Excellent study notes for all science topics in year 10 Essay Sample
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Excellent study notes for all science topics in year 10 Essay Sample
Structure of the atom
· An atom is the smallest part of an element that can be part of a chemical reaction – in other words, an atom is the smallest particle that can exist naturally
· When two or more atoms join up they form a molecule. Atoms are generally found in the form of molecules.
· An atom consists of a nucleus, which is made up of protons and neutrons.
· Protons are positively charged particles. Neutrons have no charge. There is an outer layer made up of negatively charged electrons, which keep orbiting the nucleus in a random manner.
· The number of protons and electrons are always equal in an atom. Because of this, the atom has got a neutral charge.
· The protons and electrons weigh more or less equal and the total number of protons and neutrons put together make the atomic weight, e.g. if an atom has two protons and two neutrons, the atomic weight is 4, since the electrons hardly weigh anything in comparison.
· Electrons spin in shells around the nucleus. There are many shells; the shell closest to the nucleus is filled first.
· Elements are naturally occurring pure substances. They contain atoms of one type only. The number of protons defines the element, e.g. hydrogen has 1 proton while chlorine has 17.
· The number of protons in an element is called its atomic number. The number of protons and neutrons in an element is called its mass number.
· In nature there are different forms of the same element. These different forms are called isotopes. An isotope contains the same number of protons but different number of neutrons compared the most common form of the element.
· When elements gain or lose electrons, they form charged particles called ions.
· Radiation is powerful and dangerous rays that are produced when atoms are broken up.
· Radioactive elements have unstable nuclei. As unstable nucleus breaks down or decays into a more stable nuclei, radiation is emitted in the form of particles or rays.
· There are three main types of radiation: alpha particles, beta particles and gamma rays.
· The half-life of a radioactive substance is the time required for half of the substance to decay
· Exposure to radiation can lead to changes in cells and chromosomes that may lead to cancer
· Alpha particles are made up of 2 protons and 2 neutrons. They travel for only a few centimeters and can be stopped by a piece of paper.
· Beta particles are made up of high speed electrons formed by the breakdown of neutrons. They can travel a few meters through the air and can be stopped by 1cm thickness of wood or a sheet of aluminum
· Gamma rays are not particles but very high-energy radiation. They are not charged and are emitted by radioactive atoms with excess energy. They can travel for kilometers through the air and can be stopped by thick concrete blocks or 2-3cm thickness of lead.
· Nuclear energy is released when changes are made within the nucleus of the atom.
· Nuclear fission is splitting heavy atoms into lighter atoms. When this occurs, a large amount of energy is released.
· Advantages of using atomic energy include: producing power, Medicinal uses (using ‘tracers’ to find diseases), Industry, Agriculture (tagging) and the environment (used to monitor pollution)
· Disadvantages of using atomic energy: Weapons, Radiation and Nuclear Waste
Producers are organisms that make their own food from the sun’s energy. We also call them autotrophs.
Consumers are organisms that eat other organisms, either producers or other consumers as food. We also call them heterotrophs.
Decomposers are organisms which consume dead matter and begin to make it decompose.
An ecosystem is a network of organisms that live in an environment and interact with each other by consuming or being consumed. The ecosystem can be seen as the combination of all the living and non-living parts. Within the ecosystem, numerous food chains exist and link together to form food webs. At the end of every food chain, and therefore part of every food web, are decomposers that return inorganic nutrients to the environment.
Numbers in Food Chains
In a food chain, the animal on top has to eat a lot of the next organism to feed itself. It continues, and as you go down the food chain, more and more organisms are required. This is because the energy level goes down.
e.g. 1 heron > 10 fish > 100 prawns > 1000 phytoplankton
Biotic and Abiotic Features
Biotic features are the living features of an environment.
e.g. plants, animals, fungi etc.
Abiotic features are the non-living components of an environment.
e.g. sunlight, rocks, water, wind, soil, temperature, humidity
Changes in Ecosystems
When a single feature of an ecosystem changes, it can have many effects on other features. Abiotic features often impact on each other. E.g. pollution in the water may cause soil pH to change.
Changes in the numbers of organisms within a food web will impact on
1. The numbers of organisms, which are eaten by the first organism.
2. The number of organisms which eat/consume the first organisms.
3. Possibly the number of organisms that are consumed by the same predators as the first organism.
The ultimate outcome of any changes is not easy to determine/predict because of the way in which organisms interrelate with each other in a complex way. Natural ecosystems usually have mechanisms, which ensure that small changes are absorbed by the system and don’t cause havoc through too much disruption.
