Presentation on theme: "Unit 1 Communication, Homeostasis and Energy"— Presentation transcript:
1 Unit 1 Communication, Homeostasis and Energy PhotosynthesisUnit 1Communication, Homeostasis and Energy
2 Which process evolved first on Earth – aerobic respiration or photosynthesis? Give reasons for your answerYou are going to present your answer with your reasons to the rest of the class!!Think about it!!! 10 minutes
3 Answer Plants and animals rely on aerobic respiration Requires oxygenOxygen is a by-product of photosynthesisUntil photosynthesis evolved there was no free oxygen in the atmospherePhotosynthesis evolved first!!Answer
4 Test yourself Where in plants does photosynthesis take place? What are the raw materials needed for photosynthesis?What is the energy source for photosynthesis?Draw a flow diagram showing how energy from sunlight is used to produce muscle contractions in your arm.
5 Learning outcomes Define the terms autotroph and heterotroph. State that light energy is used during photosynthesis to produce complex organic molecules.Explain how respiration in plants and animals depends upon the products of photosynthesis.State that, in plants, photosynthesis is a two-stage process taking place in chloroplasts.
6 The importance of photosynthesis Photosynthesis transfers light energy into the chemical potential energy of organic molecules.Photosynthesis releases oxygen from water, so all aerobes depend on photosynthesis for their respiration.
7 Heterotroph and Autotroph an organism that uses an external energy source and inorganic molecules to make complex organic molecules.ChemoautotrophPhotoautotrophHeterotrophOrganism that needs to take in complex organic molecules which act as a source of energy and as usable carbon compounds.
8 Energy in Living Organisms In order to maintain life, organisms need a source of energy.In most organisms this is provided by the oxidation of organic molecules.Autotrophic nutritionSynthesise organic materials from inorganic sources e.g. photosynthesisHeterotrophic nutritionObtained in organic form8
9 Photosynthesis: an outline Photosynthesis (p/s) is the fixation of carbon dioxide and its reduction to carbohydrate, using hydrogen from water
10 Photosynthesis Equations Word equation for photosynthesisLight energyCarbon dioxide + watercarbohydrate + oxygenchlorophyll
18 Chloroplast Structure 3 – 10μm diameterEnvelope of 2 phospholipid membranesStroma = fluid interiorThylakoids are series of flattened sacs, which form stacks (grana) in places
19 Chloroplast function Grana Provides a LSA to hold pigments, electron carriers, and enzymes for light dependent reactions.Photosystems arranged in funnel like structure in thylakoidMembrane of grana holds ATPsynthase (chemiosmosis)
20 Chloroplast Function Stroma Site of light independent reactions (carbon fixation)Contains sugars, organic acids and enzymes for Calvin cycleStore starch grainsLoop DNA – codes for chloroplast proteins
21 Chloroplast Function Lamellae Do not contain chlorophyll Form a network between the grana
22 Learning Outcomes Define the term photosynthetic pigment. Explain the importance of photosynthetic pigments in photosynthesis.State that the light-dependent stage takes place in thylakoid membranes and that the light-independent stage takes place in the stroma.
23 Trapping Light energyThe fate of light which strikes the leaf
24 Trapping the Light Energy The fate of light which strikes the leaf Light shining on leaf (100%)12% light reflected83% light absorbed, but only 4% of this is used in photosynthesis5% of light transmitted
25 These values will be affected by the amount of chloroplasts in the leafhow shiny the leaf ishow thick the leaf isFeatures of light that make it importantspectral quality (colour)intensity (brightness)duration (time)Visible light has a wavelength between 400nm and 700nm
26 Absorption of LightLeaves contain a variety of photosynthetic pigments, of which chlorophyll is the most obvious.It is these pigments which absorb light energy.There are two different groups of pigmentschlorophylls – chlorophyll a, chlorophyll bCarotenoids – xanthophyll, caroteneDifferent photosynthetic pigments absorb different wavelengths.
