Photosynthesis PDF - Buzzing Biology

Photosynthesis Photosynthesis is the process by which green plants produce their own food (glucose) using light energy from the sun trapped by chlorophyll Sunlight 6CO2 + 6H2O C6H12O6 + 6O2 C...

Photosynthesis Photosynthesis is the process by which green plants produce their own food (glucose) using light energy from the sun trapped by chlorophyll Sunlight 6CO2 + 6H2O C6H12O6 + 6O2 Chlorophyll Sunlight Carbon dioxide + Water glucose + Oxygen Chlorophyll It takes place in the chloroplast of the cell using chlorophyll which absorbs light energy Therefore, chlorophyll is the source of electrons The dark stage takes place in the stroma (liquid interior) The light stage takes place in the grana (granum – one stack) Plants convert light energy into chemical energy What is the role of photosynthesis? To produce food for plants & animals To produce oxygen for aerobic respiration of animals To remove carbon dioxide from the air Responsible for forming fossil fuels What are the sources of the reactants required for photosynthesis? Reactant Source Sunlight is the normal source of light for photosynthesis. Light Light provides energy in the form of electrons. Buzzing Biology LC H1 Concise Notes Book  It is obtained from the atmosphere (external) through the Carbon stomata in the leaves or from the process of respiration in the dioxide leaf (internal) It is absorbed from the soil by the roots by osmosis, and passes Water up through the xylem in the stem to the leaves. Water is another source of electrons for photosynthesis. The following factors increase the rate of photosynthesis and thus increase plant production and improve crop yield in a greenhouse: 1. Increase the artificial lighting in greenhouses or use a range of colours of lights. This greater range of light means more energy can be absorbed 2. Increase the artificial carbon dioxide level to increase the CO2 concentration (e.g. burning of gas) which results in an increased supply of carbon atoms to the dark stage 3. Greenhouses trap heat produced by the sun, which helps to increase the temperature and heat it to the crop’s optimum temperature, hence, increasing enzyme activity The process of photosynthesis – it is divided into 2 stages 1. Light stage (light dependent) 2. Dark stage (light independent) Doesn’t require light but requires the Energy is provided by light products of the light stage to take place Reactions will take place in the This allows reactions to proceed presence or absence of light as energy so quickly that no enzymes are is provided by ATP and enzymes control required them (therefore, it is affected by temperature) Buzzing Biology LC H1 Concise Notes Book The light stage 1. Light absorption Chloroplasts have a range of pigments, including chlorophyll, each of which absorbs a different colour of light In general, plants absorb all the colours of white light except green. Therefore, most plants are green as green light is reflected by plants 2. Light energy is transferred to electrons Pigments are arranged in clusters in the chloroplast, and transfer absorbed energy from one to another until it reaches the reaction centre chlorophyll Once the light energy reaches the reaction centre chlorophyll, it is transferred to electrons, which energises them to become high-energy electrons These high-energy electrons are then passed to electron acceptors/carriers, and flow from these along 1 of 2 different pathways ATP = Adenosine Triphosphate ADP = Adenosine Diphosphate NAD = Nicotinamide Adenine Dinucleotide NADP = Nicotinamide Adenine Dinucleotide Phosphate Buzzing Biology LC H1 Concise Notes Book Pathway 1 – Cyclic photophosphorylation/electron flow 1. Light energy is absorbed by the pigment molecules and is passed from pigment molecule to pigment molecule until it reaches the reaction centre chlorophyll molecule 2. At the reaction centre molecule, the light energy is transferred to electrons, energising them, resulting in high-energy electrons 3. A single energised electron is then picked up by an electron acceptor molecule 4. It is passed through many electron acceptors, known as an electron transport chain. As it does this, it loses excess energy 5. This energy is used in the process of phosphorylation resulting in the formation of ATP 6. Energy + ADP + P ATP + water 7. The electron then returns to the reaction centre chlorophyll after losing this energy as it is now a low-energy electron 8. It is then re-energised and the cycle begins again 9. ATP is later used as a source of energy in the dark stage reactions Buzzing Biology LC H1 Concise Notes Book Pathway 2 – Non-cyclic electron flow 1. Light energy is absorbed by the pigment molecules and is passed from pigment molecule to pigment molecule until it reaches the reaction centre chlorophyll molecule 2. At the reaction centre molecule, the light energy is transferred to electrons, energising them, resulting in high-energy electrons 3. 