Huge changes may upset the balance of nature within an ecosystem. This could cause the extinction of one or more organisms which would cause havoc. Humankind can cause these kinds of disruptions.
Body Under Attack
· Microbes that cause diseases are called pathogens
· Pathogenic microbes include: some bacteria, viruses, fungi and protozoan
There are three microbial kingdoms for different microbes. They are different in their size, cell structure and internal organelles. Viruses and prions are not cellular life forms, but they are microbes and they do cause disease.
· Kingdom Monera: Bacteria and cynobacteria belong to this kingdom. Their cells do not have a nucleus with a membrane. The microbes of this kingdom are the smallest (5-20 m) and bacteria that cause tuberculosis (TB) and Tetanus belong in this kingdom.
· Kingdom Protista: Unicellular organisms and algae belong to this kingdom. Their cells have membrane-bound nuclei. The microbes of this kingdom are the second smallest (around 50 m) and protozoa that cause malaria and sleeping sickness belong to this kingdom.
· Kingdom Fungi: are organisms that do not contain chlorophyll but their cells are surrounded by cell walls and have membrane-bound nuclei. The microbes of this kingdom are the larger than the others (around100 m). Yeasts are beneficial microbial fungi. Tinea and Thrush are diseases caused by pathogenic fungi.
· Viruses and Prions: are bodies much smaller than cells which are composed of some genetic material surrounded by a protein coat. They can only reproduce by invading a host cell. Viruses cause influenza, polio and AIDS. Prions are protein particles that cause diseases such as CJD in humans and BSE (commonly known as mad cow disease). Viruses and prions are not cellular life forms, but they are microbes and they do cause disease.
Resisting Pathogenic Microbes
The human body has many defenses to prevent the attack of pathogenic microbes. These include:
· The Skin: Microbes cannot penetrate unbroken skin. Harmless bacteria live on the skin, they use the oils secreted from the skin to create acids that prevent other bacteria and fungi from growing
· Acid in your stomach: Pathogens which enter the body can be destroyed by acidic gastric juices.
· Mucus in your airways: Mucus traps pathogens that you breathe in. Microscopic hairs transport these pathogens to your mouth where they can be coughed out or swallowed and destroyed.
· White blood cells: body produces white blood cells called phagocytes that consume and destroy microbes that enter the bloodstream.
· Antibodies: These are proteins produced by the body that attach themselves to pathogens or foreign substances and allow phagocytes to destroy them. They kill bacterial infections but not viruses.
Immunisation against diseases
When a pathogen enters your body, there is an immediate response. Your body’s defences destroy the invader. Once the danger is over, your body has acquired immunity to that disease. If that microbe attacks again, your body has antibodies that are ready to deal with it. Scientists have developed vaccines from dead or ineffective microbes, if these are injected into your blood, you develop immunity to that disease.
Faulty Cell Division
Not all diseases are caused by invasions of the body cells by microbes. Some diseases are non-infectious. These include: Genetic diseases (haemophilia, down syndrome), Nutritional diseases (scurvy, anorexia), Environmental diseases (lead poisoning) and organ and tissue system diseases (cancer, heart disease). Below is some info about cell division:
· Cells divide in multicellular organisms to allow the organism to grow or to replace worn out cells.
· The renewal of cells is controlled by a code in the cell’s nucleus, inside the nucleus of a cell that is preparing to divide there are stands called chromosomes
· The genetic code for that organism is contained within the chromosomes in the form or a fixed sequence of chemical molecules known as nucleotides
· These nucleotides are arranged in a large double helix molecule called DNA
· Cancer can result when the genetic code on the chromosomes is not correctly copied and abnormal cells are formed
· The body’s defences usually remove them before they do any harm, but sometimes the defences cannot cope with the cells and they continue to divide uncontrollably forming a mass of cells called a tumor or cancer
· Carcinogens are chemicals that cause changes (or mutations) on the genetic code
· When cells divide, the genetic code is copied and the new cells have the same chromosome number as the parent cell (46 in humans).
· Sometimes this copying process goes wrong and cells produced have an extra chromosome
· If an extra copy of chromosome 21 is present in the sperm or egg, this leads to a cell with 47 chromosomes.
· Babies born with 47 chromosomes in their cells have a condition called Down Syndrome. Down Syndrome leads to facial differences, reduced mental ability, heart defects and infertility.
