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IGCSE
Biology
Notes

Refined by KmQ

Unit 1 : Characteristics of living
things

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Biology is the study of living organisms
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MRS GREN
Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition
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Movement
Most organisms are able to move their whole body even plants can shift their stem towards
the sunlight and their roots move towards healthy soil
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Respiration
IT is the breakdown of food inside a living organism IT IS VITAL for survival
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Anaerobic Respiration which is the incomplete breakdown of food
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Equation, Glucose & O2 (not enough) to form CO2 Lactic Acid or
Alcohol (depending on the organism) & a little ENERGY
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Sensitivity
It is the ability to detect and respond to a stimulus
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Growth
It is the permanent increase in size and quantity of cells using materials absorbed from the
environment
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Reproduction
It is forming new individuals of the same species either sexual (2 parents) or asexual (1
parent) \
6
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Egestion is the removal of undigested
products which haven’t entered the cell
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Nutrition
It is the intake of food material from the environment
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Heterotrophic nutrition: Organisms that need readymade food including herbivores, carnivores &
omnivores
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Organisms are split into the following:

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•
•
•
•
•
•
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Kingdom
Phylum
Class
Order
Families
Genus
Species

Many Organisms

Few features in common

Individual Organism

Many features in common

A specie is a group of organisms that share the many similar appearances and can bread with
each other
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The first name is the name of the genus while the second name is the species name
e
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WOLF (Cannis Lupus) (must be italic and underlined)
The main groups of living are the 5 kingdoms
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The five kingdoms are: Bacteria, Protoctista, Fungi, Plants, and
Animals
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IT has a
protein coat around the DNA or RNA sometimes has spikes
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How a virus multiplies
1
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The genetic material multiplies
3
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Bactria
The size of bacteria
is about 0
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It is only seen under high
powered microscopes
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studyguide
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Fungi
•
•
•

Mostly multicellular (many cells) (yeast is an exception)
Cell wall made of chitin
IT has cytoplasm & it may be a saprophyte or a parasite

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•

It reproduces asexually by spore formation or by budding (in yeast) but in bad conditions
it reproduces sexually for survival

Yeast budding

Single fungi cell
Structure of a mould fungus

Budding is when a yeast cell splits into two cells and it keeps happening over and over again
numbers can get up to millions in just a day
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Plants

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Plants produce seeds from inside the flower
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Seed plants are divided into conifers and angiosperms
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Feature
Seed
Leaves
Root

Conifers

Monocotyledons
Dicotyledons
Seed
containing
one Seed
containing
two
cotyledon
cotyledons
Leaves containing parallel Leaves containing branched
veins
veins
Fibrous
root
system Tap root system with lateral
(adventitious)
roots
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studyguide
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The chordates and the invertebrates
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Comparison between Annelids, Nematodes and Molluscs
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Adaptation to insects on life on lands
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•
•
•
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Body covered in flexible chateaus exoskeleton
1 or 2 pair of wings
Joined legs for quick movement
Can live on all food materials
Can camouflage to hide from enemies

Chordates (or Vertebrates)
Chordates are vertebrates which are animals with back bones they consist of: Fish,
Amphibians, Reptiles, Birds, and Mammals
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Fish
•
•
•

Body covered in moist scales
Has fins to swim and gills for gas-exchange
Lays eggs in large amounts (eggs are soft with no shells)

2
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Some can camouflage e
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frogs
Young live in water & have gills & adults live on land & have lungs
Have 4 limbs
Lays soft non shell eggs
Has an ear drum

3
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Birds
•
•
•
•

Body covered in feathers
Beak for feeding
2 limbs and 2 wings
Lays water proof hard shells

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5
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studyguide
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Difference between plant and animal cells

Feature

Plant cell

Cell wall

•

Chloroplast
Vacuole
Food stored within
Carbohydrates
Protein
fats
Shape

•
•
•
•
•
•
•

Size

•

Present and made
from cellulose
Present
Present
Starch, glucose
Can store protein
Oil
Regular
shape
because of cell wall
Large

• Animal cell
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Absent

•
•
•
•
•
•
•

Absent
Absent

•

small

Glycogen
Cant store protein
Fats
Irregular shape

Similarities of animal and plant cells
1
...

