AQA Biology- Unit 3

• Substances absorbed AGAINST a concentration gradient.
• Requires the use of energy from respiration.
• Known as ACTIVE TRANSPORT.
• Think of how pushing a ball up a hill requires energy.

• Villi line the walls of the small intestine.
• They have a large surface area and an extensive network of capillaries.
• This network of capillaries absorbs products of digestion by diffusion and active transport.

• Millions of little air sacs in the lungs.
• They are very close to the blood capillaries making them effective at exchanging oxygen and carbon dioxide because:
  - They have a large, moist surface area.
  - They have an excellent blood supply.
• Carbon Dioxide DIFFUSES from the blood into the alveoli.
• Oxygen DIFFUSES from the alveoli into the blood.
• This means the deoxygenated blood has swapped its carbon dioxide for oxygen and is now OXYGENATED.

Trachea- Windpipe.
Bronchus- Branch of Trachea.
Bronchiole- One of many branches of the Bronchi.
Ribs- Protects the contents of the Thorax.
Diaphragm- Muscular 'sheet' dividing the Thorax and Abdomen.

• STOMATA allow carbon dioxide in and oxygen out (by diffusion).
• This however, also leads to loss of water vapour through TRANSPIRATION.
• Transpiration is quicker in hot, dry, windy conditions.
• The size of stomata is controlled by a pair of guard cells.
• If plants are losing lots of water, the stomata can close to prevent wilting and dehydration.

• The body's transport system. Consists of the HEART, the BLOOD VESSELS and the BLOOD.
• Carries blood from the heart to all the cells of the body to provide them with food and oxygen (oxygenated blood).
• Carries waste products (including carbon dioxide) away from the cells (deoxygenated blood).
• Blood is pumped to the lungs so that carbon dioxide can be exchanged for oxygen.

• Blood is composed of four components: PLASMA, RED BLOOD CELLS, WHITE BLOOD CELLS and PLATELETS.
• PLASMA is a straw-coloured liquid which transports...
  - Carbon dioxide from the organs to the lungs.
  - Glucose from the small intestine to the organs.
  - Other wastes (eg. urea) from the liver to the kidneys.
• RED BLOOD CELLS transport oxygen from the lungs to the organs
  - They have no nucleus so that they can carry lots of HAEMOGLOBIN (a red pigment which can carry oxygen).
  - In the lungs, haemoglobin combines with oxygen to form OXYHAEMOGLOBIN. In other organs, oxyhaemoglobin splits up into haemoglobin and oxygen.

• WITH OXYGEN.
• When glucose is combined with oxygen inside living cells it breaks down and releases energy. This process is aerobic respiration.
• Doesn't produce energy as quickly as anaerobic respiration.
• However is a very efficient method of producing energy. Provides a lot more energy than anaerobic respiration.

GLUCOSE + OXYGEN ---> CARBON DIOXIDE + WATER + ENERGY

• WITHOUT OXYGEN.
• When there is no oxygen presentm glucose cannot break down completely in living cells.
• This incomplete breakdown of glucose releases a little bit of energy very quickly inside the cells. This is anaerobic respiration.
• The waste product from anaerobic respiration is LACTIC ACID.
• Lactic Acid accumulates in the tissues. When this happens, the muscles become fatigued.
• After exercisem the body needs oxygen to break down the lactic acid; the oxygen needed is called an OXYGEN DEBT.

GLUCOSE ---> ENERGY + LACTIC ACID

• Their function is to maintain the concentrations of dissolved substances and to remove all urea.
• It is made up of blood vessels and tubules (small tubes).
• The three stages:
  - Nearly everything is forced out of the blood into the tubules.
  - The substances we want to keep are reabsorbed back into the blood.
  - Unwanted substances are released as urine.

•  In a dialysis machine, a person's blood flows between partailly permeable membranes.
• As the blood flows through the machine, it is seperated from the dialysis fluid only by the partially permeable membranes.
• These membranes allow all the urea and any excess substances to pass from the blood to the dialysis fluid. This restores the concentrations of dissolved substances in the blood to their normal levels.
• Dialysis fluid contains the same concentration of useful substances as blood. This ensures that glucose and essential mineral ions are not lost through diffusion.

• A kidney transplant enables a diseased kidney to be replaced by a healthy one from a donor.
• The main problem with kidney transplants is the possibility of rejection by the immune system therefore these precautions are taken:
  - A donor kidney with a tissue type as close as possible to that of the recipitant is used. Best achieved if donor is a relative.
  - The bone marrow of the recipitant is irradiated to stop the production of white cells.
  

