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Boardworks GCSE Science: Biology

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Presentation on theme: "Boardworks GCSE Science: Biology"— Presentation transcript:

1 Boardworks GCSE Science: Biology
Plant Hormones Plant Hormones 1

2 Boardworks GCSE Science: Biology
Plant Hormones 2

3 What do plants need to grow?
Boardworks GCSE Science: Biology Plant Hormones This plant hasn’t been looked after very well. What do plants need to grow healthily? sunlight water mineral nutrients an air supply If a plant cannot get these from its environment, can it move to somewhere else? Photo credit: © 2007 Jupiterimages Corporation Plants are rooted to one place. However, they can control their direction of growth. 3

4 What controls plant growth?
Boardworks GCSE Science: Biology Plant Hormones Plants grow in response to their environment. The shoots of these tulips grow upwards and the roots grow downwards. If a plant was unable to do this, it might not be able to get enough water or sunlight from its environment. Photo credit: © 2007 Jupiterimages Corporation To what environmental factors do plants respond to make sure they grow properly? 4

5 What do plants respond to?
Boardworks GCSE Science: Biology Plant Hormones Plants are very sensitive and their growth is affected by their environmental conditions. Any condition that affects plant growth is called a stimulus. What are three types of stimuli that plants respond to? Teacher notes: Students can design and carry out experiments to vary the amounts of light and water plants have access to, and observe the effects on growth. light water gravity Which stimulus will have the strongest effect on the plant? 5

6 Boardworks GCSE Science: Biology
Which stimulus? Boardworks GCSE Science: Biology Plant Hormones Teacher notes This voting activity can be used to start students thinking about which of these stimuli plants respond most strongly to. Later material in the presentation shows that plants will respond most strongly to water. The activity could be repeated after covering this material to see if students’ ideas have changed. 6

7 Boardworks GCSE Science: Biology
Plant Hormones 7

8 Boardworks GCSE Science: Biology
What is a tropism? Boardworks GCSE Science: Biology Plant Hormones A tropism is a growth movement in response to a stimulus. Plants grow towards or away from stimuli. A growth movement towards a stimulus is called a positive tropism. What is growth away from a stimulus called? A growth movement away from a stimulus is called a negative tropism. Will all the parts of a plant respond to a stimulus in the same way? 8

9 Are there different types of tropisms?
Boardworks GCSE Science: Biology Plant Hormones Plant responses to stimuli are given specific names: light water gravity phototropism hydrotropism geotropism Teacher notes Geotropism is also sometimes referred to as gravitropism. What do the names of each tropism mean? Which parts of a plant respond to these different stimuli? 9

10 Boardworks GCSE Science: Biology
Defining tropisms Boardworks GCSE Science: Biology Plant Hormones Teacher notes This matching activity could be used as a plenary or revision exercise on plant growth movements. Students could be asked to complete the questions in their books and the activity could be concluded by the completion on the IWB. Photo: © 2011 Photos.com 10

11 How do tropisms affect growth?
Boardworks GCSE Science: Biology Plant Hormones This plant does not have a very straight stem. What might have caused this? The plant was placed on a window sill and received light from one direction only. The shoots of plants grow towards sunlight. What is the name of this type of plant response? The response to sunlight is called phototropism. 11

12 Phototropism experiment
Boardworks GCSE Science: Biology Plant Hormones Teacher notes This virtual experiment investigates how phototropism occurs, using grass seedlings as a experimental subject. It could be used as a precursor to running the practical in the lab or as a revision exercise. Suitable prompts include: Stage 1: Why is it important to have a control? Stage 2: How might removing the tips affect growth? Stage 3: How might covering the tips affect growth? Stage 4: How can we make this a fair test? In this experiment, the distance from the light does not affect growth. However, students can check this by repeating the experiment and altering the order of the seedlings if required. Stage 5: What do you predict will happen and why? Stage 6: Why are the seedlings place in a box? Stage 7: What do the results suggest about the conditions required for phototropism to occur? 12

13 Do plants have hormones too?
Boardworks GCSE Science: Biology Plant Hormones Like humans, plants use hormones, (chemical messengers) to control their development. Hormones produced by plants control growth, flowering and fruit ripening. The growth of shoots and roots is controlled by a group of hormones called auxins. These chemicals are produced in the tips of the shoots and roots. What environmental stimuli might cause a plant to produce auxins? 13

14 Hormones and phototropism
Boardworks GCSE Science: Biology Plant Hormones Teacher notes This animated activity illustrates how auxins act on plant cells in response to light. While viewing the animations it should be highlighted that auxins are produced in the growing tip of the plant but act on the cells below the tip to cause growth. This content is higher tier for OCR Gateway GCSE Science. 14

