MOVEMENT OF PARTICLES

MOVEMENT OF PARTICLES

Particles move in three main ways:

(1)   Diffusion

(2)   Osmosis

(3)   Active Transport

DIFFUSION

Diffusion is the movement of particles from an area of HIGH concentration to an area of LOW concentration. Particles can be solid, liquid, or gas. Diffusion is passive – it  requires NO energy as it happens along a concentration gradient.

IMPORTANCE OF DIFFUSION

Many important substances can move across the cell membranes by diffusion. These substances are:

Oxygen, Carbon Dioxide, and Nutrients.

ORGANS OF DIFFUSION

(1)   Lungs – the lungs have alveoli, tiny air sacs that ensure there is a wide surface area for gas exchange

(2)   Small Intestine – the small intestine has villi, small thin projections where absorption of food takes place

(3)   Placenta – in pregnant women: food and oxygen pass from the mother to the foetus and waste passes from the foetus to the mother

(4)   Plants – leaf

ADAPTATIONS OF ORGANS FOR DIFFUSION

The organs have specific features that allow diffusion to take place efficiently. They are:

• Thin/ flat – substances pass through quickly and easily
• Wide – a wide or large surface area allows many substances to pass through at any one time
• Close to blood – the blood carries the diffused substances around the body
• Moist – substances dissolve in water before they diffuse

DIFFUSION IN ANIMALS

Oxygen enters the lungs. Carbon dioxide exits the lungs.

DIFFUSION IN PLANTS

During Photosynthesis, Carbon dioxide enters the stomata. Oxygen exits the stomata.

OSMOSIS

Osmosis is the movement of WATER particles from an area of HIGH water concentration to an area of LOW  water concentration across a SEMI-PERMEABLE MEMBRANE.

Osmosis is passive – it  requires NO energy as it happens along a concentration gradient. Osmosis is a type of diffusion. Osmosis is the diffusion of water particles across a semi-permeable membrane.

Semi-permeable membrane = selectively-permeable membrane = partially-permeable membrane.

This membrane has small holes to allow only some things to pass through and not others.

A SOLUTION

A Solution is made up of a solute and a solvent. For example in a solution of salt water, the solute is the salt (the thing that is dissolved) and the solvent is the water (the thing that does the dissolving).

DILUTE AND CONCENTRATED SOLUTIONS

A dilute or weak solution has a high concentration of water molecules – more water than copper sulphate.

A concentrated or strong solution has a low concentration of water molecules – more copper sulphate

than water.

In Osmosis, water moves from a weak/ dilute solution (where there is a high concentration of water) to a strong/ concentrated solution (where there is a low concentration of water).

OSMOSIS IN LIVING THINGS

In living things such as plants and animals, the solvent is water and the solution is called an aqueous solution. Cells have a partially permeable cell membrane. The cytoplasm inside the cell is an aqueous solution and the surrounding outside the cell is another aqueous solution. Diffusion takes place where particles can spread easily from one place to another. The cell membrane only allows the smallest particles to pass through. It is partially permeable/ selectively permeable/ semi- permeable. Partially permeable membranes allow water molecules through.

OSMOSIS IN ANIMALS

If the solution outside the cells is very dilute (watery) then water will enter the cytoplasm and the cells may swell and burst. If the cytoplasm itself is very dilute, water will move out of the cell and the cell will shrivel up. An example of osmosis is when water enters the blood in the colon (large intestine).

OSMOSIS IN PLANTS

Plants need osmosis to provide the pressure to support the stem and leaves. Water moves into the plant cells by osmosis. The cytoplasm fills and swells. The cytoplasm now pushes against the cell wall. This makes the cell rigid and firm (turgid). The stem and leaves stay upright. Water enters the roots of plants

If the fluid outside the plant cell is more concentrated than the cytoplasm, then water will leave the cell cytoplasm by osmosis. The vacuole shrinks. The cell is no longer rigid/ turgid. It becomes flaccid. If a lot of water leaves the plant cell, the cytoplasm will be pulled away from the cell wall. This is called plasmolysis.

DIFFERENCES BETWEEN OSMOSIS AND DIFFUSION

ACTIVE TRANSPORT

Active Transport is the movement of particles from an area of LOW concentration to an area of HIGH concentration using ENERGY from respiration.

ACTIVE TRANSPORT IN ANIMALS

Glucose is absorbed into the blood in the intestines and kidney.

ACTIVE TRANSPORT IN PLANTS

Mineral ions are absorbed from the soil.

ACTIVE AND PASSIVE TRANSPORT

Diffusion and Osmosis are forms of passive transport – they require no energy.

Active transport requires energy from respiration.