igcse biology revision

IGCSE Biology Revision

Life Processes

• Movement• Respiration• Sensitivity• Growth• Reproduction• Excretion• Nutrition

Mrs Gren – or –many naughty rabbits eat green rhubarb stems

Plant and Animal Cells

(cellulose)

mitochondria

Cell specialisation

Cell organisation

system

organism

Transport In and Out of Cells

• Diffusion – from a high to a low concentration until they are evenly spread

• Osmosis – from a region of high water concentration to a region of low (weak to a strong solution) through a semi permeable membrane

• Active transport – from a low to a high concentration across a cell membrane

using ATP

Digestion

Balanced Diets• Carbohydrates• Protein• Lipids / Fats• Vitamins• Minerals• Fibre• Water

The DuodenumAmylase Starch Maltose

Protease Proteins and polypeptides

Amino acids

Lipase Fats Fatty acids and Glycerol

The IleumMaltase Maltose Glucose

Sucrase Sucrose Glucose and Fructose

Lactase Lactose Glucose and Galactose

Peptidase Polypeptides Amino acids

Lipase Fat Fatty acids and Glycerol

Absorption and Assimilation

Glucose and amino acids are absorbed into the blood

Fatty acids and glycerol are absorbed into the lacteal

Assimilation• All digested glucose and amino acids pass

into the liver in the Hepatic Portal Vein.• Fats enter the lymphatic system which

enters the blood and returns them to the liver.

• The food is used for growth, repair, respiration.

• Excess food is mostly stored as fat.

Food Testing

• Starch – add iodine – turns black• Glucose or reducing sugar – add

Benedict's solution and boil – turns brick red

• Protein – Biuret test – add NaOH or KOH and then 1% copper sulphate – a violet colouration

Aerobic Respiration

• C6H12O6 + 6O2 6H2O + 6CO2 + energy

Anaerobic Respiration

• AnimalsGlucose Lactic acid• YeastGlucose Ethanol and carbon dioxide

Oxygen debt – the amount of oxygen needed to breakdown the lactic accumulated

Structure of Thorax

The Thorax

Breathing in

• Is controlled by the intercostal muscles and the diaphragm.

• When we breathe in the intercostal muscles contract and the ribs move up and out. The diaphragm contracts and moves down.

• This increases the space inside the chest and air rushes into the lungs.

Breathing out

• The intercostal muscles and the diaphragm relax.

• The ribcage drops down and the diaphragm moves upwards.

• This reduces the space inside the chest and pushes air out of the lungs.

Breathing Rate and Depth

• Rate - how many breaths per minute• Depth – how much air is being taken in,

normally ½ litre per breath• Measured with a spirometer

% of different gases in inhaled and exhaled air

Gas Inhaled air (%)

Exhaled air (%)

Oxygen 20 16

Carbon dioxide

0.04 4

Nitrogen 79 79

Water vapour

Variable level

100% saturated

Gaseous exchange

What makes the lung good at gaseous exchange?

• Large surface area – greater volume of gases exchanged

• Good blood supply – O2 and CO2 exchanged more quickly

• Thin membranes – allows diffusion• Moist lining – for the gases to dissolve

Keeping the Lungs Clean

• Dust, bacteria and other particles stick to the mucus secreted by cells lining the airways

• Cilia attached to these cells waft the mucus and dirt out of the lungs and it is swallowed.

• Acid in the stomach kills the bacteria

Effects of Smoking

•Tar causes cancer

•Nicotine is addictive

•Smoking removes the hairs that keep the lungs clean

Photosynthesis

lightcarbon dioxide+water glucose+oxygen

chlorophyll

6H2O + 6CO2 C6H12O6 + 6O2

Leaf Structure

• The leaf has a waxy cuticle to stop it losing water.

• The epidermis is a protective layer of cells and contains no chloroplasts.

• The palisade layer contains the most chloroplasts as it is near the top of the leaf. The chloroplasts contain the pigment chlorophyll. It is here that photosynthesis takes place.

• The palisade cells are arranged upright. This means the light has to pass through the cell lengthways and so increases the amount of light absorbed.

