Cell cycle

1. The cell
 Cells are the smallest functional units of the
body or the cell is the basic unit of
biological organization of the human body.
 Our bodies are made up of trillions of cells.
They are grouped together to form tissues.
 Although cells have different functions in the
body, they all have certain common
structural properties.

2.  All cells are composed of protoplasm,
which is an aqueous colloidal solution of
carbohydrates, proteins, lipids, nucleic acids,
and inorganic salts surrounded by a limiting
cell membrane.
 The protoplasm of the cell is subdivided into
two sections: the protoplasm inside the
nucleus is called nucleoplasm and the
protoplasm outside the nucleus is called the
cytoplasm.

3.  A cell consists of a plasma membrane
inside which are a number of cell
organelles suspended in a watery fluid
called cytoplasm.
 There are TWO types of cells in the body
1. Body/Somatic/Diploid cells
2. Reproductive/Sex/Haploid cells

4. Human Body Cells
 *All human body cells have 46 chromosomes (23 pairs)
inside their nuclei (nuclei is plural of nucleus) except
sex cells (23 chromosomes).
 Body cells are also called somatic cells. They make up
our body/body parts/organs, e.g. skin, heart, brain, lungs,
intestine, bones, etc and the cells of all these organs have
46 chromosomes or 23 pairs which is a complete set of
chromosomes.
 A cell having a complete set of chromosomes i.e. 46
chromosomes is also called a Diploid cell (2n; n=23).
 Therefore, a body cell can be called to as somatic cell or
a diploid cell. They all mean the same.

5. Human body/somatic/diploid cell
 Inside this type of cell, inside
the nucleus there are 46
chromosomes as shown in
figure1.
 They are arranged in pairs.
 We can say 46 chromosomes or
23 pairs of chromosomes.
 2n means 2xn; n=23;
so 2x23=46
Figure 1. Chromosomes in
a male somatic cell

6. Human Sex Cells
 Sex cells are also called reproductive cells or gametocytes or
simply gametes.
 They are produced by the reproductive organs in both males
and females.
 In males the reproductive organs are the testicles or testes and
they produce the sex cells called as spermatozoa (sperms or
sperm cells).
In males
Singular – spermatozoan/sperm/sperm cell;
Plural – spermatozoa/sperms/sperm cells
 In females the reproductive organs are the ovaries and they
produce the sex cells called as ova (eggs/egg cells).
In females
Singular – ovum/egg/egg cell;
Plural – ova/eggs/egg cells

7.  All sex cells have an incomplete
set of chromosomes i.e. half the
number of chromosomes which is
23 chromosomes is also called a
Haploid cell (n) (n=23).
 As shown in Figure 2., the
chromosomes are not arranged in
pairs.
 Therefore, a sex cell can be called
to as gamete or a haploid cell.
They all mean the same. Figure 2. Chromosomes in
male sex cell

9. Figure 3. A chromosome contains the DNA which is the genetic material
of our body, and these are all present inside the nucleus of the cell.

10. Figure 4.
A chromosome
consists of two strands
of filaments attached
at a point.
The two strands are
called the sister
chromatids and the
point of attachment is
the centromere
(consisting of two
kintochore) and is
made of protein.

11. Mitosis
 Mitosis is the process of cellular reproduction/division
that occurs in the nucleus of somatic cells and results in
two identical nuclei. It is subdivided into four stages:
prophase, metaphase, anaphase, and telophase.
 If a somatic cell having 46 chromosomes divides, it will
produce two daughter cells with the same number of
chromosomes i.e. 46 chromosomes in each.

12. Figure 5. During Mitosis, the DNA coils up/condense to form
chromosomes. The centrioles also play an important role during this cell
division.

13. Bone cells (Body cells)

14. Muscle cells (muscle fibres)
(Body cells)

15. Nerve cells (Neurons) (Body
cells)

16. Reproductive/Sex/ haploid cells
Source: Write a short note on ovum and sperm, Questions & Answers, Vedantu Learn
Live Online.
https://www.vedantu.com/question-answer/write-a-short-note-on-ovum-and-sperm-
class-12-biology-cbse-5fc5b21ee78fd35e20fad788

17. Cell structures

18. Fig. The plasma membrane

19. Plasma membrane
 Consists of two layers of phospholipids
(fatty substances) with protein and sugar
molecules embedded in them.
 Cholesterol is also present in plasma
membrane.

20. Endoplasmic
reticulum

22. Golgi bodies

24. Mitochondri
a

25. Mitochondria

26. The cell cycle
 The cell cycle is an orderly sequence
of events by which a somatic cell
duplicates its contents and divides in
two.
 The cell cycle is divided into three
main stages: interphase (the stage in
which great activity is occurring but
this activity is not visible; thus, this
stage used to be called a “resting
stage”), mitosis, and cytokinesis.

27. Stages of the
cell cycle

28. Interphase - means between
phases
 This phase, the longest and most dynamic
part of a cell’s life, is not part of cell
division.
 Cell is growing, metabolizing, and
maintaining itself.
 Interphase has three subphases: growth
one (G1), synthesis (S), and growth two
(G2).

29.  G1 is the primary growth phase of the cell. It
occupies the major portion of the life span of the
cell. It is the time when the centrioles begin to
make copies of themselves in animal cells.
 The synthesis or S phase is when the strands of
DNA duplicate themselves.
 The G2 phase is the final phase for the preparation
of cell division. Centrioles finish replicating and
each cell now has two pairs. Tubulin is
synthesized.