Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

CBSE Notes
ncert Science(bio)
The Fundamental Unit of life -CELL
topics :
●

Introduction , Discovery

●

Cell theory

●

Types

●

Structural organisation of cell
○

plasma membrane

○

cell wall

○

nucleus

○

cytoplasm

● Cell organelles
○ ( ER , Golgi apparatus , Lysosomes, mitochondria, Plastids, Vacuoles
...
" It is the smallest unit capable of performing all essential
life processes, such as growth, reproduction, and metabolism
...

Without cells, life as we know it would not exist
...
" Understanding cells not only explains how organisms grow
and function but also provides insights into diseases, genetics, and the intricacies of life
at its most basic level
...
He noticed small, box-like
structures and named them "cells," derived from the Latin word cella, meaning "a small
room
...

Robert Brown discovered nucleus in 1831
...
It was first proposed in 1838-39 by two German scientists, Matthias Schleiden, a
botanist, and Theodor Schwann, a zoologist
...

The three main postulates of the cell theory are:

1
...

2
...

2
...


This theory forms the basis for understanding complex life processes and diseases at
the cellular level
...
Additionally, it did not explain the origin of the first cell
on Earth
...
Prokaryotes and Eukaryotes
...
They do not
have a nucleus or many of the specialized parts seen in more advanced cells
...
They are found in
plants, animals, and humans, with a proper nucleus and many tiny structures inside that
perform specific jobs
...


Features

PROKARYOTES

EUKARYOTES

nucleus

No true nucleus , genetic
material is present in nucleoid

true nucleus enclosed by the
nuclear membrane

size

Smaller ( 1- 10 microns )

Larger ( 10 - 100 microns )

organelles

Membrane bound organelles
are absent

Membrane bound organelles
are present

ribosomes

Smaller ( 70S )

larger ( 80S )

cell division

Binary fissions
( asexual reproduction)

Mitosis and meiosis ( sexual
and asexual reproduction)

example

Bacteria , algae etc

Plants , animals , fungi etc
...
This
classification highlights how different organisms rely on cellular organization to
perform life processes
...
Unicellular Organisms : Unicellular organisms are made up of a single cell that
performs all the necessary functions of life
...

● microscopic in size
...

●

Reproduce mostly through simple methods like binary fission or budding
...


2
...
These cells are specialized and organized
into tissues, organs, and systems
...
g
...


● Larger and more complex in structure
...
)
● Reproduce through more complex processes like sexual reproduction or spore
formation
...


Plant and Animal cell :

Plant cell

Animal cell

Cell wall is present

Cell wall is absent

Larger vacuoles

Smaller or absent

Plastid are present

Plastids are absent

Stores energy as starch

Stores energy as glycogen

Nucleus on the side

Nucleus in center

Lysosomes are absent

Lysosomes are present

7

Structural Organisation of a Cell

The main features found in almost every cell are ;
Plasma membrane , Cell wall ( in plants ) ,Nucleus and Cytoplasm
...
Plasma membrane :

The outermost covering of the cell , also called a selectively permeable members
●
...

● it is present in both Prokaryotic and eukaryotic cell
...


Important processes and mechanisms :

• Diffusion : Movement of substances from region of high concentration to region of
low concentration

• Osmosis: Diffusion of water molecules (from higher concentration to lower
concentration ) through the membrane
...
eg , Sodium - Potassium
•Passine transport: Does not require energy eg- diffussion, Osmosis
...

• Exocytosis : Expelling material out of cell
...
Such solution is known as hypotonic
solution
...
Such solution is known as hypertonic solution
...
Cell wall :

In plant cells ,cell wall is the rigid outer covering , outside the plasma membrane
...

● Provides shape to the cell
...

● It is made of cellulose in plants , chitin in fungi
...
Nucleus :

The control center of the cell and controls all activities of cell
...

● Stores genetic information
...


10
(a) Nuclear Membrane :

● A double-layered protective membrane surrounding the nucleus
...

● Regulates the movement of RNA, proteins, and other molecules
...
)
● store house of RNA’s

(c) Chromatin :

● A thread-like structure made of DNA and proteins, called chromatin fibres
...

● Condenses to form chromosomes during cell division
...

● contains information in the form of DNA ( deoxyribo nucleic acid ) molecules

11

4
...

● Contains 75 -85 % water + proteins , carbs , minerals etc
● It hels in the exchange of materials by organelles
● Stores chemicals such as amino acid , glucose , vitamins
...


CELL ORGANELLES

1
...

It acts as circulatory system to transport materials ( especially proteins ) between
cytoplasm and nucleus
...
Rough endoplasmic reticulum (RER):
○ Ribosomes are present
○ Synthesizes protein
○ Produces antibodies
○ Increases rate of protein synthesis, used for membrane-biogenesis
(formation of new cell membrane)
2
...
It is composed of
two subunits – smaller and larger
...
Golgi Apparatus :

Structure:
● Composed of three main components: cisternae, vacuoles, and vesicles
...


13
Functions:
● Cell secretion : Packages and transports proteins and lipids
...

● Packaging and modification : Accumulates enzymes, hormones, and proteins,
then transports them to their destination
...


2
...

Functions:
● Intracellular digestion: Breaks down foreign materials, pathogens, and worn-out
organelles
...

● Autolysis (suicidal bags): Self-destruction of the cell through enzyme release
...
Mitochondria :

Structure:
● Known as the "Powerhouse of the Cell" *
● Double-membrane structure:
○ Outer membrane: Smooth and permeable
...

● Contains matrix (fluid inside), which has enzymes, ribosomes, and DNA
...

● Self-replication: Has its own DNA and ribosomes, enabling it to produce proteins
and divide independently
...
Plastids :
(only in plant cells)

Types:
● Chloroplasts: Contain chlorophyll, essential for photosynthesis
...

● Leucoplasts: Colorless plastids that store starch, oil, and proteins
...

● Contains stroma (fluid), which has enzymes, DNA, and ribosomes
...

● Storage: Leucoplasts store important substances like starch
...


5
...

● Larger in plant cells and smaller in animal cells
...

● Helps maintain cell shape and rigidity in plant cells
...
( in unicellular organisms )

16



---