Science- biology paper 2


The importance of homeostasis

  • Homeostasis= regulation of internal conditions of a cell or organisim in response to internal or external changes
  • Important because it keeps bodily conditions constant for enzyme action and cell functions- controls blood glucose concentration+ body temperature+ water and ion levels
  • Control systems can involve responses using nerves+ chenical responses using horemones
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Control systems

  • All include receptors (detect stimuli)+ co-ordination centres (recieve and process info from receptors) and effectors (bring about responses to restore optimum levels)
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The nervous system

  • Enables humans to react to surroundings and co-ordinate behavior
  • Info from receptors travels to the central nervous system (brain+spinal chord)
  • The CNS co-ordinates the response of effectors (muscles+glands)
  • Reflex actions are automatic, rapid to protect the body and DON'T INVOLVE THE CONSCIOUS PART OF THE BRAIN
  • 1. Pain is detected by receptors
  • 2. Electrical impulses travel from the receptors to the sensory neurone and diffuses across the synapse to the CNS
  • 3. The impulse passes through the relay neurone
  • 4. It diffuses across the synapse to the motor neurone
  • 5. The motor neurone carries the impulse to the effector
  • 6. The effector (usually muscle) responds
  • Neurones are NOT DIRECTLY CONNECTED to eachother
  • They communicate via SYNAPSES
  • When the electrical impulse reaches the SYNAPSE, a chemical is released, the chemical diffuses across the gap betweeen two neurones
  • Electrical impulses are generated in the sensory neurone
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The endocrine system

  • The endocrine system is made up of glands which secrete horemones into the blood stream 
  • Horemones= chemical messengers that are carried in the blood to TARGET ORGANS which produce an effect
  • Slower and last longer than effects of the nervous system
  • Pituitary gland is part of the brain= the master gland, it secretes several horemones in response to body conditions
  • Some of the horemones act on other glands to stimulate the release of other horemones and bring about effects
  • Adrenaline- produced by adrenal glands in times of fear or stress- increases heart rate increasing the delivery of oxygen of glucose to the brain and muscles- prepares the body for fight or flight response
  • Thyroxine- produced by thyroid glands- increases metabolic rate- controls growth and development- controlled by negative feedback
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Control of blood glucose

  • Cocentration is monitored and controlled by pancreas
  • If the concentration is too high, the pancreas releases more insulin- insulin causes glucose to move from blood into cells
  • Liver and muscle cells- excess glucose is converted into glycogen for storage 
  • If the concentration is too low, the pancreas releases glucagon- glucagon stimulates glycogen, is converted into glucose and is released into the blood- this is an example of negative feedback
  • Type 1 diabetes- caused by pancrease failing to produce enough insulin= high blood glucose levels and is normally treated through insulin injections
  • Type 2 diabetes- caused by body cells not responding to insulin, obesity is a risk factor- treated with a carbohydrate controlled diet and regular exercise
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  • Variation= differences in characteristics of individuals in a population#
  • could be due to differences in GENETICS, ENVIRONMENT or COMBINATION OF BOTH
  • Sexual reproduction cause different combinations= variaton
  • ONLY MUTATIONS make new alleles
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  • Evolution= the gradual change in inherited characteristics of a population over time- may lead to the formation of a new species
  • Charles Darwin came up with the theory of eveolution- humans evolved from apes- all species evolved from simple life, the first evolved 3 billion years ago
  • Natural selection happens when 

1. more born than can survive in a species 2. differences in genes- show variation in phenotypes 3. Characteristics- the best for the invironment are more likely to survive 4. breeding- genes that help survive are passed to offspring

  • Different populations of the same species evolve differently
  • Differences in environments lead to different characteristics favoured by natural selection
  • NEW SPECIES= 2 populations of 1 species are so different they can't interbreed to produce FERTILE OFFSPRING
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Evidence for evolution

  • When Darwin's theory was published people weren't knowledgeable about how inheritance and variation works
  • Proven- characteristics are passed from one gene to next via genes
  • Fossils are evidence for evolution 
  • Fossils are remains of organisims from billions of years ago found in rocks

How can a fossil be formed?

