Revision Notes for CBSE Class 11 Biology Chapter 8 (Cell the Unit of Life) - Free PDF Download
Section–A (1 Mark Questions)
1. What is totipotency?
Ans. Totipotency is the ability of a single cell to divide and produce all the differentiated cells in an organism.
2. Which organelle is called the powerhouse of the cell?
Ans. Mitochondria is known as the powerhouse of the cell.
3. Who first saw and described a live cell?
Ans. Anton Von Leeuwenhoek first saw and described a live cell.
4. What is the composition of plasma membrane of human erythrocyte?
Ans. In human beings, the membrane of the erythrocyte has approximately 52% protein and 40% lipids.
5. Expand PPLO.
Ans. PPLO - Pleuro Pneumonia Like Organisms
Section–B (2 Mark Questions)
6. Name semi-autonomous cellular organelles present in eukaryotic cells.
Ans. Mitochondria and chloroplasts are the two semi-autonomous cellular organelles present in eukaryotic cells. Chloroplasts are present in plant cells only while mitochondria are present in both plant and animal cells.
7. Answer the following questions.
(i) Who first explained that cells arise from pre-existing cells?
(ii) Which organelle is known as the protein factory of the cell?
Ans. (i) Rudolf Virchow first explained that cell arise from pre-existing cells.
(ii) Ribosome is known as the protein factory of the cell.
8. What are the main functions of cell wall?
Ans. Functions of cell wall:
(i) It provides a definite shape to the cell.
(ii) It protects inner contents of cells
(iii) It protects delicate plasma membrane present below it.
(iv) It allows transport of various substances to & from the cell.
(v) It prevents cell contents from drying up.
9. Name the organelles responsible for the respective functions.
(a) Major site for synthesis of lipid
(b) Site for synthesis of ribosomal RNA (rRNA)
Ans. (a) Major site for synthesis of lipid: Smooth endoplasmic reticulum is responsible for synthesis of lipids.
(b) Site for synthesis of ribosomal RNA (rRNA): Nucleolus is the site for synthesis of ribosomal RNA (rRNA)
10. Why are lysosomes called “suicidal bags”?
Ans. Lysosomes are sac-like structures bounded by a single membrane which contains several digestive enzymes. These enzymes when released from lysosomes bring about breaks down of various cytoplasmic structures. It helps in digestion of food particles, other foreign bodies, old worn-out organelles of cell often resulting in death of cell hence are referred as suicidal bags of cell.
11. Explain in a single sentence.
(i) Mesosome
(ii) Acrocentric chromosome
Ans. (i) Mesosome: Differentiated form of cell membrane in prokaryotes which are essentially infoldings of cell membrane.
(ii) Acrocentric chromosome: Chromosome in which the centromere is situated close to its end forming one extremely short and one very long arm.
Mastering Class 11 English Chapter 8: Cell the Unit of Life - Notes, Question and Answer, and Tips for Success
The cell is the smallest, basic structural, and functional unit of living things; hence it is generally referred to as ‘building blocks of life. Cells are capable of independent existence and performing essential functions of life. All organisms including plants and animals are made up of one or more cells and all that cells come from pre-existing cells. Robert Hooke was the scientist who first discovered cells in a piece of cork.
Different Types of Cell
In the human body, different types of cells are present such as hepatocytes in the liver, nephrons in the kidney, neurons in the brain, etc. The different types of cells are grouped to form tissues. These tissues perform specific functions.
Cell Theory
In 1839, two scientists named Schleiden who was a German botanist, and Schwann who was a British zoologist, announced the cell theory. The modern theory of the cell includes-
- Every living organism is made up of cells.
- The cell is said to be the basic structural and functional unit of living things.
- All cells arise from the pre-existing cells by division method and this was given by Rudolf Virchow.
- All energy flow takes place within the cells.
- Cells contain the hereditary information which is passed from cell to cell during cell division.
- All cells have the same chemical composition.
Structure of Eukaryotic Cells
Plasma Membrane
The plasma membrane is a dynamic, fluid-structure that is present in the external boundary of the cell and separates the interior of the cell from the outside environment. It is selectively permeable Based on the can that only allows specific solutes to pass through it. In 1972, Jonathan Singer and Garth Nicolson proposed the fluid mosaic model of the plasma membrane. According to this model, the membrane is a quasi-fluid structure in which proteins are embedded throughout the lipid bilayer and this lipid bilayer provides fluidity and elasticity to the membrane. The bilayer is composed of two layers of amphipathic molecules that contain polar heads and nonpolar tails.
