Cell : The Unit of Life: Class 11 Biology NCERT Chapter 8

Key Features of NCERT Solutions for Class 11 Biology Chapter 8 – Cell: The Unit of Life

In chapter 7 of NCERT Class 11 Biology book: Structural Organization In Animals, you must have learned about how a  human body contains billions of cells operating a multitude of functions. In this chapter: Cells: The Unit Of Life, you will know about how a cell is defined as the most basic, structural, and functional unit of all living organisms. 

What is the one ordinary thing in each and every living thing? Be it plants, animals, individuals, or even single-cell life forms, we are totally included cells. Similarly, cells have earned the title of being the primary unit of life. Let us learn in comprehension with respect to cells. 

Survey disclosure of cell layer, piece of cell film( for example erythrocyte), talk about different models on the structure of the membrane, Elaborate fluid mosaic model of the cell layer, take a look at transport through cell layer (dynamic, assimilation and reserved process). Discuss cell divider. Clarify the relationship of the cell divider. Depict the different kinds of cell divider found in different life forms. A conversation about plasmolysis with the assistance of Rheo leaf, list components of cell divider. 


Cell Organelle 

Structure of Cell 

Quick revision notes

The cell is viewed as a focal fundamental and functional unit of life considering the way that the basic structure of all the living creatures is included cells. 

Thusly a cell is known as the fundamental unit of life. Let us find a few solutions concerning cell study and cell theory. 

The cell was found by an English scholar Robert Hook in the year 1665. He conveyed this data in his book ‘Micrographia‘. He saw that dead cells in a melancholy stopper cut in a free amplifying central point. Moreover, this was the start of cell study and disclosure. 

For what reason would they say they were named cells? Since the telephones resembled the little rooms of a Buddhist group which were called cellullae. In this manner, the name cell was given. 

  • Anton Von Leeuwenhoek orchestrated an improved amplifying instrument and observed the first free-living cells (Bacteria) in the year. 
  • Robert Brown A Scottish Botanist discovered the centre in the year 1831. 
  • A Zoologist Dujardin observed the semifluid living material inside a cell and named it Sarcode. 
  • Purkinje in the year 1840 renamed it as ‘Cell material – The First Substance’. 

A cell can be viewed as a closed vessel, inside which endless designed reactions occur simultaneously. These reactions are under exceptionally precise control with the objective that they add to the life and approach of new cells. 

Cell Theory 

A German botanist M.J. Schleiden in the year 1838 found that all plants are made of cells. A German Zoologist T. Schwann in the year 1839 likewise said that all the animals are incorporated cells. They normally introduced their disclosures as Cell Theory. 

Cell : The Unit of Life

Postulates of Cell Theory are 

  • Each living animal is made out of cells. 
  • All cells are essentially near in structure and limits. 
  • The limit of a living being with everything considered is the inevitable result of the activities and joint efforts of constituents of the cell. 

Modern Cell Theory 

In the year 1858 expert Rudolf Virchow presented the thought ‘Omnis Cellula e Cellula’, which infers that each living cell ascends out of earlier cells. After the improvement of this theorize in cell speculation, it was called Modern Cell Theory. 

Cell Facts 

  • Cells move actively and in size. 
  • A nerve cell is the longest cell of our body. It may be about 1m long. 
  • Ostrich egg is the hugest cell. 
  • Red Blood Corpuscles are the littlest cell in the human body and female ovum is the biggest cell in the human. 
  • Two or three life forms might be included a lone cell (Unicellular Organisms), eg; Amoeba. Others are multicellular. 
  • Legitimate division of work is seen in multicellular life forms as various organs perform various roles but in unicellular animals, the single-cell plays out all the limits. 

Types of Cells 

Cells are of two sorts depending upon the nearness or presence of traits of the nucleus 

Prokaryotic cell 

Cell : The Unit of Life: Prokaryotic cell 

Eukaryotic cell 

Cell Organelle 

A little organ-like structure present inside the cell is known as a cell organelle. It has specific beautifying operators and plays out a specific limit. Subordinate upon the closeness or nonattendance of layer, cell organelles can be portrayed into three portrayals: 

  • Without layer: Some cell organelles like ribosomes are not constrained by any film. They are in prokaryotic comparatively as eukaryotic life forms. 
  • Single-layer bound: Some organelles are constrained by a singular film. 
  • Twofold layer bound: Cell organelles like mitochondria and chloroplast are twofold film bound organelles. They are just in an eukaryotic cell. 

