Biology 1 Topic 1


Classification is a way of organising living organisms into groups.

They are first divided into five kingdoms, (Plantae, Animalia, Fungi, Protoctists and Prokaryotes).

Plants contain chlorophyll and are autotrophs, meaning they make their own food through photosynthesis, They're multicellular and have rigid cell walls.

Animals are heterotrophs, meaning they can't make their own food. They are also multicellular but don't have a cell wall or chlorophyll

Fungi are saprophytes, meaning they feed off dead organisms, they're multicellular including a cell wall but no chlorophyll

Protoctists are unicellular and have a nucleus (algae). 

Prokaryotes are unicellular but don'thave a nucleus (bacteria). 

These are then divided into Phylum which includes Chordata (an organism with a backbone). 

The order of Classification goes   Kingdom, Phylum, Class, Order, Family, Genus, Species. 

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Accurate classification

Classification isn't easy to do accurately.

Organisms in the same species can interbreed to create fertile offspring, but it's not easy to classify organisms into these species. This is because:

  • Not all organisms reproduce in the same way as each other.
  • Sometimes if a male and female that are in the same species reproduce they produce fertile offspring that isn't in the same species due to being too genetically different.
  • Members of the same species don't always look alike, this is due to variation within a species e.g dog breeds. 
  • A ring species is a group of related populations that live in neighbouring areas. The populations next to each other can interbreed to produce fertile offspring, but those that live further apart can't.

The binomial system gives any organism a two-part Latin name, based on the genus and species. This helps scientists; identify species, study species, conserve species and target conservation efforts.

Keys are series' of questions used to identify different species' (options are narrowed down as more questions are asked). 

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Different species look different. A dog doesn't look like a donkey.

But even organisms in the same species can look different for example; human hair colour. These differences are down to variation in genes and the environment. 

Different genes cause genetic variation. Our genes are made up of the genes we inherit from our parents, meaning we may share some similarities. We get some from our mother and others from our father, the combination of genes from our mother and father is what causes genetic variation. 

Genetic variation is also caused by mutations, which can cause differences in characteristics.  

Characteristics can be influenced by our environment. For example getting a suntan or your hair being bleached in the sun. The environmental factors that cause this include; diet, exercise, temperature, light level and the amount of water.

Most characteristics are affected by both genes and environment. For example; height is based on genetics (the max height you can be) but your environment affects how tall you grow. 

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Continuous and Discontinuous variation

Continuous variation is when individuals in a population vary within a certain range (not in distinct categories). An example of this is height. 

  • Animals can be any mass within a range.
  • Microorganisms e.g. the width of E. coli bacteria varies within a range.
  • Plants can have any number of leaves within a range. 

The graph of continuous variation is an example of a normal distribution curve. 

Discontinuous variation is when individuals fit into only one of a selection of distinct categories, examples include:

  • Animals having only one blood group
  • Microorganisms can either be antibiotic-resistant or not
  • Plants e.g. the colour of a courgette is either yellow, dark green or light green. 

To test different types of variation you could measure the hand span of a group of people (continuous), or you could record the eye colour of a group of people (discontinuous). 

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Extreme environments

Some organisms have adapted to living in certain extreme conditions.

These include:

  • The deep sea: there is no light which means plants can't grow and food is scarce. In order to adapt some fish emit light, other have huge mouths to trap small particles of food and some have huge eyes and long feelers to locate prey and see better.
  • High temperatures: Some organisms live in hot places such as volcanic vents. These organisms use the chemicals in the vents to support bacteria as they can make their own food using chemical energy. This is called chemosynthesis. The conditions they live in are extremely hot and under high pressure
  • Extreme cold: Animals that live in polar regions have adapted to the cold.
    • Polar bears are compacted so have a smaller surface area, meaning they have reduced heat loss. They also have thick fur and blubber to keep warm and trap air to their skin. 
    • Penguins have a thick layer of insulating fat and oily feathers to reduce heat loss, they're also known to huddle together to conserve heat and are streamlined so can catch fish quickly. 
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Natural selection and Evidence for Evolution

Natural selection means "survival of the fittest".

Evolution is the slow/continuous change of an organism over time whilst it adapts.

This is when an organism has a gene that helps it to survive better, it will normally be passed on to it's own young. Over time, there will be a higher proportion of individuals with the beneficial characteristic. 

The evidence for it includes:

  • Common ancestors, we share.
  • Closely related species
  • Growing in resistance in animals (rats and the poison warfarin).

Scientists will validate evidence for certain evolution by discussing the evidence and making sure it is valid and reliable. This can be done through; scientific journals; peer review and scientific conferences. 

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Speciation and genes

Speciation is the development of a new species.

This occurs when animals of the same species are so different that they can no longer breed to produce fertile offspring. The process is:

  • Isolation is when populations are separated, this can occur due to a physical barrier for example; earthquakes or floods. 
  • Conditions on either side of this barrier may be slightly different (might have different climates). This difference means they may develop different characteristics which will become more common due to natural selection.
  • Eventually, the change in characteristics/genes will be so great that they will no longer be able to breed to produce fertile offspring. This is because they have become two different species

Body cells have a nucleus which contains genetic material in chromosomes. In humans, we have 23 pairs which each contains genes (short sections of DNA).

There can be different versions of the same genes, these are called alleles. Since they're two copies of each gene, they're two alleles, these can be the same or different.  

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Genetic diagrams

Genetic diagrams show the possible genes of offspring.

These diagrams use letters to represent alleles. If an organism has two alleles of the same gene then it's homozygous, if the two alleles are different it's heterozygous. 

If they are different then only one will be physically present. The allele for the characteristic that is shown is the dominant one, shown using capitalised letters.

In order for an organism to display a recessive gene, then both it's alleles will have to be recessive. 

Genotype means what alleles you have. Phenotype means the actual characteristic


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Genetic disorders

Genetic disorders are caused by faulty alleles which can create faulty proteins. 

Cystic fibrosis is a genetic disorder which is caused by a recessive allele. It affects the cell membrane and causes someone's body to produce sticky mucus in their air passage, gut and pancreas.  

Symptoms involve breathing difficulties, lung infections, malnutrition and fertility problems. The recessive allele that causes cystic fibrosis can be found in 1 out of 30 people. 

For a child to suffer from cystic fibrosis both parents must either be carriers or sufferers. If both parents are carriers there is a 1 in 4 chance of their child having cystic fibrosis and a 2 in 4 of them being carriers. 

Sickle cell anaemia is also caused by a recessive allele, it causes a person's red blood cells to be a funny shape. As they are a strange shape, they can become stuck in capillaries, which deprives the body of oxygen. 

Symptoms include tiredness, painful joints and muscles, fever and anaemia. If two parents are carriers there is a 1 in 4 chance of their child having sickle cell anaemia. 

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