Biology Notes for IGCSE 2014 (all in one)

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Business Studies Notes for IGCSE (All in one) in pdf

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# 155 Summary of Human and Ecosystem

CO₂ and methane are greenhouse gases, trapping outgoing long wavelength radiation in the atmosphere and warming the Earth. Increased concentrations of these gases are causing global warming.

#154 Conservation of species, recycling sewage and paper

Koala is an endangered animal.

Conservation is the process of looking after the natural environment. Conservation attempts to maintain or increase the range of different species living in an area, known as biodiversity.

#153 Pesticides, herbicides, nuclear fallout and non-biodegradable plastics

DDT spraying. 

Some pesticides are non-biodegradable and stay in the environment for a long time. For example, DDT has been a very effective insecticide, used to kill mosquitoes to reduce the spread of malaria. However, because it does not break down, it enters water systems such as lakes, where it is absorbed into plankton. 

#152 Greenhouse gases and global warming

Some gases in the Earth’s atmosphere stop heat radiating into space from the Earth. This is called the greenhouse effect and the gases involved are called greenhouse gases. They include:methane, CO₂ and water vapour. An increased greenhouse effect can lead to global warming and climate change.

15 Human and Ecosystem pdf

#151 Air pollution by sulfur dioxide (SO2), acid rain

SO₂ released into the air when coal and oil are burned. Power stations burn large amounts of these fossil fuels. SO₂ dissolves in the water vapour in clouds, forming sulphuric acid (H₂SO₄₎. When it rains, the rain is acidic.

#150 Overuse of fertilisers, water pollution by sewage

It is very tempting for farmers to increase the amount of fertilisers applied to crops to try and increase crop yields. However, this can lead to the eutrophication of rivers and lakes and the sequence occurs.  

# 149 Undesirable effects of deforestation

Deforestation is the removal of large areas of forest to provide land for farming and roads, and to provide timber (wood) for building, furniture and fuel. Deforestation has a number of undesirable effects on the environment.

#148 The human influences on the ecosystem

The use of modern technology resulted in increased food production.

14. Ecosystem pdf

# 147 Summary of Ecosystem

Energy enters ecosystems in sunlight. Producers (photosynthetic plants) capture some of this energy and transfer it to organic substances such as carbohydrates. Consumers (animals and fungi) gets their energy by eating producers or other consumers. 

#146 Population size, factors affecting the rate of growth

A population is a group of organisms of one species, living in the same area at the same time. Factors affecting the rate of population growth include food supply, predation and disease. 

#145 Effects of combustion of fossil fuels on CO2 level

Photosynthesis takes CO₂ out of the atmosphere and replaces it with O₂. Respiration and combustion both do the opposite: they use up O₂ and replace it with CO₂.

#144 Nitrogen cycle

Nitrogen is essential for the formation of amino acids to make proteins. The nitrogen cycle describes the ways in which nitrogen is recycled.

#143 Nutrient cycles - Carbon and water cycles

Most of the chemicals that make up living tissue contain carbon. When organisms die the carbon is recycled so that it can be used by future generations. Four main processes are involved: photosynthesis, respiration, decomposition and combustion. 

#142 Food chain and energy efficiency

In term of conversations of energy, there is an increased efficiency in supplying green plants  as human food and a relative inefficiency in feeding crop plants  to animals.

#141 Food pyramids of numbers, biomass and energy

A food pyramid shows the relative sizes of different components at the various trophic levels of a food chain. There are three types of ecological pyramid we use: numbers, biomass and energy.

# 140 Food web

Food web is a network of interconnected food chains showing the energy flow through part of an ecosystem.

#139 Food chain

Credit: BBC Bitesize

Food  chain is a chart showing the flow of energy (food) from one organism to the next beginning with a producer.

#138 Energy flow, energy loss

The Sun is the principal source of energy input to biological systems. The Earth receives 2 main types of energy from the Sun: light (solar) and heat. Photosynthetic plants and some bacteria can trap light energy and convert it into chemical energy.

13. Inheritance pdf

#137 Summary of inheritance

Chromosomes are long thread of DNA made up of strings of genes. In a diploid cell, each of a pair of homologous chromosomes carries the same genes in the same position. A diploid cell therefore has 2 copies of each gene.

