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Biology > Photosynthesis > Flashcards

Photosynthesis Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Where is chlorophyll located?

A

In the photosystems on the thylakoid membrane

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2
Q

What is chlorophyll?

A

A mix of coloured proteins that can absorb light

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3
Q

What colour is chlorophyll a?

A

Blue/ green

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4
Q

What colour is chlorophyll b?

A

Yellow/ green

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5
Q

What colour are Carotenoids?

A

Orange

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6
Q

What colour are Xanthophylls?

A

Yellow

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7
Q

What is the advantage of having a range of pigments in the photosystems?

A

They each absorb different wavelengths of visible light and this maximises the spectrum of visible light absorbed. Which therefore increases the amount iof light energy absorbed.

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8
Q

What is a light harvesting system?

A

Where energy of different wavelengths is absorbed ad this energy is then transfered to the reaction centre

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9
Q

What is the reaction centre?

A

Contains chlorophyll a and is where light dependent reactions occur.

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10
Q

What forms the light harvesting system?

A

Chlorophyll b, xanthophylls, pheophytins and carotenoids embedded

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11
Q

What makes up the photosystems?

A

The light harvesting system and the reaction centre

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12
Q

What is the purpose of the light-dependent stage?

A

To harvest light energy to split water and to create ATP and reduced NADP which are both used in the light-indepedent stage.

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13
Q

Where does the light-dependent stage occur?

A

Occurs on the thylakoid membranes (grana).

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14
Q

What are the 4 key stages of the light-dependent stage?

A
  1. Non-cyclic photophosphorylation
  2. Cyclic photophosphorylation
  3. Photolysis
  4. Chemiosmosis
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15
Q

What are the two photosystems and what are they both involved in?

A

PSI and PSII
They are both involved in non-cyclic photophosphorylation

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16
Q

Which photosystem is used first in non-cyclic photophosphorylation?

A

PSII

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17
Q

What light wavelength does PSII absorb?

A

Absorbs light with a wavelength of 680nm

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18
Q

What light wavelength does PSI absorb?

A

Absorbs light with a wavelength of 700nm

19
Q

What happens when light energy is absorbed by PSII?

A

Causes electrons within the reaction centres to become excites and released.

20
Q

Non-cyclic photophosphorylation: What happens once electrons are released from the cytoplasm?

A

They then move along an electron transport chain (ECT)

21
Q

What are the electrons that are released from PSII replaced by?

A

Electrons produced by photolysis

22
Q

What is photolysis?

A

Light energy splits water into protons, (H+ ions), electrons and oxygen

23
Q

Non-cyclic photophosphorylation: What is the reaction for photolysis?

A

H2O → 2H+ + 2e- + ½O2

24
Q

Non-cyclic photophosphorylation: When the electrons move down the ECT what else happens?

A

Chemiosmosis
- The energy given by electrons moving through the electron transport chain enables H+ ions (protons) to pass from a low conc in the stroma (via a proton pump) to a higher conc in the thylakoid lumen- down the electrochemical gradient
- This creation of this proton gradients across the membrane later drives the synthesis of ATP in photophosphorylation

25
Q

Non-cyclic photophosphorylation: What happens to excited electrons from PSI?

A

They pass along an electron transport chain, these electrons then combine with hydrogen ions (produced by the photolysis of water and transported out of the thylakoid lumen by ATP synthase) and the carrier molecule NADP to give reduced NADP.

26
Q

Non-cyclic photophosphorylation: What creates ATP?

A
  • There is proton gradient across the membrane created by the movement of H+ from stroma into the thylakoid lumen.
  • Protons move down their concentration gradient, into the stroma, via an enzyme called ATP synthase. The energy from this movement combines ADP and inorganic phosphate to form ATP.
27
Q

What is cyclic photophosphorylation?

A

Only uses PSI
Electrons from the chlorophyll molecule aren’t passed onto NADP, but are passed back to PSI via electron carriers.
Means that electrons are recycled and repeatdly flow through PSI.
This process doesn’t produce any NADP or oxygen- it only produces small amounts of ATP.

28
Q

What is the light-idependent stage sometimes known as?

A

The Calvin cycle

29
Q

Where does the light-indepedent stage take place?

A

Stroma in chloroplasts

30
Q

What is the first step in the Calvin Cycle?

A

RUBP (a five carbon molecule) and carbon are fixed by RUBISCO to make a 6 carbon molecule (that is very unstable).

31
Q

Light indepedent stage: What happens to the unstable 6 carbon molecule?

A

It splits into 2 to make two 3-carbon molecules known as GP.

32
Q

Light indepedent stage: What happens to GP?

A

Energy from ATP and hydrogen from reduced NADP (both produced in the light dependent stage) are used to reduce GP to TP (triose phosphate) which is a 3 carbon molecule.

33
Q

Light indepedent stage: What happens to TP?

A

Most (5 out of every 6 molecules of TP produced) is used to regenerate RuBP which requires ATP.
Some is used to produce useful organic molecules

34
Q

Light indepedent stage: What useful organic compounds can TP produce?

A
  • Can condense to become hexose phosphates, which can be used to produce starch, cellulose, or sucrose
  • Can be converted to glycerol while 3 glycerol phosphates can be converted to fatty acids. These molecules join together to form lipids for cell membranes.
  • Can be used in the production of amino acids for protein synthesis
35
Q

What happens if the temperature is too low?

A

Photosynethsis involves enzymes (ATP synthase and RuBiSCO). If the temperature falls below 10ºC the enzymes become inactive.

36
Q

What happens to the enzymes if the temperature is too high?

A

If the temperature is more than 45ºC the enzymes may start to denature.

37
Q

What happens to stomata if the temperature is too high and how does this affect photosynethsis?

A

Stomata close to avoid loosing too much water. This causes photosynthesis to slow down because less CO2 enters the leaf when the stomata are closed.

38
Q

What happens to the thylakoid membranes if the temperature is too high and how does this affect photosynethsis?

A

The thylakoid membranes may become damaged. This could reduce the rate of light-dependent stage reactions by reducing the number of sights available for electron transfer.

39
Q

What happens to the membranes around the chloroplasts if the temperature is too high and how does this affect photosynethsis?

A

Could be damaged, which could cause enzymes important to the Calvin cycle to be released into the cell. This would reduce the rate of the light-idependent stage reactions.

40
Q

What happens to the chlorophyll if the temperature is too high and how does this affect photosynethsis?

A

Chlorophyll could be damaged. This would reduce the amount of pigment that can absorb light energy, which would reduce the rate of light-dependent stage reactions.

41
Q

What is the saturation point?

A

Where a factor is no longer a limiting the reaction- something else is.

42
Q

What is the optimum temperature for photosynethsis?

A

25ºC

43
Q

What is the optimum CO2 concentration for photosynethesis?

A

0.4%

Biology (20 decks)

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