Hydrophobic interactions are the primary forces for organizing lipid bilayer. There are three types of lipid and two types of protein present in the plasma membrane. Lipids are phospholipids, glycolipids, and sterol and the proteins are peripheral proteins and integral proteins. Peripheral proteins are proteins that are held with the bilayer loosely and can be easily removed. While the integral proteins are proteins that are held in the lipid bilayer very tightly and cannot be removed easily.
Cell Wall
The cell wall is a rigid non-living structure that surrounds the plasma membrane. The cell wall is mostly found in plant and fungal cells that provide shape to the cell. It also protects the cell against mechanical damage or infection and also prevents the entry of unwanted macromolecules.
Cell walls are important for cell-to-cell interaction and transport. The cell wall is made up of three parts i.e., primary wall, middle lamella, and secondary wall. Plasmodesmata are the connections that are present between the cytoplasm of the neighboring cells and the middle lamella.
Ribosomes
Ribosomes are specialized cell organelle which is composed of RNAs and proteins hence, they are known as ribonucleoprotein. Ribosomes units come together to translate genetic information which is stored in messenger RNA (mRNA) into proteins. Functional ribosomes consist of two subunits of unequal size, known as large and small subunits where small subunits read mRNA and large subunits form a polypeptide chain of amino acids. Eukaryotic cells generally possess two types of ribosomes: cytosolic and organellar. The ribosome found in prokaryotes is the 70S and 80S in eukaryotes where S stands for sedimentation coefficient. It is the ratio of a velocity to the centrifugal acceleration that helps to measure the particle's size based on the sedimentation rate.
Endoplasmic Reticulum
It is the largest single membrane-bound intracellular compartment which is mainly found in eukaryotic cells. It is formed by an interconnected network of closed and flattened membrane-bound structures and the membrane-enclosed sac is called the lumen. Based on the presence or absence of ribosomes, ER can be of two types i.e., rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). When ribosomes are present on ER, it gives a rough appearance to the structure hence it is known as rough ER. When ribosomes are absent in the ER membrane, it is known as smooth ER.
Proteins synthesized by ribosomes that are present on the membrane of RER enter into the lumen by the process of co-translational translocation. Before reaching their final destination there are five principal modifications of proteins that take place in the lumen. These modifications are - the addition and processing of carbohydrates, formation of disulfide bonds, proper folding, specific proteolytic cleavages, and assembly into multimeric proteins. The SER performs different functions like the synthesis of essential lipids, steroid hormones, metabolism of carbohydrates, detoxification, and calcium regulation.
Golgi Complex/Golgi Apparatus
It is a single membrane-bound organelle that forms a part of the endomembrane system. Golgi complex is mainly found in the cytosol of the eukaryotic cells and is made up of flattened membrane sacs known as cisternae. A Golgi stack normally contains 4-8 cisternae. Each Golgi stack has two faces- the cis face and the trans face. Both faces are also called the entry face and exit face, respectively. The main functions of the Golgi apparatus include protein packaging and secretion.
Lysosomes
It is a single membrane-enclosed organelle that contains hydrolytic enzymes that are responsible for the breakdown of various biomolecules. These hydrolytic enzymes include nucleases, proteases, lipases, glycosidases, phosphatase, phospholipases, and sulphatases. For optimal activity, the enzyme requires an acidic environment inside the lysosomes with a pH of about 5.0. There remains present a proton pump inside the lysosomal membrane. This proton pump transports the proton from inside the membrane using ATP as a source of energy. Lysosomes are responsible for the digestion of both intracellular as well as extracellular materials as they can break down virus particles or bacteria in the phagocytosis of macrophages.
Vacuoles
Fluid-filled vesicles are known as vacuoles and are mostly found in the cytoplasmic matrix of the cell. There is a membrane that surrounds the vacuole known as tonoplast. Similar to the pH of lysosomes the lumen's pH is also acidic. Vacuoles in plant cells are larger than those in animal cells and they contain water, dissolved inorganic ions, sugars, enzymes, etc. it is different from another type of vacuole called contractile vacuole because they perform osmoregulation and pumps excess water out of the cell. The example includes the vacuole in Amoeba.
Mitochondria
It is found in all eukaryotic cells and is known as a site for aerobic respiration. They are called the powerhouse of the cell because it synthesizes ATP as the energy currency of the cell. They are the double membrane-bound cell organelle that contains circular DNA molecules and ribosomes. The space present between the outer and the inner membrane is known as intermembrane space. The inner membrane structure is complex because it is convoluted to form cristae. Cristae help in increasing the surface area inside the mitochondria.
