SCIENCE SEMESTER II NOTES
Biology
 Resources plants need: light, carbon dioxide, water, warmth, minerals.
 Minerals are nutrients that living organisms need in small amounts for
health, growth and repair. Also called mineral salts.
 Most plants make their own food using a process called photosynthesis.
Photosynthesis is a process involving a series of chemical reactions in
which carbon dioxide and water are converted into glucose and oxygen.
 A lot of energy is stored in glucose.
 Oxygen from photosynthesis is used for respiration.
 Glucose: sugar made by carbohydrates (in animals) by photosynthesis (in
plants).
 Palisade cells are adapted for photosynthesis. Guard cells are adapted to
form a hole through which gases can move by diffusion.
 Plants need a constant supply of water because they lose water through
stomata.
 Carbohydrates: Carbon, hydrogen and oxygen.
 Plants use starch as a store of energy. Plants use glucose to make starch in
chloroplasts.
 At night when photosynthesis stops (doesn’t receive light), plant uses starch
to make other compounds, which it transports out of the leaf.
 Starch test:
1. Boil the leaves to make them soft
2. Put in hot ethanol to remove green colour
3. Wash the leaves in water
4. Add the iodine solution.
 Iodine solution stains skin and clothing, stings in eye.
 Ethanol catches fire very easily, irritates eyes.
 Roots take in water and minerals; roots use specialised root hair cells to
absorb water.
 Root hair cells have bits sticking out of them that look a bit like hairs. A root
hair gives a cell a lot of surface area which helps them absorb water quickly.
These cells also absorb mineral salts.
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 Transpiration is the loss of water vapour through the stomata on the surface
of the leaves. The route taken by water through the plant into the roots, up
the stem and out the leaves is transpiration stream.
 Plants also need water to give cells their shapes. Without enough water plant
cells start to collapse and the plant wilts (becomes floppy)
 Xylem cells have thick walls containing lignin which makes them strong
stopping from collapsing.
 Xylem cells form long thin tubes that run from the roots up the stems to the
leaves.
 Plants need phosphorus from phosphate salts for respiration and growth
without it; reduced plant growth. Plants need potassium from potassium salts
to help plants absorb and transport water, without it; the edges of leaves turn
brown.
 Blood vessels carry the clean blood away from kidneys, ureters carry blood
to bladder.
 The treatment done for kidney damage is called dialysis. Blood vessels in
the patient’s arms connected to a dialysis machine, which pumps their blood
through a fine set of filters and removes the urea.
 Variation is the differences between characteristics.
 Variation with a distinct set of options is discontinuous variation. Vice versa
but varies gradually is continuous variation.
 Variation: environmental/ inheritance
 To get reliable results, repeat the experiment.
 Chromosome: structure containing a molecule of DNA, which carries
genetic information in genes.
 DNA: substance that carries genetic information.
 DNA has a special structure. It is one molecule made of two backbone
strand spirals, twisting around each other to make a double-helix shape.
 Gene: section of DNA that controls the development of a specific
characteristic.
 James Watson & Francis Crick: 1st scientists to discover structure of DNA.
 For sexual reproduction to occur, an organism needs to produce gametes.
 Human body cells: 46 chromosomes | Human gametes: 23 chromosomes
 Cytoplasm: store of food in egg cells
 Embryo is a small ball of cells that develops from a fertilised egg cell. It
becomes attached to the uterus lining and develops into a fetus.
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 The tip of the sperm cell contains substances (acrosomes) that allow it to
break through the jelly layer and cell membrane of the egg cell. Only one
sperm cell can break through the jelly coat of the egg cell.
 Identical twins are formed when a fertilised egg cell splits into two cells, and
each cell then develops into an embryo.
 Between 8 to 10 weeks after fertilisation, the embryo’s organs form and its
heart starts to beat.
 Soft blue cheese can contain listeria bacteria. Infection with this bacterium is
very rare, but if it occurs it can harm the fetus or even cause it to die.
 Pregnant women are told to eat leafy green vegetables and brown rice as it
contains a vitamin called folic acid. A lack of it may cause spinal bifida,
problem in walking.
 Drugs affect how a person’s body works, they may change how it grows and
develops. Many drugs can pass into fetus’ blood through the placenta and
some can harm the fetus.
 Smoke substances: carbon monoxide and nicotine.
 Smoking reduces the amount of oxygen a fetus gets, it also increases the
chance of stillborn baby (dead when born).
 A child's sex is determined by the chromosome that the male contributes.
Males have XY sex chromosomes while females have XX sex
chromosomes; the male can contribute the X or Y chromosome, while the
female must contribute one of their X chromosomes.
 Adaptation: organism’s characteristic that helps to survive in certain
ecosystem.
 Evolution: a gradual change in something overtime.
 Natural selection: the process by which organisms have better adaptions for
new environmental conditions making them more likely to survive and
reproduce than other species.
 Charles Darwin’s theory states that evolution is caused by Natural Selection.
 Adaptation of Cactus:
o Spines instead of leaves to reduce water loss through transpiration
o Thick waxy covering to reduce water loss through evaporation.
o A special tissue in stem to store water
o Wide - spreading roots to absorb water very quickly
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Chemistry
 Atomic number: number of protons or electrons | mass number: protons +
neutrons
 First shell: max 2 electrons | second & third shell: max 8 electrons
 Chemical Property: a property that is seen when a substance take part in a
chemical change.
