Diet and exercise
a) A healthy diet contains the right balance of thedifferent foods you need and the right amount of energy. Carbohydrates, fats and proteins are used by the body to release energy and to build cells. Mineral ions and vitamins are needed in small amounts for healthy functioning of the body. A person is malnourished if their diet is not balanced. This may lead to a person being overweight or underweight. An unbalanced diet may also lead to deficiency diseases or conditions such as Type 2 diabetes.
b) A person loses mass when the energy content of the food taken in is less than the amount of energy expended by the body. Exercise increases the amount of energy expended by the body.
c) The rate at which all the chemical reactions in the cells of the body are carried out (the metabolic rate) varies with the amount of activity you do and the proportion of muscle to fat in your body. Metabolic rate may be affected by inherited factors.
d) Inherited factors also affect our health; for example cholesterol level.
e) People who exercise regularly are usually healthier than people who take little exercise.
How our bodies defend themselves against infectiou
a) Microorganisms that cause infectious disease are called pathogens. b) Bacteria and viruses may reproduce rapidly inside the body and may produce poisons (toxins) that make us feel ill. Viruses damage the cells in which they reproduce. c) The body has different ways of protecting itself against pathogens. d) White blood cells help to defend against pathogens by: ingesting pathogens producing antibodies, which destroy particular bacteria or viruses producing antitoxins, which counteract the toxins released by the pathogens. e) The immune system of the body produces specific antibodies to kill a particular pathogen. This leads to immunity from that pathogen. . f) Semmelweis recognised the importance of hand-washing in the prevention of spreading some infectious diseases. By insisting that doctors washed their hands before examining patients, he greatly reduced the number of deaths from infectious diseases in his hospital. g) Some medicines, including painkillers, help to relieve the symptoms of infectious disease, but do not kill the pathogens. h) Antibiotics, including penicillin, are medicines that help to cure bacterial disease by killing infectious bacteria inside the body. Antibiotics cannot be used to kill viral pathogens, which live and reproduce inside cells. It is important that specific bacteria should be treated by specific antibiotics. The use of antibiotics has greatly reduced deaths from infectious bacterial diseases. Overuse and inappropriate use of antibiotics has increased the rate of antibiotic resistant strains of bacteria. i) Many strains of bacteria, including MRSA, have developed resistance to antibiotics as a result of natural selection. j) Mutations of pathogens produce new strains. Antibiotics and vaccinations may no longer be effective against a new resistant strain of the pathogen. The new strain will then spread rapidly because people are not immune to it and there is no effective treatment. l) People can be immunised against a disease by introducing small quantities of dead or inactive forms of the pathogen into the body (vaccination). Vaccines stimulate the white blood cells to produce antibodies that destroy the pathogens. MMR vaccine is used to protect children against measles, mumps and rubella.
The nervous system
a) The nervous system enables humans to react to their surroundings and coordinate their behaviour.
b) Cells called receptors detect stimuli (changes in the environment).
Receptors and the stimuli they detect include:
■ receptors in the eyes that are sensitive to light
■ receptors in the ears that are sensitive to sound
■ receptors in the ears that are sensitive to changes in position and enable us to keep our balance
■ receptors on the tongue and in the nose that are sensitive to chemicals and enable us to taste and to smell
■ receptors in the skin that are sensitive to touch, pressure, pain and temperature changes.
c) Light receptor cells, like most animal cells, have a nucleus, cytoplasm and cell membrane.
d) Information from receptors passes along cells (neurones) in nerves to the brain. The brain coordinates the response. Reflex actions are automatic and rapid. They often involve sensory, relay and motor neurones.
In a simple reflex action:
■ impulses from a receptor pass along a sensory neurone to the central nervous system
■ at a junction (synapse) between a sensory neurone and a relay neurone in the central nervous system, a chemical is released that causes an impulse to be sent along a relay neurone
■ a chemical is then released at the synapse between a relay neurone and motor neurone in the central nervous system, causing impulses to be sent along a motor neurone to the organ (the effector) that brings about the response
■ the effector is either a muscle or a gland, a muscle responds by contracting and a gland responds by releasing (secreting) chemical substances.
