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A Level Biology > Module 5 Section 5: Photosynthesis > Flashcards

Module 5 Section 5: Photosynthesis Flashcards

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1
Q

Why do plants and animals need energy

A

Living things need energy for:
Photosynthesis (plants only)
Muscle contraction (animals only)
Maintaining body temperature (animals only)
Active transport
DNA replication
Cell division
Protein synthesis

Without energy these biological processes would stop and the plant or animal would die

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2
Q

What do microorganisms need energy for

A

DNA replication
Cell division
Protein synthesis
Motility (movement)

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3
Q

What is photosynthesis

A

This is how plants make glucose
A process where energy from light is used to make glucose from H2O and CO2 (light energy converted into chemical energy in the form of glucose)
Energy stored as glucose until plants release it by respiration

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4
Q

How do animals get their energy

A

Animals can’t make their own food
They get glucose by eating plants or other animals
They then respire the glucose to release energy

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5
Q

What is respiration

A

Living cells release energy from glucose
This energy is used to power all the biological processes in a cell

Two types:
Aerobic respiration: uses oxygen
Anaerobic respiration: without oxygen

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6
Q

What is a metabolic pathway

A

A series of small reactions controlled by enzymes
E.g. respiration and photosynthesis

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7
Q

What is phosphorylation

A

Adding phosphate to a molecule
E.g. ADP is phosphorylated to ATP

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8
Q

What is photophosphorylation

A

Adding phosphate to a molecule using light

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9
Q

What is photolysis

A

The splitting (lysis) of a molecule using light (photo) energy

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10
Q

What is hydrolysis

A

The splitting (lysis) of a molecules using water (hydro)

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11
Q

What is decarboxylation

A

The removal of carbon dioxide from a molecule

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12
Q

What is dehydrogenation

A

The removal of a hydrogen from a molecule

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13
Q

What are redox reactions

A

Reactions that involve reduction and oxidation

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14
Q

Key points about redox reactions

A

If something is reduced it has gained electrons (e-) and may have gained hydrogen or lost oxygen
If something is oxidised it has lost electrons and may have lost hydrogen or gained oxygen
If something is oxidised, something else is always reduced

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15
Q

What is a coenzyme

A

A coenzyme is a molecule that aids the function of an enzyme
Usually work by transferring a chemical group from one molecule to another

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16
Q

What is the coenzyme used in photosynthesis

A

NADP
This transfers hydrogen from one molecule to another
This means that it can reduce (give hydrogen to) or oxidise (take hydrogen from) a molecule

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17
Q

What are some examples of coenzymes used in respiration

A

NAD, coenzyme A and FAD
NAD and FAD transfer hydrogen from one molecule to another meaning they can reduce (give hydrogen to) or oxidise (take hydrogen from) a molecule
Coenzyme A transfers acetate between molecules

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18
Q

What are chloroplasts and what is their structure

A

Location of photosynthesis in plant cells
Small flattened organelles found in plant cells
Have double membrane called chloroplast envelope
Thylakoids (fluid filled sacs) are stacked up in the chloroplasts into grana (singular: granum)
Grana are linked together by sections of thylakoid membrane called lamellae

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19
Q

How do chloroplasts absorb light energy and what are the structures of these features

A

Chloroplasts contain photosynthetic pigments (e.g. chlorophyll a, chlorophyll b and carotene)
These are coloured substances that absorb the light energy needed for photosynthesis
Pigments found in thylakoid membranes and attached to proteins
Protein and pigment together is called a photosystem

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20
Q

What does a photosystem contain

A

Contains two types of photosynthetic pigments:
Primary pigments and accessory pigments

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21
Q

What are the two photosystem used by plants

A

There are two photosystems used by plants to capture light energy
Photosystem 1:
Arranged around molecules of chlorophyll a
Peak absorption of light at 700nm
Reaction centre is known as P700

Photosystem 2:
Arranged around molecules of chlorophyll a
Peak absorption of light at 680nm
Reaction centre known as P680

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22
Q

What is the stroma

A

These are contained within the inner membrane of the chloroplast and surrounding the thylakoids
They are gel-like substances
Contains enzymes, sugars and organic acids
Also contain chloroplast DNA and excess carbohydrates that have not been used

