AQA GCSE Core Biology

• A healthy diet contains the right balance of the different foods you need and the right amount of energy
• A person is malnourished if their diet is not balanced
• An unbalanced diet may also lead to deficiency diseases or conditions such as Type 2 diabetes
• A person loses mass when the energy content of the food taken in is less than the amount of energy expended by the body
• Metabolic rate = rate at which all the chemical reactions in the cells of the body are carried out and is affected by inherited factors and physical activity
• Inherited factors also affect our health; for example cholesterol level

• Microorganisms that cause infectious disease are called pathogens
• Bacteria and viruses produce toxins which make us feel ill
• White blood cells help to defend against pathogens by: producting antitioxins, ingesting pathogens and producing antibodies
• If a large proportion of the population is immune to a pathogen, the spread of the pathogen is very much reduced
• Antibiotics cannot be used to kill viral pathogens, which live and reproduce inside cells (so cannot be accessed)
• Antibiotics are not used to treat non-serious infections, such as mild throat infections, so that the rate of development of resistant strains is slowed down
• People can be immunised against a disease by introducing small quantities of dead or inactive forms of the pathogen into the body (vaccination) - WBC are stimulated to produce antibodies

• Cells called receptors detect stimuli (changes in the environment) eg. eyes - light, ears - sound and position
• In a simple reflex action:    
•       Stimulus - Receptor - Sensory neurone - Spinal cord (CNS) - Relay neurone - Motor     neurone - Efecctor - Response
• The effector is either a muscle or a gland, a muscle responds by contracting and a gland responds by releasing (secreting) chemical substances.

• Internal conditions in the body are controlled:
• The 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.
• Hormones are secreted by glands and are usually transported to their target organs by the bloodstream.

• 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.
• Auxin controls phototropism and gravitropism (geotropism).
• Plant growth hormones are used in agriculture and horticulture as weed killers and as rooting hormone
• Auxin goes towards the dark side of a plant and stimulates growth in this area, causing it to bend.

• Drugs change the chemical processes in peoples' bodies so that they may become dependent or addicted
• New drugs are tested for toxicity, efficacy and dose
• Clinical trials - low to high dosage (if successfull) and placebo
• 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 however some babies were born with limb abnormalities
• More recently, thalidomide has been used successfully in the treatment of leprosy
• 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.

• Plants compete for light, space, water and nutrients
• Animals compete for food, mates and territory
• Animals may be adapted for survival in dry and arctic environments by means of: changes to surface area (of skin), thickness of insultating coat (fur), amount of body fat, camouflage
• Plants may be adapted to survive in dry environments by means of: changes to surface area (of leaves), water storage tissues, root systems

• Changes in the environment affect the distribution of living organisms
• Lichens can be used as air pollution indicators, particularly of the concentration of sulfur dioxide in the atmosphere (less lichens = more pollution)
• invertebrate animals can be used as water pollution indicators and are used as indicators of the concentration of dissolved oxygen in water.

• Photosynthesis converts light energy to chemical energy
• The amounts of material and energy contained in the biomass of organisms is reduced at each successive stage in a food chain because: some materials and energy are always lost in the organisms' waste materials
• Some energy is lost through processes such as respiration and movement

• Materials decay because they are broken down (digested) by microorganisms
• Microorganisms are more active and digest materials faster in warm, moist, aerobic conditions
• The decay process releases substances that plants need to grow

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 back 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.

• Asexual reproduction can be used to produce individuals that are genetically identical to their parent.
• Variation within the same species can be due to inherited factors (alleles) and environmental factors
• Environmental factors that affect variation include: climate, diet and lifestyle
• The nucleus of a cell contains chromosomes. Chromosomes carry genes that control the characteristics of the body

• Cloning techniques include:
• Tissue culture (plant cuttings) – 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.
• New genes can be transferred to crop plants
• 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

• Darwin proposed the theory of natural selection
• 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
• Lamrack proposed that an organism can pass on characteristics acquired during its life time