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OCR A-level Biology > Photosynthesis > Flashcards

Photosynthesis Flashcards

1
Q

What is an autotroph?

A

An organism that synthesises its own nutrients

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2
Q

What is a photoautotroph?

A

An organism that uses light to synthesise nutrients via photosynthesis

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3
Q

What is the overall photosynthesis equation?

A

6CO2 + 6H2O = C6H12O6 + 6O2

remember the devils equation (666)

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4
Q

What is a photon?

A

A particle of light

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5
Q

What is carbon fixation?

A

The process where carbon dioxide is converted to sugars

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6
Q

What does Carbon fixation do in terms of the environment?

A

Helps to regulate CO2 levels in the atmosphere and oceans

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7
Q

What is it called when rates of photosynthesis and respiration are equal in a plant?

A

Compensation point

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8
Q

Describe the general structure of a chloroplast

A

Double membrane with an inter-membrane space

Stroma - a fluid matrix

Grana - Stacks of thylakoid membranes

Inter-granal lamellae - Connect grana together

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9
Q

What stage of photosynthesis takes place in the grana?

A

Light-dependent stage

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10
Q

Describe the structure of the thylakoids

A

A membrane that is folded into a disc-like sac

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11
Q

Why are the thylakoids folded?

A

Provides a large surface area which is important for:

Distribution of photosystems and photosynthetic pigments

Distribution of electron carriers and ATP synthase enzymes

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12
Q

Where do the products of the light-dependent stage go?

A

Diffuse out of thylakoids into stroma

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13
Q

What is the stroma made up of?

A

Enzymes needed to catalyse light independent stage

Starch grains

Oil droplets

Small ribosomes

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14
Q

Describe the structure of a Photosystem

A

A funnel shaped structure in the thylakoid membrane

Contains photosynthetic pigments which absorb specific wavelengths of light

A primary pigments reaction centre at the bottom which is either P700 or P680

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15
Q

What are the two types of Chlorophyll a in a photosystem?

A

P700 and P680

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16
Q

Why do photosystems contain a range of pigments?

A

So the plant can absorb a range of appropriate wavelengths

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17
Q

Which photosystem would you find P700 in?

A

PS1

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18
Q

Which photosystem would you find P680 in?

A

PS2

19
Q

Name 2 accessory pigments?

A

Carotenoids

Xanthophylls

20
Q

What are the 4 stages of the Light-dependent stage?

A

Light harvesting in Photosystems
Photolysis of water
Photophosphorylation
Formation of NADPH (reduced NADP)

21
Q

What catalyses Photolysis?

A

An enzyme in PS2

22
Q

Which Photosystem does photolysis occur in?

A

PS2

23
Q

Why does photolysis occur?

A

To provide H+ ions for photophosphorylation

Provide e- to replace lost electrons in photophosphorylation

24
Q

What is photophosphorylation?

A

Production of ATP from ADP and Pi

25
Q

What are the two types of photophosphorylation?

A

Non-cyclic

Cyclic

26
Q

Which photosystem (s) does non-cyclic photophosphorylation occur in?

A

PS1 and PS2

27
Q

Which photosystem (s) does cyclic photophosphorylation occur in?

A

Only PS1

28
Q

Which type of photophosphorylation produces more ATP?

A

Non-cyclic

29
Q

Describe the process of Non-cyclic photophosphorylation

A

In PS2:
Photon strikes PS2 and energy is channeled to primary pigment

Energy excites a pair of electrons which escape the chlorophyll molecule

Electron carrier in thylakoid captures electrons

electrons are replaced by those from photolysis

Redox reactions pass e- down ETC in thylakoid releasing energy

This energy used to pump H+ into the inter-membrane space

Protons accumulate in the inter-membrane space forming an electrochemical gradient

Protons diffuse via channels associated with ATP synthase stimulating ATP production

As H+ passes through channel it is accepted by NADP to form NADPH

In PS1:
Photon excites an electron that is lost

protein-iron-sulphur complex called ferredoxin accepts the electrons and passes them to NADP in the Stroma

30
Q

Describe the process of Cyclic photophosphorylation

A

Photon excites an electron in PS1 that is lost

Pass electron to ETC that then passes it back to PS1

ATP is produced as the electron moves down ETC

The cycle continues

31
Q

Where does the light-independent stage occur?

A

Stroma

32
Q

What are the 2 sources of CO2 for the light independent stage?

A

From the air, diffuses through the stomata of the leaf

From respiration, CO2 produced as a by-product

33
Q

What is the Calvin Cycle?

A

The series of reactions where CO2 is converted to organic molecules

34
Q

What is the role of RuBP (ribulose bisphosphate)?

A

A carbon dioxide acceptor

35
Q

What is RuBisCO?

A

An enzyme that catalyses the reaction between CO2 and RuBP

36
Q

Describe the stages of the Calvin Cycle

A

CO2 reacts with RuBP to form an unstable 6C compound (catalysed by RuBisCO)

6C compound breaks down into GP, the carbon has now been fixed

GP is reduced using H+ from NADPH from the LDR. This makes TP (triose phosphate). This uses ATP from the LDR

10/12 TP molecules are used to reform RuBP, the other 2 are the product.

37
Q

Does the Calvin Cycle run when it is dark?

A

No, though it doesn’t directly use light energy is requires the products of the LDR which does use light energy

38
Q

What are the uses of TP?

A

Synthesise carbohydrates such as Glucose, Sucrose, Starch and Cellulose

Synthesise Amino acids, Fatty acids and Glycerol

Reform RuBP

39
Q

What are the main factors affecting photosynthesis?

A

Light intensity
Carbon Dioxide Concentration
Temperature
Water Stress

40
Q

What is the limiting factor?

A

It is the factor that is preventing the rate of photosynthesis getting any faster

41
Q

What happens to concentrations of GP, TP and RuBP when light intensity falls?

A

GP cant be reduced to TP

TP levels fall and GP accumulates

RuBP falls because there is no TP to regenerate it

42
Q

What happens to concentrations of GP, TP and RuBP when CO2 concentration falls?

A

RuBP cant accept it

No GP formed

No TP formed

43
Q

What happens to the rate of photosynthesis at different temperatures?

A

It is an enzyme catalysed reaction

Low temperatures it is slow

At optimum (30’C) it is at its fastest

Above 45’C enzymes become denatured and reaction slows

44
Q

What happens to rate of photosynthesis when a plant is under water stress?

A

When plant is under water stress it closes stomata to reduce water loss

This also reduces gaseous exchange

Makes CO2 less available so photosynthesis greatly decreases

OCR A-level Biology (24 decks)

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