 Physical Property: the property that can be observed without changing the
basic nature of the substance.
 Molecule: a group of two or more atoms joined together.
 Covalent bond: two non-metal atoms sharing a pair of electrons because of
electrostatic force.
 Ion: gained an electron to be negatively charged or lost one electron to be
positively charged. Metals lose, non-metals gain.
 Ionic bond: a strong electrostatic attraction between negatively and
positively charged ion.
 The law of conservation of mass states that there is no loss or gain of mass
during the reaction.
 Metals have a giant structure. They are made up of positive metal ions
surrounded by electrons. The electrostatic attraction between the positive
ions and electrons are strong metals are able to move; this is why metals can
conduct electricity.
 Giant structure bonds are very strong. To melt a giant structure these bonds,
have to be overcome which requires a lot of energy, therefore the giant
structures have high boiling and melting points.
 Density is how much mass something has in a certain volume.
𝑚𝑎𝑠𝑠
 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 =
𝑣𝑜𝑙𝑢𝑚𝑒
 Particle theory explains that everything is made up of atoms.
 Combustion: chemical reaction between a substance and oxygen, which
transfers energy as heat and light.
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Name of acid
Hydrochloric acid
Sulfuric acid
Nitric Acid
Type of Salt
Chloride
Sulfate
Nitrate
 metal + acid  metal salt + hydrogen
 carbonate + acid salt + water + carbon dioxide
 Making a soluble salt: First, pour some dilute acid into a beaker. Then add a
spatula of the metal or solid metal carbonate and stir with a glass rod. The
reaction will produce a soluble salt. You need to keep adding the solid, one
spatula at a time, until no more reacts.
 Purifying the salt: You will now have a mixture of a salt solution and solid.
To purify the salt, the other substances need to be removed.
 Using filtration: You remove the solid by filtering the mixture. The excess,
or unreacted, solid stays in the filter paper. The salt solution goes through
the filter paper and collects in the container below.
 Using evaporation: remove the water from the solution by evaporation. This
forms salt crystals; the process is called crystallisation.
 Displacement reaction: a chemical reaction in which a more reactive metal
takes place of a less reactive metal.
 Factors affecting the rate of reaction: temperature, surface area,
concentration.
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Physics
 Temperature is a measure of the average thermal energy of the particles in a
substance.
 Conduction: thermal energy transferred through a substance; particle to
particle; occurs mainly in solids.
 Insulator: poor thermal conductor.
 Convection: thermal energy transfer that occurs in fluids, liquids and gases,
 Radiation: transfer of energy by waves
 Voltage: a measure of energy in a circuit
 𝑉=









𝐼
𝑅
Amplitude = height = volume
Wavelength = pitch = frequency
Infrasound: too low frequency to hear
Ultrasound: too high frequency to hear
Humans: 20Hz to 20 000Hz
Crest: Highest point of a wave
Trough: Lowest point of a wave
Constructive interference: added to make bigger wave.
Destructive interference: combine to cancel each other
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Earth & Space
 Bacteria and fungi are the decomposers in the carbon cycle. They feed on
dead animals and plants.
 Respiration and combustion are the sources of carbon cycle. Photosynthesis
is the sink.
 Droughts cause dry vegetation, wild fires and inconvenience to humans if
reservoirs run out.

 Movement of particles due to heating are called convection currents.
 The earth’s core causes heating in parts of the mantle, creating convection
currents.
 The craters on moon indicate that man
 Capture hypothesis: the moon is a large asteroid that has been pulled into
orbit of earth due to earth’s gravitational force.
 Co-formation hypothesis: Moon and Earth formed together, close to each
other, at the same time.
 Collision hypothesis: A large object roughly the same size and mass as the
planet mars collided with earth, releasing rocks that were pulled together to
form the moon.
 Meteor: asteroid that enters earth | Meteorite: left behind after meteor
collides.
 Shock wave: the squeezing of a volume of air caused by an explosion.
 Gas: hydrogen and helium
 Dust: carbon, silica and oxygen
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 Some nebulae are produced when a very large star explodes at the end of its
life. Other nebulae are produced when the force due to gravity causes
interstellar gas and dust to gather together.
 We can observe nebula when the light from nearby stars reflects of it or is
blocked by it. Sometimes radiation that passes through the nebula causes
atoms of gas to gain energy, which then re emit the light we see. Pink colour
is reemitted by hydrogen gas.
 When a nebula is formed by the force due to gravity, the dust and gas are
slowly pulled together. Some parts of the nebula become denser, and atoms
of hydrogen are pulled closer to each other. Eventually the forces of
attraction become so strong that the nuclei of pairs of hydrogen atoms merge
in a process called nuclear fusion. This process releases huge amounts of
energy in the form of electromagnetic waves.
 The dense part of a nebula is known as a stellar nursery.
 Red supergiant: a huge, red coloured star that is formed when a massive star
expands towards the end of its life.
 Supernova: explosion of star at the end of its life which produces nebula.
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