This document provides an overview of cell division through mitosis. It begins by defining chromosomes and describing how DNA is packaged within cells. It then explains the stages of the cell cycle, including interphase and its subphases. The document delves into the stages of mitosis - prophase, metaphase, anaphase and telophase. It describes how identical daughter cells are produced and discusses the roles of centrioles, centrosomes and spindle fibers. The document concludes by comparing mitosis in animal and plant cells, focusing on differences in cytokinesis.
14. Three Main stages in the Cell Cycle
3. Interphase
(growth
- 90% of the time)
2. Cytokinesis
(Cytoplasm
division)
1. Mitosis
(nuclear division)
15. Interphase has three subphases:
3. G2
(Gap 2)
2. S phase
(DNA synthesis)
1. G1
(Gap 1)
16. What happens in each subphase?
synthesis and
replication of
organelles
synthesis of
proteins and RNA
DDNNAA ssyynntthheessiiss
cells that
do not
divide again
enter G0
18. The length of the Cell Cycle depends
on:
The type of cell:
usually the more
specialised the cell
the less likely it is
to divide
External factors e.g.:
temperature
food
oxygen supplies
RBC are
replaced at
a rate of 2-3
million/sec Nerve cells
usually never
divide
21. Question:
Suggest explanations for the following
observation.
Interphase is not a static stage of
the cell cycle. (2)
Proteins and RNA are synthesised,
DNA is replicated and organelles are
synthesised or replicated.
22. Question :
This question is concerned with cell division.
Give a brief description of the Cell Cycle. (2)
Nuclear division is followed by cytokinesis which
results in two cells.
Each cell enters interphase where proteins and RNA
are synthesized during the G1 phase.
DNA replicates during the S phase and organelles are
synthesized or replicated during the G2 phase.
23. Question:
The graph below illustrates how the quantity of
DNA, within a mammalian somatic cell, varies
during different phases of the cell’s cycle.
Additionally the graph shows the two growth
phases, G1 and G2, which are separated by an
intermediate phase S.
a) In terms of the
graph above, explain
what is happening
within the cell during
phase S. (2)
24. DNA replicates. Each chromosome consists of two
sister chromatids.
b)State ONE process other than cell growth which
occurs during phase G2. (1)
Organelles are synthesised or they replicate.
25. Cells divide for three reasons:
1.For growth e.g.
formation of a
bud in Hydra
2. To produce
gametes or spores
3.To replace
damaged cells
Mucor Salmon gametes mixing
26. TWO types of cells in the body
Non-reproductive
or somatic cells
Non-reproductive
or somatic cells
Gametes &
Spores
Gametes &
Spores
diploid number
of chromosomes (2n)
phagocyte
neurones
haploid number (n)
spermatozoa
pollen grains
(microspores)
27. Life cycle of animals
Human
Human
Haploid(n) – 23 chromosomes
Haploid(n) – 23 chromosomes
Diploid Diploid ((22nn)) – – 4 466 c chhrroommoossoommeess
29. - the process by which a cell nucleus
divides to produce two daughter
nuclei containing identical sets of
chromosomes to the parent cell
Mitosis in
root tip
30. - the process by which a cell nucleus
divides to produce four daughter nuclei
each containing half the number of
chromosomes of the original nucleus
- also called reduction division
Meiosis forms the ovum and
spermatozoa in animals.
33. Binary fission
in Amoeba
Budding in Yeast
4. Asexual reproduction
Single-celled eukaryotes reproduce
asexually
Simple multicellular eukaryotes
reproduce asexually
Hydra by budding
34. Mitosis occurs in
Animals
Animals
In Non-reproductive
or somatic cells
In Non-reproductive
or somatic cells
All cells in the body
except reproductive cells
phagocyte
Plants
•In meristem cells
•Tip of root /shoot
36. Centrioles
organelles in the cytoplasm
only found in animals cells
absent in higher plants
occur in pairs
lie at right angles to each other
able to self replicate
Mitotic
centre
(centrosome)
Mitotic
centre
(centrosome)
Centriole
37. Centrosomes
are organelles located near the nucleus
are not membrane-bound and serve as a
mitotic centre in animals – absent in plants
divide and migrate to opposite poles of the
cell during mitosis
38. Centrosomes
centrosomes and NOT centrioles are
responsible to assemble the spindle fibres
Spindle fibres
formed during mitosis and meiosis
it arranges the chromosomes into their
correct positions in preparation for cell
division.
Spindle
fibres
39. The spindle serves as a:
1. ‘railroad track’ along which the
chromosomes will move
2. framework keeping the two poles
apart
42. Interphase – prior to mitosis
each chromosome now exists as a pair of
chromatids joined together by a centromere
43. Interphase – prior to mitosis
at this stage each cell is 4n (four copies of
each DNA molecule, two in each
chromosome of a homologous pair)
A homologous pair Four copies of each
DNA molecule
44. Interphase – prior to mitosis
Chromosomes:
are long & thin
dispersed in nucleus
cannot be seen individually
Centrioles have replicated
Diffused
chromosomes
52. PROPHASE
in animal cells:
the centrioles move to opposite poles of the cell
asters form Asters: short microtubules
radiating from the centrioles
Function of asters:
help to manipulate chromosomes
during nuclear division to ensure
that each daughter cell has the
appropriate complement of
chromosomes
53. PROPHASE
the nucleolus disappear
the nuclear membrane
breaks up
spindle fibre is formed
58. METAPHASE
Chromosomes line up around the equator of the
spindle, attached by their centromeres to the spindle
fibres.