Control in the human body
a) Ithe water content of the body – water leaves the body via the lungs when we breathe out and via the skin when we sweat to cool us down, and excess water is lost via the kidneys in the urine the ion content of the body - ions are lost via the skin when we sweat and excess ions are lost via the kidneys in the urine temperature – to maintain the temperature at which enzymes work best blood sugar levels – to provide the cells with a constant supply of energy. b) Many processes within the body are coordinated by hormones. Hormones are secreted by glands and are usually transported to their target organs by the bloodstream. Hormones regulate the functions of many organs and cells. For example, the monthly release of an egg from a woman’s ovaries and the changes in the thickness of the lining of her womb are controlled by hormones secreted by the pituitary gland and by the ovaries. d) hormones are involved in the menstrual cycle of a woman. Hormones are involved in promoting the release of an egg: (FSH) is secreted by the pituitary gland and causes eggs to mature in the ovaries. It also stimulates the ovaries to produce hormones including oestrogen (LH) stimulates the release of eggs from the ovary oestrogen is secreted by the ovaries and inhibits the further production of FSH. e) The uses of hormones in controlling fertility include: giving oral contraceptives that contain hormones to inhibit FSH production so that no eggs mature – oral contraceptives may contain oestrogen and progesterone to inhibit egg maturation – the first birth-control pills contained large amounts of oestrogen. These resulted in women suffering significant side effects – birth control pills now contain a much lower dose of oestrogen, or are progesterone only – progesterone-only pills lead to fewer side effects giving FSH and LH in a ‘fertility drug’ to a woman whose own level of FSH is too low to stimulate eggs to mature, for example in IVF) reatment – IVF involves giving a mother FSH and LH to stimulate the maturation of several eggs. The eggs are collected from the mother and fertilised by sperm from the father. The fertilised eggs develop into embryos. At the stage when they are tiny balls of cells, one or two embryos are inserted into the mother’s uterus (womb).
Control in Plants
a) Plants are sensitive to light, moisture and gravity:
■ their shoots grow towards light and against the force of gravity
■ their roots grow towards moisture and in the direction of the force of gravity.
b) Plants produce hormones to coordinate and control growth. Auxin controls phototropism
and gravitropism (geotropism).
c) The responses of plant roots and shoots to light, gravity and moisture are the result of unequal distribution of hormones, causing unequal growth rates.
d) Plant growth hormones are used in agriculture and horticulture as weed killers and as rooting hormones.
a) Scientists are continually developing new drugs.
b) When new medical drugs are devised, they have to be extensively tested and trialled before being used. Drugs are tested in a series of stages to find out if they are safe and effective. New drugs are extensively tested for toxicity, efficacy and dose: in the laboratory, using cells, tissues and live animals in clinical trials involving healthy volunteers and patients. Very low doses of the drug are given at the start of the clinical trial. If the drug is found to be safe, further clinical trials are carried out to find the optimum dose for the drug. In some double blind trials, some patients are given a placebo, which does not contain the drug. Neither the doctors nor the patients know who has received a placebo and who has received the drug until the trial is complete. c) Candidates should be aware of the use of statins in lowering the risk of heart and circulatory diseases. d) Thalidomide is a drug that was developed as a sleeping pill. It was also found to be effective in relieving morning sickness in pregnant women. Thalidomide had not been tested for use in pregnant women. Unfortunately, many babies born to mothers who took the drug were born with severe limb abnormalities. The drug was then banned. As a result, drug testing has become much more rigorous. More recently, thalidomide has been used successfully in the treatment of leprosy and other diseases. e) Candidates should be aware of the effects of misuse of the legal recreational drugs, alcohol and nicotine f) Cannabis is an illegal drug. Cannabis smoke contains chemicals which may cause mental illness in some people. g) The overall impact of legal drugs (prescribed and non-prescribed) on health is much greater than the impact of illegal drugs because far more people use them. h) Drugs change the chemical processes in peoples’ bodies so that they may become dependent or addicted to the drug and suffer withdrawal symptoms without them. Heroin and cocaine are very addictive. i) There are several types of drug that an athlete can use to enhance performance. Some of these drugs are banned by law and some are legally available on prescription, but all are prohibited by sporting regulations. Examples include stimulants that boost bodily functions such as heart rate; and anabolic steroids which stimulate muscle growth.
a) To survive and reproduce, organisms require a supply of materials from their surroundings and from the other living organisms there.
b) Plants often compete with each other for light and space, and for water and nutrients from the soil.c) Animals often compete with each other for food, mates and territory.
d) Organisms, including microorganisms, have features (adaptations) that enable them to survive in the conditions in which they normally live.
e) Some organisms live in environments that are very extreme. Extremophiles may be tolerant to high levels of salt, high temperatures or high pressures.
f) Animals and plants may be adapted for survival in the conditions where they normally live, eg deserts, the Arctic. Animals may be adapted for survival in dry and arctic
environments by means of:
■ changes to surface area
■ thickness of insulating coat
■ amount of body fat
■ camouflage. Plants may be adapted to survive in dry environments
by means of:
■ changes to surface area, particularly of the leaves
■ water-storage tissues
■ extensive root systems.
g) Animals and plants may be adapted to cope with specific features of their environment, eg thorns, poisons and warning colours to deter predators.
a) Changes in the environment affect the distribution of living organisms.
b) Animals and plants are subjected to environmental changes. Such changes may be caused by living or non-living factors such as a change in a
competitor, or in the average temperature or rainfall.
c) Living organisms can be used as indicators of pollution:
■ lichens can be used as air pollution indicators, particularly of the concentration of sulfur dioxide in the atmosphere
■ invertebrate animals can be used as water pollution indicators and are used as indicators
of the concentration of dissolved oxygen in water.
d) Environmental changes can be measured using non-living indicators such as oxygen levels, temperature and rainfall.