The inner membrane is rich in phospholipid known as cardiolipin which makes the membrane-impermeable to solutes. The inner membrane contains enzyme complexes known as ATP synthase or F0-F1 ATPase and they play an important role in the synthesis of ATP molecules.
Plastids
They are double-membrane cell organelle that is generally found in algae and plant cells. Like mitochondria, they also contain double-stranded DNA and ribosomes in their structure. They are divided into three different types- leucoplast, chromoplast, and chloroplast. Plastids contain a pigment that plays an important role in photosynthesis and is also responsible for the synthesis and storage of food.
The Chloroplast surrounds the fluid-filled structure known as stroma that contains a stack of sacs called a granum. There are some organized flattened membranous sacs called the thylakoids. Each granum is connected to the other with the help of flat membranous tubules known as stroma lamellae.
chromoplasts are the type of plastids that are responsible for pigment synthesis and storage. They give different colors to the fruit, flowers, and aging leaves like yellow, orange, or red colors.
However, the leucoplast is colorless plastids that are generally present in unexposed areas of plants. It plays an important role in the storage of starch, lipid, and proteins and is divided into three different parts- amyloplast that stores starch, Elaioplast that stores lipids in fats, proteinoplast stores proteins.
Nucleus
The nucleus is a double membrane structure found in all eukaryotic cells except RBCs (red blood cells). It contains the majority of the genetic material that transfers from parents to offspring during cell division. In the nucleus, the DNA is packed in the form of chromosomes with histones proteins, it controls the function and growth of the cell. The gene is a fragment of DNA that codes for a protein.
There are two types of chromosomes found- Euchromatin and heterochromatin where euchromatin is a less compact structure and can be transcribed into mRNA. while Heterochromatin is a compact structure and hence cannot be transcribed into mRNA.
The Nuclear membrane is a double-layered system that is impermeable to large molecules. The outer layer is combined with the Endoplasmic reticulum. The presence of nuclear pores in the membrane regulates the movement of solutes in and out of the nucleus. A perinuclear is a space that presents between these two layers.
The nucleolus is the solid and spherical structure that is present inside the nucleus of eukaryotic cells. It is involved in the assembly of ribosomes during protein synthesis. It disappears during the cell division and reappears after the cell division.
Peroxisomes
Peroxisomes are small, membrane-bound cell organelles that are mainly found in all eukaryotic cells. They contain oxidative enzymes that help in various metabolic activities. The major function of peroxisomes is the breakdown of fatty acids. Peroxisomes can be derived from the smooth endoplasmic reticulum of the cell. Proteins found in peroxisomes are matrix soluble proteins and membrane proteins known as peroxins.
Cytoskeleton
It is made up of a network of proteinaceous filaments in the cytoplasm that provides mechanical support to the cells. The cytoskeleton maintains the shape of the cell and helps in cell motility. It also organizes the organelles and facilitates the movement of solutes across the cell.
Cilia and Flagella
They are the hairy outgrowths that help in the locomotion of the organisms. Cilia are the short structure that helps in attachment while flagella are relatively long structures in the form of a whip and it helps in movement of the organism. They are covered by a plasma membrane and possess a core made from numerous microtubules running parallel to the long axis. This core is called an axoneme which shows a 9+2 arrangement. Here 9 is the number of pairs of radially arranged microtubule doublets and 2 is the central pair of microtubules.
Centrosomes and Centrioles
Centrioles are a pair of cylindrical structures that compose the centrosome. Centrioles are perpendicular to each other and present in the cytoplasm where they help in organizing microtubules. It is made up of nine symmetrically arranged peripheral triplet fibrils of tubulin protein. The proteinaceous part that presents in the center of the centriole is called a hub; it is connected by spokes to the peripheral fibrils. The centrioles form the network of threads across the cell during cell division. Apart from this, they also form the base of flagella.
Structure of a Prokaryotic Cell
Prokaryotic cells are small, single-celled organisms that lack a true nucleus and membrane-bound organelles.
Prokaryotes mainly include bacteria, mycoplasma, cyanobacteria, and PPLOs. The prokaryotes are much smaller and more rapidly dividing than eukaryotes. They have generally been divided asexually by binary fission and conjugation. They vary in shape and size but their basic organization remains the same. In prokaryotes, a cell wall surrounds the cell except for mycoplasma. In the case of bacteria, they also contain an extra circular DNA called plasmids. They lack all cell organelles except for ribosomes where protein synthesis takes place.
