Year 10 biology

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The nervous system

Sense organs detect stimuli-

.Stimulus= a change in your environment that you need to reat to

.Eyes,ears,nose,tongue and skin are sense organs and contain different receptors

.Receptors are groups of cells that detect stimuli

.Receptors change stimuli into electrical impulses

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The five sense organs


.Light receptors - detect light. The cells have a nucleus,cytoplasm and cell membrane


.Sound receptors - detects sounds. Also, balance receptors detect changes in position


.Smell receptors - detect chemical stimuli


.Taste receptors - detect chemical stimuli


.Receptors that detect touch,pressure,pain and temperature change

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Sensory neurones-

.The nerve cells that carry signals from the receptors to the central nervous system

Relay neurones-

.The nerve cells that carry signals from sensory neurones to motor neurones

Motor neurones-

.The nerve cells that carry signals from the central nervous system to the effector muscles or glands


.Muscles contract and glands secrete hormones

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.CNS is where all the information from the sense organs is sent, and where responses are coordinated

.CNS is made up of the brain and the spinal cord

.Neurones (nerve cells) transmit the information as electrical impulses

.These impulses travel very quickly to and from the CNS

.Instructions from the CNS are sent to the effectors (muscles and glands) which then respond

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Synapes and Reflexes

Synapses connect neurones-

.The conection (gap) between two neurones is called a synapse

.The nerve signal is taken across the gap by chemicals

.These chemicals set off a new electrical signal in the next neurone

Reflexes help prevent injury-

.Reflexes are automatic responses to certain stimuli - they just happen

.Reflexes are much quicker than normal responses because you dont have to think about them

.They help to stop you injuring yourself,e.g. bright light makes your pupils smaller to prevent eye damage

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How reflexes work

.A sharp object hits your hand

.Impulses are sent along a sensory neurone to the CNS

.Impulses reach a synapse between the sensory neurone and a relay neurone. Here the chemicals are released, causing impulses to be sent along the relay neurone

.Impulses reach a synapse between the relay neurone and a motor neurone.Chemicals are released,which cause impulses to be sent along the motor neurone

.Impulses are sent along the motor neurone to the effector.Here its a muscle, which contracts to move your hand away from the sharp object

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Hormones are chemical messengers sent in the blood-

.Hormones are chemicals released directly into the blood

.They're carried in the blood to other parts of the body

.Hormones only affect particular cells in particular places - target cells

Where are hormones produced?-

.The pituitary gland - This produces many important hormones including FSH and LH. They're involved in the menstral cycle

.Ovaries - Produce oestrogen, which is involved in the menstral cycle

Nerves vs. Hormones-

.Nerves - very fast action, act for a very short time and act on a very precise area

.Hormones - slower action, act for a long time and act in a more general way

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The menstral cycle (stages)

Stages of the mentral cycle-

Stage 1 (day 1 to 4) -

.Lining of the uterus breaks down and bleeding starts

Stage 2 (day 4 to 14) -

.Lining of the uterus builds up,ready for a fertilised egg

Stage 3 (day 14) -

.Egg is released

Stage 4 (day 21 to 28) -

.Lining of the uterus is maintained

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Hormones controlling the different stages

FSH (Follicle-stimulating Hormone)-

.Produced by the pituitary gland

.Causes an egg to mature in one of the ovaries

.Causes ovaries to produce oestrogen


.Produced in the ovaries

.Inhibits FSH (stops more FSH being released)

LH (Luteinising Hormone)-

.Causes the release of an egg from the ovaries

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Reducing fertility

Hormones can be used to reduce fertility-

.Oestrogen reduces fertiltiy becuase it inhibits FSH, so no eggs can mature

.The pill is an oral contraceptive (a birth-control pill that you swallow)

.The first version of the pill contained high levels of oestrogen and progesterone

.But there were concerns about a link between oestrogen in the pill and side effects like blood clots

.The pill now contains lower doses of oestrogen so has fewer side effects


.It reduces the risk of getting some types of cancer and getting pregnant


.It doesnt protect against STDs and there's still a very slight chance of getting pregnant

