Biology 1 Edexcel Science Overview Revision Notes.

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Grouping living things:

We can group living organisms based on external characteristics (phenotype). Some characteristics are unique to a group (such as feathers) and some are common to several (backbone).

Five vertebrae groups are:

  1. Fish
  2. Amphibians
  3. Reptiles
  4. Birds
  5. Mammals

Vertebrates are either cold-blooded (poikilothermic) or warm blooded (homeotherm).

Fish, amphibians and reptiles are piokliotherms. Birds and mammals are homeotherms.

All living things are grouped into one of five kingdoms

  1. Animalia – multicellular; cells do not have chlorophyll or a cell wall; they feed hetrotrophycally (find food from their environment)
  2. Plantae – Multicellular; cells have chlorophyll and a cellulose cell wall; they obtain food autotrophycally (make food by photosynthesis)
  3. Fungi – Multicellular; cells do not have chlorophyll and are surrounded by a cell wall NOT made out of cellulose. They feed Saprophytically (on dead organic matter)
  4. Protocista are unicellular but with a nucleus
  5. Prokaryote – Unicellular without a distinct nucleus


A species is a pair of two species that are able to breed together to produce fertile offspring. However, this is not always the case. Plants often produce fertile offspring and not all organisms reproduce sexually (some a-sexually)

Identification, variation and adaptation

There is continuous and discontinuous variation. Discontinuous includes eye colour and hair colour (limited options) whereas continuous includes height (constantly changing and has many different options)

Tongue rolling is discontinuous variation as people can either roll their tongue or not roll their tongue.

  • Variations such as those seen in hybrid ducks, which have characteristics of both parent species, can make classification complicated.
  • Ring species refers to chain of species that are closely geographically connected. Species within the chain show variation, they can still interbreed and produce hybrid offspring. However, the variations between the species at each end of the chain  are so great that they cannot interbreed. They are distinct species.

Adaptations can result from genetic mutations being passed through species or from environmental affecting factors. Polar bears, for example, have evolved through Darwinism to have thick fur and small ears to stop the release of heat.

Bacteria in deep-sea hydrothermal vents use the hydrogen sulfide from the 90ºc water releases to produce energy.

Evolution explains how we originate from the same animals and how natural selection, survival of the fittest and many other environmental and genetic mutations have meant that we change over the years and keep only the advantageous characteristics.

Genetic variation

Each sperm cell and egg contains half a set of chromosomes (23 from each in a human). Inherited characteristcs are controlled by genes which are sections of chromosomes. Chromosome are long molecules of DNA wound tightly in protein.

Our parents pass 50% of each characteristic during fertilization. However, the crossing over of genes (exchange of bits of chromosomes between pairs) and genetic mutations affect how we look and are.

Genetic terms:

Each chromosome in a pair carries the same genes in exactly the same place (locus). However, chromosome pairs may have different alleles on each chromosome.

If the alleles ofa pair are the same, the individual is homozygous for the characteristic.

If the alleles are different they are heterozygous.

An allele may be dominant or recessive. Dominant alleles mask the effects of a recessive allele.

All of the characteristics that make up an individual are the phenotype.

All of the genes are the individual’s genotype.

Pedigree – chart of characteristic showing genes passed from one generation to the next. They provide info about purity of lineage.

Monohybrid inheritance

Monohybrid is about a single characteristic, as studied by Mendel in his study about a pea plant.

Mendel cross-bred pure-breeding short plants with pure-breeding tall plants

He collected and grew the plants’ seeds and discovered their offspring were always tall. The ‘tall’ gene was the dominant one.

He then bred offspring together and found some plants were tall and some were short – this shortness was called a recessive gene.

A PUNETT SQUARE can be used to summarise the result of Mendel’s crosses between pure-breeding parent plants and first-generation plants.


Punnet squares are used to predict the probabilities of outcomes

You can use ‘T’ as dominant and ‘t’ as recessive.

This means is 50% pure-breed blue eyes and 50% recessive

The phenotype ‘blue eyed’ is expressed only in homozygous plants because the allele t is the same.

Genetic disorders

A change in a gene’s DNA is called a mutation

As genes carry instructions for building a protein, a mutation may alter a type of protein or cause no protein to be made at all.

If sperm and eggs carry a mutation, then any offspring will inherit the mutated gene.

Genetic disorders are the result of inheriting gene mutations.

Genetic mutations that cause mishaps:

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Cystic fibrosis and sickle cell disease 

Cystic fibrosis affects the movement of fluid in the lungs and causes thick, sticky mucus to form, particularly in the lungs and digestive tract.

Symptoms include:

  • mucus blocking airways of the lungs and causing breathing difficulties
  • lung infections because of bacteria becoming trapped in the mucus
  • problems digesting food, which can lead to malnutrition
  • bone disease

Treatments for cystic fibrosis include: nourishing diet, physiotherapy and massage.

Sickle cell disease:

Sickle Cell caused by a mutation that alters hemoglobin molecules and ...

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