Biology AS > Plant Response > Flashcards

Plant Response Flashcards

(54 cards)

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1
Q

Define a tropism

A

A directional growth response of a plant to an external stimulus, where growth is towards or away from the stimulus.

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2
Q

What is phototropism?

A

A growth response to light, where shoots show positive phototropism by growing towards the light.

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3
Q

Define gravitropism

A

A growth response to gravity, where roots show positive gravitropism and shoots show negative gravitropism.

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4
Q

Which hormone controls plant tropisms?

A

Auxin

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5
Q

Where is auxin made in shoots?

A

Auxin is produced in the apical meristem / shoot tip.

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6
Q

How does auxin move through a shoot?

A

Auxin moves from the tip downwards and is redistributed to the shaded side of the shoot.

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7
Q

What does auxin do to shoot cells?

A

Auxin stimulates cell elongation in shoot cells.

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8
Q

Explain how phototropism occurs in shoots

A

• Light causes auxin to move to the shaded side
• Higher auxin concentration on shaded side
• Auxin stimulates cell elongation
• Cells on shaded side elongate more
• Shoot bends towards the light

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9
Q

How does auxin affect root growth?

A

High concentrations of auxin inhibit cell elongation in roots.

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10
Q

Explain how roots respond to gravity

A

• Auxin accumulates on the lower side of the root
• High auxin concentration inhibits cell elongation
• Cells on upper side elongate more
• Root bends downwards

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11
Q

Why do shoots show negative gravitropism?

A

Auxin accumulates on the lower side of the shoot, stimulating cell elongation there, causing the shoot to grow upwards.

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12
Q

What are statoliths?

A

Starch-filled organelles that settle due to gravity and help the plant detect direction of gravity.

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13
Q

Where are statoliths located?

A

In root cap cells.

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14
Q

State one function of the root cap

A

• Protects the growing tip
• Contains statoliths for gravity detection

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15
Q

Give one reason plant hormones are useful

A

They allow plants to respond to environmental stimuli despite lacking a nervous system.

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16
Q

One difference between plant and animal hormones

A

Plant hormones act locally and slowly, whereas animal hormones act via the bloodstream and can be faster.

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17
Q

What is the acid growth hypothesis?

A

Auxin stimulates proton pumps in the cell surface membrane, causing H⁺ ions to be pumped into the cell wall, lowering pH and allowing cell wall loosening.

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18
Q

How do proton pumps cause cell elongation?

A

• Auxin activates proton pumps
• H⁺ ions pumped into cell wall
• Cell wall pH decreases
• Hydrogen bonds break
• Cell wall becomes more extensible

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19
Q

What are expansins?

A

Proteins activated at low pH that break hydrogen bonds between cellulose microfibrils, allowing the cell wall to stretch.

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20
Q

Why does cell elongation involve water uptake?

A

Lowered water potential causes osmosis, increasing turgor pressure, pushing the cell wall outwards.

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21
Q

Difference between tropic and nastic responses

A

Tropic: directional growth response
• Nastic: non-directional response, usually reversible

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22
Q

Give an example of a nastic response

Study These Flashcards
A

Opening and closing of stomata in response to light or water availability.

23
Q

Why is stomatal movement not a tropism?

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A

It is non-directional, reversible, and does not involve growth.

24
Q

What did Darwin’s experiment show?

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A

What did Darwin’s experiment show?

