Paper 1: Topic 4 Bioenergetics - Photosynthesis (LV)

Question 1

State the word equation for photosynthesis

Answer 1

Carbon dioxide + water → glucose + oxygen

remember to write light and chlorophyll above the arrow between the reactants (left hand side) and products (right hand side)

Question 2

State the chemical symbol equation for photosynthesis

Answer 2

CO₂ + H₂0 → C₆H₁₂O₆ + O₂

_{You must be able to write this equation in the correct format for the exam}

Question 3

Describe the process of photosynthesis

Answer 3

Green plants and algae use light energy to convert carbon dioxide and water into glucose and oxygen.

Question 4

State the raw materials needed for photosynthesis

Explain how the plant obtains both of these raw materials

Answer 4

1. Carbon dioxide (obtained from the air when carbon dioxide diffuses into the leaf through the stomata)
2. Water (absorbed by the root hair cells and then transported up the plant to the leaves in the xylem by transpiration)

Question 5

Other than the 2 raw materials what else is needed for photosynthesis to occur

Answer 5

Light

Chlorophyll

Question 6

Name the waste product of photosynthesis

Answer 6

Oxygen

Question 7

Define the term endothermic

Answer 7

A chemical reaction that absorbs energy from the environment

In photosynthesis the energy is absorbed from the light and transfered to the chloroplasts

Question 8

Is photosynthesis an endothermic or exothermic reaction?

Answer 8

Endothermic

Question 9

State 5 uses of glucose in plants

Answer 9

1. For respiration to produce ATP
2. Converted to insoluble starch for energy storage
3. Converted to cellulose to make new cell walls
4. To produce amino acids to produce new proteins for growth and repair of tissues and organs
5. To make oils or lipids for energy storage in seeds

Question 10

What nutrients do plants need to make amino acids?

Answer 10

Glucose (from photosynthesis) and nitrate ions (taken up from the soil by root hair cells)

Question 11

State 3 reasons why plants store starch

Answer 11

1. It is does not affect the water potential of the cell
2. It is insoluble
3. It stores a lot of energy per molecule

Question 12

Where do plants store starch?

Answer 12

In their roots, stems and leaves

Question 13

State 3 factors that affect the rate of photosynthesis

Answer 13

3 from

• Temperature
• Light
• Concentration of carbon dioxide
• Amount of chlorophyll present

Question 14

State 3 aspects of light that affect the rate of photosynthesis

Answer 14

1. Wavelength (not all wavelengths can be used by plants)
2. Duration (length of time there is light)
3. Intensity (how much light is available)

Question 15

Define the term ‘limiting factor’

Answer 15

The variable that limits the reaction from occurring any faster

Question 16

What are the 4 limiting factors that can affect the rate of photosynthesis?

Answer 16

1. Temperature
2. Light
3. Concentration of carbon dioxide
4. Quantity of chlorophyll in the leaves

HINT: do NOT say water - this is found in all plants cells and therefore very very rarely a limiting factor

Question 17

Describe a situation when carbon dioxide may be a limiting factor for photosynthesis

Answer 17

At night when the stomata are closed

This prevent gas exchange occurring in the leaf

Question 18

Describe a situation when temperature may be a limiting factor for photosynthesis

Answer 18

A cold winter’s day when air temperatures are very low

Question 19

Describe a situation when light intensity may be a limiting factor for photosynthesis

Answer 19

Night time!

Or a very cloudy day

Question 20

Describe a situation when chlorophyll may be a limiting factor for photosynthesis

Answer 20

When the plants are deficient in magnesium (referred to as environmental stress)

If the plant has a disease such as tobacco mosaic virus (reduces the amount of chlorophyll)

Question 21

What is meant by the term environmental stress

Answer 21

When a plant can’t obtain all the nutrients it requires for healthy growth e.g. lack of mineral ions, lack of water (drought)

Question 22

How can the rate of photosynthesis be studied

Answer 22

Measure the volume of oxygen produced in a given period of time

Question 23

How can oxygen production be measured?

Answer 23

• By the displacement of water using an upturned measuring cylinder filled with water

OR

• By collecting the gas in a gas syringe

Question 24

How can you ensure that carbon dioxide is not a limiting factor when investigating the rate of photosynthesis?

Answer 24

Study the rate of photosynthesis using an aquatic plant

Add hydrogen carbonate to the water to ensure an excess of carbon dioxide is available

Question 25

How can you prevent temperature affecting the rate of photosynthesis if you are investigating the effect of light intensity?

Answer 25

• Use a heat screen between the plant and the light source e.g. a beaker filled with water to absorb the heat energy emitted from the light bulb

Or

• Use a set of apparatus that can be immersed in a thermostatically controlled waterbath

Question 26

At what temperature do photosynthetic enzymes usually become denatured?