3
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Cell membrane
Nucleus
Cytoplasm
Organelles
Organelles are found in the cytoplasm each one has a specific job e
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mitochondria
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Cell wall: Non living structure which is made of cellulose
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2
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Cytoplasm: jelly like substance where most chemical reactions happen
4
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It controls the activities of the cell and carries genetic
materials
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Vacuole: A fluid made of cell sap
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Chloroplast: Large bodies containing chlorophyll e=where Photosynthesis takes place
7
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Specialization of cells 1-4 (plants) 5-9 (animal)
1
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It has a large
number of mitochondria to provide energy for active up take
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Xylem vessels: It transports water and minerals to the plant
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It has thick
cell walls
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Phloem cells: They transport sugar and amino acids to the body from the place they were
made (the leaf)
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The cell wall where 2
phloem cells join together has holes which allows the cytoplasm of both cells to
communicate passing down the dissolved food
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Guard cell (stomata): Allows O2 and CO2 to pass in and out the leaf
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5
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It has no nucleus, t has
hemoglobin which absorbs oxygen, its shape gives it a high surface area and it is small to fit
in capillaries
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Nerve cells: they conduct electrical impulses which travel to & from the brain
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They
also have a layer of fat for insulation
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White blood cells: These occur in large amounts in the blood stream
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They are able to change shape and can penetrate the blood vassals to
enter tissues
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8
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9
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Tissue, organs & systems
Cells are the structural unit of life many cells join together to form tissues
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Many tissues join together to make an
organ
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Organs join
together to make systems which are groups of organs working together to make a certain
job
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Unit 4 : Diffusion, active transport
and osmosis
All the chemicals reacting in the cells need to get in and out either by a Passive
process: This doesn’t need energy e
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osmosis and diffusion or an active process:
one that requires energy e
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active transport
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Diffusion:
It is the movement of a molecule from a reign of high concentration to a reign of
low concentration down the concentration gradient which is the difference in
concentration of the substance, the greater the difference the higher the rate of
diffusion
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Osmosis:
It is the movement of water from a reign of high concentration (a dilute solution)
to a reign of low concentration (a concentrated solution) down the concentration
gradient through a semi permeable membrane
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3
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Unit 5 : Enzymes
Enzymes are portions that act like biological catalysts which speed up reactions
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Most enzymes are
inside the cell but some act outside it
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If the PH is too high or
too low then the enzyme will be denatured and won’t work
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Unit 6 : Nutrition and digestion
Nutrition is obtaining food materials from the
environment for growth and repair
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2
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4
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6
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Protein
Fats
Carbohydrates
Vitamins
Minerals
Fibers
Water

Tests for Food

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Carbohydrates
Carbohydrates are made in the chemical structure of carbon , hydrogen and oxygen
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E
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glucose
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g
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These are 2 monosaccharides joined together; they are sweeter
than monosaccharide’s and dissolve in water
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g
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Made out of many mono and disaccharides, they are insoluble in
water and don’t have a sweet taste
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Carbohydrates are very important because they produce energy
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Carbohydrates are always stored as
polysaccharides because this does not affect the osmotic pressure
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Fats
Fats are a source of energy
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(the amount of oxygen in fats is about half the one in carbohydrates)
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Proteins
Proteins are made from amino acids and the elements carbon, hydrogen, nitrogen and
sometimes sulphur
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They are used in growth
and repair and in enzymes and make up antibodies
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They are not digested but give the stomach something to
push against and work harder
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Minirals

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Vitamins

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Digestion
•
•
•
•
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Ingestion: taking food into a living organism
Digestion: Breaking down large insoluble food molecules into small soluble ones
Absorption: The process by which food molecules enter the blood stream
Assimilation: Making use of the absorbed food substances
Egesting: Getting rid of undigested materials
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The alimentary canal is lined with (epithelial, Goblet, and Muscle cells)

The mouth
Food is ingested and chewed
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This increases the surface area for the action of enzymes
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1
...

2
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As food does not remain in the mouth for very long, only a small
amount of starch is digested here
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Oesophagus
This tube pushes the food to the stomach by way of rhythmic contractions
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1
...

2
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They work in conjunction with each other to force the food down
to the stomach in a rhythmic wave
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It is called peristalsis
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The

