GCSE Revision Booklet Biology Unit B1 Influences on life
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Classification, Inheritance and variation Classification Each different organism (living thing) has a unique classification that gives it a binomial (two word) name. E.g. dogs are called Canis familiaris in the binomial system. This system is divided into 7 divisions in a rank order they are: Kingdom → phylum → class → order → family → genus → species So dogs have the following classification: Kingdom – Animalia (Animal) Phylum – Chordata (vertebrate) – these are animals with a spine Class – mammalia (mammal) Order – Carnivora (Carnivores) Family – Canidae Genus – Canis Species – familiaris Use this phrase to help your remember the order Keep Plates Clean Or Family Gets Sick.
The five kingdoms are: Animalia – all animals e.g. jellyfish, worms, chimpanzees Plantae – all green plants e.g. ferns, moss, conifers and roses Fungi – any fungus big or small e.g. moulds, yeast, mushrooms Protoctista – only one cell but, with a nucleus e.g. amoeba & paramecium Prokaryotes – only one cell but with no nucleus e.g. bacteria & blue-green algae Scientists do not classify a virus as a living thing because they do not show all seven processes for life.
The five chordate (vertebrate) groups are: Fish – gills, fins, wet scales, external fertilisation Amphibian – smooth skin, lungs or gills, external fertilsiation Reptile – dry scaly skin, eggs with hard shells, internal fertilisation Bird – wings, feathers, eggs with hard shells, internal fertilisation Mammal – hair/fur on body, give birth to live young, feed young on milk, internal fertilisation A Species is a group of similar organisms that can interbreed and produce fertile offspring. A Hybrid is the infertile offspring that occurs, when two different species breed/reproduce.
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Evolution Charles Darwin (1809 – 1882) proposed the theory of evolution that scientists accept today. Evolution is the slow, continual change of organisms over a very long time. All living things on the Earth have developed from the first simple life forms that arrived 3,000,000,000 years ago.
One of the effects of evolution is that species will become better adapted to their environment. If these species don’t adapt they may become extinct due to being unable to deal with any of these factors: 1) increased competition, 2) changes in the environment, 3) new diseases, 4) new predators My key observations: • variation – in any population of organisms there will be some differences • over-production – many organisms produce more offspring than survive to adulthood • struggle for existence – there is competition of survival and resources between the organisms. • survival – those with helpful characteristics are more likely to survive to breed • useful characteristics – inherited by the offspring • gradual change – of the species over a period of time as useful characteristics are passed to offspring. Darwin’s theory of Natural Selection 1) Each species shows variation:
3) The “better adapted” members of these species, are more likely to survive – “Survival of the Fittest” and reproduce.
2) There is competition within each species for food, living space, water, mates etc.
4) These survivors will pass on their better genes to their offspring who will also show this beneficial variation.
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Evidence for Darwins theory Fossil records – despite some gaps show how much (or how little) different organisms have changed since life developed on Earth. Antibiotic-resistant bacteria – bacteria reproduce rapidly and can evolve in a short time, if the mutation (such as antibiotic resistance) is an advantage, they are more likely to survive and evolve further. DNA – Scientists can now examine the DNA of different species and see how closely related they are to each other, e.g. Chimpanzees and humans share 96% of our DNA Adaptation Every organism has certain features that allow it to survive in its habitat – so the organism is adapted to its habitat, organisms living in different environments will have different adaptations. You need to be able to explain how organisms are adapted to survive in different habitat extremes. You give the feature and then explain how it helps. Artic or Antartic Environment Animals Thick layer of fat and fur- insulation against the cold Small surface area to volume ratio – to minimise heat loss A greasy coat, which sheds water after swimming. White fur – to camouflage. Large feet to prevent sinking in the ground
Plants Grow close to the ground – stop it being blown by the wind Have very small leaves – prevent water loss
Deep Sea Hydrothermal Vents Thick layer of bacteria – to protect it from predators. Makes a paper like tube – to hide it from predators
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Variation Variation means “differences” within a species” Some of this variation is due to our parents “inherited variation”, but some of it is due to our upbringing and the environment in which we live “Environmental variation” Inheritance Only
Environmental Only
Blood Group Natural Eye colour Natural Hair Colour
Scars Injuries
Both Inherited and Environmental Height Weight
Some features in organisms show either continuous or discontinuous variation. Continuous variation Is a characteristic in any species that changes gradually over a range of values. Examples include: height, weight, foot length etc So height ranges from the smallest person in the world to the largest person and all the possible values in between. A graph showing continuous variation will look like this (it is known as a bell shaped curve or normal distribution) if you have data from a large sample size.
