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AS/A-Level Biology > Photosynthesis simplified: > Flashcards

Photosynthesis simplified: Flashcards

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1
Q

What are the two stages of photosynthesis?

A

Light dependent reaction

Light-independent reaction

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2
Q

Where does the light dependent reaction occur?

A

Thylakoid membranes

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3
Q

Where does the light independent reaction occur?

A

Stroma

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4
Q

Where is chlorophyll located?

What are the most common types?

A

In the photosystems on the thylakoid membrane.

Chlorophyll a (blue/green)
Chlorophyll b (yellow/green)
Carotene  (orange)
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5
Q

Why is it good that each pigment in leaves absorbs slightly different wavelengths of visible light?

A

Maximises the spectrum of visible light that the plant can absorb and therefore increases the amount of light energy absorbed.

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6
Q

How can the pigment in chlorophyll be isolated?

A

Using chromatography

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7
Q

Describe the process of chromatography:

A
  • Pigments are added to chromatography paper which is placed in a solvent.
  • Solvent dissolves the pigments.
  • More soluble pigments move further up the chromatography paper.
  • This is converted to an Rf value - can be used to compare and identify pigments.
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8
Q

What is the equation for Rf value?

A

Rf value = distance moved by pigment from origin to centre of pigment spot / distance from origin to solvent front

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9
Q

What is the purpose of the LDR?

A

To use light energy and water to create ATP and NADPH which can then be used in the light-independent stage.

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10
Q

What are the 3 key stages of the LDR?

A
  1. Photolysis
  2. Photoionisation of chlorophyll
  3. Chemiosmosis
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11
Q

Describe photolysis in the LDR in photosynthesis:

A
  1. Light energy is absorbed by chlorophyll in photosystem II and splits water into oxygen, H+ and e-.
  2. H+ is picked up by NADP to form NADPH - used in the LIR.
  3. e- are passed along ETC and replace the electrons lost in chlorophyll.
  4. Oxygen used for respiration or diffuses out of leaf through stomata.
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12
Q

Describe photoionisation of chlorophyll in the LDR in photosynthesis:

A
  1. Light energy is absorbed by chlorophyll and energy results in e- exciting and raising up an energy level to leave chlorophyll.
  2. Chlorophyll has been ionised by light.
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13
Q

Describe chemiosmosis in the LDR in photosynthesis:

A
  1. e- move along ETC in thylakoid membrane.
  2. As they move, they releases energy and some energy is used to pump protons from photolysis across chloroplast membranes.
  3. Concentration gradient - causes protons to diffuse through ATP synthase - chemiosmosis.
  4. Results in production of ATP.
  5. Protons combine with co-enzyme NADP to become NADPH.
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14
Q

What is the LIR also known as?

A

The Calvin Cycle

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15
Q

What does the calvin cycle use and what does it form?

A

Carbon dioxide, reduced NADP and ATP to form a hexose sugar.

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16
Q

In the calvin cycle, what happens to the ATP and the NADPH?

A

ATP - hydrolysed to provide energy

NADPH - donates hydrogen to reduce molecules GP in the cycle.

17
Q

What enzyme catalyses the LIR?

A

RuBisco

18
Q

Is the LIR temperature sensitive?

A

Yes as it involves enzymes.

19
Q

Where does the LIR occur?

A

Stroma

20
Q

Describe each step of the calvin cycle:

A
  1. CO2 reacts with ribulose bisphosphate to form glycerate 3-phosphate (3C)
  2. Catalysed by rubisco.
  3. ATP and NADPH from LDR reduce GP into triose phosphate.
  4. Some carbon from TP leaves to be converted into useful organic substances.
  5. Rest of it is used to regenerate RuBP with energy from ATP.
21
Q

How did Calvin examine the products in the LIR?

A

Using radioactive carbon.

Allows carbon molecules to be labelled and traced.

Then measured the amount of radioactive GP and RuBP under different conditions, mainly in light and dark, as way to prove which factors impact the LIR.

22
Q

What are 3 limiting factors of photosynthesis?

A
  1. Temperature
  2. Carbon dioxide concentration
  3. Light intensity
23
Q

Give an example of how each limiting factor in photosynthesis could be controlled:

A

Temperature - heating a greenhouse

Carbon dioxide - burning fuel, eg a paraffin burner

Light intensity - artificial lighting

24
Q

What are the products of the light dependent reactions?

A

ATP
Reduced NADP
Oxygen

25
Q

What are the products of the light independent reactions?

A

ADP
Inorganic phosphate
NADP
Organic substances

26
Q

Where is rubisco found in a plant cell?

A

Stroma

27
Q

When the carbon dioxide concentration decreases….

A

… the amount of RuBP increases (less is CO2 reacts with it to convert it into GP).

… the amount of GP decreases.

… the amount of triose phosphate decreases (as less GP is present, so less is converted into TP).

28
Q

When a plant moves from light to dark, the amount of RuBP decreases - why?

A

Any RuBP present is converted into GP by rubisco.

Levels of RuBP decrease.

RuBP cannot be regenerated from TP using ATP (no products from LDR) and so levels of RuBP remain low.

29
Q

What wavelengths of light can plants not absorb?

A

Green light - this is reflected as plants are green.

30
Q

Why might the pondweed reaction not be an accurate measure of the oxygen produced in photosynthesis?

A

Some of the oxygen produced in photosynthesis will be used in respiration and so it will not diffuse out of the leaf and be collected in the syringe.

31
Q

Increasing light intensity …

A

… increases the overall rate of photosynthesis (both the rate of the LDR and the LIR)

32
Q

How many carbon atoms are there in 1 molecule of glycerate 3-phosphate?

A

3

33
Q

How many carbon atoms are there in 1 molecule of ribulose bisphosphate?

A

5

34
Q

During which stage of photosynthesis is water used?

A

LDR - more specifically photolysis.

AS/A-Level Biology (190 decks)

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