This power point presentation was intended for the grade 8 learners. Science 8 Quarter IV

2. REVIEW!
Digestion Process
A. anus 1. ________
B. esophagus 2. ________
C. large intestine 3. ________
D. mouth 4. ________
E. rectum 5. ________
F. small intestine 6. ________
G. stomach 7. ________

3. REVIEW!
Digestion Process
A. anus 1. ________
B. esophagus 2. ________
C. large intestine 3. ________
D. mouth 4. ________
E. rectum 5. ________
F. small intestine 6. ________
G. stomach 7. ________
D
B
G
F
C
E
A

4. CHROMOSOME

5. Animal Cell Nucleus

6. DID YOU
KNOW?

7. The composition of the nucleus are the genetic
materials of an organism such as chromosome,
deoxyribonucleic acid or DNA and the gene.

8. Chromosome a threadlike
structure of nucleic acids and
protein found in the nucleus
of most living cells, carrying
genetic information in the
form of genes.
Gene a unit of
heredity which is
transferred from a
parent to offspring
and is held to
determine some
characteristics of
the offspring.
DNA is the genetic material
located inside a
chromosome in the
nucleus of the cell.
The DNA is a helical
structure consisting of two
strands

9. The DNA from the
parents is transmitted to
the offspring to ensure
the continuity of life. The
DNA is a helical structure
consisting of two strands

10. Histones
The organization or
packaging of DNA
molecules by proteins or
histones to form different
levels of chromosome
packaging. This is
necessary so that the long
and numerous DNA
molecules can be
organized and be
accommodated inside the
nucleus of a eukaryotic
cell.

11. Histones
Shows a structure called
nucleosomes which is
composed of globular
structures known as
histones where the DNA
strands are attached, and
coiled looking like beads
attached on a string in a
form of chromatin
measuring up to 11 nm.
Linkers
Nucleosome
(8 histones)

12. Histones
Linkers
Nucleosome
(8 histones)
Solenoid
(6 nucleosome)
The next level of
organization is a series of
chromatin molecules
forming a 30-nanometer
chromatin fiber of packed
coiled nucleosomes called
solenoid.

13. Histones
Linkers
Nucleosome
(8 histones)
Solenoid
(6 nucleosome)
This solenoid level of
packaging becomes
supercoiled forming loops
that are visible and are
usually called chromatin
loops which further leads to
condensation of the
chromosomes up to 700 nm.
Supercoil

14. Histones
Linkers
Nucleosome
(8 histones)
Solenoid
(6 nucleosome)
When the DNA molecules
is replicated and undergoes
also packaging and coiling,
it would form the entire
mitotic chromosome or
metaphase chromosome
which measures up to
1,400 nm
Supercoil

15. Parts of Chromosome
Two identical halves of a
replicated chromosome
after the Synthesis phase or
the S phase of the cell cycle.

16. Parts of Chromosome
The attachment points of the two
chromatids of a chromosome. It
is also described as the
constriction point which divides
the chromosome into two
sections, or “arms.”

17. Parts of Chromosome
Short arm – or p arm -
upper arms of the
chromosome which is
usually shorter.
Q arm - lower arms of
the chromosome which
is usually longer.

18. Chromosome number
•Every organism has its own specific number of
chromosomes
Examples: Human = 46 chromosomes or 23 pairs
Dog = 78 chromosomes or 39 pairs
Goldfish = 94 chromosomes or 47 pairs
Lettuce = 18 chromosomes or 9 pairs

19. CELL CYCLE

21. The same thing happens with the living cells. The
cell cycle can be compared to as the life cycle of a
cell, a series of growth and developmental steps a
cell undergoes between its “birth” and
reproduction.

22. Cell Cycle - series of events cells go through as they
grow and divide.
•Cell grows, prepares for division, then divides to
form 2 daughter cells – each of which then begins
the cycle again.
•The cell cycle may be divided into two stages:
•The interphase where the chromosomes are
long, and extended.
•The cell division or mitotic phase where the
chromosomes become condensed or
thickened.

23. Interphase is the interval between two cell divisions.
During this stage, the cell is not dividing; it merely grows.
The chromosome doubles or replicates itself because the
DNA molecule contained in the chromosome produces a
precise copy of itself.

24. Interphase is the interval between two cell
divisions. During this stage, the cell is not dividing;
it obtains nutrients and metabolizes, grows,
replicates its DNA in preparation for mitosis.

