bioligy revision cards!


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Drugs and solvents are powerfull chemicals that change the way you think, feel and behave. However not all drugs are harmfull.

A drug is a chemical which affects the bodies nervous system

stimunlants such as caffeine and cocaine speed up the nervous system

Depresents such as heroin slows the nervous system down.

Drug trails are taking place every day, but what is put out into the shops needs to be trailed and tested repeatedly.

Thalidomide was an over the counter drug which was a sleeping pill, but also found to help woman suffering from morning sickness. Because the drug wasn't tested properly many woman were delievering babies with disformalities. Thalidomide is now banned, but was found to have help people with leprosy.

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Controlling Disease!

Microorganisms that cause disease are known as pathogens.

Bacteria are different from animal cells

- the cells do not have a proper nucleus

-they do have a cell wall outside the cell membrane

-they are much smaller

Viruses aren't really cells at all

-they have a protein coat outside them

-inside they have just a few genes

Viruses invade healthy cells using its genetic material to make more virus particles

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Barriers to disease!

The body has a number of ways of stopping pathogens getting in.

-the skin acts as a barrier

-air passages to the lungs make a  that traps the pathogens tiny hairs called cilia push it to the throat where it can be swallowed.


-Ingesting the pathogens and destroying them with enzymes

-Producing antibiotics which destroy particauler bacteria and viruses

-Making antitoxins which neutrilise the toxins released by pathogens.


A vaccine contains a mild or dead form of bacteria/virus, when in the body it stimulates the white cells to produce antibodies

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Adaption and Competition

An adaption is a feature that enables an organism to survive in its normal habitat

Different organisms have to cope with a variety of different conditions.

For organsims to survive they may adapt special features or a certain type of behaviour

In nature competition means animals and plants competing for resources that are in short supply

plants usually compete for space, light, water and nutrients from the soil.

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Sexual reproduction

Nucleus of a cell contains chromosomes which carry the genes that control the body.

Mnay genes have different forms alleles which may produce different characteristics.

Sexual reproduction- involves the fusion (joining) of male and female gametes.

Asexual reproduction- Where there is no fusion of cells and only one indiividual is needed as the single parent.

Asexual reproduction results in indeviduals that are genetically identical to the parents and are known as clones.

Sexual reproduction results in offspring that have a mixture or genes from each of the two parents. These individuals show more variation than offspring produced by asexual reproduction.

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new plants can be produced quickly and cheaply by taking cuttings from older plants.

the new plants are genetically identical to the parent plant.

tissue culture- using small groups of cells from part of a plant

embryo transplants-splitting apart cells from a deveolping anmal embryo before they become specialised, then transplanting the identical enbryo's into host mothers.(surrogates)

Fusion cell and adult cell cloning- The nucleus from an adult cell can be inserted into an egg cell with no nucleus. The cell divides to produce an individual with all the characteristics of the adult nucleus donor.

disadvantage- widespread use in agriculture reduces the number or alleles available for selective breeding.

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Genetic Engineering

Genetic engineering means transferring genes from one type of cell to another.

Genes carry all the instructions for how your body works, the technique used in genetic engineering is to get the cells of microbes to make the usefull chemicals

- first the human gene that codes for the usefull chemical is identified ( eg, insuling)

-special enzymes are used as "chemical scissors" to cut out the usefull gene from the rest of the DNA

-A circular piece of DNA, called a plasmid, is removed from a bacterium.

- The human gene is inserted into the plasm- Anilid and the plasmid put back into a bacterium.

- The bacterial cells multiply very rapidly in a fermenter. They make exact copies of themselves and the human gene. So lots of the usfull chemical, like insulin, is produced.

-Animals and plants can also go through the procedure.

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Fossils are the preserved remains of animals and plants from millions of years ago.

Fossils form in a number of ways

- The hard parts of animals do not decay easily. Bones, teeth and scales may get burned by sediment which turns to rock. The hard parts become replaced by minerals giving an exact copy.

