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Biology Unit 4 > 3.4.3 Photosynthesis > Flashcards

3.4.3 Photosynthesis Flashcards

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1
Q

What are the two stages of photosynthesis?

A

Light dependent and light independent reactions

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2
Q

What is used and what is produced in the light dependent stage (LDS)?

A

Light energy is used to split water and make ATP, oxygen and NADPH.

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3
Q

Where does the Light dependent stage occur?

A

Thylakoid membranes inside chloroplasts

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4
Q

What does the light independent stage use and produce?

A

Does not need light, but uses CO2 and the product of the light dependent stage; ATP and NADPH, in the synthesis of Glucose

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5
Q

What are stacks of thylakoid vesicles called?

A

Grana/Granum

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6
Q

Why is it beneficial for plants to have different pigments of chlorophyll?

A

Each different pigment absorbs light at different wavelengths, so the more pigments the plant has, the more of the visible spectrum can be absorbed

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7
Q

Why do plants that grow in bright conditions typically have lighter coloured leaves than those that typically grow in shaded conditions?

A

Those in shaded conditions have a higher concentration of chlorophyll to make better use of the little light they get, so they are darker.

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8
Q

What is another word for the light dependent stage of photosynthesis?

A

Photophosphorylation

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9
Q

Explain the process of Photophosphorylation/Light Dependent Stage

A
  1. Light energy is absorbed by the chlorophyll molecule which causes an electron to be excited to a higher energy level and emitted
  2. The electron is then carried along the Electron Transmission Chain, going down energy levels each time it is passes to the next acceptor, which produces ATP at each point in the chain.
  3. Water is split through photolysis, to produce oxygen, Hydrogen ions and an electron.
  4. The electron replaces the lost electron in the chlorophyll
  5. Oxygen diffuses out of the chloroplast and into the air
  6. The hydrogen ion is recombined with the electron in the final electron acceptor and is taken up by NADP to become NADPH
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10
Q

Explain the Calvin cycle/Light Independent Stage

A
  1. CO2 binds to Ribulose Biphosphate and forms Glycerate-3-phosphate, catalysed by the enzyme rubisco.
  2. Glycerate-3-phosphate is reduced and activated to form Triose phosphate with energy from ATP and NADPH from the last stage.
  3. ADP+Pi and NADP return to thylakoid fro recycling
  4. Most Triose phosphate is used to regenerate RuBP but some leaves the cycle and is used to synthesise glucose which is used to make all other organic compounds that the plant needs.
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11
Q

What is the simplified formula for photosynthesis?

A

Carbon dioxide + water (+ light energy) –> Glucose + Oxygen

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12
Q

What are the main limiting factors of photosynthesis?

A

Light intensity, Temperature and Carbon Dioxide concentration.

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13
Q

Can too much light ever be a limiting factor? (Excluding heat from the sun)

A

No, but the optimum for photosynthesis is 10 kilolux which is exceeded on a sunny day

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14
Q

Can too much carbon dioxide also be a limiting factor, along with not enough?

A

Yes, above 1% is harmful, but CO2 is only 0.035% of air so it is more often a limiting factor because it is too little.

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15
Q

How is light a limiting factor?

A

Light is the source of energy for the production of ATP and NADPH in the light dependent stage, so not enough light can limit the rate of photosynthesis.

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16
Q

How is CO2 a limiting factor?

A

Carbon dioxide is used as the substrate for the rubisco reaction in the Calvin cycle, so not enough of it can limit the rate of this process.

17
Q

How can temperature be a limiting factor?

A

Temperature affects the rate of all enzyme reactions and there are many enzymes involved in photosynthesis. This also means that too high of a temperature can also be a limiting factor because it will denature enzymes.

18
Q

How many carbons are there in each stage of the Calvin Cycle?

A 
CO2 = 1
RuBP = 5
GP = 3 (x2)
TP = 3 (x2)
Glucose = 6
19
Q

How much of TP is used to regenerate RuBP in the Calvin Cycle?

A

5/6 molecules

20
Q

Name 3 reasons why ATP is a suitable energy source molecule

A
  • Releases energy in small amounts
  • Soluble molecule
  • Involves a single reaction to break down
21
Q

Explain why humans need to produce more than their bodymass in ATP every day

A
  • ATP is unstable and cannot be stored
  • Used by active transport and muscle contraction constantly
  • Only releases a small amount of energy at a time
22
Q

Why is radioactively labelled carbon dioxide used in experiments that track the levels of different products of photosynthesis in a plant?

A

Radioactive labelling allows the products to be detected

23
Q

Why does the level of GP in a plant increase in the dark?

A

Because no photosynthesis means no ATP and NADPH, so GP is not converted to TP, but RuBP still combines with CO2 to make GP.

24
Q

Explain the role of chlorophyll in photolysis.

A
  • Absorbs light energy
  • Causing it to lose excited electron
  • Gains electron from photolysis of water
25
Q

Explain how light energy is converted to chemical energy in Photophosphorylation

A
  • Light energy absorbed by chlorophyll
  • Emits excited electron, carried along ETC
  • Energy used to produce ATP
26
Q

Explain why in an area of high light intensity and carbon dioxide concentration that the level of GP in a plant stays the same

A
  • GP made from carbon dioxide and RuBP
  • GP converts to TP using ATP and NADPH
  • Rate of production = Rate of use
27
Q

Explain why in an area of high light intensity but low/no carbon dioxide does the level of RuBP rise

A
  • No CO2 so cannot bind with to form GP

- RuBP reformed/regenerated from TP

28
Q

Plants produce ATP in their chloroplasts during photosynthesis. They also produce ATP during respiration. Explain why it is important for plants to produce ATP during respiration in addition to during photosynthesis. (5 marks)

A

In the dark no ATP production in photosynthesis
And some tissues are just unable to photosynthesise/ produce ATP
Also ATP cannot be moved from cell to cell/stored
And plants uses more ATP than produced in photosynthesis
ATP for active transport
ATP for synthesis (of named
substance)

Biology Unit 4 (9 decks)

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