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Stomach
When the food reaches the stomach gastric juice is released from the stomach lining
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1
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2
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The stomach has two rings of muscles at the top and bottom, called sphincter muscles
which prevent food from leaving the stomach while it is being churned around
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It is then allowed to continue on
its journey a bit at a time
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Digestive enzymes from the wall of the duodenum and from
the pancreas are added
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Another substance is added from the gall bladder
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It contains bile, which play a vital role
in fat digestion
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Bile salts breakdown the large fat drops into tiny
droplets which can mix better with water to create an emulsion
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The pancreatic secretions contain hydrogen carbonate ions to neutralize the stomach
acid
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Ileum
As food is digested the products are absorbed into the blood
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1
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2
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3
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4
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Colon
By the time the food reaches the large intestine all nutrients have been absorbed
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The water is absorbed here
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Unit 7 : Plant nutrition
(photosynthesis)
Green plants make their own food from sunlight
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The epidermis is a protective layer of cells and
contains no chloroplasts
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It is here that
photosynthesis takes place
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The spongy layer contains fewer chloroplasts,
enough to catch what the palisade layer cannot
absorb
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The vascular bundle provides the leaf with water via the xylem vessels
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The stomata (stoma - singular) are tiny pores that allow carbon dioxide to enter the leaf
while oxygen leaves the leaf
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At night the pores close, opening in the daytime
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studyguide
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Temperature
When the temperature rises the rate of photosynthesis rises also
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There is
an optimum temperature however
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Beyond this
temperature the enzymes controlling the reaction become denatured and the
reaction quickly comes to a halt
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As the light intensity
decreases the rate of photosynthesis decreases
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There comes a point though that any extra light energy will not increase the rate of the reaction
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At this point light is no longer a limiting factor
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This is because the plant has to spend a certain amount of time doing nothing, waiting
for more carbon dioxide to arrive
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There is a point at which further addition of carbon
dioxide will not increase the rate of photosynthesis
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Plant mineral requirements
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These mineral ions may be needed to make
certain chemicals or needed to make certain reactions work properly
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Below is a table of some of the common minerals and their uses
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Sulphur

•

Sulphates

•

To make
proteins

•

Poor growth,
yellow leaves
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Magnesium

•

Magnesium
salts

•

To make
chlorophyll

•

Yellowing between
veins of leaves
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•

Yellowing in young
leaves
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studyguide
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The
transport system in plants is the vascular bundles (xylem and phloem)

Water enters the plant via the roots by osmosis they are then carried up the xylem vassals
through transpiration which is when water is lost through the stomata
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The xylem vessels themselves are very thin tubes, like capillary tubes
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The cells which made the xylem vessels died to produce a continuous column
or tube
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studyguide
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Plants can have needle-like leaves
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-like fibers
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It creates a microclimate around the
leaf
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The
hairs prevent this humid air from being blown away
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Leaves can be folded
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The leaf blade is curled in on itself so that the stomata are on the
inside
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These substances need to be transported to the parts of the plant which cannot
make their own food
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Sieve tube
elements (the cells which make up phloem tubes) are arranged in long columns
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The cell walls at each end of the phloem cell are perforated to form sieve
plates
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The companion cell supplies the sieve tube elements with some
requirements as the sieve tube element cannot make things like proteins on
its own
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The effect of
temperature, humidity, wind speed and light intensity can therefore be looked at
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studyguide
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studyguide
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Humans have a double circulatory system which
means that the blood is pumped twice around the body once to the heart and another to the
rest of the body
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The blood traveling through to the body doesn’t pass through
them one at a time but rather the blood is separated amongst them such as a parallel circuit
in physics
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studyguide
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There are two chambers to each side of the
heart
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The
larger one is called the ventricle
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The right side of the heart receives deoxygenated blood from the
body and pumps it to the lungs, however the left side of the body receives oxygenated blood
and pumps it around the body so its force must be stronger
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In the heart both sides are pumped together and at the same time
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Blood enters the atria from the veins and is then forced into the
ventricles
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There are a number of sphincter
muscles and valves that prevent blood flowing the wrong way
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When blood flows the wrong way the valves bulge out, blocking the path
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2) The semi-lunar valves close, preventing back flow into the
ventricles
...

4) Blood from the veins flows into the atria, which begin to fill
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Diagram
shown)

(only

one

side

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ATRIAL
SYSTOLE
1) The atria contract, forcing blood into the ventricles, which fill
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VENTRICULAR
SYSTOLE
1) The ventricles contract, forcing blood into the aorta &
pulmonary
artery
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This happens because
the pressure of blood in the ventricles is higher than the
pressure in the atria
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3) The walls of the aorta & pulmonary artery expand
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There are muscles in the wall of
the heart that receive hormones from the brain telling it to speed up or slow down e
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adrenaline
...
This is one of the most
important arteries in the body because it supplies the heart with all the nutrients it needs
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This is how
coronary heart diseases (CHD) happen by the buildup of fats on the inside of the vessel
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Reasons for CHD:
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•
•
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Inheritance
Fatty diet: eating too much fats
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There are different types of
blood vessels
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These vessels split up into smaller
ones called arterioles
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It is from these
vessels that movement of particles to & from the blood takes place
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Veins

