B3.2 The Endocrine System - Plant Hormones

Question 1

<p>What is a tropism?</p>

Answer 1

<p>A growth response made by a plant in response to a particular stimuli in their environment.</p>

Question 2

<p>What is the difference between a positive and negative tropism?</p>

Answer 2

<ul> <li>Positive = growing towards stimulus</li> <li>Negative = growing away from stimulus</li></ul>

Question 3

<p>Define 'phototropism'.</p>

Answer 3

<ul> <li>Growth in response to light</li> <li>Stems = positively phototropic</li> <li>Roots = negatively phototropic</li></ul>

Question 4

<p>Define 'gravitotropism'.</p>

Answer 4

<ul> <li>Growth in response to gravity</li> <li>Stems = negatively gravitrophic</li> <li>Roots = positively gravitrophic</li></ul>

Question 5

<p>Another term used for gravitropism.</p>

Answer 5

<p>Geotropism</p>

Question 6

<p>A plant hormone that enables a plant to grow towards, or away from a stimulus.</p>

Answer 6

<p>Auxin.</p>

Question 7

<p>Where is auxin made?</p>

Answer 7

<p>Roots and shoots.</p>

Question 8

<p>How does auxin cause a response to a stimulus?</p>

Answer 8

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

Question 9

<p>How does the response to auxin differ between roots and shoots?</p>

Answer 9

<ul> <li>Auxin causes increased growth in shoots</li> <li>Auxin causes decreased growth in roots</li></ul>

Question 10

<p>How do plants respond to light?</p>

Answer 10

<ul> <li>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</li> <li>This lead to a build up on the shaded side</li> <li>The cells on the shaded side elongate</li> <li>The shoot bends towards the light</li></ul>

Question 11

<p>How do plants respond to gravity?</p>

Answer 11

<ul> <li>Gravity causes auxins to gather on the lower side of the root and shoot</li> <li>In roots auxins inhibit growth so the side with the least auxins elongates and grows down towards the force of gravity.</li> <li>In shoots auxins stimulatesgrowth so the side with the most auxins elongates and grows down away from the force of gravity.</li></ul>

Question 12

<p>State three plant hormones commonly used in agriculture and horticulture?</p>

Answer 12

<ol> <li>Auxins</li> <li>Ethene</li> <li>Gibberellins</li></ol>

Question 13

<p>Why is ethene unique to the other two hormones?</p>

Answer 13

<p>It is a gas.</p>

Question 14

<p>This hormone is used to help to regulate fruit development, without itfruit is often small.</p>

Answer 14

<p>Auxins.</p>

Question 15

<p>What isethene?</p>

Answer 15

<ul> <li>Ethene is a hormone that stimulates the conversion of starch into sugar which causes fruit to ripen – this is why unripe fruit is not as sweet as ripe fruit.</li> <li>This hormone is the only plant hormone that is a gas</li></ul>

Question 16

<p>How is ethene used commercially?</p>

Answer 16

<ul> <li>To ripen fruit</li> <li>Stimulate the conversion of starch into sugar which causes fruit to ripen – this is why unripe fruit is not as sweet as ripe fruit.</li></ul>

Question 17

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

Answer 17

<p>Gibberellins</p>

Question 18

<p>List the common agriculturaland horticulturaluses of plant hormones.</p>

Answer 18

<ul> <li>Growing cuttings</li> <li>Tissue culture</li> <li>Ripening fruit</li> <li>Killing weeds</li> <li>Kromoting flowering</li> <li>Producing seedless fruit</li></ul>

Question 19

<p>How can plant hormones be used to kill weeds?</p>

Answer 19

<ul> <li>Most weeds have broad leaves</li> <li>Auxin in herbicides causes the broad-leafed weeds to grow too quickly.</li> <li>They are unable to sustain the high growth rate, causing them to die</li></ul>

Question 20

<p>Explain how a cutting can be grown.</p>

Answer 20

<ul> <li> <p>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.</p> </li> <li> <p>Rooting powder containing auxin can be used to stimulate root growth in cuttings.</p> </li></ul>

Question 21

<p>What is a tissue culture?</p>

Answer 21

<p>Amethod that uses auxin to grow whole plants from a plant tissue sample.</p>

Question 22

<p>How have gibberellins made farming more productive?</p>

Answer 22

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

Question 23

<p>How can seedless fruit be produced?</p>

Answer 23

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

Question 24

<p>How can ripening in fruit be delayed?</p>

Answer 24

<ul> <li>By spraying plants with auxins.</li> <li>Allows harvesting at the same time</li> <li>Prevents fruit from dropping from trees to early</li></ul>

Question 25

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

Answer 25

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