B1.4 Photosynthesis Flashcards
What is photosynthesis?
The process by which a cell captures energy in sunlight and use it to make glucose
How is carbon dioxide taken in?
Diffuses from the air through the stomata in the leaf
How is water taken in?
Through the roots through osmosis
What is the word equation for photosynthesis
Carbon dioxide + water -> glucose + oxygen
Is photosynthesis exothermic or endothermic?
Endothermic
Chemical equation for photosynthesis
6Co2 + 6H2O -> C6H12O6 + 6O2
Where does photosynthesis occur?
In the plants chloroplast, generally in the green parts of a leaf because chlorophyll is the green pigment which transfers energy from the sun.
What happens in the 2 stages of photosynthesis?
Stage 1(light dependent) - energy transferred by light splits water into hydrogen ions and oxygen gas
Stage 2(light independent) - carbon dioxide gas combines with the hydrogen ions to form glucose. Oxygen remains
What happens to the glucose produced?
Used in respiration to make atp energy
Some glucose is stored as sugar in fruits and the stem, such as sucrose and fructose
Some glucose is used to synthesis larger molecules for growth(increase biomass) eg cellulose and protein
Most of it is converted to starch
Why is some glucose converted to starch?
It is converted to starch to be a store of energy for use at night when the plant cannot photosynthesise.
How can you test for starch?
Kill the leaf by putting it in boiling water and then boiling ethanol which removes all the chlorophyll. Then wash the ethanol off the leaf and put it on a white tile.
Next add iodine to the leaf. It will turn from yellow to blu/black if starch is present
How do you destarch a plant?
Put it in a dark cupboard for 24 hours so that all the starch is used up
How can you prove that chlorophyll is needed for photosynthesis?
Take a variegated lead which is stripy coloured. De starch it and then leave it in sunlight. Test for starch using iodine. Some areas should turn black while others stay yellow
How do you prove that light is needed for photosynthesis?
Take a destarched leaf and put some card to cover up part of the leaf. Place the lead in sunlight and then remove the card after hours. Test for starch. The part that was covered up should be yellow
How do you prove that carbon dioxide is needed for photosynthesis?
Put a destarched plant in a polyethylene bag and tie it tightly. Place a pot of soda lime somewhere inside to absorb carbon dioxide and water vapour. Place the plant in sunlight and then test for starch
How do you prove that oxygen is given of during photosynthesis?
Place an aquatic plant in a beaker and put a test tube was over. Measure the bubbles given off or take the test tube and put a glowing splint in it to see if it lights
What 3 limiting factors affect the rate of photosynthesis?
Light intensity, CO2 concentration, temperature.
What is a limiting factor?
A limiting factor is a factor that stops photosynthesis from happening. Increasing other factors will have no effect unless you increase the limiting factor
How do you measure rate if photosynthesis?
Mainly by measuring oxygen given off
Or measure the biomass since glucose is used to produce new cells
Use rate = 1/time
How does light intensity affect rate of reaction?
The higher the light intensity, the faster the rate of photosynthesis until a certain point where a limiting factor stops it. This is because light transfers energy for photosynthesis (stage 1).
How can you investigate the light intensity affect?
Place a light source at different distances from the plant and measure rate of photosynthesis by measuring oxygen using a gas syringe. Use the inverse square law to find the light intensity (y axis)
What is the inverse square law?
Light intensity (lux) = 1/distance^2
How does CO2 affect the rate of photosynthesis?
The greater the CO2 concentration the faster the rate of reaction until a point where there is a limiting factor. CO2 is usually the limiting factor.
How do you control CO2 concentration in an experiment?
Dissolve potassium hydrogen carbonate to water which releases CO2
How does temperature affect the rate of photosynthesis?
Since photosynthesis is Enzyme controlled, the higher the temperature, the faster the rate until the optimum point for the enzymes is reached. If the plant is too hot enzymes will denature and if it is too cold they will work too slowly
How do you control temperature in an experiment?
Use a water bath
