Biology - General Certificate of Secondary Education, 2003

AQA

Life Processes and Living Things

extension strands

   

Locomotion
10.24 Skeleton and Movement  KS3 The role of the skeleton and joints, and the principle of antagonistic muscle pairs (for example biceps and triceps) in movement.
  FT and HT Vertebrates have an internal skeleton which provides the framework for support and movement.

Bones are rigid to provide support for the body and for muscle attachment. At a joint:
  • the bones at a joint are held together by strong fibres called ligaments;
  • the ends of the bones in a joint are covered with a smooth layer of
  • cartilage which stops the bones rubbing together;
  • a membrane in the joint secretes synovial fluid which is oily making the surface of the cartilage slippery and helps the joint to move easily.
Care should be taken when exercising to avoid:
  • sprains - which occur when the ligaments and other tissues in a joint are torn by a sudden wrench;
  • dislocations - which occur when a bone is forced out of a joint.
Muscles only move bones at a joint by contraction. Muscle tissue contains fibres which contract when supplied with energy from respiration.

Increased muscle activity requires glucose and oxygen to be at a faster rate and increases the rate of removal of carbon dioxide and heat from muscle tissues.

Candidates should be able to predict the effect of muscles and bones on movement in unfamiliar situations.

Regular exercise:
  • keeps muscles toned, so the fibres are slightly tensed and read contract;
  • increases muscle strength and avoids muscles feeling stiff and sore after exercise;
  • keeps joints working smoothly;
  • maintains an efficient supply of blood to the muscles, the heart and the lungs.
  HT Skeletal tissues have physical properties which adapt them for their functions. Bone resists compression, bending and stretching. Bone is hardened by deposits of calcium phosphate. Living cells and proteins in bone prevent it from being brittle.

(Candidates will not be expected to give details of the microscopic structure of bone.)

Ligaments have tensile strength and some elasticity. This makes it possible for joints to bend without the bones being easily dislocated.

Cartilage is strong but not rigid. This enables it to be slightly compressed and to absorb shock.

Tendons, which attach muscles to bones, have tensile strength and little elasticity.
10.25 Adaptations for movement  FT and HT Fish are adapted for movement in water by having:
  • a zig-zag arrangement of muscles that produces wave-like movements of the body,
  • a tail with a fin providing a large surface area that pushes backwards against the water and moves the fish forward;
  • a streamlined body shape which reduces resistance.
Birds are adapted for flight by having:
  • wings that provide a large surface area to push downwards on the air and lift the bird upwards;
  • flight feathers that provide this large surface area while being strong and light;
  • honey-combed bones that retain strength while reducing mass:
  • a streamlined body shape which reduces resistance.
  HT Swimming in fish is assisted by:
  • a gas-filled swim-bladder that provides buoyancy;
  • median fins that keep the fish upright by increasing the vertical surface area;
  • paired fins that enable up, down and backwards movement.
Flight in birds is assisted by:
  • the aerofoil shape of the wing creating lower pressure above the wing and so generating lift;
  • the flight feathers of birds have interlocking barbs which help to maintain a flat surface, and hollow shafts which provide lightness;
  • the arrangement of the primary and secondary feathers in the wing enabling the downbeat to provide both lift and forward
  • propulsion, while allowing air flow between the feathers during the upstroke;
The large sternum and keel give a large surface area and a rigid framework for muscle attachment. The arrangement of bones in the wing has evolved from the typical pentadactyl limb. The structure is comparable to that of the human arm, but with a reduced number of digits and wrist bones.
   

Patterns of feeding
10.26 Feeding adaptations in invertebrates  FT and HT Mussels are filter feeders. They feed on microscopic organisms (plankton) in water. This feeding method involves:
  • beating hair-like cilia to draw a current of water through the body;
  • having gills which act like a sieve to trap plankton;
  • using other cilia to rnove the trapped plankton into the mouth.
Mosquitoes feed on blood. This feeding method involves:
  • mouthparts that are adapted to suck blood from capillaries.
  • a sharp needle-like tube (proboscis) that can penetrate skin.
  • muscles in the throat that help them to draw blood from a capillary.
  • saliva containing a substance that prevents the blood clotting being secreted into the capillary.
  HT The saliva of the mosquito may contain parasites that cause diseases, such as malaria. Parasites are organisms that live in or on another organism and obtain food from it. The malarial parasite is a single- celled organism that feeds and reproduces inside human blood cells. Rupture of the blood cells causes severe fever. Mosquitoes enable the parasites to be transmitted from one person to another.

Aphids, butterflies and houseflies also feed by sucking fluids into their mouth.

Candidates should be able, when provided with appropriate information, to explain the adaptations that enable these insects to feed on fluids.
10.27 Feeding in mammals  FT and HT Mammals have teeth which may be used to bite off pieces of food and to chew it into smaller pieces before swallowing. The shapes of teeth are suited to their function.

