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AQA A-level Biology > Topic 5: Photosynthesis > Flashcards

Topic 5: Photosynthesis Flashcards

1
Q

What is the word equation for photosynthesis?

A

Water+ Carbon Dioxide -> Glucose+ oxygen

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2
Q

What is the chemical equation for photosynthesis?

A

6H20 + 6CO2 -> C6H12O6 + 6O2

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3
Q

When do plants produce ATP?

A

In both respiration and photosynthesis

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4
Q

Photosynthesis is a process that is common in all photoautotrophic organisms. What is a photoautotrophic organism?

A

Organisms that make their own organic molecules using light

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5
Q

How is the leaf adapted for photosynthesis to occur effectively?

A
  • the palisade layer is located near the top of the leaf so it can absorb the maximum light
  • phloem is used to remove the end product
  • waxy cuticle is transparent for light absorption
  • guard cells allow gas exchange
  • the leaf is thin which means short diffusion pathway, large surface area for light absorption
  • has xylem to transport water
  • the palisade layer has a large number of cells for maximum photosynthesis
  • the spongy mesophyll has large air spaces for gas exchange
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6
Q

What are the organelles in chloroplasts that are essential for photosynthesis?

A

Thylakoids
Thylakoids stacked up= grana
Lamellae- bits of thylakoid membrane linking grana, they contain chlorophyll
They also have a phospholipid bilayer

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7
Q

What are the pigments needed for photosynthesis and where are they found?

A

Photosynthetic pigments= chlorophyll B and carotene
They are found in the thylakoid membranes and are attached to proteins
The proteins and the pigment are called a Photosystem

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8
Q

What is a Photosystem?
How many are in photosynthesis?

A

It is the protein and the photosynthetic pigment
There are 2 used by plants to capture light energy and they absorb light best at different wavelengths

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9
Q

What surrounds the thylakoids?

A

Stroma

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10
Q

What is stroma?

A

It is a gel-like substance that surrounds the thylakoids
It contains enzymes, sugars and amino acids
Carbohydrates produced by photosynthesis that aren’t used straight away are stored as starch grains in the stroma

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11
Q

What reaction occurs in the stroma?

A

The light independent reaction
It contains all the enzymes needed for this process

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12
Q

Why is the stroma located where it is?

A

It surrounds the grana so the products of the light dependent can easily diffuse into it
These products are used in the light independent

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13
Q

Why is the stroma important?

A

It contain all the enzymes needed for light independent reactions
It also contains DNA and ribosomes so the chloroplast can quickly produce the proteins needed in the light independent

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14
Q

What are the 2 stages of photosynthesis?

A

The light dependent reaction
The light independent reaction

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15
Q

What product of the photosynthesis equation is produced in the light dependent reaction and why?

A

Oxygen
During the process where ATP transfers energy, and NADPH transfers hydrogen to the light independent reaction, H2O is oxidised to make oxygen

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16
Q

What is the reactant from the photosynthesis equation that is used in the light dependent reaction?

A

Water

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17
Q

What is the product from the photosynthesis equation that is produced in the light independent reaction and how?

A

Glucose
The ATP and the NADPH from the light dependent reaction supply the hydrogen to make CO2 into glucose

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18
Q

What is the reactant in the photosynthesis equation that is used in the light independent reaction?

A

Carbon dioxide

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19
Q

Is the light independent reaction completely independent from light?

A

It doesnt directly use light energy but it does rely on the products of the light dependent reaction- which does require light

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20
Q

Is the light independent reaction completely independent from light?

A

No
Although the reaction itself doesnt directly use energy it relies on the products of the light dependent reaction- which does need light
So the reaction will be limited if the products of the light dependent are

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21
Q

What are the products of the light dependent that are needed for the light independent and why?

A

ATP- it transfers energy
NAPDH (reduced NADP) which transports hydrogen ions

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22
Q

Where does the light dependent reaction occur?

A

Thylakoid membranes

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23
Q

What is photoionisation?

A

When the light energy is absorbed by the chlorophyll it gives them more energy and eventually causes them electrons to be released from the chlorophyll
This is called photoionisation because the chlorophyll is left as a positively charged ion as a result of

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24
Q

What is the energy released from photoionisation used for?

A
  1. Making ATP from ADP and Pi- photophosphorylation
  2. Making NADPH from NADP
  3. Splitting water into protons (H+ ions), electrons and oxygen- photolysis
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25
Q

What is photophosphorylation?

A

The process of adding phosphate to a molecule using light

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26
Q

what is photolysis?

