Presentation on theme: "Photosynthesis Unit 1 Communication, Homeostasis and Energy."— Presentation transcript:
Photosynthesis Unit 1 Communication, Homeostasis and Energy
Think about it!!! 10 minutes Which process evolved first on Earth – aerobic respiration or photosynthesis? Give reasons for your answer You are going to present your answer with your reasons to the rest of the class!!
Answer Plants and animals rely on aerobic respiration Requires oxygen Oxygen is a by-product of photosynthesis Until photosynthesis evolved there was no free oxygen in the atmosphere Photosynthesis evolved first!!
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.
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.
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.
Heterotroph and Autotroph Autotroph an organism that uses an external energy source and inorganic molecules to make complex organic molecules. ▪ Chemoautotroph ▪ Photoautotroph Heterotroph Organism that needs to take in complex organic molecules which act as a source of energy and as usable carbon compounds.
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 nutrition Synthesise organic materials from inorganic sources e.g. photosynthesis Heterotrophic nutrition Obtained in organic form
Photosynthesis: an outline Photosynthesis (p/s) is the fixation of carbon dioxide and its reduction to carbohydrate, using hydrogen from water
Photosynthesis Equations Word equation for photosynthesis Light energy Carbon dioxide + water carbohydrate + oxygen chlorophyll
Photosynthesis Equations Light energy nCO 2 + nH 2 0 (CH 2 O)n + nO 2 chlorophyll Light energy 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 chlorophyll Overall Chemical Equation Balanced Equation for hexose sugars
Photosynthesis experiments Testing a leaf for starch What are the requirements for photosynthesis Light Chlorophyll carbon dioxide
Factors affecting the rate of photosynthesis Factors limiting photosynthesis chlorophyll (enzymes) carbon dioxide Light Water Temperature
Photosynthesis Photosynthesis is a 2 stage process Light dependent reactions ▪ thylakoid membranes Light independent reactions ▪ Stroma
Learning outcome Explain, with the aid of diagrams and electron micrographs, how the structure of chloroplasts enables them to carry out their functions.
Chloroplast – electro micrograph x y z
Chloroplast Structure 3 – 10μm diameter Envelope of 2 phospholipid membranes Stroma = fluid interior Thylakoids are series of flattened sacs, which form stacks (grana) in places
Chloroplast function Grana Provides a LSA to hold pigments, electron carriers, and enzymes for light dependent reactions. Photosystems arranged in funnel like structure in thylakoid Membrane of grana holds ATPsynthase (chemiosmosis)
Chloroplast Function Stroma Site of light independent reactions (carbon fixation) Contains sugars, organic acids and enzymes for Calvin cycle Store starch grains Loop DNA – codes for chloroplast proteins
Chloroplast Function Lamellae Do not contain chlorophyll Form a network between the grana
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.
Trapping Light energy The fate of light which strikes the leaf
Trapping the Light Energy The fate of light which strikes the leaf Light shining on leaf (100%) 12% light reflected 83% light absorbed, but only 4% of this is used in photosynthesis 5% of light transmitted
These values will be affected by the amount of chloroplasts in the leaf how shiny the leaf is how thick the leaf is Features of light that make it important spectral quality (colour) intensity (brightness) duration (time) Visible light has a wavelength between 400nm and 700nm
Absorption of Light Leaves 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 pigments chlorophylls – chlorophyll a, chlorophyll b Carotenoid s – xanthophyll, carotene Different photosynthetic pigments absorb different wavelengths.
Absorption and Action Spectra Absorption Spectrum A graph of absorbance of different wavelengths of light by a pigment Action Spectrum A graph of the rate of photosynthesis at different wavelengths of light. Chlorophylls absorb red and blue violet regions of light, and reflect green Carotenoids absorb the blue-violet region of the spectrum.
Absorption and Action Spectra
The Chemistry of photosynthesis
Learning Outcomes Outline 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.
Photosynthesis is a two-stage process Evidence for this comes from experiments with isotopes of oxygen. Plants provided with C 18 O 2 combine the atoms into carbohydrates Plants provided with H 2 18 O release the 18 O atoms as oxygen gas All the oxygen released by photosynthesis comes from water.
