Biology - EDEXCEL IGCSE - Finished

So that's all there is to IGCSE Biology. Once again now all you have to do is learn these notes, memorise them and then you're done.

Good luck in your exams!

PS. I've attached a complete copy in case you're too lazy to read it from the blog (it has a mighty 31 pages).

Click here

Biology - EDEXCEL IGCSE - Use of Biological Resources

Use of Biological Resources:

Greenhouse features:

Feature	How and Why
Soil ions	Fertilisers are added to ensure minerals are present for growth. For example, nitrates are added for DNA and magnesium are added for chlorophyll
Soil pH	Adding lime to make soil more alkaline to create a more suitable pH
Carbon dioxide, light and heat	Glass of greenhouse increases light intensity as well as creating heat. All increase rate of photosynthesis. Fuels can be burnt to create carbon dioxide and heat, needed for photosynthesis.

Pest control:

Disadvantages of using pesticides:

·        Pest may develop resistance against pesticides

·        May cause bioaccumulation and biomagnification which affects the food chain

·        Not specific

Disadvantages of biological control:

·         Does not completely eradicate a pest

·         Less fast

·         More expensive

Fish Farming:

Feature	How and Why
Water quality	Temperature and oxygenation of the water can be controlled to maximize growth
Predators	Fish protected by nets to prevent predators entering
Food	Frequent and high quality feeds. Frequent to ensure that the fish always has glucose for respiration
Diseases	Antibiotics used to kill pathogens and pesticides used to kill parasites to stop fish contracting diseases
Removal of waste products	This ensures that bacteria do not breakdown the organic material and create depletion of oxygen

Use of microorganisms:

The industrial fermenter is kept in aseptic conditions. This involves using hot steam to sterilise the inside of the fermenter. This ensures that there are no microorganisms present to contaminate the product or to create competition. As well as this, the temperature, oxygen concentration, pH and carbon dioxide concentration are all controlled and monitored.

Production of beer:

1.    Barley seeds are soaked in water and laid in the Malthouse to germinate. This creates amylase to digest starch.

2.    The seeds are killed by being heated and dried to make malt

3.    Malt is ground up and mixed with water in a mash tun. The amylase breaks down starch to maltose.

4.    Mash is boiled and filtered

5.    Hops are added for taste and yeast is added to ferment sugars, making beer

6.    Beer is centrifuged, filtered and sometimes pasteurized

7.    Beer is put into casts or barrels.

Production of yoghurt:

1.    Milk is pasteurized at 90°C for 20 minutes

2.    Milk is homogenized to disperse the fat globules

3.    Bacteria is added

4.    Bacteria anaerobically respire to create lactic acid. The low pH causes the lactose to coagulate.

5.    The thickened yoghurt is stirred and cooled to 5°C

6.    Flavourings, colourings and fruit are added

Selective breeding:

Organisms can be controlled by the use of selective breeding. This is where specific organisms with the desired characteristics are chosen and bred together. This method has been able to produce crops that give higher yields, are more resistant to diseases and pests and are more nutritious. The same method can also be applied to animals, producing cows that produce more milk or animals that have an increased resistance to diseases.

Genetic Modification:

Transgenic organisms are organisms which contain the DNA from at least 2 species.

Genetic modification is used to create organisms that are capable of producing the desired proteins that we need such as insulin. This is achieved by first removing the desired gene that codes for the protein production using restriction enzyme. The same restriction enzyme is used on the plasmid of a bacteria. The plasmid and the desired gene are then joined using DNA ligase (an enzyme) to create recombinant DNA. The plasmid is then added back to a bacterium which acts as the vector. The bacteria divide by binary fusion and is eventually placed in fermenters to mass produce the required protein. Viruses can also be used as the vector.

Cloning:

Micropropagation:

First the tip of the stem of the plant is removed using a scalpel. These parts are called explants. The explants are placed in an agar medium that contains nutrients and plant hormones needed for growth. The explants with shoots are then moved to another culture medium containing a different balance of plant hormones that encourages root formation. When the explants have grown roots they are transferred to compost and kept in a greenhouse. The greenhouse is kept moist to reduce water loss. The conditions are also kept aseptic to prevent diseases.

Micropropagation is good as it can produce a large number of plants rapidly. Plants can be grown at any time of the year and plants that are difficult to grow from seeds can be propagated.

Cloning:

To clone an animal, first an egg is taken from a female and enucleated (nucleus removed). Then a body cell is taken from the animal being cloned and inserted into the enucleated egg by giving both a small electric shock. The new cell is then allowed to undergo mitosis until it becomes an embryo where it is then implanted in the uterus of the surrogate mother. The surrogate will then give birth to an animal that is genetically identical to the animal that is being cloned.