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Increasing fertility

.Some women have levels of FSH that are too low to cause their eggs to mature

.This means that no eggs are released and the woman cant get pregnant

.The hormones FSH and LH can be injected by these women to stimulate egg release in their ovaries


.It helps a lot of women to get pregnant


.It doesnt always work and it can cause multiple pregnancies (twins e.c.t)

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.IVF stands for in vitro fertilisation

.It involves giving FSH and LH to a woman to stimulate egg production

.Then the eggs are collected from th woman's ovaries and fertilised in a lab using the man's sperm

.The fertilised eggs are then grown into embryos

.Once the embryos are tiny balls of cells, one or two of them are transferred to the woman's uterus (womb) 


.It can give an infertile couple a child


.Some women have a strong reaction to the hormones and multiple births can happen - these are risky for the mother and babies 

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Plant hormones

.A plant growth response is called a tropism

Auxins are plant growth hormones-

.Plant growth is controlled by hormones called plant growth hormones

.They control the growth of shoots and roots,flowering and the ripening of fruit

.The plant hormones that control the growth of the shoots and the roots are called auxins - they move through the plant in solution (dissolved in water)

.Auxins are involved inthe growth responses of plants to light (phototropism) and gravity (geotropism)

.Auxins are made in the tips of the shoots and roots

.Shoots are positively phototropic (grow towards light)

.Shoots are negatively geotropic (grow away from gravity)

.When plants grow towards light - increase the plants chances of survival

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Plant hormones (2)

Auxins change the direction of root growth-

.Roots are negatively phototropic (grow away from light)

.Roots are positively geotropic (grow towards gravity)

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Commercial uses of plant hormones

.Plant hormones can be used to speed up or slow down plant growth


.Selective weedkillers  are plant growth hormones that only affect weeds

.The weedkillers change the weeds' normal growth patterns,which soon kills them

.Grass and crops aren't affected by these weedkillers

Rooting powder-

.A cutting is part of a plant that has been cut off it

.Normally,if you stick cuttings in the soil they wont grow

.But if you add rooting powder, which contains a plant growth hormone, they will produce roots rapidly and start growing as new plants

.This lets growers produce lots of clones of a really good plant very quickly

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Controlling the ripening of fruit and dormancy

Ripening fruit-

.Plant hormones can be used to delay the ripening of fruits

.This allows the fruit to be picked white its still unripe - less easily damaged

.Ripening hormone is then added and the fruit will ripen on the way to the supermarket - so its perfect just as it reaches the shelves


.Lots of seeds wont germinate (start growing) until they've been through certain conditions - dormancy

.Plant hormones can break this dormancy and cause seeds to germinate

.These hormones can be used to make seeds germinate at times of year when they wouldn't normally

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.Drugs alter the chemical reactions in your body

Drugs change your body chemistry-

.The chemical changes caused by a drug can make people become addicted to it

.If the drug isn't taken,an addict can suffer withdrawal symptoms - often unpleasent

.Some drugs are medicines that may be prescribed by a doctor, or got over the counter

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Performance-Enhancing drugs

.Some athletes take performance-enhancing drugs to make them better at sport - steriods increase muscle size and stimulants increase heart rate

.But some drugs can have negative health effects - steriods can cause high blood pressure

.Some of these drugs are banned by law, some are prescription-only, but all are banned by sporting bodies

Against drugs-

.Its unfair if people gain advantage by taking drugs

.Athletes may not know the health risks

For drugs-

.Drug-free sport isn't really fair anyway - some athletes may have different coaches

.Athletes have the right to make their own decisions about whether taking drugs is worth the risk or not

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Recreational drugs

Can be illegal or legal-

.Illegal drugs are often divided into two main classes - soft and hard

.Hard drugs are generally more harmful, but soft drugs can be harmful too - heroin and ectasy (hard drugs), and cannabis (a soft drug) can all cause heart and circulatory system problems

