1. Photosynthesis and ATP synthesis 2

Question 1

Explain cyclic photophosphorylation

Answer 1

Light is absorbed by PSI

light energy is passed on to electrons and excites them in the chlorophyll a molecules at the reaction centre.

In each chlorophyll a molecule, one of the electrons becomes so energetic that it moves to a higher energy level and leaves the chlorophyll molecules completely.

The electron is then passed along the chain of electron carriers (e transport system)

The energy from the electron is used to make ATP.

The electron, now having lost its extra energy, eventually returns to chlorophyll a in PSI.

Question 2

The electron transport system consists of a series of carrier molecules and, as electrons pass from one carrier molecule to the next, energy is released.

This energy release causes

Answer 2

H+ to be actively pumped into the thylakoid from the stroma across the thylakoid membrane.

The concentration of H+ inside the thylakoid space is therefore higher than in the stroma outside.

Thus, a H+ gradient is created across the thylakoid membrane.

The H+ can diffuse back across the thylakoid membrane and into the stroma only via specific protein channels called chemiosmotic channels.

As H+ flow from inside the thylakoid membrane to the outside of the thylakoid down their electrochemical gradient (proton gradient), energy is generated to drive the enzymatic conversion of ADP and P (inorganic phosphate found in the cytosol) into ATP.

The reactions of the Calvin cycle that occur in the stroma require a larger amount of ATP than NADPH and this is where the ATP is used up.

Question 3

Chemiosmotic channels are formed by

Answer 3

enzyme complexes called ATP synthase

Question 4

Non-cyclic photophosphorylation involves what type of photosystem

Answer 4

both kinds of photosystem.

PSI and PSII

Question 5

Non-cyclic photophosphorylation results in

Answer 5

the production of ATP and NADP

Question 6

what are the three stages of Non-cyclic photophosphorylation

Answer 6

1 ) Photolysis of water produces protons (H+ ions), electrons and 0 2

2) Energy from the excited electrons makes ATP…
3) reduced NADP is generated

Question 7

explain the first stage of Non-cyclic photophosphorylation where Photolysis of water produces protons (H+ ions), electrons and O2 takes place

Answer 7

The chlorophyll a molecules of PSII absorb light energy

the excited, high energy electron from chlorophyll leaves the reaction centre chlorophyll a molecule of PSII (and moves down the electron chain-photophosphorylation)

As soon as the high-energy electrons leave the reaction centre, PSII immediately takes up replacement electrons from a water molecule

the water molecule splits into two electrons, two H+ (protons) and an oxygen atom. (two oxygen atoms from two water molecules combine to form a molecule of oxygen)

The H+ stay inside the thylakoid space and contribute to the formation of a proton gradient which is used to generate ATP.

the reaction for this is
2H2O → 4H+ + 4e− + O2

Question 8

The light-dependent splitting of water molecules is called

Answer 8

photolysis

Question 9

Photolysis is

Answer 9

chemical process by which molecules are broken down into smaller units through the absorption of light

the light-dependent splitting of water molecules

Process by which light energy breaks down a molecule

Question 10

explain the second stage of Non-cyclic photophosphorylation where energy from the excited electrons makes ATP…

Answer 10

High-energy electrons from PSII are taken up by an electron acceptor, which transfers them to an electron transport system.

The electron transport system consists of a series of molecules that act as electron carriers and as the electrons are transported along,

energy is released and used to transport H+ into the thylakoid and stored in the form of a proton gradient across the thylakoid membrane

The production of ATP occurs when the H+ inside the thylakoid flow down their electrochemical gradient to the outside of the thylakoid (the stroma) via the ATP synthase (which is embedded in the thylakoid membrane)

the energy of this movement combines ADP an inorganic phosphate (Pi) to form ATP

(Chemiosmosis-production of ATP using an electrochemical gradient)

Question 11

Chemiosmosis is

Answer 11

the process by which a Hydrogen pump pumps protons into the thylakoid membrane.

The production of ATP using an electrochemical gradient

H+ passively flows through the ATP synthase which leads to the creation of ATP.

