7. photosynthesis

Question 1

photosynthesis background

Answer 1

• All green plants contain chloroplasts which contain a green pigment called chlorophyll.
• Plants are autotrophs (they make their own food)
• In a food system they are classed as primary producer
• Plants use simple materials (carbon dioxide, water) as raw materials to make food (glucose)
• photosynthesis is controlled by enzymes.

Question 2

sunlight in photosynthesis

Answer 2

sunlight provides energy to drive photosynthesis. Light is trapped by the chlorophyll in the chloroplast.

Question 3

photosynthesis word equation

Answer 3

light
energy
carbon dioxide ———————-> glucose+oxygen
chlorophyll

Question 4

there are two distinct stages in photosynthesis
1. light dependent stage

Answer 4

• light energy that is trapped in the chlorophyll is used to spilt the water molecules into hydrogen + oxygen (photolysis).
• ATP molecules are formed from ADP + pi.
• Hydrogen and ATP that are made in stage 1 are passed to be used in stage 2.
• oxygen is a by product and diffuses out of leaf.

Question 5

2. carbon fixation stage

Answer 5

• this stage is controlled by enzymes so it is temperature dependent.
• the ATP from the light dependent stage is used to combine the hydrogen (from stage 1) with carbon dioxide that has diffused into the leaf, these are combine to form glucose.

Question 6

what are the uses of sugar.

Answer 6

1. some can be used right away for respiration.
2. some can be converted to structural carbohydrate cellulose.
3. some can be converted to starch (storage carbohydrate) so it can be converted back to glucose if needed for respiration.

Question 6

what are the uses of sugar.

Answer 6

1. some can be used right away for respiration.
2. some can be converted to structural carbohydrate cellulose.
3. some can be converted to starch (storage carbohydrate) so it can be converted back to glucose if needed for respiration.

some of the carbohydrates made from photosynthesis can be converted to proteins and fats.
The plant requires nitrate from the soil to make protein - nitrate is absorbed through the roots.

Question 7

factors affecting photosynthesis (limiting factors)

Answer 7

1. light intensity
2. temperature (enzymes are required)
3. carbon dioxide concentration

1 ~ as light intensity increases, this will increase the rate of photosynthesis until another factor becomes limiting.
3 ~ As CO2 concentration increases so will photosynthesis rate increase until another factor becomes limiting.
2 ~ as temperature increases so does photosynthesis increase until 37/40 C when enzymes become denatured.