Discontinuous variation A characteristic of any species with only a limited number of possible values. Examples include: gender, blood group, eye colour So human blood only has four possible values A, B, AB, or O) A discontinuous graph looks like the one below, it will not form a bell shape.
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Inheritance All cells in the body (except the red blood cells) contain a nucleus which controls the cell. Chromosome
The nucleus contains chromosomes
Chromosomes are made from long DNA molecules
gene A gene is a short section of DNA
Every persons DNA is unique (except for identical twins), this is why DNA can be used to identify people. Alleles Different forms of the same gene are called alleles and they can be dominant or recessive • the characteristics controlled by a dominant allele develops if the allele is present on one or both chromosomes in a pair • the characteristic controlled by a recessive allele develops only if the allele is present on both chromosomes in a pair e.g. the genes controlling the hairline growth on a human forehead has a recessive allele for a straight hairline and a dominant allele for a widows peak hairline. In genetic diagrams a dominant allele will always be shown by a capital letter, while the recessive allele is shown as a lower-case letter. So if the genotype is WW or Ww the person will have a widows peak hairline, but if the genotype is ww the person has a straight hairline. However the Ww genotype displays a widows peak hairline, but they are carrying the allele for a straight hairline.
WW
W
Ww
ww
W
Ww
w
w
Ww
Ww
Note: WW is described as being homozygous for the dominant allele ww is described as being homozygous for the recessive allele Ww is described as being heterozygous
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Cystic fibrosis Cystic fibrosis (Cf) is caused by a recessive allele. People with CF produce abnormally thick sticky mucus in their lungs and airways, so sufferers are more likely to get respiratory diseases. If a child has CF then both parents must either have CF or be carriers of the CF allele Mother
father
F f
F FF Ff
f Ff ff
. Mother
father
F f
F FF Ff
F FF Ff
Sicke cell disease Sickle cell disease is another recessive conditions so the genetic crosses for it will be similar to the ones above for Cystic fibrosis. In Sickle cell anemia the red blood cells become misshapen and can stick together which can block blood vessels. Sickle cell disease sufferers can become very tired and quickly get out of breath. If the sickle cells block a blood vessel, this can be fatal.
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Responses to a changing environment Homeostasis Homeostasis means “controlling internal conditions” using the nervous system and hormones.
Waste products that need to be removed + how CO2
Produced by respiration, removed via lungs Produced by liver breaking down amino acids, removed by kidneys and transferred to bladder
Urea
Internal conditions that need controlling + how Temperature Ion content Water content Blood Glucose
Increased by shivering, lost by sweating Increased by eating, lost by sweating + urine Increased by drinking, lost by sweating + urine Increased and decreased by hormones
Controlling water content (Osmoregulation) Water loss is controlled by water loss from • the lungs, when we exhale (breathe out) • the skin by sweating • the body, in urine produced by the kidneys Osmoreceptors in pituitary
Less ADH is released In the kidneys
Water Increases
Normal Water Level
Water Increases
Water Decreases
ADH is released In the kidneys
Osmoreceptors in pituitary
Controlling the Ions (salts) in the body This is controlled to protect cells by avoiding too much water entering or leaving them. Ion content is controlled by loss of ions from: • the skin by sweating • the body, in urine produced by the kidneys
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Controlling body temperature (Thermoregulation) Human enzymes usually work best at 37°C, this is our core body temperature. High temperatures can cause dehydration, heat stroke and death if untreated Low temperatures can cause hypothermia and death if untreated. The brain monitors the body’s temperature, if you are too hot or too cold it sends nerve impulses to the skin. Hairs on the skin are controlled by the erector muscle, when it contracts the hairs stand end (goosepimples) trapping warm air near the skin, if it is too hot the erector muscle relaxes so the hair can lie flat.