Question 12

explain the third stage of Non-cyclic photophosphorylation where reduced NADP is generated

Answer 12

After the high-energy electrons have travelled along the electron transport system they have lost energy and become low-energy electrons.

The low-energy electrons enter PSI.

The PSI antenna complex absorbs solar energy and the high-energy excited electrons leave the reaction centre chlorophyll a

then the electrons are taken up by an electron acceptor, which passes them to NADP. The electrons, NADP and H+ bind and become NADPH

Question 13

Photosystem I uses light energy to

Answer 13

reduce NADP to NADPH

Question 14

Photosystem II uses light energy to

Answer 14

oxidize water molecules to form oxygen (O2 ), H+ and electrons

Question 15

the non-cyclic electron pathway starts with

Answer 15

PSII

Question 16

the only mechanism by which ATP is generated during photosynthesis is by

Answer 16

the proton gradient across the thylakoid membrane

Question 17

Cyclic photophosphorylation only uses PSI. It’s called ‘cyclic’ because

Answer 17

the electrons from the chlorophyll molecule aren’t passed onto NADP, but are passed back to PSI via electron carriers.

This means the electrons are recycled and can repeatedly flow through PSI.

This process doesn’t produce any reduced NADP or O , — it only produces small amounts of ATP

Question 18

Both cyclic and non-cyclic photophosphorylation stop

when

Answer 18

there is no light because ATP synthesis and NADP

reduction (i.e. production of NADPH) require light

Question 19

The rates of cyclic and non-cyclic photophosphorylation depend on

Answer 19

each other because they are linked by the exchange of ATP and ADP and NADP and NADPH with the Calvin cycle and photosystems

Question 20

The Z-scheme is

Answer 20

simply a way of summarising what happens to electrons during the light dependent reactions.

It is a kind of graph, with the y-axis indicating the ‘energy level’ of the electron

Question 21

explain the Z-scheme, summarising non-cyclic photophosphorylation

Answer 21

1) light hits photosystem II. The red vertical line going up shows the increase in the energy level of electrons as they are emitted from this photosystem.
2) If you keep following the vertical line showing the increasing energy in the electrons, you arrive at a point where it starts a steep dive downwards. This shows the electrons losing their energy as they pass along the electron carrier chain.
3) Eventually they arrive at photosystem I.
4) You can then track the movement of the electrons to a higher energy level when PSI is hit by light, before they fall back downwards as they lose energy and become part of a reduced NADP molecule.

Question 22

the electrons in the z scheme come from

Answer 22

the splitting of water molecules

Question 23

The thylakoid membrane contains several protein complexes that perform different functions associated with photosynthesis.

The protein complexes are:

Answer 23

PSI is a protein complex in association with the antenna complex of chlorophyll a molecules and the enzyme that reduces NADP to NADPH

PSII is a protein complex in association with the antenna complex of chlorophyll a molecules.
PSII splits water to give oxygen and H+ that contribute to electrochemical gradient across the thylakoid membrane.

ATP synthase complex has an ion channel that allows H+ to flow down their electrochemical gradient from the inside of the thylakoid space to outside in the stroma thereby generating ATP from ADP.

Question 24

A cytochrome is

Answer 24

a protein that contains a haem group that serves as electron carriers in respiration and photosynthesis

A cytochrome complex transports electrons from PSII and PSI.

Question 25

A cytochrome complex transports

Answer 25

electrons from PSII and PSI.

Question 26

haem is an

Answer 26

ion-containing prosthetic group such as that in haemoglobin

Question 27

The Calvin cycle takes place in

Answer 27

the stroma of the chloroplasts

Question 28

Products of Calvin Cycle

Answer 28

triose phosphate from CO2 (used to make glucose and other useful organic substances)

ribulose bisphosphate (a 5-carbon compound)

Question 29

Calvin cycle needs what to keep it going?

Answer 29

ATP and H+ ions

Question 30

The Calvin cycle is also known as carbon dioxide fixation because

Answer 30

carbon from CO2 is ‘fixed’ into an organic molecule.