27 Absorption and Action Spectra Absorption SpectrumA graph of absorbance of different wavelengths of light by a pigmentAction SpectrumA graph of the rate of photosynthesis at different wavelengths of light.Chlorophylls absorb red and blue violet regions of light, and reflect greenCarotenoids absorb the blue-violet region of the spectrum.
32 Learning OutcomesOutline how light energy is converted to chemical energy (ATP and reduced NADP) in the light-dependent stage.Explain the role of water in the light-dependent stage.
33 Photosynthesis is a two-stage process Evidence for this comes from experiments with isotopes of oxygen.Plants provided with C18O2 combine the atoms into carbohydratesPlants provided with H218O release the 18O atoms as oxygen gasAll the oxygen released by photosynthesis comes from water.
34 Harvesting LightIn p/s the light energy absorbed by the p/s pigments is converted to chemical energy.The absorbed light energy excites electrons in pigment molecules.In functioning photosystems this is the energy which drives the process of photosynthesis.
35 There are two categories of p/s pigment Primary pigmentschlorophyll aAccessory pigmentschlorophyll a, chlorophyll b and carotenoids
36 Light-dependent reactions Water is split in a reaction called photolysis,These reactions provide the energy to:Synthesis ATP from ADP and Pi (photophosphorylation)Transfer H+ and e- to NADP to form reduced NADP
37 Photophosphorylation Photophosphorylation can be cyclic or non cyclic depending on the pattern of electron flow in one or both photo systemsCyclic photophosphorylationPSINon cyclic photophosphorylationPSII & PSI
38 Harvesting Light Photosystems Pigments are arranged into light harvesting clusters called photosystemslight energy absorbed by pigments is passed to the primary pigment, which acts as a reaction centre.
39 Photosystems Photosystem I Photosystem II Arranged around chlorophyll a molecule with an absorption peak at 700 nm.Reaction centre P700Photosystem IIChlorophyll a molecule with absorption peak at 680nmReaction centre P680
41 Cyclic Photophosphorylation ElectronacceptorElectron carriersADP + PiATP2e-Light energy absorbed by Chlorophyll aPSI
42 Cyclic Photophosphorylation involves only photosystem I, which has a chlorophyll a with a reaction centre P 700.An electron from the molecule is excited to a higher energy level.It is captured by an electron acceptor, and then is passed back to one of the chlorophyll a P700 molecules.This happens due to a chain of electron carriers .
43 Cyclic photophosphorylation The whole process releases energy to make ATP from ADP and inorganic phosphate.This ATP will then be used in the light – independent reaction.
45 Non-cyclic photophosphorylation involves both photosystems.Both absorb light and the electrons which are excited leave the reaction centres of P680 and P700 of the chlorophyll a molecules.Electron acceptors pass the electrons along chains of electron carriers.The P700 of the photosystem I absorbs electrons from photosystem II.Replacement electrons from the photolysis of water go to photosystem II.
46 Non-cyclic photophosphorylation The electrons lose energy passing along the electron chain and this goes towards synthesising ATP.The photolysis of water releases two protons/H+sH+ combine with electrons from photosystem I and NADP to give reduced NADP (NADPH + H+)
47 The Photolysis of water H2O 2H e- + ½O2Oxygen is released as a waste productThe H+ and e- are transferred to NADP to give reduced NADP2H+ + 2e- + NADP reduced NADPThe reduced NADP then passes onto the light independent reactions
48 Pupil ActivityComplete the diagram of Photophosphorylation
49 Prep Question – 10 marksDescribe the structure of a chloroplast and then give an account of the role played by chlorophyll in photosynthesis. Refer to action and absorption spectra in your answer.Write in bullet points and include a diagram.
50 Jan 03 Question 1 (a) blue and red light used in photosynthesis; (light of) wavelength 420 – 450 nm, gives high rate / AW;(light of) wavelength 650 – 690 nm, gives high rate / AW;(light of) wavelength of 500 – 650 nm / green light, less effective / reflected;sharp / AW, drop after 680 – 690 nm;
51 (b) (i) (ii) (iii) chlorophyll a; chlorophyll b; carotenoids / carotene;xanthophylls;phaeophytin;(ii)absorb/ trap/ capture / harvest, light / transfer energy / transfer electrons;(iii)granum/ thylakoid (membrane) / lamella / quantasome;
52 Light independent reactions The light independent reaction involves the fixation of carbon dioxide, and it takes place in the stroma of the chloroplast.
