B3.2 The Endocrine System - Plant Hormones Flashcards

1
Q

What is a tropism?

A

A growth response made by a plant in response to a particular stimuli in their environment.

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2
Q

What is the difference between a positive and negative tropism?

A
  • Positive = growing towards stimulus
  • Negative = growing away from stimulus
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3
Q

Define โ€˜phototropismโ€™.

A
  • Growth in response to light
  • Stems = positively phototropic
  • Roots = negatively phototropic
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4
Q

Define โ€˜gravitotropismโ€™.

A
  • Growth in response to gravity
  • Stems = negatively gravitrophic
  • Roots = positively gravitrophic
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5
Q

Another term used for gravitropism.

A

Geotropism

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6
Q

A plant hormone that enables a plant to grow towards, or away from a stimulus.

A

Auxin.

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7
Q

Where is auxin made?

A

Roots and shoots.

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8
Q

How does auxin cause a response to a stimulus?

A

The stimulus causes an uneven distribution of the hormone auxin, which causes an unequal growth rate, causing the root or shoot to bend.

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9
Q

How does the response to auxin differ between roots and shoots?

A
  • Auxin causes increased growth in shoots
  • Auxin causes decreased growth in roots
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10
Q

How do plants respond to light?

A
  • When light hits one side of a shoot the auxin on that side both moves away from the light, and is broken down (denatured) by the light
  • This lead to a build up on the shaded side
  • The cells on the shaded side elongate
  • The shoot bends towards the light
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11
Q

How do plants respond to gravity?

A
  • Gravity causes auxins to gather on the lower side of the root and shoot
  • In roots auxins inhibit growth so the side with the least auxins elongates and grows down towards the force of gravity.
  • In shoots auxins stimulates growth so the side with the most auxins elongates and grows down away from the force of gravity.
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12
Q

State three plant hormones commonly used in agriculture and horticulture?

A
  1. Auxins
  2. Ethene
  3. Gibberellins
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13
Q

Why is ethene unique to the other two hormones?

A

It is a gas.

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14
Q

This hormone is used to help to regulate fruit development, without it fruit is often small.

A

Auxins.

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15
Q

What is ethene?

A
  • Ethene is a hormone that stimulates the conversion of starch into sugar which causes fruit to ripen โ€“ this is why unripe fruit is not as sweet as ripe fruit.
  • This hormone is the only plant hormone that is a gas
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16
Q

How is ethene used commercially?

A
  • To ripen fruit
  • Stimulate the conversion of starch into sugar which causes fruit to ripen โ€“ this is why unripe fruit is not as sweet as ripe fruit.
17
Q

This hormone ends the dormancy period for seeds and buds, causing shoots and flowers to open.

A

Gibberellins

18
Q

List the common agricultural and horticultural uses of plant hormones.

A
  • Growing cuttings
  • Tissue culture
  • Ripening fruit
  • Killing weeds
  • Kromoting flowering
  • Producing seedless fruit
19
Q

How can plant hormones be used to kill weeds?

A
  • Most weeds have broad leaves
  • Auxin in herbicides causes the broad-leafed weeds to grow too quickly.
  • They are unable to sustain the high growth rate, causing them to die
20
Q

Explain how a cutting can be grown.

A
  • A cutting is a part of plant removed from the main shoot, so it does not have roots, so it is unable to absorb water or minerals.
  • Rooting powder containing auxin can be used to stimulate root growth in cuttings.
21
Q

What is a tissue culture?

A

A method that uses auxin to grow whole plants from a plant tissue sample.

22
Q

How have gibberellins made farming more productive?

A
  • Gibberellins can be used to end seed dormancy by promoting germination
  • Enables farmers to control when crops begin to grow - can trigger winter germination in a greenhouse
  • Enables farmers that plants all grow at the same time - all ready to harvest at same time
  • Can use to extend growing season/have two growing seasons
23
Q

How can seedless fruit be produced?

A

Gibberellins can be sprayed on flowers to stimulate fruit growth, even though there are no seeds.

24
Q

How can ripening in fruit be delayed?

A
  • By spraying plants with auxins.
  • Allows harvesting at the same time
  • Prevents fruit from dropping from trees to early
25
Q

Why do horticulturists and gardeners take cuttings and develop them with auxins?

A

The cuttings produce identical plants, or clones, so a good plant can be quickly and cheeply reproduced in this way.