Biology unit 1


Inherited factors:

Inherited factors (Genes) are not lifestyle factors, but they can affect health.

For example, some people have genes that give them a higher blood cholesterol level than other people who eat the same diet.

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Body mass:

If more energy is expended in exercise than gained in food -> The body loses mass.

If more energy is gained in food than expended in exersise -> The body gains mass.

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Pathogens and infection:

Micro-organisms that cause disease are called pathogens. 

Pathogens include some bacteria and viruses.

When a few pathogesn infect us, they can reproduce very rapidly. 

Large numbers of pathogens can make us ill.

Bacteria are much smaller than our cells and they may release toxins that make us ill. 

Some types of bacteria invade and destroy our body cells.

Viruses are much smaller than bacteria.

They take over body cell's DNA causing the cell to make toxins or cause damage.

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Semmelweis was a doctor is 1800s who wondered why many women died of infection soon after childbirth.

He realised that doctors might transfer infection between patients on their hands.

He insisted that doctors washed their hands before examining a patient.

Death rates fell rapidly in wards where doctors washed their hands.

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The immune system:

The body has different ways of protecting itself against pathogens.

The immune system helps to protect the body against pathogens. 

White blood cells are part of the immune system.

1- Some white blood cells ingest pathogens and destroy them.

2- Some white blood cells produce chemical antibodies that attach to pathogens and destroy them.

3- Some white blood cells produce anti- toxins that destroy toxins made by pathogens.

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The antibodies produced by a white blood cell are specific for one kind of pathogen.

This means they can only destroy that kin dof pathogen.

They cannot destroy another kind of bacterium or virus.

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White blood cells respond to infection by making antibodies.

After an immune system remembers how to attack that pathogen.

The white blood cells release more antibodies more quickly. So the pathogens are killed before you even feel ill.

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Vaccination is a way of making someone immune to a disease. 

This means injecting dead or weakened pathogens of that disease.

This causes white blood cells to create antibodies in the same way they would if the body was actually infected.

If the live pathogens infects you in the future, your immune system remebers the pathogens so remebers how to destroy them quickly so you dont fall ill.

You are immune.

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Mutation of Pathogens:

A mutation produces a new strain of a pathogen.

Anti-bodies against the old strain may not recognise the new strain.

People who were vaccinated against the the old strain are not immune to the new one. 

The new strain may spread rapidly causing an epidemic or pandemic. 

Epidemic= Many people catching the disease at the same time.

Pandemic= Many people in different places have the same disease at the same time.

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Using anti-biotics:

Antibiotics are medicines that kill bacterial pathogens inside the body. 

Specific bacteria are only killied by a specific antibiotic so the correct antibiotic must be used.

Deaths form bacterial diseases have greatly decreased where antibiotics are used.

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Antibiotic resistance:

Mutation can produce new anti-biotic resistance strains of bacteria. 

When the antibiotic is used, non-resistant bacteria die but reisitant bacteria survive and reproduce. 

The population of resistent bacteria increases. Infections can only be treated with a new antibiotic.

If there is no new antibiotic to control the infection, it may spread rapidly, causing an epidemic or pandemic.

Antibiotics do not cause bacteria to become resistant, nor does failing to complete the course of antibiotics.

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Problems with viruses:

Viruses reproduce inside the cells of another organism and damage the cells. 

However, antibiotics do not affect viruses. 

Drugs that kill viruses may also harm human cells, so viral diseases can be harder to treat.

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The action of disinfectants and antibiotics can also be studied using cultures of microorganisms.

Other microorganisms from the air and surfaces can easily contaminate cultures when they are becoming prepared. Several techniques can help to prevent this. 

1-  Sterilising dishes and culture media: Steriliation kills microorganisms. Petri dishes can be sterrilised by autoclaving or heating to high temperatures.

2- Sterilising inoculating loops: The loop is sterilised in a hot flame and then cooled, before using it to transfer microorganisms to the growth medium.

3- Sealing petri dishes: The lid  is secured to the dish with tape to stop microorganisms from the air from getting in.

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Stimulus: A change in the surroundings.

Nervous system: Detects stimuli and coordinates a response. 

Response: Change in organism's behavious as a result of a stimulous. 

Eye > Is sensitive to light.

Ear -> Sensitive to sound and helps us to balance.

Nose -> Chemicals in the air (smell).

Toungue-> Chemicals in solids and liquids (Taste).

Skin -> Touch, pressure, pain and temperature.

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Nerves contain nerve cells (Neurons), they connect to the central nervous system (Brain and spinal cord) to receptors and effectors. The brain co-ordinates a responce.

Reflex actions are automatic responces that are very fast and do not involve thought. 

1- A receptor cell responds to a stimulous by producing an electrical impulse.

2- The impulse passes from the receptor along a sensory neuron to the central nervous system. 

3- The impulse passes from the sensory neurone to a relay neuron in the central nervous system.

