Revision

1. Revision B1

2. What is DNA? They consist of long strands of a substance called deoxyribonucleic acid, or DNA for short. Chromosomes… are X-shaped objects found in the nucleus of most cells A section of DNA that has the genetic code for making a particular protein is called a gene.

3. Sex cells and chromosomes Human body cells each contain 23 pairs of chromosomes.Parents pass on their genes to their offspring in their sex cells:   • Female sex cells are called egg cells, or ova. • Male are called sperm.

4. Sex cells and chromosomes Human body cells each contain 23 pairs of chromosomes.Parents pass on their genes to their offspring in their sex cells:   • Female sex cells are called egg cells, or ova. • Male are called sperm. Male Female

5. Gender • All normal egg cells produced by a human ovary have an X chromosome. • Half of the sperm carry an X chromosome, and half a Y.

6. Variation in a species Most characteristics, such as height, are determined by several genes working together. They are also influenced by environmental factors. These include:   • climate • diet • physical accidents • culture • lifestyle. For example, an individual might inherit a tendency to tallness, but a poor diet during childhood will result in poor growth and a shorter individual.

7. Alleles (pronounced al-eels) • Chromosomes carry genes • Different versions of the same gene are called alleles • For any gene, a person may have the same two alleles or two different ones: • If both the alleles are the same, the individual is homozygous for that gene. • If the alleles are different, they are heterozygous for that gene. • Alleles may be either recessive or dominant.

8. A recessive allele only shows if the individual has two copies of the recessive allele. For example, the allele for blue eyes is recessive. You need two copies of the allele to have blue eyes. • A dominant allele always shows, even if the individual only has one copy of it. For example, the allele for brown eyes is dominant. You only need one copy of it to have brown eyes (and two copies will still give you brown eyes).

9. Cystic Fibrosis • Cystic fibrosis (CF) is caused by a recessive allele, written as f. • You need to inherit two copies of the faulty allele to be born with CF. If you have just one copy, you are a carrier, but will not experience any symptoms. If two carriers have a child together, there is a one in four chance of it inheriting the disorder. The genetic diagram shows why.

10. Huntington’s disorder • Huntington’s disorder is caused by a dominant allele, written as D. • The symptoms usually develop in middle age, and include problems controlling your muscles and forgetfulness. • You only need to inherit one copy of the faulty allele to have Huntington’s disorder

11. Genetic Testing • http://news.bbc.co.uk/player/nol/newsid_6230000/newsid_6235300/6235373.stm?bw=bb&mp=rm

12. Gene Therapy • Gene therapy involves inserting copies of a normal allele into the chromosomes of an individual who carries a faulty allele. The basic processGene therapy involves these basic steps:   • Doing research to find the gene involved in the genetic disorder. • Cutting out the normal allele (special enzymes are used to do this). • Making many copies of the allele. • Putting copies of the normal allele into the cells of a person with the genetic disorder.

13. Asexual reproduction • Asexual reproduction only requires one parent, unlike sexual reproduction, which needs two. • As a result, the offspring are genetically identical to the parent, and each other. They are clones.

14. Cloning • Twins are genetically identical because they are formed after one fertilised egg cell splits into two cells. They are natural clones. • Fusion cell cloning involves replacing the nucleus of an unfertilised egg with one from a different cell. The replacement can come from an embryo. If it is from an adult cell, it is called adult cell cloning.

16. Revision C1

17. The Atmosphere The Earth is surrounded by a mixture of gases called the atmosphere. The main gases in the atmosphere are:   • nitrogen (about 78%) • oxygen (about 21%) • argon (about 1%). There are smaller proportions of other gases, including:   • water vapour • carbon dioxide. The pie chart shows the relative amounts of the three main gases.