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23
Q

What is the structure of chloroplast DNA and where is it kept

A

Found in stroma and is often circular
Can be multiple copies in each chloroplast

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24
Q

Where are excess carbohydrates stored in chloroplasts

A

Stored as starch grains in the stroma

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25
Q

What are the two stages of photosynthesis

A

Light dependent reaction
Light independent reaction

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26
Q

What is the light dependant reaction

A

Reaction needs light energy
Takes place in thylakoid membranes of chloroplasts
This is where light energy is absorbed by photosynthetic pigment in the photosystems and converted to chemical energy
The light energy is used to add a phosphate group to ADP to form ATP, and to reduce NADP to form reduced NADP
(Reduced NADP is an energy rich molecule because it can transfer hydrogen and electrons to other molecules)
ATP transfers energy and reduced NADP transfers hydrogen to the light independent reaction
During the process H2O is oxidised to O2

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27
Q

What is the light independent reaction

A

Also called Calvin cycle
Doesn’t use light energy directly
Does rely on products from light dependant reactions
Takes places in the stroma of the chloroplasts
Here, the ATP and reduced NADP from the light dependent reaction supply the energy and hydrogen to make glucose from CO2

28
Q

Method of using thin layer chromatography to separate photosynthetic pigments

A

Grind up several leaves with anhydrous sodium sulfate and some propanone

Transfer the liquid to a test tube, add some petroleum ether and gently shake the tube
Two distinct layers will form in the liquid - the top layer is the pigments mixed in with petroleum ether

Transfer some of the liquid from the top layer into a second test tube with some anhydrous sodium sulfate

Draw a horizontal pencil line near bottom of a chromatography plate
Build up single concentrated spot of the liquid (from step 3) on the line by putting drops and ensuring each one is dry before adding the next (this is point of origin)

Once the point of origin is completely dry, put the plate into a glass beaker with some prepared solvent (e.g. mixture of propanone, cyclohexane and petroleum ether) - just enough so that point of origin is a little bit above the solvent
Put lid on beaker and leave plate to develop
As the solvent spreads up the plate, the different pigments move with it, but at different rates - so they separate

When the solvent has nearly reached the top, take the plate out and mark the solvent front (furthest point solvent has reached) with a pencil and leave the plate to dry in a well-ventilated place

Should be several new coloured spots on the chromatography plate between the point of origin and the solvent front
These are the separated pigments
Calculate Rf values and look them up in a database to identify what the pigments are

29
Q

What is light energy absorbed by photosystems for in the light dependent reaction

A

Making ATP from ADP and inorganic phosphate (this is phosphorylation)
Making reduced NADP from NADP
Splitting water into protons (H+ ions), electrons and oxygen (called photolysis)

30
Q

What types of phosphorylation does the light dependant reaction include

A

Non-cyclic and cyclic
Each of these processes have different products

31
Q

What are primary pigments

A

Primary pigments are reaction centres, where electrons are excited during the light dependent reaction
Made up of two forms of chlorophyll a

32
Q

What are accessory pigments

A

Accessory pigments make up light harvesting systems
They surround reaction centres and transfer light energy to them to boost the energy available for electron excitement to take place
Made up of other forms of chlorophyll a, caretanoids, chlorophyll b

33
Q

What are electron carriers and what is their role in the light dependant reaction

A

Photosystems in thylakoid membrane are linked by electron carriers
These are proteins that transfer electrons
An electron transport chain is formed from electron carriers and photosystems
This is a chain of proteins through which excited electrons flow

34
Q

What is the light dependent reaction split into

A

Non-cyclic photophosphorylation
Cyclic photophosphorylation

35
Q

Process of non-cyclic photophosphorylation and draw out diagrams (long one)

A
36
Q

Process of cyclic phosphorylation with diagram

A

Only uses photosystem 1
This is cyclic as the electrons from the chlorophyll molecule aren’t passed onto NADP
They are instead passed back to photosystem 1 via electron carriers in a cycle
This doesn’t produce any NADP or O2 but does produce small amounts of ATP

37
Q

Draw zigzag diagram for cyclic and non-cyclic photophosphorylation

A
38
Q

What can the light independent reaction also be called

A

Can also be called the Calvin cycle
Or carbon dioxide fixation as CO2 is fixed into an organic molecule