Stomata

Water moves into the guard cells by osmosis and the stoma opens

Guard cells

stoma

During the daytime the rate of photosynthesis is greater than the rate of respiration

Day

During both the day and night respiration occurs in plants.

Night

Limiting Factors

• Photosynthesis is a chemical reaction, its rate depends upon temperature, how much CO2 is available, light intensity, amount of chlorophyll or water.

• Without enough light a plant cannot photosynthesise very fast, even if there is plenty of water and carbon dioxide. Increasing the light intensity will make photosynthesis faster.

• Sometimes photosynthesis is limited by the level of carbon dioxide. Even if there is plenty of light a plant cannot photosynthesise if it has run out of carbon dioxide.

• Temperature can be a limiting factor too. If it gets too cold the rate of photosynthesis will slow right down; equally, plants cease to be able to photosynthesise if it gets too hot.

• If you plot the rate of photosynthesis against the levels of these three limiting factors you get graphs like the ones below.

Maximising growth

• Understanding the factors that limit photosynthesis enables greenhouse farmers to maximise the conditions for plant growth. They often use paraffin lamps inside the greenhouse because burning paraffin produces carbon dioxide as well as heat, and so makes photosynthesis proceed faster. They may also use artificial light to enable photosynthesis to continue beyond daylight hours.

Uses of Glucose

• Turned into starch for storage• Converted into lipid/fat for storage –

energy rich• Nitrogen can be added and turned into

protein• Stored in fruit• Used in respiration

Mineral Requirements

Magnesium for chlorophyll

Nitrogen for growth

Phosphorus for cell membranes and DNA

Remember how to test leaves for starch

The Heart

The Heart• Pumps blood

around the body

• Pumps blood to the lungs

• To pick up oxygen

• Remove carbon dioxide

Double Circulation

Heart

Lungs

Heart

Body

Heart

Greater pressure,

better oxygenation,

faster flow

Arteries Veins and Capillaries

Thick walls, oxygenated blood, away from heart

Thin walls, deoxygenated blood, to the heart, valves

Link arteries to veins, site of exchange of metabolites and waste

Blood

Red blood cells, transport oxygen, biconcave, no nucleus,

White blood cells, defence, engulf bacteria, produce antibodies

Platelets

• Used in the clotting of blood

• Damage cause them to clump and they begin the conversion of soluble fibrinogen (blood protein) into insoluble fibrin which meshes over the wound and traps red cells. They dry and form a scab

Blood Cells

Tissue exchange

Glucose

Waste

PLASMA

The lymphatic system

• Transports excess fluid from the tissues

• Transports digested fat

• Contains white blood cells that fight infection

William Harvey

• 1578-1657• Observed blood flow around the body• Noticed existence of valves in veins• Concluded blood pumped via veins round

body• Major medical breakthrough!

Galen

• Lived 1,000 years before Harvey• Did not use the scientific method

– Observation and experimentation• Thought blood went from side to side• Did not realise transport existed round

body through capillaries

Transport in Plants

A plant's transport system is made up of two types of tubes - strong, thick pipes called xylem vessels, and thinner tubes called phloem vessels. The cells of these vessels are modified to make them suited to performing their special functions                                                       Together xylem and phloem form the vascular tissue, often also referred to as the vascular bundle.

The Plant Transport System

Xylem consists of dead cells with no end walls, which contain lignin to form stiff tubes. They are impermeable.

Phloem consists of living cells lined with cytoplasm, with walls made of cellulose and perforated end walls. They are permeable, and are surrounded by companion cells.

Water is taken up the plant from the roots to the leaves (for photosynthesis and transpiration) - in xylem vessels .Minerals dissolved in the water are taken up the plant to the shoots and leaves - in xylem vessels.Food (the product of photosynthesis) is taken from the leaves and moved up and down the plant to any part which needs it (for growth or for storage) - in phloem vessels.