4- The impulse passes from the relay neurone to a motor neurone. 

5- The impulse passes along the motor neurone to the effector. 

Effectors are muscle that respond by contracting or glands that respond by secreting chemicals.

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Controlling internal conditions:

Water content: Water is lost from:

The lungs when we brethe out. 

Skin in sweat to cool us down.

Kidneys in urine. 

Ion content: Ions are lost from:

   Skin in sweat.

   Kidneys in urine.

Water and ions are taken in to the body by food and drink.

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The menstrual cycle:

It is controlled by several hormones:

FSH: From the Pituitary gland. Causes the egg in the ovaries to mature -> Stimulates the ovaries to produce hormones including oestrogen.

LH: From the Pituitary gland. Causes an ovary to release an egg.

Oestrogen: Secreted in the ovaries. Prevents further production of FSH so no more eggs mature this month.

1- The lining of the womb breaks down.

2- Lining of the womb gets thicker.

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Oral contraception:

They contain hormones that inhibit the release of FSH which means: 

No eggs mature.

So no more eggs are ready to be released from an ovary.

They may contain oestrogen and progesterone.

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Increasing fertility:

Fertility drugs contain the hormones LH and FSH.

The drugs can help women who produce too little FSH by stimulating eggs to mature and then be released.


1- Fertility drugs given to a woman to stimulate eggs to mature.

2- Eggs are taken from the ovaries.

3- The eggs are mixed with sperm in a dish for fertillisation.

5- When the embryos are tiny balls of cellsm one or two of them are placed in the mother's womb to develop. 

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Plant responses:

Plants respond and change in light, moisture and gravity by changing how they grow. 

Growth in response to light is Phototropism.

Plants response to gravity is Geotropism.

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Plant hormones:

Auxin is the plant hormone that controls phototropism and geotropism.

Auxin is produced in the shoot or root tip then moves away from the tip to where it affects cells.

Auxin causes plant shoot cells to elongate more rapidly. 

Auxin reduces elongation in plant root cells.

If different cells in a root or shoot contain different amounts of auxin, this causes unequal growth rates. 

This will change the direction of growth of the whole shoot or root.

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Auxin and Geotropism:

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Plant hormones:

Plant growth hormones can be used in: Agriculture (Growing crops in a field).

    Horticulture (Growing flowers, fruit and veg).

Weedkillers: (Herbicides): They kill broad leaved weeds in grass such as wheat. Killing the weeds in                                      crops reduces competition for water and nutrients in the soil.

Rooting hormones: Plant hormones are used in rooting powder. If the stem of a plant cutting is                                   dipped in the powder, the stem will develop roots more quickly.

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New drugs:

1- In the lab: They are tested on animals, cultures of cells and cultures of tissues. These models                        help to predict how the drugs may behave in the human body.

2- Clinical trial- Stage 1: Healthy volunteer, Very small drug dose to check that the drug is not toxic.

3- Clinical trials- Stage 2: Different patients with the disease are given the drug in different doses.                                     This tests if it is effective and to find out what the optimum dose should be.

A placebo is a mock of the drug. Patients given this drug are unaware and their results are compared with the real drug results.

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Thalidomide and statins:

Using Thalidomide: It caused problems when it was first subscribed.

1- Developed as a sleeping pill.

2- Also used to control morning sickness in pregnant women. 

3- Caused severe limb abnormalities in babies born to many women who took the drug. 

4- Thilidomide was then banned: Though it is now used to treat diseases such as leprosy.

Due to thilidomide, drugs are now not tested on pregnant women and they are more throughly checked also.

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Recreational drugs:

A drug used for pleasure rather that medical purposes:

Legal: Tobacco , Alcohol.

Illegal: Cocain, cannabis, heroin. 

Cannabis is a gateway drug and can also lead to mental health issues and illness.

Addiction: They change chemical processes in the body to make the person dependent on it. They will begin to need more and more for it to have an effect. If the person stops taking the drug, they will have withdrawal symptoms.

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Drugs in sport:

Stimulants: Increase the rate of body functions such as heart rate. This means that more oxygen                      and sugar get to the muscles more quickly so they can release energy more quickly.

Anabolic sterioids: Stimulate muscle growth. Bigger muscles can help move bigger weights.

Drug bans in sport:

It is considered unethical in sporting competition. This is because ... 

Side effects of the drugs can harm the athletes. 

It may give an unfair advantage to other athletes which do not use them. 

Some sports drugs are legal and can be perscrbed but all are banned in sporting competition.

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Plants compete for: Light and space, water and nutrients. 

Animals competer for : Survical, territory, food and mates.

Many organisma are food of other organisms. Some animals and plants have special features that deter preditors... 

Some animals advertise they are poisonous with bright colours. 

Some uses colours to make them look freightening : 'Eyes'.

Some plants have big thorns, some are poisonous.