Human teeth are adapted to deal with a wide range of foods. The incisors and canines are used for biting. The premolars and molars are used for chewing and crushing food.

Dogs have teeth and jaws that are adapted for a carnivorous diet:
  • the incisors are small and can be used to pull meat apart;
  • the canines are sharp and pointed and may be used to grip prey, as well as for tearing meat;
  • the premolars and molars include special large carnassial teeth which can be used to shear meat and crush bones;
  • the jaws move only up and down in order to provide a firm scissor action.
Candidates should be able to relate the shape of teeth to their functions and to interpret diagrams of skulls and their dentition.
  HT The digestive systems of mammals are adapted to the diet consumed. Mammals do not produce an enzyme that breaks down cellulose. Mammals with a largely herbivorous diet often have cellulose-digesting bacteria in their digestive system which enable them to break down cellulose to sugars.

Sheep and cows have a rumen between the oesophagus and stomach which contains these bacteria. To enhance digestion, part-digested material from the rumen is re-chewed in the mouth.

Rabbits have cellulose-digesting bacteria in a large appendix/caecum which opens into the junction between the small and large intestines. Because the food that is digested here has already passed through the small intestine, rabbits eat their own faeces.

Carnivores have no need for cellulose-digesting bacteria, and their digestive system does not have special sections to contain them.

The relationship between cellulose-digesting bacteria and herbivores is an example of mutualism as both organisms benefit from living together. The herbivores obtain sugar from the cellulose, and the bacteria get a supply of cellulose and other nutrients.
   

Controlling Disease
10.28 Treating infectious disease  FT and HT (This section builds on knowledge of the causative agents of disease from Section 10.11)
  Candidates should be able to describe Pasteur's evidence that decay and disease can be caused by living organisms.

Microorganisms that cause disease are called pathogens.

Diseases may be treated with medicines that contain useful drugs. Some medicines, including painkillers, help to relieve the symptoms of disease, but do not kill the pathogens.

Antibiotics, including penicillin, are medicines that help to cure bacterial disease by killing infective bacteria inside the body. Antibiotics cannot be used to kill viral pathogens, which live and reproduce inside cells. It is difficult to develop drugs which kill viruses without also damaging the body's tissues.

Many strains of bacteria have developed resistance to antibiotics as a result of natural selection. It is, therefore, necessary to have a range of different antibiotics and to select the one that is most effective for treatment of a particular infection. To prevent further resistance arising it is important to avoid over-use of antibiotics.

People can be immunised against a disease by introducing small quantities of dead or inactive forms of the pathogen into the body. Antigens, which are usually protein-based, in the vaccine stimulate the white cells to produce antibodies. These react with and destroy the antigens.

This makes the person immune to future infections by the pathogen, because the body can respond by rapidly making the correct antibody, in the same way as if the person had once had the disease. This is called active immunity.

Vaccination can be used to protect against viral pathogens. An example is the MMR vaccine used to protect children against measles, mumps and rubella.

If a person has already been exposed to a dangerous pathogen, it is necessary to inject antibodies directly to provide immediate protection. This is called passive immunity. An example is the use of rabies antibodies after a person has been bitten by a dog that may possibly have rabies.
  Candidates should be able, when provided with additional information, to explain how the treatment of disease has changed as a result of increased understanding of the action of antibiotics and immunity.
  Candidates should be able, when provided with appropriate information, to evaluate the advantages and disadvantages of being vaccinated against a particular disease.
  HT Two types of white blood cells (lymphocytes) are involved in the immune response. These are T cells and B cells.

T cells have receptors on their surface membrane that recognise and attach to an antigen. T cells can then destroy cells that have this antigen.

T cells also stimulate B cells to multiply and form clones which secrete antibodies. Antibodies are specific to a particular antigen. Memory cells remain in the body and antibody production takes place very rapidly if the same antigen enters the body for a second time. This immunological memory provides immunity following a natural infection and after vaccination.
10.29 Treating kidney disease  FT and HT
  FT and HT People who suffer from kidney failure may be treated either by using a dialysis machine or by having a healthy kidney transplanted.

In a dialysis machine a person's blood flows between partially permeable membranes. Waste urea passes out from the blood into the dialysis fluid. Treatment by dialysis restores the concentrations of dissolved substances in the blood to normal levels and has to be carried out at regular intervals.

A kidney transplant enables a diseased kidney to be replaced by a healthy one from a donor. However, the donor's kidney may be rejected by the immune system unless precautions are taken. To prevent rejection:
  • a donor kidney with a 'tissue-type' similar to that of the recipient is used;
  • the bone marrow of the recipient is treated with radiation to stop white cell production;
  • the recipient is kept in sterile conditions for some time after thetransplant operation;
  • the recipient is treated with drugs that suppress the immune response.
  Candidates should be able to evaluate the advantages and disadvantages of treating kidney failure by dialysis or kidney transplant.
  HT During dialysis it is important that useful substances in the blood, such as glucose and mineral ions, are not lost. To prevent this the dialysis fluid contains the same concentrations of these substances as blood plasma. This ensures that only waste substances and excess ions and water diffuse into the dialysis fluid.