· There is no cure for this condition
· A life cycle is the series of steps for an organism between the time of it’s creation to the time it reproduces
· Humans, plants and animals reproduce sexually
· Bacteria and other singe celled micro-organisms, yeast, fungi and some plants reproduce asexually
· Fertilization and pollination: The process whereby the pollen (sperm) meets
· Plants can reproduce asexually through vegetative reproduction. They can grow a new part, which can become separate from the ‘parent’ plant. E.g. grasses grow runners (rhizomes) which can supporta new plant. Plants can also reproduce with runner (strawberries, grass), tubers (potato) and bulbs (onion).
· When flowers pollinate, the pollen travels down the style of the flower and meets with the ovule in the ovary of the flower. When the pollen meets the ovule, pollination occurs.
How different organisms reproduce asexually:
· Amphibians release lots of eggs into the water where they are fertilized externally by the sperm of the male fish
· The eggs of reptiles and birds are fertilized inside the reproductive tracts of the female. The fertilized egg is then laid.
· Mammals- the human way…
The main events in Human Reproduction
· Ovulation: one female ovum is released from the ovaries
· The ovum moves down fallopian tube by beating cilia
· In fallopian tube, ovum meets about 100 sperm. Sperm swim by beating their tails
· Sperm releases enzymes to breakdown tough membrane of ovum. 1 sperm will get through and fertilise the egg. Other sperm will be locked out by changes in the membrane of the egg.
· The fertilized zygote moves down fallopian tube toward uterus. When it moves, it divides and implants itself to the spongy lining of the uterus wall
· The placenta forms to link embryo to the mother. Vital nutrients and oxygen pass from mother to baby
· After 8 weeks, the embryo is called a foetus and it is recognisably human
· After approx. 30 weeks, the foetus is mature enough to be born
· During labour, the baby is forced by muscular contractions through the birth canal and it’s connection to the placenta is cut. The baby must now breathe for itself.
The Uterus, Menstruation and Pregnancy
· The uterus is the pear shaped organ in which a fertilized egg develops into a baby. It is about 8 cm long and 5 cm wide.
· The uterus wall is muscular. These muscles allow it to stretch to accommodate the pregnancy and to push the baby from the uterus at the time of birth
· The menstrual cycle begins with menstruation, which lasts approximately 5 days. After the lining has been shed, the wall of the uterus repairs itself and at about 6 days it starts to thicken once more. Hormones released from the ovary control this process. Specialised spongy tissue rich in blood vessels is laid down continuously, reaching it’s maximum in a few days before the end of the cycle.
· At the same time, changes are also occurring in one of the ovaries. The egg is enclosed in a region called the follicle. The follicle increase ion size under the influence of hormones released from the pituitary gland in the brain. At day 14, ovulation occurs- the egg bursts out of the follicle and enters the mouth of the fallopian tube. The follicle then develops further to form a bland called the corpus luteum, which releases hormones to maintain the uterus wall for a possible pregnancy.
· If sperm is not present, the lining of the uterus is maintained until day 22 of the cycle, after this time, the corpus leteum in the ovary begins to degenerate. The cells gradually die and the next menstruation begins at the end of day 28.
· If sperm are present in the vagina close to the time of ovulation, there is time for fertilization to occur.
· If fertilization occurs, a series of hormonal changes prevents menstruation and the uterus lining in maintained.
· Hormones continue to maintain the pregnancy until about day 280 (measured from the beginning of the menstrual cycle) when the baby is born.
· The pregnancy or gestation period lasts about 270 days.
Puberty is the time when a child begins to become sexually mature. There are large changes in hormonal levels. At the beining of puberty, the pituitary gland in the brain releases hormones that travel through the bloodstream to the testes or ovaries and stimulate them to release sex hormones.
Puberty in males:
· Begins at about 12-14 years old and lasts about 4 years. The testes are stimulated to produce sex hormones including testosterone that flow through bloodstream and produces the male secondary sexual characteristics:
· Growth of pubic hair as well as body hair, enlargement of the testes and penis, increased muscle development, thickening of the vocal cords and a deepening of the voice, the development of sexual desire
Puberty in females:
· Begins at about 11-13 years old and lasts about four years. The ovaries are stimulated to produce oestrogen and progesterone that flow through bloodstream and produces the female secondary sexual characteristics:
· Growth of pubic hair as well as body hair, growth of breasts, changes in the bones especially hips that widen, redistribution of fat especially on the hips and thighs, the development of sexual desire
Measuring Distance in space
Space is too vast to measure distance in kilometers. Astronomers use the unit light-year instead.