  • Hard parts of animals don't decay easily
  • Parts HAVE NOT DECAYED because some conditions for decay are ABSENT
  • Parts of organisim could be replaced by other material as it decays
  • Traces of organisims  are preserved- allow scientists to look at how organisims change over time
  • Problems= gaps in the fossil record because some of the early life forms are soft bodied= few traces left, some of the traces could have been destroyed by GEOLOGICAL ACTIVITY
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Evidence for evolution part 2

  • Antibiotic-resistant bacteria are the result of natural selection
  • Bacteria evolve rapidly and reproduce fast 
  • When they reproduce, mutations occur
  • some are resistant to anti-biotics and are not killed
  • The survivors reproduce to create a resitant strain
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Selective breeding

  • Humans use selective breeding/ artificial selection to produce: food crops from wild plants and domesticated animals from wild animals
  • Selective breeding= humans breed plants and animals for desirable characteristics


1. Choose parents with desirable characteristics 2. Breed 3. Choose offspring with best desirable characteristic 4. Breed 5. Continue over generations

Selected characteristics

  • Disease resistance in food crips
  • Animals for increased milk and meat
  • Dogs for temprement (gentle nature)
  • Large and unsual flowers
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Genetic engineering

  • Genetic engineering= changing the characteristics of an organisim by introducing another organisims gene


1. Enzymes isolate the needed gene 2. Gene is inserted into a vector= bacteria/plasmis/virus 3. Vector inserts the gene into the needed cells 4. if it's inserted into an egg/embryo all the cells in the organisim get's the new gene

  • GM crops are genetically enginnered to be resistant to disease and herbicides and produce bigger, better quality fruit
  • some are concerned about GM crops and the long term effects on populations of wild flowers, insects and human health
  • Fungi/bacteria cells and genetic engineering can be used to create useful substances (human insulin)
  • In the future GM crops may be used to cure and prevent inherited diseases in humans
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Sex hormones+ control of menstrual cycle

  • controls human reproduction- causes development of secondary sexual characteristics
  • Oestrogen- ovaries- female sex horemone- puberty= eggs mature + be released= ovulation
  • Testosterone- testes- male sex horemone- stimulates sperm production
  • Menstrual cycle- monthly cycle of egg being released
  • FSH= follicle stimulating horemone- pituitary- eggs to mature+ stimulates ovaries produce oestrogen
  • Oestrogen- ovaries- stops FSH+ stimulates LH- makes uterus lining thicken/grow
  • LH= luteinising horemone- pituitary- stimulates egg release
  • Progesterone- empty follicle in ovaries- maintains uterus lining+ stop LH and FSH
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Reducing fertility

  • Fertility reduced by CONTRACEPTION
  • Hormonal= oral (the pill)- Oestrogen+progesterone- stop FSH, injection/implant/patch- slow release progesterone- stop egg release (months/years)
  • Non-Hormonal= barrier (condom/diaphram)- prevent sperm getting to egg, intrauterine devices- no embryo implanting into uterus, spermicides, abstanance, sterilisation- cutting ducts+tying fallopians
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Increasing fertility

  • Doctors can give FSH+LH in FERTILITY DRUG- if woman's FSH= too low to stimulate egg maturation
  • In Vitro Fertilisation (IVF) treatment= 1. Give woman FSH+LH, stimulate egg growth- 2.Collect woman's eggs- 3.Fertilise eggs with father's sperm in lab- 4. Insert 1 or 2 eggs into uterus
  • Pro= gives woman chance to have baby
  • Cons= emotionally+ physically stressfull, low success rates, multiple births, risk to baby+mother
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Asexual reproduction

Asexual reproduction

  • Only one parent- no fusion of gametes= no mixing of genetic info
  • Production of genetically identical offspring
  • Mitosis
  • Lots of plants reproduce asexually- strawberries= send out long shoots (runners), touch ground+ grow new plant- daffodils= lots of smaller bulbs, grow
  • Lots of fungi- spores
  • Malerial prostists- when in human host
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Sexual reproduction and meiosis