During a transplant operation, transfusion of blood may be required. This blood must be matched with the blood group of the recipient to prevent agglutination.

In the ABO system of blood grouping there are:
  • antigens on the surface of red blood cells;
  • antibodies in the plasma.
Candidates should be able to interpret compatibility tables for the ABO blood groups.
   

Applied Microbiology
10.30 Using microorganisms to make food and drinks  FT and HT Microorganisms are used to make food and drink:
  • bacteria are used in yoghurt and cheese manufacture;
  • moulds are used to produce the distinctive colour and taste of blue cheeses;
  • yeast is used in making bread and alcoholic drinks.
Both moulds and yeast are Fungi. Yeast is a single-celled organism. The cells have a nucleus, cytoplasm and a membrane surrounded by a cell wall. Moulds have thread-like structures called hyphae, which have walls surrounding cytoplasm and many nuclei. The hyphae do not contain separate cells. Moulds reproduce asexually by means of spores.

Candidates should be able to compare the structures of moulds and yeast with those bacteria and viruses (section 10.11).

Yeast can respire without oxygen (anaerobic respiration), producing carbon dioxide and ethanol (alcohol). This is called fermentation. In the presence of oxygen yeast carries out aerobic respiration and produces carbon dioxide and water. Aerobic respiration provides more energy and is necessary for the yeast to grow and reproduce.

In baking:
  • a mixture of yeast and sugar is added to flour;
  • the mixture is left at a warm temperature;
  • the carbon dioxide produced by the respiring yeast makes the dough rise;
  • the bubbles of gas in the dough expand when the bread is baked making the bread 'light'.
In brewing beer and wine-making, carbohydrates are used as an energy source for yeast to respire.

For making beer:
  • the starch in barley grains is broken down into a sugary solution by enzymes in the germinating grains, in a process called malting;
  • the sugary solution is extracted then fermented;
  • hops are then added to give the beer flavour.
(Candidates are not expected to know the details of the industrial process).

In wine-making the yeast uses the natural sugars in the grapes as its energy source.

In the production of yoghurt:
  • a starter culture of bacteria is added to warm milk;
  • the bacteria ferment the milk sugar (lactose), producing lactic acid;
  • the lactic acid causes the milk to clot and solidify into yoghurt.
To make cheese:
  • a starter culture of bacteria (different from that used in yoghurt production) is added to warm milk;
  • curds are produced that are more solid than yoghurt;
  • these curds are separated from the remaining liquid part of the milk (whey);
  • bacteria and moulds are added to the curds to slowly ripen the cheese.
Microorganisms can be grown in a culture medium containing carbohydrates as an energy source, mineral ions, and in some cases supplementary protein and vitamins. These nutrients are often contained in an agar medium which can be poured into a petri dish.

In order to prepare useful products, uncontaminated cultures of microorganisms are required. For this:
  • petri dishes and culture media must be sterilised before use to kill unwanted microorganisms;
  • inoculating loops used to transfer microorganisms to the media must be sterilised by passing them through a flame;
  • the lid of the petri dish should be sealed with adhesive tape to prevent microorganisms from the air contaminating the culture.
In school and college laboratories, cultures should be incubated at a maximum temperature of 25°C to prevent the growth of pathogens that might be harmful to humans. In industrial conditions higher temperatures can produce more rapid growth.
10.31 Growing microorganisms in fermenters  FT and HT Microorganisms can be grown in large vessels called fermenters to produce useful products such as antibiotics.

Industrial fermenters usually have:
  • an air supply - to provide oxygen for respiration of the microorganisms;
  • a stirrer to keep the microorganisms in suspension and maintain an even temperature;
  • a water-cooled jacket to remove heat produced by the respiring microorganisms;
  • instruments to monitor factors such as pH and temperature.
The antibiotic, penicillin, is made by growing the mould, Pencillium, in a fermenter. The medium contains sugar and other nutrients. The Penicillium only starts to make penicillin after using up most of the nutrients for growth.
  HT Fuels can be made from natural products by fermentation. Biogas, mainly methane, can be produced by anaerobic fermentation of a wide range of plant products or waste material containing carbohydrates. On a large scale, waste from, for example, sugar factories or sewage works can be used. On a small scale, biogas generators can be used to supply the energy needs of individual families or farms. Many different microorganisms are involved in the breakdown of materials in biogas production.

Candidates should be able to evaluate the advantages and disadvantages of given designs of biogas generator.

Ethanol-based fuels can be produced by the anaerobic fermentation of sugar cane juices and from glucose derived from maize starch by the action of carbohydrase. The ethanol is distilled from the products of the fermentation and can be used in motor vehicle fuels.

  Candidates should be able, when provided with appropriate additional information, to interpret economic and environmental data relating to production of fuels by fermentation and their use.
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