OCR GCSE Science 7.2 Photosynthesis PDF

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TLR RL SRE TIN ses hes a 1] TNE GT CEN 20 hie j : we Pie No RICH S » NE En, A te 3 / Be TLE Ca Clu » ‘ od dy. ! ox “Fr v ; “ - ’ AL y 0 y. We need to take in food for obtaining energy and for growth. Walth a vite However, most plants do not eat. How do they get their food? and answer the questions. [ Plants make food by photosynthesis Plants can make their own food by photosynthesis". Photosynthesis mainly occurs in the leaves of the plants. Green leaf cells contain chloroplasts”. Inside chloroplasts, a green pigment” called chlorophyll”* absorbs light energy for the process (Fig 7.4). a chloroplast (contains chlorophyll) a green leaf cell Fig 7.4 Chloroplasts in green leaf cells TTT TT rrr EE TTR Ee nn ITT TT ITT TTT TT I OT a a a a EE 14 Sricioevhiliets %&{ERA chloroplast #4588 pigment 2% chlorophyll 4% %  Photosynthesis The light energy absorbed by chlorophyll is used to change carbon dioxide and water into food (glucose”). At the same time, oxygen is produced as a by-product” (Fig 7.5). In the process, light energy absorbed by chlorophyll is converted to chemical energy in food. light energy — from the sun carbon dioxide 3 ar B ya Sag TG used to produce PLT Fo useful substances e.g. proteins™, chlorophyll All living things, including » chlorophyll plants, are mainly made up of carbon- containing chemicals (e.g. carbohydrates”, proteins). Carbon dioxide taken up for oxygen (by-product) — r e l e a s e d i n t o ai r photosynthesis is the source of carbon in these compounds. : RR Te} products of ~ pho t o s y n t h e s i s - Fig 7.5 The process of photosynthesis AS Link The process of photosynthesis is an example of chemical change’. You will learn more It is a change in which one or more new substances are formed. In about chemical change and physical change in photosynthesis, the new substances formed are food (glucose) and Bk 3B, Unit 13. oxygen. They are the products of this chemical change. The raw materials consumed in a chemical change (e.g. carbon dioxide and water used in photosynthesis) are called reactants’. A A physical change” is a change in which no new substance is formed. It does not involve a change in chemical composition. For example, water changes from liquid to gas during evaporation, but no new substance is formed in the process. EE LL LL LE EE I I I EE ER glucose WEE by-product BlZEmm product £X¥) carbohydrate fix7/kK{L&¥ protein ERE 15 chemical change {£2 #{t reactant RFE¥) physical change #32 #1k  Photosynthesis involves a series of chemical reactions. The equations” below summarize the process of photosynthesis. Word equation” : | light energy eH CalIDOIl = | PS n% a AlOX1AcC J 5 “\"1 al Y —p chlorophyll + (ovgen) reactant reactant product by-product the substances undergoing the reaction the substances produced in the reaction (raw materials used in photosynthesis) (new substances formed in photosynthesis) AS Link Chemical equation” You will learn more about writing chemical equations in Bk 3B, Unit 13. In the chemical equation above: e The substances are represented by chemical formulae”. The chemical formula indicates the type and number of atoms in the molecule. e The numbers before the chemical formulae represent the ratio of different types of molecules involved in the reaction. Carbon dioxide Chemical formula carbon oxygen hydrogen oxygen atom ? QQ g0 Substance and a molecular model T A carbon dioxide A water molecule is A glucose molecule is An oxygen molecule is molecule is made up made up of 2 hydrogen | made up of 6 carbon made up of 2 oxygen of 1 carbon atom and atoms and 1 oxygen atoms, 12 hydrogen atoms. | 2 oxygen atoms. atom. atoms and 6 oxygen 3 atoms. 16 equation RFE word equation X FR MEX chemical equation {LRM chemical formula {£53  I Tran NTPs omy on Photosynthesis Some of the glucose produced in photosynthesis is used by the plant. * to provide energy immediately. Others are converted into starch and stored in green leaf cells for later use. Hence, starch is also considered a product of photosynthesis. “Go further. (¢] Glucose and starch Glucose is a kind of sugar. It is soluble in water and tastes sweet. Foods like grapes and honey are rich in glucose. Starch is insoluble in water and it does not taste sweet. Foods like rice and potato are rich in starch. Fig 7.6 Grapes are rich in glucose Fig 7.7 Rice is rich in starch Key point * Plants make their own food by a process called pho St nih e615. During the process, they change Chon diowde and __ oXygerv into food (glucose) using light energy. During photosynthesis, li ght energy is converted to Clem 17% energy in food. e Word equation of photosynthesis: gy energy light ener Cocoon dioxide + wiley loopy hod Glucose)t OXYgor e Chemical equation of photosynthesis: 600, + 61,0 CHG +. 