Chapter 21 Cell Division BackNext Home 2 21.1How do cells divide? All organisms will eventually die

Chapter 21

Cell Division

Back Next

Home 2

21.1 How do cells divide?

All organisms will eventually die ...

Back Next

Home 3

21.1 How do cells divide?

However, life continues because organisms are able to produce offspring ...

Back Next

Home 4

21.1 How do cells divide?

The process of producing offspring is called ...

ReproductionReproduction((生殖作用生殖作用 ))

which involves the processes of cell divisioncell division

Back Next

Home 5

21.1 How do cells divide?

Cell divisionCell division

Mitotic cell division

(有絲細胞分裂 )

Meiotic cell division

(減數細胞分裂 )

… both involves replication of genetic material

Back Next

Home 6

21.1 How do cells divide?

Genetic information is carried in …

Chromosome

Deoxyribonucleic acidDeoxyribonucleic acid

((去氧核糖核酸去氧核糖核酸 ))

DNADNA

Back Next

Home 7

21.1 How do cells divide?

Chromosome

when highly coilsDNA

molecule

special protein

one chromosome

Back Next

Home 8

one chromosome21.1 How do cells divide?

Chromosome

chromatid (染色單體 )

chromatid

Back Next

Home 9

~ Word corner ~

** Chromo- Coloured

Chromosome

Brief RevisionBrief Revision

Back Next

Home 10

21.1 How do cells divide?

Chromosome

exist in pairs

homologous chromosome (同源染色體 )

Back Next

Home 11

21.1 How do cells divide?

Chromosome

number of pairs varies with different species

e.g. 23 pairs

humanshumans

Back Next

Home 12

21.1 How do cells divide?

Chromosome

number of pairs varies with different species

e.g.39 pairs

dogsdogs

Back Next

Home 13

21.1 How do cells divide?

Chromosome

number of pairs varies with different species

e.g.7 pairs

peaspeas

Back Next

Home 14

21.1 How do cells divide?

Chromosome

with 2 sets of chromosomes : diploid (二倍體 ) (2n2n))

with 1 set of chromosomes : haploid (單倍體 ) (nn))

Back Next

Home 15

** Haplo- Single

~ Word corner ~

** Di- Two

Diploid, Haploid

Brief RevisionBrief Revision

Back Next

Home 16

Mitotic cell division

mitosis(nuclear division)

cytoplasmic division

21.1 How do cells divide?

Mitotic cell division

two identical cells produced same chromosome no. as parent

Extension

Back Next

Home 17

• DNA molecules are replicated

MitosisJust before mitosis

cell membrane

nuclear membranes

chromosomes

Extension

Back Next

Home 18

MitosisStage 1

Nuclear membranes disintegrate

Chromosomes become visible

Extension

Back Next

Home 19

MitosisStage 2

Chromosomes line up at the middle of the cell

Extension

Back Next

Home 20

MitosisStage 3

Chromatids separate and move to the opposite ends

Extension

Back Next

Home 21

MitosisStage 4

New nuclear membranes are formed

Chromosomes become invisible again

Mitosis is now complete!

Extension

Back Next

Home 22

Cytoplasmic divisionIn animal cells

cell membrane constricts at the middle

Extension

Back Next

Home 23

Cytoplasmic divisionIn plant cells

new cell walls and cell membranes

form between two nuclei

Extension

Back Next

Home 24

Meiotic cell division

meiosis(nuclear division)

cytoplasmic division

Meiotic cell division four identical cells produced

reduce the chromosome no. by half

Extension

consists of two divisions

Back Next

Home 25

1) Chromosomes shorten and thicken

MeiosisFirst meiotic division

cell membrane

nuclear membranes

Extension

Back Next

Home 26

2) Homologous chromosomes pair up

MeiosisFirst meiotic division

Extension

Back Next

Home 27

Each chromosome consists of two chromatids

MeiosisFirst meiotic division

Extension

3) Nuclear membranes disintegrate

Back Next

Home 28

MeiosisFirst meiotic division

Extension

4) Homologous pairs line up at the middle of the cell

Back Next

Home 29

MeiosisFirst meiotic division

Extension

5) Members of each homologous pairs separate and move to the opposite ends of the cell

Cytoplasm starts to divide

Back Next

Home 30

MeiosisFirst meiotic division

Extension

6) New nuclear membranes are formed

Back Next

Home 31

MeiosisSecond meiotic division

Extension

7) Chromosomes line up again

Back Next

Home 32

MeiosisSecond meiotic division

Extension

8) Chromatids separate

Cytoplasm starts to divide

Back Next

Home 33

MeiosisSecond meiotic division

Extension

9) 4 daughter cells are formed (each has a haploid number of chromosomes)

Nuclear membranes are formed

Back Next

Home 34

1) Growth1) Growth

Significance of cell division

3) As a way of asexual3) As a way of asexual reproduction reproduction

2) 2) Repairing damageRepairing damage2) 2) Repairing damageRepairing damage

Mitotic cell division

Back Next

Home 35

Significance of cell divisionMeiotic cell division

1) Formation of haploid gametes

2n n (in gametes, i.e. sperm and egg)

meiosis

the diploid number of chromosomes can be restored after fertilization

sperm (n) + egg (n) fertilization zygote (2n)

Back Next

Home 36

aA

b B

Significance of cell divisionMeiotic cell division

2) Creation of genetic variations among gametes

Aa

B b

2 pairs of homologous chromosomes

homologous chromosomes arrange randomly at the middle of the cell

aA

B b

Back Next

Home 37

aA

b B

aA

B b

A

B

a

b

A

b

a

B

OR

OR

members of each homologous pair separate

Gametes with different genetic combinations

Independent aIndependent assortmentssortment((獨立分配獨立分配 ))

Back Next

Home 38

Brief RevisionBrief RevisionWhat is the difference between mitosis and meiosis?

Mitosis Meiosis

11 Place of occurrence

22 Pairing of homologous

chromosomes

33 Separation of homologous chromosomes

44 Number of divisions

Body cells

Does not occur

Does not occur

1

Sex organs

Occurs

Occurs

2

Extension

Back Next

Home 39

Brief RevisionBrief RevisionWhat is the difference between mitosis and meiosis?

Mitosis Meiosis

11 Place of occurrence

22 Pairing of homologous

chromosomes

33 Separation of homologous chromosomes

2, body cells

Diploid (2n)

Forms cells for growth, repair and

asexual reproduction

4, gametes

Haploid (n)

Forms haploid gametesso that the diploidcondition can berestored in the zygoteafter fertilization

55 Number and types of daughter cells

66 Chromosome number of each daughter cell

77 Significance

Extension