II: 6.2 - Plant nutrition

Question 1

Define

photosynthesis

Answer 1

The fundamental process by which plants manufacture
carbohydrates from raw materials using energy from light.

Question 2

State the word equation and balanced symbol equation for photosynthesis.

Answer 2

carbon dioxide + water ^light→_chlorophyll glucose + oxygen

6CO₂ + 6H₂O ^light→_chlorophyll C₆H₁₂O₆ + 6O₂

Question 3

How is carbon dioxide taken in by plants for photosynthesis?

Answer 3

The carbon dioxide moves to the leaf from the atmosphere by diffusion through tiny holes in the leaf called stomata.

Carbon dioxide is not present in a high concentration in air, but compared to its concentration inside the leaf, it is more in the air. This is because the cells inside the leaf are always doing photosynthesis (at daytime), converting the carbon dioxide into the glucose quickly, thus the concentration of it inside the leaf decreases, making a concentration gradient for diffusion from the atmosphere to the leaf.

Question 4

How is water taken in by plants for photosynthesis?

Answer 4

The water is absorbed by the roots of the plants, then they are transported (by the transpiration stream) upwards through a hollow tube called the xylem vessel, till it reaches the leaf where photosynthesis takes place, it enters the leaf through holes in the xylem.

Excess water leaves the cell through the stomata, in a process called “transpiration”.

Question 5

What is the role of chlorophyll in photosynthesis?

Answer 5

Chlorophyll is the green pigment present in the chloroplasts of photosynthesising cells. Chlorophyll traps light energy and converts it into chemical energy for the formation of carbohydrates and their subsequent storage.

Question 6

What is a variegated leaf?

Answer 6

A variegated leaf is a leaf which contains green and non-green parts. As the green parts contain chlorophyll they can photosynthesise, but the non-green parts do not contain chlorophyll and so they cannot photosynthesise.

Question 7

Describe an experiment to test if starch is present in a green leaf

Answer 7

Apparatus:

Boiling tube, ethanol, iodine, water bath, beaker, green leaf, ceramic tile, test tube holder, watch, tweezers/forceps

Method:

1. Boil the leaf in water for 1 minute. Remove and cool.
2. Roll leaf & place in boiling tube
3. Cover leaf in ethanol and heat in water bath until the leaf turns white (heat indirectly as ethanol is flammable).
4. Remove & dip in boiling/hot water until softened
5. Remove & cool by spreading the leaf flat on the tile
6. Drop iodine solution onto the leaf.

Result:

If the solution turns blue-black, starch is present. Else, no starch is present.

Question 8

Describe an experiment to investigate if chlorophyll is necessary for photosynthesis.

Answer 8

Apparatus:

1 variegated plant, apparatus for starch test

Method:

1. Destarch a variegated potted plant by leaving it in a dark cupboard for 2-3 days
2. Test one leaf for starch to be sure it is destarched
3. Leave the plant in the sunlight for 6-8 hours
4. Test one leaf for starch

Results:

Areas of the leaf that were previously green should trun blue-black. Non-green areas should be brown/yellow

Question 9

Describe an experiment to investigate whether light is necessary for photosynthesis.

Answer 9

Apparatus:

1 potted plant, foil, apparatus for starch test

Method:

1. Destarch 1 living, potted plant by leaving it in a cupboard for 2-3 days
2. Cut a piece of foil to make a stencil and use it to cover a leaf on the plant
3. Leave the plant in the sun for 6-8 hours
4. Uncover the leaf and test it for starch

Results:

Covered parts and varigated parts of the leaf will stay brown/yellow; other parts will stay blue-black

Question 10

Describe an experiment to investigate if carbon dioxide is necessary for photosynthesis.

