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How plants-get-food
- 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 2 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. 90.72kg soil 90.20kg soil
- 5. Animals get their food … Plants make their food by photosynthesis 5 by eating plants or ... ... plant products, or (c) other animals
- 6. 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 6O 2 + 6 molecules of carbon dioxide combine with 6 molecules of water to make one molecule of glucose and 6 molecules of oxygen 7 CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 H 2 O H 2 O H 2 O H 2 O H 2 O H 2 O
- 9. 9 sunlight (energy) water water carbon dioxide
- 11. cell wall nucleus chloroplast cytoplasm vacuole 11
- 12. 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 13 epidermis palisade cell ( photosynthesis) vessel ( carries water) stoma ( admits air )
- 16. How plants get their food (2) How Plants get their Food (2) How Plants Get Their Food (2)
- 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 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 KNO 3 K + + NO 3 -
- 22. 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. 22
- 25. QUESTIONS In the questions which follow, choose the best answer from the four alternatives 24
Editor's Notes
- Notice how little the leaves overlap each other. This enables them to trap the maximum amount of sunlight. the importance of this will be explained later in the presentation
- Most fungi and bacteria get their food by breaking down organic matter, such as plant and animal remains (detritus). They then absorb the soluble breakdown products. These organisms are called detritivores . The name ‘Photosynthesis’ is derived from ‘photo’ (light) and ‘synthesis’ (building up). Plants synthesize their food with the aid of sunlight. (Slides 9 and 10).
- When a plant is photosynthesising, it is taking in carbon dioxide and giving out oxygen. Plants which live in ponds, streams etc. are immersed in the water they need for photosynthesis
- This reaction is summarised by the equation 6CO 2 + 6H 2 O = C 6 H 12 O 6 + 6O 2
- Without sunlight, photosynthesis could not take place. Without photosynthesis, plants could not survive. Without plants, most animals would die out because, ultimately, animals depend on plants for their food. e.g. sunlight >>>> plants >>>> herbivores >>>> carnivores
- The carbon dioxide comes from the air. The water comes from the soil. The energy comes from sunlight.
- It is not only the leaves that contain chlorophyll; any green part of a plant, leaves, leaf stalk, stem, sepals will contain chloroplasts.
- These are called palisade cells and they are present in the upper layers of a leaf where most sunlight is absorbed. The chloroplasts are present in the cytoplasm lining the cell
- The water travels from the roots, through the stem and into the leaf in a system of vessels. The carbon dioxide diffuses into the leaf through tiny pores called stomata.
- The palisade layer traps most of the sunlight. The vessel carries water from the stem to the leaf. Carbon dioxide enters through the stoma and diffuses through the air spaces between the cells.
- The chemistry of carbohydrates is dealt with in the section ‘Chemicals of Living Cells’.
- Before it is transported, glucose is converted to sucrose. Two glucose molecules combine to make a molecule of sucrose. 2C 6 H 12 O 6 = C 12 H 22 O 11 + H 2 0 glucose sucrose It is the sucrose which is transported throughout the plant
- Pyracantha. Some of the food made in the leaves is sent to the berries
- Carbohydrates may be (a) oxidised to provide energy for chemical reactions. (b) turned into starch and stored in storage organs such as potatoes and parsnips. (c) turned into cellulose which builds the cell walls. (d) Combined with nitrogen (from nitrates) to make amino acids , which are combined to make proteins
- Proteins are needed for making the cell structures, e.g. cytoplasm, nucleus, chloroplasts. The plant can grow only by making new cells and cell structures Strictly speaking, it is not nitrates salts that are taken up but nitrate ions. When a salt such as potassium nitrate, is dissolved in water it splits into positively charged potassium ions and negatively charged nitrate ions. KNO 3 becomes K + and NO 3 - The plant may take up either or both of these ions.
- Nitrates are needed for making proteins. Phosphates are needed for DNA and for chemical reactions involving energy release. Sulphates are needed for some proteins. Iron is needed for certain enzyme reactions. Magnesium is needed for making chlorophyll.
- Some of these plots have received different types of fertiliser. Some have had only manure added to the soil. Some had neither manure nor fertiliser for many years
- The chemical fertilizer contains all the mineral ions needed by the plants. The other fertilizers are lacking in one of the essential ions. Which of these mineral ions appears to be the most important?