39
Q

Where does the Calvin cycle take place

A

Takes place in the stroma of the chloroplasts

40
Q

What does the Calvin cycle produce

A

Makes triose phosphate from CO2 and ribulose bisphophate (5 carbon compound)
Triose phosphate can be used to make glucose and other useful organic substances
Reactions linked in a cycle which means the starting compound, ribulose bisphosphate is regenerated

41
Q

What does the Calvin cycle need to keep going

A

Needs ATP and H+

42
Q

First step of the Calvin cycle: production of glycerate-3-phosphate

A

CO2 enters the leaf through the stomata and diffuses into the stroma of the chloroplast
It is then combined with ribulose bisphosphate (RuBP) which is a 5C compound
Produces an unstable 6C compound which quickly breaks down into 2 molecules of a 3C compound called glycerate 3-phosphate (GP)
Ribulose bisphosphate carboxylase (RuBisCO) catalyses the reaction between CO2 and ribulose bisphosphate

43
Q

Second step of the Calvin cycle: glycerate 3-phosphate is reduced to triose phosphate

A

ATP (from light dependant reaction) provides energy to turn GP into another 3C compound called triose phosphate (TP)
This requires H+ ions which come from reduced NADP (from light dependent reaction)
Reduced NADP is recycled to NADP (used in light dependent reaction again)
Triose phosphate can then be converted into useful organic compounds e.g. glucose

44
Q

Third step of Calvin cycle: ribulose bisphosphate is regenerated

A

5 out of every 6 molecules of triose phosphate produced in the cycle aren’t used to make hexose sugars and are instead used to regenerate RuBP
Regenerating RuBP uses the rest of the ATP produced by light dependent reaction

45
Q

What types of useful organic substances can TP and GP be converted into

A

Carbohydrates: hexose sugars (e.g. glucose) are made by joining two triose phosphate molecules together and larger carbohydrates (e.g. sucrose, starch, cellulose) are made by joining hexose sugars together in different ways
Lipids: made using glycerol (synthesised from triose phosphate) and fatty acids (from glycerate 3-phosphate)
Amino acids: some amino acids are made from glycerate 3- phosphate

46
Q

How many turns of the Calvin cycle are needed to make 1 hexose sugar

A

Needs to turn 6 times

47
Q

Why does the Calvin need to turn 6 times to make 1 hexose sugar

A

3 turns of the cycle produce 6 molecules of triose phosphate as 2 molecules of TP are made for every one CO2 molecule used
5/6 of these TP molecules are used to regenerate RuBP
Means that only after 3 turns of the cycle, 1 TP molecule is produced that’s used to make a hexose sugar
A hexose sugar has 6 carbons so two TP molecules must be used which means that the cycle must turn 6 times to produce two molecules of TP to make 1 hexose sugar
6 turns of the cycle need 18 ATP and 12 reduced NADP from light dependent reaction

48
Q

What are the optimum conditions for photosynthesis

A

High light intensity of a certain wavelength
Temperature around 25°
CO2 at 0.4%

49
Q

Why is high light intensity of a certain wavelength optimum for photosynthesis

A

Light is needed to provide the energy for the light-dependent reaction - the higher the intensity of the light, the more energy it provides.
Only certain wavelengths of light are used for photosynthesis.
The photosynthetic pigments chlorophyll a, chlorophyll b and carotene only absorb the red and blue light in sunlight.
(Green light is reflected, which is why plants look green.)

50
Q

Why is temperature around 25° optimum for photosynthesis

A

Photosynthesis involves enzymes (e.g. ATP synthase, RuBisCO).
If the temperature falls below 10 ° the enzymes become inactive, but if the temperature is more than 45 °C they may start to denature

51
Q

Why is too high of a temperature bad for photosynthesis

A

Stomata close to avoid losing too much water. This causes photosynthesis to slow down because less CO2 enters the leaf when the stomata are closed

Thylakoid membranes may be damaged which could reduce the rate of the light-dependent stage reactions by reducing the number of sites available for electron transfer.
The membranes around the chloroplasts could be damaged, which could cause enzymes important in the Calvin cycle to be released into the rest of the cell.
This would reduce the rate of the light -independent stage reactions.