53 Learning OutcomesOutline how the products of the light-dependent stage are used in the light-independent stage (Calvin cycle) to produce triose phosphate (TP).Explain the role of carbon dioxide in the light-independent stage (Calvin cycle).State that TP can be used to make carbohydrates, lipids and amino acids.State that most TP is recycled to RuBP.
55 Calvin Cycle Light independent reactions The stages are:Carbon dioxide is linked with a molecule of ribulose bisphosphate (RuBP), which is a 5 carbon sugar, using the enzyme ribulose bisphosphate carboxylase.A highly unstable 6C structure is formed which immediately splits into 2 molecules of the 3 carbon compound glycerate-3-phosphate (GP).GP is converted into triose phosphate (3C) with the addition of hydrogen from reduced NADP and energy from ATP
56 The fate of triose phosphate Triose phosphate has two purposes within the cellSynthesis of moleculesSynthesis of hexose sugars, starch and celluloseSynthesis of amino acids5/6 are used in the conversion to RuBP so that more CO2 can be taken up
57 The fate of the products of photosynthesis Specialist carbohydratesglucosefructoseSucroseCelluloseLipidsAmino acids and proteinsNucleic acidsGrowth factors, vitamins, hormones, pigments
59 Factors Limiting Photosynthesis How can the rate of photosynthesis be measured?Which Environmental factors could limit the rate of photosynthesis?
60 Learning outcomesDiscuss limiting factors in photosynthesis, with reference to carbon dioxide concentration, light intensity and temperature.Describe how to investigate experimentally the factors that affect the rate of photosynthesis.
61 Factors affecting photosynthesis Raw materialsWaterCarbon dioxideEnergy in the form of sunlightLight independent stage requires a relatively high temperatureThe light-dependent reactions are not directly affected by temperature, why is this?
62 Quick revision In the light-dependent stage what is water a source of? Hydrogen ions used in chemiosmosisHydrogen ions accepted by NADPElectrons to replace lost by oxidised chlorophyll
63 Limiting factorsIf any of these factors are in short supply, it can limit the rate at which photosynthesis takes placeThe factor in the shortest supply is known as the limiting factor.
65 Light Intensity Light drives the light-dependent reactions More light, more photosynthesisAt a point where increasing light intensity has no effect on the rate of photosynthesis, light is no longer the limiting factor
66 Carbon Dioxide Concentration Carbon dioxide in air is about 0.04%Carbon dioxide is needed for the Calvin cycleIf a plant is given extra CO2 they will photosynthesis faster
67 Carbon Dioxide Concentration Over which part of this curve is carbon dioxide the limiting factor for photosynthesis?Suggest why the curve flattens out at high levels of CO2.
69 temperature Temperature affects the kinetic energy of molecules Higher the temperature, the faster the molecules moveMore collisionsRate of reaction increasesAt temperatures that are too high, enzyme molecules denature and the rate of reaction slows down.
70 Learning outcomesDescribe the effect on the rate of photosynthesis, and on levels of GP, RuBP and TP, of changing carbon dioxide concentration, light intensity and temperature.
71 Effect of light on the Calvin Cycle The Calvin cycle depends on the products from the light-dependent reactions.
72 Effect of light on the Calvin Cycle Explain why the Calvin cycle stops running when there is no light and the TP is used up.
73 Effect of light on the Calvin Cycle Make a copy of this diagram and add another line to show what you would expect to happen to the levels of RuBP during this 8 minute period.
74 Effect of temperature on the Calvin cycle What effect would you expect a rise or a fall in temperature to have on the relative levels of GP, TP and RuBP?When answering this assume that the temperature does not go high enough to denature the enzymes.Explain your reasoning.
75 Effect of carbon dioxide concentration on the Calvin cycle If CO2 is in short supplyLess for RuBP to react withLess GPLess TPInitial accumulation of RuBP