15 Boardworks GCSE Science: Biology
Discovery of auxins Boardworks GCSE Science: Biology Plant Hormones Teacher notes This five-part historical sequence illustrates the experiments that helped develop the current understanding of auxins. This activity could be used to deepen students’ understanding of auxins and phototropism. It also provides an example of how scientific knowledge develops and the importance of experiments. Suitable prompts include: Part 1: Why did covering the area below the tip have no affect on growth? Part 2: Why did mica stop phototropism but not gelatine? This could be used check students’ understanding of the terms “permeable” and “impermeable”. Part 3: Why did phototropism take place when the mica was placed on the light side but not when it was placed on the shady side? Part 4: How were the plants able to grow without their tips? Part 5: How did Frits Went know that auxins collected in the shady side? More information about auxins is available at: (Charles Darwin - The Power of Movement in Plants) (tropisms) These weblinks were working correctly at the time of publication. Boardworks Ltd takes no responsibility for the content of external websites. 15

16 Boardworks GCSE Science: Biology
Which way up? Boardworks GCSE Science: Biology Plant Hormones How do plants always grow the right way up? Plants respond to gravity to grow in the right direction. 16

17 Hormones and geotropism
Boardworks GCSE Science: Biology Plant Hormones Teacher notes This five-stage animation shows a simple experiment that could be used to test how shoots and roots respond to gravity. A broad bean has been used in this animation as they make good test subjects because they germinate quickly. Suitable prompts include: Stage 1: How can you investigate the seedlings response to gravity? Stage 2: Where are auxins produced? Stage 3: How does the shoot respond to gravity? Stage 4: Does the root respond to gravity in the same way as the shoot? It should be highlighted to students that auxins speed up growth in the shoots but slow down growth in the roots. Stage 5: What would happen if the plant did not respond to gravity in this way? Would it be able to survive? Note that geotropism is sometimes referred to a gravitropism. 17

18 How do roots respond to water?
Boardworks GCSE Science: Biology Plant Hormones Roots always grow towards water, which is a positive tropism. Roots will grow sideways, or even upwards, towards water. Roots always have a stronger response to water than gravity to ensure that a plant gets the water it needs. 18

19 How do roots and shoots respond to stimuli?
Boardworks GCSE Science: Biology Plant Hormones Plant stimuli affect certain parts of the plant in different ways. Shoots grow towards sunlight. They are positively phototropic. Shoots grow away from gravity. They are negatively geotropic. Roots grow away from sunlight. They are negatively phototropic. Roots grow towards gravity. They are positively geotropic. What experiments can be used to test these ideas? 19

20 Tropisms and auxins – true or false?
Boardworks GCSE Science: Biology Plant Hormones Teacher notes This true-or-false quiz could be used as a plenary or revision exercise on tropisms and auxins, or at the start of a lesson to gauge students’ existing knowledge of the subject matter. Coloured traffic light cards (red = false, yellow = don’t know, green = true) could be used to make this a whole-class exercise. For question four, it should be highlighted to students that auxins speed up growth in shoots, but slow down growth in roots. The worksheet “Plant Hormones” accompanies this section. 20

21 Boardworks GCSE Science: Biology
Plant Hormones 21

22 How can plant hormones be used?
Boardworks GCSE Science: Biology Plant Hormones Plant hormones are naturally-occurring chemicals, but they can also be produced synthetically for uses in gardening and agriculture, such as: growing cuttings ripening fruit killing weeds. controlling dormancy This content is higher tier for Edexcel GCSE Science. making seedless fruit. Why are these purposes useful for gardeners and farmers? 22

23 Boardworks GCSE Science: Biology
How are cuttings grown? Boardworks GCSE Science: Biology Plant Hormones A cutting is a part of plant that is removed from the main shoot. Do cuttings have everything they need to grow? A cutting does not have roots and so has no supply of water or minerals. To stimulate root growth, cuttings are dipped into rooting powder. This contains plant growth hormones. This content is higher tier for Edexcel GCSE Science. Cuttings are genetically identical to the parent plant. This allows growers to copy successful plants. 23

24 Growing plant cuttings
Boardworks GCSE Science: Biology Plant Hormones Teacher notes This four-stage simulation investigates how rooting powder can be used to encourage growth in cuttings. It could be used as a precursor to running the practical in the lab or as a revision exercise. This content is higher tier for Edexcel GCSE Science. 24