Chlorophyll could be damaged.
This would reduce the amount of pigment that can absorb light energy, which would reduce the rate of the light-dependent stage reactions.

52
Q

Why is 0.4% CO2 optimum for photosynthesis

A

Carbon dioxide makes up 0.04% of the gases in the atmosphere.
Increasing this to 0.4% gives a higher rate of photosynthesis, but any higher and the stomata start to close

53
Q

How may light, temperature or CO2 limit photosynthesis

A

All three of these need to be at the right level to allow a plant to photosynthesise as quickly as possible.
If one of these factors is too low or too high, it will limit photosynthesis
Still limited if the other two are at perfect level

54
Q

What are the common limiting factors of photosynthesis out of the 3

A

On a warm, sunny, windless day, it’s usually CO2 that’s the limiting factor, and at night it’s the light intensity.
Any of these factors could become the limiting factor, depending on the environmental conditions

55
Q

How to read graph of photosynthesis being limited by light intensity

A

Between points A and B, the rate of hotosynthesis is limited by the light tensity. So as the light intensity increases, so can the rate of photosynthesis.
Point B is the saturation point - increasing light intensity after this point makes no difference, because something else has become the limiting factor.
The graph now levels off.

56
Q

How to read graph of photosynthesis being limited by temperature

A

Both these graphs level off when light intensity is no longer the limiting factor.
The graph at 25°C levels off at a higher point than the one at 15 °C, showing that temperature must have been a limiting factor at 15 °C

57
Q

How to read graph of photosynthesis being limited by CO2 concentration

A

Both these graphs level off when light intensity is no longer the limiting factor.
The graph at 0.4% CO2 levels off at a higher point than the one at 0.04%, so CO2 concentration must have been a limiting factor at 0.04% CO2
The limiting factor here isn’t temperature because it’s the same for both graphs (25 °C)

58
Q

How can photosynthesis be affected by water stress

A

When plants don’t have enough water, stomata will close to preserve that little water they do have
This leads to less CO2 entering the leaf for the Calvin cycle and slowing photosynthesis down

59
Q

How does low light intensity affect the mechanisms of the Calvin cycle

A

In low light intensities, the products of the light dependent stage (reduced NADP and ATP) will be in short supply
Means that conversion of GP to TP and RuBP is slow
So the level of GP will rise (as it’s still being made) and levels of TP and RuBP will fall (as they’re used to make GP)

60
Q

How do changes in temperature affect the mechanisms of the Calvin cycle

A

All the reactions in the Calvin cycle are catalysed by enzymes
At low temperatures, all of the reactions will be slower as the enzymes work more slowly
This means the levels of RuBP, GP and TP will fall
GP, TP and RuBP are affected in the same way at very high temperatures, because the enzymes will start to denature

61
Q

How does CO2 conc affect the mechanisms of the Calvin cycle

A

Low levels of CO2 means slower conversion of RuBP to GP (as there’s less CO2 to combine with RuBP)
The level of RuBP will rise (as it’s still being made)
Levels of GP and TP will fall as they’re used up to make RuBP

62
Q

What is the width of opening of the stomata called

A

Stomatal aperture

63
Q

What is a saturation point

A

The point where a limiting factor is no longer limiting the reaction
Something else has become the limiting factor

64
Q

How to investigate limiting factors of photosynthesis

A

A test tube containing the pondweed and water is connected to a capillary tube of water
Tube of water is connected to a syringe.
A source of white light is placed at a specific distance from the pondweed.
The pondweed is left to photosynthesise for a set amount of time.
As it photosynthesises, the oxygen released will collect in the capillary tube
At the end of the experiment, the syringe is used to draw the gas bubble in the tube up alongside a ruler and the length of the gas bubble is measured.
This is proportional to the volume of O2 produced.
Any variables that could affect the results should be controlled, e.g. temperature, the time the weed is left to photosynthesise.
The experiment is repeated and the average length of gas bubble is calculated, to make the results more precise.
The whole experiment is then repeated with the light source placed at different distances from the pondweed.

65
Q

How to work out the exact volume of O2 produced in the capillary tubes

A

Need to know the radius of the capillary tube

66
Q

How else to measure rate of photosynthesis using O2

A

Counting number of O2 bubbles produced
This is less accurate

A Level Biology (27 decks)

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