B1 - Cells
Characteristics of living things: movement, respiration, sensitivity, growth, reproduction,
excretion, nutrition
Note: respiration is different from breathing, respiration is chemical processes that break down
glucose and other substances to release energy.
Human cannot see teeny-tiny things such as cell, atom, etc. with naked eye  need to use a
microscope: hand lens magnifies about 10 times, light microscope magnifies about 1500 times,
electron microscope magnifies about 10 million times.
Plant and animal cells have:
- Nucleus: store genetic information on chromosomes, which is made of DNA
- Cytoplasm: jelly-like, contains 70% of water, is where metabolic reactions take place.
- Cell membrane: is a very thin layer of protein and fat, it is partially permeable (allow
certain substances to go through)
- Vacuole: plant cells have large vacuoles made of sugar and other substances called cell
sap, animal cells have smaller vaculoes
Only plant cells have:
- Cell wall: made of cellulose (fibers criss-crossing over one another)  form a very
strong covering  make the cell have a fixed shape and prevent the cell from bursting when
absorbing too much water. Because of big spaces between fibers, it is fully-permeable (allow
everything to go through)
- Chloroplast: contains green pigment called chlorophyll which plays an important role in
photosynthesis
Note: In textbook, it is said that vaculole exists both in plant and animal cells, but in mark
schemes for past papers, they said vacuole exists only in plant cells other than animal cells.
B2 - Movement in and out of cells
Diffusion: movement of molecules from a region of higher concentration to a region of lower
concentration as a result of random movement: concentration of CO2 outside the leaf is higher
than inside the leaf  CO2 will diffuse from outside to inside the leaf.
Osmosis: is the diffusion of water. Water moves from a region of highter water potential to a
region of lower water potential: when we drink water, areas ouside cell membrane have more
water potential than inside  water moves from outside to inside.
- When animal cells surrounded by water  water move in cells by osmosis  the cell swells 
cell membrance stretch, cell gets bigger and even burst.
- When plant cells surrounded by water  water moves in cells by osmosis  cytoplasm and
vacuole will swell  the cell wall prevents the cell from bursting.
Turgid: when there is plenty of water inside plant cells
Flaccid: when there is little water inside plant cell
IGCSE Biology Summary - by KhanhEdu
Plasmolsed: when there is so little water inside plant cell that the cell membrane shrinks and
tears away from cell wall  plants will die
Visking tubing: is something like cell membrance, which lets some substances pass through, but
not others. They are partially permeable.
Biological molecules
The bodies of living things are made up of:
Inorganic substances: water( about 80 %), oxygen, carbon dioxide, some acids, bases and salts.
Water is an important solvent for metabolic reactions to take place. Plasma needs water to
dissolve glucose to be transported around the body. Water also dissolve enzymes and nutrients so
that digestion can take place.
Organic substances: carbohydrates, proteins, fats
Structure of carbohydrates:
Carbohydrates: made from C, H, O
Monosaccharides: simplest form of carbohydrates, soluble in water: glucose(C6H12O6), fructose.
Disaccharides: more complex form of carbohydrates, soluble in water: sucrose, maltose, lactose.
All of the carbohydrates above are called sugars
Polysaccharides: most complex form of carbodydrates, almost not soluble in water: starch,
glycogen, cellulose.
Functions of carbohydrate:
- Provide energy by respiration: glucose will be transformed into energy both in animals and
plants.
- Transport energy: In animal's body, glucose is transported in plasma in blood. In plants,
glucose is changed into sucrose to be transported. When energy is needed, sucrose is changed to
glucose.
- Storing energy: plants store energy as starch whereas in animals, glycogen is stored in liver
and muscles.
- Making cell wall: cellulose protects and make the fixed shape of cells.
Testing for carbohydrates
- Testing for reducing sugars (glucose, maltose): Add Benedict's solution to food and heat it,
the color of mixture gradually changes from blue  green  yellow  orange  brick red
- Testing for starch: add iodine solution to sample of food, color changes from orange-brown 
blue-black
Structure of fats: made from C, H, O, made up of 1 glycerol and 3 fatty acids, insoluble in
water
Function of fats:
IGCSE Biology Summary - by KhanhEdu
- Release energy: one gram of fat releases twice energy than a gram of carbohydrates. Most cells
only use fats when all the available carbohydrates have been used up.
