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IGCSE Combined Science revision notes
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Notes for IGCSE Combined science course offered by Cambridge International Examinations. These notes cover the Biology, Chemistry and Physics sections of the course.
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IGCSE COMBINEDSCIENCE NOTES
Name:……………………………………………………
Form:……………………………………………………
School:………………………………………………….
………………………………………
COMPILED BY B.N MUPETI
2020 Edition
,CONTENTS PAGE NUMBER
Biology
B1. Characteristics of living organisms 01
B2. Cells 01
B3. Biological molecules 05
B4. Enzymes 07
B5. Plant nutrition 09
B6. Animal nutrition 11
B7. Transport 16
B8. Gas exchange and respiration 21
B9. Coordination and response 25
B10. Reproduction 27
B11. Organisms and their environment 34
B12. Human influences on ecosystems 36
Chemistry
C1. The particulate nature of matter 38
C2. Experimental techniques 40
C3. Atoms, elements and compounds 44
C4. Stoichiometry 51
C5. Electricity and chemistry 53
C6. Energy changes in chemical reactions 55
C7. Chemical reactions 56
C8. Acids, bases and salts 60
C9. The Periodic Table 67
C10. Metals 71
C11. Air and water 75
C12. Organic chemistry 77
Physics
P1. Motion 82
P2. Work, energy and power 94
P3. Thermal Physics 102
P4. Properties of waves, including light and sound 110
P5. Electrical quantities 120
P6. Electric circuits 124
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, Biology section
Characteristics of living organisms
Describing the characteristics of living organisms by defining the following terms
Movement: movement refers to an action by an organism causing a change of position or
place.
Reproduction: reproduction refers to processes that make more of the same kind of organism.
Sensitivity: sensitivity refers to the ability to detect and respond to changes in the
environment.
Growth: growth refers to the permanent increase in size and dry mass by an increase in the
number of cells, cell size, or both.
Respiration: respiration refers to the chemical reactions in cells that break down nutrient
molecules and release energy.
Excretion: excretion refers to removal, from organisms, of toxic materials and substances in
excess of requirements. These toxic materials are waste products of metabolism and
substances taken in excess.
Nutrition: nutrition refers to taking in of materials for energy, growth and development.
The seven characteristics could be memorized by the term “MRS. GREN” using the first
letters of each characteristic mentioned above.
Cells
Cell structure
Stating that living things are made of cells
Living organisms are made of cells. Cells are very small; hence, they can only be seen under
a microscope. We have two types of cells namely plant and animal cells.
Describing and comparing the structure of a plant and animal cell.
Note similarities: both contain a cell membrane, cytoplasm and nucleus
Note differences: in addition, a plant cell contains a cell wall, chloroplasts, and a sap vacuole
Combined Science notes by B.N Mupeti Page 1 of 128
, Biology section
Stating the functions of the structures found in cells
1. Cell wall: This is a non-living thick rigid layer surrounding the cell. It is made of
cellulose, and it gives the cell its shape (angular, rectangular or rounded) and prevents
it from bursting. It also allows the plant to support itself. The cell wall is permeable
i.e. it allows all substances to move into or out of the cell. Only the semi-permeable
membrane will allow or dis-allow entry or exit of some substances into the cell.
2. Cell membrane: This is a partially permeable membrane. It controls the movement of
substances into and out of the cell.
3. Cytoplasm: This is a jelly like substance made up of mostly water and structures.
Metabolic reactions occur in the cytoplasm.
4. Chloroplasts: These are green discs which contain chlorophyll (which is a green
pigment that traps sunlight for photosynthesis).
5. Nucleus: Controls all activities of the cell.
6. Sap vacuole: A vacuole is a large room in the center of the cell. It contains cell sap.
The cell sap stores dissolved sugars, mineral salts and amino acids. It also controls the
movement of water in and out of the cell.
