Plant structures and their functions

Question 1

Describe photosynthetic organisms

Answer 1

The main producers of
food and therefore biomass.

Question 2

Describe photosynthesis in plants and algae

Answer 2

An endothermic reaction that uses light energy to react carbon dioxide and water to produce glucose and oxygen

Question 3

Explain the effect of temperature as limiting factors on the rate of photosynthesis

Answer 3

Increase in temperature, the rate of photosynthesis increases. The reaction is controlled by enzymes, the trend continues up to a certain temperature until the enzymes begin to denature and the rate decreases.

Question 4

Explain the effect of light intensity as limiting factors on the rate of photosynthesis

Answer 4

The higher the light intensity, the faster the rate of photosynthesis.

Question 5

Explain the effect of carbon dioxide concentration as limiting factors on the rate of photosynthesis

Answer 5

Carbon dioxide is needed to make glucose. As the concentration increases, the rate of photosynthesis increases.

Question 6

CORE PRACTICAL - Investigate the effect of light intensity on the
rate of photosynthesis

Answer 6

1. Use a ruler to place the flask and pondweed 15cm from the lamp.
2. Leave the apparatus for around 10 minutes to allow the pondweed to adjust.
3. Connect the gas syringe to the flask and record the change in volume on the syringe after 5 minutes.
4. Move the lamp 10cm further away and measure volume change again. Repeat.

Plot your results on a graph of distance from lamp on the x-axis and change in gas volume on the y-axis.

Question 7

Explain how the rate of photosynthesis is inversely proportional to the distance from a light source

Answer 7

As the distance between the light source and the plant increases, the light intensity decreases. The light intensity is inversely proportional to the square of distance – called the inverse square law.

Question 8

Explain how the structure of the root hair cells is adapted to absorb water and mineral ions (3)

Answer 8

Root hair cells: specialised to take up water by osmosis and mineral ions by active transport from the soil as they are found in the tips of roots.
o Large surface area due to root hairs, meaning more water can move in.
o Large permanent vacuole affects the speed of movement of water from the soil to the cell.
o Mitochondria to provide energy from respiration for the active transport of mineral ions into the root hair cell.

Question 9

Explain how the structures of the xylem are
adapted to their function in the plant (2)

Answer 9

Xylem cells: specialised to transport water and mineral ions up the plant from the roots to the shoots.
o A chemical called lignin is deposited which causes the cells to die. They become hollow and are joined end-to-end to form a continuous tube so water and mineral ions can move through.
o Lignin is deposited in spirals which helps the cells withstand the pressure from the movement of water.

Question 10

Explain how the structures of the phloem are
adapted to their function in the plant (3)

Answer 10

Phloem cells: specialised to carry the products of photosynthesis to all parts of the plant.
o Cell walls of each cell forms structures called sieve plates when they break down, allowing the movement of substances from cell to cell.
o Despite losing many sub-cellular structures, the energy these cells need to be alive is supplied by the mitochondria of the companion cells.
o These cells use this energy to transport sucrose around the plant.

Question 11

Explain how water and mineral ions are transported through the plant by transpiration

Answer 11

Transpiration is the loss of water vapour from the leaves and stems of the plant. It is a consequence of a gaseous exchange, as the stomata are open so that this can occur.

Question 12

What is the structure and function of the stomata? (5)

Answer 12

Guard cells close and open stomata.
o Kidney shaped
o Thin outer walls and thick inner walls
o When lots of water is available to the plant, the cells fill and change shape, opening the stomata.
o This allows gases to be exchanged and more water to leave the plant via evaporation.
o More stomata are found on the bottom of the leaf, allowing gases to be exchanged whilst minimising water loss by evaporation as the lower surface is shaded and cooler.

Question 13

Describe how sucrose is transported around the plant by translocation

Answer 13

Translocation is the movement of food substances such as sucrose made in the leaves up or down the phloem, for use immediately or storage. Translocation only occurs in the phloem.

Question 14

Explain how the structure of a leaf is adapted for photosynthesis and gas exchange

Answer 14

Chlorophyll - Chlorophyll is green, which is the most efficient colour for absorbing light, meaning most light possible is absorbed.
Thinness - Leaves are very thin, meaning CO2 has a short distance to enter the leaf and oxygen has a short distance to diffuse out.
Large surface area - Leaf can absorb more light at once, maximising the rate of photosynthesis.

Question 15

Explain the effect of light intensity of the rate of water uptake by a plant

Answer 15

Leads to an increased rate of photosynthesis, so more stomata open to allow gaseous exchange to occur. Meaning, more water can evaporate leading to an increased rate of transpiration.

Question 16

Explain the effect of air movement of the rate of water uptake by a plant

Answer 16

If more air is moving away from the leaf due to it being blown away, then the concentration of water vapour surrounding the leaf will be lower. This will mean a steeper concentration gradient resulting in diffusion happening faster, increasing the rate of transpiration.

Question 17

Explain the effect of temperature of the rate of water uptake by a plant

Answer 17

Molecules move faster, resulting in evaporation happening at a faster rate and therefore the transpiration increases.

Question 18

Demonstrate an understanding of rate calculations for transpiration

Answer 18

Measuring the uptake of water by the plant gives an indication to the rate of transpiration.
Place a leaf shoot in one end of the potometer and use a ruler to measure how far the bubble travels up the capillary tube in a set time. The further the bubble moves in this time, the greater the rate transpiration and thus the greater rate of water uptake.

Question 19

Explain how plants are adapted to survive in extreme environments (3)

Answer 19

Leaf shape and size – many desert plants do not have leaves, reducing the amount of water lost as a result of transpiration.
Presence of a waxy cuticle – many leaves have a waxy cuticle on top, preventing evaporation of water in environments where water is scarce.
Stomata – when closed it can prevent evaporation of water in extreme environments and opened when CO2 is needed for photosynthesis. This is useful as it means the plant can adapt when water is scarce.

Question 20

Explain the role of auxins

Answer 20

Most plants show positive phototropism as they grow towards the light source.
o Growth hormone (auxins) moves to the shaded side of the shoot.
o Stimulates cells to grow more there.
o This means the shoot bends towards the light (positive phototropism).
o The plant receives more light, meaning photosynthesis can occur at a faster rate.
Most shoots show negative gravitropism as they grow away from gravity (horizontal).
o Auxins moves to the lower side.
o Cells of the shoot grow more on the side with most auxins, so it stimulates cells to grow there.
o Making the shoot to bend and grow away from the ground.
o This is beneficial as light levels are likely to be higher further away from the ground.

Question 21

Describe the commercial uses of auxins (3)

Answer 21

1. As weedkillers: Weedkillers contain auxin and have been synthesised, so they only affect broad-leaved plants (weeds). The increased amount of auxin causes the cells to grow too rapidly, resulting in the weed dying.
2. As rooting powders: Plants with desirable features are cloned to make more plants with the same feature. Take a cutting from the desired plant and apply rooting powders (containing auxins) and place it in the ground. Roots grow and the new plant begins to grow.
3. To promote growth in tissue culture: Another way to clone a plant. Cells from the plant are taken and placed in a growth medium and hormones such as auxins are added. The cells begin to form roots and shoots.

Question 22

Describe the commercial uses of gibberellins

Answer 22

1. Used in germination for fruit and flower.
2. They allow fruits to grow heavier and larger increasing yields.
3. Encourage flowering plants to flower at a faster rate.

Question 23

Describe the commercial uses of ethene (2)

Answer 23

1. Controls fruit ripening, used in the food industry.
2. Involved in controlled cell division and stimulates enzymes that result in fruit ripening, reducing wastage as more fruit is suitable to be sold.