What are photosystems?

A

Large complexes of proteins and pigments (light-absorbing molecules) that are optimized to harvest light. They play a key role in the light reactions.

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4
Q

What are the different types of photosystems called?

A

Photosystem I (PSI) and photosystem II (PSII)

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5
Q

What do photosystems contain?

A

They contain many pigments that help collect light energy, as well as a special pair of chlorophyll molecules found at the core (reaction center) of the photosystem.

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6
Q

What is the special pair of chlorophyll molecules found at the reaction centre in PSI called?

A

P700

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7
Q

What is the special pair of chlorophyll molecules found at the reaction centre in PSII called?

A

P680

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8
Q

What is the standard form of the light-dependent reactions called?

A

Non-cyclic photophosphorylation

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9
Q

What is photophosphorylation?

A

Using light energy to make ATP.

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10
Q

What is photolysis?

A

The splitting of water molecules in the presence of light into an electron, proton and oxygen.

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11
Q

What happens first in PSII?

A

When a photon of light is absorbed by one of the many pigments in photosystem II, energy is passed inward from pigment to pigment until it reaches the reaction center.

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12
Q

What happens at the reaction centre in PSII?

A

Energy is transferred to P680, boosting an electron to a high energy level. The high-energy electron is passed to an acceptor molecule and replaced with an electron from water. This splitting of water releases the oxygen we breathe in.

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13
Q

What does the first high-energy electron go down after the acceptor molecule? (after PSII)

A

It travels down an electron transport chain, moving from high energy state to a low energy state, losing energy as it goes.

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14
Q

What does the released energy from the electron transport chain cause?

A

Some of it drives the pumping of H+ ions from the stroma into the thylakoid lumen, building a H+ concentration gradient. The H+ ions from photolysis also add to this gradient.

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15
Q

How do H+ ions return to the stroma?

A

As the H+ ions flow down their gradient and into the stroma, they pass through ATP synthase, driving ATP production in a process known as chemiosmosis.

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16
Q

What happens in PSI?

A

The electron arrives at photosystem I and joins the P700 special pair of chlorophylls in the reaction center. When light energy is absorbed by pigments and passed inward to the reaction center, the electron in P700 is boosted to a very high energy level and transferred to an acceptor molecule.

17
Q

How is the special pair’s missing electron replaced in PSI?

A

It is replaced by a new electron from PSII (arriving via the electron transport chain).

18
Q

What happens to the second high-energy electron after the acceptor molecule? (after PSI)

A

It travels down a short second leg of the electron transport chain. At the end of the chain, the electron is passed to NADP+ (along with a second electron from the same pathway) to make NADPH.

19
Q

How is cyclic photophosphorylation different from non-cyclic?

A

The electrons cycle repeatedly through PSI and the first portion of the electron transport chain but do not pass through PSII. Only ATP is produced, not NADPH.

20
Q

What are photosynthetic pigments?

A

They are light-harvesting molecules found in the thylakoid membranes of chloroplasts. Examples include chlorophyll a, chlorophyll b, and carotenoids.

21
Q

What happens to the pigment in the photosystems when it absorbs a photon?

A

It is raised to an excited state, meaning that one of its electrons is boosted to a higher-energy orbital.

22
Q

What do most of the pigments in a photosystem act as?

A

They act as an energy funnel, passing energy inward to a main reaction center.

23
Q

How is energy transferred between pigments in a photosystem?

A

When one of these pigments is excited by light, it transfers energy to a neighboring pigment through direct electromagnetic interactions in a process called resonance energy transfer.

24
Q

What type of chlorophyll is the special pair of chlorophyll molecules at the reaction centre?

A

chlorophyll a

25
Q

What is the function of ferredoxin in photosynthesis?

A

Ferredoxin (a protein) passes the electron from PSI to NADP+ reductase which then transfers electrons to NADP to make NADPH. This will then be used in the Calvin Cycle.

26
Q

What are the light-independent reactions also called?

A

The Calvin Cycle reactions

27
Q

How does CO2 reach the stroma of chloroplasts?

A

CO2 enters the interior of a leaf via pores called stomata and diffuses into the stroma of the chloroplast.

28
Q

Where does the Calvin Cycle take place?

A

In the stroma of chloroplasts.

29
Q

What is the light-independent reaction dependent on?

A

The products of the light dependent reactions: ATP and NADPH.

30
Q

What are the 3 main stages of the Calvin Cycle?

A
  1. Carbon fixation
  2. Reduction
  3. Regeneration
31
Q

What happens to CO2 in carbon fixation?

A

A CO2 molecule combines with a five-carbon acceptor molecule, ribulose-1,5-bisphosphate (RuBP). This step makes a six-carbon compound that splits into two molecules of a three-carbon compound, 3-phosphoglyceric acid (3-PGA).

32
Q

What is carbon fixation catalsysed by?

A

The enzyme ribulose biphosphate carboxylase, or RuBisCo.

33
Q

What happens to the 3-PGA in the reduction stage?

A

ATP and NADPH are used to convert the 3-PGA molecules into molecules of a three-carbon sugar, glyceraldehyde-3-phosphate (G3P) / triose phosphate (TP). This stage gets its name because NADPH donates electrons to, or reduces, a three-carbon intermediate to make G3P.

34
Q

What happens in the regeneration stage?

A

Some G3P molecules go to make glucose, while others must be recycled to regenerate the RuBP acceptor. Regeneration requires ATP and involves a complex network of reactions (“carbohydrate scramble”).

35
Q

How many turns of the Calvin cycle are required to make one G3P molecule that can exit the cycle and go towards making glucose?

A

3

36
Q

How many G3P molecules are made with 3 turns of the Calvin cycle and where do these go?

A

6, 5 of which go into regenerating RuBP and 1 can go towards making glucose.

37
Q

How many turns of the Calvin cycle are required to make one glucose molecule?

A

6

38
Q

How much ATP and NADPH is used in the Calvin cycle to make one molecule of glucose?

A

18 ATP and 12 NADPH

39
Q

How many ATP and NADPH are used per cycle?

A

3 ATP and 2 NADPH

Biology - Module 5 (2 decks)

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