Edexcel B1 GCSE Revision Notes

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  • Created on: 04-01-15 12:25
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Biology Revision
Classification is organising living organisms into groups
Biologists classify organisms into groups based on how closely related they are to one
They are divided into 5 kingdoms: plants, animals, fungi, protocists and prokaryotes.
Plants make their food by photosynthesis. This is because they contain chlorophyll and
are autotrophs. They are multicellular and have rigid cell walls, which support the cells.
Animals are multicellular and don't have cell walls or chlorophyll. Animals are
heterotrophs. This means that they cannot make their own food and therefore have to
move about to find thing to eat.
Fungi are saprophytes. This means that they feed off dead organisms and decaying
material. They are multicellular and have a cell wall, but they don't have chlorophyll.
Protocists are unicellular- they are single celled and they have a nucleus.
Prokaryotes are also unicellular but they don't have a nucleus
Kingdoms are subdivided into smaller groups of organisms that have things in common
Vertebrates have a backbone and an internal skeleton. Invertebrates don't have this,
although some have an external skeleton.
Vertebrates are divided into five groups; fish, amphibians, reptiles, bird and mammals.
These are called classes.
Scientists divide vertebrates into classes based on three main things; how they absorb
oxygen, how they reproduce and how they regulate their internal body temperature.
Not all organisms interbreed- some reproduce asexually but they're still the same
If a male from one species breed with a female from a second species you'll get a
hybrid and these can fertile.
A ring species is a group of related populations that live in neighbouring areas. The
population that live next to each other can interbreed to produce fertile offspring.
In binomial system, each species is given a two-part Latin name. The first part refers to
the genus that the organisms belong to and the second part refers to the species.
The binomial system has helped scientists to; identify species, study species, conserve
species and target conservation efforts.
A key is a series of questions that you can use to figure out what an unknown organism
is. You start at question 1 and the answer to those questions is used to narrow down
your options of what it could be.

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Variation is differences within a species. There are two causes of variation; genes and
the environment.
All plants and animals have characteristics, meaning that in some way they are all
similar to their parents.
The characteristics are determined by the genes inherited from their parents
The combining of genes from 2 parents causes genetic variation.
Some characteristics are determined only by genes.
The environment that an organism lives in is also causes differences between
members of the same species.…read more

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Before scientists can publish their work it has to undergo peer review. This is when
other scientists read and review the work, to check it's valid and that experiments are
carried out to the highest possible standard.
Speciation and Genes:
Speciation is the development of a New Species
Speciation occurs when population of the same species become so different that they
can no longer breed together to produce fertile offspring.
Isolation is where populations of species are separated.…read more

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Sickle cell anaemia is also caused by a recessive allele. This is a genetic disorder
characterised by funny-shaped red blood cells.
The red blood cells can get stuck in the capillaries, which deprive the body cells of
oxygen. Symptoms include tiredness, painful joints and muscles, fever and anaemia.
Homeostasis is maintaining a stable internal environment
Conditions in your body need to be kept stable in order for the cells to function
properly.…read more

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The affected cells are called target cells. They have right receptors to respond to that
hormone- target organ.
Hormones travel at same speed as blood and have long lasting effects.
Neurones transmit information around the body
Neurones-the nerve cells- transmit information as electrical impulses.
They have branched endings called dendrons- they can connect with lots of other
Electrical impulses passed along axon of cell
Myelin sheath along the axon that acts as an electrical insulator, this stops impulses
getting lost- speeds up electrical impulses.…read more

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Relay neurones are many short dendrons and axons carry nerve impulses from sensory
neurones to motor neurons.
Sensory neurones are long dendrons and short axons carry nerve impulses from the
receptors in the sense organs to the CNS.
Reflexes are an automatic response to certain stimuli- they can reduce the chances of
being injured.
The passage of info in a reflex is called a reflex arc.
A reflex arc goes through the central nervous system.…read more

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Phototropism- the growth of a plant in response to light. Shoots grow towards the
Gravitropism (geotropism) - the growth of a plant in response to gravity. Roots grow
Auxin is the plant hormone that controls growth at the tip of shoots and roots.
It is produced in the tops and diffuse backwards to stimulate the cells behind the tips
to elongate.
The plant won't grow if it has no shoot
Shoots are positively phototropic.…read more

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Drugs have a big effect on what happens in your body.
Drugs can be beneficial or harmful.
Most drugs are chemical substances and affect the central nervous system
Tolerance develops when taking drugs so the body gets used to having it therefore you
have to have a higher dose to give the same effect.
Depressants- (alcohol) these decrease the activity of the brain. Slows down responses
of the nervous system- slow reactions.…read more

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The eyes- they produce a chemical called lysozyme which kills bacteria on the surface
of the eye.
The stomach- It kills of pathogens which you may eat in food. Killed by hydrochloric
acid in stomach.
Bacteria can mutate meaning that mutations cause them to become resistant to an
antibiotic. If treated only non resistant strains of bacteria will be killed
The bacteria will survive and reproduce and population will increase.
This could cause serious infection which cannot be treated.…read more

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Fertilisers which contain nitrates are essential to modern farming. Without the nitrates
wouldn't grow as well. This is because crops take nitrates out of the soil and these
nitrates need to be replaced.
Some of the fertiliser finds its way into rivers, lakes and seas. This can easily happen if
too much is applied or if it rains soon afterwards.
Too many nutrients in the water cause big growth, death and decay involving most of
plant and animal life.…read more


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