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68. TELOPHASE
the chromosomes:
reach the poles of the cell
uncoil and lengthen
spindle fibres disintegrate
nuclear envelope re-forms
nucleoli reappear
mitosis is complete at the
end of telophase
69. TELOPHASE can be viewed as a reversal
of prophase, bringing the cell back to the
state of interphase
Animal Cell Plant Cell
76. Cell division is still not complete at the
end of mitosis: as the division of the
cytoplasm has not yet begun
cytokinesis:
the division of the cytoplasm
cytokinesis normally:
follows telophase
leads into the G1 phase
of interphase
81. Cytokinesis: Plant Cells
Cell Plate Formation
Vesicles from the
Golgi apparatus
appear at the
equatorial plate.
Contents of
vesicles form the
cell plate – the
beginning of the
new cell wall.
These fuse to form
new plasma
membrane.
89. Question:
A researcher is provided with onion bulbs which are
sprouting following dormancy. She intends to use these
bulbs to study mitosis in onion cells.
Which parts of the bulb are suitable for this purpose?
2-3 mm from the root tips
90. Q: Account for the changes in the quantity of DNA in
the cell during mitosis. (2)
At the end of mitosis, quantity of DNA returns to the
original value as sister chromatids separate.
M
G1
S
G2
91. Question:
The drawing shows a stage of mitosis
in an animal cell.
a)Name this stage of mitosis.
Anaphase
b) Describe and explain what happens
during this stage which ensures that two
genetically identical cells are produced.
The centromere splits and the sister
chromatids carrying the same genetic
information move to opposite poles.
92. The table shows the average duration of each stage of
the cell cycle in the cells of a mammalian embryo.
Give one piece of evidence from the table which
indicates that these cells are multiplying rapidly.
Stage Mean duration /
minutes
Interphase 12
Prophase 50
Metaphase 15
Anaphase 10
Telophase 42
Interphase is short.
93. Question :
A student examined the cells in the garlic root
tip under the microscope, and obtained the
following data.
What do you conclude?
Stage Number of cells
Prophase 74
Metaphase 18
Anaphase 8
Telophase 10
Prophase is the
LONGEST phase
and anaphase
the SHORTEST.
94. Question:
A scientist intends to observe mitosis in cells of the
common onion (Allium cepa).
1. Which part of the onion plant should the
scientist use for observing cells undergoing
mitosis? (1)
Root tip.
2. Why is this part of the plant particularly
suitable for this purpose? (2)
The root tip is a growing point in plants. It
contains a meristematic region where cells are
continuously dividing.
95. 3.Describe how the scientist would process
the specimen (the plant structure referred to
in Question 1) in order to be able to observe
mitosis through a light microscope. Your
answer should refer the steps required to
prepare the specimen, to the staining
procedure and to the temporary mounting of
the specimen on a microscope slide. (9)
96.
97. The tips have been
stained red with
Feulgen stain.
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101. QQuueessttiioonn::
4. The scientist draws some of the cells that
have been observed. In which stage of the
cell cycle are the cells shown below? (4)
Cell A: metaphase
Cell B: interphase
Cell C: anaphase
Cell D: prophase
102. 10. In humans, each cell (except sex cells) has how many chromosomes? ______
11. After mitosis, how many daughter cells are produced? _______
12. After mitosis (in a human cell), each daughter cell has how many chromosomes? _____
13. How many phases are in MITOSIS? ___________
14. Which phase of the cell cycle is the longest? _________
15. During which phase does cytokinesis begin? __________
108. Cloned animals:
(Reproductive Cloning)
First cloned rabbit
by Chinese scientists
First cloned horse
by Italian Scientists
Snuppy: first cloned dog
from South Korea.
CC “CopyCat”
First cloned cat
from Texas.
Ralph: The first cloned
rat by French scientists
109. Tissue Culture
• used to produce clones
of a plant
• More identical plants
produced in a short
time.
110. Genetically Engineering
• Involves the insertion of DNA from one organism
into another OR modification of an organism’s
DNA in order to achieve a desired trait.
+ A strawberry
= resistant to frost
4 5
Arctic fish DNA strawberry
111. The Benefits of Genetic
Engineering
1. Human Insulin
2. Crops with herbicide resistance
3. Crops with virus resistance
4. Crops that are drought tolerant
5. Control the ripening of fruits
6. Crops with increased nutrition
7. Milk production in cows with
hormones
112. Disadvantages of Cloning
• No variation
• Same level of resistance to diseases or
pests
• Danger: Entire population of clones could
be eliminated if not resistant to new threat.
115. CCoollcchhiicciinnee
Is made from autumn
crocus (Colchicum
autumnale) - poisonous
Added to actively dividing
cells to inhibit spindle
formation
116. Chromatid pairs remain in their metaphase
positions
This technique enables the number and
structure of chromosomes to be examined
under the microscope
117. The DNA content of the cell as shown below
is 10 units.
What will the DNA content be at the end of
mitosis?
Every cell contains a complete copy of “the blueprint of life”
DNA consists of two strands of nucleotides - 4 bases (A,G,T,C)
23 pairs of chromosomes
If unwound and tied together, human DNA in one cell would stretch ~ 5 feet, but would be only 50 trillionths of an inch wide!
Genes are specific sequences of DNA, each of which “codes” for a protein with a specific function
Genes are copied each time a cell divides, passing on the blueprint