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GCSE - Biology > Topic 6 - Plant Structures And Their Functions > Flashcards

Topic 6 - Plant Structures And Their Functions Flashcards

1
Q

What is photosynthesis?

A

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

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2
Q

Write the word equation for photosynthesis

A

Carbon dioxide + water -> glucose + oxygen

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3
Q

Write the symbol equation for photosynthesis

A

6CO₂ + 6H₂O -> C₆H₁₂O₆ + 6O₂

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4
Q

Why is photosynthesis important

A

Produces glucose which has wide range of uses:

  • used in respiration to release energy
  • converted to starch and stored - broken down to glucose when plant requires energy
  • used to make complec organic molecules which are used for growth, making up an organisms biomass (transferred through food chains)
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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

Endothermic - takes in energy in form of light

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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 2 main stages of photosynthesis

A
  1. Chlorophyll absorbs light energy which is used to split water into oxygen gas (waste product) 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 temp provides more KE for enzymes involved so rate increases as temp rises
Optimum temp usually 25°C
If temp too high (around 45°C) enzymes denature and rate decreases

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12
Q

Explain how light intensity affects the rate of photosynthesis

A

Rate of photosynthesis is directly proportional to light intensity
As light intensity increases, rate of photosynthesis increases

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13
Q

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

A

Another factor becomes limiting (temp or CO ₂)

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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

Using the inverse square law where: light intensity ∝ 1/distance²

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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. Thus, 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 does the rate of photosynthesis eventually plateau even if CO ₂ concentration continues to increase?

A

Another factor becomes limiting (temp or light intensity)

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18
Q

Why do plants require water (3)

A

Photosynthesis
Maintenance of structure (turgidity)
Cooling effect

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19
Q

Why do plants require mineral ions?

A

For growth eg nitrates are requires to produce proteins

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20
Q

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

A

Root hairs

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21
Q

How is water transported into root hairs?

A

Lower concentration of water in root hair cells than in soil

Water diffuses down its concentration gradient into root hair cells by osmosis

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22
Q

How are mineral ions transported into root hairs?

A

Lower concentration of mineral ions in the soil than in the root
Root hair cells take up mineral ions by active transport

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23
Q

Outline how plant roots are adapted for the absorption of water and minerals

A

Plant roots are composed of millions of root hair cells which have:
Long hairs that extend from the cell body, increasing the surface area for absorption
Many mitochondria which produce ATP for active transport of mineral ions

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24
Q

Name the two plant transport tissues

A

Xylem

Phloem

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25
Q

Whats the function of the xylem?

A

Transports WATER and MINERALS up the plant, from roots to leaves via TRANSPIRATION stream

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26
Q

Describe how the xylem is adapted to its function

A

Composed of dead cells laid end-to-end to form a long, hollow, continuous column
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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27
Q

Whats the function of the phloem?

A

Transports SUGARS up and down the stem from photosynthetic tissues (eg mature green leaves) to non photosynthetic tissues (eg developing seeds) via translocation

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28
Q

What are the 2 cell types that make up the phloem?

A

Sieve tube elements

Companion cells

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29
Q

Describe how phloem is adapted to its function

A
  • Sieve tube elements are long, thin cells, laid ened-to-end with perforated end plates to enable flow of sugars. Contain no nucleus and little cytoplasm to allow sugars to flow easily
  • Companion cells (adjacent to sieve tube elements) contain a dense cytoplasm, nucleus and mitochondria. Provide energy for processes in both cell types
30
Q

What is transpiration

A

Loss of water vapour from the parts of a plant exposed to the air due to evaporation and diffusion

31
Q

Where does the majority of transpiration take place?

A

Leaves

32
Q

Describe the process of transpiration

A

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

33
Q

How does the transpiration stream transport mineral ions?

A

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

34
Q

What are stomata?

A

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

35
Q

What are guard cells?

A

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

36
Q

How do guard cells control the size of stomata

A

To open stomata: Water enters guard cells. They swell and become turgid. They bend and draw away from each other opening stomata.
To close stomata: Water leaves guard cells. They become flaccid, closing stomata.

37
Q

What 3 factors affect the rate of transpiration?

A

Light intensity
Temperature
Air movement

38
Q

How does high light intensity affect rate of transpiration?

A

High light intensity, greater no of stomata open to allow gas exchange for photosynthesis.
Rate of photosynthesis increases so more water taken up from the soil, pushing water up the xylem
More water vapour diffuses out of stomata sp rate of transpiration increases

39
Q

How does low light intensity affect rate of transpiration?

