edexcel biology b1 notes

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B1 Topic 1 Variation
Classification: This is organising living organisms into groups.
Scientists classify organisms into groups according to how closely related they are to each other.
Nowadays scientists look at characteristics of organisms and many more features to place them into groups, for
example the system scientists use nowadays is to separate the organisms into 7 key groups in order to classify
Animalia Heterotrophic which means they feed The Animalia kingdom have a complex cell structure
off other animals or organisms, they with nucleus they are multicellular which means they
digest other organisms have a group of cells they also have no cell walls but
have a cell membrane.
Plantae Autotrophic feeders hence make their The Plantae kingdom have a complex cell structure with
own food using green pigment a cellulose cell wall and nucleus
Fungi Saprophytic feeders hence they digest The fungi kingdom are multicellular however they have
and eat other organisms outside the cell walls not made out of cellulose unlike plants and
body have a complex cell structure with nucleus
Protoctista These consist of seaweed and algae Mostly unicellular yet few are multicellular but they have
a complex cell structure with nucleus.
Prokaryotae This kingdom mainly includes bacteria These organisms are unicellular and have a simple cell
structure with NO nucleus.
Vertebrates and invertebrates
Vertebrates are animals which have a backbone or a spinal column, the backbone is a series of small bones calle
vertebrae invertebrates are animals which do not have a backbone. Animals have backbones to support their
body. Vertebrates and invertebrates are two groups used to classify animals. As well as this other factors are use

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As the groups become smaller the animals in that group seem to have mo
and more characteristics.
Scientists find it hard to classify some animals into the animal groups which are mammals, reptiles, fish, birds and
amphibians. For example the duck billed platypus.
The duckbilled platypus has many characteristics that connect it to different animal groups for example its duck b
connects it to bird group, but the fact that it has mammary glands and various other features makes the duck bille
platypus a mammal.…read more

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Also unrelated to the animal kingdom the definition of species is not always so clear cut
for example in plants and various fungi, different species can breed and produce fertile plants.
Ring Species
These are a group of related species that live in neighbouring areas, the species that live closer together
can interbreed to produce fertile offspring however the species that live the longest distance away or in
other terms on either ends of the ring cannot interbreed to produce fertile offspring.…read more

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This type of variation can be any number within a certain range for example human heights they
range from a variety of numbers but all within a certain range, another example of continuous
variation is weight.
Discontinuous variation
This type of variation is when there are a fixed set of values. For example shoe size, eye colour.
Discontinuous variation has fixed data.
Reasons for variety
There is variation in organisms as they are each adapted to their habitat hence have differences.…read more

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Evolution means the gradual change over time.
Competition this is when there is only a limited amount of resources and the organisms have to compete to
get the resources.
Glossary definition: when organisms need the same resources as each other, they struggle against each
other to get those resources.…read more

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The genotype is the alleles in the organism and the phenotype is the characteristic of the organism or how it
looks. If both the alleles in an organism are the same we call them homozygous however if the organism
has different alleles they are heterozygous.
The genotypes produced can also be shown in a punnet square.…read more

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Homeostasis this is when your body maintains stable conditions in your body in order for certain chemical
processes to happen. In basic word homeostasis is maintaining a stable internal environment.
Osmoregulation this is maintaining or regulating the water level in your body, keeping a balance between
the amount of water you drink and the amount of water you lose.…read more

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Neurotransmissions which are the travelling of these impulses
Dendron this is the ending of a branch in the neurone it connects to other neurones.
Axon This is where the electrical impulse is sent through.
Dendrites these are the endings of the branches of the Dendron and these receive the impulse.
Myelin sheath blankets the
axon preventing it from losing
the impulse as well as
speeding up the impulse.…read more

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Reflex arc Diagram then explain thoroughly.
A reflex arc is the connection between a
sensory neuron and a motor neuron often via a
relay neurone that allows reflex actions to
Hormones are produced and released by glands called endocrine glands. Hormones act as chemical
messengers travelling via blood. These chemical messengers cause certain parts of the body to respond to
them. For example when there is a rise in the human growth hormone the muscles and bones begin to
grow.…read more


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