Sexual reproduction

  • Fusion of male+female gametes- sperm+egg in animals, pollen+egg in flowering plants
  • Mix of genetic info- variation of offspring
  • Formation of gametes- meiosis
  • Cell divides by meiosis- copies of genetic info made, cell divides x2 form 4 gametes- each=single set chromosomes- important, halves number chromosomes in gametes
  • fertilisation can restore full chromosome number
  • All gametes=genetically different
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  • Some characteristics= controlled by single gene (fur colour in mice, red-green colour blindness)
  • Gene- different forms= alleles
  • GENOTYPE=combination alleles present in gene
  • PHENOYPE= how the alleles are expressed
  • If 2 alleles present= same- HOMOZYGOUS, if 2 alleles present= different- HETEROZYGOUS
  • Most characteristics controlled- multiple genes
  • 1 gene involved= MONOHYBRID INHERITANCE
  • Predict genetic outcome= PUNNET SQUARES
  • CAPITALS FOR DOMINANT ALLELES, lower case for recessive alleles
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Inherited disorders and sex determination

Inherited disorders

  • Some disorders= caused by inheritance of alleles
  • Polydactyly- DOMINANT ALLELE- extra digits
  • Cystic fibrosis- recessive allele- cell membrane disorder, mucus build up in lungs+digestive system

Sex determination

  • Only 1/23 pairs chromosomes carries sex determination gene= SEX CHROMOSOMES
  • Females- sex chromosomes= **, Males-sex chromosomes=XY
  • Offspring (sexual reproduction) inherit 1 chromosome from each parent- X from mother, X or Y from father
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  • Living things= classified into groups- structure+characteristics
  • One of main systems- Carl Linneaus- KINGDOM, PHYLUM, CLASS, ORDER, FAMILY, GENUS, SPECIES
  • Organisims= named by binomial system- 2 parts to name- 1st= genus, 2nd= species
  • New models because microscopes got better- scientists learnt more about cells, biochemical processes= better understood
  • Now 3-domain system by Carl Woese- ARCHEA(primitive bacteria-extreme environments), BACTERIA(truebacteria), EUKARYOTA(protists,fungi,plants, animals)
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  • Throughout Earth's history, different organisims=formed by evolution+ some become EXTINCT
  • EXTINCTION caused by- changes to environment over long periods of time, new predators, new diseases, new/successful competators, catastrophic event (volcanic erruptions/ asteroid collisions)
  • Great auk= extinct-over hunting
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Evolutionary trees

  • Method used by scientists- show how organisims= related
  • Use current CLASSIFICATION data= living organisims, FOSSIL DATA= extinct organisims
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Relationships between organisims

  • Ecosystem= all the organisims living in a habitat+ non living parts of habitat
  • Different levels of organisation in ecosystem- INDIVIDUAL ORGANISIMS, POPULATIONS (groups of individuals of same species), COMMUNITIES (made up of many populations living together)
  • Survive+ reproduce- organisims require certain resources from habitat+other living organisims
  • Competition= trying to get enough of rescources
  • Plants in community/habitat compete for LIGHT, WATER, SPACE+MINERAL IONS from soil
  • Animals compete for FOOD, MATES, TERRITORY
  • Species rely on eachother for FOOD, SHELTER, POLLINATION, SEED DISPERSAL= interdependance
  • Interdependance= removing a species from habitat can affect whole community
  • Stable community- all species+environmental factors= in balance- population sizes stay constant
  • Tropical rainforests+ancient oak woodlands= stable communities
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  • Factors affect communites= ABIOTIC (non-living) or BIOTIC(living) 
  • Abiotic factors= light intensity, temperature, moisture levels, soil PH+ mineral content, wind intensity+direction, CO2 levels for plants, O2 levels for sea life
  • Biotic factors= food availability, new predators, new pathogens/diseases, a species outcompeting another
  • ADAPTATIONS= features of organisim that help them survive in their habitat
  • Adaptations= structural, behavioral, functional
  • EXTREMEOPHILES= organisims that live in extreme environments
  • Extremeophiles- bacteria living in deep sea vents
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Studying ecosystems

  • POPULATION= group of 1 species living in habitat
  • Scientists like to estimate size of population- might involve sampling using QUADRAT


