Organisation flashcards

Key points

• A tissue is a group of similar cells working together on a particular function, such as muscle tissue.
• An organ is a group of different tissues working together, such as the stomach, the heart or a leaf.
• An organ system is a group of organs working together, such as the digestive system.
• Organ systems work together to make up a whole organism.

The stomach as an organ

Key points

• An enzyme is a protein that acts as a biological catalyst: it speeds up a reaction without being used up.
• The substrate binds to a region of the enzyme called the active site.
• The active site has a specific shape that only one substrate fits: the lock and key model.
• Enzymes control the reactions of metabolism, breaking molecules down and building them up.

Key points

• Warming speeds an enzyme up, to its optimum temperature: about 37 °C for most human enzymes.
• Above the optimum the active site changes shape, the substrate no longer fits, and the enzyme is denatured.
• Each enzyme has an optimum pH, and a pH far from it denatures the enzyme too.
• Protease in the stomach works best in acid; the small intestine's enzymes work best in slightly alkaline conditions.
• Cold only slows an enzyme down: it does not denature it.

Key points

• Mix amylase, starch solution and a buffer of one pH, kept at a set temperature in a water bath.
• Every 10 seconds, add a drop of the mixture to a fresh drop of iodine solution on a spotting tile.
• When the iodine stays orange-brown, all the starch has gone: record the time.
• Repeat at other pH values. The shortest time shows the optimum pH.

Starch all gone after 50 s

Key points

• Digestion breaks large, insoluble molecules into small, soluble ones that can be absorbed into the blood.
• Carbohydrases, such as amylase, break starch down into simple sugars.
• Proteases break proteins down into amino acids.
• Lipases break lipids (fats and oils) down into fatty acids and glycerol.
• The body uses the products to build new carbohydrates, lipids and proteins; some glucose is used in respiration.

Key points

• Bile is made in the liver, stored in the gall bladder and released into the small intestine.
• It is alkaline, so it neutralises the hydrochloric acid from the stomach.
• That gives the slightly alkaline pH the enzymes in the small intestine work best at.
• Bile emulsifies fat into small droplets, giving lipase a much bigger surface area, so fat is digested faster.

Key points

• Starch: add iodine solution. Orange-brown turns blue-black.
• Reducing sugars, such as glucose: add Benedict's solution and heat in a water bath. Blue turns green, yellow, orange or brick red.
• Protein: add biuret reagent. Blue turns purple.
• Lipids: add Sudan III stain, and a red-stained oily layer forms on top.

Key points

• The right side pumps blood to the lungs to collect oxygen; the left side pumps it round the body.
• Blood enters the atria, then the ventricles pump it out. Valves stop it flowing backwards.
• Right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium.
• Left ventricle → aorta → body → vena cava → right atrium.
• The left ventricle has a thicker muscle wall, to pump blood all round the body at higher pressure.

Key points

• Arteries carry blood away from the heart at high pressure: thick, muscular, elastic walls.
• Veins carry blood back to the heart at low pressure: thinner walls, a wide space inside and valves.
• Capillaries have walls one cell thick, so the diffusion distance between blood and cells is short.
• Capillaries are where substances are exchanged with the body's cells.

Rate of blood flow

Key points

• Plasma is the liquid part. It carries the cells, and dissolved substances such as glucose, carbon dioxide and urea.
• Red blood cells carry oxygen. No nucleus leaves room for haemoglobin, and a biconcave disc shape gives a large surface area.
• White blood cells defend the body against pathogens.
• Platelets help the blood clot at a wound.

Key points

• Non-communicable diseases are not caused by pathogens, so they cannot be passed on.
• Smoking is linked to lung disease, lung cancer and heart disease.
• A poor diet and too little exercise lead to obesity, a risk factor for Type 2 diabetes and heart disease.
• Alcohol damages the liver and brain. Smoking and alcohol in pregnancy harm the unborn baby.
• A correlation alone is not proof: a cause needs a mechanism, such as carcinogens in smoke damaging DNA.

Key points

• Fatty material builds up inside the coronary arteries, which supply the heart muscle with blood.
• The arteries narrow, so less blood flows and the heart muscle gets too little oxygen.
• Stents hold the arteries open. Statins lower blood cholesterol, slowing the build-up.
• Faulty valves can be replaced. A failing heart can be replaced by a donor heart, and an artificial heart can keep a patient alive while they wait.

Key points

• Cancer is the result of cells dividing without control, forming a tumour.
• Benign tumours stay in one place, usually inside a membrane, and do not invade other parts of the body.
• Malignant tumours are cancers: they invade nearby tissue and spread in the blood to form secondary tumours.
• Risk factors include smoking, obesity, UV light and some viral infections, and some cancers have genetic risk factors.

Key points

• Xylem carries water and mineral ions from the roots up to the stems and leaves.
• Xylem is hollow tubes made of dead cells, strengthened by lignin.
• Phloem carries dissolved sugars from the leaves to the rest of the plant, for use or storage.
• Phloem is long cells with pores in their end walls, so the sap can move from cell to cell.
• The movement of sugars through phloem is translocation, and it goes both up and down the plant.

Key points

• Transpiration is the loss of water vapour from the leaves, mostly through the stomata.
• It pulls a continuous stream of water up the xylem from the roots: the transpiration stream.
• Guard cells open and close the stomata, controlling water loss and gas exchange.
• It is faster when it is warm, dry, windy and bright.

A potometer reading