Osmosis

Question 1

What is the definition of diffusion?

Answer 1

Movement of molecules from an area of high concentration to an area of low concentration, down the concentration gradient, until equilibrium is reached.

This is a random and passive process - no energy required.

Question 2

What are some examples of diffusion?

Answer 2

Oxygen diffusing from red blood cells into body cells.

In lungs oxygen diffuses into blood capillaries and carbon dioxide diffuses in opposite direction.

Diffusion of soluble food products across the villi in the ileum into the bloodstream.

Exchange of materials between mother and baby in placenta.

Diffusion of neurotransmitter substance across a synapse.

Question 3

What is the definition of active uptake?

Answer 3

Movement of substances against concentration gradient. Requires energy obtained through respiration, which requires oxygen.

Question 4

What are some examples of active uptake?

Answer 4

Plants absorb minerals from soil into root hair cells.

In small intestine, remaining nutrients continue to move into bloodstream.

Question 5

What is the definition of osmosis?

Answer 5

Diffusion of water from dilute solution to more concentrated solution through a selectively permeable membrane.

Question 6

What is turgid pressure?

Answer 6

Pressure created by cell when vacuole becomes filled with water.

Question 7

What does turgid mean?

Answer 7

State of a plant cell when it has gained enough water by osmosis for cell membrane to push against the cell wall by making the cell wall firm. Turgor provides support in plants.

Question 8

What does flaccid mean?

Answer 8

Cells that have low pressure so become droopy and floppy.

Question 9

What does wilting mean?

Answer 9

Loss of rigidity of stems and leaves.

Question 10

What does plasmolysis mean?

Answer 10

A plant cell is plasmolysed when it has lost water by osmosis and its membrane separates from the cell wall.

Question 11

What does selectively permeable mean?

Answer 11

Ability of a membrane to allow some substances to pass through while preventing others.

Question 12

What does permeable mean?

Answer 12

A membrane which allows all substances to pass through it.

Question 13

What does impermeable mean?

Answer 13

A membrane which does not allow any substances to pass through it.

Question 14

What is lysis?

Answer 14

Animal cell have no cell wall so in dilute solutions osmosis causes them to sweep up and burst.

Question 15

What is crenation?

Answer 15

When animal cells shrink due to being in concentrated solutions making them lose water.

Question 16

What do plants use water for?

Answer 16

1. Support (turgor).
2. Transpiration.
3. Transport - as water moves through plant it carries minerals.
4. Raw material in photosynthesis.

Question 17

What is transpiration?

Answer 17

Evaporation of water from mesophyll cells followed by diffusion through air spaces and stomata.

Question 18

How does temperature affect the transpiration rate of a plant?

Answer 18

In warmer conditions water evaporates faster.

Question 19

How does wind speed affect the rate of transpiration in a plant?

Answer 19

Evaporation is faster in higher wind speeds as wind rapidly removes evaporating water away from stomata, maintaining a steep diffusion gradient.

Question 20

How does light/darkness affect the rate of transpiration in a plant?

Answer 20

Many plants close their stomata in darkness (during the night) to reduce water loss.

Question 21

How does the surface area of leaf affect the rate of transpiration in a plant?

Answer 21

Greater the surface area the greater the number of stomata, and the faster evaporation takes place.

Question 22

How does the bubble potometer help to calculate the rate of water uptake by a plant?

Answer 22

Measures water uptake in leafy shoot.

Water evaporates from leaves which sucks water up through capillary tubing, drawing air bubble towards plant shoot.

Distance air bubble travels in given time used to calculate rate of water uptake.

Question 23

What is the apparatus setup for the bubble potometer?

Answer 23

1. Reservoir/syringe re-sets air bubble position so experiment can be repeated. All junctions sealed with Vaseline to prevent air leaks.
2. Whole apparatus set up underwater to prevent development of unwanted air bubbles.
3. Air bubble introduced into water column by lifting end of tubing out of water and replacing it.
4. Scale along tubing measures distance of the air bubble over period of time.

Question 24

How does the weight potometer help to calculate the rate of water uptake in a plant?

Answer 24

Can accurately measure volume of water taken up by shoot but cannot give an accurate value for transpiration itself.

Question 25

How long is the plant placed on the top-pan balance?

Answer 25

24hrs and mass recorded.

Question 26

What must be done if a potted plant is used instead of a cut shoot?

Answer 26

Compost around shoot must be covered by polythene to stop evaporation or soil water as water must only escape by transpiration through the plant.

Question 27

What is the apparatus setup for the weight potometer?

Answer 27

1. Humidity - clear polythene bag placed around plant produces humid conditions as evaporated water molecules are trapped in bag.

Clear bag = light gets through for photosynthesis.

2. Wind speed - can be investigated using a fan.
3. Temperature - compare rates in cool or warm rates.

Question 28

How is the washing line method used to compare water loss in different conditions?

Answer 28

Leaves detached from plant/tree, numbered and weighed before being attached to a string. After period of time leaves are reweighed and loss of leaf mass compared between two conditions.

Question 29

What is the equation for % percentage change?

Answer 29

Initial mass - final mass / initial mass x 100%