Osmosis And Plant Transport

Question 1

Define osmosis

Answer 1

The diffusion of water molecules from a dilute solution to a more concentrated solution, across a selectively permeable membrane

Question 2

What does the selectively permeable cell membrane allow?

Answer 2

Allows water and other small molecules to diffuse across

Question 3

Plant cells reacting to osmosis: high concentration

Answer 3

Water moves out of the cell by osmosis
The surrounding solution had a very high concentration
Water is lost from the cytoplasm and vacuole
The cell has become plasmolysed

Question 4

Plant cells reacting to osmosis: medium concentration

Answer 4

No net movement of water. The surrounding solution is equal in concentration to the cytoplasm

Question 5

Plant cells reacting to osmosis: low concentration

Answer 5

Water moves into the cell by osmosis
The surrounding solution has a very low concentration
Water is gained by the cytoplasm and vacuole
The cytoplasm and cell wall stretch outwards
The cell has become turgid

Question 6

What happens when osmosis causes animal cells to swell up and burst?

Answer 6

It lyses

Question 7

In concentrated solutions water loss causes the cells to shrink. When this happens to red blood cells it is called ….

Answer 7

Crenation

Question 8

Animal cells reaction to osmosis: high concentration

Answer 8

Water leaves the cell by osmosis. The surrounding solution is more concentrated than the cytoplasm
Water moves out, diluting the external solution.
The cytoplasm pulls away from the cell membrane

Question 9

Animal cells reaction to osmosis: medium concentration

Answer 9

No net movement of water.

The concentration of surrounding solution and cytoplasm are equal

Question 10

Animal cells reaction to osmosis: low concentration

Answer 10

Water enters the cell by osmosis. The surrounding solution is less concentrated than the cytoplasm. The volume of the cytoplasm increases. There is no cell wall to limit water entry
The cell lyses

Question 11

Two other examples of diffusion in humans

Answer 11

Oxygen from air sacs in the lung to blood and from blood to cells
Soluble foods from gut to blood

Question 12

Osmosis is responsible for water movement in: (3)

Answer 12

• tissue fluid to cells
• soil water to root hairs
• xylem to leaf mesophyll cells

Question 13

Name four reasons why water is important to plants (4)

Answer 13

• for support when plant cells absorb water and become turgid
• for transport. Water is a solvent which many substances dissolve into and are therefore transported around the plant
• photosynthesis in which water is a raw material
• Providing water for the process of transpiration itself

Question 14

Define transpiration

Answer 14

Transpiration is the evaporation of water from mesophyll cells followed by diffusion through air spaces and the stomata

Question 15

Stages of transpiration: (4)

Answer 15

• water diffuses from the soil into the roots. Roots are covered in root hair cells which increase surface area of the roots
• water travels up the stem in the xylem. It diffuses from an area of higher water concentration to an area of lower concentration
• water travels through veins in the leaves. It then diffuses our of the veins into cells and air spaces. From these spaces water evaporates through the stomata into the air
• the loss of water through transpiration in the leaves sets up a concentration gradient continuously pulling water from the soil into all parts of the plant

Question 16

Environmental factors that affect the rate of transpiration? (4)

Answer 16

Air temperature
Wind speed
Humidity
Light intensity

Question 17

Humidity explanation

Answer 17

Humid environments have high levels of water vapour in the air, this decreases the rate of transpiration because the air is already saturated with water. Transpiration will decrease when humidity increases

Question 18

Temperature explanation

Answer 18

High temperatures heat the leaves and cause water to evaporate more quickly
Warm air is also able to absorb more water vapour than cool air. This means a temperature increase will increase the rate of transpiration

Question 19

Wind speed explanation

Answer 19

When it is windy, air saturated with water vapour is quickly moved away from the plant and replaced by drier air. The water concentration in the air will stay lower than in the plant and this increases transpiration.

Question 20

What else affects transpiration rate?

Answer 20

A greater surface area means that there are more stomata and therefore more water can be lost

Question 21

Precautions when using the water uptake potometer

Answer 21

Cut the shoot underwater

Ensure that the apparatus is airtight and there are no leaks

Question 22

How would results be recorded using a water uptake potometer

Answer 22

Distance the bubble moves in a set period of time

Question 23

What is the weight potometer used for?

