Osmosis 2.1

Question 1

What is diffusion?

Answer 1

Diffusion is the movement of molecules from a region of high concentration to a region of low concentration.

Question 2

What is osmosis?

Answer 2

Osmosis is the diffusion of water molecules from a dilute solution to a more concentrated solution, through a selectively permeable membrane.

Question 3

What type of membrane is involved in osmosis?

Answer 3

A selectively permeable membrane.

Question 4

What direction do water molecules move during osmosis?

Answer 4

From a dilute solution to a more concentrated solution.

Question 5

Red blood cells in an ISOTONIC SOLUTION

Answer 5

There is no net movement of water into or out of the cells by osmosis, so their volume, size and shape remain the same.

Question 6

Red blood cells in a HYPERTONIC SOLUTION

Answer 6

Red blood cells lose water by osmosis and shrivel or crenate.

Question 7

Red blood cells in a HYPOTONIC SOLUTION

Answer 7

Red blood cells gain water by osmosis and swell and burst.

Cell fragments are sometimes referred to as ‘ghosts’. Cell lysis takes place.

Question 8

What is osmosis?

Answer 8

Osmosis is the movement of water across a selectively permeable membrane from an area of high concentration to an area of low concentration.

Question 9

What role does the cell membrane play in osmosis?

Answer 9

The cell membrane is selectively permeable, allowing water to enter while controlling other substances.

Question 10

What is lysis in the context of red blood cells?

Answer 10

Lysis refers to the bursting of red blood cells due to excessive water intake.

Question 11

Why do red blood cells burst in water?

Answer 11

They lack a cell wall, which would normally limit water intake, leading to lysis.

Question 12

What happens to red blood cells in water?

Answer 12

Water enters cell from a high concentration of water outside the cell to a low concentration of water inside the cell through a semi permiable membrane. There is no cell wall to limit water intake, therefore causing cell lysis.

Question 13

What happens to plants in water/dilute solution?

Answer 13

Water has moved into the cell by osmosis and the cell has become turgid; has a large vacuole and the cell membrane is pushed against the cell wall; the cell wall now limits the further entry of water by osmosis and ensures the plant cell does not lyse.

Question 14

What happens to a plant in a concentrated solution?

Answer 14

If a plant cell loses too much water by osmosis a condition called PLASMOLYSIS takes place.
During plasmolysis so much water leaves the cell by osmosis that the contents shrink,
pulling the cell membrane away from the cell wall.

Question 15

Why is the transpiration stream is very important?

Answer 15

(1) The supply of water to the leaves as a raw material for PHOTOSYNTHESIS.
(2) The TRANSPORT OF MINERALS in the water through the roots and up the xylem to the leaves and other parts of the plant.
(3) As water passes through the plant it enters cells by osmosis to provide SUPPORT through turgor.
(4) Providing water for the process of transpiration itself.

Question 16

What is transpiration?

Answer 16

Transpiration is the evaporation of water from the mesophyll cells followed by diffusion of water vapour through airspaces and stomata.

Question 17

What factors affect the rate of transpiration from a plant?

Answer 17

Temperature, wind speed, surface area, humidity, and light intensity.

Question 18

How does temperature affect transpiration?

Answer 18

Higher temperatures generally increase the rate of transpiration.

Question 19

What role does wind speed play in transpiration?

Answer 19

Increased wind speed can enhance transpiration rates by removing moisture from the leaf surface.

Question 20

How does surface area influence transpiration?

Answer 20

Larger surface areas can lead to higher rates of transpiration.

Question 21

What is the effect of humidity on transpiration?

Answer 21

Higher humidity levels can decrease the rate of transpiration.

Question 22

How does light intensity impact transpiration?

Answer 22

Increased light intensity typically raises transpiration rates due to enhanced photosynthesis.

Question 23

Why do plants need to reduce water loss?

Answer 23

Plants need to reduce water loss by transpiration, particularly those in hot climates, to conserve water.

Question 24

How do plants reduce water loss?

Answer 24

Plants reduce water loss by closing the stomata/guard cells.

Question 25

Where are stomata commonly found?

Answer 25

Stomata are most commonly found on the lower surface or underside of leaves.

Question 26

Why is the lower surface of leaves advantageous for stomata?