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Animals in the artic:  Small ears to reduce heat loss. Less surface area. 

White colour to camouflage in to their surroundings. 

Thick fur and blubber to insulate.

Large feet for better grip on ice.

Animals in dry environments: Camels -> Hump of fat that is a food store, fat also releases water as                                                           a result of respiration.

      Can drink large quantities of water at a time.

      Have a thick coat on top of their bodies to protect from the       sun. 

Elephants: Large ears transfer body heat to air quickly.

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Extreme and Extremophiles:

Extreme environments: High levels of salt, temperature and pressures.

Extremophiles: Organisms that have adaptations so they can tolerate very extreme environments.                         Many extremophiles are microorganisms.

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Environmental factors -> Living -> Prey, competition, predator. 

-> Non living -> Light, temperature, rainfall, oxygen, pollution.

Pollution indicators:

Lichens: Indicates lots of air pollution or no air pollution (Clean air lichens).

Blood worms: Highly polluted water.

Mayfly larvae: Unpolluted water.

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Energy and biomass:

A source of energy for most food chains is light energy from the sun. 

Light energy from the sun -> Small amount of energy captured by green algea and plants -> Photosynthysis -> Chemical energy stored in substances in cells and tissues. 

Mass of living material = Biomass.

Pyramids of biomass: 

Start at the bottom of the food chain.

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Materials in living organisms (Biomass) -> Dead organisms -> Wate from living animals -> Decay by microorganisms -> Materials in environment -> Materials removed from the environment by organisms and used for growth and other processes.

Recycling kitchen and garden waste: 

They can be used to make compost, The conditions needed are ... 

Moisture, warmth and oxygen.

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The carbon cycle:


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The carbon cycle:

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In the cell: Nucleus, cytoplasm -> Chromosomes carrying genes -> Different genes control the development of different characteristics. 

Causes of differences: 

Inherited genes (Eye colour).

Combination of causes (Weight, skin colour).

Differences in conditions which they developed (Scars from falling off a bike - Environmental causes).

Differences between individuals  of the same kind.

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Sexual reproduction: Gamete from the mother fuses with one from the father -> Mixes genetic information form each parent -> Offspring have different combinations of genes so show variety in characteristics. 

Asexual reproduction: No fusion of gametes only on parent -> No mixing of genetic information -> All offspring  have the same genes as parent and each other.

Taking plant cuttings: New plants can produced quickly and cheaply by taking cuttings from a older plant. 

Several cuttings taken from parent plants. 

Cuttings grown into new plants that are genetically identical (Clones).

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Tissue culture: Plant tissue culture is like taking plant cuttings, but with very small pieces that contain just a few plant cells.

The new plants are all clones because their cells contain the same genes as the parent plant.

Embryo transplants: Splitting embryos makes it possible to produce small numbers of clone animals at the same time. This is most often done with high-quality farm animals.  

  • All  offspring are genetically identical (Clones).
  • Each embryo is placed in the womb (Uterus) of a different surrogate mother to develop until ready for birth.

Adult cell cloning: 

  • Cells devide to form embryos. 
  • Embryo inserted into womb of adult female c to develop until birth.
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Embryo transplants:


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Adult cell cloning:


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Genetic engineering:

Genetic engineering is the transfer of a gene from one organism to a different organism so that the desired characteristics is produced in that organism.

The gene for a characteristic is 'Cut out' of a chromosome using enzymes -> The gene is inserted into a chromosome inside the nucleus of a cell in a different organism -> The cell of this organism now produces the characteristic from the gene.

GM crops have been genetically modified to give them new characteristics such as:

Resistance of the attack by insects.

Resistance to herbicides, so that fields can be sprayed to kill weeds, but not the crop. 

These characteristics can help the crop grown better and produce more food.

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Issues with new science:

Economic: Related to money -> Is it worth the cost. 

Social issues: People and society -> Are there benefits greater than the problem.

Ethical: Rights, fairness -> Is it fair? 

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Change over time. 

Organisms are classified as plants, animals or microorganisms using the similarities and differences. 

They can show how organisms are related.

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Evolution tree:

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Evolution tree:

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Theories of evolution:

1- Darwins: Evolution happens through natural selection -> This only works on inherited characteristics.

Relatively rapid evolution can occur if.... A new form of a gene occurs due to mutation.

There is a large change in the environment.

Individuals in a species vary in their characteristics some of these variations are caused by genes.

Some variatins are better suited to the environment than others.

Individuals with the better suited variations are more likely to breed successfully and pass on genes for the better suited variations. 

The next generation will contain more individuals with the better genes suited for variation.

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Theories of evolution:

Lamarck's theory: Long before Darwin, Lamark thought evolution was due to the inheritance of characteristics changed by the environment.

Environmental factor, Weight training -> Causes an aquired characteristic -> Aquired characteristics inherited by offspring. 

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