GCSE AQA Biology B1

 1.1 - 1.5

• A balenced diet keeps someone healthy-without it, someone is malnourised. Too much food can lead to someone becoming overweight, and too little food can lead to someone becoming underweight.
• Meatabolic rate-rate of chemical reactions in cells, affected by daily activity, genes, gender, age.
• Cholesterol-good: HDL. Bad: LDL. HDL cholesterol used for cell membranes and vital substances.
• High LDL levels can lead to heart disease, type 2 diabetes, cardiac arrest.
• Pathogens are microbes-bacteria or virus.
• Pathogens can produce toxins to make you feel ill, though it is rarely done by viruses-they usually invade cells, damaging them.
• A doctor called Semmelweiss realised that infection could be transferred by direct contact, telling his staff to wash their hands between dissecting a dead body and helping women give birth.
• The skin helps stop pathogens entering the body.
• Pathogens are also trapped by mucus and killed by stomach acid.
• White blood cells-they can ingest pathogens. They can produce antibodies to help destroy pathogens. They can produce antitoxins to counteract the toxins that pathogens produce.

1.6 - 1.10

• Antibitocis can kill infective bacteria, such as penicillin, first discovered by Aexander Felming in 1928.
• Viruses are difficult to kill because they reproduce inside body cells, so treatment could damage those cells-immune system usually overcomes it.
• Painkillers and other drugs can relieve symptons but don't kill the pathogen.
• Cultures of bacteria can be investigated. You sterilise the inoculating loop through a flame, then dip in culture then drag it in a zig-zag line across the agar in the petri dish. Seal the dish with tape but not all the way around so oxygen can enter. Sterilise the loop again.
• MRSA-a 'super bug' bacterium that has become resistant to many antibiotics through natural selection by mutating, sometimes due to overuse of antibiotic.
• Vaccines have a dead or inactive form of a virus. WBCs produce antibodies. This is so real infection would mean fast production of the anitbody for the virus-antibodies recognise the antigen (protein shape) of pathogen.
• MMR vaccine-Measles, mumps, rubella.
• Most need to be vaccinated to protect society from serious diseases, like measles, which can cause deafness and death.

2.1 - 2.4

• Receptors detect stimuli. Receptors are in the eye, ear, nose, tongue & skin.
• Light stimulates receptors in eye so electrical impulses pass to the brain along neurons.Stimule include: sounds, chemicals, temperature, touch, pain.
• Brain + spinal cord= CNS.
• Sensory neurons- recpetors to CNS.
• Motor- CNS to effector organ (muscle/gland).
• Reflex- 1. Receptor detects stimulus. 2. Sensory to CNS. 3. Relay passes on. 4. Motor neuron stimulated, passes to effector. 5. Action is taken. Does not go to the brain, so it's quicker.
• Synapse- Gap between 2 neurones-chemicals transmit impulse across.
• Mentrual cycle: 1. FSH-made by pituitary gland, matures an egg, oestrogen production.                  2. Oestrogen-made by ovaries, inhibits FSH production, causes womb lining, LH production.
  3. LH- made by pituitary gland, gets matured egg to be released-ovulation.
• Contraceptive-have oestrogen or progesterone. Progesterone-only pills: fewer side effects. Prevent production of FSH-no eggs mature
• Contraceptives-plan preganancies, reduce family size, but can have side effects, is unethical, against religion.
• IVF- FSH and LH injections. Eggs collected from woman, fertilised with man and become an embryo-transplanted into woman. Helps infertile couples. However, expensive and not always successful.