Answer 26

The lower surface receives less direct sunlight, resulting in less water loss by evaporation.

Question 27

What is the function of a thick waxy cuticle in plants?

Answer 27

To reduce water loss by transpiration/evaporation.

Question 28

How do some leaves increase diffusion distance?

Answer 28

By having more layers, such as two palisade mesophyll layers.

Question 29

What process allows the cut shoot to take up water?

Answer 29

The shoot takes up water by transpiration as water evaporates from the leaves.

Question 30

What can be calculated using the distance the air bubble moves?

Answer 30

The distance the air bubble moves can be used to calculate the RATE OF WATER UPTAKE.

Question 31

What is the purpose of the reservoir or syringe in the experiment?

Answer 31

The reservoir or syringe is used to reset the air bubble to zero to REPEAT the experiment.

Question 32

Why is it important to record replicate results?

Answer 32

Recording replicate results ensures that the results are RELIABLE.

Question 33

What environmental factors can the potometer measure?

Answer 33

The potometer can measure how windspeed, temperature, or humidity affect the rate of water uptake.

Question 34

How do higher temperatures affect water uptake?

Answer 34

Higher temperatures increase the rate of evaporation and transpiration, thus increasing the rate of water uptake.

Question 35

What effect does higher humidity have on water uptake?

Answer 35

Higher humidity reduces evaporation and transpiration, slowing the rate of water uptake.

Question 36

What must be kept constant when changing an environmental factor?

Answer 36

Other environmental factors such as temperature, humidity, and light must be kept constant.

Question 37

How does leaf surface area affect transpiration rate?

Answer 37

A larger leaf surface area means more stomata, leading to greater water loss by transpiration.

Question 38

What happens if the number of leaves or leaf surface area is reduced?

Answer 38

Fewer leaves or reduced leaf surface area means fewer stomata, which slows down the rate of transpiration.

Question 39

What is a critical step to prevent air leaks in the potometer?

Answer 39

The stem of the shoot must be cut and attached to the potometer while underwater to prevent air from entering.

Question 40

What should be done to the connection between the shoot and rubber stopper?

Answer 40

Smear the join with petroleum jelly to reduce leaks and prevent air from entering.

Question 41

Describe how you would use a bubble potometer to investigate the difference in water loss at higher levels of humidity

Answer 41

1. record the distance moved by the air bubble; 2. in a set time; using a timer. 3. reset the air bubble to zero using the reservoir/ syringe; 4. repeat the experiment to ensure the results are reliable and to calculate an average; 5. repeat the experiment except this time cover the plant shoot in a plastic bag to increase the humidity; 6. keep all other environmental factors/ conditions the same (wind speed/ temperature/ light intensity) in both experiments to ensure results are valid.

Question 42

Describe how to use a bubble potometer to investigate the difference in water loss between upper and lower leaf surfaces

Answer 42

1. Cover lower leaf surfaces with Vaseline; 2. record the distance moved by the air bubble; 3. in a set time; using a timer. 4. reset the air bubble to zero using the reservoir/ syringe; 5. repeat the experiment to ensure the results are reliable and to calculate an average; 6. repeat the experiment except this time use the same sized shoot but cover the upper leaf surfaces with Vaseline; 7. keep all other environmental factors/ conditions the same (windspeed/ temperature/ and humidity) in both experiments to ensure results are valid.

Question 43

Mark scheme script for investigating a factor with weight potometer

Answer 43

1. Record the mass of the apparatus containing the plant initially/ at start; 2. Leave for a given time; 3. Record mass at end/ change in mass/ take final mass from original; 4. divide change in mass by time (to work out rate); 5. named variable constant - (not the one you are investigating) – temperature/ humidity/ windspeed/ same type of plant/ same species of plant; 6. Repeat for reliability and to calculate an average; 7. Repeat with factor you are asked to investigate or change e.g. reduce the surface area of leaves used/ place a fan a set distance from the plant (if investigating wind speed)/ place a plastic bag over the plant if investigating humidity; 8. named variable constant – (not the one you are investigating – suggest what conditions would be used for the control experiment) – temperature/ humidity (low humidity so no plastic bag) / wind speed (still conditions) / same type of plant/ same species of plant; 9. Repeat for reliability and to calculate an average;