Arteries

Blood travels to heart

Blood travels away from heart

Large Lumen

Narrow Lumen

Thin wall with few elastic fibres

Thick wall with lots of elastic fibres

Thin muscular layer

Thick muscular layer

Valves present to prevent back flow No valves
Blood travels constantly

Blood travels in pulses

Blood under low pressure

Blood under high pressure

Blood moves slowly

Blood moves rapidly

Blood
The blood transport5 nutrients, gases, waste, hormones and heat The blood is also the main
defense against diseases as it has platelets that form clots and they have white blood cells
which have phagocytes which engulfs bacteria and lymphocytes which produce antibodies
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Clotting
When we cut ourselves we not only lose blood but we also make it easier for bacteria to get
inside our bodies
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For this to be effective it needs to be quick
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This enzyme is
released into the plasma when the platelets come into
contact with air or damaged cells
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Fibrin is sticky and forms long
threads creating a net, which traps some red blood cells
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Phagocytes,
attracted to the damaged site, engulf the pathogens
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This protects the
wound as the skin heals beneath
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studyguide
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Their role in defence
against disease is different
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When these are encountered a
phagocyte will surround the foreign body and engulf it
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There are two types of lymphocytes, B-lymphocytes and T-lymphocytes
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B-cells make special proteins called antibodies
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They work in a number of ways but all ways are effective
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When they find them they
inject them with toxins, which destroy them
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When you encounter the pathogen again, your
body remembers the past infection and is ready to fight it
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This is known as immunity
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All cells have on their surface proteins, which are called
antigens
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Transplant
Sometimes people get transplant s from other people with organs that have different antigens
so the body might attack the new organ
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Material exchange
Blood travels via arteries until it reaches smaller vessels called capillaries
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1
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These vessels are very leaky and are only wide
enough for one cell at a time to pass through
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The blood pressure forces some of the blood plasma to leak out of the capillary
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Large objects like red
blood cells and protein molecules cannot pass through the walls of the capillary
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It is from this fluid that
materials will diffuse into the cells
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White blood cells are the only cells, which can leave the blood, so they can hunt down
pathogens
...
Waste materials like carbon dioxide and urea diffuse from the cells into the tissue fluid
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5
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If it did not return the tissues would swell
with fluid
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Eventually the fluid (called lymph) drains back into the blood
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The blood leaves the capillary beds and travels back to the heart via veins
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Breathing is the
mechanical movement to ventilate the respiratory surface, it includes inhaling and exhaling
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2 types of respiration:

Aerobic respiration
It is the breakdown of glucose in the presence of O2
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This process is slow and is controlled by many enzymes
& the energy produced is not used immediately but stored as ATP
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studyguide
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In this process the energy produced is
relatively small and the product is variable
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In
the human body lactic acid is a product to anaerobic respiration during heavy exercise
...
That’s why we continue
breathing heavily after exercise the breakdown of lactic acid is called Oxygen dept
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studyguide
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This allows the lungs to move freely inside the pleural cavity
...
The trachea is a tube kept
in a rigid shape due to rings of cartilage
...
These lead into
the lungs
...
These end in tiny air
sacs called alveoli
...
The surface area of all
these alveoli is very large so as to be able to absorb oxygen very quickly
...
The cells lining the airways
have very tiny hair like structures called cilia on them
...
The beating cilia force the mucus and any particles of dirt up out of the lungs
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Characteristics of the alveoli
•
•
•
•

Large surface area: Big amounts of O2 can diffuse
Thin walls so gas exchange can happen
Rich supply of capillaries
Moist so gas dissolves in water

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The diaphragm and breathing
When we breathe in the diaphragm muscle contracts, pulling the sheet down
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These together increase the volume of the chest
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When we breathe out the diaphragm relaxes as does the intercostal muscles
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This forces air out of the
lungs
...

The
lungs
themselves are just like
balloons which are inflated
and deflated
...
Note that other
gasses
don’t
diffuse
because the concentration
of them in and out of the
body are not different
...
studyguide
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•
•

•

Nicotine This is the substance which makes smoking addictive
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It also makes the smoker more shaky
...