Answer 10

Apparatus

2 potted plants, soda lime (potassium hydroxide), plastic bag/belljar, apparatus for starch test

Method:

1. Destarch both plants
2. Next to one plant, put a small container of soda lime to absorb the carbon dioxide. Cover this plant with a plastic bag or a closed bell jar
3. Cover the other plant with an opened plastic bag or bell jar
4. Leave in sunlight for 6-8 hours
5. Conduct starch test

Results:

The leaves next to the soda lime stay brown/yellow, the leaves from the other plant turn blue-black.

Question 11

Describe an experiment to investigate if oxygen is produced during photosynthesis.

Answer 11

Apparatus

Pondweed, beaker, boiling tube, funnel, water, wooden splint, lighter

1. Set up the equipment so that the pondweed is under a funnel in a beaker filled with water, with a boiling tube over the end of the funnel. Do this is a washtrough filled with water so that there is no air present.
2. Leave the equipment for a few days (depending on the conditions)
3. If gas is produced, it will gather at the top of the test tube, displacing the water. Test this gas for oxygen by placing a glowing splint into it.

Results:

If the gas is oxygen the splint will relight.

Question 12

Define

limiting factor

Answer 12

An environmental factor that, when in short supply, restricts life processes.

Question 13

What are the limiting factors of photosynthesis?

Answer 13

• Light intensity
• Carbon dioxide levels
• Temperature
• Water

Question 14

Explain how light intensity affects the rate of photosynthesis.

Answer 14

• As the amount of light increases, the rate of photosynthesis increases as there is more energy available
• The limiting factor is light
• Increasing the amount of light after a certain point has no effect on the rate as chlorophyll is absorbing the maximum amount of light energy
• The limiting factor is now carbon dioxide or temperature

Question 15

Describe an experiment to investigate the effect of varying light intensity on photosynthesis.

Answer 15

Apparatus:

Pondweed, light bulb, stopwatch, beaker, ruler

Method:

1. Place pondweed in the beaker filled with 500ml of water
2. Set lamp on a specific distance (60cm) from the beaker
3. Switch lamp on. Be careful not to touch the hot lamp during the experiment.
4. Give the pondweed time to start photosynthesising, then start the stopwatch. Count and record the number of bubbles produced within 2 minutes.
5. Repeat with decreasing distance from lamp to beaker.

Results:

Rate of photosynthesis increases as the lamp is brought closer to the plant, showing that increased light intensity increases the rate of photosynthesis.

Question 16

Explain how varying carbon dioxide levels affect the rate of photosynthesis.

Answer 16

• As the amount of CO₂ dioxide increases, the rate of photosynthesis increases as CO₂ is used as a raw material in photosynthesis
• The limiting factor is CO₂
• Increasing amount of CO₂ after a certain point has no effect on rate as the plant has the maximum amount of CO₂ it can take
• The limiting factor is now light or temperature (warmth)

Question 17

Explain how varying temperatures affects the rate of photosynthesis

Answer 17

• As temperature increases, the rate of photosynthesis increases until it reaches optimum temperature 40°C, where there is a good amount of energy for reactions
• The limiting factor is the temperature
• Increasing the temperature above 40°C will cause the enzymes to denature
• This will decrease rate of photosynthesis

Question 18

Explain the use of carbon dioxide enrichment, optimum light and optimum temperatures in glasshouse systems.

Answer 18

To increase the crop yield, farmers control the limiting factors:

• CO₂ enrichment: paraffin is burnt to increase CO₂ concentration by three times the original amount and doubling the yield
• Optimum temperature: thermostatically controlled heaters make the temperature right for the enzymes to work
• Optimum light: light has a high intensity for more photosynthesis, the correct wavelengths (red and blue not green) and duration controls production of fruit

Question 19

State the name and function of A (also K)

Answer 19

Cuticle

A waxy layer that helps to reduce water loss by evaporation.

Question 20

State the name and function of B

Answer 20

Upper epidermis

Protects the underlying tissues. It is transparent to allow sunlight to pass through.

Question 21

State the name and function of C

Answer 21

Palisade mesophyll cell

Undergo photosynthesis to produce energy-rich food compounds for the plant. Have many chloroplasts and are closer to the top of the leaf to maximise photosynthesis.

