Powerpoint photosynthesis,how plants-get-food (1)


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  • 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?
  • Powerpoint photosynthesis,how plants-get-food (1)

    1. 1. How Plants Get Their Food (1)
    2. 2. 2How do plants get their food ? 90.20kg 90.72kg soil soilIn the 17th Century, A Belgian physician, van Helmont, set up anexperiment in which he planted a willow sapling in a weighedamount of soil.The soil was watered but nothing else was added. After 5 years, thetree had gained 74kg in weight but the soil had lost only 52g.van Helmont concluded that the tree had made 74kg of new growthfrom water alone
    3. 3. 3van 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.
    4. 4. 4 FeedingAnimals get their food by eating plants, or other animals Carnivores eat animals Herbivores eat plantsPlants 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 soilThe first stage by which plants make food is called PHOTOSYNTHESIS
    5. 5. Animals get their food … 5 or (c) other animals ... plant by eating products, plants or ...Plants make their food by photosynthesis
    6. 6. 6 PhotosynthesisGreen plants take in carbon dioxide (CO2)from the airThey take up water (H2O) from the soilThe plants combine the CO2 with the H2O tomake the sugar, glucose (C6H12O6) 6CO2 + 6H2O = C6H12O6 + 6O2Oxygen (O2) is a by-product of this reaction
    7. 7. 7 CO2 H2 O CO2 H2 O CO2 H2 O C6H12O6 CO2 H2 O + 6O2 CO2 H2 O CO2 H2 O6 molecules of carbon dioxide combine with 6 molecules of waterto make one molecule of glucose and 6 molecules of oxygen
    8. 8. 9 EnergyIt takes energy to make CO2 combine with H2OThis energy comes from sunlightThe energy is absorbed and used by a substance called chlorophyll
    9. 9. 9carbon sunlightdioxide (energy) water water
    10. 10. 10 ChlorophyllChlorophyll is a green coloured chemicalIt is present in the leaves of green plantsThe chlorophyll in the cells is packaged into tiny structures called chloroplastsThe next slide shows a diagram of leaf cells with their chloroplasts
    11. 11. 11 Leaf cells with chloroplasts cell wallchloroplast nucleus cytoplasm vacuole
    12. 12. All the reactions to combine CO2 and H2O take 12 place in the chloroplast sunlight palisade cell of leaf waterin the chloroplast,carbon dioxide andwater combine tomake sugar carbon dioxide
    13. 13. epidermis 13 palisade cell ( photosynthesis) Cell structure of a leaf The palisade cells are in the uppermost layers of the leaf vessel (carries water)stoma (admits air)
    14. 14. 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
    15. 15. 15What 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 grainsIn darkness the starch is changed back into glucose and transported out of the cell
    16. 16. How Plants Get Their Food (2)(2)How plants get their food
    17. 17. 17 Other FoodGlucose and starch are carbohydratesCarbohydrates can be oxidised during respiration to produce energyPlants need more than carbohydratesThey need proteins for making new cytoplasm and cells for growthTo make proteins plants combine glucose with compounds of nitrogen, (nitrates)
    18. 18. 18 other sugars fruits energye.g. seed germination protein GLUCOSE starch cytoplasm cellulose cell wallsstorage e.g. starch in potato
    19. 19. IonsWhen a salt such as potassium nitrate dissolvesin water it separates into two ions, a potassiumion and a nitrate ion KNO3 K+ + NO3-The potassium ion (K+) carries a positive charge.The nitrate ion (NO3-) carries a negative chargeThese ions move freely and independently in thesoil water and it is in this form that they aretaken up by plants
    20. 20. 19 NitratesNitrate ions are present in the soil, dissolved in waterThe plants take up nitrate ions in the soil waterThe nitrate ions are conducted through the roots to the stem and then to the leavesIn the leaves, the nitrate ions and glucose are combined to make proteinsThis process is called assimilation
    21. 21. 20 Mineral ionsNitrates are not the only ions that plants need to take in from the soilThey need phosphate, sulphate, iron, potassium and magnesium ionsThis is the reason why farmers and gardeners add fertiliser to the soilThese fertilisers usually contain nitrates, phosphates and potassium (NPK)
    22. 22. 21 Effects of fertilisersThese are experimental strips of wheat. Varying amounts andtypes of fertiliser have been added to the soil to see which givethe best plant growth
    23. 23. Average yearly wheat yields from 22 experimental plots 3000 Chemical fertilizer 2500 Farmyard No manure magnesiumKg per hectare 2000 No phosphate 1500 No No 1000 manure nitrate 500 0
    24. 24. 23TO SUM UPPlants combine carbon dioxide from the air, and waterfrom the soil to make glucose.The energy needed for this process comes from sunlightThe sunlight is absorbed by chlorophyll contained in thechloroplasts of the leaf.The glucose can be used for energy or to make othersubstances.To make other substances, the glucose must be combinedwith other chemical elements such as nitrogen andpotassium.These chemical elements are present as ions in the soiland are taken up in solution by the roots.
    25. 25. 24 QUESTIONSIn the questions which follow, choose the best answer from the four alternatives
    26. 26. 25 Question 1For a plant to make glucose it needs(a) CO2 and H2O(b) CO2, H2O and sunlight(c) CO2, H2O, sunlight and chlorophyll(d) CO2, H2O, sunlight, chlorophyll and nitrates
    27. 27. 26 Question 2A by-product of photosynthesis is(a) Water vapour(b) Oxygen(c) Carbon dioxide(d) Nitrogen
    28. 28. 27 Question 3The plant needs to take in nitrate ions in order to make(a) Protein(b) Cellulose(c) Starch(d) Sugars
    29. 29. 28 Question 4Chlorophyll is present only in(a) The cytoplasm(b) The vacuole(c) The cell wall(d) The chloroplasts
    30. 30. 29 Question 5The food made by photosynthesis is transported round the plant in the form of(a) Glucose(b) Sucrose(c) Starch(e) Cytoplasm
    31. 31. 30 Question 6Which mineral ions are needed for making protein?(a) Magnesium ions(b) Sulphate ions(c) Phosphate ions(d) Nitrate ions
    32. 32. 31Incorrect
    33. 33. 32Correct