Osmosis and Transpiration

Question 1

What is Osmosis?

Answer 1

Osmosis is the diffusion of water from an area of high water concentration (dilute solution) to an area of low water concentration (concentrated solution) across a selectively-permeable membrane.

Question 2

What would happen to an animal cell when placed in: a) a concentrated solution b) a dilute solution

Answer 2

a) In a concentrated solution an animal cell would shrink and become crinkly. This process is known as crenation. This is because the cell would begin to lose water as the water concentration is higher inside the cell than it is outside the cell.

b) In a dilute solution an animal cell would grow until it eventually bursts. This is known as “cell lysis.” This occurs because the water concentration is higher outside the cell than it is inside the cell meaning more water would enter.

Question 3

What would happen to a plant cell if it is placed in: a) a concentrated solution b) a dilute solution

Answer 3

a) in a concentrated solution the plant cell would become flaccid and plasmolysed as the cytoplasm is pulled away. This is because the water concentration is higher inside the cell than outside so water exits the cell.

b) in a dilute solution the plant cell will become more rigid which will make it become ‘turgid’. This occurs because the water concentration is higher outside the cell than inside so water fills up the plant cell. Plant cells don’t have a skeleton but instead the leaves and shoots can be supported by the turgid pressure, the pressure of water inside their cells.

Question 4

What is a hypotonic solution?

Answer 4

A very dilute solution with a high water concentration

Question 5

What is a hypertonic solution?

Answer 5

A very concentrated solution but low water concentration

Question 6

What does semi permeable/ selectively-permeable mean?

Answer 6

Allows certain substances to pass through it but not others i.e. Permeable to solvents but not large molecules

Question 7

What is transpiration?

Answer 7

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

Question 8

What are the 4 main factors affecting transpiration rate?

Answer 8

-Light
-Temperature
-Wind
-Humidity

Question 9

What are the 4 reasons the transpiration stream is important?

Answer 9

1. It supplies water to the leaves to be used as one of the raw materials for photosynthesis.
2. The movement of water will also transport minerals through the root and up to the stem to the leaves and other parts of the plant.
3. As water passes through the plant it will enter cells by osmosis to provide support through turgor pressure.
4. Providing water for the actual process of transpiration itself.

Question 10

In the ‘weight potometer’ experiment, why is it essential that a layer of oil covers the surface of water?

Answer 10

This is to prevent water from evaporating so the only water lost is due to transpiration.