IGCSE Biology Revision - Core

Key topics!

MRS GREN• Movement = moving from one place to another• Respire = release of energy from food• Sensitivity = response to stimuli• Growth = increase in cell number• Reproduction = production of offspring• Excretion = removal of waste (urine, CO2)• Nutrition = taking in/making food

Plants• Multicellular• Contain chloroplasts photosynthesis• Cellulose cell walls• Store carbs as starch/sucrose• Eg: peas, beans, maize, rose etc

Animals

• Multicellular• Do NOT contain chloroplasts no photo• No cell walls• Usually have a NS• Move from one place to another• Store carb as glycogen

Fungi• No photo• Organised into mycelium made from hyphae• Hyphae contain many nuclei• Some are single celled (eg: yeast)• Cell wall made of chitin• Feed by extracellular digestion release enzymes. Known as

saprotrophic nutrition• Store carbs as glycogen

Bacteria

• Microscopic; single celled• Have a cell wall, cell membrane, cytoplasm

and plasmids• Lack nucleus but have a circular chromosome

made of DNA• Most are decomposers; some can photo• Eg: Lactobacillus bulgaricus, Pneumonococcus

Protoctists

• Microscopic single celled• Amoeba – live in water have features of

animal cells;• Chlorella – have chloroplasts and are more

like plants;• Plasmodium – causes malaria.

Viruses

• Small particles – smaller than bacteria• Parasitic and live inside cells• Wide variety to shapes and sizes• No cell structure – protein coat• Contain DNA or RNA• Eg: TMV (causes discolouration of tobacco

leaves – stops chloroplasts forming), HIV (causes AIDS)

Pathogenic?

• Some bacteria, all viruses, some fungi, some protoctists.

Cells

Organisation

• Organelles cells tissue organ system

Diffusion, Osmosis, Active Transport

• Diffusion HL conc, down the gradient, seen in lungs

• Osmosis H L through PPM, seen in collecting duct. Water only.

• AT LH against/up conc gradient. Requires energy. Seen in roots (minerals) and in PCT (glucose)

Factors affecting rate of movement of substances into/out of cells

• SA:Volume ratio• Temp• Conc gradient

Balanced dietCarbs Energy

Fats Insulation

Protein Growth and repair

Vitamin A/C Night vision/prevent scurvy

Iron/calcium Prevent anaemia/strong bones

Water Cell hydration

Fibre Keep intestines healthy

Chemical elements present in carbs, fats and proteins???

Biochemical tests for glucose and starch???

Digestive system

• Enzymes• Emulsification• Neutralisation• Adaptations of SI

Digestion – the 3 main food groups - all

Digestion is the breakdown of large, insoluble molecules into smaller, soluble ones. ENZYMES are needed to break down large molecules (above) into smaller ones.

•Lipids fatty acids + glycerol

•Starch maltose glucose

•Proteins amino acids

Absorption takes place in the small intestine Food is transported in the plasma of the blood.

Enzymes

• Are biological catalysts• Speed up biochemical reactions in cells• Affected by temp (increase in KE up to

optimum, then denatured)

Breathing system

• Inhale – diaphragm contracts, IC muscles contract– volume of thorax

increases; pressure decreases

• Adaptations of lungs

Smoking

• Effects on heart• Nicotine increases heart

rate• Higher BP• Narrows coronary

arteries• More likely to have a

heart attack

• Effects on lungs• Reduces SA of alveoli –

breathlessness• Development of

emphysema• Bronchitis – narrowing of

bronchioles• Lung cancer• RBCs carry CO reduced

efficiency of transport of O2

Aerobic Respiration

• The release of energy from food. It is not breathing!

• Glucose + oxygen carbon dioxide + water + energy

• C6H12O6 + 6O2 6CO2 + 6H2O + energy

Anaerobic respirationThe word equation is:

Glucose lactic acid + some energy

Anaerobic respiration usually happens during vigorous exercise. It is only useful for a short time ie: during a sprint. During anaerobic respiration lactic acid builds Up in muscles – this is what causes cramp. It must be oxidised:

Lactic acid + oxygen carbon dioxide + water

This is called OXYGEN DEBT.

Heart

LA

RV

RA

LV

Tricuspid valveBicuspid valve

Semi-lunar valves

Coronary arteries

Circulation – be able to name blood vessels

Blood vessels

Blood -• Is composed of 4 things:(a) Red blood cells – carry

oxygen (haemoglobin, biconcave, large SA, no nucleus)

(b) White blood cells – phagocytes (engulf, digest) and lymphocytes (produce antibodies)

(c) Platelets – form scabs(d) Plasma – yellow liquid

which carries blood cells and dissolved products such as urea, CO2, food, temp.

Kidney

• Nephrons• Ultrafiltration• Selective

reabsorption• High water in blood =

LESS ADH = LESS permeability of CD = LESS reabsorption = MORE urine

Nervous System

• Reflexes• Stimulus receptors

SRM effectors response

• Fast, doesn’t involve brain

• Synapses• Neurotransmitter

diffuses across gap

The eye

• Key labels

Hormones

• Adrenaline adrenal glands increases HR

• Insulin pancreas lowers sugar levels on blood. Stored as glycogen in liver

• ADH pituitary gland water reg (H)

• Oestrogen ovaries repairs

• Progesterone ovaries maintains

• Testosterone testis secondary sexual characteristics

Reproduction

• Male • Female

•TIME FOR A BREAK!!!!!!!!!!

