Chapter 3: Movement into and out of cells

Diffusion (4 marks)

• net movement of particles from a region of high concentration to low concentration

• Diffusion moves down a concentration gradient

• Particles move randomly in diffusion

• Diffusion is a passive process (energy from respiration isn’t needed)

Factors affecting rate of diffusion and how

• temperature: if temperature increases, diffusion increases because there is an increase in kinetic energy so particles would move faster.

• Surface area: if surface area increases, diffusion increases because there is a larger surface area over which diffusion can occur

• Concentration gradient: if concentration gradient increases, diffusion increases because there is faster net movement of particles from an area of high concentration to low concentration as a result of random movement.

• Distance: if distance decreases, diffusion increases because random movement of particle over a shorter distance takes less time

Osmosis (4 marks)

• net movement of water particles from a region of higher water potential to a region of lower water potential

• Water particles move down a concentration gradient

• Water particles pass through a partially permeable membrane

• Osmosis is a passive process (energy from respiration isn’t needed)

Effect of solution outside being hypotonic, isotonic and hypertonic in animal cells

Hypotonic: water particles go into the cell and eventually, cell will burst and die

Isotonic: no net movement of particles

Hypertonic: water particles move out of the cell, if too much moves out, the cell will shrivel and die

Osmosis in plant cells

Hypotonic: water moves in the cell and will gain tugor pressure. It will be turgid - becomes stiff and supports the plant

Isotonic: no net movement of water particles

Hypertonic: water moves out of the cell. When plants lose a little bit of water, tugor pressure decreases and becomes flaccid. (Less stiff and no longer helps support the plant.) When it loses a lot of water, the cytoplasm and vacuole shrink so much and cell becomes plasmolysed and will probably die

Active transport (4 marks)

• net movement of particles from and area of lower concentration to an area of higher concentration

• Particles move against the concentration gradients

• Particles pass through partially permeable membrane

• Requires carrier proteins and energy from respiration

Carrier proteins

They pick up the substance the cell needs and pass them through the membrane.

The proteins pump the particles into the cell

Example of diffusion

• movement of carbo dioxide and oxygen in leaves

• Movement of carbon dioxide in the alveoli of the lungs

Example of osmosis

• absorption of water from the soil

• Reabsorption of water in the kidneys

Examples of active transport

• root hair cell taking nitrates and other ions from the soil

• Absorbing glucose in the small intestines