Energy in biomass
a) Radiation from the Sun is the source of energy for most communities of living organisms. Green plants and algae absorb a small amount of the light that reaches them. The transfer from light energy to chemical energy occurs during photosynthesis. This energy is stored in the substances that make up the cells of the plants.
b) The mass of living material (biomass) at each stage in a food chain is less than it was at the previous stage. The biomass at each stage can be drawn to scale and shown as a pyramid of biomass.
c) The amounts of material and energy contained in the biomass of organisms are reduced at each successive stage in a food chain because:
■ some materials and energy are always lost in the organisms’ waste materials
■ respiration supplies all the energy needs for living processes, including movement. Much of this energy is eventually transferred to the surroundings.
a) Living things remove materials from the environment for growth and other processes. These materials are returned to the environment either in waste materials or when living things die and decay.
b) Materials decay because they are broken down (digested) by microorganisms. Microorganisms are more active and digest materials faster in warm, moist, aerobic conditions.
c) The decay process releases substances that plants need to grow.
d) In a stable community, the processes that remove materials are balanced by processes that return materials. The materials are constantly cycled.
The carbon cycle
a) The constant cycling of carbon is called the carbon cycle.
In the carbon cycle:
■ carbon dioxide is removed from the environment by green plants and algae for photosynthesis
■ the carbon from the carbon dioxide is used to make carbohydrates, fats and proteins, which make up the body of plants and algae
■ when green plants and algae respire, some of this carbon becomes carbon dioxide and is released into the atmosphere
■ when green plants and algae are eaten by animals and these animals are eaten by other animals, some of the carbon becomes part of the fats and proteins that make up their bodies
■ when animals respire, some of this carbon becomes carbon dioxide and is released into the atmosphere
■ when plants, algae and animals die, some animals and microorganisms feed on their bodies
■ carbon is released into the atmosphere as carbon dioxide when these organisms respire
■ by the time the microorganisms and detritus feeders have broken down the waste products and dead bodies of organisms in ecosystems and cycled the materials as plant nutrients, all the energy originally absorbed by green plants and algae has been transferred
■ combustion of wood and fossil fuels releases carbon dioxide into the atmosphere.
Why organisms are different
a) The information that results in plants and animals having similar characteristics to their parents is carried by genes, which are passed on in the sex cells (gametes) from which the offspring develop.
b) The nucleus of a cell contains chromosomes. Chromosomes carry genes that control the
characteristics of the body.
c) Different genes control the development of different characteristics of an organism.
d) Differences in the characteristics of different individuals of the same kind may be due to
■ the genes they have inherited (genetic causes)
■ the conditions in which they have developed (environmental causes)
■ or a combination of both.
a) There are two forms of reproduction:
■ sexual reproduction – the joining (fusion) of male and female gametes. The mixture of the genetic information from two parents leads to variety in the offspring
■ asexual reproduction – no fusion of gametes and only one individual is needed as the parent. There is no mixing of genetic information and so no genetic variation in the offspring. These genetically identical individuals are known as clones. b) New plants can be produced quickly and cheaply by taking cuttings from older plants. These new plants are genetically identical to the parent plant. c) Modern cloning techniques include: ■ tissue culture – using small groups of cells from
part of a plant ■ embryo transplants – splitting apart cells from a developing animal embryo before they become specialised, then transplanting the identical embryos into host mothers ■ adult cell cloning – the nucleus is removed from an unfertilised egg cell. The nucleus from an adult body cell, eg a skin cell, is then inserted into the egg cell. An electric shock then causes the egg cell to begin to divide to form embryo cells. These embryo cells contain the same genetic information as the adult skin cell. When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female to continue
its development. d) In genetic engineering, genes from the chromosomes of humans and other organisms can be ‘cut out’ using enzymes and transferred to cells of other organisms. e) Genes can also be transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they develop with desired characteristics:
■ new genes can be transferred to crop plants ■ crops that have had their genes modified in this way are called genetically modified crops (GM crops) ■ examples of genetically modified crops include ones that are resistant to insect attack or to herbicides ■ genetically modified crops generally show increased yields. f) Concerns about GM crops include the effect on populations of wild flowers and insects, and uncertainty about the effects of eating GM crops on human health.
a) Darwin’s theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago.
b) The theory of evolution by natural selection was only gradually accepted because:
■ the theory challenged the idea that God made all the animals and plants that live on Earth
■ there was insufficient evidence at the time the theory was published to convince many scientists
■ the mechanism of inheritance and variation was not known until 50 years after the theory was published.
c) Other theories, including that of Lamarck, are based mainly on the idea that changes that occur in an organism during its lifetime can be inherited. We now know that in the vast majority of cases this type of inheritance cannot occur.
d) Studying the similarities and differences between organisms allows us to classify living organisms into animals, plants and microorganisms, and helps us to understand evolutionary and ecological relationships. Models allow us to suggest relationships between organisms.
e) Evolution occurs via natural selection: ■ individual organisms within a particular species may show a wide range of variation because of differences in their genes
■ individuals with characteristics most suited to the environment are more likely to survive to breed successfully
■ the genes that have enabled these individuals to survive are then passed on to the next generation.
f) Where new forms of a gene result from mutation there may be relatively rapid change in a species if the environment changes.