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GCSE Biology unit 1 > Photosynthesis (2) > Flashcards

Photosynthesis (2) Flashcards

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1
Q

What is an important difference between animals and plants in the source of their food?

A

Animals must feed on plant and animal material

While plants are able to make their own food

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2
Q

How do plants make their own food?

A

A process called photosynthesis
The word photo means light and the word synthesis means making, therefore photosynthesis is when plants use light energy from the sun to make their own food I.e. Light is converted into chemical energy

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3
Q

Where does photosynthesis occur ?

A

It occurs in chloroplasts, particularly located in the leaves

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4
Q

What are chloroplasts?

A

Chloroplasts are structures which contain green pigment called chlorophyll (this is what makes a plant appear green) the pigment traps the light energy from the sun that is needed for photosynthesis. The brighter the light the quicker photosynthesis will take place.

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5
Q

What raw materials are need by plants to carry out photosynthesis?

A

Carbon dioxide - from the air (this enters through the stomata)
Water - from the soil (this enters through the roots)

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6
Q

The products of photosynthesis are:

A

Glucose (sugar) - produced from the conversation of the raw materials and this is usually converted immediately into starch for storage
Oxygen - a waste product produced and this is released into the air

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7
Q

Why is photosynthesis also important for animals?

A

Animals rely on plants for their food and it also releases oxygen back into the air which is needed for respiration

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8
Q

The word equation for photosynthesis is:

A

Light energy
Carbon dioxide + water ———> glucose + oxygen
Chlorophyll

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9
Q

A balanced chemical equation for photosynthesis is:

A

6CO + 6H 0 ——> C H 0 + 60

2 2 6 12 2

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10
Q

What do all living organisms need to consume and why?

A

Food in order to provide the energy they need to survive

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11
Q

label the leaf as a site of photosynthesis

A

first page of photosynthesis booklet

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12
Q

where does the process of photosynthesis take place in most plants

A

in the leaves, which are arranged in a certain way on the plant to ensure each leaf can absorb as much light as possible

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13
Q

how are leaves adapted and why is this?

A

they are usually highly adapted for light absorption and gas exchange to allow photosynthesis to take place efficiently

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14
Q

adaptions for light absorption

A
  • there is a short distance from top to bottom, which allows all cells to receive light
  • leaves are broad and flat to create a large surface area for light absorption
  • waxy cuticle is transparent to allow light to enter
  • palisade mesophyll layer is composed of tall,thin cells packed together near the upper surface of the leaf to receive light. these cells are rich in chloroplasts to absorb light energy
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15
Q

adaptions for gas exchange

A

intercellular air spaces (gaps between cells) in the spongy mesophyll layer allow gases to move more easily from the stomata to the palisade mesophyll layer
- stomata allow carbon dioxide and oxygen to enter and leave the leaf. These are small pores that occur between cells in the epidermis. Each stoma is surrounded by two guard cells. These can change shape in order to control the size of the pore between them. Stomata tend to be open during the day and closed at night.
most land plants have more stomata on the underside of the leaf than on the top

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16
Q

what are the products of photosynthesis and what are they used for

A
  • oxygen, used in the process of respiration (excess oxygen will diffuse out of the leaves through the stomata)
  • g;ucose, can be used in a number of ways, or converted into a range of products the plant requires
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17
Q

the uses of glucose (important)

A

RESPIRATION - used in respiration to provide energy. word equation for respiration is
glucose + oxygen -> carbon dioxide + water + energy

STORAGE - in many plants it is coverted into starch and lipids (fats and oils) for storage e.g. in the roots. the starch is converted back to sugar when needed and transported to other parts of the plant

GROWTH - glucose can be converted into a range of products which enable the plant to grow including

  • cellulose (for cell walls)
  • chlorophyll(for trapping light for photosynthesis)
  • protein (for growth and repair)
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18
Q

what are photosynthesis experiments?

