Topic 6: diffusion, osmosis and plant functions

Question 1

what is diffusion?

Answer 1

The net movement of particles from an area of high density to an area of low density- down the graidient.

Question 2

What is osmoses?

Answer 2

The net movement of water particles from an area of low concentration to an area of high concentration.
(think of it as a percentage - if there 1 litre of water with 20% sugar in and next to it there is 10 ml of water, the 10 ml will have a higher concentration as it is just water)

Question 3

How do plants absorb water from the soil?

Answer 3

osmosis

Question 4

How do plants transport water and nutrients?

Answer 4

Through the xylem and Phloem

Question 5

What does the Xylem do?

Answer 5

Transports water and nutrients From the roots to the leaves

Question 6

What does the phloem do?

Answer 6

Transports the food produced in the leaves to the rest of the plant.(translocation)

Question 7

How do selective weed killers only kill pests?

Answer 7

They contain a growth hormone which is absorbed by mainly the weeds and causes them to grow to much and die.

Question 8

What are auxins?

Answer 8

Growth hormones which contribute to phototropism and gravitropism

Question 9

What is phototropism?

Answer 9

When a plant grows towards the light due to having more auxins in the shaded side so it grows round to face the light.

Question 10

What is gravitropism

Answer 10

When a plant grows upwards due to have more auxins in the die facing down.

Question 11

What is the difference in structure between the xylem and phloem?

Answer 11

• Xylem vessels consist of dead cells. They have a thick, strengthened cellulose cell wall with a hollow lumen
• Phloem vessels contain living cells and sieve tube elements which have very little cytoplasm so that there is a lot of space to transport sucrose and other nutrients. They also have companion cells providing the energy for active transport.

Question 12

What is transpiration and how does it help with the transportation of water?

Answer 12

Transpiration is when water evaporates from the leaves stomata. This means water is always being lost out of the leaves, which causes water to be drawn up the xylem, acting similar to a straw.

Question 13

What factors increases transpiration?

Answer 13

• Light
• temperature
• wind
• humidity

Question 14

How does light increase the rate of transpiration?

Answer 14

When there is more light, photosynthesis can happen at a faster rate, which means more carbon dioxide needs to be taken in so the stomata in the leaf widen.
This also mean more water can evaporate out of the larger stomata, so more water is drawn up through the xylem.

Question 15

How does temperature increase the rate of transpiration?

Answer 15

Temperature increases how quickly evaporation and diffusion occurs because the particles have more energy.

Question 16

How do stronger winds increase the rate of transpiration?

Answer 16

Water vapour is removed quickly by air movement, speeding up diffusion of more water vapour out of the leaf.

Question 17

How does humidity increase the rate of transpiration?

Answer 17

osmosis out of the leaf is slowed down as the gradient from concentration of water is closer, as the air is already full of water vapour.

Question 18

Why is the movement of water important for a healthy plant?

Answer 18

• Cooling
• photosynthesis
• support
• movement of minerals

Question 19

What are two ways in which the plant is adapted to reduce water loss?

Answer 19

• Guard cells on the stomata to close the stomata if there is not enough water
• A waxy cuticle (waterproof covering over the leaf)

Question 20

Where does photosynthesis take place?

Answer 20

in the chlorophyll, which is in the chloroplast

Question 21

What is translocation?

Answer 21

The transportation of sucrose around a plant through the phloem

Question 22

How is the leaf adapted for photosynthesis?

Answer 22

• Air containing CO2 sounds most of each cell, so that gas exchange can occur over most of the surface
• epidermis cells are transparent so let light pass through to the cells with more chlorophyll in
• xylem brings the cells water
• stomata allow CO2 into the leaf and allow oxygen to escape.

Question 23

How can you measure the rate of transpiration?

Answer 23

Using a potometer:

1) note the start position of the air bubble
2) note the end position of air bubble
3) divide the distance moved by the bubble, by the time taken.

Question 24

How does phototropism work?

Answer 24

Auxins in the top of the plant move way from the light (to the shaded side of the plant), which causes that side to grow quicker. This causes the plant to curve round into the direction of the light.

Question 25

How do roots know to grow down, and shoots to grow up?

Answer 25

In roots, the auxins inhibit cell elongation. Because of gravity, the auxins accumulate near the bottom of the root. This cause the opposite side to grow faster and bend downwards.

In the shoot, auxins stimulate cell elongation, so it bends upwards.

Question 26

What are gibberellins?

Answer 26

A plant hormone which stimulates the germination of seeds. This can be used to increase the yield of crops and cause fruit to grow bigger, without seeds.

Question 27

How do selective weed killers work?

Answer 27

They cause the selected weed to grow themselves to death without affecting the other plants.