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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$$ed $iger. %igers& $i'e all hybrids are
infertile.
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4.1 WHAT IS A SPECIES?
Each species has a two-word Latin
name. (or e)amp$e& human species is
Homo sapiens.
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4.1 WHAT IS A SPECIES?
*ideo on $iger+
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4.! *A,IATI- I A SPECIES
Members of a same species are not all
exactly alike. Differences #eteen
individua$ mem#ers of a species are ca$$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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