66 e Glucose produced in plants during photosynthesis can be used immediately for energy or stored as Starch for later use.  (33 Tests for the products of photosynthesis We cannot see photosynthesis happen. How do we know whether a plant has carried out photosynthesis? We can test whether the products of photosynthesis (i.e. starch and oxygen) are produced in the plant. If either of them is produced, we can infer that photosynthesis has occurred in the plant. ® Practical 7.3 \ Test for starch in a green leaf Aim To test for starch produced in a green leaf during photosynthesis Apparatus and materials per group boiling tube 1 tripod 1 beaker (250 cm?) 1 wiré gauze 1 forceps 1 pair potted plant with green leaves 1 | glass rod 1 gas lighter 1 spot plate 1 starch solution white tile 1 iodine solution e Wear disposable gloves. | Bunsen burner 1 distilled water o NBER TE RAUTEDLL vovssvre | insulating mat 2 alcohol (70%) Avoid contact with skin. Part | lodine test 1 Add a drop of iodine solution into a well on a spot plate. 2 Add two drops of starch solution into the same well. Observe and record the colour change of the iodine starch: iodine solution solution. solution 3 Add a drop of iodine solution into another well. Add two drops of distilled water into the same well. Observe and record the colour change of the iodine solution. \ Results Original colour of Colour of iodine solution after mixing with... iodine solution Go — Hack 18  Photosynthesis Part Il Test for starch in a green leaf 1 Your teacher will give you a potted plant. The plant has been put under sunlight for several hours. Pick a green leaf from the plant. 2 Boil the leaf in water for 10 minutes. This destroys the cell membranes of the leaf cells, so that alcohol and iodine solution (to be added later) can get into the cells. A Refer to Skill reminder 4 Alternatively, a hotplate on p. 193 for how to use a can be used to boil the Bunsen burner. leaf. Bunsen——— no.) Wear safety spectacles! burner | turned on | Caution Be careful of the hot apparatus and water. 3 Turn off the Bunsen burner. Your teacher will help you move the hot beaker onto an insulating mat. 4 Fill a boiling tube with alcohol until it is one-third full. Use a pair of forceps or a glass rod to put the leaf into the boiling tube. ad Alcohol is flammable. Use the smallest volume as far as possible. Ensure the room is well-ventilated. alcohol # Use it only in the absence of beakeron naked flame. insulating mat a hot water 5 Put the boiling tube into the beaker of hot water for 10 minutes. This dissolves chlorophyll from the leaf cells, so that any colour change of the leaf will not be masked” by its green colour. 4 The alcohol turns green ___— hot water because it dissolves the chlorophyll from the leaf cells. LL LEE EL ET TR  6 Use a pair of forceps or a glass rod to transfer the leaf from the boiling tube to the hot water again. This removes the remaining alcohol from the leaf and makes the leaf soft. a CS - hot water 7 Use a pair of forceps to take the leaf out of the hot water and spread it on a white tile. Record the colour of the leaf. white tile 8 Add 10 drops of iodine solution to the leaf to test for starch. Record the colour change of the leaf. Caution i =) San lodine is harmful. a Avoid contact with skin. Results Before adding iodine solution After adding iodine solution Colour of the leaf J hi To / P ale ORL Glue - X " Discussion What do the results show? ST, Gir Li is present in the leaf. 20  Photosynthesis » Practical 7.4 Test for oxygen produced during photosynthesis (Teacher demonstration) Aim To test for oxygen produced in green water plant during photosynthesis B—— | Apparatus and materials per class test tube 1 table lamp 1 | beaker (1000 cm?) 1 green water plant (e.g. Hydrilla™) 1 | filter funnel 1 gas lighter 1 stopper 4 dilute sodium hydrogencarbonate® solution | wooden splint 1 1 Your teacher will prepare the set-up below. Sodium hydrogencarbonate breaks down to form carbon dioxide. It provides the water plant with carbon dioxide for carrying out photosynthesis. test tube dilute sodium hydrogencarbonate solution filter funnel water plant (cut end of the stem facing upwards) stopper 2 Leave the set-up in bright light for at least 24 hours. Observe what happens to the set-up. What do you observe on the leaves of the water plant? (os bubbles IA Formed Oh He leawes. 