Plants - leaves

• Palisade – where photo takes place

• Spongy – air spaces for diffusion

• Xylem – water• Phloem –

sucrose/amino acids• Guard cells – allow CO2

and O2 in/out of leaf

Leaf adaptations

• Broad – more SA• Thin – faster diffusion• Palisade layer near surface• Stomata – gases in

Key word equations balance them as well!

• Photosynthesis:

Carbon dioxide + water oxygen + glucose

Glucose + oxygen carbon dioxide + water + energy

•Respiration

Factors affecting photo

• Temp• Light• CO2

Transpiration

• Is the loss of water from a plant (evaporation)

• Measured using a potometer

• Factors affecting: – Humidity (the more

moisture the less transpiration occurs – think diffusion)

– Wind– Temperature– Light (opens

stomata)

Auxins

• Phototropism = auxin accumulates on the shady side; stimulates cell elongation on that side; shoot bends towards light; more photo

• Geotropism (TA) auxin accumulates on lower side, growth is retarded; roots curve down; anchorage, more minerals and water

Plant repro

• Pollination – transfer of pollen from anther to stigma

• Fertilisation – when male and female gametes fuse

Insect pollinated

• Dull• No scent• Anthers hang

outside of plant• Pollen is lighter

•TIME FOR A BREAK!!!!!!!!!!

Inheritance and Genetics

Genetic terminologyWord MeaningChromosome Structures found in nucleus of cell (46 in humans

– diploid; 23 in eggs and sperm – haploid)

DNA Sequences of bases. Chromosomes are made of DNA

Gene A short section of DNA that codes (makes) a protein

Allele A different form of the same gene

Genotype Eg: Aa- two alleles which together determine the phenotype (features an individual has)

Phenotype The physical characteristics seen

Homozygous Both alleles are the same. Eg: AA/aa

Heterozygous Both alleles are different. Eg: Aa

Dominant Only one allele needed for gene to be expressed. Eg Huntingtons

Recessive Both alleles needed for gene to be expressed. Eg CF

Structure of DNA• Double helix – two

strands twisted round each other

• Adenine pairs with Thymine (AT)

• Cytosine pairs with Guanine (CG)

Genetic crosses – will come up!

• Start with parental phenotype (identify who is who as well)

• Give parental genotype underneath corresponding phenotypes

• Show gametes • Put into punnet square• Calculate ratios of phenotypes

Types of reproduction

Sexual Asexual

•2 parents required•Offspring will be genetically different•Leads to variation and increased alleles in a population

•1 parent required•Offspring will be genetically identical to parent (clones)•Decreased frequency of variation and decreased alleles

Mitosis• Asexual reproduction• Leads to all “daughter cells”

being genetically identical to parent

• Same number of chromosomes as parent in resulting cells

• Happens in all cells in the human body except the sex cells

• 2 cells at end

Meiosis

• Sexual reproduction• Results in variation• Halves the number of

chromosomes at end• Happens in sex cells

(gametes) only• 4 cells at end

Egg and Sperm

• Eggs are always X• Sperm can be X or Y• Make sure you can set

out a genetic diagram to show that there is a 50/50 chance of a couple having a boy/girl

Mutations• Occur in DNA• They are rare and random• Some can be beneficial (natural selection)• Some can be neutral (ie: a change doesn’t affect the

organism)• Some can be harmful (eg: genetic disorders)• Mutations can be inherited

Natural Selection

• If a mutation is beneficial and offspring inherit it they are more likely to survive compared to other offspring

• They reproduce and pass on the favorable mutation

• The characteristic increases within a population

• Takes many generations.

Genetic Engineering

• Cut• Restriction enzymes• Identify vector• Cut with same restriction enzyme• Stick gene into vector using DNA ligase• Insert into bacteria = recombinant bacteria• Fermenter

Cloning - plants

• Micropropagation (or tissue culture)• Explants are removed from parent plant• Sterilise to remove bacteria• Put explants into agar which contains

minerals, hormones• Grow (plantlets form) and then transfer to

compost• All are genetically identical to parent plant

Cloning - animals

• Dolly!• Empty egg cell (enucleated)• Take skin cell nucleus (must be diploid)• Fuse and allow to divide into a ball of cells• Implant into uterus of surrogate• Will be genetically identical to the organism

the diploid cell was taken from.

Selective breeding

• Select desirable characteristics from male and female

• Mate/breed• Female gives birth• “Best” offspring are chosen and the process is

repeated for many generations.

•TIME FOR A BREAK!!!!!!!!!!

Food Chains

• Green plant Greenfly Ladybird Bird

• Can you name the producer? Carnivore? Herbivore?

• What would happen if all the greenfly died out? • What would happen if all the Ladybirds died out?

Factors affecting population size

• Amount of nutrients available• Competition for food• Competition for light (if a plant)• Predation• Disease

Pyramids of number

• Shows the number of living things at each stage in the food chain.