18. Burning… • When a hydrocarbon burns it joins with oxygen… Methane + oxygen →

19. Burning… • When a hydrocarbon burns it joins with oxygen… Methane + oxygen → The heat you supply with a match Splits up the atoms… This bit needs energy, lets say 10 Joules

20. Burning… • When a hydrocarbon burns it joins with oxygen… Methane + oxygen → → Carbon dioxide + water The atoms then recombine to make carbon dioxide and water When these atoms recombine, they release 15 Joules This bit needed 10 Joules…

21. Combustion

23. Pollutants from burning fossil fuels • Most of the UK’s electricity is produced by power stations that are fuelled by fossil fuels, which contain carbon. • carbon dioxide, CO2 • carbon monoxide, CO (when there is not enough oxygen, so burning is incomplete) • particulate carbon, C (soot and smoke from incomplete burning) • sulfur dioxide, SO2.

24. Hazards of pollutants • The pollutants generated by burning fuels do not disappear when they enter the atmosphere. For example, carbon dioxide is used by plants in photosynthesis

25. Reducing pollution from power stations • The only way to reduce the amount of carbon dioxide given off by power stations is to burn less fossil fuels. This means using less electricity

26. Reducing pollution from vehicles • Designing engines that are more efficient. • Using public transport, such as buses and trains, instead of cars. • Walking instead of driving.

27. Cleaning exhaust gases • Catalytic converters are devices that convert harmful waste gases into less harmful ones • Nitrogen monoxide is reduced to nitrogen. • Carbon monoxide is oxidised to carbon dioxide.

28. P3

29. How big? How old? The Universe began with a “big bang” about 14 thousand million years ago. Our solar system was formed about five thousand million years ago

30. The solar system The solar system consists of:   • the Sun (a star) • planets and dwarf planets in orbit around the Sun • satellites (moons) in orbit around most of the planets • comets and asteroids in orbit around the Sun

31. Comets and asteroids • CometsComets are balls of ice and dust that orbit the Sun. Their orbits are different to those of planets: they are elliptical. • AsteroidsAsteroids are rocky objects, and smaller than planets. Most are found in an “asteroid belt” in orbit around the Sun between Mars and Jupiter. • It is thought that an asteroid colliding with the Earth helped to drive the dinosaurs to extinction.

32. Stars

33. The structure of the Earth The Earth is almost a sphere. These are its main layers, starting with the outermost:   • the crust (relatively thin and rocky) • the mantle (has the properties of a solid, but can flow - very slowly) • the core (made from nickel and iron).

36. Problems Wegener’s theory of continental drift was rejected by many geologists. Some of the reasons for this were:   • The movement of continents could not be detected (because they only move by a few centimetres per year). • No-one could provide a good explanation of how whole continents could move apart. • Wegener was not a geologist (he trained as an astronomer and meteorologist). • There were other, simpler, explanations for the same evidence. • It was felt his idea was too big for the evidence at hand.

37. Seafloor spreading Magnetic field reversalSeafloors spread by about 10cm per year. This spreading leaves a characteristic pattern of magnetism in the rocks on the ocean floor that can be "read" by scientists. The Earth’s magnetic field has not always had the same North-South alignment. Every so often it reverses direction - for thousands or millions of years. Iron-rich minerals in molten magma line up in the magnetic field, and this alignment is preserved when the magma solidifies.

39. Stars

40. Galaxies and the Universe • There are thousands of millions of galaxies in the Universe. Each contains thousands of millions of stars. The Milky Way is the galaxy that contains our Sun - the star at the centre of the solar system.  

41. The Big Bang • Scientists have gathered a lot of evidence and information about the Universe. • It states that about 14 thousand million years ago all the matter in the Universe was concentrated into a single incredibly tiny point. This began to enlarge rapidly in a hot explosion, and it is still expanding today • expand for ever • eventually stop expanding, or • eventually stop expanding, but then contract again in a “big crunch”.

42. Hubble’s Law • Astronomers have discovered that distant galaxies are moving away from us. The further away they are, the faster they are moving. This is called Hubble’s Law.

43. Optical telescopes • They can only be used at night. • They cannot be used if the weather is poor or cloudy. • They cannot be used in areas where there is bright street lighting (“light pollution”).

44. Alien planets • Astronomers have detected planets around some nearby stars. As there are a lot of stars in the Universe, many scientists think it is likely life exists on other planets. But there is no evidence to support this view. • You may wish to view this BBC News item from 2006 about how a new type of research radio telescope could pick up TV transmissions from alien civilisations (if they exist).