Photosythesis

Question 1

Why do plants need photosynthesis?

Answer 1

To make glucose (food)

Question 2

Why are leaves green?

Answer 2

Because of the chlorophyll that gives it pigment.

Question 3

What is the word equation for photosynthesis?

Answer 3

Carbon dioxide + water —> sugar + oxygen

Question 4

What is the symbol equation for photosynthesis?

Answer 4

5Co2 + 6H2O —> C6H12O6 + 6O2

Question 5

What is photosynthesis?

Answer 5

It is an endothermic reaction (meaning it takes in heat) as it requires light energy to react carbon dioxide and water to produce glucose and oxygen.

Question 6

What happens to glucose made by plants?

Answer 6

Glucose is used, the remaining is turned into larger chains of starch that can be stored

Question 7

How do you test a leaf for starch? (4marks)

Answer 7

-place the leaf in boiling water for 30 seconds, which softens the leaf and kills it.
- place the leaf in ethanol and heat it in a water bath for 10 minutes to remove the chlorophyll and decolorize the left.
-after rise the leaf in cold water
-Add a few drops of iodine solution onto the leaf and if startch is present it will turn blue/black

Question 8

Suggest and explain what would happen if you tested a plant that had been left in a room with a lower temperature or a lower concentration of carbon dioxide.

Answer 8

It wouldn’t turn blue/black because it wouldn’t have been able to photosynthesise so starch would not be present

Question 9

What are some limiting factors of photosynthesis?

Answer 9

-carbon dioxide concentration
-light intensity
-temperature
-water
-chlorophyll

Question 10

Explain how oxygen is used in cells

Answer 10

Used for respiration to release energy

Question 11

What do plants need for photosynthesis?

Answer 11

-carbon dioxide
-water
-sunlight
-chlorophyll
-warm temperature (because it is an enzyme controlled reaction)

Question 12

Describe the light intensity graph and how it affects the rate of photosynthesis

Answer 12

-As light intensity increase the rate of photosynthesis also increases,this is shown by a steep line. Here light intensity is the limiting factor as it controls how fast the reaction happens.
-The rate of photosynthesis is slowing down shown by the curve line.
-The rate of photosynthesis becomes constant shown by the straight line. This is due to not having enough of Co2, water or chlorophyll or the temperature decreasing.

Question 13

Explain how you would set out an investigation on the effects of changing light intensity on the rate of photosynthesis.

Answer 13

-set out equipment
-place the lamp 20cm away from the plant and measure the rate of photosynthesis by counting the number of bubbles produced within a minute
- repeat for different distances e.g 40,60,80
-repeat the experiment to identify any anomaly’s and calculate a mean

Question 14

What are some control variables when investigating how the change in light intensity affects photosynthesis?

Answer 14

-Same type of plant
-same number of leaves
-same type of bulb
-same volume of water
- same concentration of Co2
-same temperature

Question 15

What could you improve when doing the practice to find how light intensity affects photosynthesis?

Answer 15

-Counting the number of bubbles is inaccurate as humans miscount some of the bubbles that may be produced fast
-use a gas syringe and a stop watch to measure the volume of gas produced which in a certain time.
-bubbles can give off heat which can effect the rate of photosynthesis, so use LED bulbs.

Question 16

What is glucose used for in photosynthesis?

Answer 16

-needed for respiration to release energy.
-used to make cellulose cell walls
-used to make amino acids needed to make proteins for growth
-excess glucose is converted to starch for storage
-used to make fats