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Biology revision
Variables
Independent- Something you can control
Dependent- something you cannot control
Categoric variable- things that can be described by a word ( put in categories)
Discrete variable- given in whole numbers ( number of boys in a school)
Ordered variable- data that can be put into order without a number ( height by
eye)
Continuous variable- one that is measured
Dependent variable always on the side of a bar chart, independent on the
bottom
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g
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Most common pathogens are bacteria and viruses
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Can be treated and killed with
antibiotics like penicillin as it is a bacterium that kills other bacteria so that it
has less competition for food
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Need a carbohydrate energy source to
grow
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Made up of a coat of
protein and a strand of DNA
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Antibiotics don’t work on viruses because virus`s reproduce inside
the cell so without killing your own cells they can’t be killed
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It protects against disease by:
Ingesting microorganisms- ingest pathogens, destroying them and preventing
them from causing disease
Produce antibodies- produce special chemicals called antibodies that target
particular bacteria or viruses and destroy them
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Once antibacterial have produced a type of
antibody they can produce it again quickly
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They are symptom relievers not pathogen killers
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Bacteria that kills other
bacteria that may take its food source
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Can’t be used on viruses
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Resistance Bacteria can become resistant to antibiotics as antibiotics
unwillingly do natural selection
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If the strong ones survive then they reproduce
making more strong bacteria that is now resistant to antibiotics
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In the period of time
the white blood cells are making the antibodies the pathogen damages your
body and that causes you to be ill
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So that you don’t get severely ill or die due to really bad pathogens you are
given a vaccination
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The antigen in the vaccine stimulates the white blood cells to start
making antibodies the pathogen without the chance of getting ill
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Cells recognise antigens as
`self ‘ or` foreign ‘

Pathogens can get into the body through:
Droplet infection- people breathing in pathogens that others release through
talking, sneezing or coughing
Direct contact- spread through direct contact to the skin (herpes)
Contaminated food and drink- eating raw or undercooked food or drinking
water containing sewage
Through a break in the skin- through cuts, scratches and needle punctures
The skin stops pathogens getting to soft tissue inside
Changing pathogens:
Many types of bacteria have developed antibiotic resistance as a result of
natural selection
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Another problem caused with the mutation of bacteria and particularly viruses
is that new forms of disease can appear
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Flu is caused by a
virus that mutates easily so every year new strains appear that can fool our
immune systems
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From hard parts of organisms which did not decay

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When harder parts of the organism were replaced by other minerals over
a long period of time (most common)
The oldest rock contains the simplest life forms the newest rock contains
more complicated life forms
Fossils also give evidence of animals becoming extinct (dinosaurs,
mammoth)
Lamarck
All animals evolved from a primitive worm and individual animals adapted
to suit their environment
The change from worm to other organisms was due to the inheritance of
acquired characteristics
Problems with his idea:
No evidence for the fountain of life
People did not like the tought of being descended from worms
Not all changes were passed onto offspring

Evolution- Charles Darwin
One of the effects of evolution is that a species will become better
adapted to their environment
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All the
creatures from the islands showed a marked relationship with those from
the American continent
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He saw different types of finches on the islands which
lead him to think of mutations as

Biology revision- coordination+control
The nervous system
Enables us to respond to our surroundings
Any change to our surroundings is known as stimuli
The cells in our body that detects stimuli are called receptors
Voluntary responses involve the brain
Automatic and rapid responses do not involve the brain (reflex actions)
Neurons- special cells that conduct electrical impulses, Bundles of hundreds of
neurons are called nerves
An impulse travels along the neuron until it reaches the central nervous system
Types of neurons:
Sensory neurons- carry impulses from your sensory organs (brain and spinal
cord)
Relay neurone- found in central nervous system, link sensory neurone to
motor neurone
Motor neurons- carry information from your central nervous system to the
body
-cause a response in an effector organ (muscles and glands) muscles respond
by contracting, glands respond by secreting chemicals called hormones
The human nervous system is made up of sense organs, the nerves, the brain
and spinal cord
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As
oestrogen levels rise the lining of the womb develops, once the egg is mature
the rising levels of oestrogen slow down the production of FSH until it stops
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When LH reaches its peak
itstimulates the release of the egg so that it comes out
IN Vitro fertilization (IVF)
Women given hormones to stimulate egg production
Eggs harvested from ovaries
In a Petri dish sperm added to some eggs to fertilize them
2/3 fertilized eggs implanted into the uterus to develop
Used if:
Not enough eggs being produced
Oviducts blocked
Poor quality sperm
Homeostasis
Maintain a constant internal environment
Things to keep constant:
Carbon dioxide levels, temperature, blood sugar levels, water content of the
body, Ion content
Thermoregulatory centre:
Controls the body temperature
Contains receptors sensitive to temperature change in blood flowing through
the brain
If the body gets too hot the enzymes denature (change shape) and cannot
catalyse the reactions in cells
Cooling down:
Vasodilation- skin capillaries open wider increasing the blood flow to lose more
heat by radiation from the skin

Sweating:
Rising core temperatures causes thermoregulatory centre to send impulses to
the body to bring about a response to cool the body down
Hairs on the body lie down
Heating up:
Vasoconstriction-skin capillaries get narrower slowing down the blood flow to
conserve heat
Hairs stand up to trap air in them which will then get hot
Less sweat made
Hormones and the control of plant growth
Plant roots sensitive to gravity and water
Plant responses:
Geotropism- response to gravity
Negative tropism- a response away from a stimulus
Phototropism- response to light
Tropism- any response to a stimulus
Positive tropism- response toward the stimulus
Hydrotropism- response to water
Auxins- growth of shoots and roots controlled by a group of hormones,
produced in the tip of the shoots and roots
One of the hormones used by plants for growth
Different effects depending where it is
Any concentration promotes growth
At the roots high concentration inhibits growth, small concentration promotes
growth

