Chapter 2: Movement of substances

Question 1

Define diffusion.

Answer 1

Diffusion is the net movement of particles from a region where they are of higher concentration to a region where they are of lower concentration; that is, down a concentration gradient (until equilibrium is reached).

Question 2

What is a concentration gradient?

Answer 2

The difference in concentration of particles between two regions.

Question 3

What are the factors that affect the rate of diffusion?

Answer 3

1. Concentration gradient
2. Diffusion distance
3. Surface area-to-volume ratio

Question 4

What is the effect of concentration gradient on the rate of diffusion?

Answer 4

The steeper the concentration gradient, the higher the rate of diffusion.

Question 5

What is the effect of diffusion distance on the rate of diffusion?

Answer 5

The shorter the diffusion distance, the higher the rate of diffusion.

Question 6

What is the effect of surface area-to-volume ratio on the rate of diffusion?

Answer 6

The larger the surface area-to-volume ratio, the higher the rate of diffusion.

Question 7

[Application]
Why are the cells in our body very small?

Answer 7

-The larger the cell, the smaller the surface area-to-volume ratio, lowering the rate at which substances move in and out of the cell-> not beneficial for the cell to grow bigger
-Therefore, cells involved in absorption have an increased surface area to volume ratio

Question 8

Define osmosis.

Answer 8

Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.

Question 9

What is water potential?

Answer 9

Water potential is a measure of the tendency of water molecules to move from one place to another.

Question 10

How does the water potential of surroundings affect a plant cell? (when higher, lower & the same)

Answer 10

WHEN WATER POTENTIAL OF SURROUNDINGS IS:
Higher
-Cell expands and becomes turgid, cell wall prevents the cell from bursting
The same
-No change in size and shape
Lower
-Cell becomes flaccid
-Cytoplasm shrinks away from cell wall and becomes plasmolysed

Question 11

How does water potential of surroundings affect an animal cell? (when higher, lower & the same)

Answer 11

WHEN WATER POTENTIAL OF SURROUNDINGS IS:
Higher
-Cell expands, burst or lyse
The same
-No change in size and shape
Lower
-Cell shrinks and becomes crenated

Question 12

Why is turgor important in plants?

Answer 12

-Maintains the shape of soft tissues in plants
-Loss of turgidity causes the plant to eventually wilt
-To reverse plasmolysis, water may be added to dilute soil solution to maintain turgor
-Changes in turgor could also cause the movements of some plant parts (e.g. opening & closing of stoma)

Question 13

Define active transport.

Answer 13

Active transport is the process in which cellular energy is used to move the particles of a substance across a membrane against its concentration gradient, that is, from a region were the particles are of lower concentration to a region where they are of higher concentration.

Question 14

Where does active transport occur? (name 2 examples)

Answer 14

Active transport only occurs in living cells, where energy can be obtained through respiration
(e.g. active transport of dissolved mineral salts by root hair cells, active transport of glucose and amino acids by cells in the small intestine of humans)

Question 15

[Application]
Why did the (_____) expand/shrink when placed in (distilled water/—solution)

(Describe general frame-> steps)

Answer 15

1. Compare water potential
2. State direction of movement
3. Mention process+ppm
4. Describe outcome