B1.4

Question 1

How does the plant get carbon dioxide and water

Answer 1

Carbon dioxide diffuses in from the air into the plant through the stomata

Water enters the roots from the soil through the root hair cells by osmosis

Question 2

Equation for photosynthesis

Answer 2

Glucose + oxygen —> carbon dioxide + water

6CO2 + 6H20 —> C6H12O6 + 6O2

Question 3

What are the 2 stages of photosynthesis

Answer 3

Stage 1- light dependent- energy transferred from light splits water molecules into oxygen gas and hydrogen ions.

Stage 2- light independent - carbon dioxide gas combines with the hydrogen ions to make glucose.

Question 4

Is photosynthesis endothermic or exothermic

Answer 4

Photosynthesis is an endothermic reaction as energy is transferred from the surroundings to keep it going

Question 5

Why do you test a leaf for starch?

Answer 5

You can show that light, carbon dioxide and chlorophyll are essential for photosynthesis by testing a leaf for the presence of starch.

Question 6

How do you test a leaf for starch?

Answer 6

1. Take a leaf and place it in a beaker of boiling water for a minute to kill it
2. Place the leaf into a boiling tube of boiling ethanol to remove the chlorophyll
3. Wash the leaf with water to remove the ethanol
4. Spread it out on a white tile and add iodine solution onto the leaf.
5. If starch is present it will turn from yellow brown to blue black

(Before doing this you have to destarch the plant by placing it in the dark

Question 7

How can you prove chlorophyll is needed for photosynthesis?

Answer 7

Place a destarched variegated plant in sunlight for a few hours. You then test one of its leaves for the presence of starch

Question 8

How can you prove light is needed for photosynthesis?

Answer 8

Take a destarched plant and cover part of one of its leaved with black card of tin foil so that light cannot reach the covered area of the leaf

Place the plant in sunlight for several hours.
Then remove the card from the leaf and test it for the presence of starch.

Question 9

How can you prove carbon dioxide is needed for photosynthesis?

Answer 9

Take a destarched plant and place it inside a polythene bag.

Before you seal the bag ass a pot of soda lime (it absorbs co2 and water vapour).

Place the plant in sunlight for several hours before testing one of its leaves for the presence of starch.

Question 10

How can you prove that oxygen is given off during photosynthesis?

Answer 10

Place an upturned test tube above an aquatic plant.
Put the apparatus in light
When you have collected a full tube of gas, place a splint inside the test tube and it will relight because of the oxygen present

Question 11

What factors affect the rate of photosynthesis

Answer 11

Light intensity
Carbon dioxide
Temperature
These are all the limiting factors

Question 12

How can you measure the rate of photosynthesis

Answer 12

By measuring how much oxygen or glucose a plant makes in a given time

Question 13

How do you CALCULATE the rate of photosynthesis

Answer 13

Rate = 1➗time

Question 14

How does light intensity affect the rate of photosynthesis?

Answer 14

The higher the light intensity, the faster the rate of photosynthesis. This continues until photosynthesis reaches its maximum rate

Question 15

How does carbon dioxide affect the rate of photosynthesis?

Answer 15

The grater the carbon dioxide concentration, the faster the rate of reaction. However there isn’t much co2 in the atmosphere meaning co2 is the limiting factor

Question 16

How does temperature affect the rate of photosynthesis?

Answer 16

Photosynthesis is a series of enzyme controlled reactions, therefore, the higher the temperature, the faster the reactions occur. If the temperature is too high, the enzymes will denature and the reaction will stop.

Question 17

Inverse square law (calculating relative light intensity)

Answer 17

Relative light intensity= 1➗ (distance from light source2)