Question 31

Carbon enters the calvin cycle as ___ and leaves as ___

Answer 31

Carbon enters the Calvin cycle as carbon dioxide and leaves as sugar

Question 32

The fixation of carbon dioxide is the

Answer 32

conversion of carbon dioxide to an organic compound

Question 33

The Calvin cycle (Light independent stage) can be divided into three basic steps

Answer 33

1) Carbon Fixation
2) Reduction of Glycerate-3-Phosphate
3) Regeneration of RuBP

Question 34

the Calvin cycle is where

Answer 34

the now ATP and reduced NADP that have been formed in the light-dependent stage are used to help to produce carbohydrates from carbon dioxide.

Question 35

explain what happens in the first stage of the Calvin cycle where carbon fixation takes place

Answer 35

CO2 enters the leaf through the stomata and diffuses into the stroma of the chloroplast.

Here, it’s combined with ribulose bisphosphate (RuBP), a 5-carbon compound. This reaction is catalysed by the enzyme rubisco. •

This gives an unstable 6-carbon compound, which quickly breaks down into two molecules of a 3-carbon compound called glycerate 3-phosphate(GP)/ 3-phosphoglycerate(PGA)

Question 36

What is the first product of the Calvin cycle

Answer 36

3-phosphate(GP)/ 3-phosphoglycerate(PGA)

Question 37

glycerate 3-phosphate(GP) is also called

Answer 37

3-phosphoglycerate(PGA)

Question 38

The chloroplast stroma contains an enzyme called

Answer 38

rubisco

Question 39

Rubisco full name is

Answer 39

Ribulose-1,5-bisphosphate carboxylase

Question 40

what is thought to be the most abundant enzyme in the world

Answer 40

Rubisco

Question 41

explain what happens in the second stage of the Calvin cycle where the Reduction of Glycerate-3-Phosphate takes place

Answer 41

The hydrolysis of ATP (from the light dependent reaction) provides energy to turn the 3-carbon compound, GP, into a different 3-carbon compound called triose phosphate (TP).

this reaction also requires ATP to supply the energy and H+ ions, which come from reduced NADP (also from the light-dependent reaction).
Reduced NADP is recycled to NADP.

Some triose phosphate is then converted into useful organic compounds (e.g. glucose) and some continues in the Calvin cycle to regenerate RuBP

Question 42

what is the first carbohydrate that is made in photosynthesis

Answer 42

triose phosphate (TP)

Question 43

RuBP molecules each contain

Answer 43

five atoms of carbon

Question 44

explain what happens in the third stage of the Calvin cycle where the Regeneration of RuBP takes place

Answer 44

Five out of every six molecules of TP produced in the cycle aren’t used to make hexose sugars, but to regenerate RuBP.
energy for this reaction is supplied by ATP

Regenerating RuBP uses the rest of the ATP produced by the light-dependent reaction.

Question 45

diagram showing the Calvin cycle

Answer 45

chegg

Question 46

Function of Rubisco

Answer 46

to catalyse the reaction in which carbon dioxide combines with a substance called RuBP(ribulose bisphosphate).

Question 47

Rubisco is

Answer 47

a plant enzyme involved in the light independent stage of photosynthesis which catalyzes the fixing of atmospheric carbon dioxide during photosynthesis by catalyzing the reaction between carbon dioxide and RuBP

Question 48

the enzyme that fixes the carbon dioxide is

Answer 48

Ribulose bisphosphate carboxylase (RuBP carboxylase

Question 49

RuBP carboxylase has a relatively low enzymatic rate because it

Answer 49

catalyses the fixation of a few molecules of its substrate (carbon dioxide) per second

Question 50

In a cycle, the starting molecule must be

Answer 50

regenerated in order for the cycle to continue

Question 51

For every three turns of the Calvin cycle what happens?

Answer 51

five molecules of PGAL are used to regenerate three molecules of RuBP
a molecule of carbon dioxide is also entering the Calvin cycle at every turn and the carbon dioxide is reduced

the net gain is one PGAL molecule. This means that one PGAL molecule is available to the plant to be used to generate other organic compounds that it needs.