Question 22

State the name and function of D

Answer 22

Bundle sheath

Protects the vascular bundle (the xylem and phloem)

Question 23

State the name and function of E

Answer 23

Xylem

Transports water. Also helps to support the plant due to strong lignin rings.

More information about the function of the xylem in Plant Transport.

Question 24

State the name and function of F

Answer 24

Phloem

Transports food in the form of dissolved nutrients

More information about the function of the phloem in Plant Transport.

Question 25

State the name and function of G

Answer 25

Lower epidermis

Protects the tissues above it

Question 26

State the name and function of H

Answer 26

Spongy mesophyll cells

Undergo photosynthesis. Have air spaces between them to allow for the diffusion of gases to the palisade mesophyll cells.

Question 27

State the name and function of I

Answer 27

Guard cell

Opens and closes the stoma, undergoes photosynthesis

Question 28

State the name and function of J

Answer 28

Stoma

Allows gases such as CO₂, O₂ and water vapour to diffuse in and out of the leaf. Usually placed on the underside of leaves to reduce water loss by evaporation.

Question 29

State the name and function of L

Answer 29

Vein

Includes the xylem, phloem, and the bundle sheath cells protecting them.

Question 30

Describe an experiment to investigate if gaseous exchange takes place in plants, and how photosynthesis affects this.

Answer 30

Apparatus:

3 boiling tubes, bungs, test tube rack, distilled water, sodium hydrogen carbonate indicator, foil

Method:

1. Set up three test tubes with the indicator in them
2. Put leaves in two of them (but not inside the indicator)
3. Place bungs on all three test tubes
4. Cover one test tube with foil
5. Leave in sunlight for 1 hour

Results:

• The indicator in the covered test tube turned yellow (more acidic), indicating that the leaf underwent respiration only, producing CO₂
• The indicator in the test tube with the leaf without foil turned purple (less acidic), indicating that the leaf underwent more photosynthesis than respiration and used up the CO₂ in the test tube
• The indicator in the third test tube has no change (control)

Question 31

What is the compensation point?

Answer 31

This is the point where the rate of photosynthesis in a plant exactly matches the rate of respiration. There is no net intake or output of carbon dioxide or oxygen.

Question 32

What is the importance of nitrate ions in plant nutrition?

Answer 32

Nitrogen is needed for the synthesis of amino acids and proteins for plant growth, to make enzymes and cells.

A plant with nitrogen deficiency will have be small, have slow growth, pale top leaves, dead bottom leaves and roots slightly affected.

Question 33

What is the importance of phosphorous in plant nutrition?

Answer 33

Phosphorous is used to make roots.

A deficiency in phosphorous results in short roots, leading to poor growth as less water is absorbed, so less photosynthesis takes place.

Remember: Phos-for-roots

Question 34

What is the importance of potassium in plant nutrition?

Answer 34

Potassium helps to make the flowers of the plant.

A deficiency in potassium results in fewer flowers, fewer fruits and less seeds.

Question 35

What is the importance of magnesium in plant nutrition?

Answer 35

Magnesium is needed for the synthesis of chlorophyll.

A deficiency in magnesium results in yellowed leaves, stunted growth but normal roots.

Iron is a micronutrient that also helps in the synthesis of chlorophyll.

Question 36

What are nitrogen fertilisers and how are they used?

Answer 36

Nitrogen fertilisers provide nitrogen in the form of nitrate ions, nitrite ions or ammonium ions. Some fertilisers (NPK fertilisers) also provide phosphorous and potassium.

Question 37

What are the dangers of overusing fertilisers?

Answer 37

Overusing fertilisers can lead to eutrophication.

1. Fertiliser run-off into rivers & lakes
2. Algal bloom: rapid growth of aquatic plant life due to fertilisers
3. Smaller plants die due to competition for resources such as oxygen and space
4. Decomposition of dead plant material by microbes uses more oxygen
5. Death of other living things