2.5 - 7

• Internal conditions controlled-water & ion content, temperature, blood sugar level.
• Water leaves when we breathe & sweat. Excess lost in urine, by kidneys. Ions also lost in sweat & kidneys.
• Temperature must be constant for enzymes to work. Blood sugar-energy source for cells, controlled by pancreas.
• Plants-phototropism, gravitropism.
• Auxin-plant growth hormone controlling phototropism and gravitropism.
• Unequal distribution of auxin=unequal growth-bends the root or shoot.
• Gravitropism- auxin gathers on lower side of shoot, so in the shoot there is more growth on the auxin side of shoot, making it bend upwards, opposite the force of gravity. In roots, the side with the least auxin grows more to make it bend downwards towards the force of gravity.
• Phototropism- side of shoot furthest away from light has more auxin. Side with most auxin frows more, making the shoot bend towrds the light.
• Plant growth hormones can be used as weed killer and to stimulate root growth.
• Using hormones in women- can be used to prevent unwanted preganancies, helps to plan them, but can have side effects of headaches and high blood pressure.
• Using hormones in plants- can encourage root growth, encourage fruit to ripen, but if used incorrectly can damage the environment-weedkillers could harm other plants.

3.1 - 3.6

• Medicines are tested to check for safety, side effects and effectiveness.
• Firstly, tested on cells & tissues or organs-testing for safety.
• Then on animals-informations on doses and side effects.
• Healthy human volunteers-very low doses to check for side effects.
• Patients-checks for effectiveness. Afterwards, bigger trials are given to find the best dose.
• Double-blind trials-placebo-doesn't contain drug that is being tested. Neither doctor nor patients know who has got the real drug or placebo.
• Statins-lower LDL levels-given to older people to take daily.
• Some prefer to take non-prescribed drugs.
• Drugs- a substance that alters chemical reactions in a body. You get addicted easily because it affetcs your nervous system and suffer withdrawal symptons if someone stops taking it. Some are recreational and illegal, prescribed, or legal and recreational.
• Cannabis-can cause mental illness, depression, brings people in contact with harder drugs, but not all cannabis users go on to use hard drugs. However, nearlt all heroin users used to use cannabis.
• Steroids-build up muscle mass for sport. Other drugs could be for stamina, or pain killers to ignore an injury. Could be seen as unethical.
• Most performance enhancing drugs-expensive-unfair for those who can't afford. Can damage body.

4.1- 4.5

• Plants need- light, CO2, water, O2, nutrients .
• Animals- food, water, O2.
• Features of organisms that help with survival=adaptations.
• Most organisms live in temperature below 40 degrees C so enzymes work.
• Extremophiles-microorganisms, adapted to live in conditions where enzymes don't usually work, they would denature.
• Animals-in cold climated, thick fur & fat keeps them warm. Colours of animals help with camouflage. Small SA:V ratio - conserve energy more easily, but harder to cool down. Might feed at night in a hot climate to conserve water & not get too hot.
• Plants- leaves have holes called stomata where water vapour can be lost through, so some leaves are wrapped up into needles, or covered in wax to stop it. Swollen stem can store water. Might have extensive root systems. Some have thorns, poisonous chemicals & warnng colours to put animals off.
• Competition- animals- compete for food, water, space, mates. Predators compete with prey. Predators can compete for prey, prey can compete to run away.
• Competition- plants- compete for water, nutrients & light. Some plants might flower before others do, to get enough of what they need. Deep roots can reach underground water better. Dispersion processes are to avoid competing with themselves, like water, explosions, wind, using animals.

4.6 - 4.8

• Some unusual adaptations help organisms become successful competitors.
• Venus fly traps-eat insects, use sweet, sticky nectar and bright red colours to attract insects.
• Non-living- Measuring temperature, rainfall, light and oxygen levels can measure environmental change, using rain gauges, thermometers, oxygen meters, data loggers.
• Living- Lichens indicate air pollutions, are sensitive to sulphur dioxide. More species of lichen, cleaner the air. Freshwater invertebrates indicate levels of water pollution-concentration of dissolved oxygen in the water. The wider the range of those, the cleaner the water. However, some only live in polluted water.
• Changes in environment can affect distribution of organisms, so birds might fly further North if it is too warm, but others might have competitiors.