25
What did Darwin’s experiment show?
The signal from the tip is a chemical substance (auxin), not electrical.
26
What did Went’s experiment prove?
Auxin causes cell elongation, and unequal distribution causes bending.
27
Give one use of auxins in agriculture
• Rooting powders • Weed killers (synthetic auxins) • Preventing premature fruit drop
28
How do synthetic auxins act as herbicides
They cause uncontrolled growth, leading to death of the plant.
29
Germination process
Water enters the seed. This absorption of water causes the embryo to synthesise gibberellins. In response, amylase and maltase enzymes are synthesised. The amylase enzymes hydrolyse the starch stored in the endosperm into maltose. This can then be broken down into glucose, which provides the embryo with sugars that are essential for energy and growth. Through this mechanism, gibberellins activate the mobilisation of stored starch reserves, starting the germination process.
30
Synergistic
This is when different hormones work together, giving a greater response than they would on their own.
31
Antagonistic
This is when different hormones have opposing effects, like one promoting growth and one inhibiting it. The balance between them determines the response of the plant.
32
Photoperiodism
sensitivity of plants to the levels of light in their environment. (deciduous trees (those that lose their leaves in autumn))
33
Abscission
plants lose their leaves.
34
Abscission is triggered by:
Lengthening of the dark period during autumn, which leads to reduced photosynthesis rates. The energy demands for respiration outweighing glucose availability. The need for dormancy to avoid winter-related damage.
35
Stages of abscission:
A decrease in light prompts a decrease in auxin levels. The hormone ethene is released by the leaves. Ethene helps switch on genes in cells in the abscission zone at the base of the leaf stalk. Enzymes digest and weaken the cell walls in the separation layer. Vascular tissues are sealed off, blocking transport to the leaf. Fatty material is deposited in the cells in the inner, protective layer of the abscission zone. Cells within the separation layer swell with water, straining the weakened walls. Environmental factors such as winds separate the leaf from the plant. The protective layer that remains forms a scar to prevent the entry of pathogens.
36
How plants prevent cellular freezing
Synthesising compounds like sugars, amino acids, and proteins that act as antifreeze and prevent the cytoplasm from freezing. Modulating gene expression to bolster cold resistance. Adjusting sap solute concentrations to lower the freezing point.
37
types of chemical defences against herbivores
Tannins Alkaloids (toxic or poisonous to animals, discouraging some herbivores from consuming the plant or even killing them.) Pheromones – attract predators of herbivores
38
Volatile organic compounds for pest control ways
Attracting predators Repelling herbivores Signalling neighbouring plants
39
How can phototropism be investigated experimentally?
1. Grow seedlings in darkness. 2. Shine light from one side. 3. Observe shoots bending towards the light.
40
What controls are used in phototropism experiments
Light from all directions • Foil caps covering shoot tips • Agar blocks with/without auxin
41
How can geotropism/ gravitropism be investigated?
1. Place germinating seeds horizontally. 2. Rotate them on a clinostat to remove directional gravity. 3. Observe growth direction of shoots and roots.
42
How are gibberellins used commercially?
• Improve fruit size and shape (e.g. grapes) • Break seed dormancy
43
How is ethene used commercially
ripens uniformly Reduces spoilage & damages during storage and transport.
44
Role of gibberellins in stem growth
plant growth regulators that stimulate seed germination and regulate plant height via stem growth.
45
abiotic stresses
Changes in day length. Excessive cold and heat. Lack of water or excess water.
46
What is the role of abscisic acid (ABA) in plants?
hormone that signals plants to conserve water during heat or drought conditions.
47
What triggers the production of ABA in plants?
Low water availability triggers the production of ABA.
48
Explain the role of ABA in plants.
• ABA is produced in response to low water availability. • It moves from roots to leaves. • Binds to guard cell receptors → changes ion concentration → water leaves → turgor decreases. • Stomata close → reduces water loss.
49
Give an example of a mechanical response to herbivory.
Leaf folding in response to touch (e.g. Mimosa plant).
50
What is Thigmotropism
growth towards or away from touch or physical contact.
51
What is Etiolation
the rapid upward growth that takes place in a plant grown in the dark.
52
Features of Etiolated plants
thin and pale due to a lack of chlorophyll.
53
Advantages of using synthetic auxins as weedkillers:
Simple and cheap to produce Low toxicity to mammals Selective, affecting only broad-leaf plants
54
If evaluate, what to write? Give eg
-SUPPORTING REASON -AGAISNT (No statistical test, no scale, no units, correlation not causation) -ISSUES WITH VALIDITY (No control variables, no method given , no control group )
Biology AS
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