B1.4 Flashcards
Photosynthesis
The transfer of energy from the sun to make glucose.
Carbon dioxide + water = glucose + oxygen
6CO2 + 6H2O = C6H12O6 + 6O2
Happens in the chloroplasts of plant, therefore in green areas so mostly leaves but some in stems…
ENDOTHERMIC REACTION
Where do plants get their reactants?
Carbon dioxide - through the stomata
Water= through root hair cells by osmosis
What are the stages of photosynthesis (IMPORTANT)
What does light indeoednt ions specifically bind with and why?
Stage 1= LOGHT DEPENDENT. This is where the where energy from the sun (therefore dependent on light) splits molecules into hydrogen and oxygen ions.
Stage 2 (light independent) this is where carbon dioxide gas combines with hydrogen ions to make glucose
What happens to glucose produced and oxygen
So aside respiration and food store as starch what else?
Oxygen is used for respiration, rest is just a waste product.
Glucose: some gets used immediately for respiration which happens all the time. Others:
1) converted into other sugar molecules like fructose and sucrose which is in fruit
2) converted with nitrogen from soil to form proteins for growth and repair
3) converted and stored as starch for a supply (potatoes)
4) make fats and oils for growth too,
Summary: fats oils, proteins, starch, sugars for fruit
How do you prove things are needed for photosynthesis? STARCH
To prove starch is produced in photosynthesis:
1) take a leaf and place it into boiling water for a minute to kill it, to ensure no more photosynthesis will take place
2) then (use forceps) place it into a boiling tube of ethanol to remove all the chlorophyll. (MAKE SURE TO USE WATER BATH AS ethanol IS FLAMMABLE)
3) wash the leaf with water to remove the ethanol
4) spread it out and add a few drops of iodine. If there is starch it should turn from yellow brown to blue black
Test for Chlorophyll needed for photosynthesis.
Also why destarch a plant first?
First destarch the sample , leave it in dark for 24 hours. To test for photosynthesis we can just test for production of starch but we have to destarch it to make it fair and know for a fact where the starch comes from.
Use a variegated leaf (one with not full chloroplasts) and then leave it in sunlight for a few hours. Test for starch , it should be present only in the places where chlorophyll is present.
Test for light needed for photosynthesis
Take a destarched plant. Cover a part of a leaf with a black card. Then leave it in sun for a few hours. Test for starch, it should only be present in the exposed areas
Proving carbon dioxide is needed for photosynthesis
Take a destarched plant, place it in a polythene bag to ensure no carbon dioxide from outside can enter. Inside add a pot of soda lime- this absorbs all carbon dioxide. Leave in sun then test for starch, none should be present…
How to prove oxygen is produced in photosynthesis
Use an UPTURNED test tube above an aquatic plant like pondweed, and leave in light.
After a while remove the test tube and use a glowing splint. It should relight because of presence of oxygen
(Or you ca attach it to a capillary tube and a syringe, to more actively measure it.)
What is a limiting factor? What is most common
A limiting factor is a factor that if in short supply, will limit the rate of photosynthesis. This includes carbon dioxide concentration, light intensity and temperature (chlorophyll too I guess) others like water are thought to be abundant.
2) co2 as there is only 0.04% in atmosphere
What happens in each graph
- co2: as co2 conc increases, so does the rate of photosynthesis until a maximum, where it then plateaus as now co2 is now longer the limiting factor and further increasing it no longer increases rate of photo.
- light intensity same as before, no or little light then photo will stop
- temp: increase temp, so does photo, but after optimum temp as photosynthesis is an enzyme controlled reaction (37° again) it will denature and reactions will eventually stop.
Rate of photosynthesis can be calculated by?
Using oxygen release, so 1/ time it took to collect the amount of oxygen. Use elodea tests pondweed ones and alter the conditions.
How to alter the conditions to investigate rate of photosynthesis?
What is inverse square law for light?
1) light intensity- you can just move a light source further away from a plant. These are inversely proportional, so make sure to do 1/d^2
2) co2 conc= use different amounts of POTASSIUM carbonate hydrogen powder in each test, as mor releases more co2 into air,
3) temperture: place the apparatus in water baths of different temperatures.
