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KS3 Biology

7D Variation and Classification



Contents

Spotting variation

What causes variation?

Summary activities

The classification system


What are the differences between these organisms?

Spot the differences


There are lots of differences between these organisms.

For example: some have leaves; some lay eggs; some eat plants.

These organisms are different because they are all from different species.

Spot the differences


There are also differences between organisms of the same species.

For example, these people are all from the same species but how many differences between them can you spot?

Spot the differences – same species


Even though people are all from the same species, there are many ways in which they are different from each other.

Some of them are male, some are female, some are tall, some are short.

The differences that occur both between different species and within the same species are called variation.

What is variation?


Contents

Spotting variation


Summary activities




Variation is caused by two factors:

1. Some features are cause by inherited factors.

These are features that are passed on from parents. For example, natural hair colour is an inherited feature.

2. Some features are caused by environmental factors.

These are features that are affected by the surroundings. For example, someone can be born with brown hair which then gets lighter in the Sun or might be dyed a different colour.



Environmental or inherited?


Sometimes it is not easy to determine whether a feature is inherited or environmental.

Scientists have now decided that only four characteristics are truly inherited and not affected by the environment at all.

Can you guess what they are?

Environmental or inherited?

1. natural eye colour2. natural hair colour3. blood group4. some inherited diseases


Some features are caused by a mixture of inheritance and the environment, for example, nose shape.

Someone might have a nose that looks just like their mum’s.

How can the environment affect skin colour?

What about other features?

But if they were in an accident, they might break their nose and put a kink in it.

So their initial nose shape was probably inherited but over time it is likely to have been affected by the environment.


Contents

Spotting variation


Summary activities




There is a lot of variation between organisms, but some organisms also have many features in common.

How many features common to both cows and dolphins can you think of?

Common features

Compare a cow and a dolphin, you might think they do not have many things in common but you will be surprised.


Common features


Cows and dolphins have several features in common.

Many other organisms also share common features.

Scientists use common features to put organisms into groups.

Grouping organisms based on their common features is called classification.

What is classification?


Sort these organisms into four groups based on their similarities.

Classification – grouping organisms


One way that a scientist might have grouped theseorganisms is to put them into the following four groups:

These groups come from the scientific system for classifying organisms.

Classification – grouping organisms

1. Plants

2. Birds

3. Mammals

4. Reptiles


The classification system begins with very big groups that include a lot of organisms and then moves down to smaller groups made up of fewer organisms.

The biggest groups are called the kingdoms.

All living things are classified into five different kingdoms.


plants protoctistaanimals monerafungi

living things


The five kingdoms


Which kingdom?


Classifying animals

How can different types of animals be classified?


Animal classification

invertebratesvertebrates

animals

Invertebrates are animals that do not have a backbone. They have soft inner bodies which are held in shape by a flexible covering of outer cells or by a hard covering called

an exoskeleton.

Vertebrates are animals that have a backbone. They have a firm body

because of the muscles that connect to their

skeleton.

The animal kingdom is divided into two groups:


Animal classification


Animal classification – activity


Features of vertebrates


Which type of vertebrate?


Which classification group?


whaletuna

perch

shark

sprat

sturgeon

trout

flounder

salmon

seahorse

In terms of classification, which of these organisms is the odd one out and why?

The odd one out

The whale is the odd one out. All of the rest are fish, a whale is a mammal.

whale


ravenpenguin

platypus

duck

kiwi

swanrobin

eaglepigeon

owl

In terms of classification which of these organisms is the odd one out and why?

The odd one out

The platypus is the odd one out. All of the rest are birds, a platypus is a mammal.

platypus


In terms of classification which of these organisms is the odd one out and why?

caterpillar

ladybird

ant

moth

horse fly

silverfish

scorpion

cockroach

lice

cicada

The odd one out

The scorpion is the odd one out. All of the rest are insects, a scorpion is an arachnid.

scorpion


Contents

Spotting variation


Summary activities




Glossary

classification – Sorting living things into groups.

environmental variation – Differences between organisms that are due to the environment.

inherited variation – Differences between organisms that are due to their parents.

invertebrate – An animal without a backbone.

kingdom – The largest groups that living things are sorted into.

species – A group of organisms that can reproduce with each other to produce viable offspring.

variation – The differences between living things.

vertebrate – An animal with a backbone.


Anagrams


Multiple-choice quiz

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