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Biology > Topic 6 - plant structures and functions > Flashcards

Topic 6 - plant structures and functions Flashcards

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
Describe how the xylem is adapted to its function
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
26
What is the function of the phloem?
It transports sugars up and down the stem from photosynthetic tissues to non-photosynthetic tissues via translocation
27
What are the two cell types that make up the phloem?
Siege tube elements | Companion cells
28
Describe how the phloem is adapted to its function
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
29
What is transpiration?
The loss of water vapour form the parts of a plant exposed to the air due to evaporation and diffusion
30
Where does the majority of transpiration take place?
Leaves
31
Describe the process of transpiration
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
How does the transpiration stream transport mineral ions?
Mineral ions are dissolved in the water that is carried by the transpiration stream
33
What are stomata?
The pores found in the lower epidermis of a leaf which allow gas exchange
34
What are guard cells?
Specialised cells surrounding the stoma that change shape to control the size of the pore
35
How do guard cells control the size of the stomata?
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
What factors affect the rate of transpiration?
Light intensity Temperature Air movement
37
Describe how light intensity affects the rate of transpiration
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
Describe how low light intensity affects the rate of transpiration
At a low light intensity, fewer stomata are open so the rate of transpiration decreases
39
Describe how temperature affects the rate of transpiration
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
Describe how air movement affects the rate of transpiration
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
What apparatus is used to measure the rate of transpiration?
Potometer
42
What is assumed when measuring the rate of transpiration using a potometer?
The rate of water uptake = the rate of transpiration
43
How can the rate of transpiration be calculated using a potometer
Rate of transpiration = distance moved by bubble/time taken
44
What is translocation?
The movement of sugars up and down a plant fro the source to the sink, via the phloem
45
Describe how leaves are adapted for photosynthesis
They are broad Thin They have photosynthetic pigments and vascular bundles (xylem and phloem)
46
How are tissues of the leaves adapted for photosynthesis and gas exchange?
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
Describe how plants are adapted to live in hot, dry conditions
``` 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
What are plant tropisms?
The growth of a plant in response to a stimulus
49
What is positive tropism?
The growth of a plant towards a stimulus
50
What is negative tropism?
The growth of a plant away from a stimulus
51
What are the two main types of plant tropism?
Photosropism | Gravitropism
52
Define phototropism
A plant’s growth response to light
53
Define gravitropism
A plant’s growth response to gravity
54
What are auxins?
A group of plant hormones involved in plant tropisms | They control growth in plant roots and shoot tips
55
Compare the effect of auxins in plant shoots and roots
Auxins stimulate growth in plant shoots | They inhibit growth in plant roots
56
Where are auxins produced?
Root and shoot tips
57
How do auxins move through a plant?
They diffuse through the plant is solution
58
Are plant shoots positively or negatively phototropisch? How does this affect shoot growth?
Positively phototropic | Plant shoots grow towards the light
59
Explain why plant shoots are positively phototropic
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
Are plant shoots positively or negatively gravitropic? How does this affect shoot growth?
Negatively gravitropic | Plant shoots grow upward, away from gravity
61
Explain why plant shoots are negatively gravitropic
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
Are plant roots positively or negatively phototropic? How does this affect root growth?
Negatively phototropic | Plant roots grow away from the light
63
Explain why plant roots are negatively phototropic
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
Are plant roots positively or negatively gravitropic? How does this affect root growth?
Positively gravitropic | Plant roots grow downwards, towards gravity
65
Explain why plant roots are positively gravitropic
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
Explain how plant tropisms increase the chance of survival
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
Describe the role of auxins in commercial plant cultivation
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
What are gibberellins?
Plant hormones that control germination and flowering
69
Describe the role of gibberellins in commercial plant cultivation
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
How do gibberellins trigger germination?
In the presence of water, they break seed dormancy initiating germination
71
Why is ethane important in commercial plant cultivation?
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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