Sweating cools you down. When you are too hot, sweat is secreted onto the surface of hot skin by glands underneath the skin. The sweat evaporates using the heat energy from your body, which takes the heat away from the skin and cools you down. Blood vessels near the surface of the skin can swell (vasodilation) which cause more blood to be passed to the surface of the skin and the heat is radiated away, or they can get smaller (vasoconstriction) this prevents heat loss as less blood goes to the surface of the skin so less heat gets radiated out.
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Hormones Glands in the hypothalmus section of the brain Thyroid gland
Adrenal glands Pancreas Ovaries (in females)
Testes (in males)
Gland Ovary Ovary Pancreas Testes
Hormone Oestrogen Progesterone Insulin & Glucogon Testosterone Insulin released by the pancreas
Target organs Overies, uterus Uterus Liver Male reproductive organs Liver converts Glucose to glycogen
Glucose Increases
Glucose Decreases
Normal Blood Glucose Level Glucose Increases
Glucose Decreases Liver converts Glycogen to glucose
Glucogon released by the pancreas
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Diabetes Diabetes is a disorder in which the blood glucose levels can be too high, there are three main types of diabetes: Type 1 diabetes is caused by a lack of insulin due to either a genetic disorder or as a side effect of a viral infection. The diabetes is controlled by monitoring the diet Injecting insulin People with type 1 diabetes have to monitor their blood sugar levels throughout the day as the level of their activity and diet changes, which will affect the amount of insulin the will need to take in. Type 2 diabetes is caused by a person becoming resistant to insulin due to them being very overweight. It can be controlled by diet and exercise. The number of people who suffer from type 2 diabetes is rising due to increasing obesity. A person in considered obese if they have a body mass index (BMI) of over 30, if they have a BMI of 20 or under they are considered to be underweight. The formula for BMI is:
weight in kilorams (kg) height in metres2 (m2)
It is important to remember that the BMI calculation is just a guide and it has many flaws, people who have good muscle tone and who are not particularly tall may have a BMI of over 30 despite having a very healthy lifestyle. Plant hormones A ‘tropism’ is a growth in response to a stimulus. Auxin is a plant hormone that is made in the stem tips and roots, which controls the direction of growth. Plant hormones are used in weedkillers, rooting powder and to control fruit ripening. Response Part of plant Direction of growth Advantage Positive Stem tip Growth towards light To get maximum light phototropism for photosynthesis Negative Root tip Growth away from light Less chance of drying phototropism out Positive Root tip Towards gravity More chance of finding geotropism moisture Negative Stem tip Away from gravity More chance of finding geotropism light. Controlling the direction of growth A plant grows towards the light because light destroys the auxin in that side of the stem, so growth on that side of the plant slows down. On the shaded side the plant has more auxin, so growth on that side speeds up. This results in the plant bending towards the light to maximise photosynthesis.
A = The tips have been cut off removing the auxin, so phototropism can’t happen. B = The tinfoil caps stop the light destroying the auxin, so it remains evenly distributed and the shoots grow straight up. C = The light destroys the auxin on the that side of the plant, so more auxin is on the shaded side causing the cells to elongate, so the shoot bends towards the light. 11
The nervous system Receptors and effectors Receptors are groups of specialised cells that detect stimuli and turn them into electrical impulses. A lot of receptors in humans are found in the sense organs. The Central Nervous system (CNS) in humans is made up of the brain and spinal cord.
Effectors An effector is any part of the body the produces a response: • muscles contracting or relaxing • glands releasing a hormone. Table showing examples of reactions Stimulus Receptor Bright light Eye Sour taste Tongue Losing balance Fluid in the ear Sitting on a drawing pin Skin
Effector Iris muscle contracting Muscles in the mouth Muscles in the body Muscles in the legs
Response Pupil gets smaller Spittiing out the food Steadying the body Jumping out of the seat.
Neurones (Nerve cells) The three different neurones are: Sensory neurones carry signals from receptors to the CNS. Relay neurones carry messages from one part of the CNS to another. Motor neurones carry signals from CNS to effectors. Dendrite Axon
Nerve ending
Cytoplasm Myelin sheath Cell membrane Nucleus
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A neuron is a specialised cell that typically has tiny branches called dendrons at each end and a long fibre called the axon carrying the signals. The axon is surrounded by a fatty layer to protect it known as a myelin sheath, it also allows the impulses to travel faster. Synapses The tiny gap between the neurones is called a synapse. The gap is bridged using chemicals that diffuse across it so that the next neurone can transmit the signal.