-Soft parts can form fossils if decay is slow. They can be replaced with hard minerals which take on exactly the same shape.

- If conditions for decay are absent then the plant or animal may be preserved, eg. if buried in peat bogs or in the ice.

Fossils give scientists imformation about how much or how little different organisms have changed since life began on earth.

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Mutations are new forms of genes resulting from changes in existing genes.

Mutations can occur naturally but can also occur due to

- Exposure to ionising radiation, eg. ultra-violet light

- The greater dose of radiation, the greater chance of mutation

-Certain chemicals.

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Evolution is the gradual change in the characteristics of a species over time

The theory of evolution states that all species of living things which exist today have evolved from simple life-forms which first developed more than three billion years ago!

Charles Darwin's theory of evolution by natual selection was only gradually accepted by other scientists. Darwins theory of natural selection as follows:

- Organisms produce large numbers of offspring.- In any particauler species there is variation between individuals, because of differences in their genes.- Predation, disease and competition cause many individuals to die. There is a "struggle for existence" between individuals of the same species.-Individuals with characteristics most suited to their enviroment are more likely to survive and breed. This is often called "survival of the fittist"

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Since life on earth began, many species have become extinct.

This may have been due to changes in the enviroment, such as climate, or the appearance of new preators, new diseases, or new compititions. Unless evolution occurs and species become better adapted to survive these changes they may become extinct.

Most mutations are harmfull and can result in uncontrolled cell devision of body cells. These are cancers. But some mutations are eutral in their effects and may increase the changes of survival of an organism and any offspring that inherit the mutant gene.

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Acid Rain

Burning fossil fuels may release sulfur dioxide and nitrogen oxides. These gases dissolve in rain making it more acidic.

Acid rain can:

- Cause trees to lose all its leaves

- Make lakes and rivers acidic that all aquatic life is killed.

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Population Growth

During th last 300 years the population on earth has gone from 1billion - 6billion. This rapid growth is still continuing. As well as the rise in population, living standerds have also increased.

As a result:

- Raw materials like non-renewable energy resources are being rapidly used up;

- More waste is being produced;

- I fhtis waste isnt disposed of properly more  pollution will be caused.

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The greenhouse effect

The "greenhouse effect" is the trapping of heat in the earths atmosphere due to increasing levels of gases such as carbon dioxide and methane.

This effect may result in an increase of a few degrees in the earths temperature. This is known as global warming.

The effects of global warming are:

- A rise in see level and flooding low-lying land

- Big changes in weather patterns in different parts of the world.

Greenhouse gases are increased because of;

- Increased burning fossils fuels

- Increased cattle and rice farming. ( both release methane)

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Eutrophication results from excess fertilisers being washed from soil into lakes and rivers.

The sequence on events is;

- Water plants grow rapidly

-due to competition for light many plants die

-there is an increase on microorganisms feeding on dead plants

-the oxygen level in the water goes down as microorganisms use of respiration

- many fish and other aquatic animals die from depletion of oxygen.

Untreated sewage also provides food for microbes and so can also cause eutrophication.

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All of our receptors start with a stimulus (a change we can detect). Receptors are cells that can detect stimuli.

Information from receptors passes along cells in nerves called neurons to the brain. The brain co-odinates the response.

Stimulus                                                              Receptor

Light                                                                    Eyes

sound and balance                                             Ears

taste and smell                                                   Nose and tongue

Touch, pressure and                                          Skin

temperature change

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How the body reacts to a stimulus

Refelx actions often includes three neurons: sensory, relay and motor.

Impulses from the receptor pass along the sensory neurone, to the brain or spinal cord. As a junction (synapse) between the sensory neurone and a relay neurone in the brain or spinal cord, a chemical is released which triggers off an impulse in the relay neurone. A chemical is again released into the synapse between the relay neurone and a motor neurone.