Cloning provides the opportunity to clone transgenic animals in order to produce commercial quantities of human antibodies or organs for transplantation.

Biology - EDEXCEL IGCSE - Ecology and the Environment

Ecology and the environment

The organism in the environment:

Ecosystem - a distinct, self-supporting system of organisms interactions with each other and with a physical environment.

Population - all the organisms of a particular species found in an ecosystem.

Community - the population of all the species in an ecosystem.

Habitat - the places where specific organisms in an ecosystem live.

Niche - the role of a certain species.

Quadrats:

1.     Divide sample area into a numbered grid using a tape measure.

2.    Select pairs of coordinates at random.

3.    Place each quadrant at the coordinate and count the number of each species or percentage cover.

4.    Repeat several times (at least 10).

5.    Calculate the mean average.

To overcome biased data random sampling is used though the selection of coordinates at random.

To overcome data due to chance many repeats are done.

Feeding relationships:

Humans inhabit many of the Earth’s ecosystems. An ecosystem is a distinct, self-supporting system interaction with each other and with their physical environment.

Ecosystems have:

•   Producers - green plants that photosynthesise.

•   Consumers - animals that eat plants or other animals.

•   Decomposers - Microorganisms that break down dead material and help in recycling nutrients.

•   Physical environment - the non-biological components such as water, soil and air.

Plants are the source of all the food that animals, including humans, eat. They also create oxygen which aerobic organisms need for respiration. Plants can create oxygen from glucose, starch, sugars such as fructose or sucrose, cellulose and lipids.

Food chains are made up of trophic levels:

Producer —> Consumer (primary, secondary, tertiary etc.)—> Decomposers

Energy and substances are transferred along a food chain. Every time energy is transferred a lot is lost through the lack of digestion and therefore passes out as faeces. Some form excretory products such as urea and some is respired to release energy. Not only this, but a large amount of energy is also lost through respiration. Because of this, only around 10% of energy is used to create new cells and therefore can be passed on to the next trophic level. This means that generally food chains are short as organisms must eat many organisms from the trophic level below. This creates a pyramid shaped pyramid of energy transfer.

Food chains - shows which organisms eats which organisms and shows the direction in which this happens.

Food web - formed when food chains are linked together. They show a more realistic view of a food chain as obviously most organisms eat more than one source of food.

Pyramid of number - represent the flow of energy through a good chain by telling us the number of organisms at each trophic level.

Pyramid of biomass - similar to a pyramid of number except that it uses the total amount of living material rather than number of organisms. It is more realistic that a pyramid of number as the pyramid of biomass will almost always be pyramid shaped. It therefore shows the efficiency of every transfer between trophic levels better.

Pyramid of energy transfer - similar once again to the other pyramids except that it uses the amount of energy as the measure. It is the most realistic way of representing energy transfer. However, it is hard to measure and difficult to scale.

Cycles within ecosystems:

Water Cycle:

Carbon Cycle:

Nitrogen Cycle:

Human influences on the environment:

Carbon Monoxide:

This is a colourless, odourless and tasteless gas which can cause death by asphyxiation. Haemoglobin bind with this rather than oxygen and so a person may become unconscious if it’s breathed in for a certain time as a result of a lack of oxygen.

Sulfur Dioxide:

This is a major constituent of acid rain which kills plants and also ruins the landscape.

Green House Gases:

These include water vapour, carbon dioxide, nitrous oxide, methane and CFCs (chlorofluorocarbons).

The level of greenhouse gases has risen rapidly in the past 100 years. The increasing burning of fossil fuels such as coal, oil and natural gases as well as petrol and diesel in vehicle engines has led to this. The increasing deforestation also means that the greenhouse gas carbon dioxide is used less in photosynthesis.

The increasing levels of greenhouse gases has resulted in the enhanced greenhouse effect. The normal greenhouse effect is where gases absorb some long wavelength infra-red radiation from the sun and re-emit some as longer wavelength IR. This heats up the surface of the Earth. However, with too much greenhouse gases, global warming has occurred where the earth heats up quicker than it should. This has caused the melting of the ice caps and therefore sea level rises, changing ocean currents meaning warm water is redirected to cooler areas, more rainfall in some areas (climate changes), species to become extinct as they cannot adapt fast enough and changes to agricultural practices as some pests become more abundant. Furthermore, changes to the food chain occurs as well as mass migration.