- Store energy: fats build up underneath the skin, can be used to release energy when needed
- Keep heat inside the body
- Plants store oils in their seeds: peanut, coconut, etc.
Testing for fats:
ethanol emulsion test: shake food with ethanol then pour the mixture into water, mixture changes
from transparent to emulsion containing millions of tiny opaque droplets.
Structure of proteins: made from C, H, O, N, S, there are millions of different proteins made up
of combination of 20 different animo acids. Some are soluble: haemoglobin, others are insoluble:
keratin
Functions of proteins:
- Make new cells: making keratin in hair and fingernail, haemoglobin in blood.
- Make cell membrane and cytoplasm.
- Make enzyme.
Testing for proteins: mixing the food with water, add dilute copper sulfate solution, then all
dilute potassium hydroxide solution, color change from blue  purple
Enzyme: is a catalyst made from proteins speeding up reactions inside body: amylase digests
starch, protease digests protein, catalase break down hydrogen peroxide to water and oxygen
The reactant in an enzyme-controlled reaction is called substrate
Every enzyme has a dent call active site, this has a shape that is complementary to the shape of
substrate. Enzyme breaks down substrate as the lock and key mechanism.
Properties of enzymes:
- all enzymes are proteins
- enzymes are denatured and inactive at high temperature
- enzymes work best at a particular temperature
- emzymes work best at a particular pH
- emzymes are catalysts, which means they stay unchanged after the reaction
- emzymes are specific, each kind of enzyme will only catalyse one kind of chemical reaction
Plant nutrition
Plants make organic substances (carbohydrates, lipids, proteins, vitamins) from inorganic
substances (carbon dioxide, water, minerals)
Animals feed on organic substances made by plants
IGCSE Biology Summary - by KhanhEdu
Photosynthesis (happens mostly in leaves): carbon dioxide + water  (sunlight + chlorophyll)
glucose + oxygen
Struture of leaves:
epidermis: top and bottom of leaf  protect the inner layers of cells
cuticle: waxy substance on top of upper epidermis  stop water from evaporating
stomata (singular: stoma): in lower epidermis  taking in carbon dioxide by diffusion
palisade mesophyll: contain chloroplasts
spongy mesophyll: large air spaces between them for letting in the CO2
xylem vessels: carry water
phloem tubes: carry sucrose
Leaf adaptation to obtain more carbon dioxide: large surface area help it expose to as
much air as possible, after diffusing through stomata, carbon dioxide easily go through air spaces
between spongy mesophyll  diffuse through cell wall and cell membrane of each cell.
Leaf adaptation to obtain more water:
Leaf adaptation to obtain more sunlight:
- Broad, flat surface of leaves help them to obtain as much sunlight as possible.
- Epidermal cells are transparent which allows sunlight to penetrate thought it and reach all the
palisade mesophyll cells which contain many chlorophyll.
- Chloroplasts inside palisade cells often arranged broadside on to expose as much chlorophyll as
possible to sunlight.
Uses of glucose:
- provide energy
- change to sucrose for transporting energy because sucrose is less reactive than glucose
- change to starch for storing energy
- combine with nitrate ions from the soil to make amino acids, which can be built up into
proteins  weak growth or yellow leaves will happen if there is deficiency in nitrogen.
- combine with nitrate ions or magnesium ions to make chlorophyll  yellowing between
the leaves will happen if there is deficiency in magnesium.
Animal nutrition
A balanced diet: contain all of these seven types of nutrient: carbohydrate (rice, noodle),
proteins (meat, fish, egg, milk), fats (cheese, butter), vitamins (fruit, vegetables, sunlight),
mineral (water), water, fibre (roughage): vegetables.
Vitamin C: found in oranges, limes. It makes the stretchy protein collagen found in skin.
deficiency disease: scurvy which causes pain in joints and muscles, bleeding from gums.
IGCSE Biology Summary - by KhanhEdu
Vitamin D: found in butter, egg yolk, sunlight. It helps calcium to be absorbed for making bones
and teeth. Deficiency disease: rickets, in which bones become soft and deformed.
