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Biology A level > Plant Responses > Flashcards

Plant Responses Flashcards

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1
Q

What is Phototropism

A

Growth towards light

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2
Q

What is Thigmotropism

A

Growth in response to touch stimulus

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3
Q

What is geotropism

A

Growth in response to gravity

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4
Q

What is Hydrotropism

A

Growth towards water

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5
Q

Why do plants respond to their environment

A

To avoid abiotic stress
Maximise photosynthesis
Obtain more resources
Avoid grazing/disease
Ensure germination is done in suitable conditions

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6
Q

What are the chemical defences of plants

A

Tannins - toxic to microbes, taste bitter to animals
Alkaloids - taste bitter
Pheromones - signalling molecules released in response to grazing to alert other plants

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7
Q

What is a tropism

A

Directional growth in response to external stimuli

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8
Q

What are Nastic responses

A

Non-directional responses to external stimuli

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9
Q

What is photoperiodism

A

Responses to day length or photoperiod

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10
Q

What controls plant responses

A

Hormones produced in small quantities in a variety of tissues

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11
Q

What is the role of auxins

A

Inhibit leaf abscission and lateral growth
promote cell elongation
Produced at apices and transported to zone of elongation

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12
Q

What is the role of gibberellins

A

Promote seed germination and stem growth

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13
Q

What is the role of abscisic acid

A

Stomatal closure
Inhibits seed germination and growth

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14
Q

What is the role of ethene

A

Promotes fruit ripening

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15
Q

What is the role of cytokinins

A

promotes cell division

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16
Q

What causes phototropism

A

Auxins move towards shaded area of shoot and promote those cells to elongate. This causes the shoot to be towards the light

17
Q

How do auxins elongate cells

A

It increases the stretchiness of the cell wall by using a hydrogen pump to cause H+ to accumulate in cell wall
This causes a lower pH there and disrupts H+ bonds within cellulose, causing the wall to be less rigid
This means the cell can expand as it takes o water

18
Q

Where does negative phototropism occur

A

In roots

19
Q

How does negative phototropism occur

A

Auxins transported to shaded side, causing elongation to be inhibited there so that the root bends away from light

20
Q

What is abscission

A

leaf or fruit fall from the plant

21
Q

How is abscission caused

A

Auxin production decreases and ethene production increases
This causes production of cellulase - cell wall digested in abscission zone
Petiole separates from stem

22
Q

What is apical dominance

A

When auxins from apex inhibit lateral growth

23
Q

How do gibberellins promote seed germination

A

Seeds absorb water and embryo releases gibberellin
Gibberellin causes amylase to produce
Amylase breaks down starch into glucose
Glucose used for respiration so embryo can grow

24
Q

How does abscisic acid cause stomatal closure

A

ABA binds to receptors on guard cell membranes
This causes K+ ions to leave the cell and the water potential of the cell increases
Water leaves guard cell by osmosis and stomata closes

25
Q

What are the commercial uses of Auxin

A

In rooting powders to promote root growth Used in cloning to promote root growth
Used as weed killer - promotes excessive growth

26
Q

What experimental evidence supports the role of gibberellins in germination

A

Mutant seeds with unable to make gibberellins do not germinate

27
Q

What is Bankanae

A

A fungal plant disease that contains gibberellic acid - causing plants to grow tall

28
Q

What experimental evidence proves that gibberellin promotes stem growth

A

Pea plants do not have the gene that codes for an enzyme that activates gibberellin end up as dwarf plants

29
Q

What is synergism

A

when hormones work together to produce a greater response

30
Q

How do plants prevent freezing

A

The cytoplasm of the plant cell and sap in vacuoles contain solutes which lower the freezing point

Biology A level (19 decks)

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