Movement into & out of cells

Question 1

Where does the energy for diffusion come from?

Answer 1

the kinetic energy of random movement of
molecules and ions

Question 2

What is diffusion?

Answer 2

The net movement of particles from a region of higher concentration to a region of lower concentration (i.e. down a concentration gradient), as a result of their random movement requiring no energy to do so

Question 3

What is a concentration gradient?

Answer 3

The difference in concentration between two areas (larger concentration gradient means faster diffusion)

Question 4

Why can particles not diffuse in a solid?

Answer 4

Because in solids particles can’t move

Question 5

What happens when the particles are evenly distributed?

Answer 5

It has reached equilibrium. The net movement is 0 and while particles still move they aren’t moving in a specific direction

Question 6

What are the factors that affect diffusion?

Answer 6

1. Concentration gradient (the larger it is, the faster the rate of diffusion)
2. Temperature (More energy associated with the particle at higher temperatures means faster rate of diffusion)
3. Surface area (The larger the surface area in contact between the two regions the faster the diffusion)
4. Distance (The larger the distance, the longer time to diffuse)

Question 7

Is a cell membrane required for diffusion?

Answer 7

No

Question 8

What is the importance of the diffusion of gases and solutes in living organisms?

Answer 8

• Getting raw materials for respiration or photosynthesis
• Removing waste products
• Importing or exporting products

Question 9

Why is water important to living organisms?

Answer 9

Many substances are able to dissolve in it (it is a solvent)

Question 10

Name some situations where water is important as a solvent in organisms?

Answer 10

• Dissolved substances can be easily transported around organisms
• Digested food molecules in the alimentary canal dissolve in water to be absorbed into the blood (for transport to cells
• Toxic substances can dissolve in water to be (easily) excreted in urine
• Water is also an important part of the cytoplasm and plays a role in ensuring metabolic reactions can happen as necessary in cells

Question 11

How does water move into cells?

Answer 11

By osmosis through the partially permeable membrane

Question 12

What are plants supported by?

Answer 12

The pressure of water inside the cells pressing outwards on the cell wall

Question 13

What is osmosis?

Answer 13

the net movement of water molecules from a region of higher water
potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane

Question 14

What’s active transport?

Answer 14

the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration (i.e. against a concentration gradient), using energy from respiration

Question 15

What do protein carriers do?

Answer 15

move molecules or ions across a membrane during active transport

Question 16

What’s the importance of active transport?

Answer 16

Active transport is vital process for the movement of molecules or ions across membranes. Including:
- uptake of glucose by epithelial cells in the villi of the small intestine and by kidney tubules in the nephron
- uptake of ions from soil water by root hair cells in plants

Question 17

easy biological examples of water as a solvent

Answer 17

Digestion- water used to dissolve solutes from food
Excretion- water used to dissolve solutes in urine
Transport- Water used to dissolve solutes in blood

Question 18

What is turgor pressure?

Answer 18

The pressure within cells that pushes at the cell wall or membrane, more water inside the cell means higher turgor pressure

Question 19

Why is turgor pressure important to plants?

Answer 19

So plants stay upright and have exposure to sunlight

Question 20

What is a hypertonic solution?

Answer 20

One that has higher solute concentration than the cell

Question 21

What’s a hypotonic solution?

Answer 21

One that has a lower solute concentration than the cell

Question 22

What’s an isotonic solution?

Answer 22

One that has an equal concentration of solutes inside and outside the cell

Question 23

What happens to a plant cell in a hypertonic solution?

Answer 23

There’s a net movement of water out of the cell, causing a reduction in turgor pressure. This first makes the cell flaccid then after some time the cell membrane begins to pull back from the cell wall and the cell becomes plasmolysed.

Question 24

What happens to a plant cell in a hypotonic solution?

Answer 24

There’s a net movement of water into the cell, causing an increase in turgor pressure and the cell membrane to push against the cell wall. This makes the cell turgid

Question 25

What happens to a plant cell in an isotonic solution?

Answer 25

There is no net movement of water so the cell stays the same