Unit 3 Biology GCSE

Plants:

• The plant takes in water and mineral ions through its roots
• Most of the water and mineral ions are absorbed by root hair cells
• These provide a large surface area.
• Waterdiffuses into the root hair cell by osmosis and then moves by osmosis into the surrounding cells, then finally up the xylem vessel to be carried up the stem.
• Ionsare moved into the root hair cells by active transport (this requires energy from respiration, so if the soil is waterlogged, there is no oxygen for respiration and so active transport cannot occur)
• Carbon dioxide and oxygen move in and out respectively of leaves through the stomata. Leaves are adapted for efficient gaseous exchange by being very thin - this means that there is only a short distance for gases to travel to and from the palisade layer (where photosynthesis occurs). They also have a large surface area - this is provided by the large, flat leaf and internal airspaces within the leaf. They have a large concentration gradient (from a high concentration to a low concentration) due to photosynthesis.

• The stomata are holes in the top and bottom of the leaf (there are more on the bottom) which allow gases to diffuse in and out easily. Unfortunately, water is also lost through these by transpiration. This is why there are more stomata on the bottom surface of the leaf than on the top, so that water is not lost as easily by evaporating. When a plant loses too much water, the stomata close because the guard cells which make the hole join together instead of bending something like () << that is supposed to be a stoma!
• When a plant does lose too much water it wilts and then dies. :( Sad times.

For Unit 3, you have to know about the blood, heart and also about the excretory system, and I don't mean the passing of waste from digestion.

Blood:

• The blood is made up of red blood cells - these are biconcave discs which have no nucleus, therefore allowing for more room to carry oxygen. The oxygen is transfered to the blood in the lungs from the alveoli. It combines with the haemoglobin, a red pigment in the cells to form oxyhaemoglobin. Once at an organ, the oxyhaemoglobin goes to form oxygen and haemoglobin and the oxygen is transfered to the organ and its cells for aerobic respiration. (This will be explained later)
• It also contains white blood cells which form part of your immune system. They attack pathogens in the blood.
• It is also made of plasma, a yellow liquid which everything floats in. The plasma carries the red blood cells, white blood cells, platelets which clot the blood (when a person is a haemophiliac, they do not have any platelets. These can be donated.)