Topic 2 Photosynthesis

Question 1

What is photosynthesis?

Answer 1

A chemical change which happens in green leaves which is the first step towards making food. It is an endothermic reaction

Question 2

Where does photosynthesis take place?

Answer 2

Chloroplasts where chlorophyll absorbs light

Question 3

Word equation for photosynthesis

Answer 3

Carbon dioxide + water (light and chlorophyll) —> glucose + oxygen

Question 4

Balanced equation for photosynthesis

Answer 4

6CO2 + 6H2O —> C6H12O6 + 6O2

Question 5

What else is photosynthesis important for?

Answer 5

Animals as it produces food and oxygen

Question 6

What is destarching? How do you do it?

Answer 6

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

Question 7

What is oxygen usually considered as in photosynthesis?

Answer 7

A waste product

Question 8

What factors limit photosynthesis?

Answer 8

Light, carbon dioxide and temperature

Question 9

What does light do to rate of photosynthesis?

Answer 9

Speed up ROP, but only until the optimum. Beyond this light makes no difference to photosynthesis

Question 10

What is the optimum?

Answer 10

The point at which increasing the factor will make no difference to ROP

Question 11

What does carbon dioxide do to ROP?

Answer 11

Speed up the ROP until the optimum. After this carbon dioxide makes no difference

Question 12

What does temperature do to ROP?

Answer 12

Speeds up ROP until the optimum (30 degrees). Enzymes controlling photosynthesis will become denatured, meaning beyond the optimum it makes no difference

Question 13

When does respiration happen?

Answer 13

24/7

Question 14

When does photosynthesis happen?

Answer 14

In light

Question 15

Word equation for respiration

Answer 15

Glucose + oxygen —> carbon dioxide + water + energy

Question 16

What is the name of MY RED LIP indicator?

Answer 16

Hydrogencarbonate or bicarbonate indicator

Question 17

What does MY RED LIP mean?

Answer 17

MY = More means Yellow (increased CO2 levels)
RED = red is normal (normal CO2 levels)
LIP = Less Is Purple (decreased CO2 levels)

Question 18

Does respiration and photosynthesis happen during the day?

Answer 18

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

Question 19

Does respiration and photosynthesis happen at night?

Answer 19

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

Question 20

Does respiration and photosynthesis happen at dawn/dusk?

Answer 20

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

Question 21

What is the compensation point? Describe it

Answer 21

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

Question 22

Waxy cuticle

Answer 22

Transparent defence layer to prevent water loss

Question 23

Upper and lower epidermis

Answer 23

Underneath the cuticle, the cells which produce the cuticle

Question 24

How many layers does the mesophyll have?

Answer 24

Two, the palisade layer and spongy layer

Question 25

Palisade layer

Answer 25

Cells are tightly packed to absorb sunlight with many chloroplasts

Question 26

Spongy layer

Answer 26

Large surface area due to air spaces between many cells to allow gas exchange. Has many chloroplasts

Question 27

What adaptations do the lower epidermis and waxy cuticle have?

Answer 27

Stomata and guard cells

Question 28

Stomata

Answer 28

Tiny holes within the upper/lower epidermis

Question 29

Guard cells

Answer 29

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

Question 30

How to carry out starch test (with conclusion)

Answer 30

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

Question 31

How to carry out test for chlorophyll in photosynthesis (with conclusion)

Answer 31

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

Question 32

How to carry out test for carbon dioxide in photosynthesis (with conclusion)

Answer 32

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

Question 33

Is oxygen produced in photosynthesis experiment (with conclusion)

Answer 33

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

Question 34

How to measure the ROP using elodea (with conclusion)

Answer 34

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

Question 35

What happens in the mesophyll layers?

Answer 35

Photosynthesis