Biology - Movement Of Substances

Question 1

What is a concentration gradient?

Answer 1

Difference of concentration of the same particles in two regions.

Question 2

What is the net movement of particles?

Answer 2

The overall movement of particles when the movement of particles in one direction is greater than the movement of particles in the opposite direction.

Question 3

What is diffusion?

Answer 3

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient.

Question 4

Characteristics of diffusion and factors affecting it

Answer 4

• Steeper concentration gradient –> faster rate of diffusion
• Equilibrium is reached over time
• Rate of diffusion can be affected by: concentration gradient, diffusion distance, temperature, surface area to volume ratio
• Passive process, no energy input required

Question 5

When is a water potential gradient established?

Answer 5

Established when a partially permeable membrane separates two solutions of different water potentials.

Question 6

What is osmosis?

Answer 6

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 7

Characteristics of osmosis

Answer 7

• Rate of osmosis affected by: water potential gradient, distance which water molecules need to move, temperature, surface area to volume ratio
• Passive process, no energy input required

Question 8

Names of different concentrations and effect on cells

Answer 8

Hypotonic solution: Higher water potential
- Animal cell becomes lysed and bursts
- Plant cell becomes turgid
Isotonic solution: Normal water potential
- Animal and plant cells normal
Hypertonic solution: Lower water potential
- Animal cell becomes shriveled (could shrink/crenate)
- Plant cell becomes plasmolysed

Question 9

Plant cells in a hypotonic solution

Answer 9

Water enters cell into vacuole –> Cell swells due to having a cell wall and not bursting (cell wall is strong and relatively inelastic) –> Prevents over-expansion of cell by exerting an opposing pressure as water enters the cell
The pressure exerted by the water in the vacuole is the turgor pressure. When the cell is stretched to its maximum, it becomes fully turgid.

Question 10

Plant cells in a hypertonic solution

Answer 10

Water leaves the cell out of the vacuole by osmosis. Vacuole and cytoplasm decrease in size. The plasma membrane pulls away from the cell wall leaving a gap, which is called plasmolysis (to fully plasmolysed when fully withdrawn). Cell is flaccid.

Question 11

Why is turgor important in plants?

Answer 11

• Maintains the shape of soft tissues in plants
• Remain firm and erect because of turgor pressure
• Stomata open and close due to turgor of the guard cells

Question 12

Definition of active transport

Answer 12

Active transport is the movement of ions or molecules across a membrane from a region of its lower concentration to a region of its higher concentration against its concentration gradient, with the use of energy in the form of Adenosine Triphosphate (ATP).

Question 13

Characteristics of active transport

Answer 13

• Active process
• Requires additional energy input
• Energy obtained from the breakdown of ATP into Adenosine Diphosphate and free phosphate to release the stored energy
• Only occurs in living cells