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Biology > Topic 6 - plant structures and functions > Flashcards

Topic 6 - plant structures and functions Flashcards

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1
Q

What is photosynthesis?

A

A chemical reaction that takes place inside photosynthetic organisms (e.g. plants) converting light energy into chemical energy

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2
Q

What is the word equation for photosynthesis?

A

Carbon dioxide + water -> glucose + oxygen

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3
Q

What is the symbol equation for photosynthesis?

A

6CO2 + 6H2O -> C6H12O6 + 6O2

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4
Q

Why is photosynthesis important?

A

It produces glucose which is used in respiration to release energy, is converted into starch and stored and used to make complex organic molecules which are used for growth

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5
Q

Where does photosynthesis take place?

A

Within chloroplasts

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6
Q

What type of reaction is photosynthesis?

A

An endothermic reaction that takes in energy

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7
Q

What is chlorophyll?

A

A pigment found in chloroplasts that absorbs light

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8
Q

Describe the two main stages of photosynthesis

A
  1. Chlorophyll absorbs light energy which is used to split water into oxygen gas and hydrogen ions
  2. Carbon dioxide combines with hydrogen ions to form glucose
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9
Q

What factors affect the rate of photosynthesis?

A

Temperature
Light intensity
Carbon dioxide concentration

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10
Q

What is a limiting factor?

A

A variable that limits the rate of a particular reaction

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11
Q

Explain how temperature affects the rate of photosynthesis

A

Higher temperatures provide more KE for enzymes involved in photosynthesis so the rate increases as temperature rises
The optimum temperature is usually 25°C
If the temperature becomes too high (around 45°C) enzymes become denatured and the rate of photosynthesis decreases

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12
Q

Explain how light intensity affects the rate of photosynthesis

A

Rate of photosynthesis is directed proportional to light intensity, as the light intensity increases, the rate of photosynthesis increases

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13
Q

Why does the rate of photosynthesis eventually plateau even if light intensity continues to increase?

A

Another factor becomes limiting

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14
Q

How can the effect of light intensity on the rate of photosynthesis be measured in the lab?

A

Using a light meter

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15
Q

Why does the rate of photosynthesis decrease as the distance from a light source increases?

A

Light intensity is inversely proportional to the square of the distance from the light source. This, as the distance increases, light intensity decreases and the rate of photosynthesis decreases

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16
Q

Explain how carbon dioxide concentration affects the rate of photosynthesis

A

As carbon dioxide concentration increases, the rate of photosynthesis increases

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17
Q

Why do plants require water?

A

Photosynthesis
Maintenance of structure
Cooling effect

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18
Q

Why do plants require mineral ions?

A

For growth

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19
Q

What structure in plants is adapted for the uptake of water and minerals?

A

Root hairs

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20
Q

How is water transported into root hair?

A

There is a lower concentration of water in root hair cells than in the soil
The water diffuses down its concentration gradient into root hair cells by osmosis

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21
Q

How are minerals transported into root hair?

A

There is a lower concentration of mineral ions in the soil then in the root
The root hair cells take up mineral ions by active transport

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22
Q

How are plant roots adapted for the obsorbtion of water and minerals

A

They are composed of millions of root hair cells which have long hairs that extend from the cell body, increasing the surface area and many mitochondria which produce energy for active transport of mineral ions

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23
Q

Name the two plant transport tissues

A

Xylem and phloem

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24
Q

What is the function of the xylem?

A

It transports water and minerals up the plant, from the root to the leaves via the transpiration stream

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25
Q

Describe how the xylem is adapted to its function

A

It is composed of dead cells laid end to end to form a long, hollow, continuous columns
There are no end walls which provides little resistance to the passage of water
Thick cell wall strengthened with lignin to provide support

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26
Q

What is the function of the phloem?

A

It transports sugars up and down the stem from photosynthetic tissues to non-photosynthetic tissues via translocation

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27
Q

What are the two cell types that make up the phloem?

A

Siege tube elements

Companion cells

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28
Q

Describe how the phloem is adapted to its function

A

The siege tube elements are long thin cells, laid end-to-end with perforated end plates to enable to flow of sugars, they contain no nucleus and little cytoplasm
The companion cells contain a dense cytoplasm, nucleus and mitochondria. They provide energy for processes in both cell types

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29
Q

What is transpiration?

A

The loss of water vapour form the parts of a plant exposed to the air due to evaporation and diffusion

30
Q

Where does the majority of transpiration take place?

A

Leaves

31
Q

Describe the process of transpiration

A

Water evaporates from the cell surfaces and diffuses out of the stomata
Water molecules are drawn up the xylem vessels to replace the water that has been lost
This causes more water molecules to be absorbed from the soil into root hair cells

32
Q

How does the transpiration stream transport mineral ions?

A

Mineral ions are dissolved in the water that is carried by the transpiration stream

33
Q

What are stomata?

A

The pores found in the lower epidermis of a leaf which allow gas exchange

34
Q

What are guard cells?

A

Specialised cells surrounding the stoma that change shape to control the size of the pore

35
Q

How do guard cells control the size of the stomata?

A

Open: water enters the guard cells, they swell , they bend and draw away from each other
Close: the water leaves and they become flaccid

36
Q

What factors affect the rate of transpiration?