Sewage must be treated as they contain pathogenic bacteria which can cause diseases if drunk and also because aerobic bacteria in the water will deplete the amount of oxygen in the water by breaking down the organic material in the sewage. This then causes death to species not adapted to low oxygen levels.

Eutrophication occurs when excess minerals such as nitrates and phosphates enter a body of water from sewage or fertilisers. Fertilisers can enter the water through leeching as nitrates and such are washed out of the soil by rain since it dissolves in water. This can also occur through surface run offs. Excess minerals stimulates the growth of algae. An algal bloom will develop and block out the light needed for photosynthesis and are also decomposed as they die. This is done by aerobic bacteria which uses up oxygen in the water. This causes oxygen depletion, causing many fish and plants to die. In severe cases, the water will become anoxic (containing very little oxygen) and become smelly from the gases such as hydrogen sulphide and methane which are released by the bacteria. Only anaerobic bacteria can survive conditions like these.

Deforestation:

Each year tens of thousands of hectares of rainforests are cut down. This causes several problems:

1.    Soil erosion occurs as it is exposed due to lack of a canopy meaning the soil is down or washed away.

1.    Leeching occurs where minerals are washed out by rain. This occurs as there are no tree roots to hold the soil together.

2.    Destruction of habitats and reduced biodiversity occurs. Around 50-70% of all species live in rainforests.

3.    The water cycle is disturbed as trees are an important part of returning water vapour from the soil.

4.    The balance in atmosphere oxygen and carbon dioxide changes as photosynthesis decreases. This will cause global warming

Biology - EDEXCEL IGCSE - Reproduction and Inheritance

Reproduction and Inheritance

Asexual Reproduction is when a single parent copies its genetic information, forming a daughter which is genetically identical (clone) to itself. It involves no gametes and fertilisation.

Sexual Reproduction involves gametes which fuse to create a zygote and eventually an embryo which is not genetically identical to the parents.

Fertilisation involves the fusion of a male and female gamete to produce a zygote which then undergoes cell division and develops into an embryo.

Reproduction in Plants

Insect Pollinated Plant:

Wind Pollinated Plant:

 

Adaptations of wind and insect pollinated plants:

Feature	Insect Pollinated	Wind pollinated
Stamen	Enclosed - to force insect to make contact	Exposed - so that wind can easily blow it away
Stigma	Enclosed - insect must make contact Sticky - pollen sticks to it	Exposed - easier to catch pollen Feathery - large surface area to catch pollen
Petals	Brightly coloured, large and scented to attract insects	Small and not scented or coloured as there is no need
Nectaries	Present so as to attract insect	No nectary
Pollen grains	Large, spiky and sticky to attract insects	Small, light, and aero-dynamic so that it can be easily carried bu the wind

Fertilisation:

1.    Pollination occurs where pollen is transferred from the anthers to the stigma. The stigma must be ripe so that chemicals can be produced for the production of pollen tubes and a sugary substance for energy.

2.    The pollen tube grows down through the style and into the ovary. It enters the ovule by the micropyle.

3.    The male nucleus moves out of the pollen grain and moves down the channel created by the pollen tube and ion the ovule.

4.    Fertilisation occurs where the male and female gamete fuse to form a zygote.

5.    The zygote undergoes mitosis in a seed to create an embryo.

Seed and fruit formation:

1.    The petals and anthers die as there is no longer any need for them.

2.    The ovule wall becomes the testa which protects the embryo.

3.    The cotyledon provides the food store for the embryo.

4.    The plumule is the embryonic shoot ad the radicle the embryonic roots.

5.    The ovary becomes the fruit.

Germination:

1.    The dormant seed is buried in soil.

2.    Water is absorbed by the seed through the micropyle.

3.    Food reserve (starch) in the cotyledon is mobilised.

4.    The testa splits as the seed expands.

5.    The radicle grows downwards. The root develops and begins to absorb water directly.

6.    The plumule begins to grow upwards with the cotyledon still fueling growth.

7.    The embryonic leaves of the plumule now clear of the ground and begin to photosynthesise.

Germination requires:

1.    Heat for enzymes to act efficiently.

2.    Water for chemical reactions to take place.

3.    Oxygen for respiration to release energy.

4.    Light is not needed.

Reproduction in Humans:

Male:

Sperm is stored and created in the testes. During intercourse it travels along the sperm duct in the penis and mixes with secreted liquid from the seminal vesicle to form semen. One ovum is released into the fallopian tube each month and when it is in the tube a sperm can fertilise it.