Question 52

why is the Calvin cycle needed?

Answer 52

The products of the light-dependent stage cannot be stored as a long-term supply of energy for a plant.

Neither can they be used to build up the large molecules that plants need for structural support, information storage and metabolic functions such as catalysing reactions.

This means a further set of reactions is necessary to produce molecules to fix carbon and therefore make it possible to produce organic molecules

Question 53

The recycling of RuBP is important because

Answer 53

otherwise it would have to be produced from something else.

For example, it could be produced from stored starch which would be a waste of the energy used to make starch in the first place

Question 54

Rubisco is active when

Answer 54

active in the light, but less active or inactive in the dark.

Oxygen acts as a competitive inhibitor

Question 55

Of 12 molecules of triose phosphate produced, ten of these are used to

Answer 55

produce six molecules of RuBP and two may be used to produce hexose or glycerol

Question 56

what is the starting molecule for the synthesis of starch and cellulose

Answer 56

Glucose phosphate

Question 57

In times of rapid photosynthesis, starch grains may be

Answer 57

stored temporarily in the chloroplast. Later, the starch is reconverted to glucose and transported to other parts of the plant.

Question 58

The Calvin cycle is the starting point for

Answer 58

making all the organic substances a plant needs.

Triose phosphate (TP) and glycerate 3-phosphate (GP) molecules are used to make carbohydrates, lipids and amino acids

Question 59

what are the fates of the triose phosphate produced during reduction of Glycerate-3-Phosphate in the Light Independent/Calvin cycle stage of photosynthesis?

Answer 59

1) Five-sixths of it are used to regenerate RuBP.

2) The remainder can be converted into other carbohydrates.
For example, two triose phosphates can combine to produce a hexose phosphate molecule.
From this, glucose, fructose, sucrose, starch and cellulose can be formed.

3) can also be used to make lipids like glycerol and fatty acids which gives plant oil
eg-coconut, corn and castor oil

4) and to make amino acids.
for amino acid production, plants need TP + nitrogen containing ions from the soil in the form of nitrate ions or ammonium ions or root nodules

Question 60

glycerol is synthesized from

Answer 60

triose phosphate

Question 61

fatty acids is synthesized from

Answer 61

glycerate 3-phosphate

Question 62

what is the form in which plants usually transport sugars through the phloem

Answer 62

sucrose

Question 63

examples of storage organs of starch

Answer 63

yams, sweet potatoes and cassava

Question 64

Root nodules are

Answer 64

are enlargements or swellings on the roots of legumes that are inhabited by symbiotic nitrogen-fixing bacteria

Question 65

The Calvin Cycle Needs to Turn how many times to make One Hexose Sugar?

Answer 65

The Calvin Cycle Needs to Turn Six Times to Make One Hexose Sugar

Question 66

The Calvin Cycle Needs to Turn Six Times to Make One Hexose Sugar because

Answer 66

Three turns of the cycle produces six molecules of triose phosphate (TP), because two molecules of TP are made for every one CO2 molecule used.

Five out of six of these TP molecules are used to regenerate ribulose bisphosphate (RuBP).

This means that for three turns of the cycle only one TP is produced that’s used to make a hexose sugar.

A hexose sugar has six carbons though, so two TP molecules are needed to form one hexose sugar.

This means the cycle must turn six times to produce two molecules of TP that can be used to make one hexose sugar.

Six turns of the cycle need 18 ATP and 12 reduced NADP from the light-dependent reaction.

Question 67

Photorespiration is a

Answer 67

process that occurs when the enzyme RuBP carboxylase catalyses a reaction with oxygen instead of carbon dioxide

Question 68

The conditions under which photorespiration occur are related to

Answer 68

environmental factors.

In hot dry weather, stomata on leaves are closed to prevent water from being lost from inside the leaf

Question 69

how is phosphoglycolate formed?

Answer 69

When the stomata are closed, photosynthesis can still occur and one of the by-products of photosynthesis is oxygen which builds up in the intercellular spaces.