Transpiration

•Temperature

•Humidity

•Air movement

•Light

Ecology – Competition and Adaptation

Keeping warm Keeping cool

Plant adaptations

Not being eaten

Reducing water loss

Predators, Prey and Co-operation

Snowshoe hare

Arctic fox

Food Chains

Woodland Food Web

Pyramid of Numbers

Remember not always pyramid shape

Pyramid of biomass

grass

rabbitfox

Biomass is dry weight – water has been removed

Decomposition

Decomposers are bacteria and fungi

Organic matter- ammonium compounds-nitrite-nitrate

Plants and animals die and decay

The Carbon Cycle

Nitrogen Cycle

Food Production and farming methods

• Monoculture• Hedgerow removal• Biological pest control• Pesticides and herbicides and insecticides

Energy and Waste

• Burning fossil fuels such as coal, oil or gas• Greenhouse effect• Sulphur dioxide and nitrous oxides are

formed which dissolve in water to form acid rain

• Reduce the demand for energy so it reaches a sustainable level- will not use up the resources or pollute the planet

Global Warming and Acid Rain

ConservationTo prevent habitats and organisms from disappearing

Limit or ban hunting. Gene banks of frozen eggs, sperm or embryos. Zoos and captive breeding programmes. Preserve habitats

The Nervous System

Stimulus

Receptor

Sensory Neuron

Central nervous system

Motor neuron

Effector

Response

Motor neuron

The Eye

AccommodationLong distance – lens long and thin, ciliary muscle relaxed, suspensory ligaments taut

Near – lens short and fat ciliary muscle contacted, suspensory ligaments loose

Nerves Synapses and Drugs

Some drugs stimulate synapses like a neurotransmitter, LSD and nicotine

Others block the enzyme that normally breaks down the neurotransmitter

Alcohol depresses synaptic activity in the brain and acts as a depressant. So do solvents

The CNS and Reflex Actions

Hormones

• Proteins that are chemical messengers in the body

• Carried in the blood to target cells• Response is slower• May last for hours• Can stimulate more than one target

Controlling glucose, • After eating a lot of carbohydrate blood sugar

level rises.• Islets of Langerhans in the pancreas release

insulin, the glucose is stored as glycogen in the liver.

• The blood sugar level drops .• When blood sugar levels are low the insulin

production stops.• Glucagon is produced by the pancreas allowing

glucose release from the liver and muscles.

Uses of Hormones

• Controlling fertility – the contraceptive pill, may contain oestrogen and progesterone and controls the release of pituitary hormones and ovulation

• Mini pill, progesterone allows ovulation but makes the vagina and uterus unsuitable for sperm

• Anabolic steroids build muscle – reduce the production of testosterone

Uses of plant hormones

• Auxins allow plants to respond to the environment – tropic responses

• Auxin (IAA) causes -• They stimulate shoots to grow rapidly• Stops side shoots growing• Stimulates growth of roots from the base

of stems or leaves• Auxin from seeds cause fruit to swell

Plant responses and AuxinsHormone rooting powder causes roots to grow from cut stems

Seedless fruits –grapes, cucumbers, bananas. (parthenocarpy)

Selective weedkillers 2-4-D causes weeds to grow too fast and results in death, grass doesn’t take it up well

Q 3,4,5 page 102 for Wednesday

Homeostasis

Temperature Control Water Control Salt Balance Sugar control Carbon Dioxide Control Urea

Temperature Control

•Thermoregulation keeps the body at constant temperature (37oC).•Enzymes work best.•Temperature is regulated by the hypothalamus.

Temperature Control•Heat is made in most cells but in particular muscle and liver.•Heat is lost by convection, conduction and radiation.•Evaporation of water from a surface removes heat.

Keeping Cool

•Vasodilation, more blood flows nearer the skin and heat is lost.•Sweating, evaporation causes heat loss.•Hairs lie flat allowing more heat out.

Keeping Warm

•Vasoconstriction - less blood flows to the skin’s surface, keeping heat in. You may look pale!!•Decrease in sweat.•Shivering generates heat (respiration).•Hairs stand up and trap insulating air.

Carbon dioxide

• Excess carbon dioxide results in a drop in the body’s pH (acidic).

• Breathing out removes this excess.• The rate and depth of breathing will alter

to suit the amount of CO2.