A

investigations to show that photosynthesis is taking place in a plant or particular raw materials are needed for the process e.g. the starch test

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19
Q

explain the starch test and why it is done

A

a way of showing photosynthesis is taking place is to show that starch is being produced in a green leaf ( starch is produced from the glucose made in photosynthesis) the solution used to test for the presence of starch is iodine solution

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20
Q

what colour is iodine solution?

A

yellow/brown

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21
Q

what colour does iodine become when it reacts with starch

A

blue/black

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22
Q

Why is using iodine to show that a green lead contains starch not easy?

A

The iodine will not soak into the leaf because the leaf is covered with a thin layer called the cuticle which is made of waterproof material. Another problem is the dark green colour of the leaf caused by the presence of chlorophyll, even if the iodine soaked into the leaf it would be very difficult to see any colour change. The starch test overcomes these problems

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23
Q

The starch test step 1

A

Place the leaf in boiling water for at least 30 seconds to kill the leaf and ensure no further reactions take place

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24
Q

The starch test step 2

A

Boil the leaf in alcohol to remove the green chlorophyll from the leaf the flame of the Bunsen burner must be turned off because ethanol is flammable and must not be exposed to a direct flame

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25
Q

The starch test step 3

A

Dip the leaf in warm water this will soften the leaf as the ethanol makes it very brittle

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26
Q

The starch test step 4

A

Add iodine to the leaf to test for the presence of starch, if starch is present the iodine will turn from yellow/brown to blue/black this shows photosynthesis has taken place

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27
Q

How can a leaf be destarched? And why is this done

A

Leave in a dark cupboard for 48 hours. This will ensure any starch already present in the leaves will be removed and stored elsewhere in the plant, or used by the plant during this period (by being converted into glucose which will be used in respiration) the importance of this is that if the starch test at the end of the investigation is positive, it shows that the starch must have been produced during the period of investigation

28
Q

How do we prove that light is needed for photosynthesis?

A

A leaf from a destarched plant is partially covered with black paper or light-proof foil and left for several days. Then the leaf is removed from the plant and tested for starch

29
Q

If light is essential for photosynthesis what results would you expect?

A

The area under the foil/paper would not contain starch as it did not receive light to photosynethise therefore it would not go blue/black with iodine

30
Q

How do we prove carbon dioxide is needed for photosynthesis?

A

Two leaves need to be compared on the one destarched plant. An experimental leaf will be without carbon dioxide and a control leaf will have a good supply of carbon dioxide. Carbon dioxide will be removed from the air surrounding the experimental leaf by adding sodium or potassium hydroxide (soda lime) to a bag/flask surrounding the leaf. The control leaf will have a bag/flask with a little water in it (or a chemical that increases carbon dioxide levels) and therefore there will be carbon dioxide present. After two days under these condititions the leaves are removed and tested for starch.

31
Q

If carbon dioxide is an essential raw material for photosynthesis what results would you expect?

A

The experimental leaf will not contain starch as it did not receive carbon dioxide to photosynthesise, therefore it would not go blue/black with iodine.

32
Q

What is a variegated plant?

A

A plant that has leaves that are part green and part white. These leaves are very useful for proving that chlorophyll is needed for photosynthesis since the white parts of the leaves do not contain chlorophyll (chlorophyll produced the green colour). A variegated plant is destarched, a leaf is removed and then tested for starch.

33
Q

Draw diagram of a variegated leaf and what it looks like after being tested for starch

A

In photosynthesis booklet

  • green
  • White
  • variegated leaf
  • blue/black
34
Q

If chlorophyll is necessary for photosynthesis what results would you expect from the variegated leaf after a starch test?

A

The white area would not contain starch as it does not have chlorophyll to trap sunlight for photosynthesis therefore it would not go blue/black with iodine

35
Q

Name one way of measuring the rate of photosynthesis and explain

A

One way is measuring the rate of production of oxygen. It is difficult to collect oxygen from a terrestrial (land) plant so an aquatic (water) plant is used e.g. Elodea (Canadian pondweed). The apparatus is set up as shown below.