A

Splitting of a molecule using light energy

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27
Q

True or false: there is more than one type of photophosphorylation in the light-dependent reaction

A

True there is 2: cyclic and non cyclic

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28
Q

What is the difference between cyclic and non-cyclic photophosphorylation?

A

Non-cyclic produces ATP, NADPH and oxygen whereas cyclic produces just ATP
Cyclic only uses Photosystem 1 whereas Non-cyclic uses both photosystems

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29
Q

How are the photosystems linked?

A

By electron carriers

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30
Q

What are electron carriers?

A

Proteins that transport electrons

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31
Q

What do the photosystems and electron carriers form together?

A

An electron transfer chain

32
Q

What is an electron transfer chain?

A

A chain of proteins through which excited electrons flow

33
Q

Summarise non-cyclical photophosphorylation into 4 stages

A
  1. Light energy excites electrons in the chlorophyll
  2. Photolysis of water produces protons, electrons and oxygen
  3. Energy from excited electrons makes ATP
  4. Energy from excited electrons generates NADPH
34
Q

Explain the role of light energy in non cyclic photophosphorylation and what it does to the electrons

A
  • light energy is absorbed by Photosystem 2
    It excites the electrons in the chlorophyll so they move to a higher energy level
    The high energy electrons are released from the chlorophyll and move down the electron transfer chain to Photosystem 1
35
Q

When the excited electrons leave Photosystem 2, what happens as a result/ how is light energy involved?

A

When the excited electrons move down the electron transfer chain, they have to be replaced
Light energy splits water into protons (H+ ions), electrons and oxygen

36
Q

What is it called when light energy splits water?

A

Photolysis

37
Q

What happens to the electrons that that left Photosystem II and moved down the electron transfer chain?

A

As they move down the ETC, they lose energy

38
Q

Why do the electrons moving down the ETC lose energy/ where does it go?

A

The energy is used to transport protons (h+ ions) into the thylakoids so that there is a higher concentration of protons in the thylakoids than the stroma- producing a proton gradient across the thylakoid membrane

39
Q

What is the importance of creating a proton gradient across the thylakoids membrane?

A
  • protons will move down the gradient into the stroma via the enzyme ATP synthase which is embedded in the thylakoids membrane
    The energy released from this movement combines ADP and Pi to form ATP
40
Q

ATP synthase is an enzyme, and so it is specific to ATP. How does the movement of protons impact it?

A

The protons change the structure of ATP synthase which means it can then catalyse the formation of ATP from ADP and Pi

41
Q

Explain how the excited electrons generate NADPH

A

-light energy is absorbed by Photosystem I which excites the electrons further to a higher energy level
The electrons are then transferred to NADP along with a proton from the. Stroma to form reduced NADP (NADPH)

42
Q

What replaces the excited electrons that leave Photosystem I that are used to reduce NADP?

A

Electrons from Photosystem II

43
Q

What is chemiosmosis?

A

The process by which the movement of hydrogen ions across a biological membrane generates ATP

44
Q

According to the specification, where in photosynthesis is the chemiosmotic theory applicable?

A

When the production of ATP involves electron transfer associated with the transfer of electrons down the ETC and the passage of protons across the chloroplast membrane and is catalysed by ATP synthase embedded in these membranes

45
Q

Describe the process of cyclic photophosphorylation

A

Electrons are recycled, they aren’t passed onto NADP but are put back into Photosystem I via electron carriers
This means they can repeatedly flow through Photosystem I

46
Q

What are the products of cyclic photphosphorylaytion?

A

Small amounts of ATP
No reduced NADP or oxygen though

47
Q

What 3 reactions occur in the light-dependent reaction?

A

Photoionisation of chlorophyll
Photophosphorylation
Photolysis

48
Q

Summarise the process of the light dependent reaction

A
  • light excites electrons in the chlorophyll, their energy level is raised
    Chlorophyll is photoionised
    Electrons are passed down a series of electron carriers
    Protons are pumped into thylakoids space & diffuse back into stroma via ATP synthase
    ATP is synthesised- described by chemiosmotic theory
    Electrons from Photosystem I reduce NADP
    Electrons from photolysis replace ones lost from Photosystem II
49
Q

Where do the products of the light dependent reaction go?

A
  • electrons replaced in chlorophyll
    -protons and electrons reduce NADP
  • oxygen gas is released, can be used in aerobic respiration
    ATP is used in light independent reaction, as is NADPH
  • NADPH reduces CO2 to form glucose in the light independent reaction
50
Q

What is the light independent reaction also known as?

A

The Calvin cycle or the Calvin-Benson cycle

51
Q

Why does the light independent reaction require the products of the light dependent reaction?

