Year 10 Biology complete

Water potential

• Water potential is a depiction of the amount of water in a substance.
• Pure water has the highest water potential.
•  Equilibrium occurs when there is equal solvent to water (solute) ratio.
• The lowest possible water potential is where there is no water.
• Where there is an area of high concentration leading into an area of low concentration there is a concentration gradient.
• This is key in Diffusion, Osmosis, and Active Transport.
• Going from an area of low concentration to an area of high concentration is going against the concentration gradient.
• Diffusion
• Diffusion occurs when particles spread. Diffusion is where a substance goes from an area of high concentration to an area of low concentration (down the concentration gradient).
• Diffusion does not occur in solids.
• Products of digestion pass across the wall of the small intestine by diffusion. The concentration of these products is higher in the small intestine than in the blood, so there is a concentration gradient from the small intestine to the blood.
• Osmosis
• Osmosis is the diffusion of water molecules down a concentration gradient through a partially permeable membrane.
• A dilute concentration contains a high concentration of water molecules, while a concentrated solution contains a low concentration of water molecules.
• Net exchange is a total of how much has been transferred in total.
• Plant cells have a strong cellulose wall on the outside of the cell membrane. This supports the cell and prevents it from bursting when it gains water by osmosis.
• Turgid plant cells play an important plant in supporting a plant's structure.
• Animal cells don't have a cell wall, so they change size and shape when put into a solution of a different concentration to the cell itself. 
• During haemolysis, red blood cells gain water by osmosis and burst in a more dilute solution.
• Red blood cells shrink and become wrinkly when they lose water by osmosis, due to a more concentrated solution being outside the cell.
• This does not happen in the body though due to osmoregulation from the kidneys.
• Active transport
• Active transport transfers dissolved molecules in or out of a cell through the cell membrane from a region of low concentration to a region of high concentration. Particles must use energy from respiration to transfer molecules against the concentration gradient.
• Sometimes, dissolved molecules are at a higher concentration inside the cell than outside the cell yet because the organism still needs these molecules they must still be absorbed.
• Carrier proteins pick up specific molecules and take them through the cell membrane against the concentration gradient.
• Examples of active transport are: uptake of glucose buy epithelial cells in the villi of the small intestine, uptake of ions from soil water by root hair cells.
• A more concentrated solution is known as hypertonic to a solution inside a membrane.
• A less concentrated solution is seen as hypotonic to a solution inside the membrane.
• When there is the same concentration outside and inside the membrane, it is isotonic.

The heart and the blood

The heart

• When…