photosynthesis

Question 1

what is photosynthesis?

Answer 1

a chemical reaction where a plant uses carbon dioxide and water to produce glucose and oxygen, the reactants of respiration (‘to make their own food’)

Question 2

word equation for photosynthesis

Answer 2

carbon dioxide + water –> glucose + oxygen

Question 3

name the main organ of a plant for photosynthesis

Answer 3

the leaves

Question 4

what cell organelle traps light energy for photosynthesis?

Answer 4

chloroplasts - contain a green pigment called chlorophyll which traps light

Question 5

what is the glucose produced by photosynthesis used for?

Answer 5

• formation of cellulose cell walls
• stored in seeds (as lipids/fats)
• stored as starch, insoluble form

Question 6

what is a limiting factor?

Answer 6

a factor which, if in short supply limits or reduces the rate of photosynthesis

Question 7

what are the 3 factors that affect the rate of photosynthesis?

Answer 7

• light intensity
• carbon dioxide concentration
• temperature

Question 8

how does light intensity affect the rate of photosynthesis?

Answer 8

initially, as light intensity increases, so does photosynthesis, as plants need light energy for it to take place (endothermic reaction) - however, past the optimum, the reaction rate does not increase as another limiting factor is short in supply (e.g. carbon dioxide, temp)

Question 9

how does carbon dioxide concentration affect the rate of photosynthesis?

Answer 9

initially, as carbon dioxide increases, so does photosynthesis, as plants need carbon dioxide for it to take place (reactant) - however, past the optimum, the reaction rate does not increase as another limiting factor is short in supply (e.g. temp, light)

Question 10

how does temperature affect the rate of photosynthesis?

Answer 10

initially, as temperature increases, so does the rate of photosynthesis - this is because there are more collisions between the enzymes and the substrates.
however, past the optimum temperature, the active site of the enzyme may begin to change shape so it is no longer complimentary to the substrate (denaturation)
this would decrease the rate of reaction and eventually stop the reaction

Question 11

how can we investigate the effect of light intensity on photosynthesis? (rp 6)

Answer 11

• place a boiling tube 10cm away from an LED light source (use a ruler)
• add sodium hydrogen carbonate to the tube as this releases carbon dioxide, a reactant for photosynthesis
• put a piece of pondweed in the boiling tube (cut end should be upwards)
• wait 5 minutes, you should see some bubbles produced from the cut end of the pondweed
• start a stopwatch, count number of oxygen bubbles per minute
• repeat with 20cm, 30cm, 40cm twice more then calculate average to increase accuracy

Question 12

what are the potential problems of this practical?

Answer 12

1. bubbles may be too fast to count
2. bubbles will be different sizes

Question 13

are there any hazards we could face?

Answer 13

LED light source may get hot - handle with caution

Question 14

how can we improve this practical?

Answer 14

instead of counting bubbles, use a gas syringe to measure the volume of oxygen produced (it is much more accurate)w

Question 15

what is the inverse square law?

Answer 15

as distance increases, light intensity decreases
= 1 / distance squared