More Biology

The effect of diffrent antibiotics on bacteria can be measured in the laboratary. This is done by using small discs of paper containing antbiotics.The discs are placed in a dish containg bacteria growing on gel. The clear zone that forms around each disc is where the bacteria has been killed.gel tests arer useful, but the body is more complicated than the gel.The results in the body may be diffrent.

Immunity to a disease can be gained without ever having had the disease.A newborn baby receives antibodies from its mother in the first few days that it feeds on her milk.

Immunisation(Vaccination) usually involves injecting or swallowing a vaccine contianing samll amounts of dead or weak forms of the pathogen.

Because the patogen is weak or inactive,the vaccine does not makeyou ill,but your white blood cells still produce antibodies to destroy the pathogen .Your white blood cellswill recognise the pathogen if it gets into your body and respond by quickly producing antibodies.The pathogen does not get a chance to reproduce enough to make you ill.

Like all living organisms,bacteria and fungi need nutrient to grow and reproduce. In the labatory,nutrients are often suppliedto the microorganisums,also known as microbes, in a gel called agar. It melts at 98'C and,as a liquid, it can be poured into plstic or glass perti dishes.It solidifies at about 44'C.Microbes cannot digest agar,so it is not used up as they grow.

Besides nutrients,many microbes need a temperature between 25'C and 45'C to grow.In school laboratories,the oetri dishes are put into a cabinet , or an incubator, set at a maxamum tempurature of 25'C .Pathogens could accidently be present in the culture dishes,so keeping the temperature at  a maximum of 25'C minimises health risks from them,as they will grow much les well at low temperatures.

The air,your surfaces around you,your skin and clothes all have microorganisms on them.If you culture microorganisms in the laboratory,it involes growing very large numbers of bacterial cells.If saftey procedures are not followed, you may accidently introduce a harmful microbe into a harmless strain that you are growing.

Work is carried out near the upward draught from a lighted bunsen burner.The upward movement of air around tghe bunsen burner minimisies the risk of airborne microbes falling onto culture plates.

The nervous systerm is made up of mainy 3 parts; the brain, the spinal chord and neurones,or nerve cells.

it has receptors in the; eyes that are sensitive to light. Ears that are sensitive to sound and to changes in postion, thus enabling us to keep our balace. Tounge and in the nose that are sensitive to chemicals and enable us to taste and smell. Skin that are sensitive to touch,pressure,pain and temperature changes.

There are 3 types of neurone:

Sensory neurone-carry impulses from the receptor to the spinal chord.

Relay neuones-carry impulses through the spinal chord and up to the brain and from the brain back along the spinal chord.

Motar neurones take impulses from the spinal cord to the effector.

An effector can be a muscle that is madfe to contract, or a gland that secretes a chemical , for example a hormone.

Neurones are not joined to each other.There is a small gap between them called a synapse. When an impulse reaches the end of a neurone, chemical is released.This travels across the gap, and starts an impulse in the next neurone.This means the message can only travel in one direction.

when pain is detected by a sensory receptor in your finger,it sends an impulse along the sensory neurone to a relay neurone in your spinal chord.The relay neurone sends an impulse in an arc via a motor neurone to an efftor, a muscle, which contracts, pullig your hand away.This is called a reflex action.There are other types of reflex actions such as coughing and blinking.These are needed to protect us from being hurt or from damage our tissues.

Many of our bodys processes are controlled by chemicals called hormones. These are produced by organs called glands.the hormones pass from glands into the blood stream,which transports them aound the body .Each hormone affects one or more organs,known as target organs.

Every  month,an egg develops inside a female ovary. at the same time, oestrogen causes the lining of the womb(uterus) to become thicker, ready to recive a growing embryo. If the egg is not fertilised, the womb lining breaksdown,causing bleeding from the vagina.the monthly cycle of changesthat take place in the ovaries and womb is called the menstrual cycle.

A women can take the contraceptive pill to stop her from becoming pregnant.The pill contains hormones that have tyhe same effect on the pituatray gland as oestrogen.These hormones stop the pituitary gland making the hormone FSH.This means that no eggs will mature in the ovaries.

many women arwe infertile because of blocked oviducts, of fallopian tubes.This means that eggs cannot travel from the ovaries to the womb.Nor can sperm travel upwards to meet an egg.This type of infertility can be treated by useing IVF.This is literally means fertilisation in a test tube,which led to the term 'test tube baby'

The first stage of IVF is to obtain eggs from the women.She is given injections of FSH to stimulate the maturation of several eggs.Eggs are collected just before they aree relased from the ovary.

PLant shoots naturally grow towards the light.This is called positive phototropism.The reason plants do this is so that their leaves get the maxaimum amount of light for photosynthesis (the process where they make tgheir own food by reacting carbon dioxide and water in the presence of sunight)

Plant hormones called auxins cause this bending towards the light.They are found in the tip of the shoot. Where they are preset the cells become longer and divide faster,so the plants get taller.

Whem light is all around the auxins the plant grow straight.

When the light is shining from 1 side the auxins move the oppisite side to the light,this causes the cells to grow more.

Geotropism or gravi tropism is when a plant moves as a result of ravity.Roots are positivly geotropic as they grow towards gravity.

Auxin is produced in the tip of the roots and shoots.It travels away from the tips but sinks to the lowerside of the shoot and root as a result of gravity.

In a shoot, Wherethere is auxin that side grows more. therefore the shoots bend up.

In a root,where there is auxin that side grows less,so the other side grows longer and it bends down.