Some legal drugs have worse effects than illegal drugs-

.Tabacco and alcohol are both legal and recreational drugs

.They have a much bigger impact in the UK than illegal drugs,as so many people take them

Smoking causes-

.Lung disease


.Addiction (to nicotine)

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Fighting disease

.Microoganisms that enter the body and cause disease are called pathogens - cause infectious diseades (spread easily)

Two main types of pathogens-


.very small living cells

.Bacteria reproduce rapidly inside your body

.They make you feel ill by - damaging your cells and producing toxins (poisons)


.Not cells

.Copy themselves by invading cells and using the cells' machinery to make tons of copies

.The cell will usually then burst, releasing all new viruses - cell damage makes you feel ill

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Immune system

.Your skin, hairs and mucus in your respitory tract (airways) stop nasties getting in

.If your skin is cut, tiny bits of cells help your blood clot quicky to stop anything else getting in

.But if something does make it through, your immune system kicks in

.The most important part of your immune system is the white blood cells

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White blood cells

Three lines of attack against pathogens-

Consuming them:

  • White blood cells can engulf (surround) the pathogens and digest them 

Producing antibodies:

  • Every invading pathogen has unique molecules on its surface
  • These molecules are called antigens
  • When your white blood cells come across a foreign antigen - start to produce antibodies
  • Antibodies lock onto and kill the invading pathogens - antibodies produced are very specific to that type of antigen 
  • Some white blood cells stay in the blood after the pathogens have been fought off - memory cells
  • If the same pathogen enters your body again - cells deal with it quickly so you wont become ill - Immunity 

Producing antitoxins

  • These stop toxins produced by the invading bacteria
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  • Involve injecting small amounts of dead or inactive pathogens into the body

  • Pathogens have antigens on their surface

  • Antigens cause your white blood cells to produce antibodies to attack the pathogens
  • Some of these white blood cells become memory cells and stay in the blood
  • If you become infected with the same pathogen again, your memory cells quickly produce lots of antibodies 
  • These antibodies kills the pathogen so you dont become ill
  • For example, the MMR vaccine is used to protect children from the viruses that cause measles,mumps and rubella


  • Vaccines have helped control lots of infectious diseases that used to be common in the UK (polio)


  • Vaccines dont always work - sometimes they dont give you immunity 
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Fighting disease - drugs

  • Some drugs help you to get rid of the symptoms of a disease
  • But these drugs dont kill the pathogens 
  • Antibiotics kill bacteria
  • Different antibiotics kill different types of bacteria
  • But antibiotics dont destroy viruses 
  • Viruses reproduce using your own body cells
  • This makes it very difficult to develop drugs that destroy the viruses without killing the body cells

Bacteria can become resistant to antibiotics

  • Bacteria can mutate (have changes in their DNA)
  • Some of these mutations cause bacteria to become resistant to an antibiotic
  • Resistant strains of bacteria have increased as a result of natural selection 
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Testing antibiotics by growing microorganisms

  • Microorganisms are grown in a 'Culture medium' in round plastic dishes - Petri dishes
  • Inoculating loops are used to transfer microorganisms to the jelly
  • The microorganisms then multiply
  • Paper discs are soaked in different types of antibiotics and placed on the jelly
  • Strains of bacteria that are resistant to the antibiotics will keep growing around the discs
  • Non-resistant strains of bacteria will die
  • The petri dishes,culture medium and inoculating loops must be sterilised before use to kill unwanted microorganisms
  • The petri dish must also have a lid taped on to stop any microorganisms in the air getting in
  • In the lab (at school),microorganisms are kept at 25 degrees so that harmful pathogens wont grow
  • In industrial conditions they're kept at higher temperatures - microorganisms grow faster
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Fighting disease - past and future


  • He saw that lots of women were dying from disease after giving birth
  • He believed that doctors were spreading disease on their unwashed hands
  • Told doctors to wash their hands with antiseptic solution before seeing patients
  • This decreased death rates

