Biology GCSE Edexcel B1 Topic 1

I made these revision notes myself for when I was studying for GCSEs. I got an A* in Biology and 72 UMS in B1 by just using these notes.

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Classification, variation and inheritance B1 Topic 1
Scientists group organisms by looking at all the characteristics of each organism. Organisms with many
characteristics in common are grouped together as a species.
Different species that share many characteristics are grouped as a genus (plural genera). Genera that share
many characteristics are grouped as a family, and so on up to the level of kingdom.
The order of classification:
Kingdom Phylum Class Order Family Genus Species
The five kingdoms of organisms
Organisms may be classified into one of the five kingdoms, based on basic characteristics. For example, some
organisms are unicellular while other multicellular. Other organisms have cells which contain a nucleus, but
bacteria do not.
Another characteristic is the way the organism gets its food. Plants, for example, get their food
autotrophically using photosynthesis, while other animals feed heterotrophically by digesting other
organisms. Fungi also digest organisms but this is outside their body so they are said to feed saprophytically.
There is no kingdom for viruses because scientists do not believe they are alive; it may enter a cell and
change how it works to make copies of it cells, it does not show other life processes such as growth or
feeding which is present in other organisms.
Kingdom Main Characteristics
Animalia Multicellular; heterotrophic feeders (no chlorophyll); no
cell walls; complex cell structure with nucleus
Plantae Multicellular; autotrophic feeders using chlorophyll; cell
walls made of cellulose; complex cell structure with
Fungi Multicellular; cell walls not made of cellulose;
saprophytic feeders so no chlorophyll; complex cell
structure with nucleus
Protoctista Mostly unicellular; complex cell structure with nucleus
Prokaryotae Unicellular; simple cell structure with no nucleus
Vertebrates and invertebrates
Vertebrates are animals that have a backbone (a series of small bones called vertebrae).
All vertebrates belong to the phylum Chordata because they have a supporting rod that runs the length of
their body.
Animals that do not have a backbone are called invertebrates. The vertebrate and invertebrate groups are
then divided into smaller groups.
How to group organisms
Oxygen consumption
Organisms can be characterised in the way they absorb oxygen.
Fish ­ have gill to gain oxygen from water.
Young amphibians ­ also have gills
Adult amphibians ­ normally have lungs but can absorb oxygen through their moist skin.
Mammals, birds and reptiles ­ have lungs

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Organisms can be characterised based on how they reproduce.
External fertilisation ­ adult female releases her eggs in water and are fertilised by sperm released by an
adult male.
Internal fertilisation ­ takes place inside the female's body.
Oviparous ­ lays eggs (many vertebrate do this)
Viviparous ­ give birth to live young (mammals)
Organisms can be characterised on the way they regulate body temperature.
Homeotherms ­ keep their body temperature constant and often warmer than their surroundings from
reactions all over body.…read more

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An organism's scientific name has two Latin words, genus and species. This is called the binomial system.
Organisms that share the first word in their name are closely related. Scientists can tell from the name
whether two organisms are closely related.
The binomial system is useful in cases where organisms with common names are different species. A robin in
America is not the same bird as a robin the UK.…read more

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Genetic variation
All plants and animals have characteristics that are in some ways similar to their parents'. This is because an
organism's characteristics are determined by the genes inherited from their parents.
Most animals, and significant numbers of plants, get some genes from the mother and some from the father.
The combining of these genes from the two parents causes genetic variation. No two of the species are
genetically identical.
Genetic variation also occurs due to mutations ­ changes in an organism's genes.…read more

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Polar bears and penguins have adapted to living in the cold, freezing conditions of the Arctic and Antarctic.
Polar bears have:
o A compact shape which gives them a small surface area compared to volume which reduces heat loss.
o A thick layer of blubber for insulation which also acts as an energy store for when food is scarce.…read more

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Darwin knew there was competition between individuals. He also knew that pigeon breeders selected birds
with certain characteristics to breed which meant that those characteristics were inherited by the offspring.
Darwin realised that if the environment changes then different variations may be better suited to the new
conditions. Individuals with those variations will be more likely to survive and pass their characteristics on to
Therefore, the range of variation in characteristics of the population will gradually change over generations,
which is evolution.…read more

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Recessive allele: Version of a gene that will only have an effect if the dominant version of the gene is not
present (if both are present)
Homozygous: both alleles for a characteristic are the same the organism is homozygous for that
Heterozygous: if both alleles for a characteristic are different then the organism is heterozygous for that
Phenotype: The physical characteristics that a certain set of alleles cause.
Genotype: The alleles for a certain characteristic that are found in an organism.…read more

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Specific genetic disorders
Genetic disorders are diseases which are caused by faulty alleles. The allele for sickle cell anaemia is
recessive so two copies are needed to suffer from the illness. Sickle Cell Anaemia is bad as the red blood
cells do not function properly and they stick together and block up blood vessels. Sometimes, this can be
Sickle shaped blood cells also cannot carry oxygen very well as they have a smaller surface area so less
haemoglobin.…read more



This  a very detailed set of notes on classification, variation and inheritance which could be used not only for the Edexcel specification  but also in parts for the other biology specifications. Understanding of the key terms could be checked using the recommended flashcards.

fran morris

Wow this is brilliant thankyou so much!

James Webb

Thanks, this is brill!


Thanks! Hopefully the B1 exam goes well on Tuesday!


This is so AMAZING!! Thank you so much!!!

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