A

Light intensity
Temperature
Air movement

37
Q

Describe how light intensity affects the rate of transpiration

A

When there is high light intensity, there is a greater number of stomata open to allow gas exchange for photosynthesis
The rate of photosynthesis increases so more water is taken up from the soil, pushing water up the xylem
More water vapour diffuses out of the stomata is the rate increases

38
Q

Describe how low light intensity affects the rate of transpiration

A

At a low light intensity, fewer stomata are open so the rate of transpiration decreases

39
Q

Describe how temperature affects the rate of transpiration

A

When the temperature increases, the water molecules have more KE so the rate of diffusion increases
Photosynthesis also increases so more water is taken up from the soil, pushing water up the xylem
More water vapour diffuses out of the stomata

40
Q

Describe how air movement affects the rate of transpiration

A

The air movement increases, there is a high water concentration gradient maintained between the air spaces in the leaf and atmosphere
There is an increased rate of diffusion of water molecules out of the stomata
The rate of transpiration increases

41
Q

What apparatus is used to measure the rate of transpiration?

A

Potometer

42
Q

What is assumed when measuring the rate of transpiration using a potometer?

A

The rate of water uptake = the rate of transpiration

43
Q

How can the rate of transpiration be calculated using a potometer

A

Rate of transpiration = distance moved by bubble/time taken

44
Q

What is translocation?

A

The movement of sugars up and down a plant fro the source to the sink, via the phloem

45
Q

Describe how leaves are adapted for photosynthesis

A

They are broad
Thin
They have photosynthetic pigments and vascular bundles (xylem and phloem)

46
Q

How are tissues of the leaves adapted for photosynthesis and gas exchange?

A

Upper epidermis - transparent, allows light to reach palisade layer
Spongy mesothelioma layer - air spaces increase the rate of diffusion
Lower epidermis - contains many stomata for gas exchange
Palisade mesothelioma layer - receives most light so contains greatest concentration of cholorplasts

47
Q

Describe how plants are adapted to live in hot, dry conditions

A 
Small leaves/spines - reduce SA
Thick waxy cuticle - reduces evaporation
Thick stem - provides a storage of water
Shallow but widespread roots - large SA to absorb water
Stomata close to reduce water loss
48
Q

What are plant tropisms?

A

The growth of a plant in response to a stimulus

49
Q

What is positive tropism?

A

The growth of a plant towards a stimulus

50
Q

What is negative tropism?

A

The growth of a plant away from a stimulus

51
Q

What are the two main types of plant tropism?

A

Photosropism

Gravitropism

52
Q

Define phototropism

A

A plant’s growth response to light

53
Q

Define gravitropism

A

A plant’s growth response to gravity

54
Q

What are auxins?

A

A group of plant hormones involved in plant tropisms

They control growth in plant roots and shoot tips

55
Q

Compare the effect of auxins in plant shoots and roots

A

Auxins stimulate growth in plant shoots

They inhibit growth in plant roots

56
Q

Where are auxins produced?

A

Root and shoot tips

57
Q

How do auxins move through a plant?

A

They diffuse through the plant is solution

58
Q

Are plant shoots positively or negatively phototropisch? How does this affect shoot growth?

A

Positively phototropic

Plant shoots grow towards the light

59
Q

Explain why plant shoots are positively phototropic

A

The shoot tip is exposed to light
On the shaded side of the shoot, auxin accumulates
The cells on the shaded side elongate
The shoot tip bends towards the light

60
Q

Are plant shoots positively or negatively gravitropic? How does this affect shoot growth?

A

Negatively gravitropic

Plant shoots grow upward, away from gravity

61
Q

Explain why plant shoots are negatively gravitropic

A

Shoot placed horizontally
Due to gravity, auxin accumulated on the lower side of the shoot
The cells on the lower side elongate
The shoot bends upwards growing away from gravity

62
Q

Are plant roots positively or negatively phototropic? How does this affect root growth?

A

Negatively phototropic

Plant roots grow away from the light

63
Q

Explain why plant roots are negatively phototropic

A

Root exposed to light
On the shaded side of the root, auxin accumulates
Inhibition of cell growth on the shaded side
Root grows away from the light

64
Q

Are plant roots positively or negatively gravitropic? How does this affect root growth?

A

Positively gravitropic

Plant roots grow downwards, towards gravity

65
Q

Explain why plant roots are positively gravitropic

A

Root placed horizontally
Due to gravity, auxin accumulates on the lower side of the root
Inhibition of cell growth on the lower side
Root bends downwards growing towards gravity

66
Q

Explain how plant tropisms increase the chance of survival

A

They enable plants to respond to their environment
Shoot growth towards the light maximises light absorption
Root growth downwards increases the uptake of water and minerals from the soil and enables anchorage of the plant body to the ground

67
Q

Describe the role of auxins in commercial plant cultivation

A

Rooting powders contain auxins that stimulate the growth of roots in cuttings. This enables rapid plant cloning
Used in selective weed killers that target and alter growth patterns in broad leaved plants, killing them

68
Q

What are gibberellins?

A

Plant hormones that control germination and flowering

69
Q

Describe the role of gibberellins in commercial plant cultivation

A

Initiate germination in seeds at times of the year when they naturally wouldn’t.
Trigger flowering in plants under irregular conditions
Increase fruit size by reducing the number of flowers produced by plants
Produce seedless fruits by stimulating the growth of fruit from unpollinated flowers

70
Q

How do gibberellins trigger germination?

A

In the presence of water, they break seed dormancy initiating germination

71
Q

Why is ethane important in commercial plant cultivation?

A

Stimulates enzymes that control fruit ripening
Enables fruits to be picked while they are unrepentant and less easily damaged. They can be stimulated to ripen during transportation to shops

Biology (8 decks)

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