1 Light-year = the distance light travels in one year
= 9500 000 000 000 km
Deep space objects
Moving into deep space away from our local group of galaxies, there are structures called nebulae, novae, quasars, black holes and pulsars. Below is some info on each of them:
· Nebulae: are clouds of dust and gas. Many astronomers believe that stars form from nebulae. Bright nebulae are visible objects. They can be blue or red. Dark nebulae are not visible. Dark nebulae block or dim the light from stars and other bright objects behind them. The coal shack nebula is an example of a dark nebulae which has its effect near the Southern Cross.
· Novae and Supernovae: A nova is when huge explosions are shearing the outer layer of a star, and hot gasses are blown outwards. The star shines a hundred to tens of thousands times brighter than normal. A supernova is much more rare. The explosions in them are much greater and the star is torn apart and the brightness of the star can increase up to a billion times it’s normal rate. The most famous supernova occurred in AD 1054; it produced the crab nebula. It was bright enough to be seen during the day, and it’s brilliance lasted for days.
· Quasars and Black Holes: Quasars and black holes are among the most distant energy sources known to astronomers. Quasars are not stars, but the glaring centers of remote and turbulent galaxies. The brilliant light is thought to come from a disk of gas spiraling under intense gravity into a black hole. Some of the largest black holes have a mass equal to 1000 billion suns. The word quasar comes from ‘quasi-stellar radio source’. They were noticed because of the very strong radio waves they emit.
· Pulsars: A pulsar or neutron star emits extremely regular pulses of radio waves. Pulsars are rapidly spinning and extremely dense composed almost entirely of neutrons and having a diameter of only about 20 km. Pulsars emit radiation as intense beams from their magnetic poles.
Life cycle of a star
1. Star born in groups or cluster which are made from large quantities of interstellar hydrogen gas dust left from dying stars.
2. This matter is pulled together by gravity over billions of years to form protostar which glows a dull red as temperature increases.
3. Protostar spins into a disk and planets may form at this stage. If temperature reaches 10 million degrees Celsius, nuclear reactions fuse hydrogen and helium and a ‘main- sequence’ star is formed. This shines for about 10 billion years. The next step depends on the mass of the star. For a star the size of the sun.. go to 4. for one that is much bigger.. go to 7. and for one even bigger, go to 8.
4. Eventually, the hydrogen starts to run out and the core starts to shrink, but the star gets hotter. More nuclear reactions occur which produce a helium shell around the core. The shell cools down and expands as the core contracts and heats
5. It gets 100 times brighter than before and a red giant forms. The core continues to contract and temperature reaches over 100 million degrees
6. Remaining fuel is used up and a planetary nebula forms. Nebula will drift of and leave a white dwarf. It is small and the temperature will be about 100 000C. It will slowly cool down until a black dwarf is formed (star is effectively dead).
7. Red super giant forms and when star gets too hot (several billion degrees), it collapses on itself and forms a supernova. This burns very bright. After a few days, the only sign sucha star existed is a pulsar it leaves behind.
8. Very large super giant forms and explodes to create a supernova. The core collapses in on itself and a black hole forms.
Origins of the universe
· According to the big band theory, 10-15 billion years ago, everything in space was condensed in one point. There was a ‘big bang’ and all the matter was thrown out and formed quarks and electrons
· These quarks and electrons clumped together to form protons and neutrons, which formed the first particles of hydrogen and helium. All of this happened in the first 100 seconds
· Over a much longer period (1 billion years), the clouds of gas collapsed to form galaxies.
· Stars began to form inside these galaxies. About 5 billion years ago, the Sun formed in the Milky Way galaxy. Astronomers believe that the universe is still expanding
Technology today and different types of electromagnetic radiation
Much of the info we receive today can come from radiation outside the visible spectrum window. Visible light is only one small part of the electromagnetic spectrum of light. All forms of light radiations travel at the same speed: 300 000km/sec. Light is a wave motion that consists of moving electric and magnetic fields. This is why it is called an electromagnetic wave.