25. The interphase is divided into
three sub-stages, namely:
1. First gap period or G1 where
• cell grows initially
• synthesis of protein and
ribonucleic acid or RNA
occurs
• mitochondria increase
in number

26. The interphase is divided into
three sub-stages, namely:
2. Synthesis stage or S phase
where
• DNA are synthesized thus
replicating the chromosomes
in preparation for the next
cell division.

27. The interphase is divided into
three sub-stages, namely:
3. Second gap period or G2
where
• cell grows rapidly
• cell prepares for the actual
cell division

30. CELL DIVISION

31. Cell Division
Cell Division — process by which
a cell divides into 2 new cells
• Why do cells need to divide?
1.Living things grow by
producing more cells, NOT
because each cell increases in
size
2.Repair of damaged tissue

32. • The original cell is called the parent cell; 2 new cells are
called daughter cells
• Before cell division occurs , the cell replicates (copies) all
of its DNA, so each daughter cell gets complete set of
genetic information from parent cell
• Each daughter cell is exactly like the parent cell – same
kind and number of chromosomes as the original cell
Parent Cell
2
Daughter
Cells

33. •Many organisms, especially unicellular
organisms, reproduce by means of cell division –
called asexual reproduction – Ex: bacteria

34. The Animal Cell

35. Organelles involved in Cell Division
1. NUCLEUS
• The control center of the cell and is bound by
a nuclear membrane.
• It contains the genetic material DNA that is
replicated prior to cell division.

38. o 2 identical “sister”
chromatids attached at
an area in the middle
called a centromere
o When cells divide,
“sister” chromatids
separate and 1 goes to
each new cell

39. Chromatin
Duplicates
itself
Coils up into
chromosomes
•Chromatin to chromosomes illustration:
Why does DNA need to change
from chromatin to chromosome?
More efficient division

40. • All somatic (body) cells in an organism have the same
kind and number of chromosomes
Examples: Human = 46 chromosomes
Human skin cell = 46 chromosomes
Human heart cell = 46 chromosomes
Human muscle cell = 46 chromosomes
Fruit fly = 8 chromosomes
Fruit fly skin cell = 8 chromosomes
Fruit fly heart cell = 8 chromosomes
Fruit fly muscle cell = 8 chromosomes

41. Organelles involved in Cell Division
2. CENTRIOLES
• It is a minute cylindrical organelle arranged
near the nucleus in animal cells. They are
found in pairs and move towards the poles of
the nucleus when it is time for cell division.
• They are also involved in the development of
spindle fibers in cell division.

43. 2 types of Cell Division
Mitosis
• When body cells undergo a cell division.
• Somatic cells
Meiosis
• When sex cells undergo a cell division.
• Gametes (egg, sperm)

44. The Cell Cycle

46. MITOSIS
Prophase
– phase of chromosome condensation
Metaphase
– phase of alignment
Anaphase
– phase of separation
Telophase
– phase of nuclear formation

47. PROPHASE
• Nuclear envelope breaks down
• Nucleolus disappears
• Duplicated centrioles begin to move in
opposite poles and form spindle fibers
between them.
• Chromatin fibers become visible as they
condense, coil, and become shorter and
thicker.

48. PROPHASE

49. METAPHASE
• Chromosomes migrate randomly and line up
toward the equator.

50. METAPHASE (continued)
• Another checkpoint occurs at this stage
• When a chromosome is not properly aligned
at the mitotic spindle, mitosis will be arrested.
• As a result, of this checkpoint, sister
chromatids do not separate until a complete
set of chromosomes will be distributed to
each new individual.

51. ANAPHASE
• Sister chromatids separate and move towards
the opposite ends.

52. TELOPHASE
• Nuclei forms in both poles as new nuclear
membrane forms around the new nucleus.
• Nucleus reappears and spindle fibers begin to
disappear.
• Division of cytoplasm (Cytokinesis) begins and
is completed when the cell contents have
been divided equally to the two daughter cells
produced.

53. TELOPHASE (continued)

58. QUIZ
1. A phase that is composed of three stages and is mostly
involved in preparing the cell for cell division.
2. A phase where DNA is replicated.
3. A phase that re-checks all the necessary materials
before it proceeds mitotic phase.
4. A mitotic phase wherein chromosomes condensed and
nuclear membrane breaks.