Photosynthesis

Question 1

Photosynthesis equation

Answer 1

Carbon dioxide + Water —-> Oxygen + Glucose (—->Starch)

Question 2

Testing a leaf for starch (QWC)

Answer 2

• Collect leaf
• Heat beaker of water
• Using forceps, place leaf in water to break down cell wall and membrane (kill leaf)
• Use forceps to remove leaf and turn off Bunsen burner (ethanol is flammable)
• Place leaf in boiling tube and add ethanol to remove green colouring (chlorophyll) by heating tube in beaker
• Pour contents of tube into beaker for about a minute
• Use forceps to unfold leaf on Petri dish on white tile
• Use pipette to cover leaf in iodine solution
• Blue-black colour indicates starch is present

Question 3

Where does photosynthesis take place?

Answer 3

In leaves

Question 4

How can you prove chlorophyll is needed for photosynthesis?

Answer 4

Starch test on variegated leaf. Results will show:
Edges of leaf that are white due to lack of chlorophyll- iodine stay orange, no starch
Green area has chlorophyll- iodine turns blue/black, starch present

Question 5

Photosynthesis and respiration in plant during day and night

Answer 5

• Day = photosynthesis quicker than respiration
• CO2 respired diffused into leaf
• Respiration uses up some of oxygen made by photosynthesis, rest diffuses out of leaf
• Night = no photosynthesis
• oxygen diffuses into leaf for respiration and CO2 made by respiration diffuses out

Question 6

Explain what photosynthesis is (QWC)

Answer 6

• Photosynthesis is the process whereby light energy is changed in chemical energy (glucose)
• Takes place in leaves of plants
• Process requires sunlight, water, chlorophyll and carbon dioxide
• Produces glucose and oxygen
• Excess glucose converted to starch which is stored

Question 7

Chemical that absorbs sunlight in plants

Answer 7

Chlorophyll

Question 8

Where is the chemical that absorbs sunlight found?

Answer 8

Chloroplasts

Question 9

3 main limiting factors

Answer 9

Concentration of CO2 in air, ambient temperature, light intensity

Question 10

What is meant by a limiting factor of photosynthesis?

Answer 10

Affects the rate/speed of photosynthesis

Question 11

How CO2 and temperature limit photosynthesis

Answer 11

• Even with plenty of light, a plant can’t photosynthesise without CO2
• Higher concentration of CO2 = faster rate (until exceeds optimum)
• Rate of photosynthesis will decrease if plant too cold
• Plant can’t photosynthesise if too hot
• Any temperature higher than optimum will cause enzymes to denature