Calcium: found in milk. It strengthens bones and teeth and for blood clotting. Deficiency diease:
bones and teeth become brittle, poor blood clotting.
Iron: found in liver, red meat. It is used to make haemoglobin which carries oxygen. Deficiency
disease: anaemia (not enough red blood cells to deliver oxygen)
Heart disease: When eating much cholesterol which exists in saturated fat found in animal
foods, we are more likely to get heart disease because fat deposits build up on the inside of
arteries, making them stiffer and narrower  the heart muscles run short of oxygen and cannot
work properly  coronary heart disease.
Obesity: People who take in more energy than they use up get fat  very fat = obesity. Obese
people are more likely to get heart disease, strokes and diabetes.
Malnutrition: is caused by not eating a balanced diet
Digestion:
- Ingestion: taking substances into the body through the mouth
- Mechanical digestion: Teeth are responsible for the breakdown of food into smaller
pieces without chemical changes
- Chemical digestion: the breakdown of large insoluble molecules into small soluble
molecules, this happens mostly in stomach
- Absorbtion: the movement of digested food molecules through the wall of the intestine
to blood
- Assimilation: the movement of digested food molecules from blood into the cells of the
body
- Egestion: passing out of food the has not been digested through the anus
Teeth:
Root: The part of the tooth that is embedded in
the gum
Crown: The part of the tooth that can be seen
Enamel: The hardest part of the teeth covered
the crown, sweet food causes bacteria to make
acids which dissolve the enamel  decay
Dentine: quite hard, which contain living
cytoplasm
Pulp cavity: contains nerves and blood vessels,
supply the cytoplasm in the dentine with
IGCSE Biology Summary - by KhanhEdu
food and oxygen
Cement: cover the root of the teeth, attach to
jawbone by fibers
Types of teeth:
- Incisors: sharp-edge, chisel-shaped teeth at the front of the mouth  biting off pieces of
food
- Canines: more pointed teeth at both side of the incisors  gripping food
- Molars: large teeth at the back of the mouth  chewing food
- Premolars: teeth between canines and molars
Alimentary canal:
Oesophagus: takes food down to the stomach
Trachea: takes air down to the lungs
Epiglottis: stops food from going down to the lungs
Chyme: the mixture of food, enzymes and mucus
Goblet cells: in stomach cell, secret mucus
IGCSE Biology Summary - by KhanhEdu
Small intestine: about 5m long, quite narrow, pancreatic juice is secreted from pancrease flow
through pancreatic duct into small intestine. This fluid contains many enzymes: amylase,
protease, lipase. These enzymes do not work well in acid environments  pancreatic juice
contains sodium hydrocarbonate (NaHCO3) which neutralises the acid.
Bile: made in liver, stored in gall bladder, flows to small intestine along the bile duct. It is
yellowish green, alkaline which neutralise acidic mixture from stomach. Bile salts in the bile help
emulsify fat, making it become smaller for easily digest. There is no enzyme in bile.
Villi: in the inner wall of small intestine. cells covering the villi make enzyme which complete
the digestion of food
Large intestine: undigested food travel from small intestine to large intestine. All the remain is
indigestible food (fiber, bacteria, dead cells from inside of alimentary canal) forms faeces 
passed out at intervals through anus
Assimilation: The nutrients dissolving in plasma are taken to other parts of the body where they
become assimilated as part of a cell
Transport in plants
Xylem: run from root to stem and leaf, transport water, one direction only: upward. Xylem
contains no cytoplasm or nuclei
Phloem: transport sucrose and animo acids from the leaves where they are made, to other parts
of the plant such as roots and flowers.
Vascular bundle: a group of xylem vessels and phloem tubes
Water uptake: root hair absorb water and mineral ions from the soil, root hair is very tiny, but
there is a very large number of them  large surface area  increase rate of absorbtion, water
moves into a root hair by osmosis
Transpiration stream: movement of water from the roots, up through xylem vessels, to the
mesophyll cells and evaporate out environment, and out through stomata
Cohesion: water molecules have a strong tendency to stick together. When water is suck up,
water molecule above pull others below, create water column
Conditions that affect transpiration rate:
- temperature: the hotter it is, the faster transpiration rate is
- humidity: the higher the humidity, the less water will evaporate
Transport of manufactured food:
Leaves make carbohydrates by photosynthesis, they also use some of these carbohydrate to make
amino acids, proteins, oils and other organic substances.
