biology unit 3

Osmosis

·         Osmosis is the movement of water molecules across a partially permeable membrane from a region of high concentration to a region of low water concentration.

·         Water moves in and out of cells by osmosis

·         Tissue fluid surrounds the cells in the body.

·         Tissue fluid will have a different concentration to the fluid inside a cell.

Gas and solute exchange

·         Substances move by diffusion osmosis and active transport.

·         For photosynthesis to happen carbon dioxide and water have to get into plant cells, and for respiration to take place glucose and oxygen both have to get inside cells.

·         The structure of leaves lets gases diffuse in and out of cells.

·         Carbon dioxide diffuses into the air spaces within the leaf then it diffuses to where the photosynthesis happens.

Water vapour evaporates from the cells inside the leaf, and then it escapes by diffusion because there is a lot of air inside the leaf and less of it in the air outside.

The breathing system

·         The lungs are in the thorax which is in the top part of your body.

·         Ventilation is breathing in and breathing out.

·         Artificial ventilators can help people breath in and out. They are machines that move air in and out of the lungs.