Answer 26

45⁰C

Question 27

Give an example of a situation where photosynthetic enzymes may get denatured

Answer 27

In a greenhouse on a hot, sunny day

Question 28

Explain why counting bubbles is not an accurate method of measuring the rate of photosynthesis

Answer 28

• The size and volume of the bubble can vary
• Bubbles evolve at a very fast rate resulting in inaccurate counting
• Some bubbles may remain trapped on the underside of the leaves and not rise to the surface for counting

Question 29

Explain why white light is best used when investigating the rate of photosynthesis in a laboratory

Answer 29

White light covers a wide range of wavelengths of light (~390-700nm) so should result in faster photosynthesis

Question 30

Describe how to calculate light intensity

Answer 30

1 divided by the distance squared

Light intensity = 1/d²

Question 31

Describe how greenhouses help artificially create optimal conditions for farming

Answer 31

• Greenhouses trap light
• They also heat up quickly as the Sun’s heat gets trapped
• The raised temperature and a good source of light both increase photosynthesis

Question 32

State 2 reasons why it is important to ventilate a greenhouse in the summer

Answer 32

• To prevent the temperature rising about 45^oC as this would denature the enzymes involved in photosynthesis
• To maintain air circulation to ensure there is a sufficient carbon dioxide available

Question 33

Suggest and explain 2 ways a gardener could increase the rate of photosynthesis in his greenhouse during winter

Answer 33

Suggestion 1:

Use a paraffin heater

This will give out heat (increase enzyme activity)

And it will produce carbon dioxide as a waste gas (a raw material for photosynthesis)

Suggestion 2:

Use special lighting

This will emit the most efficient wavelengths of light for the plants It will increase light intensity and duration (to overcome the short winter daylight hours)

Question 34

State 4 factors that a gardener must consider when evaluating the effectiveness of a greenhouse

Answer 34

1. Cost of lighting
2. Cost of heating
3. Cost of fertilisers
4. Cost of pesticides & insecticides

Question 35

Explain why some gardeners use paraffin heaters in their greenhouses

Answer 35

• This will increase the temperature (increase enzyme activity)
• And it will produce carbon dioxide as a waste gas (which can then be used as a raw material for photosynthesis)

Question 36

Explain why some gardeners use light bulbs that emit specific wavelengths of light rather than white light

Answer 36

This will emit the most efficient wavelengths of light for the plants

It will increase light intensity

Using any light bulbs will increase light intensity and duration (to overcome the short winter daylight hours)

Question 37

Why do plant cells convert glucose to starch?

Try to think of 2 reasons

Answer 37

1. Starch is insoluble and can be used to store glucose
2. Starch can be broken down to release glucose which can then be used by the cells for respiration

Question 38

What test would you carry out to show the presence of lipids?

What would you observe if lipids are present?

Answer 38

Test: Sudan (III)

Positive result: 2 layers form. The top layer will be red.

Question 39

What test would you carry out to show the presence of sugars?

What would you observe if sugars are present?

What would you observe if no sugars are present?

Answer 39

Test: Benedicts test (Copper sulfate solution) added to a sample of the food and then placed in a water bath at 80^oC

Positive result:

Green - Yellow - Orange - Brick red

Negative result: Solution remains blue

Question 40

What test would you carry out to show the presence of starch?

What would you observe if starch is present?

What would you observe if no starch is present?

Answer 40

Test: Add iodine solution

Positive result: Blue-black colour

Negative result: solution remains yellow-brown

Question 41

When testing a leaf for the presence of starch why must the plant be placed in an area of bright light before the test is carried out?

Answer 41

To make sure the plant has been exposed to enough light to enable it to photosynthesise

Question 42

When testing a leaf for the presence of starch why must the leaf first be placed in boiling water?

Answer 42

To remove the waxy cuticle

Question 43

When testing a leaf for the presence of starch must the leaf be placed in ethanol?

Answer 43

To remove the chlorophyll pigment

If this was not removed the green pigment would mask the colour change of the iodine solution

Question 44

Describe how the waste product of photosynthesis is removed from the leaf

Answer 44

The oxygen diffuses from the plant cells into the air spaces inside the leaf

Then the oxygen diffuses out of the leaf to the external atompshere through the stomata

Question 45

State 3 types of cell that contain chloroplasts

Answer 45

1. Palisade mesophyll cells (contains the highest number)
2. Guard cells
3. Spongey mesophyll cells

Question 46

Decsribe and explain how temperature affects the rate of photosynthesis

Answer 46

At low temperatures the rate of photosynthesis will be low (as the enzymes are inactive)

As the temperature increases the rate of photosyntheiss increases

The rate of photosynthesis will double for every 10^oC rise intemperature upto the optimum temperature of the enzymes used in photosynthesis

After the optimum temperature the rate of photosynthesis will decrease rapidly to zero (as the enzymes are denatured)

Hint: remember when temperature increases remember the rate of diffusion will also increase as the molecules have more kionetic energy

This means the plant cells will be able to take up more carbon dioxide faster as the temperature increases

Question 47

General maths: exam questions often ask you to calculate various answers. Typical questions can be to

a) calculate a mean
b) calaculate the percentage increase in a variable

Describe how you would calculate these values

Answer 47

Calculating a mean

Add all the values together and then deivide by the number of pieces of data

Calculating the % increase in a variable

Change in the variable x 100

Original variable

Question 48

Predict the colour change for each test tube when using hydrogen carbonate indicator.

Hydrogencarbonate indicator will turn purple as there is less carbon dioxide than atmospheric levels. The indicator will turn yellow as carbon dioxide levels increase above atmospheric levels.

Answer 48