A

It uses the products to reduce carbon dioxide to make organic molecules for the plant- like glucose

52
Q

What does the light-independent reaction not directly require but still needs?

A

Doesn’t require light
But needs the products from light independent not to be limiting

53
Q

Chemical energy from ATP and electrons from NADPH do what in the light independent reaction?

A

Reduce GP to TP which is then converted into carbohydrates like glucose by enzyme reactions
The carbohydrates produced can be used as a store of energy

54
Q

Where does the Calvin-Benson cycle take place?

A

Stroma of the chloroplasts

55
Q

What is needed to keep the Calvin-Benson cycle going?

A

ATP and hydrogen ions

56
Q

What is the starting compound of the Calvin-Benson cycle?

A

Ribulose biphosphate (RuBP)

57
Q

The Calvin-Benson is a cycle- why?

A

Because the starting compound (RuBP) is regenerated

58
Q

Summarise what happens at each stage of the Calvin cycle

A
  1. Formation of glycerate 3-phosphate
  2. Formation of Triose phosphate
  3. Regeneration of ribulose bisphosphate
59
Q

How is glycerate 3-phosphate (GP) formed in the Calvin-Benson cycle?

A
  • CO2 enters the leaf through the stomata and diffuses into the stoma of the chloroplast
    -here it combines with ribulose bisphosphate (RuBP)
  • the reaction is catalysed by Rubiscon
    This gives an unstable 6-carbon compound (GP) which quickly breaks down into 2 molecules of the 3-carbon compound called glycerate 3-phosphate (GP)
60
Q

Explain how triose phosphate is formed in the Calvin-Benson cycle?

A

ATP is hydrolysed which provides the energy to reduce the 3C compound GP to a different 3 carbon compound called TP
Hydrogen ions which come from NADPH are also needed for this reaction, so NADPH is recycled to NADP
Some TP is converted into useful organic compounds but most continues in the cycle to regenerate RuBP

61
Q

Explain how RuBP is regenerated using molecules of TP and ATP

A

5/6 molecules of TP produced aren’t used to make organic compounds but are used to regenerate RuBP
Regenerating RuBP uses the rest of the ATP from the light dependent reaction

62
Q

How many molecules of TP produced are used in the regeneration of RuBP?

A

5/6

63
Q

Describe the RUBISCO enzyme

A

It is slow- one of the slowest in the world
It isn’t very efficient
It tries to also bind to oxygen which slows the process down more

64
Q

What is a Hexose sugar and how are they made in photosynthesis?

A

Hexose sugar is a 6 carbon sugar, they can be used to make larger carbohydrates
One example, is glucose which is a hexose sugar made by joining 2 molecules of TP together

65
Q

How many times does the Calvin cycle need to turn to make one hexose sugar?

A

6

66
Q

Why does the Calvin cycle have to turn 6 times to make one hexose sugar?

A

Two TP molecules are made for every CO2 molecule used
5/6 TP molecules are used to generate RuBP
So for every 3 turna of the cycle, only one TP produced is used to make a hexose sugar
Two TP are needed for each hexose sugar so the cycle must turn 6 times to make one hexose sugar

67
Q

How much ATP and NADPH are needed for 6 turns of the cycle?

A

18 ATP and 12 NADPH from the light dependent

68
Q

Why is the Calvin cycle more efficient than it seems?

A

Although it takes a lot of turns of the cycle to make one hexose sugar it makes sure that there is always enough RuBP to combine with CO2- so cycle can continue

69
Q

Summarise the reactions in the light-independent reaction

A
  • CO2 reacts with RuBP (5 carbon acceptor molecule) which is catalysed but the enzyme Rubisco
  • 2 molecules of GP are formed
  • GP is reduced to TP
  • energy for the reduction of GP from hydrolysis of ATP and electrons from NAPDH
    Triose phosphate is converted to organic compounds by enzymes
70
Q

Summarise the products of the light independent reaction

A
  1. Glucose is converted to other organic compounds by enzyme reaction
  2. Most TP is regenerated into RuBP using organic phosphate from the hydrolysis of ATP
71
Q

What is the starting point to make all organic susbstances in plants?

A

The Calvin cycle

72
Q

What are TP and GP molecules used to make?

A

Carbohydrates, lipids & amino acids

73
Q

Describe how TP is used to make carbohydrates

A

They are used to make hexose sugars
Which are used to make larger carbohydrates like sucrose, starch and cellulose

74
Q

How are lipids made from TP and GP?

A

Made using glycerol- which is synthesised from TP
And fatty acids- which are synthesised from GP

75
Q

Which product of the Calvin cycle is used to make amino acids?

A

GP
Some amino acids are made from GP

AQA A-level Biology (25 decks)

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