Stimulus -> Receptor ->Co-Ordinator -> Effector -> Response

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Hormones are chemicals that coordinate many processes in the body. They are secreted by glands and transported to their target organs through the blood stream. The body responds to these hormones. Responses may last a few minutes eg. adenaline, or go on for years eg. growth hormone. Hormones affect such body precesses as the rate of metabolism, growth and sexual development.

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Control of the menstrual cycle

Hormones in the woman control:

- monthly release of an egg from the womans ovaries

- The changes in the thickness of the lining of her uterus (womb)

These hormones are produced by the pituitary gland and ovaries. These events are known as the menstrual cycle.

- Fertility drugs which stimulate the ovaries to produce eggs 

- oral contraceptives which prevent the release of eggs from the ovaries

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Controlling fertillity

- Fertility drugs contain the hormone FSH. If this drug is given to a woman whose own level of FSH is too low, Then it can stimulate her ovaries to proudce eggs.Un fortunately, fertility treatmant does not always work. But it can also work too well, to many eggs are released resulting in multiple buirths.

- Oral conraceptives co ntain oestrogen, to inhibit FSH production so no eggs mature to be fertilised. Dwrawbacks are failure to take the pill regularly can result in pregnancy side effects such as headaches, sickness circulatory problems, can occur in some women.

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The hormones of the menstrual cycle

- the pituitary produces FSH which starts the cycle off. It causes an egg to mature in one of the ovaries. It also stimulates the ovaries to produce hormones which incules oestrogen.

- Oestrogen is secreted by the ovaries and stops the secretion of FSH by the pituitary, so no more eggs develop. It also causes the lining of the uterus to thicken to receive a fertilised egg, should that happen.

- Oestrogen also gives a signal for the pituitary to secrete another hormone called LH.

- - Lh stimulates the ovary to release an egg (ovulation). This occurs at about the middle of the menstrual cycle, when the lining of the uterus is thickened to recieve a fertilised egg.

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A balanced diet

A healthy diet contains the right balance of the different foods you need in the correct amounts

- carbohydrates for energy

- proteins for growth and repair of cells

- fats as a storeof energy and for insulation

- vitamins and minerals in small amounts for good health

A person is malnourished if their diet is not balanced. If a person does not have the right amount of certain foods, such as vitamins and minerals, they may suffer deficiency diseases.

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Metabolic rate

The food that you eat should also give you the right amount of energy. The rate at which all the chemical reactions in the cells of your body take place is called your metabolic rate.

This varies with the amount of activity you do and the proportion of muscle to fat in your body. It may also be affected by inherited factors.

The less exercize you take and the warmer it is, the less food you need. People who exercize regularly are usually fitter than people who take little exercize. When you exercize, your metabolic rate remains high for some time after you have finished.

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You need to balance your energy intake with your energy output. In the developed world too much food and too little exercize are leading to high levels of obesity and dieseases linked to excess weight:

- arthritis (worn joints)

- diabetes (high blood sugar)

- high blood pressure

- disease of the heart and blood vessels.

Some people in the developed world suffer from health problems due to lack of food, these include, muscle wasting and low body weight, reduced resistance to infections, irregular period in women.

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There two types of fat saturated fat that comes from animals and unsaturated fat that comes from planed fats can increase the level of cholesterol in the blood.

Cholesterol is a substance which is made by the liver and found in the blood. The amount of cholesterol in the blood depends upon a combination of diet and inherited factors. High levels of cholesterol in the blood are linked to an increased risk of heart disease and an increase in blood pressure due to narrowing to arteries. Lipoproteins: Low-density lipoproteins (LDLs) are "bad" cholesterol and can cause heart disease. High-density lipoproteins (HDLs) are "good" cholesterol. The balance of LDLs and HDLs is very important to good heart health. Saturated fats increase blood cholesterol levels. Mono-saturated and polyunsaturated fats may help to reduce blood cholesterol levels and to improve the balance between LDLs and HDLs. To much salt in the diet can also lead to increased blood pressure for 30% of the poplation. Processed foods often contain a high proportion of slat and fat.

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