Topic 2 Photosynthesis Flashcards
What is photosynthesis?
A chemical change which happens in green leaves which is the first step towards making food. It is an endothermic reaction
Where does photosynthesis take place?
Chloroplasts where chlorophyll absorbs light
Word equation for photosynthesis
Carbon dioxide + water (light and chlorophyll) —> glucose + oxygen
Balanced equation for photosynthesis
6CO2 + 6H2O —> C6H12O6 + 6O2
What else is photosynthesis important for?
Animals as it produces food and oxygen
What is destarching? How do you do it?
It means if the result of the experiment shows starch it means that it was produced during the investigation. To destarch a plant put it into a dark cupboard
What is oxygen usually considered as in photosynthesis?
A waste product
What factors limit photosynthesis?
Light, carbon dioxide and temperature
What does light do to rate of photosynthesis?
Speed up ROP, but only until the optimum. Beyond this light makes no difference to photosynthesis
What is the optimum?
The point at which increasing the factor will make no difference to ROP
What does carbon dioxide do to ROP?
Speed up the ROP until the optimum. After this carbon dioxide makes no difference
What does temperature do to ROP?
Speeds up ROP until the optimum (30 degrees). Enzymes controlling photosynthesis will become denatured, meaning beyond the optimum it makes no difference
When does respiration happen?
24/7
When does photosynthesis happen?
In light
Word equation for respiration
Glucose + oxygen —> carbon dioxide + water + energy
What is the name of MY RED LIP indicator?
Hydrogencarbonate or bicarbonate indicator
What does MY RED LIP mean?
MY = More means Yellow (increased CO2 levels)
RED = red is normal (normal CO2 levels)
LIP = Less Is Purple (decreased CO2 levels)
Does respiration and photosynthesis happen during the day?
Yes both. The high light intensity from the sun means the ROP is high. Therefore CO2 moves into the leaf meaning the indicator will show as purple
Does respiration and photosynthesis happen at night?
No, only respiration as there is no light for photosynthesis. Therefore oxygen moves into the leaf and CO2 leaves meaning the indicator will show as yellow
Does respiration and photosynthesis happen at dawn/dusk?
There is a lower light intensity meaning respiration and photosynthesis will both occur at the same rate (the compensation point) meaning the indicator will show as red
What is the compensation point? Describe it
Compensation point means photosynthesis and respiration happen at the same rate
Carbon dioxide produced in respiration is used for photosynthesis
Oxygen produced in photosynthesis is used for respiration
Meaning hydrogencarbonate/bicarbonate will show as red
Waxy cuticle
Transparent defence layer to prevent water loss
Upper and lower epidermis
Underneath the cuticle, the cells which produce the cuticle
How many layers does the mesophyll have?
Two, the palisade layer and spongy layer
Palisade layer
Cells are tightly packed to absorb sunlight with many chloroplasts
Spongy layer
Large surface area due to air spaces between many cells to allow gas exchange. Has many chloroplasts
What adaptations do the lower epidermis and waxy cuticle have?
Stomata and guard cells
Stomata
Tiny holes within the upper/lower epidermis
Guard cells
Surround the stomata. Changes in water pressure causes the stomata to open or close. If the guard cells are full of water they swell up and bend away from each other high open the stomata. During dry times the guard cells close
How to carry out starch test (with conclusion)
Destarch leaf and attach black strip of card onto a leaf
Take off card and place in boiling water (to kill it which stops chemical reactions and makes iodine easier to absorb)
Remove leaf and place into a boiling tube and cover with ethanol. Put back into beaker so the ethanol boils (removes chlorophyll to see colour change easier)
Add iodine. The leaf should turn blue-black except for the part that had the black card which should stay yellow-brown
CONCLUSION: the part with card did not change to blue-black as there was no starch. The only thing different is that it wasn’t getting any light therefore light is needed for photosynthesis
How to carry out test for chlorophyll in photosynthesis (with conclusion)
Repeat starch test but use a variegated leaf (this is a leaf with some parts containing chlorophyll and some without chlorophyll)
The pale part of the leaf should stay yellow-brown and the green part should turn blue-black
CONCLUSION: the green part of the leaf has turned blue-black because there is starch present. The pale part of the leaf has stayed yellow-brown as there was no starch present. The only difference was there was no chlorophyll in the pale part (variegated leaf) therefore chlorophyll is needed for photosynthesis
How to carry out test for carbon dioxide in photosynthesis (with conclusion)
Cover 2 geranium plants in plastic bags. Put soda lime into the first plant (to absorb CO2 in the air) and sodium hydrogencarbonate in the other (to give out CO2).
Carry out the starch test. The leaf from the first plant should stay yellow-brown and the leaf from the second plant should turn blue-black
CONCLUSION = the first plant stays yellow-brown while the other turns blue-black, meaning there was starch present. This plant contained sodium hydrogencarbonate which gives out CO2. The other had no CO2 and this was the only difference between them. Therefore CO2 is needed for photosynthesis
Is oxygen produced in photosynthesis experiment (with conclusion)
Add a spatula of sodium hydrogencarbonate to a beaker of water (to provide CO2)
Place pondweed (elodea) into the beaker
Cover elodea with upturned funnel. Place a test tube of water over the funnel and leave near a light source for 2 days. Make sure there is a heat shield in front of the pondweed (temperature also affects photosynthesis - we want to only see how light affects it.)
The elodea will now have produced a gas. Test it with a glowing splint - it will relight
CONCLUSION = the glowing splint relights meaning the gas produced in photosynthesis is oxygen
How to measure the ROP using elodea (with conclusion)
Darken the room
Cut a piece of elodea and attach a paper clip to weigh it down
Add a spatula of sodium hydrogencarbonate into a test tube of water (this i s a source of CO2 and will help the plant photosynthesise)
Place elodea into this test tube with the paperclip at the bottom
Place test tube into a beaker of warm water
Place lamp 5cm away from beaker and use a heat shield
Shine light onto elodea and count no of bubbles formed in 1min
Move plant further away and recount bubbles
Repeat until plant is 50cm away
CONCLUSION = light provides energy for photosynthesis therefore more light means more photosynthesis faster. Counting bubbles isn’t a very reliable way to test ROP as they have different volumes and therefore different levels of oxygen in each
What happens in the mesophyll layers?
Photosynthesis