Structure and Functions of Cells 

Structure and functions of different cell contemplations are according to the accompanying 

Cell Organelle  Event/Characteristic and Structure  Function
Cell Membrane/Plasma Membrane 
  • It exists in both plant cells and animal cells. 
  • Selectively Permeable: Allows the materials all through the cell according to the need of the cell. 
  • Involved bilipid layer and protein (Fluid Mosaic Model) 

Cell Membrane/Plasma Membrane 

  • Encases the substance of the cell. 
  • Gives shape: creature cell. 
  • Grants transport: by Diffusion and Osmosis. 
Cell Wall 
  • Present just in a plant cell. 
  • Hard and firm. 
  • Completely permeable. 
  • Involved Cellulose in plant and peptidoglycan in bacteria. 
  • Protection
  • Gives shape and bloat. 
  • Contains 80-90% water and various natural and inorganic mixes. 
  • Colloidal, Viscous, Jelly like liquid inside the cell. 
Contains mixes responsible for all the metabolic movement happening inside the cell. 

(Chief/Brain of the Cell) 

  • Made sure about by a twofold membranous nuclear membrane in a Eukaryotic Cell. 
  • Contains DNA, RNA, Protein, nucleolus, and Chromatin compose. 

Nucleus (Chief/Brain of the Cell) 

  • Controls the movement of the cell. 
  • Starts cell division. 
  • It has the chromosomes or DNA which controls the acquired characters. 
Mitochondria ( Power of a Cell/Storage Batteries) 
  • Twofold membranous structure. 
  • The self-ruling body contains its own DNA. 
  • Self-copies 
  • The essential seat of breath. 
  • Stores essentialness as ATP iotas. 

Mitochondria ( Power of a Cell/Storage Batteries) 

Golgi Bodies 

(Transportation Department of Cell) 

  • Found by Camillo Golgi in 1898. 
  • Starts from RER. 
  • Contains Sac like Cisternae and Vesicles. 
  • Has two appearances – cis face or tolerating face and trans face or giving face. 

Golgi Bodies 

  • Change, Packaging, and transport of materials 
  • Association of lysosomes, plasma membrane 
Endoplasmic Reticulum (Structure of Cell) 
  • A system of membranes. 
  • RER bears ribosomes and shows up harsh 
  • SER doesn’t have ribosomes 
  • Forms the skeletal structure of the cell. 
  • Transport of materials from one cell to other cells. 
  • Gives a surface to the synthesis of material – Proteins in RER and Lipids in SER. 
  • Development of lysosomes, Golgi bodies and vacuoles 
  • Membrane Biogenesis 
  • Detoxification of hurtful substances in the liver. 
  • Emerge from ER and GB 
  • Encircled by tonoplast and loaded up with cell sap 
  • Store cell sap which may be liquid or solid food, hurtful outcome. 
  • Give inflexibility and bloat to plant cell 
Lysosomes (Suicidal packs of Cell, trademark scrounger, cell worker) 
  • Membrane-bound organelles 
  • Present in every single creature cell and not many plant cells 
  • Little indirect single film bound structures stacked up with stomach related proteins 
Intracellular absorption of food in unicellular creatures. 
Ribosomes (Protein Factories) 
  • Without a membrane 
  • Comprise of two subunits – 60S and 40S in eukaryote both comprised of RNA 

Ribosomes (Protein Factories) 

Synthesis of Proteins 
  • Twofold membrane-bound 
  • Types- 
  1. Leucoplast – Colorless plastid; 
  2. Chromoplast – Colored Plastid – blue, red, yellow 
  3. Chloroplast – Green plastid 
  • Self-ruling self-copying body 
  • Chloroplast – Perform Photosynthesis – Helps in the arrival of oxygen 
  • Chromoplast – award concealing to blooms which help in preparation 
  • Leucoplast – Storage 
  • Amyloplast – Store starch 
  • Aleuroplast – Store Protein 
  • Elaioplast – Store fat 

Structure of Cell 

How little is a cell? If you place the tip of a pen on your skin, that will cover around one thousand cells. In human, cells vary between 10 µm and 100 (µm speaks to micron, which is 1 millionth of a meter or 1 thousandth of a millimetre).


Different cells have different shapes and sizes depending upon the limit they perform. For example, RBCs are round perfectly healthy, nerve cells are delayed, muscle cells are hub shaped, skin cells are level, etc. 

A cell is seen as a fundamental unit of life considering the way that the basic structure of all the living creatures is included a cell. In this manner, the cell is known as the essential unit of life. Cell plays out explicit capacities that are for the quality of life and which are critical for the help of life. Subsequently, the cell is known as a helpful unit of life. 