25 How do plant hormones kill weeds?
Boardworks GCSE Science: Biology Plant Hormones Weeds are unwelcome plants that compete with the plants being grown by gardeners and farmers. However, many chemicals that are potential weedkillers are toxic to animals and humans, as well as plants. Plant hormones can be used instead to make weedkillers that only affect certain plants. Most weeds have broad leaves. Cereals, which have narrow leaves, can be protected from weeds by using weedkillers that only effect the growth of broad-leaved plants. This content is higher tier for Edexcel GCSE Science. 25

26 How are hormones used to ripen fruit?
Boardworks GCSE Science: Biology Plant Hormones Fruit is often picked before it is fully ripe. Why might this help keep the fruit edible? Fruit often has to travels thousands of miles from where it is picked to where it is sold in the shops. Unripe fruit is harder and less likely to bruise than ripe fruit when transported. This content is higher tier for Edexcel GCSE Science. Photo credit: © 2007 Jupiterimages Corporation When the fruit reaches its destination, it can then be sprayed with artificial plant hormones to encourage ripening. Why might it be a good idea to wash fruit before eating it? 26

27 Which hormone makes fruit ripen?
Boardworks GCSE Science: Biology Plant Hormones Ethylene is a plant hormone that controls fruit ripening. It can be sprayed on unripe fruit to speed up ripening. Some fruit, such as bananas, actually produce a large amount of ethylene, which can cause other nearby fruits to ripen. Using artificial ethylene to ripen fruit is not just a modern practice. Ancient Egyptians exposed figs to natural gas, which contains ethylene, to encourage ripening. Teacher notes It should be highlighted to students that coal-burning engines will also produce ethylene and therefore care must be taken when transporting fruit to ensure it arrives in prime condition. Experiments can be carried out to show that a fruit such as an avocado ripens much more quickly next to some ripe bananas. This content is higher tier for Edexcel GCSE Science. Photo credit: © 2007 Jupiterimages Corporation Why might it be important to keep fruit away from coal-burning engines during transportation? 27

28 Boardworks GCSE Science: Biology
Controlling dormancy Boardworks GCSE Science: Biology Plant Hormones Seeds can lie dormant for many years. Dormant seeds don’t germinate, even in warm moist conditions. Dormancy is important as it ensures seeds don’t all germinate at the same time. This means that if there is a short period of poor growing conditions, such as a drought, some of the dormant seeds will survive. Photo: © (Swapan), Shutterstock.com Dormancy is controlled by plant hormones. Farmers can add artificial hormones to seeds to prevent them from germinating. The record for the longest dormancy is held by a 1,300-year-old lotus seed which finally sprouted in 1995. 28

29 Boardworks GCSE Science: Biology
Seedless fruit Boardworks GCSE Science: Biology Plant Hormones Plants usually reproduce using seeds found inside fruit, however people prefer to eat fruit without seeds. For some plants, farmers can produce seedless fruit by: preventing pollination selective breeding to create plants that have too many chromosomes, and so can’t produce seeds. This content is higher tier for Edexcel GCSE Science. Most plants only grow fruits if they have developing seeds. Plants that grow seedless fruit are often sprayed with plant hormones like auxin and giberellin to stimulate fruit growth, even though there are no seeds. 29

30 Boardworks GCSE Science: Biology
Using hormones Boardworks GCSE Science: Biology Plant Hormones This content is higher tier for Edexcel GCSE Science. 30

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Plant Hormones 31

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Glossary Boardworks GCSE Science: Biology Plant Hormones Teacher notes auxins – Plant hormones that control the rate of growth. cutting – Part of a plant that has been removed from the main shoot and does not have roots. dormant – An inactive state that seeds can stay in for a long period so that they do not all germinate at the same time. Dormancy is controlled by hormones. ethylene – A plant hormone used to ripen fruit. geotropism – A growth movement in response to gravity. Sometimes called gravitropism. hydrotropism – A growth movement in response to water. negative tropism – A growth movement away from a stimulus. phototropism – A growth movement in response to light. positive tropism – A growth movement towards a stimulus. rooting powder – A substance containing plant hormones, which stimulates root growth in cuttings. stimulus – Any condition that affects plant growth. tropism – Any growth movement in response to a stimulus. 32

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Anagrams Boardworks GCSE Science: Biology Plant Hormones 33

34 Boardworks GCSE Science: Biology
Multiple-choice quiz Boardworks GCSE Science: Biology Plant Hormones Teacher notes This multiple–choice quiz could be used as a plenary activity to assess students’ understanding of plant hormones. The question can be skipped through without answering by pressing the forward arrow. Students could be asked to complete the questions in their book and the activity could be concluded by completion on the IWB. 34


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