Female:

Menstruation:

Hormones are very important for this process. First the follicle stimulating hormone (FSH) stimulates the growth of the follicle containing an ovum. At the same time FSH stimulates the release of oestrogen which begins the re-thickening of the uterus lining and also slows the release of FSH and stimulates the release of LH (lutenising hormone). When LH is at its peak, ovulation occurs where the ovum is shed by the ovary. If sexual intercourse occurs, what is left of the follicle forms a structure called the corpus lute. This releases progesterone which completes the thickening of the uterus walls and inhibits production of FSH and LH, stopping any further ovulation. If the egg is not fertilised then the corpus lute breaks down and the lining of the uterus is shed through menstruation. Progesterone is also used during pregnancy to stop menstruation. It is produced by the placenta.

Placenta:

The placenta allows the embryo to obtain oxygen and nutrients and get rid of CO2 and excretionary waste (e.g. urea). The umbilical cord used to carry the blood containing the substances towards and away from the foetus. The placenta is also responsible for secreting progesterone in order to maintain a thick layer of endometrium in the uterus.

Amnion:

The amnion encloses the foetus and secretes amniotic fluid which protects the foetus from bumps while the woman is moving.

Secondary Sexual Characteristics:

Boys: controlled by testosterone

•   Growth of penis and testes.

•   Growth of facial and body hair.

•   Muscle development.

•   Breaking of the voice.

Girls: controlled by oestrogen

•   The breast develops.

•   Menstruation starts.

•   Growth of armpit and pubic hair.

Inheritance:

DNA or deoxyribonucleic acid contains two strands of alternating sugar and phosphate groups coiled to form a double helix. The strands are linked by two nitrogen bases at each "rung". There are four different bases: Adenine(A), Thymine(T), Cytosine(C), and Guanine(G). In DNA the bases are always paired. So if on one strand the base is A, the other must be T and likewise if on one strand it is C then on the other it must be G.

 

The nucleus of cells contains chromosomes on which genes are located. A gene is a section of a molecule of DNA which dictates a certain characteristic of the organism.

A certain genes can take different forms which although creates the same characteristic, doesn't create the same exact feature. For example, a gene may code for green eyes while the same gene might code for blue eyes. These different forms of the same gene are called alleles. Alleles give rise to differences in inherited characteristics.

Definitions:

•   Genes - a small section of DNA that determines a particular feature by instructing cells to produce a particular protein are called genes.

•   Alleles - an alternative form of a gene which gives rise to differences in inherited characteristics.

•   Dominant - a feature will always have two alleles. If one allele’s characteristic is present while the other is not then it is said to be dominant.

•   Recessive - if one allele is dominant then the other is said to be recessive.

•   Homozygous - contains two copies of one allele (e.g. TT, aa).

•   Heterozygous - contains two different alleles (e.g. Tt, Aa).

•   Genotype - describes the alleles each cell has for a certain feature.

•   Phenotype - a feature that results from the genotype.

•   Codominance - if two alleles are expressed in the same phenotype.

•   Diploid cells - cells with chromosomes in homologous pairs are said to be diploid. In humans the diploid number is 23 meaning each cell has 23 chromosomes.

•   Haploid cells - cells with chromosomes not in a homologous pair is said to be haploid. In humans the haploid number is 46.

The sex of a person is determined by a pair of chromosomes, XY in a male and XX in a female. The overall ratio of male and female births is 1:1

This can be shown by this diagram:

	X	X
X	XX (female)	XX(female)
Y	XY(male)	XY(male)

Mitosis is the nuclear division of somatic (body) cells to create genetically identical cells which are used for growth, repair, asexual reproduction and replacing worn out cells.

Meiosis occurs to produce haploid cells that are used in sexual reproduction. It involves a similar process to mitosis except that there are two divisions compared to one in mitosis. Meiosis creates four cells, each with half the number of chromosomes and creates genetically different gametes.

A human male can produce millions of genetically different sperm cells and a female holds thousands of genetically different egg cells. This large pool of genetically different gametes and the fact that fertilisation is random allows genetic variation of the offspring. Not only is variation produced by genetics, it can also be produced through the environment.

A mutation is a rare, random change in genetic material which can be inherited. Many mutations are harmful but some are neutral and a few are beneficial.

Mutations that are beneficial can cause the mutant organism to increase in population through natural selection. An example of this is in bacteria that have mutated to be resistant to antibiotics. The variation in the species is that there are bacteria that are resistant and those that are not. The bacteria that are resistant live for longer and can therefore multiple more while the non-mutated species die out as they lack the advantage. This means they eventually populate the entire species.

The chances of mutations can be increased through mutagens. Examples of these are ionising radiation such as ultraviolet light, X-rays and gamma rays and many different chemicals, both natural and manmade (e.g. benzene).