cell grade 8

2. Discoveries
Robert Hooke – 1665 – cell (cella) – dead cell from cork – micrographia.
Anton Von Leeuwenhoek (1632 – 1723 ) Simple Microscope – living cell
-1674.
N. Grew (1682) – cell concept
Alfonso Corti (1772) – observed living substance in the cell.
Robert Brown (1831) – nucleus in the root cells of orchid plant.
Von Mohl (1838 - 1846) & Johanus Purkinje (1839) – term protoplasm
M. J. Schleiden (1838) & Theodore Schwann (1839) – cell theory
Rudolf Wirchow (1855) – “ Omnis cellula e-cellula” – cells arise from the
pre existing cells – cell theory modification
Louis Pasteur (1862) – proved Wirchow’s statement
Knoll & Ruska (1932)- electron microscope.

3. All living organisms are composed of cells or cell products.
All the new cell as a result of division of pre – existing cells.
All cells are basically alike in chemical composition and metabolic
processes.
All functions of an organism as a whole is the outcome of the combined
activities and interactions of the constituent cells.
Cell is the structural and functional unit of all living beings.

5. Size size
Microscopic to larger one – size of an organism is not depends
on the size of the cell and it depends on the number of cells.
Shape
Many shapes ( spherical, oval, elliptical, spindle, polygonal etc,.) –
depends on different functions (nerve, sperm, muscle etc,.) –
differentiated in multicellular organisms.
Number
Unicellular (amoeba, paramecium, bacteria etc,.) – short life – a
single cell can do all the functions.
Multicellular (funigi, plants and animals) – long life – similar basic
structure and life activites. Differentiation.

6. Cell – the basic unit – performs all the functions with the help of cell
orgnelles.
Unit of protoplasm nucleus and cyto(plasm) – a life giving substance
surrounded by cell membrane.
Cell membrane or Plasma membrane
Delicate elastic membranous outer covering. Separates cytoplasm from
environment
It is a living, selectively permiable membrane
Madeup of bilayer lipids and proteins – Fluid Mosaic Model – Singer and
Nicholson.

7. Functions of plasma membrane
Provides definite shape to the cell
Functions as a mechanical barrier between external and internal
environment of the cell.
Regulates the movement of molecules in and out of cell.
The flexibility of the membrane helps the cells to engulf food and the
substance from external environment by endocytosis.
Transport across the membrane
Passive transport
 Diffusion (higher concentration to lower concentration)
 Osmosis (lower concentration to higher concentration)
Diffusion Osmosis
Takes place in solid, liquid and gas
mediums.
Takes place only in liquid medium.
Does not involve semi permiable
membrane.
Requires semi-permiable membrane.
Not much influenced by the presence
of other substances.
Influenced by concentration and type
of solute particle.

8. Active transport
Process of transport of molecules across the plasma membrane against the
concentration gradient. ATP will be used as carrier proteins. Glucose, amino
acids and ions pass through plasma membrane.
Cell wall
 Present in plant cells – outside the plasma membrane.
 Composed of cellulose, hemicellulose and pectin.
 Middle lamella (cementing layer) present in between the wall of two adjacent
cells.
 Animal cells : no cell wall ; plant cells : chitin
Cell wall Cell membrane
In plants In plants and animals
Outer layer of plant cell. Present outside in animals and inner to the cell wall
in plants
Thick and rigid. Thin and flexible.
Formed of cellulose and pectin. Formed of lipids and proteins.
Permiable. Selectively permiable.
Allowing the substance without hindrance. Mechanical barrier – regulates the movement

9. Functions of cell wall
Gives definite shape to the cells and protects again mechanical injury and
pathogens.
Provides mechanical strength to the plants.
Helps in transport of various substances across it.
Helps the plant cells to withstand a lot of variation in the surrounding
environment.
Prevents the bursting of cell on endosmosis as it is quite thick and rigid.
Nucleus
Robert Brown – 1831
Prominent spherical structure – largest organelle – controlling centre – brain of
the cell
Plants – nucleus lies towards the periphery due to central vacuole.
Has a double layered covering – nuclear membrane – transportation
Nucleus contains chromosome composed of DNA and protein.
Prokaryotes – nucleic acids – nucleoid
Organisms with nuclear membrane – eukaryote.

10. Nuclear envelop
•Double membranous structure – separates nucleus from the cytoplasm –
made up of protein and lipids.
Nucleoplasm (nuclear sap)
•Colourless cytoplasm within nuclear membrane – chromatin network and
nucleoli are suspended.
Nucleolus
•Rich in protein and RNA. Factory of ribosomes.
Chromatin network
•Coined filaments distributed in the nucleoplasm – made of DNA and
protein – during cell division chromatin become highly condensed, thick
and rod like structures known as chromosomes.
•Chromosomes – chromatids – centromeres – arms (two parts on either
side)
Chromosomes contains genes (functional units of chromosome) which
are composed of DNA. Arranged in a single linear order along the
chromosome. Genes – characters – hierarchy.

