B1.4 Photosynthesis

Question 1

Define photosynthesis

Answer 1

The process by which plants harness the energy from the sun and transfer this energy into a useable food source in the form of glucose that can be stored as starch

Question 2

State the reactants of photosynthesis

Answer 2

Carbon dioxide & water

Question 3

State the products of photosynthesis

Answer 3

glucose + oxgygen

Question 4

Photosynthesis is an ‘……..’thermic reaction.

Answer 4

Endothermic

Question 5

Endothermic means

Answer 5

a chemical reaction in which energy is transferred from the surrounding to the reacting mixture

Question 6

State the word equation for photosynthesis?

Answer 6

carbon dioxide + water (+ light) ——> oxgyen + glucose

Question 7

State the chemical equation for photosynthesis?

Answer 7

6CO₂ + 6H₂0 ( + light) ———> C₆H₁₂O₂ + 6O₂

Question 8

Why are plants and some algae termed ‘producers’?

Answer 8

They are organisms that make their own food through the process of photosynthesis

Question 9

Name the two main stages of photosynthesis?

Answer 9

1. Light dependent
2. Light independent

Question 10

State what happens in the first stage of photosynthesis?

Answer 10

The first stage is the light dependent stage of photosynthesis where energy transferred from light is used to split water molecules into oxygen gas and hydrogen ions

Question 11

State what happens in the second stage of photosynthesis?

Answer 11

The second stage is the light independent stage of photosynthesis where carbon dioxide gas combines with the hydrogen ions produced in stage 1 of photosynthesis to make glucose

Question 12

What happens to the glucose produced in photosynthesis?

Answer 12

1. Stored as starch - food store
2. Used for respiration
3. Stored in fruit as sucrose
4. Used to build cellulose cell walls
5. Combined with nitrogen to build protiens for grow and repair
6. Biosynthesis into fats and oils for food and growth

Question 13

How can you test for starch to prove photosynthesis has taken place?

Answer 13

1. Place leaf in boiling water for 1 minute to kill it
2. Place in boiling tube with ethanol
3. Place boiling tube in a water bath an boil until white (chlorophyll removed)
4. Wash leaf with water to remove ethanol and soften
5. Place on white tile and add 1-2 iodine drops
6. Watch for colour change in iodine.

Question 14

How can a leaf be ‘destarched’ before a photosynthesis experiement?

Answer 14

Keep it in the dark for a minimum of 24 hours - starch present will be used up in respiration and without light no further glucose can be produced by photosynthesis to be converted to starch.

Question 15

How do you prove chlorophyll is needed for photosynthesis?

Answer 15

1. Take a variagated plant and destarch
2. Place the destarched plant in sunlight for several hours
3. Test oneof the leave with iodine for the presence of starch

Question 16

How do you prove light is needed for photosynthesis?

Answer 16

• Take a destarched plant and cover part of one of its leaves with black card or tin foil
• Place the destarched plant in sunlight for several hours
• Remove and uncover the partially covered leaf
• Test the leaf that was partially covered with iodine for the presence of starch

Question 17

How do you prove carbon dioxide is needed for photosynthesis?

Answer 17

• Take a destarched plant cover part of one of its leaves/stems with a conical flask or polythene bag containing soda lime
• Place the destarched plant in sunlight for several hours
• Remove one of the covered leaves and test with iodine for the presence of starch

Question 18

How do you prove oxygen is given of during photosynthesis?

Answer 18

1. Place an upturned funnel and test tube over an aquatic plant in a beaker of water
2. Put the apparatus in the light for maximum photosynthesis
3. Collect a full test tube of gas
4. Place a glowing splint into the test tube to test for oxygen
5. Relights = oxygen present

Question 19

What is meant by a ‘limiting factor’?

Answer 19

Factors which can prevent an increase in the rate of photosynthesis

Question 20

State the main limiting factors which affect the rate of photosynthesis?

Answer 20

• Light intensity
• Carbon dioxide availability
• Temperature

Question 21

Which of the following is NOT a limiting factor of photosynthesis:

1. Temperature
2. Light intensity
3. Amount of chlorophyll
4. Carbon dioxide concentration
5. volume of rain

Answer 21

volume of rain

Question 22

Describes the effect of light intensity on the rate of photosynthesis

Answer 22

As light intensity increases, the rate of photosynthesis increases until another limiting factor has an effect.

Question 23

Describes the effect of temperature on the rate of photosynthesis?

Answer 23

As temperature increases, the rate of photosynthesis increases, up to a point and then any further increase in temperature decreases the rate of photosynthesis

Question 24

Why does the rate of photosynthesis drop if the temperature gets too high?

Answer 24

The enzymes involved in photosynthesis have denatured

Question 25

Describe the effect of carbon dioxide concentration on the rate of photosynthesis

Answer 25

As carbon dioxide concentration increases, the rate of photosynthesis increases until another limiting factor has an effect

Question 26

What is happening at point B on the graph?

Answer 26

Another limiting factor is preventing an increase in rate of photosynthesis.

Question 27

Based on the graph, predict where the rate of photosynthesis would plateau if the temperature was 10 degrees Celcius and the carbon dioxide concentration was 0.04%.

Answer 27

Below the 0.04% line

Question 28

Why should a farmer keep careful control of the limiting factors for photosynthesis in their greenhouse? Choose the best answer

• To maximise the rate photosynthesis to get the biggest plants
• To maximise the rate of photosynthesis in the most efficient way possible
• To maximise the light intensity for photosynthesis
• To keep the greenhouse warm for their plants

Answer 28

To maximise the rate of photosynthesis in the most efficient way possible

Question 29

Explain why commercial growers increase the carbon dioxide concentration in a greenhouse?

Answer 29

A Greenhouse is warm and light so temperature and light intensity are therefore not limiting factors.

As CO₂ concentration is the limiting factor in this situation therefore increasing CO₂ concentration with increase photosynthesis and therefore plant growth/yield

Question 30

State the inverse square law

Answer 30

relative light intensity = 1

(distance from light source)²

The law states that when you double the distance from the light source, the light intensity fall by a factor of four.

Question 31

State the limiting factor for line B

Answer 31

Temperature

Question 32

Explain why, for line A, increasing the temperature does not increase the rate of photosynthesis.

Answer 32

The carbon dioxide concentration has limited the rate of photosynthesis.