Module B3--Life On Earth

This PowerPoint explains everything you need to know about Biology Module 3 according to OCR 21st Century Science. The slides are numbered according to each topic. The PowerPoint also includes a key to understanding the topic. With this you are GUARANTEED to pass your Biology exam with flying colours!!

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Life on Earth…read more

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1. Adaptation and Variation
· Species: A group of organisms that can breed together to produce fertile offspring.
· Adaptation: Changes in the body to suit a location.
· Variation: Differences between members of the same species.
Animals and plant species survive in many different environments because they have adapted to
their environment. Adaptations help make individuals of a species more likely to survive and
produce offspring. Two different species breeding would produce infertile offspring. This means
that it is more likely that the whole species will continue to exist. For example a cactus is well
adapted to its environment in the following ways: [1] Rounded shape: Gives them a small surface
area compared to volume to reduce water loss. [2] A think waxy layer called a cuticle: further
reduces water loss. [3] Spines for leaves: Reduce water loss. [4] Thick stem: To store water. [5]
Shallow but extensive roots: To quicken water absorption over a large area. Individuals of a species
differ from each other slightly which is called variation. Most variations are passed on to the
individuals offspring. One of the causes of genetic variation is because genes change and mutate.
These mutations can be caused by coming into contact with radiation or chemicals or when
mistakes occur during cell division. If mutations occur in body cells they usually have no effect
although they can cause cancer. Mutations in sex cells have more effect because it will be passed
on to the offspring. This can cause the offspring to develop new characteristics which maybe
harmful to the organism or help it survive.
Polar bears are well adapted to their environment (the arctic) in the following ways: [1] White
appearance: Camouflage from prey in snow and ice. [2] Thick layers of fat and fur: For insulation
against the cold. [3] Small surface area to volume: Minimise heat loss. [4] Greasy coat: Sheds water
after swimming.…read more

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2. Natural Selection
· Natural Selection: Survival of the fittest
· Selective breeding: When humans choose feature they want to appear in the next generation
Natural selection is the process that causes evolution. Living things are not all the same-they vary.
Usually the resources that living things need such as food, water and space are limited. Individuals
compete for these resources in order to survive. This means only some of them survive. Some of
the variations of a particular species have an increased chance of surviving and passing on their
genes which means a greater proportion of individuals in the next generation will have the
characteristics that help them survive. Over time the species become better and better able to
survive. The `best' features are naturally selected and the species becomes better adapted to its
Selective breeding involves using only those animals or plants that have the desired feature to
breed. This differs from natural selection because selective breeding may promote features that
don't necessarily help survival.…read more

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3. Evolution
· Evolution: Process that can produce new species or can develop complex life forms from simple
Scientists estimate that life on earth began about 3500 million years ago. The first living things were
very simple. Life then evolved to become more complex and varied. Sometimes groups of
organisms become isolated from each other so they cannot interbreed. The following factors can
combine to make the two groups so different that they become two completely different species:
[1] Mutations: Can create different features in the two groups of organisms. Natural selection
works on the new features so that if they are of benefit then they spread through the population.
[2] Environment factors: The species in different places will develop different adaptations to the
different conditions they live in. There is good evidence for evolution such as: [1] Fossil records:
Show species getting more and more complex as time goes on. [2] DNA: Controls the characteristics
of living things and mutates and changes over time. All living things have similarities in their DNA
because they have all evolved from the same simple life forms. The more closely related two
species are the more similar their DNA is. Scientists use these similarities and differences in DNA to
work out how life evolved. Evolution by natural selection was proposed by Charles Darwin. He
came up with this by making many observations on organisms and applying creative thought to his
findings. Lamarck however argued that if a characteristic was used a lot by an animal then it would
become more developed. Lamarck stated that these acquired characteristics would be passed on to
offspring. However, people eventually concluded that acquired characteristics don't have a genetic
basis so they are unable to be passed on to the next generation. This is why his theory was rejected
in favour of Darwin's.…read more

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4. Biodiversity and classification
· Extinction: When a large number of species die out in a relatively short period of time.
Biodiversity includes the following: [1] The number of species on earth. [2] The range of different
types of organisms. [3] The genetic variation between organisms of the same species. Maintaining
biodiversity (by stopping species from becoming extinct) is also important because the more plants
we have available, the more resources there are for developing food crops. Also, new medicines
are discovered using chemicals produced by living things. So when the living organism becomes
extinct then their unique chemicals are no longer available. The rate of extinction is linked with the
growth of the world's population and the number of species extinctions. This suggests it is due to
human activities. In some cases humans cause extinction directly though hunting etc. but also
indirectly by destroying an organisms habitat. Classification is about organising organisms into
groups. Scientists group them together according to similarities in their characteristics and genetics.
They also classify them according to their physical features they have. All the millions of species on
earth are classified into 5 different kingdoms which are bacteria, fungi, algae, plants and animals.
They are then further divided. Classification shows us evolutionary relationships between different
organisms. Two organisms that are similar in classification with have lots of genetic and structural
characteristics so its likely that they both evolved from the same ancestor organism. Evolutionary
relationships can be shown for all living and all fossilised organisms.
There are two types of extinction: the first is called small scale extinction and is when a small
number of species becomes extinct and have little impact. The second is called planet wide mass
extinction and is when a large number of species die out or become extinct in a relatively short
period of time. A species is first threatened, then endangered and then extinct.…read more

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5. Interactions between organisms
· Interdependence: When organisms depend on other organisms.
Every living thing needs resources from it's environment. These include light, food and nutrients,
oxygen and carbon dioxide and water. If an essential factor in a habitat is in short supply the
different species need to compete for it. If there is not enough to go around some organisms wont
survive. This will limit the size of the populations in that habitat. Any change in the environment
can have knock on effects on to the other organisms. The interdependence of all living things in a
habitat means that any major change in the habitat can have far reaching effects.
The fossil record contains many species that don't exist anymore and fossils are the only way to tell
us that they existed at all. Rapid change in the environment can cause a specie to become extinct.
Here are three changes of extinction: [1] The environmental conditions change and the species
cannot adapt to the change. [2] A new species is introduced which is a competitor, disease
organism or predator of that species (this includes humans hunting them). [3] An organism in its
food web that is relevant or becomes extinct.…read more

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