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How Plants Get Their Food (1). How do plants get their food ? The soil was watered but nothing else was added. After 5 years, the tree had gained 74kg.

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Presentation on theme: "How Plants Get Their Food (1). How do plants get their food ? The soil was watered but nothing else was added. After 5 years, the tree had gained 74kg."— Presentation transcript:

1 How Plants Get Their Food (1)

2 How do plants get their food ? The soil was watered but nothing else was added. After 5 years, the tree had gained 74kg in weight but the soil had lost only 52g. van Helmont concluded that the tree had made 74kg of new growth from water alone kg soil In the 17th Century, A Belgian physician, van Helmont, set up an experiment in which he planted a willow sapling in a weighed amount of soil kg soil

3 van Helmont’s experiment was effective in showing that the plant’s food did not come from the soil. But he had overlooked the fact that air was available to the plant as well as water. Could it be that the plant made 74kg of material from just air and water? This might seem unlikely but we now know that plants do indeed make their food from carbon dioxide from the air and water from the soil. 3

4 Feeding Animals get their food by eating plants, or other animals Carnivores eat animals Herbivores eat plants Plants make their own food They combine carbon dioxide from the air with water and dissolved salts from the soil Plants do NOT get their food from the soil The first stage by which plants make food is called PHOTOSYNTHESIS 4

5 Animals get their food … by eating plants or plant products, or (c) other animals Plants make their food by photosynthesis 5

6 Photosynthesis 6 Green plants take in carbon dioxide (CO 2 ) from the air They take up water (H 2 O) from the soil The plants combine the CO 2 with the H 2 O to make the sugar, glucose (C 6 H 12 O 6 ) 6CO 2 + 6H 2 O = C 6 H 12 O 6 + 6O 2 Oxygen (O 2 ) is a by-product of this reaction

7 C 6 H 12 O 6 CO 2 H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O 6O molecules of carbon dioxide combine with 6 molecules of water to make one molecule of glucose and 6 molecules of oxygen 7

8 Energy It takes energy to make CO 2 combine with H 2 O This energy comes from sunlight The energy is absorbed and used by a substance called chlorophyll 9

9 sunlight (energy) water carbon dioxide 9

10 Chlorophyll Chlorophyll is a green coloured chemical It is present in the leaves of green plants The chlorophyll in the cells is packaged into tiny structures called chloroplasts The next slide shows a diagram of leaf cells with their chloroplasts 10

11 Leaf cells with chloroplasts cell wall nucleus chloroplast cytoplasm vacuole 11

12 All the reactions to combine CO 2 and H 2 O take place in the chloroplast sunlight water carbon dioxide in the chloroplast, carbon dioxide and water combine to make sugar 12 palisade cell of leaf

13 Cell structure of a leaf The palisade cells are in the uppermost layers of the leaf epidermis palisade cell ( photosynthesis) vessel (carries water) stoma (admits air) 13

14 Carbohydrates Glucose is one example of a carbohydrate Other examples are starch, sucrose and cellulose (in cell walls) Carbohydrate molecules contain the elements carbon, hydrogen and oxygen Living organisms can easily change one carbohydrate into another 14

15 What happens to the glucose? The glucose made by the chloroplast is either (a) used to provide energy for the chemical processes in the cell (by respiration) (b) turned into sucrose and transported to other parts of the plant or (c) turned into starch and stored in the cell as starch grains In darkness the starch is changed back into glucose and transported out of the cell 15

16 How plants get their food (2) How Plants get their Food (2) How Plants Get Their Food (2)

17 Other Food Glucose and starch are carbohydrates Carbohydrates can be oxidised during respiration to produce energy Plants need more than carbohydrates They need proteins for making new cytoplasm and cells for growth To make proteins plants combine glucose with compounds of nitrogen, (nitrates) 17

18 GLUCOSE storage e.g. starch in potato starch fruits other sugars e.g. seed germination energy cytoplasm protein cell walls cellulose 18

19 When a salt such as potassium nitrate dissolves in water it separates into two ions, a potassium ion and a nitrate ion Ions KNO 3 K + + NO 3 - The potassium ion (K + ) carries a positive charge. The nitrate ion (NO 3 - ) carries a negative charge These ions move freely and independently in the soil water and it is in this form that they are taken up by plants

20 Nitrates Nitrate ions are present in the soil, dissolved in water The plants take up nitrate ions in the soil water The nitrate ions are conducted through the roots to the stem and then to the leaves In the leaves, the nitrate ions and glucose are combined to make proteins This process is called assimilation 19

21 Mineral ions Nitrates are not the only ions that plants need to take in from the soil They need phosphate, sulphate, iron, potassium and magnesium ions This is the reason why farmers and gardeners add fertiliser to the soil These fertilisers usually contain nitrates, phosphates and potassium (NPK) 20

22 Effects of fertilisers These are experimental strips of wheat. Varying amounts and types of fertiliser have been added to the soil to see which give the best plant growth 21

23 Average yearly wheat yields from experimental plots 22

24 Plants combine carbon dioxide from the air, and water from the soil to make glucose. The energy needed for this process comes from sunlight The sunlight is absorbed by chlorophyll contained in the chloroplasts of the leaf. The glucose can be used for energy or to make other substances. To make other substances, the glucose must be combined with other chemical elements such as nitrogen and potassium. These chemical elements are present as ions in the soil and are taken up in solution by the roots. 23 TO SUM UP

25 QUESTIONS In the questions which follow, choose the best answer from the four alternatives 24

26 Question 1 For a plant to make glucose it needs (a) CO 2 and H 2 O (b) CO 2, H 2 O and sunlight (c) CO 2, H 2 O, sunlight and chlorophyll (d) CO 2, H 2 O, sunlight, chlorophyll and nitrates 25

27 Question 2 A by-product of photosynthesis is (a) Water vapour (b) Oxygen (c) Carbon dioxide (d) Nitrogen 26

28 Question 3 The plant needs to take in nitrate ions in order to make (a) Protein (b) Cellulose (c) Starch (d) Sugars 27

29 Question 4 Chlorophyll is present only in (a) The cytoplasm (b) The vacuole (c) The cell wall (d) The chloroplasts 28

30 Question 5 The food made by photosynthesis is transported round the plant in the form of (a) Glucose (b) Sucrose (c) Starch (e) Cytoplasm 29

31 Question 6 Which mineral ions are needed for making protein? (a) Magnesium ions (b) Sulphate ions (c) Phosphate ions (d) Nitrate ions 30

32 Incorrect 31

33 Correct 32


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