B1.4 Flashcards
What is photosynthesis?
To make glucose for a food source and oxygen for respiration photosynthesis occurs
Carbon dioxide + water > glucose + oxygen
CO2 diffuses from the air through the stomata
Water enters the roots from the soil through root hair cells by osmosis
Where does photosynthesis occur?
Inside the plants chloroplasts, mainly in the leaves and the green stem
Chlorophyll is in the chloroplasts, where light transfers energy from the sun
What are the 2 main stages of photosynthesis?
Stage 1 (light dependant) - energy transferred from light split water molecules into oxygen gas and hydrogen ions
Stage 2 (light independent) - carbon dioxide combines with the hydrogen ions to form glucose
What type of reaction is photosynthesis?
Endothermic reaction (energy transferred from the surroundings to keep reaction going)
What happens to the glucose produced?
Immediately used in respiration
Converted in sugar molecules (fructose, sucrose)
Converted into starch (used as an energy store to be used at night for respiration when the plant isn’t photosynthesising)
To make amino acids, cellulose
How to test for photosynthesis?
Test for starch:
1) take a leaf and place in a beaker of boiling water to kill it
2) place the leaf in a boiling tube of boiling ethanol to remove all chlorophyll
3) wash the leaf to remove ethanol and soften the leaf
4) spread on a white tile and add a few drops of iodine
5) if starch is present iodine will turn blue-black
How to prove chlorophyll is needed for photosynthesis?
Variegated leaves only have chlorophyll in some areas so:
1) place variegated leaf in the sunlight for 24 hours and do a starch test
How to prove light is needed for photosynthesis?
1) take a destarched plant and cover part of it with black card or tin foil
2) place the leaf in the sunlight for several hours
3) do a starch test
How to prove carbon dioxide is needed for photosynthesis?
1) take a destarched plant and place in a polythene bag
2) add a pot of soda lime (absorbs carbon dioxide and water vapour) and seal the bag
3) place in sunlight for several hours and then test for starch
How to prove oxygen is given off during photosynthesis?
1) place an upturned test tube above an aquatic plant
2) put the apparatus in the light for maximum photosynthesis
3) when a full tube of gas is collected place a glowing splint inside the tube, if it relights oxygen is present
What factors affect the rate of photosynthesis?
Light intensity
Carbon dioxide
Temperature
What are limiting factors?
If these factors are in short supply or the temperature is too low then the rate of photosynthesis is limited
What is the equation for rate?
Rate = 1/time
How does light intensity affect the rate of photosynthesis?
Higher light intensity = faster rate of photosynthesis
How does carbon dioxide affect the rate of photosynthesis?
Greater carbon dioxide concentration = faster rate of reaction
CO2 is normally the limiting factor
