biology

Fossil record is incomplete

·         There are many gaps in the fossil record due to a number of reasons:

o   Soft tissues decay so soft-bodied organisms leave little fossil evidence behind.

o   Other organisms did not form fossils because the hard parts were destroyed.

o   Not all fossils have been found.

o   Cell differentiation: cells change to become specialised for its job.

o   Cell division: by mitosis.

o   Cell elongation: when a plant cell expands making the cell bigger so the plant can grow (only in plants).

·         Plants have meristems (stem cells) behind the tip of their roots and shoots and these can differentiate into any plant cell. These meristems exist throughout the entire plant’s life.

·         This is how old trees can keep growing new branches.

Plasma

·         This is a yellow liquid which keeps the blood fluid and transports many things:

o   Red and white blood cells and platelets.

o   Nutrients like glucose and amino acids. They are absorbed from the gut and taken to body cells.

o   Carbon dioxide – transported by the blood from the cells to the lungs where it is removed.

o   Urea – blood transports it to the kidneys where it’s removed.

o   Hormones – transported from glands to target organs.

o   Antibodies and antitoxins produced by the white blood cells.

White blood cells

·         These help fight disease.

·         Some types can engulf and digest pathogens (phagocytes). Others (lymphocytes) produce antibodies (proteins that bind to pathogens to destroy then) and antitoxins to neutralise any toxins produced byt he microorganisms.

·         A low WBC count could increase risk of infection while a high count could mean you have an infection or even leukaemia.

Platelets

·         Fragments of cells that help with clotting of the blood.

·         Blood clots at wounds stop blood pouring out and stop microorganisms getting in.

·         Lack of platelets can caused excessive bleeding and bruising.

Red blood cells

·   Job of red bloods cells is to carry oxygen around the body. It contains the red pigment haemoglobin

    Deoxygenated blood goes to the right side and oxygenated blood into the left side.

1.        Vena cava brings deoxygenated blood from the whole body into the right atrium.

2.       The right atrium contracts and forces the blood into the right ventricle, through the valves. Valves prevent the back flow of blood.

3.       When the right ventricle is full of blood the muscles in its wall contract, forcing the blood through more valves through the pulmonary artery. This carries deoxygenated blood to the lungs where it picks up oxygen

4.       Oxygenated blood returns from the lungs to the left atrium of the heart in the pulmonary vein. When the left atrium is full it contracts and squeezes blood through valves into the left ventricle.

5.       The ventricle walls then contract and push the blood up more valves into the aorta. The aorta is a large blood vessel that carries oxygenated blood around the body. The wall of the left ventricle is thicker than the right as it needs more muscle to pump blood around the whole body whereas the right ventricle needs only pump to the lungs.

·         3 types of blood vessels:

1.       Arteries –carry blood away from the heart

2.       Capillaries – are involved in the exchange of materials

3.       Veins –carry the blood to the heart

Arteries

·         The heart pumps the blood out at high pressure so the artery walls are strong and elastic.

·         The walls are thick compared to its lumen. They contain thick layers of muscles to make them strong.

Capillaries

·         Arteries branch into capillaries.

·         Very small with very thin walls to allow substances to diffuse in and out of the blood.

·         Carry blood close to cells to exchange substances with them.

·         One-cell thick walls.

Veins

·         Capillaries join up to form veins.

·         The blood is at lower pressure so the walls don’t need to be as thick as artery walls.

·         Bigger lumen to help the blood flow despite lower pressure.

·         Valves to help keep the blood flowing in the right direction.

Digesting carbohydrates

·         Food like bread and pasta are full of large carbohydrates. They simplest carbohydrates are called sugars (glucose etc.) and they can be built up to more complex carbohydrates such as starch.

·         Carbohydrases break down carbohydrates.

·         Amylase breaks down starch into sugars (i.e. maltose). Amylase is present in saliva and secreted from the pancreas.

Digesting proteins

·         Proteases digest proteins, breaking them down into shorter chains and then amino acids.

·         Pepsin is a protease that is produced in the stomach and works best in acidic conditions e.g. pH 2-3. As the stomach walls produce acid this is the optimum place for pepsin.

·         However, the contents of the small intestine are alkaline so the proteases released into the small intestine work best around pH 8 (i.e. trypsin).

Digesting fats

·         Lipases digest fats into fatty acids and glycerol.

·         Fat and water don’t mix so at first the fats form large globules in the watery digestive juices.

·         These globules have a very small SA to volume ration so lipases can only digest the fats slowly. Bile helps by physically breaking down the large globules into tiny droplets forming an emulsion. We say bile emulsifies fats.

·         As the smaller droplets have a larger SA they can be broken down much more quickly.

·         More bile is produced after a meal.

·         Bile is alkaline when released so it helps neutralise the acidic contents of the stomach when it enters the small intestine. This is so the protease enzymes have a slightly alkaline environment to work in.

Platelets

·         Fragments of cells that help with clotting of the blood.

·         Blood clots at wounds stop blood pouring out and stop microorganisms getting in.

·         Lack of platelets can caused excessive bleeding and bruising.

Red blood cells

·   Job of red bloods cells is to carry oxygen around the body. It contains the red pigment haemoglobin

Digesting fats

·         Lipases digest fats into fatty acids and glycerol.

·         Fat and water don’t mix so at first the fats form large globules in the watery digestive juices.

·         These globules have a very small SA to volume ration so lipases can only digest the fats slowly. Bile helps by physically breaking down the large globules into tiny droplets forming an emulsion. We say bile emulsifies fats.

·         As the smaller droplets have a larger SA they can be broken down much more quickly.

·         More bile is produced after a meal.

·         Bile is alkaline when released so it helps neutralise the acidic contents of the stomach when it enters the small intestine. This is so the protease enzymes have a slightly alkaline environment to work in.