This abundant oxygen then combines with RuBP carboxylase to form one molecule of PGA and one molecule of phosphoglycolate

Question 70

phosphoglycolate is

Answer 70

a molecule that contains two carbon atoms.

Phosphoglycolate is not a useful metabolite in plants and energy must be used up to convert it into products that are useful.

No carbon is fixed during photorespiration.

Question 71

what inputs does Photosynthesis require?

Answer 71

1) raw materials in the form of carbon dioxide and water
2) energy in the form of sunlight
3) The light-independent stage also requires a reasonably high temperature

Question 72

why does The light-independent stage of photosynthesis require a reasonably high temperature

Answer 72

because the rates of reactions are affected by the kinetic energy of the molecules involved

Question 73

what happens if any of these requirements of photosynthesis is in short supply

Answer 73

it can limit the rate at which the reactions of photosynthesis are able to take place

Question 74

what are the factors affecting the rate of photosynthesis

Answer 74

1) Light intensity
2) availability of carbon dioxide
3) Temperature
4) water supply

Question 75

what does the Light provide in photosynthesis?

Answer 75

Light provides the energy that drives the light dependent reactions, so it is obvious that when there is no light, there is no photosynthesis.

Question 76

what happens if we provide a plant with more light

Answer 76

it will photosynthesise faster

However, this can only happen up to a point (a point of light intensity)

Question 77

what happens when we reach a point of light intensity?

Answer 77

if you we give the plant more light, its rate of photosynthesis does not change.

We can say that ‘light saturation’ has occurred.

Some other factor, such as the availability of carbon dioxide or the quantity of chlorophyll in the plant’s leaves, is preventing the rate of photosynthesis from continuing to increase

Question 78

explain the diagram of the effect of light intensity on the rate of photosynthesis

Answer 78

Over the first part of the curve rate of photosynthesis increase as light intensity increases.

For these light intensities, light is a limiting factor.

The light intensity is limiting the rate of photosynthesis.

If we give the plant more light, then it will photosynthesise faster.

But, from point X onwards, increasing the light intensity has no effect on the rate of photosynthesis.

Along this part of the curve, light is no longer a limiting factor. Something else is.

It is most likely to be the carbon dioxide concentration.

Question 79

Optimum Conditions for Photosynthesis are

Answer 79

High light intensity of a certain wavelength

Temperature around 25 °C

Carbon dioxide at 0.4%

a constant supply of water

Question 80

Limiting factors occur when

Answer 80

a chemical process is affected by more than one factor.

The rate of the chemical process is limited by whichever factor is nearest its minimum value.

Question 81

The limiting factor is

Answer 81

that factor which directly affects a process if its quantity is changed

What this means is that whichever factor is available in the least amount limits the rate of the chemical reaction.

The photosynthesis reactions cannot go faster when the limiting factor is holding it back

Question 82

what is the concentration of carbon dioxide in the air

Answer 82

very low, only about 0.04%

Question 83

what is the substance needed for the formation of every organic molecule inside every living thing on Earth

Answer 83

carbon dioxide

Question 84

why is the concentration of carbon dioxide inside the leaf even lower than in the air outside during daylight

Answer 84

During daylight, carbon dioxide is used in the Calvin cycle in the chloroplasts, so the concentration of carbon dioxide inside the leaf is even lower than in the air outside, providing the diffusion gradient that keeps it moving into the leaf.

Carbon dioxide concentration is often a limiting factor for photosynthesis.
If we give plants extra carbon dioxide, they can photosynthesise faster.

Question 85

diagram showing the relationship between carbon dioxide concentration and rate of photosynthesis.

Answer 85

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Question 86

diagram showing the effect of carbon dioxide at different light intensities.

Answer 86

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Question 87

Increasing the carbon dioxide concentration from 0.04 to 0.4% in photosynthesis does what?

Answer 87

gives a higher rate of photosynthesis, but any higher and the stomata start to close

Question 88

what is usually the limiting factor on a warm, sunny, windless day,

Answer 88

usually CO2

Question 89

what is usually the limiting factor during the night

Answer 89

sunlight

Question 90

if the carbon dioxide concentration is low, then the

Answer 90

rate of carboxylation catalysed by rubisco will be slower than if the concentration was higher

Question 91

what temperature affects?