Reflex Actions There are two main types of action conscious actions and reflex actions. In a conscious action the brain makes a considered response e.g. when a dog licks your hand you respond by moving your hand away Stimulus → Receptor → Sensory neurone → Coordinator → Motor neurone → Effector →Response
Sometimes a conscious action is too slow e.g. when you touch a drawing pin. In a reflex action the body bypasses the brain (the reflex arc) to produce a quicker response, in this case quickly moving your hand away. Stimulus → Receptor → Sensory neurone → Relay neurone → Motor neurone → Effector →Response
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Another example of a reflex action is our eye responding to bright or dim light. In bright light In dim light Radial muscles of the iris relax. Radial muscles of the iris contract. Circular muscles of the iris contract. Circular muscles of the iris relax. The pupil contracts so less light enters the eye. The pupil dilates so more light enters the eye
Problems and solutions in the environment Drugs Drugs can affect nerve impulses, reaction times and behaviour. A Stimulant is a drug that temporarily quickens a process in the body by speeding up the transmission of signals from on nerve cell to another. Examples include caffeine, cannabis and amphetamines. A depressant or sedative is a drug that lowers the rate of vital physiological activities, they can also reduces excitability and calm a person. They do this by slowing down the nervous system and reactions. 14
Examples include alcohol and barbiturates. A painkiller (analgesics) is a drug that blocks nerve impulses travelling to the part of the brain the perceives (recognises) pain. Examples include paracetamol, aspirin and codeine. An hallucinogen is a drug that causes a person to have hallucinations, changing the way the brain works distorting the senses. This changes the response to what we see, feel and hear. Examples include LSD, angel dust and magic mushrooms Recreational drugs Tobacco Cigarettes contain about 4,000 different chemicals most of them are harmful to the body Nicotine is an addictive drug that raises the heart beat, narrowin the arteries and so causing high blood pressure. This leads to heart disease. Tar which coats the lining of the lungs making them less able to take in oxygen. It also contains carcinogens (cancer causing chemicals). Caron monoxide which is a poisonous gas prevents the red blood cells from picking up oxygen. This puts an extra strain on the circulatory system and increases the risk of heart disease and strokes.
Non-smokers lung
Smoker’s lung
Note: There have been lots of studies and data collected about the effects of smoking. You may be expected to interpret graphs on smoking in your exam. These questions are ones where it is easy to get a few marks as long as you read the question carefully and take your time with any calculations.
Alcohol Ethanol is the name of the active ingredient in alcoholic drinks. It is quickly absorbed into the bloodstream where it starts to have an effect on the Central Nervous System (CNS). Short-term effects include sleepiness, impaired judgment, balance and muscle control. This leads to blurred vision, slurred speech and vasodilation. Long-term effects include liver damage (cirrhosis) and brain damage. The liver removes alcohol (like other toxic chemicals) from the bloodstream, however if a person consumes high volumes of alcohol, the liver cannot recover properly and then gets damaged. Transplants 15 Â Â
An organ that has been damaged can be replaced by a healthy organ from a donor – someone who had healthy organs but very recently died from other causes. A successful transplant has to have: • similar tissues from donor to patient • similar ages of donor and patient • similar locations as organs deteriorate quickly Organ donation can be an ethical issue especially as the supply of organs is limited. An ethical issue is one that has rights and wrongs. In an exam you will be expected to discuss the ethical issues involved in: • • •
liver transplants for alcoholics heart transplants for the clinically obese. parts of animals (usually pigs) being used for medical treatments.
Infectious disease Pathogens are microorganisms (microbes for short) that transmit infectious diseases either by direct contact (when bodies touch in some way) or indirect contact (carried to the person in some way e.g. mosquito carrying malaria).
