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CHAPTER 4: VARIATION AND

CLASSIFICATION

CAMBRIDGE SECONDARY ONE

SCIENCE


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4.1 WHAT IS A SPECIES?

A speciesis a group of organisms that

have the same characteristics and that

can breedith one another to produce

fertile offspring.

Very occasionally, ! organisms from

different species do breed ith each other.

Their offspring are hybridsof ! species.

A h"#rid #eteen a ma$e $ion and a fema$e

tiger is ca$$ed $iger. %igers& $i'e all hybrids are

infertile.


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Each species has a two-word Latin

name. (or e)amp$e& human species is

Homo sapiens.


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*ideo on $iger+


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4.! *A,IATI- I A SPECIES

Members of a same species are not all

exactly alike. Differences #eteen

individua$ mem#ers of a species are ca$$ed ariation.

We can sho the pattern of ariation in a

group of organisms using a fre!uencydiagram.


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4.! *A,IATI- I A SPECIES

"re!uency diagram

.um#erof

peop$e


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4./ I*ESTI0ATI0 *A,IATI-

sing the fre2uenc" diagram to co$$ect

usefu$ information

#umbe

rofpeople

$eight %cm&

'( ))()((*( )+()()( )( )'()/( )0(


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4./ I*ESTI0ATI0 *A,IATI-

The rangeis the spreadof alues. The

range for the height is '(-)0(.

The medianis the middle alue in "our

resu$ts. The median for the height is )(.

The mode is the most common alue. The

mode for the height is )(.The meanis the aerage. The meanfor

the height is 356756155611561!561/56

1456185619561561:5; < 11 = )*.(*


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4.4 C%ASSI(>I0 P%ATS

1lants

Mosses- Lie in damp, shady

places

- Do not produceflowers

- 1roduce spores for

reproduction

"erns

- 2row in shady places

- $ae leaes called fronds

- Do not produce flowers

- 1roduce spores forreproduction

3onifers

- Most grow into large trees

- 4hey hae narrow leaescalled needles

- 4hey reproduce using

seeds which are inside thecones

"lowering plants

- 5eproduce usingseeds that are

produced insideflowers


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4.8 C%ASSI(>I0 *E,TE,ATES

Vertebratesare animals ith backbones.

Vertebrates

"ish

- 6kin coered withscales

- 7reathe with gills

- Lay eggs in water

8mphibians

- 9nclude frogs, toads,newts and salamanders

- Lay eggs in water

- 4heir tadpoles breathewith gills

- 6mooth skin without

scales

5eptiles

- 6caly skins- Lie on land or in

water

- 5eproduce bylaying eggs on land

7irds- :nly ertebrates withwings, feathers and a

beak

- 5eproduce by layingeggs on land

Mammals

- Vertebrates with hair

- 2ie birth to lieyoung

- Mother suckles theoun


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4.9 C%ASSI(>I0 I*E,TE,ATES

9nertebrates are animals without

backbones.9nertebrates

Molluscs

%snails, slugs andoctopuses&

- $ae soft body

- $ae a muscularfoot

- 6ome haeshells

8rthropods

%insects, arachnids,crustaceans and myriapods&

- $ae ;ointed legs

- $ae segmented bodies

- $ae exoskeleton

8nnelids

%earthworms&

-


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4.9 C%ASSI(>I0 I*E,TE,ATES

8rthropods

9nsects

- / ;ointed legs

- 7odies diided into head,

thorax and abdomen

- Most hae pairs of wingsattached to their thorax

- 4he legs are attached to thethorax

- 8 pair of antennae on theirhead

8rachnids

- 0 ;ointed legs

- #o wings or antennae

- 6piders and scorpions

3rustaceans

- More than + pairs of;ointed legs

- pairs of antennae

- Lobsters, crabs and

shrimps

Myriapods

- Many pairs of ;ointed

legs

- 8 pair of antennae

- Millipedes andcentipedes


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