Cell:
The unit of
life
BY M. KAUR
Introduction
A cell is the basic structural and functional unit
of all living things.
Theodor Schwann
→The 2 postulates of cell theory:
▪ Cell is the basic structural and functional unit of life
▪ Cells arise from pre-existing cells
→There are 3 scientists who promoted cell Matthias
theory: Schleiden
• Theodor Schwann
• Matthias Schleiden
• Rudolf Virchow
Rudolf Virchow
Structure of a Cell
• Various Cells show different features BUT they all show a basic structural plan.
• This plan is called “Generalized cell”.
- It consists of 3 important parts:
a. Cell Membrane
b. Cytoplasm
c. Nucleus
Organelles – They are the living structure in the cytoplasm of the cell which have a
specific function to perform.
2 Types of Cells
↑ Animal Cell ↑ ↑ Plant Cell ↑
1. Cell Membrane & Cell Wall
Cell Membrane Cell Wall
• It is living. • It is non living.
• It has fine pores through which • It is made of +cellulose.
substances may enter or leave the
• It gives shape and a certain amount
cell.
of rigidity to the cell.
• It is composed of *lipoproteins. • It is freely-permeable i.e. Allows
• It is Semi-permeable i.e. It allows only substances to enter and leave the
certain substances to pass through it cell easily.
while preventing others.
• Also called Plasma Membrane.
*Lipoproteins - Any of a group of soluble proteins that combine with and transport fat or other lipids in the blood plasma.
+cellulose - A stringy, fibrous substance that forms the main material in the cell walls of plants.
2. Cytoplasm
• Contains a mixture of water and soluble inorganic and organic compounds.
• Contains all the organelles.
• All metabolic activities occur here.
• Medium for all initial steps of respiration.
3. Endoplasmic Reticulum
• It is the irregular network of double-membraned tubules.
• Continues with the plasma membrane on the outside and the nuclear membrane on
the inside.
• Has 2 types (a) Smooth Endoplasmic Reticulum and (b) Rough Endoplasmic
Reticulum.
SER
- Lacks ribosomes
- Supportive framework for the cell
- Transports substances
RER
- Has ribosomes on the surface
- Function -> Protein Synthesis
4. Mitochondria
• Shape is sausage like.
• It is double walled.
• Has its own DNA containing several genes.
• Has its own ribosomes.
• Releases energy from pyruvic acid produced in the cytoplasm in the form of ATP.
• Synthesises respiratory enzymes.
5. Golgi Apparatus & Dictyosome
• Golgi Apparatus → Humans & Animals
• Dictyosome → Plants
• They are stacks of flattened
membrane sacs.
• Consists of tubules, vesicle and
vacuoles.
• Their function is to Synthesize and
secrete enzymes.
• In animals & humans, they form
acrosome of sperms.
6. Ribosomes
• They are small granules either
scattered in the cytoplasm or
attached to the endoplasmic
reticulum.
• They are single walled dense, spherical
bodies.
• Function is to synthesize proteins.
7. Lysosomes
• Membranous Sacs that have budded
from Golgi Bodies.
• Contain 40 different types of enzymes.
FUNCTIONS
→ Intracellular Digestion.
→Destruction of foreign substances
→Destroy damaged organelles.
→Digest cartilage during the formation
of bones.
• Also called Suicide bags.
8. Centrosome
• Located near the nucleus.
• Contains one or two centrioles.
• Surrounded by radiating microtubules to for asters during cell division.
• Initiates and regulates cell division.
• Forms spindle fibers with the help of asters.
9. Plastids
• They are chloroplasts containing
chlorophyll
• They are double membraned and
contain DNA
• Have chromoplasts and chloroplasts
and Leucoplasts
10. Nucleus
• Regulates cell functions, thus called
brain of the Cell
• Spherical and dense
• Contains a network of thread like
structures called chromatin fibers that
Contain DNA
• If removed cell dies
• Contains Chromosomes
11. Nucleolus
• One or more round shaped structures in the nucleus.
• Produces ribosomes.
• Participates in protein synthesis by forming and storing
RNA.
• Dictates ribosomes to synthesize proteins.
12. Chromatin Fibers
• Made up of DNA threads
• Carry hereditary Information / genes
Thank You
