Summary chapter-8 ( cell : the unit of life ) full chapter of Class 11 .
4 views 0 purchase
Course
NEET
Institution
NEET
These notes of biology are very sufficient for you, after reading this, when you study NCERT of biology, you will understand it very well. Or you will be able to solve any upcoming question through these notes.
I am providing you complete class 11 and class 12 Biology notes here so that you can re...
Year Wise Number of Questions Analysis (2022-2013)
9
8
7
6
Number of Questions
5
4
3
2
1
0
2022 2021 2020 2020 2019 2018 2017 2016 II 2016 I 2015 2015 Re 2014 2013
Covid
Years
Topicwise Number of Questions Analysis (2022-2013)
1
13 36
36
34
32
30
28
26
24
An Overview of Cell and Cell Theory
22
20
Number of Questions
18
16
14
12
Prokaryotic Cells
Eukaryotic Cells
10
8
6
4
2
Topics
, WHAT IS A CELL? AN OVERVIEW OF CELL
Cell is the fundamental structural and functional unit of all Onion cell is a typical plant cell which has a distinct cell wall
living organisms., i.e., all organisms are composed of cells. as its outer boundary and just within it, is the cell membrane
1. Unicellular organisms: Composed of a single cell whereas the human cheek cell have an outer membrane as
2. Multicellular organisms: Composed of many cells the delimiting structure of the cell (cell wall is absent in
Unicellular organisms are capable of: animal cells).
(i) Independent existence Dense membrane bound structure is found inside each cell
(ii) Performing the essential functions of life which is called as nucleus which itself contains chromosomes
Cell is quite small and complex. So the complete and clear which in turn contain the genetic material, DNA.
view of all its components is revealed after the invention of Cells that have membrane bound nuclei are called eukaryotic
electron microscopes. whereas cells that lack a membrane bound nucleus are
prokaryotic. In both prokaryotic and eukaryotic cells, a semi-
Key Note
fluid matrix called cytoplasm occupies the volume of the cell.
P Robert Hooke first observed dead cell in plant cork.
Key Note
P Anton Von Leeuwenhoek first saw and described a live cell.
P Robert Brown discovered the nucleus. P Cytoplasm is a semi-fluid matrix which occupies the
volume of the cell. It is the main arena of cellular
activities in both the plant and animal cells.
CELL THEORY
P Various chemical reactions occur inside the cytoplasm
Cell theory was formulated by a German botanist Matthias keep the cell in the 'living state'.
Schleiden in 1838 and a British zoologist, Theodore
Schwann in 1839. Cells differ greatly in size, shape and activities. They may be
Matthias Schleiden: Examined a large number of plants and disc-like, polygonal, columnar, cuboid, thread-like, or even
observed that all plants are composed of different kinds of irregular. The shape of the cell may vary with the function
cells which form the tissues of the plant. they perform.
Theodore Schwann: Studied different types of animal cells Table 1: Some important cells and their features with their dimensions
and reported that cells had a thin outer layer which is today Cell type Feature/ Size / Shape
known as the ‘plasma membrane’.
Mycoplasma Smallest cell; 0.3 µm in length
Based on his studies on plant tissues, he concluded that the
Bacteria 3-5 µm
presence of cell wall is a unique character of the plant cells. Ostrich egg Largest isolated single cell
On the basis of this, he proposed the hypothesis that the bodies of Human red blood cell 7.0 µm in diameter
animals and plants are composed of cells and products of cells. (erythrocyte)
Rudolf Virchow: Cell theory did not explain the mechanism Nerve cells (neurons) Longest cells in humans
of formation of new cells. So, Rudolf Virchow (1855) first
explained that cells divided and new cells are formed from
pre-existing cells (Omnis cellula-e cellula). He modified the
cell theory to give it a final shape.
Features of cell theory-
All livings organisms are composed of cells and products of cells.
All cells arise from pre-existing cells.
Need to Know
P Viruses represent a connecting link between living and
non-living things. They are exception to cell theory.
P Anything less than a complete structure of a cell does
not ensure independent living.
Fig. 1: Diagram showing different shapes of the cells
26 Dropper NEET Module-1 Botany PW
, Structure of Prokaryotic Cell
Concept Application The organisation of the prokaryotic cell is fundamentally
similar even though prokaryotes exhibit a wide variety of
shapes and functions.
Fill in the Blanks: All prokaryotes are surrounded by plasma/cell membrane
1. First person who saw and described a living cell which is itself surrounded by a cell wall. Mycoplasma is an
is_________. exception where the cell wall is absent.
2. “Omnis cellula-e-cellula” which means new Nucleoid and Plasmid
cells arises from pre-existing cells was given by There is no well-defined nucleus.
scientist__________. The genetic material is basically naked, i.e., not enveloped by
True and False: a nuclear membrane.
3. Cell theory was given by Matthias Schleiden (British In addition to the genomic DNA (the single chromosome/
Botanist) and Theodore Schwann (German Zoologist). circular DNA), many bacteria have small circular DNA outside
the genomic DNA. These smaller DNA are called plasmids.
The plasmid DNA confers certain unique phenotypic
Types of Cell characters to such bacteria. One such character is resistance
On the basis of nuclear organisation, cells are classified mainly to antibiotics.
into two types:
Prokaryotic cell Key Note
Eukaryotic cell P Plasmid DNA is used to monitor bacteria transformation
with foreign DNA
PROKARYOTIC CELL P Nuclear envelope and cell organelles are absent in
prokaryotic cells.
These cells are represented by bacteria, blue-green, algae P Ribosome is the only cell organelle found in prokaryotes.
mycoplasma or PPLO (Pleuro Pneumonia Like Organisms).
Cell Envelope and its Modifications
Most prokaryotic cells, particularly the bacterial cells, have
a chemically complex cell envelope which consists of a
tightly bound three layered structure, i.e., the outermost
Typical bacteria glycocalyx followed by the middle cell wall and then the
(1-2 µm) innermost plasma membrane.
They act together as a single protective unit but each layer of
the envelope performs distinct function as well.
PPLO
(about 0.1 µm) Key Note
On the basis of the differences in the cell envelopes and the
A typical eukaryotic cell Viruses manner in which bacteria respond to the staining procedure
(0.02-0.2 µm) developed by Gram, they can be classified into two groups:
(10-20 µm)
Gram positive (those bacteria that take up the gram stain) and
Fig. 2: Diagram showing comparison of eukaryotic cell with Gram negative (those bacteria that are not able to take up the
other organisms gram stain).
They are generally smaller and multiply more rapidly than Glycocalyx
the eukaryotic cells.
Glycocalyx differs in composition and thickness among
Prokaryotes may vary greatly in shape and size. The four different bacteria. It could be a loose sheath called the slime
basic shapes of bacteria are as follows: layer in some, while in others it may be thick and tough,
Bacillus (rod-like) called the capsule.
Coccus (spherical) Cell Wall
Vibrio (comma shaped) It determines the shape of the cell and provides a strong structural
Spirillum (spiral) support to prevent the bacterium from bursting or collapsing.
P
W Cell: The Unit of Life 27
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller dkcreatorringtones. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $5.99. You're not tied to anything after your purchase.