# 136 Genetic engineering, putting human insulin genes into bacteria

Genetic engineering is a process of taking a gene from one species and putting it into another species.

#135 Variation and antibiotic-resistance strains of bacteria

Variation is the slight individual differences within populations. All living things change and evolve from one generation to the next. As they do so, more variation is produced. 

#134 Artificial and natural selection

Artificial selection is a method used by humans to produce varieties of animals and plants which have an increased economic importance. People use selective breeding to produce new varieties of a species, so that certain desirable traits are represented in successive generations. 

#133 Sickle cell anaemia and its incidence to that of malaria

Normal and sickle red blood cells.
Credit: Wellcome Trust, UK

Sickle cell anaemia is caused by a mutation in the blood pigment haemoglobin. When the faulty haemoglobin is present in a red blood cell, it causes the cell to deform and become sickle-shaped, especially when oxygen levels in the blood become low.

# 132 Mutation, Down syndrome, effect of radiation

Mutation is a unpredictable change in the genes or chromosome number, as a result of fault copying when DNA is replicated, faulty separation of chromosomes during cell division, or exposure to radiation or some chemicals.

# 131 Variation continuous and discontinous

Variation is all the differences which exist between members of the same species. It is caused by a combination of genetic and environmental factors. There are two kinds of variation: continuous and discontinuous.

# 130 Codominance and inheritance of blood group

Sometimes, neither of a pair of alleles is completely dominant or completely recessive. Instead of one of them completely hiding the effect of the other in a heterozygote, they both have an effect on the phenotype. This is called codominance.

# 129 Monohybrid cross and the punnett square

A monohybrid cross involves the crossing of individuals and the examination of one (mono) character (flower colour, pod shape...) and different (hybrid) traits (red colour, white colour) in their offspring.

The Punnett square is a useful tool for predicting the genotypes and phenotypes of offspring in a genetic cross involving Mendelian traits. 

# 128 Cell division – Mitosis and Meiosis

Mitosis is a nuclear division giving rise to genetically identical cells in which the chromosome number is maintained by the exact duplication of chromosome.

Meiosis is a reduction division in which the chromosome number is halved from diploid to haploid. 

#127 Chromosomes, DNA, genes and alleles

In the nucleus of every cell there are a number of long threads called chromosomes. 

# 126 Inheritance - key definitions

Inheritance is the transmission of genetic information from one generation to the next, leading to continuity of the species and variation within it.

12. Reproduction pdf

#125 Summary of Reproduction

Reproduction is the biological process by which new "offspring" individual organisms are produced from their "parents". It is a fundamental feature of all known life.

Two types of reproduction: sexual and asexual.

#124 Gonorrhoea

Gonorrhoea bacteria,

Credit: Science photo library

Gonorrhoea is caused by bacteria that can be passed from one person to another during sexual intercourse. Neisseria bacterium is a small, round cell. It can only survive in moist places, such as tissues lining the tubes in the productive systems of a man and a woman. 

#123 HIV/ AIDS - transmission and prevention methods

AIDS (Acquired Immune Deficiency Syndrome) is a disease caused by the HIV. 

HIV can not live outside the human body. It is an especially fragile virus  - much less tough than the cold virus. 

It is transported in body fluids. You can only become infected with HIV through direct contact of your body fluid with those of someone with the virus.

#122 Breast feeding vs formula milk?

This has been a tough question for many years: Which is better - breast milk or fomula milk? While breast milk is nutritious, it has its inconveniences. Formula milk is convenient but expensive. What to choose? 

#121 Artificial insemination, hormones in fertility drugs

An artificial insemination procedure uses a thin, flexible tube (catheter) to put sperm into the woman's reproductive tract (vagina, cervix, uterus) around the time of ovulation. For some couples with infertility problems, insemination can improve the chances of pregnancy.

#120 Method of birth control

There are 4 main groups of birth control methods: natural, chemical, mechanical and  surgical. 

#119 Sex hormones

Credit: revision world

Sex hormones (testosterone in boys and oestrogen in girls) are responsible for the development of secondary sexual characteristics at puberty.