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Gcse Biology > Topic 6 - Plant Structures And Their Function > Flashcards

Topic 6 - Plant Structures And Their Function Flashcards

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1
Q

What is photosynthesis?

A

A chemical reaction that takes place inside photosynthetic organisms converting light energy into chemical energy
Endothermic

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2
Q

Word equations photosynthesis

A

Carbon dioxide + water —> glucose + oxygen

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3
Q

Write symbol equation for photosynthesis

A

6CO2 + 6H20 —> C6H12O6 + 6O2

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4
Q

Why is photosynthesis important?

A

It produces glucose which has a wide range of uses:

Used in respiration to release energy

Converted to starch and stored - broken down to glucose when plants need energy

Used to make complex organic molecules which are used for growth, making up an organism’s biomass

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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 (in the 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 two main stages of photosynthesis

A

Chlorophyll absorbs energy (from the light from the sun) which is used to split water intp oxygen gas
Carbon dioxide combines with hydrogen ions to form glucose

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9
Q

Why do plants require water?

A

Photosynthesis
Maintaining of structure (turgidity/rigidity)
Cooling effect

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10
Q

Why do plants require mineral ions?

A

For growth e,g nitrates are required to produce proteins

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11
Q

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

A

Root hairs

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12
Q

How is water transported into root hairs?

A

Lower concentration of water in root hair cells than in the soil
Water diffuses down its concentration gradient into root hair cells by osmosis

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13
Q

How are minerals transported into root hair

A

Lower concentration of mineral ions in the soil than in root

Root hair cells take up mineral ions by active transport

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14
Q

Outline how plants 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 surface for absorption
Many mitochondria which produce ATP for active transport of mineral ions

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15
Q

Name the two plant transport tissues

A

Xylem

Phloem

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16
Q

What is the function of the xylem?

A

Transports water and minerals up the plant, from the roots to the leaves via transpiration stream

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17
Q

Describe how the xylem is adapted to its function

A

Composed of dead cells laid end-to-end to form a long, hollow, continous column
No end walls which provide little resistance to the passge of water
Thick cell wall strengthened with lignin to provide support

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18
Q

What is function of the phloem?

A

Transports sugars up and down the stem from photosynthetic tissues ( e,g mature green leaves) to non-photosynthetic (e,g developing seeds) via translocation

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19
Q

What are two cells types that make up the phloem?

A

Sieve tube elements

Companion cells

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20
Q

Describe how phloem is adapted to its function

A

Sieve tubes elements are long, thin cells, laid end-to-end with perforated end plates to enable the flow of sugars. They contain no nucleus and little cytoplasm to allow sugars to flow easily.

Companion cells (adjacent to sieve tubes elements) contain a dense cytoplasm, nucleus and mitochondria. They provide energy for processes in both cell types.

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21
Q

What is transpiration?

A

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

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22
Q

Where does the majority of transportation take place?

A

Leaves

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23
Q

Describe the process of transpiration?

A 
Water evaporates from the mesophyll cell surfaces and diffuses out of the stomata. 
Water molecules (which have cohesive properties) 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.
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24
Q

How does the transpiration stream transport mineral ions?

A

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

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25
Q

What are stomata?

A

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

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26
Q

What are guard cells?

A

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

27
Q

How do guard cells control the size of stomata?

A

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

To close the stomata:
Water leaves guard cells. They become flaccid, closing the stomata

28
Q

What factors affect the rate of transpiration?

A

Light intensity
Temperature
Air movement

29
Q

Describe how high light intensity affects the rate of transpiration?

A

High light intensity, greater number of stomata open to allow gas exchange for photosynthesis

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 - rate of transpiration increases

30
Q

Describe how low light intensity affects the rate of transpiration

A

At a low light intensity, fewer stomata are open (for gas exchange for photosynthesis) so the rate of transpiration decreases

31
Q

Describe how temperature affects the rate of transpiration

A

Temperature increases, water molecules move faster (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 the stomata:
Rate of transpiration increases

32
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

33
Q

What apparatus is used to measure the rate of transpiration?

A

Potometer

34
Q

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

A

Rate of water uptake = rate of transpiration

35
Q

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

A

Rate of transpiration = distance moved by bubble/time taken

36
Q

What is translocation?

A

The movement of sugars (sucrose, amino acids etc) up and down a plant from the source to sink, via the phloem. Requires ATP

37
Q

Identify the structures of the leaf labelled below

A 
A - waxy cuticle.   
B - vascular bundle
C - upper epidermis
D - palisade mesophyll tissue
E - spongy mesophyll tissue 
F - lower epidermis
H - stoma
I - guard cell
38
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.
Photosynthetic pigments absorb light (e.g. chlorophyll)

39
Q

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

A

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

40
Q

Describe how plants are adpated to live hot, dry conditions?

A

Small leaves/spines - reduces surface area of water loss
Thick waxy cuticle - reduces evaporation conserving water
Thick stem - provides a storage of water
Shallow but widespread roots - large SA to absorb water
Stomata sunken in pits and leaves curled - reduces air flow, lowering diffusion gradient and reducing water loss by evaporation.
Stomata close to reduce water loss

41
Q

What are plant tropisms?

A

The growth of a plant in a response to a stimulus.

42
Q

What is positive tropism

A

The growth of a plant towards a stimulus

43
Q

What is negative tropism

A

The growth of a plant away from a stimulus

44
Q

Main types of plant tropism

A

Phototropism

Gravitropism

45
Q

Define phototropism

A

A plants growth response to light

46
Q

Define gravitropism

A

A plants growth response to gravity

47
Q

What are auxins

A

A group of plant hormones involved in plant tropisms

Control growth in plant roots and shoot tips

48
Q

Compare the effect of auxins in plant shoots and roots

A

Auxins stimulate growth in plants shoot

Auxins inhibit growth in plant roots

49
Q

Where auxins produced?

A

Root and shoot tips

50
Q

How do auxins move through a plant?

A

They diffuse through the plant in solution

51
Q

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

A

Positively phototropic

Plant shoots grow towards the light

52
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 the shaded side
Shoot tip bends towards the light.

53
Q

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

A

Negatively gravitropic

Plant shoots grow upwards, away from gravity

54
Q

Explain why plant shoots are negatively gravitropic

A

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

55
Q

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

A

Negatively phototropic

Plant roots grow away from the light

56
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
Roots grows away from the light

57
Q

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

A

Positively gravitropic

Plant roots grow downwards, towards gravity

58
Q

Explain why plant roots are positively gravitropic

A

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

59
Q

How plant tropism increase chance of survival

A

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

60
Q

Describe the role of auxins in commerical plant cultivation

A

Rooting powders contain auxins that stimulates the growth of roots in cutting. Enables rapid plant cloning.

Used in selective weedkillers that target and alter growth patterns in broad-leaved plants (most weeds), killing them.

61
Q

What are gibberellins?

A

Plant hormone that control germination and flowering

62
Q

Describe the role of gibberellines in commercial plant cultivation

A

Intiate germination in seeds at times of year when the naturally wouldnt. Ensure all seeds in a batch germinate
Trigger flowering in plants under irregular/unfavourable conditions.
Also increase fruit size by reducing the number of flowers produced by plants
Produce seedless fruit by stimulating the growth of fruit from unpollinated flowers.

63
Q

How do gibberellines trigger germination?

A

In presence of water, break seed dormancy, initating germination.

64
Q

Why is ethene important in commercial plant cultivation?

A

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

Gcse Biology (14 decks)

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