3 When there is enough gas collected in the test tube, remove the test tube carefully and stopper the test tube under water. Oo oO Skill tips To avoid escape of any gas collected inside the test tube, move the test tube carefully to a position where it can be stoppered under water. TTT NT LLL rr EN NRRL RRL LR rrr EE EEE EERE RE Hydrilla 23% sodium hydrogencarbonate 5x& $4  LIA pf 2WBe L Jdeas yi Lt aJow lev 4 Prepare a glowing splint. Remove the stopper of the test tube and put the glowing splint into the tube immediately. Observe what happens to the glowing splint. me Wear safety spectacles! ) gas collected Results What happens to the glowing splint when it is put into the test tube? The glowing splint rel igh : Discussion What does the result show? The plant produced XY en during photosynthesis. Key point eo Jodine solution can be used to test for starch. It turns from brown to blue-black in the presence of starch. “e Steps of testing for starch in a green leaf and their purposes: 1 Boil the leaf in Destroy the cell membranes of the water. leaf cells. This allows alcohol and iodine solution to get into the cells. | 2 Put the leaf into Dissolve chlorophyll from the leaf hot alcohol. cells so that the colour change can be observed. Remove the remaining alcohol from the leaf and make the leaf soft. | Test for starch. 22  Photosynthesis C Investigating the necessary factors for photosynthesis In Practical 7.5 to 7.7, we will do experiments to investigate the factors necessary for photosynthesis. Before the experiments, we have to destarch the plants to ensure any starch detected at the end of the experiments is made during the experiments. ; How can we confirm We can do this by putting the plants in the dark for at least 24 hours. * thata plant is This is called destarching. During destarching, all the starch in the * destarched? leaves is broken down to glucose for use, or is converted to other substances and transported out of the leaves (Fig 7.8). transported out of the leaf dark environment Fig 7.8 Some starch is converted to other substances and transported out of the leaves during destarching ® Practical 7.5 Investigating whether light is necessary for photosynthesis Aim To find out whether light is necessary for photosynthesis =] Apparatus and materials per group | | li boiling tube 1 insulating mat 2 gas lighter 1 «Video ; beaker (250 cm?) 1 tripod 1 potted plant with green forceps 1 pair wire gauze 1 leaves Le glass rod 1 SCiSSOrs : 1 pair aluminium foil white tile 1 paper clip 1 iodine solution Bunsen burner 1 table lamp 1 alcohol (70%) | — er ——— LLL LL LLL LLL EE EL LEE hhh bhi RE EE EE JT destarching At 17 23  Setting a question Is light necessary for photosynthesis? Identifying variables Independent variable | Presence of light Controlled variables Supply of carbon dioxide Presence of chlorophyll Supply of oxygen Supply of light > Supply of water Temperature Carrying out the experiment 1 Your teacher will give you a destarched plant. Pick a leaf from the plant. 2 Carry out iodine test to test for starch in the leaf (see Practical 7.3). Caution e Wear disposable gloves. PEE EEE RR RR EE I I R, e lodine is harmful. Avoid contact with skin. -««ccoceeeeeeeiinnnns e Alcohol is flammable. Use the smallest volume as far as possible. -------euennnnn... Ensure the room is well-ventilated. Use it only in the absence of naked flame. —— EE ——— Caution 3 Use a piece of aluminium foil to wrap part of a The scissors are very sharp. Handle them leaf on the plant. The wrapped part is not exposed wit h care. to light. It is the control set-up". Draw a labelled ~~ « A control set-up is used to ensure diagram of the leaf in the space on the next page that any change observed in the experimental set-up is due to the factor to show which parts of the leaf are exposed to under investigation but not other light ant wiviehi part is not. factors. Refer to Skill builder 7.1 on p. 26 for details. 