11. Chromosome sructure

12. Controlling center – controls all the metabolic activities.
Hierarchy
Participates directly in the cell division to produce genetically identical
daughter cell by a process known as mitosis.

13. Prokaryotic Eukaryotic
Plant cell Animal cell
•Cell wall
•Plasma membrane
•Cytoplasm
•Mesosomes
•Ribosomes
•Inclusion bodies
•Nucleus
•Cell wall
•Plasma membrane
•Cytoplasm
•Nucleus
•Plasma membrane
•cytoplasm

15. Shapes of prokaryotes – coccus, bacillus, vibrio, spirillum and
spirochaete.
Prokaryotes Eukaryotes
An organized nucleus is absent.
Hereditary material (nucleoid) is not
covered by the nucleus. Nuclear
membrane is absent.
A well organized nucleus is present. It
contains hereditary material covered by
a nuclear membrane.
A single chromosome is present and is
represented by a single circuler DNA
Numbers of rod like chromosomes,
with two or several DNA molecules
Membrane bound cell organelles are
absent
Membrane bound cell organelles are
present.
No compartments are found in
prokaryotes.
Distinct compartments will be present
in eukaryotes.
Ex. : bacteria and cyanobacteria. Ex. : plants animals and fungi.

16. Cytoplasm
•Occupies the major part – living compartment of cell.
•Transparent – semi fluid, granular substance.
•Limited on the outside cell membrane – water is the main component.
Cytosol
•Fluid part of cytoplasm.
•Viscous and contains number of substances (water, ions, enzymes
vitamins, carbohydrates lipids and proteins)
•Site of biochemical reaction.
Cell organelles
•Membrane less – ribosomes
•Single membrane – ER, golgi, lysosomes, vacuoles.
•Double membrane – mitochondria and plastids.

17. Complex membrane network like
structure – runs through the cytoplasm.
Cisternae – spaces within the folds.
Connected to the both outer nuclear
membrane as well as cell membrane.
It has the membrane as same like cell membrane.
Ribosomes – no membrane.
RER – protein production and transportation
SER – fat molecules or lipids production ( helps in membrane
biogenesis )
ER works as a transport system – provides surface area for various
metabolic reactions. SER in liver cells helping detoxifying many drugs
and poisons.

18. Described by Camilo Golgi
Consists of a system of a membrane bound vescicles arranged
approximately parallel to each other in stacks called Cisterns.
Connections with membranes of ER.
Packaging.
Functions .
 Involved in synthesis and repair of cell membrane.
 Formation of lysosomes and peroxisomes.
 Secretory organelle of a cell.
 Storage and packaging.

19. Waste disposal system of the cell.
Helps in cleaning the cell by the help of powerful digestive enzymes.
Suicidal bags.
Structurally lysosomes are membrane bound sacs with digestive
enzymes made by RER.

20. Coined by Carl Benda in 1898.
Site of cellular respiration (ATP synthesis) – Power house of the cell.
Structure
 Surrounded by a double membrane covering.
 Outer membrane is porous and inner membrane is deeply folded
(cisternae) which increase the surfece area.
 Compartment enclosed by inner membrane is called matrix.
 Mitochondrion possess own single cellular DNA and ribosomes.

21. Coined by Ernst Heackel
Found only in plant cells.
Chromoplasts, Chloroplasts and Leucoplasts.
Chloroplasts : green colour plastids in leaf.
Chromoplasts : coloured plastids – carotinoids.
Leucoplasts : colourless plastids – aleuroplast : protein ; elaiopast : oil
; amyloplasts : carbohydrates.
Structure of chloroplast

22. Vacuoles
Storage sacs for solid or liquid content.
Small in animal and very big in plants (50 – 90%).
In plants vacuoles are full of cell sap to provide turgidity and rigidity.
Food vacuole – food.
Plant cell vacuole – amino acids, sugar, organic acids and proteins.
Specialized vacuoles in unicellular organisms to expel the excess water and
wastes.
Plant cell Animal cell
Larger in size Smaller in size
Cell wall - present Cell wall – absent
Plastids - present Plastids – absent
Single large vacuole Many small vacuoles
Golgi body - dictyosomes Well developed golgi body
Nucleus – peripheral side Nucleus – in centre
Centrosomes and centrioles are absebt Centrosomes and centrioles are present

23. Significance of cell division
Reproduction
Replacement of cells
growth
Prokaryotes
 Division by binary fission.
Eukaryotes
 Karyokinesis and Cytokinesis
 Mitosis and Meiosis.

26. Mitosis Meiosis
Occurs generally in somatic cells Occurs in germ cells
During normal growth of cell During gamete formation
Chromosome number remains the
same
Chromosome number reduce to
half
Two daughter cells are formed Four daughter cells are formed