Presentation on theme: "How Plants Get Their Food (1)"— Presentation transcript:
1 How Plants Get Their Food (1) 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
2 How do plants get their food ? 2How do plants get their food ?90.20kg soil90.72kg 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 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 Feeding Animals get their food by eating plants, or other animals 4Animals get their food by eating plants, or other animalsCarnivores eat animalsHerbivores eat plantsPlants make their own foodThey combine carbon dioxide from the air with water and dissolved salts from the soilPlants do NOT get their food from the soilThe first stage by which plants make food is called PHOTOSYNTHESISMost 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).
5 Animals get their food … 5by eatingplants or ...or (c) other animals... plantproducts,Plants make their food by photosynthesis
6 Photosynthesis Green plants take in carbon dioxide (CO2) from the air 6PhotosynthesisGreen 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)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 photosynthesis6CO H2O = C6H12O O2Oxygen (O2) is a by-product of this reaction
7 6 molecules of carbon dioxide combine with 6 molecules of water 7CO2H2OCO2H2OH2OCO2C6H12O6CO2H2OCO2+H2OCO2H2O6O2This reaction is summarised by the equation6CO2 + 6H2O = C6H12O6 + 6O26 molecules of carbon dioxide combine with 6 molecules of waterto make one molecule of glucose and 6 molecules of oxygen
8 Energy It takes energy to make CO2 combine with H2O 9EnergyIt takes energy to make CO2 combine with H2OThis energy comes from sunlightThe energy is absorbed and used by a substance called chlorophyllWithout 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
9 carbon sunlight dioxide (energy) water 9 The carbon dioxide comes from the air.The water comes from the soil.The energy comes from sunlight.water
10 Chlorophyll Chlorophyll is a green coloured chemical 10ChlorophyllChlorophyll 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 chloroplastsIt is not only the leaves that contain chlorophyll; any green part of a plant, leaves, leaf stalk, stem, sepals will contain chloroplasts.
11 Leaf cells with chloroplasts 11cell wallchloroplastnucleusThese 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 cellcytoplasmvacuole
12 All the reactions to combine CO2 and H2O take place in the chloroplast 12sunlightpalisade cellof leafwaterin the chloroplast,carbon dioxide andwater combine tomake sugarThe 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.carbon dioxide
13 Cell structure of a leaf 13epidermispalisade cell ( photosynthesis)Cell structure of a leafThe palisade cells are in theuppermost layers of the leafvessel (carries water)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.stoma (admits air)
14 Carbohydrates Glucose is one example of a carbohydrate 14CarbohydratesGlucose is one example of a carbohydrateOther examples are starch, sucrose and cellulose (in cell walls)Carbohydrate molecules contain the elements carbon, hydrogen and oxygenLiving organisms can easily change one carbohydrate into anotherThe chemistry of carbohydrates is dealt with in the section ‘Chemicals of Living Cells’.
15 What happens to the glucose? 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 plantor(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 cellBefore it is transported, glucose is converted to sucrose. Two glucose molecules combine to make a molecule of sucrose.2C6H12O6 = C12H22O H20glucose sucroseIt is the sucrose which is transported throughout the plant
16 How Plants get their Food (2) Pyracantha. Some of the food made in the leaves is sent to the berries
17 Other Food Glucose and starch are carbohydrates 17Other 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)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
18 GLUCOSE 18 fruits other sugars energy protein e.g. seed germination cytoplasmstarchcellulosecell wallsstorage e.g. starch in potato
19 IonsWhen a salt such as potassium nitrate dissolves in water it separates into two ions, a potassium ion and a nitrate ionKNO K+ + NO3-The potassium ion (K+) carries a positive charge. The nitrate ion (NO3-) carries a negative chargeThese 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 19NitratesNitrate 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 assimilationProteins are needed for making the cell structures, e.g. cytoplasm, nucleus, chloroplasts.The plant can grow only by making new cells and cell structuresStrictly 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.KNO3 becomes K+ and NO3- The plant may take up either or both of these ions.
21 20Mineral 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)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.
22 Effects of fertilisers 21Some 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 yearsThese 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
23 Average yearly wheat yields from experimental plots 22The 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?
24 The energy needed for this process comes from sunlight 23TO SUM UPPlants combine carbon dioxide from the air, and water from the soil to make glucose.The energy needed for this process comes from sunlightThe 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.
25 QUESTIONS In the questions which follow, choose the best 24QUESTIONSIn the questions which follow, choose the bestanswer from the four alternatives
26 Question 1 For a plant to make glucose it needs (a) CO2 and H2O 25For 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, chlorophylland nitrates
27 Question 2 A by-product of photosynthesis is (a) Water vapour 26Question 2A by-product of photosynthesis is(a) Water vapour(b) Oxygen(c) Carbon dioxide(d) Nitrogen
28 Question 3 The plant needs to take in nitrate ions in order to make 27Question 3The plant needs to take in nitrate ions in order to make(a) Protein(b) Cellulose(c) Starch(d) Sugars
29 Question 4 Chlorophyll is present only in (a) The cytoplasm 28Question 4Chlorophyll is present only in(a) The cytoplasm(b) The vacuole(c) The cell wall(d) The chloroplasts
30 Question 529The food made by photosynthesis is transported round the plant in the form of(a) Glucose(b) Sucrose(c) Starch(e) Cytoplasm
31 Question 6 Which mineral ions are needed for making protein? 30Question 6Which mineral ions are needed for making protein?(a) Magnesium ions(b) Sulphate ions(c) Phosphate ions(d) Nitrate ions