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Have you ever wondered what makes living things different from non-living ones? It’s the presence of cells, which are the tiny building blocks that give life to every organism. The NCERT notes Class 11 Biology Chapter 8 cover every topic in easy and well-understandable language with well-labelled diagrams. Important definitions and terms are highlighted in these notes for better understanding of the students. This chapter includes the cell theory, types of cells, different cell organelles, etc., which are explained in points. Students can use these NCERT Notes to gain clarity before CBSE exams as well as entrance exams like NEET.
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The NCERT Class 11 Biology Notes are a valuable resource for understanding complex topics in a simple way. The cell is the basic structural and functional unit of life because it carries out all life processes in the body. It covers topics like the definition of living and non-living organisms, characteristics of cells, types of cells, differences between prokaryotic and eukaryotic cells, cell theory, and cell organelles. Using these NCERT Notes for Class 11 regularly helps students understand important topics and common questions, which makes them feel more confident during the exam.
Also, students can refer to:
Students can easily download the complete notes for the chapter Cell: The Unit of Life in PDF format. These notes are great for quick revision and last-minute study. Students can use them for both online learning and offline revision. The PDF helps students understand and remember topics faster.
Students can understand the structure and function of cells by using these notes, which are presented in easy language and clear diagrams. Key cell organelles like the nucleus, mitochondria, Golgi apparatus, and ribosomes are described in short and clear points. Differences between prokaryotic and eukaryotic cells are also included. Important terms of this chapter help students understand the concepts easily without any further help. All topics are covered in these notes in such a way that it supports quick revision.
Matthias Schleiden, a German botanist, researched plants in 1838 and discovered that all plants consist of various forms of cells, which collectively constitute plant tissues.
At about the same period, British zoologist Theodore Schwann (1839) examined animal cells and found that they have a thin outer covering, termed the plasma membrane. He also described that plant cells possess a cell wall that is not found in animal cells.
Schleiden and Schwann collectively developed the cell theory.
But their theory didn't account for the way in which new cells are created. In 1855, Rudolf Virchow expanded on the theory by declaring that new cells come from existing cells.
Modern Cell Theory Holds That:
Prokaryotic cells are tiny compared to eukaryotic cells and reproduce rapidly. They are also available in various shapes, which are as follows:
Even though prokaryotic cells differ from each other in terms of shape and functionality, they follow a common basic structure. All prokaryotes except mycoplasma have a cell wall outside the cell membrane.
The cytoplasm is a jelly-like liquid within the cell. Prokaryotes do not have a distinct nucleus since their genetic material is not covered with a nuclear membrane. Rather, their DNA occurs freely in the cytoplasm.
Prokaryotic cells possess a complex protective layer known as the cell envelope, which is composed of:
Flagella and cilia facilitate movement, propelled by a basal body.
Pili and fimbriae are short,t hair-like structures facilitating surface attachment for bacteria.
Internal Structures
Eukaryotic cells are larger and more complex than prokaryotic cells. They have a well-defined nucleus enclosed by a nuclear membrane and contain membrane-bound organelles that perform specialised functions. Eukaryotic cells can be unicellular (like amoebas) or multicellular (like plants and animals).
Eukaryotic cells have three main parts:
Plasma Membrane – A phospholipid bilayer that protects the cell and controls what enters and exits.
Nucleus – The control centre of the cell, containing DNA and responsible for growth and reproduction.
Cytoplasm – A fluid-filled space containing organelles that carry out life functions.
Nucleus – Contains chromosomes (DNA) and directs cell activities.
Endoplasmic Reticulum (ER) – Helps in protein and lipid synthesis.
Rough ER has ribosomes and makes proteins.
Smooth ER makes lipids and detoxifies chemicals.
Golgi Apparatus – Packages and transports proteins and lipids.
Mitochondria – The powerhouse of the cell, producing energy (ATP) through cellular respiration.
Lysosomes – Contain digestive enzymes to break down waste.
Plastids (only in plants) – Help in photosynthesis (chloroplasts) and store food (leucoplasts).
Vacuoles – Store water, nutrients, and waste; larger in plant cells.
Cell Wall (only in plant cells) – Provides structure and support.
Cytoskeleton – A network of protein filaments that maintains cell shape and helps in movement.
Plant Cells have a cell wall, large vacuole, and chloroplasts for photosynthesis.
Animal Cells have centrioles and lysosomes, which help in cell division and digestion.
Eukaryotic cells allow complex life forms to exist by efficiently carrying out essential biological functions through their specialised organelles.
Cell organelles are specialised structures contained within a cell that have specific functions to maintain the cell alive and in its optimum working condition. They are membrane-bound in eukaryotic cells, while prokaryotic cells have most of them missing, except for ribosomes. Here is a detailed description of each organelle and what it does.
The nucleus is the largest organelle in eukaryotic cells.
It contains genetic material (DNA), which controls cell activities.
The nuclear membrane encloses the nucleus and has pores for the exchange of materials.