A cell can be viewed as an encased vessel, inside which limitless creation reactions occur simultaneously. These reactions are under definite control with the objective that they add to the life and improvement of new cells. 

Structure of Cells 

A summarized cell contains a film bound structure encasing a centre and cytoplasm with various little organelles floating in it. Plant and animal cell have two or three complexities.

Contrasts Between Plant Cell and Animal Cell 

Plant Cell  Animal Cell 
Cell divider is available.  Cell divider is missing. 
The nucleus is peripheral. The nucleus is focal. 
A huge central vacuole is available.  Vacuoles might be little or missing. 
Plastids are available.  Plastids are missing. 
The centriole is missing.  The centriole is available. 
Golgi bodies present as units known as dictyosomes.  Golgi bodies very much created.

Subcellular segments 

  1. Cell Membrane/Plasma Membrane: 

Present in the cell structure of the prokaryotic cell and as well as eukaryotic cell 

  • The cell layer, or plasma film, is a natural film that envelops the cytoplasm of a cell. In animals, the plasma layer is the outer furthest reaches of the cell, while in plants and prokaryotes it is by and large made sure about by a cell divider. 
  • It is versatile and adaptable 
  • A cell layer is known as an explicitly permeable film. Why? This is in light of the fact that it allows the materials all through the cell as shown by the essential of the cell. 
  • Structure: It is included bilipid layer and protein (Fluid Mosaic Model) 

Capacities: Contains the substance of a cell. 

  • Gives shape 
  • Grants transport – Transport is of two sorts Diffusion and assimilation.

Comparison of Diffusion and Osmosis 

Diffusion  Osmosis
Particles of solid, liquid or gas move from its higher fixation to cut down the focus. Dissolvable particles move from its higher fixation to its lower centre through a semipermeable film. 
It doesn’t require a semipermeable membrane  A semipermeable membrane is required 
It happens in the fluid and vaporous medium  It happens just in a fluid medium 

What will happen when a cell is set in solutions of different concentrations?

Hypotonic arrangement:

A solution which contains a more prominent measure of dissolvable and less measure of a solute when stood out from the cell is called a hypotonic game plan. Exactly when a cell is placed in a hypotonic course of action endosmosis occurs. An animal cell will develop and impact. A plant cell will restrict extending and burst in light of the closeness of hard and unyielding cell divider. For example refined water 

Hypertonic Solution:

A solution which contains less measure of dissolvable and more prominent measure of a solute when stood out from the telephone is called a hypertonic arrangement. Exactly when a cell is set in the hypertonic arrangement, endosmosis occurs. An animal cell will contract. In a plant cell, plasma layer and cytoplasm will disengage from the cell divider. This is known as plasmolysis. Right when a plasmolyzed cell is set in a hypotonic course of action, endosmosis will occur and the cell will recover its structure. This is called de-plasmolysis. For example, drenched salt arrangement

Isotonic Solution:

A solution which contains a comparable measure of dissolvable and solute when appeared differently in relation to the cell is called an isotonic game plan. Exactly when a cell is placed in the isotonic course of action, no net improvement of particles occurs. Model Ringer’s answer is isotonic when appeared differently in relation to human RBC. 

  1. Cell Wall 

Next portion of the structure of the cell is the cell divider. They are accessible just in plant cell and they are hard and rigid. 

Totally permeable 

  • The cell mass of two adjoining cells are set up together by central lamella contained Calcium Pectate 
  • Contains Cellulose in plant and peptidoglycan in organisms 
  • breaks in the cell divider (Pits) have cytoplasmic affiliations (Plasmodesmata) through which exchange of materials occur 
  • Capacity: Protection, gives shape and swell 
  1. Cytoplasm 

  • Colloidal, Viscous, Jelly like fluid inside cells. 
  • Contains 80-90% water and various normal and inorganic blends. 
  • The cytoplasm contains synthetic compounds which are at risk for all the metabolic development. 
  • The cytoplasm gives a cell its shape. 
  • Diverse cell organelles are found floating in the cytoplasm. 
  1. Nucleus (Director/Brain of the Cell) 

  • Protected by a twofold membranous atomic layer in a Eukaryotic Cell. 
  • contains DNA, RNA, Protein, nucleolus, and Chromatin sort out. 
  • Capacities: Controls the activity of the cell. 
  • Starts cell division. 
  • It has the chromosomes which are contained DNA which controls the inborn characters.

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