• The producers are usually the biggest, with less and less living things at each level.

Pyramids of biomass

• Shows the MASS of living organisms at each level. This is useful because sometimes a pyramid of number can be inverted.

Pyramid of biomass

Pyramid of number

Pyramids of energy

• Always pyramid shaped as energy is lost at each trophic level

• Why?– Excretion– Movement– Egestion

Carbon cycle

1. CO2 taken in via photosynthesis2. Animals eat plants C is passed on this way3. Animals and plants respire putting CO2 back4. Micro-organisms that are involved in decay respire5. Combustion also has an effect on CO2 levels

Eutrophication

Air pollution

• Air – CO2 from combustion of fossil fuels global warming;

• Carbon dioxide is known as a GREENHOUSE GAS.

• Sulphur dioxide - SO2 and oxides of nitrogen - NO2 from car fumes acid rain.

• Methane comes from increased cattle and rice farming global warming. Methane is also a GREENHOUSE GAS.

Water pollution

• Sewage, fertiliser and toxic chemicals• First two can lead to eutrophication

Land pollution

• Land is being used up for FARMING. Why? More people = more food.

• Trees are being cut down. This is known as DEFORESTATION. Why? More people = more space for houses.

• Deforestation leads to increased carbon dioxide levels and decreased O2. Why? Less photosynthesis!

•TIME FOR A BREAK!!!!!!!!!!

Glasshouses

• Higher temp (increases enzyme activity)• Higher CO2 (increases photo)• Higher light intensity (increases photo)• Leads to a higher yield

Fertilisers

• Contain minerals– Mg – chloropyll– NO3 – nitrates for protein and therefore growth

Biological control v pesticides

• Advantages of Bio• Specific to pest• Only one application

needed• Doesn’t harm the

ecosystem

• Disadvantages of pesticides

• Bioaccumulation• Pest resistance (not

immunity!)• Needs reapplication• May harm other pests,

disrupts food chains

Fish farming

• Feed regularly• Put antibiotics in the water• Remove nitrogenous waste (filter)• Keep predators out (cage)

Fermentation

• Is an anaerobic reaction

Glucose CO2 + alcohol

Used to make bread Mmmm beer and wine

Starch in barley grains broken downFermentation occursHops added for flavour

Yeast + sugar added to flourOptimum temp for enzymesCO2 produced and bread rises

Fermenters

Features – triple only:

Water cooling jacketPaddlesAir inNutrients inGas outletProbes attached toComputer to monitorpH, temp, O2 etc

AND ONE FINAL THING….

•GOOD LUCK!!!!!

IGCSE Biology - Extension

Enzymes and pH

• Enzymes work within a specific pH range. If removed from this = denatured.

• Not all enzymes work in neutral conditions!

Vaccination

• Dead/weakened version of the pathogen• Stimulates production of cells that produce

antibodies. Also memory cells.• Memory cells mean a faster secondary

immune response – more antibodies faster second time around.

Blood clotting

• Involves cells called platelets• BC is important as prevents loss of blood;• Stops pathogens entering wound.

The Eye

• Accommodation:Distant = SL tight, ciliary muscles relaxed;

• Light intensity: BCCRR!!!

Thermoregulation

• Hot• Sweating - removes

heat from the body as sweat evaporates

• Vasodilation – more blood flows near the surface of the skin; more heat lost via radiation

• Cold• Shivering – repeated

muscle contraction releases heat

• Vasoconstriction – less blood flows near the surface of the skin

• Hairs stand up

Respiration and photo

• Respiration happens ALL the time!

Germination

• Water needed – activates enzymes

• Warm temps – increases KE of enzymes

• Water into seed by osmosis; enzymes activated and starch broken down into glucose; glucose used for respiration

Co-dominance

• Use different capital letters• The offspring will be a mixture of the two

parents• There will be more than two phenotypes

when heterozygous parents are crossed.• Eg: RW x RW (parents are pink)• Offspring are RR, RW, WW

Mutations• Occur in DNA• They are rare and random• Some can be beneficial

(natural selection)• Some can be neutral• Some can be harmful (eg:

genetic disorders)• Mutations can be inherited

• Triple only: Mutations can increase when DNA is exposed to a mutagen (eg: ionising radiation)

Transgenics (triple only)

• Means moving genes from one species to another

• If we cloned transgenic animals we could:– Have animals that produce lots of human

antibodies– Have organs that could be used for

transplantation– But is this ethically right? Should we do this?

Nitrogen cycle

1. N taken in via NPK fertilisers or from dead material. Become proteins in plants.2. Animals eat plants so N is passed on this way3. Decay (decomposing bacteria) and excretion lead to ammonia being formed4. Nitrifying bacteria convert ammonia into nitrates – can be taken up by plants5. Nitrogen fixing bacteria on leguminous plants turn N has into nitrates.6. Denitrifying bacteria convert nitrates back into nitrogen gas

Making food• Yoghurt Starter culture of bacteria added to milk Bacteria convert lactose lactic acid Lactic acid causes milk to clot and solidify.Asceptic techniques