5.1 - 5.5

• Biomass- mass of living material in organisma.
• Pyramid- represents amount of biomass at each stage of a food chain.
• Biomass decreases as it gets further through food chain-lost throught respiration, waste material. Also, not all the food is eaten. Energy lost through waste, movement, maintaining temperature.
• Detritus feeders like worms, can start decay process by eating dead animals/plants and making waste materials, then break down the waste/dead plants & animals.
• Decomposers- bacteria and fungi. If it is more warm and wet, decay is faster. Many decomposers need oxygen too.
• Materials from waster & dead organisms are recycled, returning nutrients to the soil.
• Material from waste/dead organisms can go through sedimentation and become a fossil fuel which can be burnt in a few million years time.
• Photosynthesis can take CO2 from the atmosphere. Detritus feeders respire and release some of the CO2 they have taken in from breaking down dead/waste material back to the atmosphere.
• Humans can put organic waste in compost bins, and add worms, as well as having holes in the bin to allow air in and heat out, as well as layers of soil to speed it up.

6.1 - 5

• A nucleus of a cell has thread-like structures called chromosomes, which carry genes. In gametes-sex cells (sperm and egg)- there is only a single set of chromosomes.
• Offspring get one set of chromosomes from mother, other set from father.
• Asexual- no fusion of gametes. All genetic information is from one parent- little variety.
• Sexual- fusion of gametes. Mixing of genetic information, so offspring show variation.
• Genes are most important in controlling the appearance of an individual.
• Cloning-plant cloning can be cheap and effective. Cuttings can be taken and then grown. Taking cells from a plant and growing them under special conditions- tissue culture- is more expensive.
• Cloning-emrbyo transplants- an embryo with unspecialised cells-split into smaller groups of cells. Each group is transplanted into a host animal.
• Sometimes plants/animals are genetically modified to produce useful substances before cloning.
• Adult cell cloning- 1. a skin cell taken from animal A, only nucleus is kept. 2. an egg cell is taken from B, and the nucleus of that is discarded. 3. Empy egg shell from B and nucleus from A is joined, to become a fertilised egg with a full set of chromosomes. 4. Electric shock is given so it divides and becomes an embryo. 5. inserted into the womb of a host mother.
• Dolly the sheep-product of adult cell cloning in 1997

6.6-6.7

• Genetic engineering-involves changing the genetic makeup of an organism.
• A gene is 'cut out' of the chromosome using an enzyme. It is then put in the chromosome of another organism.
• Can put genes in different species, like bacterium- gene for insulin put in bacteria, bacteria produces lots of it to treat diabetes.
• Advantages:
  -Cloning cattle can produce herds with useful characteristics.
  -Adult cell cloning used to make copies of the best animals.
  -If a person has a faulty gene, they could have a genetic disorder that could be cured with genetic engineering.
  -Insect/herbicide resistance.
• Disadvantages:
  -GM crops-bigger yield, but new GM seed needs to be bought each year-crops are infertile.
  -Genes could be accidently introduced into wild flower populations.
  -Ethical? Long term effects on eating it?
  -Insects that aren't pests could be affected by GM crops.

7.1 - 7.4

• Darwin-theory of natural selection- organisms came from simple life forms, but a useful characteristic helped the organism survive and breed to pass the characteristic on to offspring. Evolution happened over a very long time. Now we know it is a chance mutation in the genes that causes this.
• Lamarck- the inheritance of acquired characteristics- developing a characteristic like a stretched neck would be passed on to offspring-not true because it does not change genes.
• People didn't like challenging of the theory that God created everything, and that they came from simple life forms. No one knew about genes back then, so Darwin couldn't explain it. His theory came from studying finches on the Galapagos Islands.
• Natural classification system- organisms put in groups according to similarities- easiest systems are the kingdoms.
• Evolutionary trees-tell us relationships between species, finding out common ancestors.
• However, it is hard to find fossil evidence-tissues are never found, because they decompose.