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OCR A Level Biology > Module 5: Photosynthesis > Flashcards

Module 5: Photosynthesis Flashcards

1
Q

What is the equation for photosynthesis

A

6CO2 + 6H20 → C6H12O6 + 6O2.

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2
Q

State the properties of ATP

A
  • -ATP stores or releases a small amount of energy, so none is wasted
  • Small and soluble (easily transported around the cell)
  • easily broken down, (unstable phosphate bond)
  • ATP can’t pass out of the cell, so cell always has an intermediate source of energy
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3
Q

Where does the light dependent stage happen (z scheme)

A

thylakoid membranes

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4
Q

Where does the light independent stage happen (Calvin cycle)

A

stroma

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5
Q

What is in a thylakoid membrane

A

in the membranes there are photosystems 1 and 2
-these are made up of photosynthetic pigments
primary pigment absorb light
accessory pigments help this

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6
Q

What is the use of accessory pigments

A
  • Accessory pigments that surround the primary pigment
  • absorb both similar and different wavelengths of light to chlorophyll,
  • this expands the wavelength range that can be absorbed from light for use in photosynthesis
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7
Q

What are the two photosynthetic pigments called

A

There are two types of pigments: chlorophylls and carotenoids

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8
Q

Give an example of a chlorophyll pigment

A

Chrolophyll A

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9
Q

Give an example of a carotenoid pigment

A

Carotine, chlorophyll B

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10
Q

What is the coenzyme in photosynthesis called

A

NADP

transfers hydrogen from one molecule to another

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11
Q

What happens in the light-dependent stage (cyclic phosphorylation)

A
  1. Water is at photosystem
  2. Light energy from sun used to splits water molecule into 1/2 o2 and 2h+ ions (this is called photolysis)
  3. electrons are released go into photosystem 2 and get excited
  4. The electrons go through electron carriers (electron transport chain) and lose their energy by the time they get to photosystem 1
  5. ATP is released
  6. NADP becomes reduced NADP (electron and proton from stroma) (Non cyclic)
  7. Photosystem 1 absorbs light energy and the electrons get excited (if the plant needs energy then electrons will go back to photosystem 2 to produce more energy this is called cyclic phosphorylation)
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12
Q

What happens in the light-dependent stage (Non-cyclic phosphorylation)

A
  1. electrons arrive at NADP reductase, 2 electrons are received and also receive 2 protons so it reduces NADP to reduced NADP
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13
Q

What happens in the Calvin cycle

A

1)RuBP is combined with carbon dioxide in a reaction called carbon fixation
catalysed by the enzyme RUBISCO.
2) RuBP is converted into two glycerate 3-phosphate (GP) molecules these are three-carbon molecules
3) Reduced NADP and ATP are used to convert GP to triose phosphate (TP), NAD is used in light-dependent reaction again
4) Some of 1 out of 6 TP molecules are used to make glucose which is then converted to
essential organic compounds such as polysaccharides, lipids, amino acids
and nucleic acids.
5) Remaining TP molecules (5) are used to reform RuBP with the help of ATP.

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14
Q

How can Glycerate phosphate be used

A

nitrogen from soil can be combined with GP, this makes amino acids
Also it can be used to make fatty acids and glycerol made from TP can be used to make lipids

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15
Q

How is triose phosphate used

A
  • can be used to glucose which will make starch or cellulose
  • can be used to glycerol to make lipids
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16
Q

What are the limiting factors of photosynthesis

A
  • Light intensity
  • Co2 concentration
  • Temperature
17
Q

What are the parts of a chloroplast and its functions?

A

Thylakoid membrane: fluid-filled stacks provide a large surface area

Starch grain: carbohydrate store

Outer membrane Inner membranes: contain photosystems

Granum is a stack of thylakoid membranes

Stroma: contains enzymes needed for Calvin cycle

18
Q

What happens to photosynthesis if the temperature is too high or low

A
  • -If temperature is too low the n enzymes become inactive (ATP synthase and RubIsCo)
  • If temperature is too high enzymes start to denature
  • Stomata close to avoid losing water, this means less CO2
  • Thylakoid membrane could be damaged reducing number of light-dependent reactions taking place
  • membrane around chloroplast could be damaged leading to enzymes in Calvin cycle to be released into cell
  • Chropyhyllmay be damaged reducing the amount of light energy absorbed, which reduces rate of light-dependent reactions,
19
Q

Finish the sentence

As light intensity increases …

A
  • The rate of photosynthesis increases
    • Why: more energy supplied to the plant and therefore the faster the light-dependent stage of photosynthesis can occur
    • more ATP and reduced NADP for the Calvin cycle
    • This plateus after a while because LI no longer is affecting the rate of photosynthesis, another limiting factor is
20
Q

Finish the sentence

As carbon dioxide concentration increases the rate of photosynthesis

A
  • Increases
  • more carbon dioxide that is present, the faster carbon fixation (Calvin cycle) can occur
  • Levels off because something else is a limiting factor
  • too much co2 is toxic too a plant though
21
Q

Finish the sentence

As temperature increases the state of photosynthesis

A
  • Increases until the optimum temperature is passed
  • At optiumn temps enzymes in calvin cycle active, have higher kinetic energy
  • after the optiumn temperature is passed the enzymes denature (in the light independent stage)
  • rate of photosynthesis decreases
22
Q

How does light intensity affect the light-dependent stage

A
  • If there is a low light intensity
  • Products of light-dependent stage decrease (ATP and reduced NADP)
  • Conversation of GP to TP is slow because reduced NADP is in short supply
  • Levels of GP rise because it is not being converted
23
Q

How does increased and decreased temperature affect the light-independent stage

A
  • all reactions in Calvin cycle catalysed by enzymes
  • at low temps enzymes work slowly, so levels of RuBP, GP, TP will fall,
  • At high temps enzymes start to denature
24
Q

How does low levels of carbon dioxide concentration affect the Calvin cycle

A
  • At low concs rate of conversion of RuBP to GP is slow because there is less CO2
  • Levels of RuBP will increase as its still being made, but as its not being converted to GP, TP, their levels decrease
25
Q

How does water stress affect rate of photosynthesis

A
  • Lack of water leads to stomata closing to maintain water levels
  • less Co2 enters the plant
  • so rate of photosynthesis decreases (Calvin cycle)
25
Q

How does water stress affect rate of photosynthesis

A
  • Lack of water leads to stomata closing to maintain water levels
  • less Co2 enters the plant
  • so rate of photosynthesis decreases (Calvin cycle)

OCR A Level Biology (24 decks)

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