Answer 23

• comparing transpiration rates in still and moving air (windy conditions)

Question 24

In the weight potometer experiment, what is the film of oil used for ?

Answer 24

• Film of oil is used to prevent evaporation of water from the flask

Question 25

What is plasmolysis

Answer 25

When water leaves a plant cell, the plasma membrane pulls away from the cell wall as the vacuole shrinks

Question 26

How do you measure transpiration?

Answer 26

Bubble potometer, mass potometer

Question 27

What is the syringe used for in the water uptake potometer ?

Answer 27

To reset the bubble to zero between experiments

Question 28

How to calculate % change in mass

Answer 28

% change divided by initial mass x 100

Question 29

How can the effects of osmosis be demonstrated using visking tubing?

Answer 29

Visking tubing acts as a semi permeable membrane with pores that allow the movement of water molecules but are too small to allow sugar molecules such as sucrose to pass through

Question 30

Turgid definition

Answer 30

When water is gained by the cytoplasm and vacuole and the cytoplasm and cell wall stretch outwards

Question 31

Flaccid definition

Answer 31

When a plant tissue droops through a lack of water

Question 32

When investigating the effect of surface area of leaves on the rate of transpiration in a plant, suggest why the pot was covered with a plastic bag

Answer 32

To ensure that water loss only takes place in the leaves

Question 33

Explain why the rate of transpiration is lower when some leaves are removed

Answer 33

There are fewer leaves and therefore less evaporation occurs as there is a smaller amount of diffusion of water

Question 34

During long periods of drought some trees can drop all of their leaves.
Suggest how dropping all of their leaves can help quiver trees to survive long periods of drought

Answer 34

• There are no stomata to release water from

- There is less surface area which means less evaporation

Question 35

How is the maximum rate of transpiration achieved ? (6)

Answer 35

• Transpiration is the diffusion of water from mesophyll cells to the cells and air spaces followed by evaporation from the air spaces through stomata into the air
• High wind speeds cause air saturated with water vapour to quickly move away from the plant and be replaced by drier air. This increases transpiration
• High temperatures cause more water to be evaporated around the leaf increasing transpiration
• Low humidity means there will be less air saturated with water vapour around the leaf, increasing transpiration
• Temperature also causes more evaporation inside the air spaces or cells in the leaf
• Transpiration is controlled by these three environmental factors and causes more diffusion inside the air spaces or cells in the leaf

Question 36

How do plants reduce water loss(2)

Answer 36

• They do this by closing the stomata, which are most common on the underside of leaves
• The stomata are necessary to allow gases to enter and leave the leaf, but they can be closed on occasions when it is important to conserve water

Question 37

Suggest another use for the syringe aside from resetting the experiment

Answer 37

• Or The water uptake can be measured in different environmental conditions

Question 38

Why will air leaks hinder the experiment ?

Answer 38

• Air leaks will hinder the uptake of water into the plant, so it is important that the potometer apparatus is properly sealed, particularly at the junction between the shoot and the neck of the potometer

Question 39

Why is it necessary to cut the shoot underwater?

Answer 39

To prevent the development of unwanted air bubbles in the water column entering the plant

Question 40

How are higher levels of humidity created in an experiment ?

Answer 40

Covering the shoot with a clear plastic bag

Question 41

How are valid results collected from the bubble potometer experiment ?

Answer 41

• When changing a particular environmental factor it is necessary to keep other environmental factors constant, including temperature, humidity and light

Question 42

How are reliable results created ?

Answer 42

Repeating the experiment and calculating an average

Question 43

Why is it impossible to calculate how much of the water taken up by the plant is actually transpired through the leaf surface ?

Answer 43

• Some of the water will be used in photosynthesis and in providing support through turgor, so the volume transpired will be less than the volume taken into the shoot

Question 44

What does the visking tubing act as during the Visking tubing investigation?

Answer 44

A selectively permeable membrane

Question 45

What happens if a plant doesn’t have enough water to remain turgid ?

Answer 45

Wilting occurs

Question 46

Why is a film of oil present over the water in the weight potometer experiment

Answer 46

To prevent evaporation of water from flask