AQA GCSE BIOLOGY - Unit 1 (Core)

• A healthy diet contains the right balance of the different 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 - leads to a person being overweight OR underweight. 
• An unbalanced diet could also lead to deficiency diseases or health issues such as Type 2 Diabetes. 
• A person loses mass when the energy content of the food consumed is less than the amount of energy used by the body. (Exercise increases the amount of energy expended by the body)
• The rate at which all the chemical reactions in the cells of the body are carried out is called the metabolic rate. 
• This varies with the amount of activity you do and the muscle to fat ratio in your body. It is also affected by inherited factors. 
• Inherited factors also affect out chloesterol level. 
• People who exercise regularly are usually healthier than people who don't. 

• Microorganisms that cause infectious disease are called pathogens 
• Bacteria and viruses reproduce rapidly insie the body and produce poisons that make us feel ill. 
• Viruses damage the cells in which they reproduce. 
• The body has different ways of protecting itself against pathogens with white blood cells by: 
  • ingesting pathogens 
  • producing antibodies, which destroy particular bacteria or viruses. 
  • producing antitoxins, which counteract the toxins released by pathogens. 
• The immune system produces specific antibodies to kill specific pathogens. This leads to immunity from that pathogen. 
• In vaccinations, dead or inactive forms of the pathogens are injected into the body to stimulate antibody production. The body can then respond rapidly to future infections.
• MMR vaccine is used to protect children against measels, mumps and rubella.
• If the majority of the population is immune to a pathogen, the spread of the pathogen is reduced. 
• Semmelweis recognised the importance of hand-washing in order to prevent spreading infectious diseases. 
• When he insisted doctors washed their hands before examining patients, he greatly reduced the number of deaths from infectious diseases in hospitals. 

• Painkillers help to relieve the symptoms of disease but do NOT kill pathogens. 
• Antibiotics help cure bacterial disease by KILLING the bacteria inside the body. 
• Antibiotics cannot be used to kill viruses as they are inside cells. 
• Overuse of antibiotics has increased the rate of antibiotic resistant strains of bacteria. 
• Many strains of bacteria (MRSA) have developled resistance to antibiotics as a result of natural selection. 
• Mutations of pathogens produce new strains and so anitbiotics and vaccinations may no longer be effective against the new strain. 
• The new strain will then spread rapidly because people are not immune to it and there is no effective treatement. 
• The developement of antibiotic resistant strains of bacteria means that we need new antibiotics. 
• Uncontaminated cultures of microorganisms are needed for investigating the action of disinfectants and antibiotics. 
• In school labs, cultures should be incubated to a max temperature of 25°C as it reduces chance of growing harmful pathogens. 
• In industrial conditions higher tamperatures can produce more rapid growth. 
  

• Petri dishes and culture media must be sterilised before use to kill unwanted microorganisms 

• Innoculating loops used to transfer microorganisms must be strelisised by passing them through a flame. 

• The lid of the Petri dish should be secured with adhesive tape to prevent microorganisms from the air contaminating the culture. 

• The nervous system enables humans to react to their surroundings and coordinate their behaviour 
• Receptor cells detect changes in the environment (stimuli). Receptors and stimuli they can detect: 
  • 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 allow us to keep our balance
  • receptors on the tongue and in the nose that are sensitive to chemicals (taste and smell)
  • receptors in the skin that are sensitive to touch, pressure, pain and temperature changes.
• Light receptor cells have a nuvleus, cytoplasm and cell membrane (like most animal cells)
• Information trvales from receptors along cells (neurones) in nerves to the brain which coordinates the response. 
• Reflex actions are automatic and tapid and often involve, sensory, relay and motor neurones.

• Impulses from a receptor pass along a sensory neurone to the central nervous system
• at a synapse (junction) 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 a 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 chemical subtances. 

• Internal conditions that are controlled include: 
  • the water content of the body - water leaves via the lungs when we breathe out and via the skin when we sweat to cool us down, and excess is lost via the kidneys in the urine.
  • the ion content of the body - ions are lost via te skin when we sweat and in urine. 
  • temperature - to maintain the temperature at whcih enzymes work best
  • blood sugar levels - to provide the cells with a constant supply of energy. 
• Many provesses in the body are coordinated by chemical substances called hormones. 
• Hormones ar secreted by glands and are usually transported to the organ by the bloodstream
• The monthly release of an egg from a woman's ovaries and the changes in the thickness of the lining of the womb are controlled by hormones secreted by the pituitary gland and ovaries
• Hormones are involved in promoting the release of an egg: 
  • FSH is secreted by the pituitary gland and causes eggs to mature. It also stimulates the production of oestrogen. 
  • LH stimulates the release of eggs. 
  • Oestrogen is secreted by the ovaries and inhibits production of FSH

To INHIBIT preganancy 

• oral contraceptives that contain hormones to inhibit FSH production so that no eggs mature. 
  • oral contraceptives may contian oestrogen and progesterone to inhibit eggs maturing.
  • the first birth-control pills contained large amounts of oestrogen but resulted in bad side effects. 
  • now, birth -control pills contain a much lower dose of oestrogen or only progesterone. 
  • progesterone only pills lead to fewer side effects. 

To ENCOURAGE pregnancy

• fertility drugs which contain FSH and LH can be given to a woman whose own level of FSH is too low to stimulate eggs to mature. E.g, IVF treatment 
  • IVF involves giving a mother FSH and LH  to stimulate the maturation of several eggs. 
  • The eggs are colected 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. 

