What are plants used for?

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3 What are plants used for? 3 of 48 Boardworks Ltd 2007 How many different uses of plants can you spot?

4 Using plants 4 of 48 Boardworks Ltd 2007

5 How do plants get the food they need? 5 of 48 Boardworks Ltd 2007 All living organisms need food to grow and survive. This is because food provides raw materials for growth and energy for chemical reactions. Plants are known as producers because they provide food for many other organisms. Without plants, other organisms would have no raw materials for growth or energy. Unlike animals, plants cannot move very much, so how do they get the food that they need?

6 Do plants eat soil? 6 of 48 Boardworks Ltd 2007 It used to be thought that plants got their food from the soil. This was proved to be untrue by measuring the mass of the soil in a plant pot before and after growth. The soil did not decrease in mass, even though plant mass increased. Later experiments showed that plants actually make their own food! Plants are the only living organisms that can do this. This means that all other organisms rely on plants. What is the name of the process by which plants make food?

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8 What is photosynthesis? 8 of 48 Boardworks Ltd 2007 Plants make their own food by photosynthesis. This process is a chemical reaction that uses light energy. light energy The word photosynthesis comes from the Greek language: photo means light synthesis means putting together Photosynthesis just means putting together with light.

9 Photosynthesis 9 of 48 Boardworks Ltd 2007

10 Photosynthesis: summary 10 of 48 Boardworks Ltd 2007 How can the process of photosynthesis be summarized in one sentence? Photosynthesis is a chemical reaction that takes place in the chloroplasts of green plant cells, where light energy is used to convert carbon dioxide and water into glucose and oxygen. What is the word equation for this chemical reaction? light energy carbon dioxide + water chlorophyll glucose + oxygen

11 Photosynthesis: word equation activity 11 of 48 Boardworks Ltd 2007

12 12 of 48 Boardworks Ltd 2007 What is the symbol equation for photosynthesis? The reaction of photosynthesis can be represented by the following equation: carbon dioxide + water light energy chlorophyll glucose + oxygen What is the symbol equation for this reaction? light energy CO 2 6 H 2 O C 6 H 12 O 2 6 O 2 chlorophyll Is this a balanced symbol equation? How would you balance the equation?

13 Word equation to symbol equation 13 of 48 Boardworks Ltd 2007

14 Photosynthesis equation quiz 14 of 48 Boardworks Ltd 2007

15 Does photosynthesis change the air? 15 of 48 Boardworks Ltd 2007 The evolution of photosynthesis, hundreds of millions of years ago, was one of the biggest changes to shape the Earth. Photosynthesis by plants caused major alterations to the atmosphere of Earth, turning it from a hot and hostile planet into one suitable for life. It lowered the levels of carbon dioxide in the atmosphere and raised the levels of oxygen, which is used by most organisms for respiration. Oxygen also lead to the formation of the ozone layer, which filters out harmful UV rays.

16 16 of 48 Boardworks Ltd 2007 Why are plants important to climate change? Carbon dioxide is a greenhouse gas. This means it traps heat from the Earth and stops it escaping into space, like a pane of glass in a greenhouse. Burning fossil fuels, increased travel and deforestation have caused atmospheric carbon dioxide levels to rise dangerously high. This is causing the Earth to overheat, melting the ice caps and endangering species. Photosynthesis converts carbon dioxide into storable sugars and oxygen. Planting more trees could help reduce the amount of carbon dioxide in the atmosphere.

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18 How is glucose used? 18 of 48 Boardworks Ltd 2007

19 How can you test for photosynthesis? 19 of 48 Boardworks Ltd 2007 The presence of starch in a leaf can be used to show that photosynthesis has taken place. Iodine is used to test for starch. It reacts with starch and changes colour from brown to blue-black. The starch test can be used to prove that photosynthesis needs light, carbon dioxide and chlorophyll to take place. How would you set up an experiment to test the conditions needed for photosynthesis? How would you make the experiment fair and reliable?

20 Testing leaves for starch 20 of 48 Boardworks Ltd 2007

21 Is chlorophyll needed for photosynthesis? 21 of 48 Boardworks Ltd 2007 Chlorophyll cannot be removed from a plant without killing the plant. Instead, variegated leaves can be used to show chlorophyll is essential for photosynthesis. Variegated leaves have pale parts, which do not contain chlorophyll. The green parts of the leaf contain chlorophyll and are the control. Which areas will react with iodine? Only the green areas of the leaf react with the iodine and turn blue-black. Without chlorophyll, the pale areas have been unable to produce starch and do not turn blue-black.

22 Testing leaves for starch activity 22 of 48 Boardworks Ltd 2007

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24 What is the rate of photosynthesis? 24 of 48 Boardworks Ltd 2007 Photosynthesis is a chemical reaction and so has a rate. Like many reactions, photosynthesis requires enzymes. Is the rate of photosynthesis always the same? Which factors do you think affect the rate of photosynthesis? light carbon dioxide temperature How do these factors affect the rate of photosynthesis?