Translocation: transportation of organic food from leaves to whichever part of the plant needs it
in phloem tubes
IGCSE Biology Summary - by KhanhEdu
Source: place where sucrose and amino acids are produced: leaves
Sink: places receive nutrients: roots, flowers
Transport in mammals
The circulatory system: The oxygenated blood in the left-hand side of the heart has come from
the lung is sent around the body for respiration  deoxynated blood is brought back to the righthand side of the heart  goes to the lungs to become oxygenated again
Respiration and gas exchange
Respiration is series of metabolic reactions that break down the food we eat to produce energy
supply for our uses (contracting muscles, making new cells, making protein molecules…)
Aerobic respiration (with oxygen) both in plants and animals: glucose + oxygen  carbon
dioxide + water + energy
Aerobic respiration (without oxygen) in plants: glucose  alcohol + carbon dioxide + very little
energy
Aerobic respiration (without oxygen) in animals: glucose  lactic acid + very little energy
gas exchange: allow oxygen to move in and carbon dioxide to move out
pathway to the lungs: trachea  bronchi  bronchioles  alveoli
feature of alveoli make gas exchange more efficient:
- thin wall: easier for oxygen and carbon dioxide to diffuse in and out
- large surface area
Inspired air (air taken in): 21% oxygen, 0.04% carbon dioxide, variable humidity
Expired air (air breathed out): 16% oxygen, 4% carbon dioxide, high humidity
When you are running, aerobic reaction happens, convert glucose and oxygen to energy. but
when you are running too fast, your lungs can not supply enough energy  anaerobic reaction
happens, glucose  lactic acid + very little energy
Components of tobacco smoke:
- Nicotine: addictive drug, it makes blood vessels get narrower  increase blood pressure 
hypertension
- Tar: contains many different chemicals that affect the behaviour of some of the cells in the
respiratory passages and the lungs  cause them to divide uncontrollably  cancer
- Carbon monoxide: CO diffuses from the lungs into the blood and combines with haemoglobin
 less oxygen can be carried
- Smoke particles: Little particles of carbon get trapped inside the lungs  white blood cells try
to remove them by secreting chemicals that are intended to get rid of these invading particles 
these chemicals damage the lungs
IGCSE Biology Summary - by KhanhEdu
Coordination and homeostasis
stimuli (singular: stimulus): changes in organism's environment: temperature decrease
receptors: cells receive stimuli: cells under skin sense the changes of temperature
effectors: cells respond to stimuli: muscles contract and relax to make the body shaking to
increase the temperature
coordination: the way in which receptors pick up stimuli, then pass information on to effectors
2 way to sending information from receptors to effectors:
- by means of nerves: fastest
- by chemicals called hormones: slower
reflex arc: receptor  sensory neurone  relay neurone  motor neurone  effector
voluntary action: under conscious control: reading books
involuntary action: not under conscious control, arm draws back when finger touch a hot object
The eye: is a receptor organ. Its function is to detect light, transfer the energy in the light to
electrical energy in a nerve impulse
Reproduction in plants
Asexual reproduction: offspring produced from one parent. The cells in offspring are exact copy
of parent's
Sexual reproduction: offspring produced from 2 parents. Each sex cell of each parent is a gamete.