2 energised electrons are then picked up by an electron acceptor molecule 4. They are passed through many electron acceptors, known as an electron transport chain. As they do this, they lose excess energy 5. This energy is used in the process of phosphorylation resulting in the formation of ATP and water 6. Energy + ADP + P ATP + water 7. Photolysis (the splitting of water using light energy) occurs to form electrons, protons and Oxygen: The electrons replace those electrons lost in chlorophyll. Therefore, water can be another source of electrons in photosynthesis The protons go to the proton pool and will eventually be transported by NADPH to the dark-stage reactions Oxygen is used internally for respiration or released into the atmosphere 8. NADP+ will pick up and trap these 2 low-energy electrons (therefore, they do not return to the chlorophyll) and form NADP-. This will then combine with 1 proton from the proton pool to form NADPH Buzzing Biology LC H1 Concise Notes Book Products of the light stage ATP – releases energy for the dark-stage reactions as it carries/transfers energy NADPH – supplies protons/H+ ions & electrons for the dark-stage reactions Oxygen – used for respiration or released into the atmosphere The dark stage 1. Carbon dioxide (supplies Carbon atoms) from the air (it enters via the stomata in the leaves of the plant) or respiration enters the chloroplast 2. NADPH is broken down into NADP+ to release a H+ ion/proton and 2 electrons 3. ATP is broken down into ADP, which releases a phosphate (P) and energy. This energy fuels the reaction 4. Carbon dioxide then combines with these electrons & proton and is reduced to form Glucose 5. The ADP and NADP+ return to the light stage What happens to glucose? Used up in respiration Used to produce cellulose for plant walls Stored as starch in chloroplasts, or other parts of the cell, for later use Buzzing Biology LC H1 Concise Notes Book  Exp: To investigate the effect of light intensity on the rate of photosynthesis The light intensity is varied by moving the light source (lamp) at different distances from the apparatus Elodea is used as it is an aquatic plant. Therefore, the bubbles of oxygen can easily be seen or visualised // it is easier to see the release of oxygen bubbles The rate of photosynthesis = the number of oxygen bubbles produced per minute Procedure 1. Add excess sodium bicarbonate to a test tube of water – the water is now saturated with carbon dioxide, ensuring it is not the limiting factor 2. Cut a small section of elodea and place it in the test tube with the cut end facing up. A paper clip is used to weigh the elodea down, to keep it under the water’s surface 3. Set up the water bath at set it at 25°C, using a thermometer – this maintains a constant temperature 4. Place the test tube into the water bath with the lamp 1m from the apparatus 5. Turn off the lights in the room to create a dark environment, then switch on the light on the lamp (light source) 6. Allow the elodea to adjust to the new conditions for 5 minutes 7. Then count the number of bubbles of oxygen being produced per minute 8. Repeat this process 3 times and find the average number of oxygen bubbles produced per minute – this increases the reliability 9. Increase the light intensity by moving the lamp closer (80cm, 60cm, 40cm, 20cm) to the apparatus Buzzing Biology LC H1 Concise Notes Book 10. Then repeat this method at each light intensity (ensure to allow it to adjust) Results The rate of photosynthesis increases as light intensity increases The rate of photosynthesis then levels off as the saturation point is reached This is because light intensity is no longer the limiting factor. This means that CO2 or temperature must be the limiting factor. The plant is light or CO2 saturated Or it could be that chlorophyll is damaged at very high light intensities Saturation point Buzzing Biology LC H1 Concise Notes Book