36
Q

Draw a diagram of the test for the rate of production of oxygen

A 
In photosynthesis booklet 
From top to bottom 
- test tube 
- oxygen gas collects here 
- beaker
- sodium bicarbonate is added to the water to provide carbon dioxide 
- funnel 
- pondweed
37
Q

How can it be proved that the gas collected in the test tube is oxygen?

A

Put a glowing splint into the test tube and if will relight if it is oxygen

38
Q

Explain the rate of which bubbles of oxygen are produced

A

This depends on how fast the plant is photosynthesising - the faster the rate, the faster the bubbles are given off. There are several factors which will influence the rate at which the plant photosynthesises including light intensity, carbon dioxide concentration and temperature

39
Q

What affects the rate of photosynthesis

A

The rate at which photosynthesis occurs depends on the availability of raw materials needed for the process, as well as certain environmental factors. These include: light intensity, carbon dioxide levels, temperature, availability of water

40
Q

What causes photosynthesis to occur at its maximum rate?

A

All of the factors must be present must be present at peak or optimum levels. However if one or more of these factors is in short supply the rate of photosynthesis will be limited. The material that is in short supply is known as the limiting factor and this will determine the rate of photosynthesis

41
Q

What is a limiting factor

A

The limiting factor in photosynthesis is a material needed for the maximum rate of photosynthesis which is in short supply limiting the rate of photosynthesis.

42
Q

Light intensity

Factors affecting the rate of photosynthesis

A

The effects of light can be explained by comparing the rates of photosynthesis at different light intensities. At lower light intensities, as the light intensity increases the rate of photosynthesis increases. At this part of the graph light is limiting the rate. Increasing the light intensity further does not lead to an increase in the rate of photosynthesis. Therefore so,something else must be limiting the rate e.g. Carbon dioxide or temperature

43
Q

Draw light intensity graph

A

In photosynthesis booklet

44
Q

Temperature

Factors effecting the rate of photosynthesis

A

The effects of temperature can be explained by comparing the rates of photosynthesis on a cold and hot day. At low light levels, photosynthesis is limited by the light intensity. At higher light intensities photosynthesis occurs faster on a hot day when compared to a colder day. Therefore at high light intensities, temperature is limiting the rate of photosynthesis

45
Q

Draw temperature graph

A

In photosynthesis booklet

46
Q

Carbon dioxide

Factors affecting the rate of photosynthesis

A

The effects of carbon dioxide can be explained by comparing the rates of photosynthesis at different carbon dioxide levels. At low light levels, photosynthesis is limited by light intensity. At higher
Light intensities photosynthesis occurs faster at high carbon dioxide levels. Therefore at high light intensities, carbon dioxide is limiting the rate of photosynthesis

47
Q

Draw carbon dioxide graph

A

In photosynthesis booklet

48
Q

What factors might limit the rate of photosynthesis during a bright winter afternoon in Britain?

A

Temperature

49
Q

In mid summer sunshine in southern France

A

CO2

50
Q

Explain how farmers control the rate of photosynthesis

A

In the natural environment the rate of photosynthesis and therefore growth, depends on the environmental conditions. Some farmers control or increase these factors in order to increase the rate of photosynthesis and therefore growth. This will give them a greater yield (amount of crop produced) and hence more profit.