Combined Science notes by B.N Mupeti Page 2 of 128
, Biology section
Relating the structure of certain cells to their functions:
Type of cell Where it is found Function
Ciliated cells Lining the trachea and bronchi Move mucus upwards to the back
of the throat
Root hair cells Near the ends of plant roots Absorb water and mineral salts
Xylem vessels In stems, roots and leaves of plants Transport water and mineral salts;
help in support
Palisade mesophyll Beneath the epidermis of a leaf Photosynthesis
cells
Nerve cells Throughout the bodies of animals Transmit information in the form of
electrical impulses
Red blood cells In the blood of mammals Transport oxygen
Sperm and egg cells Sperm in testes and egg cells in ovaries Fuse together to produce a zygote
Ciliated Cells:
Ciliated cells have cilia whose function is to move the mucus up the trachea and bronchi to
the throat. The mucus traps bacteria and dust particles. When it reaches the throat, mucus is
swallowed to the stomach where the acid kills the bacteria.
Root Hair Cells:
Their function is to absorb water and minerals from the soil. They are adapted by 3 ways.
One, they have a large surface area for more water intake. Two, they have a large number of
mitochondria for respiration to become more active. Three, they have a concentrated vacuole
to support the absorption of water by osmosis.
Palisade mesophyll cells:
Consist of one or two layers of closely-packed, long and cylindrical cells containing
chloroplasts. Their function is to facilitate photosynthesis. They contain numerous
chloroplasts to allow maximum absorption of light.
Leaf structure
showing one layer of
palisade mesophyll
cells
Combined Science notes by B.N Mupeti Page 3 of 128
, Biology section
Sperm cells have
a tail – to help them swim
a head which has digestive enzymes to breakdown the outer membrane of the ovum to
allow fertilization to occur
a middle piece with numerous mitochondria to provide energy for the sperm to swim
(this point is not in the syllabus though)
An egg cell
Egg cells (ova) possess a yolk which acts as a food store. The spherical shape of ova allows
cilia lining the oviducts to easily move the ovum so that it can meet sperm and be fertilized
by it.
Calculating magnification and size of biological specimens using millimetres as units
𝑠𝑖𝑧𝑒 𝑜𝑓 𝑑𝑟𝑎𝑤𝑖𝑛𝑔
Magnification = in mm
𝑠𝑖𝑧𝑒 𝑜𝑓 𝑟𝑒𝑎𝑙 𝑜𝑏𝑗𝑒𝑐𝑡
Movement in and out of cells
Defining diffusion
Diffusion is the net movement of particles from a region of higher concentration to a region
of lower concentration down a concentration gradient, as a result of their random movement.
Substances move into and out of cells by diffusion through the cell membrane. Water diffuses
through partially permeable membranes by osmosis.
Defining osmosis
Osmosis is the net movement of water molecules from a region of higher water potential
(dilute solution) to a region of lower water potential (concentrated solution), through a
partially permeable membrane. Water moves in and out of cells by osmosis through the cell
membrane. Water also enters the roots by osmosis.
Combined Science notes by B.N Mupeti Page 4 of 128
, Biology section
Investigating and describing the effects of immersing of plant tissues in solutions of
different concentrations
Water potential is a measure of the tendency of water molecules to move from one region to
another.
Dilute solutions have a higher water potential than concentrated solutions. Pure water has the
highest water potential. Water molecules that dissolve solutes are bound to the solute
particles. A dilute solution thus has a lot of unbound water molecules, giving it a higher water
potential than a concentrated solution.
Immersing plant tissues in concentrated solutions of salts make the tissues smaller (flaccid)
due to the movement of water molecules out of the tissues and into the concentrated solution.
Immersing plant tissues in pure water can make the tissues bigger (turgid) due to movement
of water molecules from the pure water and into the tissues. Cell walls in plant cells prevent
them from bursting. Absence of cell walls in animal cells can result in bursting due to too
much water uptake by cells.
Small dots are
water and large
dots are solute
particles.
Biological molecules
Listing the chemical elements that make up:
1. Carbohydrates: made up of carbon, hydrogen and oxygen only.
2. Fats: made up of carbon, hydrogen and oxygen (less oxygen than in carbohydrates).
3. Proteins: made up of carbon, hydrogen, oxygen and nitrogen. They sometimes contain
sulphur and phosphorus.
Large molecules are made from smaller molecules: e.g.
1. Starch and glycogen are made from glucose
2. Proteins are made from amino acids
3. Fats and oils are made from fatty acids and glycerol
Combined Science notes by B.N Mupeti Page 5 of 128
, Biology section
Food tests
Test for starch
1. The test for starch is called the Iodine test. Iodine is added to the sample and the colour
change (if any) is observed.
