B1.4-Photosynthesis Flashcards
b1.4.1-What is photosynthesis?
To make plants, food has to taken in carbon dioxide which diffuses from the air into the plant through the stomata and water which enters the root from the soil through the root hair cells by osmosis. These substances react together to make glucose which plants use as a food source.
Carbon dioxide + Water -> Glucose + Oxygen
6CO2 + 6H2O -> C6H12O6 + 6O2
b1.4.1-Where does photosynthesis occur?
Photosynthesis takes place inside the plants chloroplasts. Leaves and stems are green because they contain chlorophyll inside their chloroplasts. Light transfers energy from the sun to chlorophyll, where carbon dioxide and water react to make glucose.
b1.4.1-What are the different stages in photosynthesis?
Stage 1 is light dependant and when energy transferred from light splits water molecules into oxygen gas and hydrogen ions. Stage 2 is light independent and when carbon dioxide gas combines with the hydrogen ions to make glucose. Photosynthesis is endothermic as it requires energy transferred from surroundings.
b1.4.1-What happens to glucose produced by photosynthesis?
The plant uses some of the glucose in respiration while others are converted into fructose and sucrose which is stored in fruit. Glucose that is not needed straight away is converted to starch which provides a source of energy and acts as a food store.
b1.4.2-How can you test for starch?
Take the leaf you are about to test and place in a beaker of boiling water to kill it. Then place the leaf in a boiling tube of ethanol to remove chlorophyll. Wash the leaf with water to remove ethanol to soften the leaf. Spread it on a white tile and add drops of iodine solution. If starch is present, it should turn from yellow-brown to blue-black.
b1.4.2-How can you prove chlorophyll is needed for photosynthesis?
Variegated leaves only have chlorophyll in some areas of the leaf meaning some of it is white and some green. To prove chlorophyll is needed, you should place a destarched variegated plant in sunlight for hours and then test for the presence of starch.
b1.4.2-How can you prove light is needed for photosynthesis?
To prove light is needed for photosynthesis, take a destarched plant and cover part of one of its leaves with black card. Light can’t reach the covered area and place it in sunlight for hours. Then remove the card from the leaf and test the leaf for the presence of starch.
b1.4.2-How can you prove carbon dioxide is needed for photosynthesis?
You take a destarched plant and place it in a polythene bag. Add a pot of soda lime before sealing the bag as it’s a chemical that absorbs carbon dioxide and water vapour. Place the plant in sunlight for hours before testing for presence of starch.
b1.4.3-Which factors affect the rate of photosynthesis?
Light intensity, carbon dioxide and temperature are limiting factors which affect rate of photosynthesis. You can measure the rate by measuring how much oxygen or glucose a plant makes in a given time.
rate=1 / time
b1.4.3-How do light intensity, carbon dioxide and temperature affect rate of photosynthesis?
Light intensity-the higher the light intensity, the faster the rate of photosynthesis. This continues until it reaches the max rate
Carbon dioxide-the greater the carbon dioxide concentration, the faster the rate of reaction
Temperature-the higher the temperature, the faster the rate of photosynthesis. However too high temperatures mean enzymes denature and the reaction stops.
b1.4.4-How can you see the limiting factors effect on photosynthesis?
Light intensity-place a light source at different distances from the Elodea
Carbon dioxide concentration-add different masses of potassium hydrogen carbonate powder to water. Potassium hydrogen releases carbon dioxide to the atmosphere
Temperature-place the apparatus in water baths at different temperatures
relative light intensity = 1 / distance from light source^2
b1.4.4-How do the limiting factors interact?
If the carbon dioxide concentration limits rate of photosynthesis, it’s the limiting factor meaning increases in light intensity or temperature make no difference. When the carbon dioxide is greater, temperature is the limiting factor.