4 Leave the plant in bright light for four hours. aluminium foil sen A Pr PTT PRP EE EER EE EL EER EER EE rp TLL LE EE EE EE A RL ERA ARLE EARL ERA LEER EE ET RT TE SIR I RY Teeter sveannine 24 control set-up HIRE E  Photosynthesis ) 5 Pick the leaf wra ppe d with alu min ium foil from the plan t. Rem ove the alu min ium foil from the leaf. 6 Carry out iodine test to test for starch in the leaf (see Practical 7.3). Draw a labelled diagram in the space below to show the result. Recording the results Wrapped and exposed parts of the leaf Result of the iodine test ~expaeh fo |gh blye ~ bl sk Discussion 1 What is the purpose of destarching the plant before the investigation (step 1)? To ensure any starch detected at the end of the experiment is made during the experiment. What is the purpose of carrying out iodine test after destarching the plant (step 2)? To test for Starch in the leaf to make sure that it is absent in the leaf. Explain the result of the iodine test (step 6). In the iodine test, the exposed parts of the leaf wn blue ~bJacke while the wrapped part remaihs hrowp. This shows that the exposed parts produced strech while the wrapped part did not. Drawing a conclusion Light is Nees y (necessary / not necessary) for photosynthesis. 25  L Skill builder 7.1 Designing control set-ups We often include a control set-up in an experiment. The control set-up -- Experimental set-up is identical to the experimental exposed to light set-up except that the factor under @-- Control set-up investigation is absent. It is important not exposed to light for ensuring that any change observed (the factor under investigation is absent) in the experimental set-up is due to : : J EN Fig 7.9 Experimental set-up and control set-up in the factor under investigation but not Practical 7.5 | other factors. destarched green leaf A C D boiling tube without green leaf rr wrapped with aluminium foil 1”). a leaf without chlorophyll ws green leave Check your answers (p.i38) i | a ms, i SO 26  Photosynthesis » Practical 7.6 Investigating whether chlorophyll is necessary for photosynthesis Aim To find out whether chlorophyll is necessary for photosynthesis Apparatus and materials per group boiling tube 1 Bunsen burner 1 table lamp 1 beaker (250 cm’) 1 insulating mat 2 potted plant with variegated forceps 1 pair tripod 1 leaves™ (e.g. Coleus™) 1 glass rod 1 wire gauze 1 iodine solution white tile 1 gas lighter 1 alcohol (70%) — — Your teacher will give you a destarched potted plant with variegated leaves (Fig 7.10). The green parts of the gt r leaves contain chlorophyll while the non-green parts do not. Setting a question Is necessary for photosynthesis? Identifying variables Fig 7.10 Variegated leaves of Coleus Controlled variables Supply of carbon dioxide [| Presence of chlorophyll ~~ [| Supply of oxygen [] Supply of light L] Supply of water | | Temperature L] Carrying out the experiment 1 Pick a leaf from the potted plant with variegated leaves. The plant has been before the 4A Caution praga | ° W ear disposablele glgl oves ; experiment. |odine is harmful. Avoid | contact with Skin. «eeeveeeens 2 Carry out iodine test to test for e Alcohol is flammable. Use in the leaf. the smallest volume as far as possible. Ensure the room is well-ventilated. Use it only in the absence of naked flame. ---ecveeene PEt Perr e rete irene eres ene seestereaseesseseteiecreereeteaeteraaciaeie eset acteseeeseeeenetetteetereetaeseerietetetteteettrNeeeertttatcitstatteetanIeesNt een TIIet atta TRASASIStItATItItaNTAteAIIIRARARRACTRTARIRRRRARRRARRIRRRRRAY - variegated leaf BIZ Coleus + %&#k 27  3 Leave the plant in bright light for four hours. 4 Pick a leaf from the plant. Draw a labelled diagram to show the colour pattern of the leaf. 5 Carry out iodine test to test for ' in the leaf. Draw a labelled diagram to show the result of the test. Recording the results Colour pattern of the leaf Result of the iodine test Discussion 1 What is the control set-up in this investigation? Explain your answer. The part of the leaf is the control set-up. This is because this part does not contain 2 Explain the result of the iodine test (step 5). In the iodine test, the green part of the leaf while the non-green part. This shows that the green part produced while the non-green part did not. Drawing a conclusion St IEE © Chlorophyll is poo=% 28  Photosynthesis » Practical 7.7 Investigating whether carbon dioxide is necessary for photosynthesis Aim To find out whether carbon dioxide is necessary for photosynthesis Apparatus and materials per group boiling tube 1 insulating mat 2 potted plant with green | beaker (250 cm?) 1 tripod 1 leaves 1 | spatula 1 wire gauze 1 iodine solution | forceps 1 pair transparent plasticbag ~~ 2 soda lime® | glass rod 1 cotton thread 2 alcohol (70%) | White tile 1 gas lighter 1 Bunsen burner 1 table lamp 1 Your teacher will give you some soda lime (Fig 7.11). It can be used to absorb carbon dioxide from the air. () Wear safety spectacles! a Caution Wear disposable gloves. lodine is harmful. AVOIdcOREACt WIN ims iiss ss SKIN. means ‘eaten by’ POIs io he ling ~ inariveran water plant — fish — bird thing being eaten to i A aE aE I aaa the living thing that eats it. Did you notice that both food chains start with plants? Most food chains start with plants because plants can make their own food. They are called producers”. Animals that feed on plants or other animals are called consumers” in food chains. A TT I I I I I IIT er I EE TT IE 52 grassland iff food chain E¥)% producer £Z&# consumer JH##H  PhotosyntheslS Activity 7.1 Constructing a food chain The diagram below shows four living things in a forest. Construct a food chain consisting of these living things. Identify the producer and consumers in the food chain. free 3 ger ond alert wal ¢ Tree 3 | aa a — N El - Br Key point Plants are the | p roduceys and animals are the _ Lorbwmers in most food chains. er. 2 v % ' ‘ a v w ha ~ 2 Supplying oxygen A Link You will learn Most living things on Earth need oxygen to survive. Plants produce more about this in oxygen as a by-product during photosynthesis. The oxygen produced Section 7.5. is released into the atmosphere and used by other living things. Key point 33  Producers in the ocean Besides plants, algae™ and some bacteria* containing chlorophyll also make their own food. They are the major producers in the ocean. Most of them are very small and can only be seen under microscopes. Apart from providing food for animals in the ocean, they also produce more than half of the oxygen on Earth. big H » Fig 7.14 Algae under light microscope (x40) i 5 CC LOT SUT TL ES SAA S 1 Plants make their own food by photosynthesis. During the process, light energy is used to change carbon dioxide and water into food (glucose). 2 During pho tos ynt hes is, ligh t ene rgy is con ver ted to che mic al ene rgy in food. 3 Word equation of photosynthesis: carbon dioxide + water Agni energy, food (glucose) + oxygen chlorophyll 34 Chemical equation of photosynthesis: 6 CO,+ 6 HO — CH 1,04 + 6 O, 5 Glucose pro duc ed in plan ts dur ing pho tos ynt hes is can be used imm edi ate ly for ene rgy or stor ed as starch for later use. 6 Light, chlorophyll, carbon dioxide and water are the necessary factors for photosynthesis. @7 Plants are the producers and animals are the consumers in most food chains. 8 Significance of photosynthesis to other living things: » providing a source of energy through converting light energy to chemical energy; * supplying oxygen. Sestasssassaunnansansnuie TL Ll I LT LT TTT TT PT PT PPpprrprrrrrererrereopsererprery YY TY SF TERI V IR 22 RE 2 RIT RIT S IR ARPA YR PRAT R ILL SL AAA Adon didndumadbbdbididtadid ddd idl III IT ITV TRR INTIS SZ AL dll ili ly PTI LL TT PPErr FER TT EEPry PPP  Photosynthesis OT TT RE De — Questions 1 to 3: Write ‘“T’ for a true statement and ‘F’ for a false statement in the boxes provided. 1 Photosynthesis occurs in all cells in a plant. ¢ 0. 14 2 In an investigation on whether chlorophyll is necessary for photosynthesis, the green part of a variegated leaf is the control set-up. [] &p. 28 @3 Humans are consumers in food chains. T] &p. 32 4 A destarched plant was placed under a lamp for six hours. A leaf of the plant was then tested for starch using iodine solution. a How should the plant be destarched? (1 mark) Pd 1. plot ih Ho dark for 2U hours. &p. 23 b Before iodine solution was added to the leaf, the leaf was boiled and then put in hot alcohol. What is the purpose of putting the leaf in hot alcohol? (1 mark) To dissolve CMorophy | fram, fle leat cells soe Hour hinge, Lan be serve]. ¢€p. 19 ¢ What is the expected result of the test? Explain your answer. - (2 marks) Ilo 2% ond fury blue bli k be omnst a Jprit trried out Ls $ illes rs rd proqmoed. STardyin fle presence a Mt. @®5 Oxpeckers™ (a bird) feed on the blood of buffalos, and buffalos feed on grass. Construct a food chain among these three OXpecker — living things. Circle all the consumers in your food chain. V4 grass —bufly|os —0 xpecke rs (3 marks) cS & p. 32 oxpecker B45