2 gametes fuse together to produce zygote which contains the combination of chromosome from
both parents
diploid: a cell has the full number of chromosomes, which two complete sets
haploid: a cell has single set of chromosome
e.g. in humans, sperm and egg are haploid, each of them has 23 chromosomes. When two of
them fuse together to produce zygote, which is diploid and has 46 chromosomes
Plants can reproduce asexually and sexually
Stamens: male parts of a flower, contain filament, anther. Anthers contain pollen grains, which
contain the male gametes
Female parts of a flower: carpels:
- ovary: contain ovules
- ovule: contain female gametes
- style
- stigma: catch pollen grains
IGCSE Biology Summary - by KhanhEdu
Pollination: pollen taken from the anther to a stigma by insects or wind
Fertilisation: pollen nucleus (male gamete) travels along the pollen tube into the ovule. It fuses
with the ovule nucleus (female gamete) to produce zygote
Reproduction in humans
Female reproductive organs: ovaries, oviducts, uterus, cervix
Male reproductive organs: sperm, testes (singular: testis), prostate gland
HIV: one of the sexually transmitted infections, HIV infects a particular type of white blood cell
AIDS: the next stage of HIV. When get AIDS, people are very vulnerable to other infections,
such as pneumonia
Preventing HIV transmission: through sex activity, through blood contact, from mother to baby
Inheritance
Inside nucleus there is chromosomes, each chromosome contains one very long molecule of
DNA, a part of DNA molecule is called a gene. The genes determine all sorts of things about
you: color of your hair, shape of nose, etc. (there are about 20000 human genes in 46
chromosomes in humans)
Each species of organism has its own number and variety of genes: humans have 46
chromosomes.
The two chromosomes of a pair are called homologous chromosomes.
Mitosis: type of division, which produces genetically identical cells. This type happens when an
organism is growing, repairing a damaged part and in asexual reproduction.
Meisosis: reduction division in which the chromosome number is halved from diploid to haploid,
resulting in genetically different cells.
Inheritance: the transmission of genetic information from generation to generation
Phenotype: the observable features of an organism: straight hair, white fur, etc.
Genotype: the genetic makeup of an organism in terms of the alleles present: AA, Bb, cc, etc.
Allele: different forms of gene: G, g, B, a, etc.
Homozygous: gene with the same alleles: AA, BB, gg, etc.
Heterozygous: gene with different alleles: Aa, Bb, Cc, etc.
Dominant: an allele that is expressed if it is present
Recessive: an allele that is only expressed when there is no dominant allele of the gene present
e.g. In one kind of rabbit, white fur is dominant, its allele is A, brown fur is recessive, its allele is
a
 AA: white, Aa: white, aa: brown
Genetic diagram:
parents' phenotypes: grey
charcoal
IGCSE Biology Summary - by KhanhEdu
parents' genotypes Gg
gg
gamates
G or g
g
offsprings
Gg or gg
Monohybrid inheritance: the inheritance of characteristics controlled by a single gene (mono =
one)
pure breeding: A group of identical individuals that always produce offspring of the
same phenotype when intercrossed: AA, BB, etc.  pure breeding strains are always
homozygous for the pure-breeding characteristics.
probabilities in genetics: AA x aa 
AA x Aa 
AA x AA 
Aa x aa 
Aa x Aa 
aa x aa 
Sex determination:
male gamate in humans has 23 chromosomes, one of them is sex chromosome, which is XY
famale gamate in humans has 23 chromosomes, one of them is sex chromosome, which is XX
 there is a 1:1 chance of it being boy or girl
Variation and selection
discontinuous variation: fit into one of definite categories, there are no in-between categories:
blood groups: A, B, AB, O
continuous variation: e.g. height: typical value of height of a person can be anywhere between
150cm to 180cm
normal distribution
variation happens due to gene or environment
Causes of genetic variation:
Organism and their environment
Habitat: the place where an organism lives (e.g. pond, lake, river)
Population: the number of organism of the same species
IGCSE Biology Summary - by KhanhEdu
Community: all the different species live in the same habitat
Ecosystem: community + environment
Food chain: diagram showing the flow of energy from one organism to the next, beginning with
a producer
e.g. grass  grasshopper  rat  cat  snake
Food web: a network of interconnected food chains
Producer: an organism that makes its own organic nutrients using energy from the Sun: grass,
tree
Consumer: an organism that gets its energy by feeding on other organisms: deer, elephant
Herbivore: an animal that gets its energy by eating plants: cow, buffalo
Carnivore: an animal that gets its energy by eating other animals: tiger, lion
Energy losses: When energy is passed along a food chain, some of it is lost to the environment
due to: energy lost as heat, when one organism eats another, it rarely eats absolutely all of it, not
all of the food molecules are digested and absorbed,
Trophic level: stage in a food chain
Carbon cycle:
IGCSE Biology Summary - by KhanhEdu