Answer 91

Temperature affects the kinetic energy of molecules

Photosynthesis requires the action of enzymes to catalyse reactions and temperature is a factor that influences the rate of enzymatic reactions

Question 92

what happens at the higher temperature of molecules

Answer 92

The higher the temperature, the faster molecules move, and the more frequently they collide with one another.

They also collide with more energy.

Question 93

The greater frequency and energy of collisions of molecules means that

Answer 93

the reaction rate increases

Question 94

The greater frequency and energy of collisions of molecules means that the reaction rate increases.

In photosynthesis, though, this effect is only seen in

Answer 94

the light-independent reactions

Question 95

the rate of the light-dependent reactions is not directly affected by temperature, because

Answer 95

the energy that drives them comes from light, not the kinetic energy of molecules

Question 96

why plant enzymes often have lower optimum temperatures than enzymes found in mammals

Answer 96

because they have evolved to work in the environmental temperatures in which the plant normally lives

In living organisms, most reactions are catalysed by enzymes, so we also need to consider the effect of temperature on them.

Just like any molecules, their kinetic energy increases as temperature increases.

However beyond a certain temperature (different for different enzymes) they begin to lose their shape, and therefore their catalytic properties.

Question 97

plant enzymes often have lower optimum temperatures than enzymes found in mammals because they have evolved to work in the environmental temperatures in which the plant normally lives but what causes things to be complicated?

Answer 97

a peculiar property of the enzyme rubisco.

Rubisco has an unfortunate tendency to stop doing what it is supposed to do - catalyse the combination of carbon dioxide with RuBP - and start doing something else when temperature rises.

It switches to catalysing a reaction in which oxygen is combined with RuBP.

This is very wasteful, as it wastes RuBP.
It is called photorespiration

Question 98

what is the effect of photorespiration

Answer 98

it can seriously reduce the rate of photosynthesis in many plant species, when temperature and light intensity are high.

Question 99

Photorespiration is a misleading name because

Answer 99

it is not really respiration at all

Question 100

the Calvin cycle does not require what?

Answer 100

it does not require energy input from light

It does, however, need energy input from the light-dependent stage, in the form of ATP and reduced NADP

Question 101

explain the diagram of the effect of light on the Calvin cycle
The effect of light and dark on the relative levels of TP and GP in a chloroplast.

Answer 101

Imagine that light is shining on a chloroplast.

The light-dependent stage is generating ATP and reduced NADP, and the reactions of the Calvin cycle are working continuously.

Now the light is switched off.

The light-dependent stage stops, so the supply of ATP and NADP to the Calvin cycle also stops.

These substances are needed to fuel the conversion of GP to TP. So now GP can no longer be converted into TP, and the GP just builds up.

The rest of the cycle keeps running, until most of the TP is used up.

Then it grinds to a halt this diagram shows what happens to the relative amounts of GP and TP when the light is switched off.

the levels of TP plummet, while the levels of GP rise.

If the light is switched on again, they go back to their ‘normal’ relative levels

Question 102

diagram of the effect of light and dark on the relative levels of TP and GP in a chloroplast.

Answer 102

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Question 103

why increasing the supply of any other factor when one factor is already limited has no effect on crop production

Answer 103

If one factor is rate limiting, increasing the supply of any other factor has no effect on the rate of photosynthesis and therefore no effect on crop production but increasing the supply of the limiting factor will have a dramatic impact on crop production

Question 104

what will have a dramatic impact on crop production

Answer 104

increasing the supply of a limited factor factor that is already limited

Question 105

factors that affect crop production are

Answer 105

1) increasing the supply of a limited factor factor is already limited
2) light or carbon dioxide could be rate limiting at temperatures within the range tolerated by the crop
3) Water and each mineral nutrient required by a plant

Question 106

a farmer has limited capacity to affect light or carbon dioxide levels in order to increase the rate of photosynthesis, unless

Answer 106

a crop is being grown in a specialised glasshouse

Question 107

example of how Water and each mineral nutrient required by a plant can affect crop production

Answer 107

If the supply of potassium is limited in the soil, potassium may be rate limiting for crop growth.

