7D Variation and Classification

© Tony P. Thould

September 2000

WHY DO THEY LOOK LIKE THAT?

Dalmatians have spots, some Roses are red, Blackbirds are black, Ducks have webbed feet and Chickens do not because they have GENES in the nucleus of their cells that instruct them to appear like that.

Genes on the thread-like Chromosomes

Every living thing has Genes

The sheep on the left has Genes that tell it to grow horns.

The sheep on the right has no such Gene and therefore has no horns

They are both Mammals as they both have genes for Hair but they are different breeds due to having some different genes making them look different.

DIFFERENT GENES

The Ovum cell the other half set of Chromosomes

in it’s nucleus

The Ovum must be fertilised by one

sperm cell

The nucleus in the sperm cell contains a

half set of Chromosomes

FERTILIZATION

Sperm + Ovum = Foetus

Carries the Male

Chromosomes in its Nucleus

Contains the Female Chromosomes in its Nucleus

These are each a HALF SET of Chromosomes so that when they

join together they form a WHOLE SET in the seed.

A baby with a full set of

Chromosomes

The ENVIRONMENT also plays a part in how they appear. If the environment changes different, more suitable genes will come into play and change their appearance to suit the new conditions.

If the climate changed to being very hot all year then the sheep with genes for thick coats would not be suited to survive and breed. They would die out.

Those with genes for thin coats of short wool would be more suited to the changed environment and therefore breed and become common.

These plants are from the same seeds but why is one taller if they have

the same genes?FENCE

It is the environmental conditions that have caused the tallness, not the genes this time

This one is searching for the light and has had to grow taller to reach it from behind the shadow of the fence.

What will happen to the moths with the worst camouflage in each case?

These two moths have settled on a light

coloured tree. Which one is the best suited by camouflage to blend in with its’ background?

These two moths have settled on a dark

coloured tree. Which one is the best suited by camouflage to blend in with its’ background?

The poorly camouflaged moths will be seen and eaten by predators and their numbers

will drop. The best suited ones will be left to breed and increase in numbers

The light coloured moth blends in with the light background. The dark one is easily spotted.

The dark moth now blends in and the white

moth is clearly seen.

THE SAME BUT DIFFERENT!

Have a look at the people in your class - they are all around about the same age but what about their heights?

How do you explain the Variation in heights?

CLASSIFICATION

Every living thing may be placed into one of two groups :-

VERTEBRATES

Animals that have vertebrae - a backbone, a spine

INVERTEBRATES

Have no backbone - no vertebrae, no spine

FLOWERING

Have flowers which may be brightly coloured or dull. The flowers make the seeds.

NON-FLOWERING

Do not make flowers but have cones, spores or some other way to reproduce

ANIMALS

Vertebrates Invertebrates

Cat

elephant

Worm

slug

List some examples of each type of animal

PLANTS

Flowering Non-flowering

List some examples of each type of plant

BY NOW YOU SHOULD KNOW…..

•That all living things can be split up into two groups

• That all animals can be split up into two groups

•That all plants can be split up into two groups

CLASSIFICATION SUMMARY

Vertebrates Invertebrates

AN IM ALS

Flow ering Non-Flow ering

PLAN TS

LIVING THING S

VERTEBRATE GROUPS

B irds Ma m m a ls

W a rm B looded

Fish R eptiles Am phib ia ns

C old B looded

VER T EB R AT ES

INVERTEBRATE GROUPS

W orm s Insects Arachnids Molluscs Crustaceans

INVERTEBRATES

FLOWERING GROUPS

M onocotyledons Dicotyledons

FLOWERING

NON-FLOWERING GROUPS

Fungi M osses Conifers Ferns

NON-FLOWERING

GROUP CHARACTERISTICS

Mammals•Vertebrates

•Warm blooded

•Have hair or fur

•Young are born live not in an egg

•Mothers feed young on milk from special glands

The animals in this picture are all mammals - how can you tell this by looking at the photo?

BIRDS

•Vertebrates

•Warm Blooded

•Have feathers

•Lay hard-shelled eggs

FISH

•Vertebrates

•Cold Blooded

•Scales cover their body

•Live in water

•Have Gills to breathe

•Have fins

REPTILES

•Vertebrates

•Cold Blooded

•Dry Scales cover the body

•Lay eggs with tough leathery shell

AMPHIBIANS

•Vertebrates

•Cold Blooded

•Have lungs

•Smooth moist skin

•Lay eggs in water

•Live on land and in water

What other groups are there?

Find out about the scientists who came up with different ways of

classifying living things.

N

A DICHOTOMOUS KEY

Used to identify Plants or Animals by answering a series of questions about what they look like, each of which have a choice

of two answers -

DICHOTOMOUS = Two choices

ALWAYS START AT QUESTION ONE EVERYTIME

Imagine that you do not know the names of the above animals. Use the Dichotomous Key to identify them:-

Q1 Is it mainly black?……………If yes go to Q2

…………….If no go to Q3

Q2 Does it have six legs?…………If yes = Black Ant

………….If no = Collie Dog

Q3 Does it have wings?…………..If yes = Butterfly

…………...If no = Grayling

A B C D

A

B C

D EF

Q1 Is it mainly green?……………….If yes go to Q2

…………...….If no go to Q3

Q2 Does it have six legs?………...….If yes = Grasshopper

……...….If no Frog

Q3 Does it have wings?……………..If yes = Go to Q4

…………...If no = Go to 5

Q4 Is it black?……………………....If yes = Swift

…………………If no = Ladybird

Q5 Does it have legs & pincer……..If yes = Crab

………..If no = Snake

Try writing your own Dichotomous Key

Q1

A B C D