diffusion, osmosis and active transport

Diffusion

A movement of particles/substances from a high level of concentration to a low level of concentration.

Kinetic theory

Molecules are in constant random motion because of their kinetic energy, allowing dissolved molecules to move around until they're evenly dispersed.

Diffusion in solids

Particles are held together by bonds, so they only vibrate.

Diffusion in liquids

The forces of attraction are weaker, therefore the particles can move more freely.

Diffusion in gases

The forces of attraction between the particles are very weak, allowing the particles to freely move.

Rate of diffusion

Diffusion is slowest in solids, then liquids, and quickest in gas.

Effect of temperature on diffusion

The higher the temperature, the more kinetic energy the particles have, so the faster they move.

Demonstration of gas diffusion

Small strips of litmus paper were stuck in a clean, dry test tube using distilled water, and liquid ammonia was placed onto a cotton wool in the tube.

Sealing the diffusion tube

The tube was sealed at each end to prevent gas from escaping and because ammonia is toxic.

Orientation of the diffusion tube

The tube was clamped horizontally to prevent gravity from bringing the ammonia down, as atoms have mass.

Litmus paper color change

The litmus paper changed colour in a regular order because the ammonia molecules were spreading out from a high concentration to a low concentration.

Concentration effect on diffusion speed

The more concentrated the ammonia, the quicker it would travel across the tube.

Collisions and diffusion speed

Since the ammonia is more concentrated, it will have more ammonia particles, which means there are more collisions and it spreads faster.

Body heat effect on diffusion

If you hold the tube in your hands, the speed will increase because body heat means more kinetic energy, leading to more collisions and speeding up the spreading.

NET movement and concentration

The experiment tells us the higher the concentration, the molecules' NET movement will increase.

Surface area effect on diffusion

When the surface area of a membrane is larger, the rate of diffusion increases as there is more space for molecules to diffuse across the membrane.

Osmosis

The movement of water molecules across a semipermeable membrane from a region of high water concentration to a region of low concentration.

Osmosis

Specialised type of diffusion.

semipermeable meaning

A membrane that only allows certain materials to pass through.

Isotonic Solution

When a cell is placed in a solution of the same concentration, water will move in and out of the cell equally.

Flaccid

A cell lacking water is said to be flaccid.

Hypertonic Solution

When a cell is placed in a hypertonic solution, water moves out of the cell.

Plasmolysis

Plant cell losing water and shrinking cytoplasm away from cell wall.

Hypotonic Solution

The cytoplasm has lots of solutes such as sugar/salts dissolved in it, so it is more concentrated than the surrounding solution.

Turgid

Swollen

Homeostasis

Maintains a constant internal environment and prevents osmotic effects.

Active Transport

Allows the movement of substances from an area of low concentration to an area of high concentration against a concentration gradient, requiring energy.

Surface Area

The larger the surface area, the increase of surface over which minerals are absorbed.

Rate of Active Transport

The higher the rate of active transport, the higher the rate of respiration because it releases more energy.

Exchange Surfaces

In the gut, soluble food substances, like glucose, cross the gut lining into the capillaries by diffusion.

Diffusion Distance

Small diffusion distance so it doesn't take a long time.

Concentration Gradient

Steep concentration gradients

Blood Supply

Good blood supply that creates a steep concentration gradient.

Moisture

Moisture makes things diffuse more quickly.