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Biology 2 > 6. Photosynthesis > Flashcards

6. Photosynthesis Flashcards

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1
Q

What are organisms that photosynthesise called?

A

‘photoautotrophs’ as they use autotrophic nutrition

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2
Q

What is Autotrophic nutrition?

A

When inorganic chemicals are converted into organic molecules (in photosynthesis this is glucose)

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3
Q

Where does photosynthesis occur?

A

The chloroplasts

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4
Q

What is the main product of photosynthesis?

A

Monosaccharide sugar.

It can be converted to disaccharides for transport and starch for storage.

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5
Q

What is carbon fixation?

A

When Carbon dioxide is converted into sugars.
It is endothermic so requires energy.
Requires electrons for a reduction reaction
It helps to regulate the concentration of carbon dioxide in the atmosphere.

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6
Q

What are the 3 types of photosynthetic organisms?

A

Plants, Algae, Cyanobacteria

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7
Q

What are the two main stages of photosynthesis?

A

Light dependent stage- requires light to carry out.

Light independent stage- does not need light but depends on the products of the first stage.

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8
Q

How do plants use respiration?

A

During respiration, they oxidise the organic molecules that are synthesised by photosynthesis to produce carbon dioxide.
Respiration releases chemical energy that can drive the organism’s metabolism.

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9
Q

How does respiration and photosynthesis interrelate in plants?

A

The products of one process are the raw materials for the other process.

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10
Q

What is compensation point?

A

The compensation point is when photosynthesis and respiration proceed at the same rate so that there is no net gain or loss of carbohydrate.

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11
Q

What is Compensation period?

A

The time a plant takes to reach its compensation point, it is different for different plant species.
Shade plants reach the compensation point sooner.
Sun plants require a higher light intensity to achieve their optimum rate of photosynthesis

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12
Q

What is the structure of chloroplasts?

A

They are surrounded by a double membrane (the envelope), with an intermembrane space.
The outer membrane is highly permeable.
They contain a fluid-filled matrix called the stroma.
The stroma contains thylakoid membranes arranged in grana.

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13
Q

What is the structure of grana?

A

The thylakoid membrane is folded into thylakoids.
Different thylakoids form stacks.
Each stack is called a granum.
They are surrounded by the stroma, so the products of the light-dependent stage pass into it to be used in the light-independent stage.

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14
Q

How are grana adapted to their function?

A

They have a large surface area for…
Photosystems containing photosynthetic pigments that trap sunlight energy
Electron carriers and ATP synthase enzymes to convert light energy to ATP.

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15
Q

What is the structure of photosystems?

A

They are embedded with an array of photosynthetic pigments.

Each pigment absorbs light (photons) of a particular wavelength.

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16
Q

What are the different photosynthetic pigments?

A

Chlorophyll a, Chlorophyll b and the accessory pigments

17
Q

What is the role of chlorophyll a?

A

It is the main photosynthetic pigment and sits in the primary reaction centre.

18
Q

What is the role of the accessory pigments?

A

The light energy absorbed by the accessory pigments gets passed into the primary pigment reaction centre.

19
Q

What are the two forms of chlorophyll a?

A

P680 is found in photosystem II and its peak wavelength is 680nm.
P700 is found in photosystem I and its peak wavelength is 700nm.

20
Q

What are the different accessory pigments?

A

Carotenoids- absorb blue light of wavelengths 400-500nm.

Xanthophylls- absorb blue green light of wavelengths 375-550 nm.

21
Q

What is the role of the light dependent stage?

A

To make ATP and reduced NADP to be used in the light independent stage.

22
Q

What are the two stages of the light dependent stage?

A

cyclic photophosphorylation,

non-cyclic photophosphorylation.

23
Q

What are the stages of the first part of non-cyclic photophosphorylation?

A
  1. Photosystem II absorbs light.
  2. Electrons, which are in pairs, absorb this energy and become excited.
  3. Electrons pass along the electron transport chain in the thylakoid membranes.
  4. Energy is released which is used to pump the protons to the intermembrane space.
  5. Protons flow down their concentration gradient through ATP synthase, causing a proton motive force.
  6. The ATP synthase turns and combines ADP and P to form ATP.
24
Q

What happens to the electrons in the second part of non-cyclic photophosphorylation?

A
  1. They get passed to photosystem I and get excited again
  2. They pass to the electron acceptor ferredoxin and carried to NADP.
  3. At the same time photolysis is occurring where light energy, in the presence of an enzyme, splits water, releasing hydrogen ions.
  4. Hydrogen and electrons both reduce NAD and the electrons travel to PS II to replace those excited.
25
Q

What is cyclic photophosphorylation?

A

Only involves PS I
Rather than being accepted by ferredoxin, the electrons excited by PS I return to the electron transport chain.
This allows for the further formation of ATP.

26
Q

What is the light independent stage of photosynthesis?

A

Occurs in the stroma and consists of the Calvin cycle.

27
Q

What are the stages of the Calvin cycle?

A
  1. Begins with ribulose bisphosphate (5c)
  2. Carbon fixation of ribulose bisphosphate into two molecules of glycerate-3-phosphate.
  3. Conversion of glycerate-3-phosphate into triose phosphate (3c)
  4. 1/6th of triose phosphate is converted into glucose.
  5. 5/6th of triose phosphate is recycled into ribulose bisphosphate.
28
Q

How does carbon fixation of ribulose bisphosphate into glycerate-3-phosphate occur?

A

Combines with Carbon Dioxide
Catalysed by the enzyme RuBisCO
Some glycerate phosphate can be converted into amino acids with nitrogen which comes from nitrates in the soil.

29
Q

How is glycerate-3-phosphate converted into triose phosphate?

A

This step is called reduction.
ATP is broken into ADP+P.
Reduced NADP is oxidised into NADP and donates its hydrogen to the glycerate-3-phosphate.

30
Q

Why is only 1/6th of triose phosphate converted into glucose?

A

It is important to keep the cycle moving

31
Q

How is triosephosphate converted back into ribulose bisphosphate.

A 
This step is called phosphorylation
ATP is hydrolysed into ADP+P
The phosphate (P) is used to phosphorylate triosephosphate to ribulose bisphosphate.
32
Q

How many turns of the Calvin cycle are needed to complete the photosynthesis equation?

A

6

33
Q

What are the limiting factors of photosynthesis?

A

Light intensity, temperature, carbon dioxide concentration

34
Q

What impact does changing light intensity have on the Calvin cycle?

A

Glycerate-3-Phosphate cannot be reduced to Triose Phosphate as it requires ATP and reduced NADP which is produced in the light dependent stage.
Triose Phosphate levels fall and Glycerate-3-Phoshphate accumulates.

35
Q

How does temperature affect the rate of photosynthesis?

A

At low temperatures, all of the enzymes that catalyse photosynthesis work slowly.
Some other factor is limiting.
An increase in temperature increases the rate of the enzyme-catalysed reactions and therefore photosynthesis.
At very high temperatures, enzymes are damaged reducing the rate of photosynthesis, it is the limiting factor.

Biology 2 (12 decks)

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