Core Biology Summary

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B1 - You and Your Genes

  • Genes are codes for making proteins, the building blocks of cells
  • Proteins are structural, e.g. that are parts of skin, or functional, e.g. amylase
  • An organism's genotype refers to the genes it has
  • Characteristics are controlled by genes, the environment, or both
  • Body cells have 23 pairs of chromosomes
  • Sex cells have 23 single chromosomes
  • This is why children resemble both parents, but are not identical to either
  • Inheritance can be shown using genetic diagrams, e.g. Punnett Squares
  • Chromosomes determine your sex - females' 23rd chromosme pairs are **, whilst males' are XY
  • The Y chromosome carries a gene that produces a protein which causes the development of testes and male sex hormones
  • Genetic disorders are caused by faulty alleles which can be dominant (e.g. Huntington's) or recessive (e.g. cystic fibrosis)
  • Embryos, children and adults can be checked for these disorders using genetic testing
  • There are lots of ethical issues surrounding genetic testing
  • Cloning can occur naturally (e.g. plants that produce runners) or artificially (e.g. Dolly the sheep)
  • Clones are genetically identical to each other
  • Stem cells can differentiate and could potentially be used to cure diseases
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B2 - Keeping Healthy - Microbes and Disease

  • Microorganisms cause symptoms by causing cell damage or releasing toxins
  • Bacteria reproduce quickly in the human body because there are warm, moist conditions and sources of nutrients
  • Viruses need cells to reproduce and there are lots of the right kind of cells for this in the body
  • Microorganisms' reproduction can be calculated because they make copies of themselves
  • The immune system fights off invading microbes using white blood cells
  • Some white blood cells engulf and digest foreign microbes whilst others produce antibodies
  • Vaccinations use a dead or inactive version of a dangerous microorganism
  • They work because memory cells are left in the blood after infection to fight off the disease quickly if it infects again
  • Vaccines can never be completely safe due to side effects and genetic differences causing different reactions
  • Antimicrobials can inhibit or kill microbes
  • However, microbes can become resistant to them due to random mutations and natural selection/evolution
  • Therefore, courses of antibiotics should always be finished and only used when really needed
  • New drugs are tested first in laboratories and then on humans
  • There are three types of human trials: blind, double-blind and open-label
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B2 - Keeping Healthy - Our Bodies

  • The heart is a double pump system - the right side pumps deoxygenated blood to the lungs whilst the left pumps oxygenated blood around the body
  • Blood is supplied to the heart by two coronary arteries which branch from the base of the aorta
  • Arteries carry blood away from the heart to the body cells at high pressure and have strong, elastic walls
  • Veins carry blood back to the heart at lower pressure and have thinner walls, bigger lumen and valves
  • Capillaries are tiny branches of arteries that carry blood close to every cell to exchange substances with them - they have permeable walls that are only one cell thick to increase the rate of diffusion
  • Your heart rate is the number of times your heart beats in one minute and is the same as your pulse rate
  • Your blood pressure becomes high when fatty deposits build up arteries, restricting blood flow
  • This can cause blood clots which can completely block arteries
  • If the coronary artery becomes blocked, it can lead to a heart attack as the heart will receive no oxygen
  • Heart disease can be caused by factors such as poor diet, smoking, drugs and drinking alcohol
  • Homeostasis is our bodies maintaining a constant internal environment
  • Negative feedback counteracts changes to achieve this - water content is controlled by negative feedback
  • If water content is too high, less ADH is produced and the kidneys reabsorb less water
  • If water content is too low, more ADH is produced and the kidneys reabsorb more water
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B3 - Life on Earth

  • A species is a group of organisms that can breed together to produce fertile offspring
  • Species adapt to their environments, e.g. cacti are adapted to desert conditions and fish are adapted to aquatic environments
  • Individualsof the same species have differences - there is genetic variation within species
  • Natural selectionis survival of the fittest and causes adaptation and evolution
  • Selective breeding is when humans choose which individuals to breed to gain a specific characterstic
  • Life on Earth began around 3500 million years ago and all organisms evolved from simple, early life forms
  • Therefore evolution can produce new species
  • There is evidence for evolution in fossil records and the similarities of species' DNA
  • Chares Darwin'stheory was better than Lamarck's that accquired characteristics were passed on to offspring
  • Biodiversity is the variation of life on Earth and is important for development of new food crops and medicines
  • The rate of extinction of species is increasing due to direct and indirect harm from humans
  • Classification is the organisation of organisms into groups and shows evolutionary relationships
  • There is interdependence of all living things as they rely on each other for food and resources
  • Energy comes from the Sun and is transferred between organisms in food chains/webs
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B3 - Life on Earth

  • Energy is lost at each stage of a food chain due to waste products and uneaten parts
  • Carbon and nitrogen are constantly recycled in the carbon and nitrogen cycles
  • Environmental change can be measured using non-living indicators, e.g. temperature, nitrate level, CO2 level, or living indicators, e.g. lichen, mayfly nymphs, phytoplankton
  • Sustainability is living in a way which meets the needs of today's population without harming the environment so future generations can meet their needs
  • Maintaining biodiversity is an important part of sustainability
  • Packaging materials can be made more sustainable e.g. by using renewable materials, using less energy, creating less pollution (using biodegradeable materials)
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