2. Procedure: Add a few drops of iodine solution (which is brown) to the sample. If the
sample contains starch, it will turn blue-black in colour.
Test for reducing sugars 1. The test for reducing sugars is known as the
Benedict’s test.
2. Reducing sugars are glucose, fructose, galactose,
maltose and lactose. Sucrose is not a reducing sugar.
3. Procedure: Add Benedict’s solution to the sample
and mix the contents thoroughly. Heat the mixture in
a boiling water bath for 5 minutes.
4. The colour of the solution changes from blue to
green to yellow to orange to brick-red if a reducing
sugar is present.
5. Both test tubes on the left contain reducing sugar,
however, the one on the right side contains more than
Test for proteins the one on the left.
1. The test for proteins is known as the Biuret test.
2. The main reagents are aqueous sodium hydroxide (potassium hydroxide can also be used)
and copper (II) sulfate. A ready mixed reagent of the two chemicals called Biuret reagent can
also be used.
3. Procedure: First add copper sulfate solution to a solution of the food sample, followed by
either sodium or potassium hydroxide solution.
4. If proteins are present, a colour change from blue to purple will be observed.
Test for fats and oils
1. The test for fats is known as the ethanol emulsion test.
2. Fats in the sample are dissolved by adding ethanol. Water is then added to the ethanolic
mixture. Since fats do not dissolve in water, they form a cloudy white emulsion.
Combined Science notes by B.N Mupeti Page 6 of 128
, Biology section
Nutrient Test Original colour Positive result Negative result
Starch Iodine solution Brown Blue/black Brown
Reducing sugars Benedict’s solution Blue Brick red Blue
Proteins Biuret reagent Blue Purple Blue
Fats Ethanol and water ------------ Cloudy Clear
Water:
About 70% of your weight is water. Water is an essential nutrient. The functions of water
include:
• As a solvent which dissolves reactants of metabolic reactions.
• As a component of blood plasma in which red blood cells, nutrients, hormones and other
materials are carried in.
• It helps in lowering the body temperature in hot conditions in the form of sweat on the skin.
The sweat evaporates using heat energy from the body, thus lowering the temperature.
Enzymes
Enzymes are proteins that function as biological catalysts. Catalysts speed up the rate of
chemical reactions without being altered in the reaction.
Explaining enzyme action
1. Enzymes are biological catalysts that speed up the rate of chemical reactions without being
altered in the reaction. They are made of proteins.
2. They are substrate-specific. Substrates are the reactants that an enzyme acts on e.g.
amylase can only digest starch and not cellulose even though they are both polymers of
glucose.
Enzymes are believed to function using the lock and key hypothesis.
1. An active site is the region on an enzyme molecule that the substrate binds to. It is usually
a groove on the surface of the enzyme. Only the correct substrate is able to fit into the active
site.
2. Enzyme action begins when the substrate molecule binds to the active site of the enzyme to
form an enzyme-substrate complex.
3. The substrate is then converted into product molecules.
4. The product molecules depart from the active site, leaving the enzyme free to catalyse
another reaction.
Combined Science notes by B.N Mupeti Page 7 of 128
, Biology section
Investigating and describing the effect of changes in temperature and pH on enzyme
activity
Effect of temperature
1. At low temperatures, the rate of a reaction is very low because substrate particles are
moving too slowly to react. Substrate and enzyme molecules have little kinetic energy; hence
the frequency of collision is low.
2. As the temperature increases, the rate of enzyme activity increases. Substrate and enzyme
molecules gain more kinetic energy; hence the frequency of collisions between substrate
molecules and active sites of enzymes increases.
3. Enzyme activity increases up to an optimum temperature, beyond which it starts
decreasing. Enzymes which are found in the human body usually work best at about 37 °C.
4. As the temperature increases beyond the optimum temperature, enzyme activity drops
because enzymes are made of proteins, which are denatured at high temperatures.
5. At extremely high temperatures, the enzyme is completely denatured and the rate of
reaction drops to zero.
Combined Science notes by B.N Mupeti Page 8 of 128
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