  • Place 2 tape measures on ground
  • Select 2 numbers using random number table, those will be the co-ordinates
  • Place quadrat on co-ordinates
  • Count number of individual plants of 1 species in quadrat
  • Repeat to find a mean
  • Measure area of habitat and x by number of plants in 1m squared by whole area


  • Wash hands after ecology work in a habitat
  • Don't throw quadrats
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Recycling materials

  • All materials in living world need to be recycled- can be used again in future organisims
  • Carbon is recycled in nature= CARBON CYCLE- relies on DECOMPOSERS, return C to athmosphere as CO2 through respiration
  • PHOTOSYNTHESIS= main process in carbon cycle- removes CO2 from air
  • ANY action that reduces PHOTOSYNTHESIS- increase in CO2 in air

Water cycle

  • Water cycle= how FRESH WATER circulates between LIVING ORGANISIMS, RIVERS+SEA
  • TRANSPIRATION- plants- returning lots of water to air
  • Deforestation can disturb water cycle
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Feeding relationships

  • Feeding relationships in COMMUNITY= FOOD CHAINS
  • PRODUCER= beggining of food chain- synthesises molecules
  • Producer- usually green plant- glucose molecules by photosynthesis
  • CONSUMERS- eat other animals= PREDATORS- eaten= PRAY
  • Top consumers= APEX PREDATORS- carnivores, no predators
  • STABLE COMMUNITY- numbers of predators+pray, rise+fall in cycles
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  • BIODIVERSITY= variety of all different species of organisims on Earth
  • HIGH BIODIVERSITY- helps keep ECOSYSTEMS stable- species depend on eachother, food+shelter
  • Future of Human Species- maintaining good level biodiversity
  • Lots human activites= responsible for reducing biodiversity- action to stop reduction
  • Factors put biodiversity at risk+affect species disribution in ecosystem= water availability, temperature, gasses in athmosphere
  • changes because- changes in season, georaphic activity (volcanoes/storms), humans
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  • POLLUTION- kills plants+animals- reduce biodiversity
  • Human population= increasing rapidly+ in some areas, increase in standard of living
  • Means more rescources used+more waste produced
  • Unless waste+chemical materials= properly handled, more pollution caused
  • Pollution can occur- water from sewage/fertilisers/toxic chemicals, in air from gasses(sulfur dioxide) dissolves in moisture in athmosphere produce ACID RAIN, on land from landfill+ toxic chemicals( pesticides+ herbicides, may be washed from land to water)
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  • Humans can put biodiversity at risk- taking too many environmental rescorces
  • Building+ quarrying+ farming+ dumping waste- all reduce amount of available land for other animals+ plants
  • Producing garden compost destroys peat bogs- reducing area of habitat+ variety of different organisims living there
  • Decay/burning peat= CO2 release into athmosphere
  • DEFORESTATION= cutting down trees+ destroying forests
  • Tropical areas, deforestation- land for cattle+ rice, more food- grow crops to produce biofuels
  • GLOBAL WARMING= gradual increase temperature of Earth
  • Lots scientists think is being caused by changes in gasses- pollution+ deforestation
  • Gasses= CO2+ METHANE
  • Biological consequences= loss of habitat, low lying areas= flooded by sea levels rising- changes in distribution of species, temperature/rainfall changed- changes in animal migration patterns
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The geneome

  • Genetic material in neucleus of cell made of DNA
  • DNA= in chromosomes
  • GENE= small section of DNA on CHROMOSOME
  • Gene codes for sequence of amino acids that makes specific protein
  • GENOME= entire genetic material of organisisim
  • Scientists have studied human genome- could lead to future uses= genes linked to different disorders, understand cause of inherited disorders+how to treat, investigate how humans could have changed ofer time
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Sampling using transect

  • Stretch tape across area of habitat= TRANSECT LINE
  • Place quadrat at regular intervals along line
  • Count plants in quadrat each time
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Conserving biodiversity

  • Scientists+ govournments- steps to reduce pollution+ over-exploitation, help maintain biodiversity
  • Steps= breeding programmes for endangered species, protecting rare habitats (coral reefs, mangroves, heathland), encouraging farmers keep margins+ hedgegrows in fields, reducing deforestation+ CO2 emissions, recycling rescources rather than throwing in landfill
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