Photosynthesis
Photosynthesis
Photosynthesis Equation Carbon dioxide + water + light Glucose + Oxygen 6CO 2 + 6H 2 O + light C 6 H 12 O 6 + 6O 2
What is photosynthesis? Photosynthesis is the production of food from inorganic materials using light energy trapped by chlorophyll. Chlorophylls primary role is photosynthesis Autotrophs: organisms that make their own food (green plants)
What is the difference between chloroplast and chlorophyll? Chloroplast are the green structures in plants in which photosynthesis takes place. Chlorophyll is the green pigment that absorbs light in the chloroplast.
Role of photosynthesis Photosynthesis provides oxygen for organisms in order for respiration to occur. Plants use it to make food Animals get their food from plants. NOTE: In photosynthesis the light energy is used to make ATP. This ATP is used to supply energy to make glucose.
O 2 CO 2 Glucose Diagram of a chloroplast Light 2H 2 O 4e- Chlorophyll 4H + H + H + High energy H + H + electrons Used for respiration or released into the atmosphere
Stages of photosynthesis: 1) Light is absorbed by the chlorophyll 2) Water is split 3) Light energises the electrons 4) Glucose is formed
Splitting of water (photolysis) Sunlight splits water in the chloroplasts. Water splits into 4 protons (H + ), 4 electrons (e-) and an oxygen molecule. NOTE: What is the fate of the oxygen: 1) Passed out into the atmosphere 2) Plant uses it for respiration
What are the two stages of photosynthesis: Takes place in two stages Light stage (light dependent --- cannot occur without light) Dark stage (light independent --- does not require light)
Facts on the light stage: Light stage Takes place in the chloroplast Involves electrons flowing Happens very quickly so are not controlled by enzymes
Events in the Light stage: Light is absorbed Chloroplast contains range of pigments (chlorophyll) so it can absorb range of colours. They absorb all colours that make up white light except green
Events in the Light stage: Light energy transferred to electrons Pigments arranged in clusters in chloroplast Pigments transfer the absorbed energy from one to another until it reaches the chlorophyll beside the electron centre (form high energy electrons) The high energised electrons flow from the electron acceptor along one of two different pathways.
The Light Stage
Events in the Light stage: Electron flow: Pathway 1 High energy electrons pass from the electron acceptor to a series of electron acceptors and return back to the chlorophyll molecule (cyclic electron flow) Electrons are recycled and release energy which is trapped by ADP and a phosphate to form ATP. ADP + P + energy ATP + water.
Events in the Light stage: Electron flow pathway 2 There are 2 high energy electrons passed from chlorophyll to the electron acceptor. These high energy electrons do not return to the chlorophyll (energy released as they pass from electron acceptor to acceptor) The energy released is used to make more ATP ADP + P + energy ATP + water Eventually the 2 electrons combine with NADP + to form NADP -
Events in the Light stage: Electron flow pathway 2 NOTE: Chlorophyll is now short of two electrons ---- gains new electrons from splitting of water (photolysis) Protons are now attracted to the NADP - to form NADPH NADP - + H + (proton) NADPH This is a non cyclic electron flow
End products of Light stage: ATP: supplies energy for the dark stage reactions NADPH: supplies protons and energised electrons for dark stage reactions. Oxygen: made when water splits. Can be used for respiration or can be released into the atmosphere.
Light Stage and Dark Stage
The Dark Stage (Calvin Cycle) Reactions of the dark stage are controlled by the enzymes (can be affect by temperature). Takes place in different part of the chloroplast Carbon dioxide enters the chloroplast which combines with protons and electrons to form glucose. Energy to form glucose comes from the conversion of ATP to ADP and phosphate
To investigate the influence of light intensity on the rate of photosynthesis 1) Add sodium bicarbonate to water until you have excess bicarbonate (ensures a constant supply of carbon dioxide during this experiment). 2) Water bath ensures that the temperature stays constant. 3) Cut a section of Elodea. 4) Add a few drops of buffer solution (maintain the ph at 7) 5) Allow the Elodea to stabilise for 5 minutes (precaution: allow time before counting bubbles).
To investigate the influence of light intensity on the rate of photosynthesis 6) Count the number of bubbles of oxygen coming from the cut end per minute (amount of bubbles indicates the rate of photosynthesis). 7) Increase the light intensity by moving lamp closer (80cm, 60cm, 40cm, 20cm) and repeat above steps. NOTE: As the lamp is moved closer to the plant, the rate of bubble production increases. At some point, the rate of bubble production ceases to increase and the plant is said to be saturated with light.
Light Saturation Point» Light Saturation» point
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