Antibiotic resistance-

  • No. of deaths has fallen - antibiotics
  • There are strains of bacteria that are resistant to anitbiotics
  • We need to slow down the speed at which resistant types develop by not over using antibiotics
  • Drug companies are trying to develop new antibiotics that will kill resistant strains of bacteria
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  • Where genes from two organisms are mixed 
  • The mother and the father produce gamates
  • The egg and the sperm cell then fuse together
  • The offspring recieves a mixture of chromosones - inherits features from both parents
  • This mixture of genes produces variation in the offspring 


  • Asexual reproduction is where one parent cell makes a new cell by dividing into two
  • There's no mixture of gametes
  • There's no mixture of genes
  • There's no genetic variation in the cells
  • Each new cell has exactly the same genes as the parent cell - it's a clone
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Cloning - embryo transplants and tissue culture

Tissue culture - cloning plants-

  • Gardeners take cuttings from good parent plants and plant them to make copies with the same genes
  • Taking cutting is quick and cheap
  • Tissue culture is where you take a few plant cells and grow them into new plants -clones of the parent plant

Embryo transplants - e.g. cows

  • Prize bull and cow are mated
  • An embryo develops 
  • The embryo is then split many times,before any cells become specialised 
  • The embryos are put into the wombs of lots of other cows
  • The embryos are clones - all baby calves will have the same genes
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Cloning - adult cell

  • Involves taking an unfertilised egg cell and removing the nucleus
  • The nucleus from an adult body cell is put into the empty egg cell
  • An electric shock makes the egg cell divide
  • When the embryo is a ball of cells,it's implanted into the womb of an adult female
  • The embryo grows into a clone of the original adult body cell
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Genetic engineering

  • A useful gene is cut from one organism's chromosone using enzymes
  • Enzymes are then used to cut another organism's chromosone and then to insert the useful gene
  • Useful genes can be transferred into animals and plants at the very early stages of their development
  • This means they'll develop useful characteristics
  • Genetically modified crops have had their genes modified - to make them resistant to viruses, insects or herbicides
  • Genetic engineering could solve many problems - treating diseases
  • But not everyone thinks its a good idea - there are some long-term effects of genetic engineering

Pros of GMCs

  • GMCs can increase the yeild of a crop - makes more food

Cons of GMCs

  • Growing GMCs could affect the number of flowera and insects that live by the crops
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Classification - the 5 kingdoms


  • Are autotrophs - make their own food
  • Have chlorophyll - green stuff in leaves
  • Are multicellular - have lots of cells 
  • Have cell walls


  • Are hetrotrophs - have to move about
  • Are multicellular
  • Dont have cell walls
  • Dont have chlorophyll


  • Are saprophytes - feed off dead organisms 
  • Are multicellular 
  • Have a cell wall
  • Dont have chlorophyll
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Desert animals-

  • Need to lose heat
  • Have very thin layers of body fat - help them lose heat
  • Thin coat - help lose heat
  • Specific colour - good camoflage - help avoid predators 
  • Large surface area compared to their volume - helps them lose heat

Artic animals-

  • Need to save heat
  • Thick layer of body fat - insulation
  • Thick hairy coats - to keep body heat in
  • White fur - camoflage 
  • Small surface area compared to their volume - reduced heat loss
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Adaptations in plants

Desert plants-

  • E.g. Cacti
  • Store water in their thick stem
  • Have spines instead of leaves - small surface area - reduce water loss
  • Roots are spread oit over a large area - absorb water quickly

Plants' special features to prevent predators-

  • Thorns on roses
  • Poisons on bee stings and poison ivy
  • Warning colours on wasps

Microorganisms living in extreme areas-

  • Extremophiles - extreme conditions
  • E.g. hot volcanoes,salty lakes or high pressure on sea beds
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Genetic variation-

  • All plants and animals have characteristics that are similar to their parents'
  • This is because an organism's characteristics are controlled by genes passed on from their parents 
  • These genes are passed on in sex cells, which the offspring develop from
  • Most animals and quite a lot of plants get some genes from the mother and some from the dad
  • This mixing of genes from two parents causes genetic cariation
  • Some characteristics are determined only by genes 

