movement in & out of cells

Question 1

define diffusion

Answer 1

• the net movement of particles
• from a region of their higher concentration
• to a region of their lower concentration
• (i.e down a concentration gradient)
• as a result of their random movement

Question 2

where does energy for diffusion come from

Answer 2

kinetic energy of random movement of molecules & ions

Question 3

importance of diffusion of gases and
solutes in living organisms

Answer 3

• Some substances move into and out of cells by diffusion, through the cell membrane
  1. Oxygen diffuses from lungs to blood in capillaries
  2. Glucose and amino acids diffuse from small intestine cells to blood
  3. CO2 from the atmosphere diffuses into cells in leaves

Question 4

factors that influence diffusion

Answer 4

• surface area
• temperature
• concentration gradient
• distance

Question 5

define osmosis

Answer 5

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

Question 6

Describe the role of water as a solvent in
organisms

Answer 6

Transport
* water allows ;soluble molecules such as urea, glucose, amino acids to be transported around the body in the blood.
* also transports soluble mineral ions from roots to leaves in plants

Digestion
* digestive enzymes need to be in solution to work properly; water helps digestion by acting as solvent for enzmes.
* water also acts as solvent for the products of digestion, which allows them to diffuse into the blood stream

Excretion
* metabolic waste products; toxins often dissolved in water; urea removed from sweat & urine.

Question 7

Explain the effects on plant cells of immersing
them in solutions of different concentrations
Plant cell placed in higher concentrations of water molecules/dilute solution

Answer 7

• water moves into plant cell by osmosis.
• this’ll make the cell turgid.
• plant supported by pressure of water inside cells, pressing outwards on inelastic cell wall; plant cell has turgor pressure.

Question 8

Explain the effects on plant cells of immersing
them in solutions of different concentrations
Plant cell placed in lower concentrations of water molecules/dilute solution

Answer 8

• Water moves out from plant cell by osmosis
• Cells become flaccid
• Turgor pressure lost; cells become soft & floppy.
• Cell membrane tears away from wall cell, cell becomes plasmolysed
• Plant cell killed.

Question 9

define active transport

Answer 9

• 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 10

Why is active transport vital for living organisms?

Answer 10

Can move molecules up a concentration gradient
- e.g.uptake of mineral ions into root hair cells

Question 11

Describe how active transport occurs

Answer 11

Protein carriers in cell membrane
- Carrier complementary to substance being transport
- Substance transported across membrane by carrier protein using energy (ATP)
- Substance released into cell