Harvesting Light In 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.
There are two categories of p/s pigment Primary pigments ▪ chlorophyll a Accessory pigments ▪ chlorophyll a, chlorophyll b and carotenoids
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
Photophosphorylation Photophosphorylation can be cyclic or non cyclic depending on the pattern of electron flow in one or both photo systems Cyclic photophosphorylation PSI Non cyclic photophosphorylation PSII & PSI
Harvesting Light Photosystems Pigments are arranged into light harvesting clusters called photosystems light energy absorbed by pigments is passed to the primary pigment, which acts as a reaction centre.
Photosystems Photosystem I Arranged around chlorophyll a molecule with an absorption peak at 700 nm. Reaction centre P700 Photosystem II Chlorophyll a molecule with absorption peak at 680nm Reaction centre P680
Light harvesting system
Cyclic Photophosphorylation PSI Light energy absorbed by Chlorophyll a Electron acceptor ADP + Pi ATP 2e - Electron carriers
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.
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.
Non cyclic photophosphorylation PSIIPSI Electron Acceptor A 2e - Electron Acceptor B 2e - Light energy ADP + Pi ATP NADP NADPH + H + H 2 O ½O 2 + 2e - + 2H + Electron carrier
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.
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 + s H + combine with electrons from photosystem I and NADP to give reduced NADP (NADPH + H + )
The Photolysis of water H 2 O 2H + + 2e - + ½O 2 Oxygen is released as a waste product The H + and e - are transferred to NADP to give reduced NADP 2H + + 2e - + NADP reduced NADP The reduced NADP then passes onto the light independent reactions
Pupil Activity Complete the diagram of Photophosphorylation
Prep Question – 10 marks Describe 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.
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;
Light independent reactions The light independent reaction involves the fixation of carbon dioxide, and it takes place in the stroma of the chloroplast.
Learning Outcomes Outline 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.
a.k.a. Calvin cycle
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
The fate of triose phosphate Triose phosphate has two purposes within the cell Synthesis of molecules ▪ Synthesis of hexose sugars, starch and cellulose ▪ Synthesis of amino acids 5/6 are used in the conversion to RuBP so that more CO 2 can be taken up
The fate of the products of photosynthesis Specialist carbohydrates glucose fructose Sucrose Cellulose Lipids Amino acids and proteins Nucleic acids Growth factors, vitamins, hormones, pigments
Factors limiting photosynthesis
Factors Limiting Photosynthesis How can the rate of photosynthesis be measured? Which Environmental factors could limit the rate of photosynthesis?
Learning outcomes Discuss 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.
Factors affecting photosynthesis Raw materials Water Carbon dioxide Energy in the form of sunlight Light independent stage requires a relatively high temperature The light-dependent reactions are not directly affected by temperature, why is this?
Quick revision In the light-dependent stage what is water a source of? Hydrogen ions used in chemiosmosis Hydrogen ions accepted by NADP Electrons to replace lost by oxidised chlorophyll
Limiting factors If any of these factors are in short supply, it can limit the rate at which photosynthesis takes place The factor in the shortest supply is known as the limiting factor.
Light drives the light-dependent reactions More light, more photosynthesis At a point where increasing light intensity has no effect on the rate of photosynthesis, light is no longer the limiting factor
Carbon Dioxide Concentration Carbon dioxide in air is about 0.04% Carbon dioxide is needed for the Calvin cycle If a plant is given extra CO 2 they will photosynthesis faster
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 CO 2.
Carbon dioxide concentration
temperature Temperature affects the kinetic energy of molecules Higher the temperature, the faster the molecules move More collisions Rate of reaction increases At temperatures that are too high, enzyme molecules denature and the rate of reaction slows down.
Learning outcomes Describe the effect on the rate of photosynthesis, and on levels of GP, RuBP and TP, of changing carbon dioxide concentration, light intensity and temperature.
Effect of light on the Calvin Cycle The Calvin cycle depends on the products from the light-dependent reactions.
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.
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.
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.
Effect of carbon dioxide concentration on the Calvin cycle If CO 2 is in short supply Less for RuBP to react with Less GP Less TP Initial accumulation of RuBP