Inside the nucleus, the nucleolus is responsible for making ribosomes.
A network of membranes that transports materials within the cell.
Types:
Rough ER (RER): Studded with ribosomes, helps in protein synthesis.
Smooth ER (SER): Lacks ribosomes, produces lipids, and detoxifies harmful substances.
Tiny structures are responsible for protein synthesis.
Found freely floating in the cytoplasm or attached to the rough ER.
Present in both prokaryotic and eukaryotic cells.
A stack of flattened sacs that modifies, sorts, and packages proteins and lipids.
Sends these materials to their destinations within or outside the cell.
Produces lysosomes in animal cells.
Mitochondria produce energy (ATP) through cellular respiration.
They have a double membrane, with the inner membrane forming folds called cristae to increase surface area for energy production.
They contain their own DNA and ribosomes, allowing them to reproduce independently.
Small vesicles filled with enzymes that break down waste materials, old cell parts, and foreign substances.
Help in cell defence by destroying harmful invaders.
Known as suicidal bags, as they can cause cell self-destruction if necessary.
Fluid-filled sacs are used for storing water, nutrients, and waste.
Large and central in plant cells to provide support.
Smaller in animal cells and helps in waste disposal.
Chloroplasts – Contain chlorophyll and perform photosynthesis.
Chromoplasts – Provide pigments to flowers and fruits.
Leucoplasts – Store starch, proteins, and fats.
A network of protein filaments that gives the cell its shape and structure.
Helps in cell movement and internal transport.
Contains enzymes that break down fatty acids and harmful substances like hydrogen peroxide.
Help in the detoxification of the cell.
Cilia – Small, hair-like structures that help in movement and sensing the environment.
Flagella – Long, whip-like structures that help in cell movement, seen in sperm cells and bacteria.
The centrosome contains centrioles, which help in cell division by forming the spindle fibers during mitosis.
Also, Read
Here are important questions from past papers based on this chapter to help students understand the level of difficulty.
Question 1. Who proposed the fluid mosaic model of the plasma membrane?
Option 1. Camillo Golgi
Option 2. Schleiden and Schwann
Option 3. Singer and Nicolson
Option 4. Robert Brown
Answer :
An important turning point in the study of cellular organelles was reached in 1898 when Camillo Golgi discovered the Golgi Complex. All living things are made up of cells, which are the basic building blocks of life, according to the Cell Theory, which was put forth by Matthias Schleiden and Theodor Schwann in 1839. In the same vein, Robert Brown identified the nucleus as an essential part of plant cells in his groundbreaking study from 1831, which gave the first thorough description of the organelle.
Hence, the answer is option (3), Singer and Nicolson
Question 2. A common characteristic feature of plant sieve tube cells and most mammalian erythrocytes is
Option 1. Absence of mitochondria
Option 2. Presence of a cell wall
Option 3. Presence of haemoglobin
Option 4. Absence of nucleus
Answer:
A common characteristic feature of plant sieve tube cells and most mammalian erythrocytes is the absence of a nucleus at the time of maturity. In sieve tube cells, this special adaptation maximizes space for the efficient transport of sugars and nutrients within the phloem. Similarly, the erythrocytes of mammals lose their nucleus during maturation to provide more space for hemoglobin, optimizing their work of carrying and delivering oxygen throughout the body.
Hence, the answer is option (4) Absence of nucleus
Question 3. Which of the following is not true of a eukaryotic cell?
Option 1. The cell wall is made up of peptidoglycans
Option 2. It has an 80S type of ribosome present in the cytoplasm
Option 3. Mitochondria contain circular DNA
Option 4. Membrane-bound organelles are present
Answer:
The main building block of the cell walls of eukaryotic plant cells is cellulose, a structural polysaccharide. It supports the cell's structure and shields it from mechanical stress from the outside by giving it strength and stiffness
Hence, the answer is option(1), Cell wall is made up of peptidoglycans
Also Read:
The chapter-wise Notes for class 11 biology are given below:
A cell is the fundamental structural and functional unit of life. It is the smallest unit capable of independent existence and performing essential life processes. Cells can be unicellular or multicellular, varying in structure and function.
Prokaryotic cells are smaller, lack a nucleus, and contain circular DNA. They do not have membrane-bound organelles. Eukaryotic cells are larger, have a nucleus with linear DNA, and contain organelles like mitochondria, ER, and Golgi apparatus.
Eukaryotic cells consist of a plasma membrane, nucleus, cytoplasm, and organelles like mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, and vacuoles, each contributing to cell function and maintenance.
The plasma membrane regulates the entry and exit of substances, maintaining homeostasis. It is selectively permeable, allowing nutrients, gases, and waste to pass through while protecting the cell from external environments.
Plant cells have a cell wall, chloroplasts, and large vacuoles, whereas animal cells lack these structures but have centrioles and lysosomes. Plant cells perform photosynthesis, while animal cells rely on other sources of energy.
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