A

At low light intensity, fewer stonata are open so rate of transpiration decreases

40
Q

How does temp affect rate of transpiration?

A

Temp increases, water molecules have more KE so 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 - rate of transpiration increases

41
Q

Describe how air movement affects the rate of transpiration

A

Air movement increases, high water concentration gradient maintained between the air spaces in the leaf and atmosphere
Increased rate of diffusion of water molecules out of the stomata
Rate of transpiration increases

42
Q

What apparatus is used to measure the rate of transpiration?

A

Potometer

43
Q

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

A

Rate of water uptake = rate of transpiration

44
Q

How can the rate of transpiration be calculated using a potometer?

A

Rate of transpiration = distance moved by bubble/time taken

45
Q

What is translocation?

A

Movement of sugars up and down a plant, from source to the sink via phloem. Requires ATP.

46
Q

Describe how leaves are adapted for photosynthesis

A 
Broad - large SA for light absorption
Thin - short diffusion distance for gases, allows light to reach all cells
Vascular bundles (xylem and phloem) form a network to deliver water and remove glucose. Also provide support
Photosynthetic pigments (eg chlorophyll) abosrb light
47
Q

Describe how tissues of the leaves are adapted for photosynthesis and gas exchange

A

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

48
Q

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

A

Small leaves/spines -reduce SA for water loss
Thick waxy cuticle - reducde evaporation conserve water
Thick stem - prodive storage for water
Shallow but widespread roots - large SA absorb water
Stomata sunken in pits and leaves curles - reduce air flow, lowering diffusion gradient and reduce water loss (evaporation)
Stomata close to reducee water loss

49
Q

What are plant tropisms?

A

The growth of a plant in response to a stimulus

50
Q

Whats a positive tropism?

A

The growth of a plant towards a stimulus

51
Q

Whats a negative tropism?

A

Growth of a plant away from a stimulus

52
Q

What are the two main types of plant tropism?

A

Phototropism

Gravitropism

53
Q

Define phototropism

A

A plants growth response to light

54
Q

Define gravitropism

A

A plants growth response to gravity

55
Q

What are auxins

A

A group of plant hormones involved in plant tropisms

Control growth in plant roots and shoot tips

56
Q

Compare the effect of auxins in plant shoots and roots

A

Auxins stimulate growth in plant shoots

Auxins inhibit growth in plant roots

57
Q

Where are auxins produced?

A

Root and shoot tips

58
Q

How do auxins move through a plant?

A

Diffuse through the plant in solution

59
Q

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

A

Positively phototropic

Plant shoots grow towards the light

60
Q

Explain why plant shoots are positively phototropic

A

Shoot tip exposed to light
On the shaded side of the shoot, auxin accumulates
Elongation of cells on shaded side
Shoot tip bends towards light

61
Q

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

A

Negatively gravitropic

Plant shoots grow upwards away from gravity

62
Q

Explain why plant shoots are negatively gravitropic

A

Shoot placed horizontally
Due to gravity, auxin accumulates on lower side of shoot
Elongation of cells on lower side
Shoot bends upwards growing away from gravity

63
Q

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

A

Negatively phototropic

Plant roots grow away from the light

64
Q

Explain why plant roots are negatively phototropic

A

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

65
Q

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

A

Positively gravitropic

Plant root grows downwards towards gravity

66
Q

Explain why plant roots are positively gravitropic

A

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

67
Q

Explain how plant tropisms increase the chance of survival

A

They enable plants to respond to their envoronment
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

68
Q

Describe the role pf auxins in commercial plant cultivation

A

Rooting powders contain auxins that stimulate the growth of roots in cuttings. Enables rapid plant cloning
Used in selective weedkillers that target and alter growth patterns in broad leaved plants (most weeds) killing them

69
Q

What are gibberellins

A

Plant hormones that control germination and flowering

70
Q

Describe the role of gibberellins in commercial plant cultivation

A

Initiate germination in seeds at time of year when naturally wouldnt. Ensure all seeds in a batch germinate
Trigger flowering in plants under irregular conditions. Also increase fruit size by reducing no of flowers produced by plants
Produce seedless fruits by stimulating growth of fruit from unpollinated flowers

71
Q

How do gibberellins trigger germination?

A

In presence of water, gibberellins break seed dormancy, initiating germination

72
Q

Why is ethene important in commercial plant cultivation?

A

Ethene stimulates enzymes that control fruit ripening
Enables fruit to be picked while they afe unripe and less easily damaged. They can be stimulated to ripen during transportation to shops

GCSE - Biology (7 decks)

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