B1.4 Photosynthesis

Question 1

Carbon Dioxide + Water -> Glucose + Oxygen

Answer 1

CO2 - diffusion through stomata
Water - osmosis through root hair cells
Glucose - used for respiration
Oxygen - some is released, some used for respiration

Question 2

What type of reaction is photosynthesis

Answer 2

Endothermic

Question 3

Where does photosynthesis occur

Answer 3

In chlorophyll

Question 4

2 stages of photosynthesis

Answer 4

Stage 1 - light dependent - light energy splits water into oxygen gas and hydrogen ions
Stage 2 - light independent - carbon dioxide gas combines with hydrogen ions to form glucose

Question 5

Uses of glucose

Answer 5

Starch (energy store)
Sucrose (stored in fruit)
Cellulose (cell walls)
(+nitrogen) proteins
Lipids (energy store)

Question 6

Factors affecting rate of photosynthesis

Answer 6

Temperature - there is an optimum temperature and if too high, enzymes denature and rate is zero
Carbon dioxide concentration - the higher the better but it reaches its maximum rate
Light intensity - the brighter the better but eventually rate of photosynthesis will reach its maximum

Question 7

How to measure rate of photosynthesis

Answer 7

Rate=1/time

Question 8

How to measure relative light intensity

Answer 8

RLI = 1/(distance from source)^2

Question 9

Altering factors of photosynthesis

Answer 9

Light intensity - alter distance from light source
CO2 levels - add potassium hydrogen carbonate which releases CO2 to the air
Temperature - put apparatus in water bath

Question 10

Test for starch

Answer 10

More starch = more photosynthesis

1) place leaf in boiling water
2) place leaf in boiling ethanol (heat from water bath as ethanol’s flammable) to remove chlorophyll
3) wash the leaf to clean and soften
4) put iodine solution on leaf
5) starch turns yellow iodine into blue/black colour

Question 11

Test if chlorophyll is needed for photosynthesis

Answer 11

Variegated leaves are partly green (have chlorophyll)
Place destarched leaf in sunlight
Test for starch
Green parts should be black

Question 12

Test for light

Answer 12

Tape half of leaf
Leave in sunlight
Test for starch

Question 13

Test for CO2

Answer 13

Put plant in polythene bag
Put soda lime in the bag which absorbs CO2 and water
Place in sunlight
Test for starch, no starch should be present

Question 14

Test for O2 production

Answer 14

Place upside down test tube on top of pondweed
Put in sunlight
When tube is full of gas, put a glowing splint in it and see if it reignites