The Kidney

Urea

• Urea is produced when proteins and amino acids are broken down in the liver.

• It is poisonous.• The kidneys remove it but so does

sweating !!

The kidney

The kidneys have four functions:• Regulation of blood water levels • Reabsorption of useful substances into

the blood • Adjustment of the levels of salts and

ions in the blood • Excretion of urea and other metabolic

wastes

Kidneys: how they work

Kidney transplant

• This is when the diseased kidney is surgically removed and replaced by a fully functioning kidney from a deceased or a live donor.

• It is only possible after a satisfactory tissue-match. Even after a successful tissue-match the recipient's immune system has to be drugged or suppressed to stop it from rejecting the new kidney.

Kidney failure

• In the event of kidney failure due to infection or disease, the kidney can no longer remove metabolic waste products from the body. Excretion of metabolic waste is a vital function and their accumulation will result in eventual death.

• There are two solutions to the problem of kidney malfunction or failure:

• Kidney transplant • Kidney dialysis

Kidney dialysis

• In the absence of a suitable donor kidney, the alternative solution is for the patient to be hooked-up to a dialysis machine every 2 - 3 days.

• A dialysis machine mimics the functioning of the kidney. Blood from an artery in the patient's arm is pumped into the kidney machine which removes urea and excess salts from it.

• The blood is checked for air bubbles before being returned to a vein in the arm.

Osmoregulation•Is keeping the water and salt levels constant in the blood. •They are regulated by the hypothalamus.•Water moves into the cells by osmosis and could cause them to burst.

Blood concentration too high

•The hypothalamus senses too little water in the blood.•A message is sent to the pituitary gland to release anti-diuretic hormone ADH.•The hormone acts on the walls of the collecting tube recovering water

Blood concentration too low.

•Too much water in the blood stops the hypothalamus signalling the pituitary.

•Water is removed by the kidneys.

•Large amounts of dilute urine produced.

Cell Division - Mitosis

DNA

DNA structure discovered by Crick and Watson

Genetic and Environmental causes of Variation

• Variation is inherited• Genetic – skin colour• Environmental – hair length• Both – height, weight, intelligence

Asexual reproduction

• Produces identical copies called clones – onions, strawberries, potatoes, greenfly

• This type of cell division is mitosis• Cuttings and grafting in plants• Micropropogation used by growers

Mutations

• Change in the DNA of an organism caused by an error when it is copied

• Radiation and certain chemicals such as cigarette smoke can cause mutations

• Most are harmful and leads to illness or death

• Useful ones are rare but have a dramatic impact on a species and its evolution

Harmful mutations

• Down’s syndrome – an extra chromosome number 21

• Cystic fibrosis is caused by a mutation in the DNA. It is a recessive allele which affects 1 in 2000 children.

• It causes sticky mucus which blocks the lungs and pancreas

Genetic Engineering

• Is the ability to alter DNA• A gene from one organism can be

transferred into the DNA of a completely different organism

• In some cases the all the DNA is removed from a cell and replaced with the DNA from another organism

• Dolly the sheep was the first example of genetic cloning

Selective Breeding

• In animals – dogs, cows, sheep, cats and so on. To produce certain traits

• In plants for taste, texture, shelf life• Is done by choosing parents with the

required traits. These are then bred to produce offspring.

• Sexual reproduction will ensure variation

MendelStudied peas and concluded that characteristics were passed on from one generation to another.

Law of segregation – the 2 alleles separate when gametes are formed, one allele into one gamete and the other into another

Law of independent assortment – any gamete of the father can fertilise any gamete of the mother

Genetic Crosses

Evolution

• Most organisms overproduce• Population numbers remain constant• Sexual reproduction ensures that all

offspring exhibit variation• These variations are inherited from the

parents• From these Darwin produced his theory of

evolution

Darwin

Evidence for evolution

•Fossils

•Homologous structures –bat’s wing, forearm, horse’s leg.

New Species – Survival of the Fittest

• The peppered moth• Pale ones no longer camouflaged during

the Industrial Revolution – were no longer camouflaged

• Darker ones survived to reproduce and some of their offspring were even darker

• This is survival of the fittest