Sunlight breaks them down
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The area of the plant that is shaded has a
higher concentration of auxins
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Discovered that it stopped sickness in pregnancy
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Affected many women in the early stages
of pregnancy and they went on to give birth to babies with severe limb
deformities
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Cholesterol
Substance made in the liver and found in the blood
It is influenced by diet and inherited factors
Makes membranes in cells, sex hormones and hormones that deal with stress
Too much can block up the arteries and stop blood getting to organs
Statins
Drug used to lower cholesterol levels
Work by blocking a key enzyme in the production of cholesterol
Addiction- when a person is dependent on a drug
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Physical symptoms- sweating, headaches, shacking

Cannabis- class c drug
Drugs
Affect the transmissions of impulses across the junction of two neurons
Neurons are nerve cells that carry information as tiny electric signals
...
Signals cross the gap using
chemicals
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Inherited characteristics- characteristics only determined by genes
(eye colour, earlobe shape)
Acquired characteristics- change due to the environment (scars, hair
length)
Phenotype- all the observable characteristics of an organism
Genotype- full set of genes of an organism
An organism’s phenotype there for depends on its genotype and
environmental factors
Genetic information which is passed on from generation to
generation is contained in the nucleus and it contains all the plans
for making and organising a new cell
Humans have 46 chromosomes which are inside the nucleus of all
cells
Each gene is a small section of the long DNA molecule
Continuous Variation- a feature that can be measured and given a
value from a range of values (height, temp, skin colour)
Discontinuous variation- can`t be measured but is one of a few
distinct options (eye colour)
Types of reproduction:
A sexual- one parent, produces more organisms completely identical
to itself, very common in the smallest plants and animals and in
bacteria

Sexual reproduction- Joining of a male sex cell and a female sex cell
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The new plant is genetically identical to
the old one (tissue culture)
Cloning animals- farmers use embryo cloning to produce many more
top quality calves
Embryo cloning- give cow fertility hormones to make her produce a
lot of eggs
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At this
very early stage every cell of the embryo can still from all of the cells
needed for a new cow
 Divide each embryo into several different cells
 Each cell grows to an identical embryo inside the lab
 Transfer embryos into host mothers which have been given
hormone to get them ready for pregnancy
 Identical cloned calves born

Biology revision- Adaptations for survival
Adaptation in animals
Animals in cold climates- must be able to keep warm
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Surface area to volume ratio wants to be as small as
possible in these conditions
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Adaptations a dessert animal may have are: small
with a large surface area to volume ratio, long tail and big ears
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Plants take in water through their roots in the soil
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Plants lose water through small opening in their leaves (stomata),
open to allow gasses in and out for photosynthesis and respiration
but also for evaporation
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Plants in
dry conditions also store water in their tissues
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Cacti are the
most successful plants in a hot dry climate
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Competition in animals
Due to animals and plants growing alongside lots of other living
things they must compete for everything
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Carnivores compete for prey
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Carnivores also have to compete with members of their own species
for their prey as well as different species
Competition in plants
Plants compete for light, water and nutrients
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Tall plants like trees use up allot of water and minerals from
the soil and block light reaching smaller plants below
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These may be explosions to spread their seeds or having them in
fruit which animals eat and deposit somewhere else

Small plants found in woodlands often grow and flower very early in
the year so that they don’t have to compete with many other plants
so there is plenty of water, minerals and light which can reach the
plant through gaps in the branches of trees where no leaves have yet
grown
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Some have short
roots and get water and minerals from the top of the soil while
others have longs roots and get water and minerals from lower down
without affecting each over

Biology revision-Inheritance
People are different because they inherit different characteristics
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Inherit info from both parents
Cloning
Clones- genetically identical offspring produced by asexual
reproduction
New plants can be produced quickly and cheaply by cutting
trimmings of the live plant
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Fertilise eggs using sperm from a really good bull
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The nucleus from the original adult cell is placed in the
empty egg and the new cell is given an electric shock, this fuses the
new cells together and starts the process of cell division, an embryo
begins to develop, it is genetically identical to the original adult cell
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The nucleus of one cell has to
be fused with the empty egg of another animal which results in the
womb of a third animal
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desired characteristics can be copied

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some people don`t like it

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Genetic engineering
It is used to change an organism and give it new characteristics; it
involves changing the genetic material of an organism
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Genes can also be transferred to the cells of animals at an early stage
of development
Advantages

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Metabolic rate- rate at which the chemical reactions of the body are carried
out
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Type 1 diabetes- pancreas does not make any insulin
Type 2 diabetes- pancreas is under strain
BMI= weight in kg divided by height squared in m squared
Malnutrition- lack of proper nutrition
Hepatitis- disease characterized by inflammation of the liver
Influenza- A contagious viral infection of the respiratory passages causing
fever, severe aching, and catarrh
Weight problems
If you take in more energy than you use the excess is stored as fat
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Affects metabolic
rate, body shape, proportion of muscle to fat, risk of diseases as levels of
cholesterol are effected
Cholesterol- substance mad in the liver and found in the blood
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The amount of cholesterol is influenced by diet
and inherited factors
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Carried around in the blood by lipoproteins
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Fast food contains lots of saturated fat and salt and little vitamins and fibre

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