25 How does light affect photosynthesis? 25 of 48 Boardworks Ltd 2007 Light energy has to be absorbed by chlorophyll for photosynthesis to take place. light energy carbon dioxide + water chlorophyll glucose + oxygen The brighter the light, the more light energy there is, so will photosynthesis be faster or slower? More light energy means that photosynthesis will be faster. If light intensity is too high plant cells can be damaged. How is photosynthesis affected if this happens?

26 Investigating photosynthesis apparatus 26 of 48 Boardworks Ltd 2007

27 Investigation photosynthesis - experiment 27 of 48 Boardworks Ltd 2007

28 Investigation photosynthesis results 28 of 48 Boardworks Ltd 2007

29 29 of 48 Boardworks Ltd 2007 Carbon dioxide and the rate of photosynthesis Carbon dioxide is one of the raw materials used by plants to make their food. light energy carbon dioxide + water chlorophyll glucose + oxygen The concentration of carbon dioxide in the air is actually quite low (0.03%). Why is the concentration of carbon dioxide in commercial greenhouses often raised to about 0.1%? More carbon dioxide means more photosynthesis, so plants make more food and grow more quickly.

30 Does temperature affect photosynthesis? 30 of 48 Boardworks Ltd 2007 Photosynthesis is controlled by enzymes, which usually work best at warmer temperatures. Does increasing the temperature always increase the rate of photosynthesis? If it gets too hot (above 40 C), the enzymes needed for photosynthesis begin to break down and are destroyed or denatured. The rate of photosynthesis decreases or even stops completely.

31 What is a limiting factor? 31 of 48 Boardworks Ltd 2007 What is the ideal combination of factors for the maximum rate of photosynthesis? enough light enough carbon dioxide ideal temperature (not too hot or cold). How does restricting one of these facts affect the rate? If one of the factors is restricted, the rate of photosynthesis will be below the maximum possible rate. The restricted factor controls how quickly photosynthesis occurs and so limits the rate. It is called the limiting factor.

32 Light intensity and photosynthesis 32 of 48 Boardworks Ltd 2007

33 Carbon dioxide and photosynthesis 33 of 48 Boardworks Ltd 2007

34 Temperature and photosynthesis 34 of 48 Boardworks Ltd 2007

35 Limiting factors activity 35 of 48 Boardworks Ltd 2007

36 Limiting factors in a greenhouse 36 of 48 Boardworks Ltd 2007

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38 How do leaves maximise photosynthesis? 38 of 48 Boardworks Ltd 2007 Leaves are the most efficient solar panels on Earth! What does this mean? Like solar panels, leaves convert energy from the Sun into usable chemical energy. Although leaves come in a variety of shapes and sizes, they share certain features that enable the plant to maximize photosynthesis.

39 How are leaves adapted for photosynthesis? 39 of 48 Boardworks Ltd 2007 To increase photosynthesis, leaves have certain key features: thin this allows gases to reach cells easily wide and flat this create a large surface area to absorb as much light as possible veins these carry water to the cells and carry glucose away and also support leaves stomata these are pores on the underside of leaves through which gases move in and out.

40 Structure of a leaf activity 40 of 48 Boardworks Ltd 2007

41 Take a look inside a leaf 41 of 48 Boardworks Ltd 2007

42 How do gases enter and leave plants? 42 of 48 Boardworks Ltd 2007 On the underside of leaves are small holes, or pores, called stomata. A single hole is called a stoma. Each stoma is surrounded by two guard cells. When guard cells gain water, they curve outwards. This opens the stoma, allowing gases in and out. Losing water causes the guard cells to come closer together, closing the stoma. This stops the movement of gases, but also prevents water loss.

43 Leaf adaptations 43 of 48 Boardworks Ltd 2007

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45 45 of 48 Boardworks Ltd 2007 Glossary (1/2) cellulose An insoluble carbohydrate made from glucose. It is used to make cell walls. chlorophyll The green pigment inside chloroplasts that is needed for photosynthesis to take place. chloroplast The plant cell structure where photosynthesis occurs. cuticle A waxy layer on the surface of the leaf that prevents water loss. epidermis A protective outer layer of cells found on the top and underside of leaves. This layer is clear to allow photosynthesis. guard cells A pair of cells that control the opening and closing of a stoma (single hole).

46 46 of 48 Boardworks Ltd 2007 Glossary (2/2) palisade A layer of cells in the leaves, which contain lots of chloroplasts. It is the main site of photosynthesis. photosynthesis The process by which plants use carbon dioxide and water to make glucose and oxygen in the presence of light and chlorophyll. spongy layer A layer of cells that contains large spaces between cells. This allows the diffusion of gases between the stomata and palisade layer. stoma (singular) A single hole on the lower surface of the leaf that allows gases in and out. stomata (plural) Small holes in the lower surface of leaves that allow gases in and out. variegated A leaf containing areas without chlorophyll.

47 Anagrams 47 of 48 Boardworks Ltd 2007

48 Multiple choice quiz 48 of 48 Boardworks Ltd 2007