Radio astronomy: radio waves coming from space are very weak and large instruments with very sensitive detectors are needed to collect them. Radio waves are collected by a curved dish that reflects the signals to a detector. The weak signals are changed into electrical pulses and amplified, they can then be stored on s computer for later study. Unlike light telescopes which can only be used at night, radio telescopes can be used any time of the day or night. They have many advantages including: being able to provide us with a lot of info which is not visible, radio signals can travel through matter which stops light, they can travel heaps and these would usually be hidden from our view
Infra-red astronomy: since infra-red waves can travel through objects, they are a valuable source of info. Infra-red astronomy is used to determine the warmth of in the atmospheres of planets. The US COBE (Cosmic Background Explorer) satellite was launched in nov 1989. it consists of three instruments: a far infra-red spectrometer, a differential microwave radio-meter and a diffuse infra-red background experiment. Data from the COBE reveals many thing about the universe including info on the big bang theory.
Electromagnetic radiation: Long radio waves, TV waves, Microwaves, Infra-red, Visible light, Ultra-violet, X-rays and Gamma rays
Chemistry in the home
1. A compound is a chemical combination of two or more elements. Compounds are made by rearranging atoms
2. A molecule is the smallest particle of matter that can exist by itself in a free state. Some examples of molecules are: oxygen (02), ozone (03), carbon monoxide (CO), carbon dioxide (CO2), Water (H2O), Nitrogen (N2) etc
3. The bonds that hold atoms together are caused by the outer electrons of each atom being attracted to nuclei other than their own. If electron shells of atoms are full, then they do not attract other atoms, but if there are some spaces for more electrons, then the atom is constantly trying to get more electrons. You can calculate using the ionic table if ions will be lost or gained.
4. Combination reactions are reactions where two or more substances form another substance e.g…
· O2 + 2H2 2(H2O)
· Combustion reaction: Fuel + Oxygen (ignition source) combustion product + heat
· Neutralisation reaction: Acid + Base Water + salt
e.g… HCl + NaOH H2O + NaCl
· Decomposition Reaction: C6O6H12 (sugar) (heat) 6C (carbon) + 6H2O (water)
· Precipitation Reaction: if a solid substance separates from a solution by combination of ions or molecules present that solid is called a precipitate.
6. Compounds can be identified by their taste. Acids are sour. Alkaline and base are bitter. Salt is salty. Sugar/ sucrose is sweet.
Shaking all over
Structure of the earth
· Inner Core: is 1400 km thick, it is solid and around 4000°C.
· Outer Core: is around 2000 km thick, liquid and it does not transmit transverse earthquake waves
· Mantle: 2800 km thick and it consists of a number of zones
· Asthenosphere: A zone in the upper most mantle. Is very plastic (semi-molten). Zones below the Asthenosphere are more rigid/solid. The outermost layer of the mantle has solid pieces. These form part of the lithosphere
· Crust: the crust is 8-64 km thick. It is divided into continental and oceanic regions. Together with the uppermost solidified mantle, makes the lithosphere
· Tectonic plates: The earths crust is divided into a number of plates that can move on the plastic Asthenosphere, on which they sit. At the boundaries
The earth’s crust is made up of many slabs of rock. Rocks can slowly move over semi-molten material. Convection currents move the asthenosphere and cause plate movement. This can result in the following:
· Spreading zones: When the plates move apart (divergent)
· Subduction zones: When plates rise over one another, this can cause fault mountains
· Collision zones: when plates push against each other, this can cause fold mountains
· Transform fault zones: when plates push past each other, this can cause earthquakes
Many surface features are caused by plate tectonics and the interaction of plates e.g. mountains- c above
Alfred Wegner proposed in 1910 that all the continents had once been joined into a single super-continent called Pangaea. He claimed that the continents appear to fit together. This was called the ‘jigsaw theory’. Other evidence to support his theory was that““““““““ similar fossils and rock types in countries that would have fit together.
A volcano is a mountain that contains a vent, which through magma, rock, gas and steam can escape from a magma chamber beneath the earth’s crust. There are four different types of volcanoes:
· Shield volcanoes: broad flat volcanoes. They form when very fluid lava travels a long distance e.g. Hawaiian volcanoes
· Cinder cone volcanoes: are steep sided. They form when thick lava and other material is thrown into the air e.g. Mt Fuji in Japan
· Composite volcanoes: most common type. They formed of alternate layers of ash and lava e.g. Mt Eggmont in New Zealand
· Hot spots: they occur in the middle of the middle of plate as opposed to the others which only occur at plate boundaries. They result from weak spots in a tectonic plate where molten lava can break through e.g. Hawaiian islands