• DIALYSIS PROS:
  - Readily available and can be used by patients waiting for a transplant.
  - No rejection can occur.
• DIALYSIS CONS:
  - Regular sessions are very time consuming (up to 10 hours a session).
  - The diet has to be regulated.
• KIDNEY TRANSPLANT PROS:
  - No need for regular dialysis sessions, so the patient can lead a less restricted life.
  - Any healthy person with a tissue match can donate a kidney and live perfectly well with only one kidney.
• KIDNEY TRANSPLANT CONS:
  - Time restraints: a donated kidney must be transplanted within 12 hours.
  - Rejection can occur.
  - Anti-rejection drugs must be taken for the rest of the patient's life.
  - Patient must undergo irradiation of the bone marrow.
  - There is a shortage of donors.

• Yeast is used to make bread and alcoholic drinks.
• Yeast can respire without oxygen (anaerobic respiration) to produce ethanol (alcohol) and carbon dioxide from glucose.
• This is called FERMENTATION.
  
  GLUCOSE ---> ETHANOL + CARBON DIOXIDE + ENERGY
• Yeast can also respire using oxygen (aerobic respiration) to produce water and carbon dioxide.
• Aerobic respiration produces more energy and is necessary for the yeast to grow and reproduce

      GLUCOSE + OXYGEN ---> WATER + CARBON DIOXIDE + ENERGY

• Yeast to make bread:
  - A mixture of yeast and sugar is added to flour.
  - The mixture is left in a warm place.
  - The carbon dioxide from the respiring yeast makes the dough rise.
  - The bubbles of gas in the dough expand when the bread is baked, making the bread 'light'.
  - As the bread is baked, any alcohol produced during respiration evaporates off.
• Yeast to make alcoholic drinks (brewing):
  - In a process called malting, the starch in barley is broken down into a sugar solution by enzymes.
  -Yeast is added to the solution and fermentation takes place. In beer-making, hops are added to give the beer flavour. In wine-making, the yeast uses the natural sugars in the grapes as its energy source.
  - Carbon dioxide is bubbled off to leave just the alcohol.
  

• Bacteria are used to make yoghurt and cheese.
  
• How yoghurt is made:
  - A starter culture of bacteria is added to warm milk in a fermenting vessel.
  - The bacteria ferments the milk sugar (lactose) producing lactic acid which provides the yoghurt's sour taste.
  - The lactic acid causes the milk to clot and solidify into yoghurt.
  
  

  

• Microorganisms are grown in fermenters (large vessels).
• Products:
  - Penicillin, made by growing penicillium, a mould, in a fermenter. The medium contains sugar and other nutrients.
  - Mycroprotein, made using Fusarium, a fungus. The fungus is grown on starch in aerobic conditions and the biomass is harvested and purified.
  
  Water Jacket- Removes heat produced by the respiring microorganisms.
  Data logger- Moniters the mixture's PH and temperature.
  Air supply- Provides oxygen so that the microorganisms can respire.
  Paddles- Stirs the microorganisms to keep them in suspension and mantain an even temperature.

• Fuel can be made from natural products via fermentation. However, all oxygen must be removed so that anaerobic fermentation can occur.
• BIOGAS, which is mainly methane, can be produced this way using a wide range of organic or waste material containing carbohydrates.
• Anaerobic respiration can also be used to produce ethanol-based fuels from sugar cane juices or glucose derived from maize starch. The ethanol produced needs to be distilled from the other products of fermentation, and can then be used in motor vehicles.

• Preparing a Culture Medium:
  - Microorganisms are grown in a culture medium containing various nutrients that the particular microorganism may need (e.g. Carbohydrates, Mineral Ions, Vitamins and Proteins).
  - AGAR is most commonly used as the growth medium.
• Preparing Uncontaminated Cultures:
  - Petri dishes and culture medium are STERLISED using an autoclave. This is a pressure cooker which exposes the dishes and the agar to high temperatures and high pressure to kill off unwanted microorganisms.
  - Inoculating loops are heated to red heat in a bunsen flame, before being left to cool for five seconds. They are then sterile and can be used safely to transfer microorganisms to the culture medium.
  - The petri dish is then SEALED (to prevent unwanted microorganisms for entering). It should be stored upside down so that condensation forms in the lid.