Environmental factors can be easily controlled in a greenhouse to ensure that photosynthesis takes place at its optimum rate

51
Q

Name the environmental factors that can be controlled in a greenhouse and what is used to control them

A
  • temperature can be increased - parrafin heater
  • carbon dioxide levels can be increased - parrafin heater
  • light intensity can be increased - artificial lighting
  • amount of fertiliser can be increased
52
Q

Label greenhouse diagram

A

In photosynthesis booklet

  • ventilation
  • artificial light
  • sprinkler system with fertiliser
  • oil burner (parrafin heater)
  • commercial plant crop
53
Q

Explain the cost factors of increasing environmental factors to increase the rate of photosynthesis

A

It can be expensive to increase these environmental factors. A farmer must ensure that his methods are cost effective I.e. He must ensure that he is still making a profit after taking into account the cost of extra heat, artificial lighting etc. He must also ensure that he does not bring the environmental factor above its optimal level as this would be wasteful.

54
Q

When do plants respire

A

Plants respire all the time. Respiration is essential to plants because it is the process by which energy is released from the glucose produced during photosynthesis

55
Q

What is the word equation for respiration

A

(Energy released)

Glucose + oxygen –> carbon dioxide + water + energy

56
Q

What is the word equation for photosynthesis

A

(Energy needed)

Carbon dioxide + water –> glucose + oxygen

57
Q

Explain the balance of respiration and photosynthesis

A

At different times of the day the balance of photosynthesis and respiration varies

During the night : only respiration occurs as there is no light for photosynthesis therefore oxygen will enter the leaf and carbon dioxide will leave

Midday ( high light intensity) : both respiration and photosynthesis occur However, in bright light the rate of photosynthesis will be greater than the rate of respiration therefore carbon dioxide will enter the leaf and oxygen will leave

Dusk and dawn (low light intensity) : both respiration and photosynthesis occur however, photosynthesis will take place very slowly as there is less light. Therefore the rate of respiration and photosynthesis tend to be equal and there is no overall, or net gas exchange, this point is called compensation

58
Q

Draw gas exchange diagrams in a leaf for bright, dim and dark light intensity

A

In photosynthesis booklet

59
Q

What is the level of carbon dioxide a good indicator of and why?

A

The level of carbon dioxide is a good indicator of the relative balance between the processes of photosynthesis and respiration. the movement of carbon dioxide into and out of plants can be determined using hydrogen carbonate indicator

60
Q

When testing for carbon dioxide what does it mean when the indicator turns purple

A

Decreased carbon dioxide concentration

Due to the rate of photosynthesis being higher than the rate of respiration e.g. Day time (bright light)

61
Q

When testing for carbon dioxide what does it mean when the indicator stays red?

A

Normal carbon dioxide concentration of air (0.04%)

Rate of photosynthesis and respiration are equal e.g. Dusk or dawn ( low light )

62
Q

When testing for carbon dioxide what does it mean when the indicator turns yellow?

A

Increase carbon dioxide concentration.

Due to respiration producing more than photosynthesis uses up air e.g. Night time (no light)

63
Q

Testing for carbon dioxide - tube A contains pondweed and is covered with foil, what colour will the indicator turn and why?

A

It will turn yellow because the foil strip stops light entering so photosynthesis does not occur. Respiration increases carbon dioxide levels in the test tube.

64
Q

Testing for carbon dioxide - tube B contains pondweed and is uncovered what colour will the indicator turn and why?

A

It will turn purple. Both photosynthesis and respiration are taking place in the pond wee. As the rate of photosynthesis is faster than the rate of respiration, more carbon dioxide enters the plant than is produced = carbon dioxide levels drop

65
Q

Testing for carbon dioxide - tube C contains pondweed & a water beetle, it is uncovered what colour will the indicator turn and why?

A

It will turn yellow. The water beetles produce more carbon dioxide in respiration than the pondweed takes in for photosynthesis. Therefore there is an increase in carbon dioxide in the test tube.

66
Q

When testing for carbon dioxide, what would happen if there was only partial shading (e.g. Covered in muslin/tracing paper) in tube A allowing some light to enter?

A

May stay red as the Muslim will only allow some light through for some photosynthesis and respiration rates will be balanced (compensation point)

GCSE Biology unit 1 (7 decks)

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