GCSE Biology Unit 3 ( Gas & Solute exchange )

All life processes need gases, or other dissolved substances before they can take place, for example photosynthesis can't happen without carbon dioxide and water getting into the plants cells.

These substances that need to move about do it in three ways

• diffusion
• osmosis
• active transport

This is where particles move from areas of HIGH CONCENTRATION to areas of LOW CONCENTRATION e.g. when a bad smell diffuses from the trampy kid around the rest of the room or on a more scientific note through cell membranes - CO2 into the alveoli and out of the lungs

Now, this is similar however it can only happen in water (hence the blue font), moving through a partially permeable membrane again from areas of HIGH CONCENTRATION to areas of LOW CONCENTRATION

Here is the most complex type of exchange as it moves AGAINST the CONC GRADIENT, meaning from areas of low to areas of high. This is used loads in the body and in plants, two examples are

• root hair cells absorbing water & minerals
• nutrients in the gut moving into the blood

An important thing to remember is that Exchange surfaces are ADAPTED to maximise their effectiveness