• • • • •
Bacteria 1/1000 mm big Living cells (some are harmless) Affected by antibiotics Grow very quickly Examples: food poisoning, tetanus, sore throats th
• • • • •
Viruses 1/1,000,000th big Genetic info inside a protein coat Not affected by antibiotics Release poisons Examples: colds, flu, polio, chicken pox
Cell
Soft cell
,membrane
wall
Fungi • Varies wildly from microscopic to visible to the naked eye • Examples: penicillium, yeast, bread mould
Genetic head
Cell
material
nucleus
membrane
Protein tail cytoplasm
chromosome
coat Cytoplasm
vacuoles
Food storage granule
Soft cell wall
Body defences The first line of defence is the body’s natural barriers:
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Tears, saliva & mucus contain an enzyme called lysozyme that destroys microbes. nasal hairs, mucus and cilia – hairs keep out dust and larger microbes; mucus traps dust and microbes, which are then carried away by the cilia.
skin – dry dead cells difficult to penetrate and it produces oils that kill microbes, scabs form over cuts to prevent microbes entering.
The stomach contains hydrochloric acid, which destroys microbes
Plant defences Some plants produce antibacterial chemicals to help defend themselves against microbes, some of these chemicals are now used by humans. E.g. Mint and Witch Hazel are both used to prevent infection. Antibiotics Antibiotics are drugs that can destroy or prevent the growth of bacteria, they have no effect against viruses e.g. penicillin Alexander Fleming discovered penicillin by accident when he found some mould growing in a discarded petri dish. The mould was actually penicillin and it had prevented the growth of bacteria in the dish. Antifungal An antifungal is an agent that kills fungi, e.g. nyastatin treats candida albicans Antiseptic A chemical that kills microbes outside the body are known as antiseptics. e.g. dettol
Interdependence 17
Food chains shows the direction of energy flow in a particular habitat, they always start with the producers, which are usually green plants that convert the sun’s energy into food. The other organisms in the food chain are consumer. A lot of energy is lost at each stage in the chain because: • Energy is released by respiration is used for movement and other life processes, and is eventually lost as heat to the surroundings. • Energy is lost in waste materials, such as faeces. Pyramids of biomass A pyramid of biomass is a chart that is drawn to scale to showing the mass of living material at each stage in a food chain. It gives a visual representation showing how much energy is lost at each stage of the food chain. Parasitism A parasite is an organism that lives on or in a host organism, the parasite benefits and can survive better but the host is damaged by the parasite. • A tapeworm lives in the gut and gains nutrition by absorbing its food, however the host loses nutrition and may suffer from vomiting and diarrhoea. • Headlice bite the host and feed off their blood. • Mistletoe is a parasitic plant, it’s roots grow into the veins of the host tree to absorb nutrient and minerals.
Mutualism Some organisms rely on the presence of a different species, both organisms benefit. • Oxpecker birds eat the ticks and larvae that infest on the skin of buffalo. • Sea anemones give protection to the hermit carb using its stinging cells, while the hermit crab allows the sea anemone to take in the remains of it’s food. • Plants provide ants with nectar while the ant helps to keep away other insects from eating its leaves.
Pollution 18
Human beings compete with other living things for resources and space, this competition has led to the pollution of the environment. • Non-renewable energy resources, such as coal, oil, and natural gas, are being used up rapidly. • Raw materials are being used up rapidly. • More waste is being produced. • More pollution is being caused. Air pollution Smog – is a mixture of air pollutants and particulates, at high levels it can cause irritation to the eyes and lungs. Ozone – is formed when nitrogen oxides and hydrocarbons react with oxygen. Lichens are good indicators of air pollution because bushy lichens are an indicator of really clean air, leafy lichens suggest that there is a small amount of pollution present. Blackspot fungus – is Water pollution Acid Rain – is formed when the sulphur and nitrogen chemicals in car exhausts or factories react with the water vapour in clouds to make acid rain. Pesticides used to kill weeds A high precence of: Bloodworm and sludgeworm are an indicator of polluted water Stonefly and fresh water shrimp are an indicatior fo clean awrer. Eutrophication Fertilisers and sewage can easily be washed into rivers, streams and lakes.
Sustainable Development 19
Sustainable development is all about preserving the world for tomorrow. Examples include • Recycling waste – glass, metal, paper and plastic • Replanting trees after chopping them down. • Limiting the number of fish allowed in a catch. • Protecting endangered species. The Carbon Cycle All cells whether animal, plant or bacteria contain carbon because they all contain proteins, fats and carbohydrates. Carbon is passed from the atmosphere, as carbon dioxide, to living things passed from one organism to the next in different compound, and then returned to the atmosphere as carbon dioxide again.
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