• 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
• Plants produce hormones to coordinate and control growth. Auxin controls phototropism and gravitropism. 
• The responses of plant roots and shoots to light, gravity and moisture are the result of unequal distribution of hormones, causing unequal growth rates. 
• Plant growth hormones are using in agriculture as weed killers and as rooting hormones. 

positive tropism – the plant grows towards the stimulus

negative tropism – the plant grows away from the stimulus.

• Shoots have positive phototropism (grows towards the light) but negative gravitropism (grows against the froce of gravity)
• Roots have a negative phototropism (grows away from the light) but a positive gravitropism (grows in the direction of the force of gravity. 

• Scientists are continually developing new drugs 
• Statins lower the risk of heart and circulatory diseases. 
• Thalidomide was a sleeping pill but also found to be effective for relieving morning sickness. However, it had not been tested for use on pregnant women so many babies who's mothers took the drug were born with limb abnormalities. The drug was then banned. 
• The misuse of illegal recreational drugs such as ecstasy, cannabis and heroin may have adverse effects on the heart and circulatory system. 
• Cannabis is illegal and the smoke contains chemicals which can cause mental illness. 
• The overall impact of legal drugs is bigger than the impact of illegal drugs because more people use them. 
• Drugs change the chemical processes in peoples' bodies so that they may become dependant or addicted and suffer withdrawal symptoms without the drug. Heroin and cocaine are very addictive. 
• Some drugs athletes can use to enhance performance are banned and some are available on prescription, but all are prohibited by sporting regulations. E.g, stimulants that boost bodily functions like heart rate; anabolic steroids which stimulate muscle growth. 

New drugs are rigorously tested for toxicity 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, whcih does not contain the drug. Neither the doctors not the patients know who has received the placebo and who has received the drug until the trial is complete. 

• To survive and reproduce, organisms require a supply of materials from their surroundings and from the other living organisms there. 
• Plants often compete with each other for light and space, and for water and nutrients from the soil. 
• Animals often compete with each other for food, mates and territory. 
• Organisms, including microorganisms, have adaptations that enable them to survive in the conditions in which they normally live. 
• Some organisms live in environments that are very extreme. Extremophiles my be tolerant to high levels of salt, high temperatures or high pressures. 
• Animals and plants may be adapted to cope with specific features of their environment , eg, thorns, poisons and warning colours to deter other predators. 

• 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

• Changes in the environment affect the distribution of living organisms. 
• Animals and plants are subjected to environmental changes which can be caused by living or non living factors such as a change in a competitor, or in the average temperature of rainfall. 
• Living organisms can be used as indicators of pollution: 
  • lichens can be used as air pollution indications, particularly of the concentration of sulfur dioxide in the atmosphere
  • invertabrate animals can be used as water pollution indicators and are used as indicators of the concentration of dissolved oxygen in water. 
• Environmental changes can be measured by using non-living indicators such as oxygen levels, temperature and rainfall.
  • oxygen levels in water can be measure using oxygen probes connected to a data logger
  • rainfall is measured by using a rain gauge. The depth of rain is usually measured daily, eg, at the same time every morning. 
  • temperature can be measured by a thermometers. Digital thermometers have the advantage that no one needs to be there to take the reading.  

• Most living organisms obtain energy from teh Sun. Green plants and algae absorb a small amount of the light that reaches them. The transfer of light energy to chemical energy occurs during photosynthesis. This energy is stored in the substances that make up the cells of the plants. 
• 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 
• The amounts of material and energy contained in the biomass of organisms are reduced at each 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. 

• 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 fie and decay. 
• Materials decay because they are broken down by microorganisms. Microorganisms are more active and digest materials faster in warm, mois, aerobic conditions. 
• The decay process releases substances that plants need to grow
• In a stable community, the processess that remove materials are balanced by processes that return materials, The materials are constantly cycled.

• 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 cabron 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 have broken down the wast 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

• The information that results in plants and animals having similar characteristics to their parents is carried by genes which are passed on in the gametes from which offspring develop
• The nucleus of a cell contains chromosomes. Chromosomes carry genes that control the characteristics of the body 
• Different genes control the developement of different characteristics of an organism 
• Differences in the characteristics of different individuals of the same kind may be due to differences in: 
  • the genes they have inherited 
  • the conditions in which they have developed 
  • or a combination of both

• There are two forms of reproduction:
  • sexual reproduction -the fusion of male and female gametes. The mixture of the genetic information from two parents leads to varitey in offspring. 
  • asexual reproduction - no fusion of gametes and onlyone individual is needed as the parent. There is no mixing of genetic information and so no genetic variation in the offspring. These genetically indentical individuals are known as clones. 

• New plants can be produced quickly and cheaply by taking cuttings from older plants. These new plants are genetically identical to the parent plant
• In genetic engineering, genes from the chromosomes of humans and other other organisms can be 'cut out' using enzymes and transferred to cells of other organisms. 
• Genes can also be transferred to the cells of animals, plants or microorganisms at an early stage in their developement 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 GM crops 
  • examples of genetically modified crops include ones that are resistant to insect attack
  • genetically modified crops generally show increased yields
• 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. 

• 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 transplating 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 uterus of an adult female to continue its developement. 

• 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. 
• 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 the Earth
  • there was insufficient evidence at the time the theory was published to convince many scientists 
  • the mechanism of inheritence and variation was not known until 50 years after the theory was published 
• Other theories include Lamarck's which is based 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. 
• Studying the similarities and differences between organisms allows us to classify living organisms into animals, plant and microorganisms, and helps us to understand evolutionary and ecological relationships. Models allow us to suggest relationships between organisms. 
• Where new forms of a gene result from mutation there may be relatively rapid chane in a species if the environment changes. 

• 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.