So, increasing the light intensity will have no or little effect on crop production in these circumstances

Question 108

what can reveal which factor is going to be rate limiting in a range of circumstances and therefore which factor could be increased to make maximum impact on crop production at any one time

Answer 108

Analysis of the climate, soil and atmospheric environment of a crop

Question 109

Analysis of the climate, soil and atmospheric environment of a crop can reveal what?

Answer 109

which factor is going to be rate limiting in a range of circumstances and therefore which factor could be increased to make maximum impact on crop production at any one time

Question 110

The ability of plants to transfer light energy into chemical energy means that

Answer 110

they can be used to provide fuels for us to use

for example, for generating electricity or in vehicle engines

Question 111

As stocks of fossil fuels run down, and as carbon dioxide levels in the atmosphere continue to increase, there has been a sharp increase in the use of

Answer 111

crop plants to produce fuels rather than food.

For example, rape seed is being used to produce biodiesel, rather than food for animals or humans

Question 112

why is using crop plants to produce fuels good?

Answer 112

Using plants to provide fuels is theoretically ‘carbon-neutral’.

The carbon dioxide that is given out when the fuels are burnt is matched by the carbon dioxide that the plants take in as they photosynthesise and grow

Question 113

why is using crop plants to produce fuels bad?

Answer 113

the energy that is used in harvesting the plants, converting the biomass to a useful form of fuel and transporting that fuel to points of sale, then there is still a net emission of carbon dioxide to the atmosphere

the increasing quantity of crops to produce biofuels is having an effect on the availability and price of food

effects on ecosystems.
Producing large quantities of biofuels will take up large areas of land

Question 114

example of how using crop plants to produce fuels is having an effect on the availability and price of food

Answer 114

as huge areas of land in the USA are taken over to grow corn (maize) for fuel, there is less maize on sale for cattle feed or human food.

Prices have increased, in some cases so much so that poorer people, especially in neighbouring countries like Mexico, are finding it much more difficult to buy enough food for their needs

Question 115

example of how using crop plants to produce fuels is having an effect areas of land

Answer 115

Producing large quantities of biofuels will take up large areas of land

There is a danger that some countries will cut down forests to provide extra land for this purpose, damaging habitats and endangering species that live there

Question 116

Photosynthesis uses light energy to cause

Answer 116

carbon dioxide and water to react to produce carbohydrates and oxygen

The light energy is transformed to chemical energy in the carbohydrates

Question 117

The chloroplasts are arranged in the cytoplasm how?

Answer 117

around the outer edge of the cell, and can be moved to maximise light absorption

Question 118

Inside the chloroplast, membranes form what?

Answer 118

fluid-filled sacs called thylakoids, which in turn form stacks called grana

Question 119

The chlorophyll molecules are found where?

Answer 119

within photosystems I and II

Question 120

The factor that is in the shortest supply at any one time during photosynthesis is known as

Answer 120

the limiting factor

Question 121

If crops are grown in glasshouses, these limiting factors of photosynthesis can be

Answer 121

adjusted to increase the rate of photosynthesis and therefore the productivity of the crop

Question 122

What is the function of the chlorophyll found in plant cells?

Answer 122

Absorbs light for photosynthesis.

Question 123

Is photosynthesis an exothermic or endothermic reaction?

Answer 123

Endothermic

Energy needs to absorbed for the reaction to occur

Question 124

Hydroponics is

Answer 124

the growth of plants in aqueous solutions containing essential minerals (e.g. nitrogen, potassium, phosphorus, magnesium, calcium and sulfur).

Question 125

hydroponics makes to so that plants can

Answer 125

produce fruits and vegetables without the presence of soil and the readily available water supply aids growth.

In field conditions, plants have to take up water from the soil solution via their root hairs but in hydroponics the roots are suspended in water.

Question 126

Greenhouse technology is used for

Answer 126

sustainable crop production in places with adverse climatic conditions.