Carbon Monoxide This is created due to incomplete burning of the tobacco
...
If the smoker is pregnant then the baby will get less
oxygen than usual
...
It prevents the cilia in the lungs from
working and so the dirt and tar cannot be removed from the lungs
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Unit 11 :Excretion
It is the removal of waste products of metabolism and substances in excess of
requirements from organisms
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Organs that excrete:

The urinary system consists of two kidneys, two ureters a
bladder and a urethra
...
The blood is entered to the kidney by
the aorta and id filtered the clean blood then returns to the
heart and the urine then goes down the ureters and to the
bladder then to the urethra
...
Urea is a harmful substance
made in the liver it is made when proteins are broken
down
...
studyguide
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Most substances including O2 glucose
most of the water and some salts are absorbed
at the tubules to join the renal artery
...
Then the rest of the unwanted
substances are passed to the urter and then
out of the body
...
)

Osmoregulation
Is keeping the water and salt levels constant in the blood
...
If the concentration of water is too low e
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during heavy exercise as a
lot of water is removed by sweating the blood becomes too concentrated so the
hypothalamus senses too little water in the blood
...
This makes the membranes of the collecting
ducts become more permeable to water so more water passes
...
If the
concentration of water in the blood is too high then water moves into the cells by
osmosis and could cause them to burst so the water in the blood stops the
hypothalamus signalling the pituitary
...
The concentration
of urine depends on many factors e
...
diet, exercise and temperature
...
studyguide
...
It is only possible after a
satisfactory tissue-match
...

Dialysis:
In the absence of a suitable donor kidney, the alternative solution is for the
patient to be hooked-up to a dialysis machine every 2 - 3 days
...
Blood from an artery in the
patient's arm is pumped into the kidney machine which removes urea and
excess salts from it
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Unit 12: Homeostasis and
Hormones
IT is the maintenance of the conditions of the internal body environment
...

Hormones are chemical messages and chemicals released from an endocrine
gland into the blood controlled by the brain
...


Temperature cam be maintained by the skin
...

Hair: Sleeps and stands up to trap air which insulates temperature
...


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Blood sugar levels should be maintained
...

Blood sugar too low
Messages sent to pancreas to produce glucagon
Glucagon converts glycogen to glucose
Messages sent to pancreas to stop glucagon
...
c
...
A symptom of this illness is the presence of
glucose in urine
...
Phototropism is growth in response
to light
...

Hydrotropism is a response to water whereby the roots grow towards it
...
Roots show positive geotropism while shoots show negative
geotropism (in that they grow away from gravity)
...
Plant hormones are used in rooting powder to stimulate the
development of roots from plant cuttings
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Unit 13 :The nervous system
Any nervous action is a result of a stimulus
...
This could be
a noise, smell or the changes in blood sugar level
...
There are lots of
different types of receptors; some can sense light, while others can
sense heat etc
...
It gives a message to the
effectors to do something
...
This could be a muscle
which contracts or organs like the liver which may perform a complex
task like lowering the blood sugar levels after a meal
...

A stimulus cam be internal or external
...
An example of an
internal stimulus will be an increase in body temperature
...


Nerve cells
•
•
•

Motor neurons: transmit impulses from the CNS to the effecter muscle
Sensory neuron: transmits messages from the sensory neuron to the
CNS
Relay neuron: Links the motor with the sensory neuron
...
studyguide
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A synapse joins two neurons together
...

Have branched ends that receives impulses
...
studyguide
...
It is attached to special receptor cells or in some cases the
nerve's end is a receptor itself
...
It is here that the
cell meets with another neuron (or neuron) at a junction called a synapse
...
This causes a swelling
called a ganglion
...
studyguide
...
These cells have very long axons at the end of which are motor end plates
where the nerve cell can stimulate the effecter organ
...
The spinal
reflex does not need to pass through the brain but pass through a relay neuron
...


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Synapse
The synapse is a junction where two or more nerve cells meet
...
The synapse is also a way
of controlling the direction in which impulses travel
...
When an impulse reaches the synaptic knob, it releases vesicles of
a chemical called a neurotransmitter to be released into the synaptic cleft
...

When enough of the receptors have been filled an electrical impulse is triggered in this
neuron and off it travels
...
studyguide
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Choroid: A layer that absorbs light so no internal reflection happens
Retina: contains light sensitive cells
...

Vitreous humour: Helps maintain the shape of the eyeball
Lense: Responsible for the refraction of light in the eye
Suspensory ligament: Adjust the lenses shape
Iris: Controls the entry of light
...
studyguide
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The retina is
composed of two types of light sensitive cells
...
As a result they can only see in black and white
...

Cone Cells
There are three different types of cone cell, each sensitive to a different colour of light
...

These cells need a great deal of light in order to work and as a result are not able to
'see' in dim light
...


Accommodation
It means the ability of the lens to detect far and near objects by changing its thickness to
be able to see far and near

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