Environmental variation-

  • Any difference that's caused by the environment an organism lives in 
  • E.g. A plant grown on a sunny windowsill would grow healthy and green
  • But the same plant grown in darkness would grow tall and spindly - the leaves will turn yellow
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Factors to survive-


  • light 
  • water 
  • space
  • nutrients from the soil


  • space (territory)
  • food
  • mates

Organisms compete with other species for the same reason

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Environmental change

Causes of environmental change-

  • The environment in which plants and animals live changes all the time
  • Living factors - infectious disease, predator , prey or food and competitors 
  • Non-living factors - an increase or decrease in average rainfall or average temperature

Affects on the population-

Population size increases:

  • E.g. if the number of prey increases, then there's more food for predators and their number increase too

Population size decreases:

  • E.g.the number of bees in the USA is falling rapidly - pesticides may be harming bees, there's less food available and there's more disease

Population distribution changes:

  • A change in distribution means a change in where an organism lives
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Measuring environmental change

  • Some organisms are very sensitive to changes in their environment 
  • These organisms are inducator species


  • Lots of lichens = clean air
  • Sulpher dioxide pollution comes from cars and power stations
  • Lichens can't live where there's lots of sulpher dioxide in the air

Mayfly Larvae:

  • Sewage in a river leads to less oxygen in the water 
  • Mayfly larvae can't live where there's not much oxygen in the water
  • Lots of mayfly means the water is clean
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Other living indicators


  • Lots of sludgeworms means that the water is polluted
  • Sludgeworms live in water without much oxygen
  • It is an invertibrate like Mayfly's


  • Lots of phytoplankton means that the water is polluted
  • Their numbers increase when rivers and lakes are polluted by things like fertilisers and sewage

Non-living indicators:

  • Scientists use satalites to measure the temperature of the sea surface
  • They measure rainfall using rain gauges - how much the average rainfall changes each year
  • They use dissolved oxygen meters - how much oxyen there is in the water 
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Energy transfer

  • Energy from the Sun is the source of energy for nearly all life on earth 
  • Green plants and algae use a small amount of the light energy from the Sun to make food - photosynthesis
  • This energy's stored in the cells of plants and algae
  • The energy goes through the food chain as animals eat plants and other animals 
  • Respiration supplies (releases) the energy for all life processes, including movement 
  • Most of this energy is eventually lost to the surrondings as heat 
  • Material and energy are also lost from the food chain in the organisms' waste materials
  • This explains why you get biomass pyramids - most biomass is lost and does not become biomass in the next stage
  • Also, why you hardly get food chains with more than 5 stages - so much energy is lost at each stage that there is not enough left to suport more organisms
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Materials returning to the environment:

  • Living things are made of materials they take 
  • Materials are returned to the environment in waste products or when dead organisms decay
  • Materials decay - they're broken down by microorganisms
  • Most microorganisms work best in warm,moist conditions with plenty of oxygen
  • Compost bins recreate these ideal conditions 
  • All the important materials are recycled - return to the soil (ready to use by plants)
  • In a stable community the materials taken out of the oil are balanced by those that are put back 
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The carbon cycle

  • Carbon dioxide is removed from the air by green plants and algae during photosynthesis
  • The plants and algae use the carbon to make carbohydrates, fats and proteins
  • Some of the carbon is returned to the air as carbon dioxide when plants and algae respire
  • Some of the carbon becomes part of the fats and proteins in animals when the plants and algae are eaten
  • The carbon then moves through the food chain
  • Some of the carbon is returned to the air as carbon dioxide when the animals respire
  • When the plants,algae and animals die, microorganisms and detritus feeders feed them
  • When these organisms respire, carbon dioxide is returned to the air
  • Animals also produce waste, which is broken down by ditritus feeders and microorganisms
  • Compounds in the waster are taken up from the soil by plants as nutrients and go back into the food chain
  • When the wood and fossil fuels are burnt (combustion) this releases carbon dioxide back into the air 
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