C16 - Plant Responses Flashcards by Mary Skuodas

Define Tropism

A growth response by a plant in response to a unidirectional stimulus

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Define phototropism

A growth response by a plant in response to a unidirectional light

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Define geotropism

A growth response by a plant in response to gravity

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Define hydrotropism

A growth response by a plant in response to water

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Define node

Point at which a petiole/leaf attaches to stem

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Define internodal length

Length between two adjacent nodes

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Define lateral shoots

Side shoots, those below the apical shoot/bud

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Define apical shoot

The topmost shoot

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Define apical dominance

When the main central stem grows more strongly than the side stems

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Define abscission

Leaf drop

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Define synergism

When several hormones work together to give a greater response

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Define antagonism

When hormones have opposite effects (one promotes, one inhibits)

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Define meristem

tissue of undifferentiated stem cells

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Define deciduous

A plant that looses its leaves in autumn/winter

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Why do plants need hormones

Movement (tropism)
Seed germination
Fruit ripening
Abscission
Growth
Protection (herbivores and abiotic stress)

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What makes a tropism positive or negative

Positive - towards stimulus

Negative - away from stimulus

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Name the 4 plant growth hormones we study

Gibberellins
Ethene
Auxins
ABA (abscisic acid)

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What are the roles of gibberellins?

cause stem elongation
trigger metabolism of food stores at germination
stimulate pollen tube growth in fertilisation

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Describe how gibberellins are used in seed germination

Seed absorbs water, embryo activated and gibberellins produced
Gibberellins switch on genes that code for amylases and proteases
Stimulates enzymes to break down food stores in seed
ATP produced, grows and breaks out of the seed coat

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What is the experimental evidence for the role of gibberellins

seeds bred to not produce gibberellins do not germinate
(if applied to seeds externally they will then germinate)
-inhibitors of gibberellins applied they do not germinate

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Name an application of gibberellins in industry

Affect length of internode (few gibberellins = short stems)
Dwarf plants made
-reduces waste
- reduced vulnerability (eg. wind)

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What is the role of auxins?

responsible for geotropism and phototropism

- Stimulates elongation in shoots and inhibits elongation in roots

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Describe how auxins cause cell elongation

1) auxins bind to receptors on cell surface membrane
2) Stimulates H+ ions to be actively pumped across cell membrane into cell wall
3) H+ ions lower pH to 5
4) Expansins activated
5) Loosen cellulose cell wall - more plastic
6) water diffuses into vaculole, causing it to expand, along with the rest of the cell

Describe how the concentrations of auxins change ina shoot in response to unilateral light

Auxin produced in the tip
Diffuses down stem
Diffuses to shady side
Causes shaded side cells to elongate thus bending it towards the light

Evidence for phototropism: How would the growth a plant shoot change if... exposed to unilateral light

Grow towards the light | Positive phototropism

Evidence for phototropism: How would the growth a plant shoot change if... Shoot tip removed and exposed to unilateral light

no response as auxins produced in the tip

Evidence for phototropism: How would the growth a plant shoot change if... Lightproof cover placed over shoot tip and exposed to unilateral light

No response | Ausins act on tip in response to light

Evidence for phototropism: How would the growth a plant shoot change if... Thin layer of mica placed on sunny side and exposed to unilateral light

Bends towards light | Hormone still able to diffuse along shaded side and act on those cells causing elongation

Evidence for phototropism: How would the growth a plant shoot change if... Thin later of mica place on shaded side and exposed to unilateral light

No response | Hormone not able to diffuse down shadede side and have its effect

Evidence for phototropism: How would the growth a plant shoot change if... tip removed, gelatin inserted and tip replaced and exposed to unilateral light

Movement of the chemical still possible, gelatin would stop electrical messages thus it must be a hormone

Evidence for geotropism

Plant placed on a clinostat that rotates slowly Evens out gravitational force and grows straight out Plant replaced sideways not on clinostat - Shoot grows up and roots grown down

Descibe the process of geotropism

Starch statoliths in root tip Sink to the bottom of the cells in the roots in response to gravity Causes downwards growth

Describe what a plant with apical dominance will look like as opposed to a plant without apical dominance

Apical domincace - tall, thin, apical shoot leads the way | Without - bushy, fat, lateral shoots grow strongly

What are the 3 wasy plants can respond to abiotic stress

Leaf loss Preventing freezing Stomatal control

Why is leaf loss bebficial to a plant

In winter, less daylight = less photosynthesis - glucose required to prevent leaves from freezing becomes greater than the glucose able to be produced - greater surface area, more likely to be affected by high winds etc.

What is photoperiodism?

Reponse to lack fo light caused by phytochrome - light sensitive pigment

Descibe the process of abscission

- falling auxin levels - ethene produced - triggers gene activation (enzymes produced) - enzymes digest cell wall in separation zone - vascular bundles sealed off - Cells below swell and push leaf off Fat deposited in cells acting as a scar

Why is freezing dangerous for plant cells?

Water expand Destroy membrane Die

How do plants respond to the risk of freezing?

produce solutes that dissolve in the vacuole, this lowers the freezing point

How does stomatal control help a plant respond to it environment

Closed stomata - conserve water | Open stomata - allows CO2 in an helps coll the plant by evaporation of the water

What hormone controls stomatal opening and closing

ABA (abscisic acid)

How does ABA control the stomata

Increased ABA dereases the water potential of the stomata Water moves out of the cells Cells become flaccid and close (turgid means they open)

What are the 3 types of plant responses

Chemical Physics Mechanical

Give an example of a mechanical repsonse in plants

Thorns and hairs to deter herbinvores Leaves that drop when touched Mimicry

Give a physical response in plants to stress

Cellulose cell walls Tough waxy cuticle Layers of dead cells around the stem

What are tannins

Chemical response in plants | toxic to insects

What are alkaloids?

Chemical repsonse in plants nitrogenous act as drugs

What are volatile organic compounds (VOCs)

Chemical reposnse in plants | smelly repellents

Names 4 types of chemical response in plants

pheromones tannins alkaloids VOCs

Name 3 commercial uses of plant hormones

ripening hormone rooting powder weed killers

Describe how plant hormones can be used in artificial ripening

Ethene can be sprayed on to unripe plants to ripen them

State an advantage of artificial ripening

Unripe plants can be transported more easily and produced less waste

Outline the reaction that causes ripening fruits to become sweeter

Starch --> maltose (hydrolysed by amylase) | maltose --> glucose

As ethene concentration increases what happens to CO2 prodcution

Increases as respiration increases, then decreases as starch hydrolyses

What does hormone rooting powder do

Dipping cuttings into auxins | stimulate root growth from cut stem

How do weed killers use plant hormones

Dicot auxins applied to area Absorbed by broad leafed dicot weeds but not moncot crops causes rapid and unsustainable growth ---> death