In motile bacterial cells, they possess one or more flagella. A flagellum is a long structure in the form of a whip that is made up of basic parts: filament, hook, and the basal body. A pilus can also help the bacteria in conjugation while Pili and fimbriae help in attachment to substrate or host.
Cell The Unit of Life Notes Biology Chapter 8- PDF Download
Cell: Definition
According to Chapter 8 Biology Class 11 notes ‘cell’ is nothing but the basic unit of life. Unicellular organisms can exist independently and carry out the necessary functions of life. Independent living is ensured by a substance which is less than a complete structure of a cell.
Therefore, if you follow the notes of Chapter 8 Biology Class 11 you will get to know that the fundamental structural and functional unit of each and every living organism is called ‘cell’.
What is Cell Theory?
Ch 8 Bio Class 11 notes of Vedantu perfectly depict the theory of cell. A German botanist known as Matthias Schleiden tested a huge number of plants and noticed that all plants consist of various kinds of cells. The tissues of the plants are composed of those cells.
A contemporary British zoologist named Theodore Schwann examined various kinds of animal cells. He found that a thin outer layer was present in every cell. This very particular layer is known as ‘plasma membrane’ today. The ‘cell theory’ was coined by Schleiden and Schwann. According to Chapter 8 Class 11 Biology notes of Vedantu the main two points of cell theory are as follows:
a) Each living organism is composed of cells and products of cells.
b) All cells originate from pre-existing cells.
Cell: A to the Point Analysis
All the animal cells and plant cells are composed of the cell membrane in the outer layer of the cell.
If you deeply go through the Biology Class 11 Chapter 8 notes of Vedantu you can see that a dense membrane-bound structure is present inside the cell which is known as the nucleus.
The nucleus is the basic unit of the genetic substance DNA.
The cytoplasm is the semi-fluid matrix which occupies the inside arena of the cell.
Apart from the nucleus, there are some other membrane-bound components also present inside the cell which are known as organelles.
There are various organelles present inside the cell such as endoplasmic reticulum (ER), the Golgi complex, lysosomes, mitochondria etc. These membrane-bound organelles are not present in the prokaryotic cells.
An example of a non-membranous organelle is the ribosome. It is found both in the prokaryotic cell and in the eukaryotic cell.
Cells, as Class 11 Biology Chapter 8 cell the unit of life notes inform you, are categorized based on size, shape and activities. The smallest cell on the earth is known as Mycoplasmas. The egg of an ostrich is known as a single isolated cell.
In multicellular organisms, human nerve cells are the longest cells.
There are also cells of various shapes such as disc-like, polygonal, columnar, cuboid etc.
What are Prokaryotic Cells?
Vedantu’s Class 11 Chapter 8 Biology notes give the perfect definition of the prokaryotic cell with examples. A prokaryotic cell is defined by the absence of membrane-bound nuclei. The examples of prokaryotic cells are bacteria, blue-green algae, Mycoplasmas etc.
Ribosomes and Inclusion Bodies
If you follow the Class 11 Biology Chapter 8 cell, the unit of life notes of Vedantu, you will get a sound idea about the ribosome. Ribosomes are present in both prokaryotic and eukaryotic cells. Ribosomes are connected with the plasma membrane of the cell in case of the prokaryotes. The size of Ribosomes is about 15 mm by 20 mm and consists of two subunits namely 50S and 30S units. Those two subunits form 70S prokaryotic ribosomes. The inclusion bodies include phosphate granules, cyanophycean granules and glycogen granules.
What are Eukaryotic Cells?
Biology Chapter 8 Class 11 notes perfectly define the eukaryotic cell. A eukaryotic cell is defined by the presence of membrane-bound nuclei.
Cell Membrane
The basic structure of cell membrane, as informed in Notes of Biology Class 11 Chapter 8 is composed of lipids and proteins.
The main lipids are the phospholipids.
The later study of the cell membrane revealed that the cell membrane is composed of proteins and carbohydrates.
Cell Wall
From Class 11 Bio Ch 8 notes, you will learn that a rigid non-living structure comprises the outer covering for the plasma membrane of fungi and plants are known as the cell wall.
The function of the cell wall is to give shape to the cell and to protect the cell from mechanical damage and infection.
Endomembrane System
The endomembrane system of the cell consists of the following components:
a) The Endoplasmic Reticulum (ER): Small tubular structures dispersed in the cytoplasm.
b) Golgi Apparatus: These are the densely stained reticular structures present near the nucleus.
c) Mitochondria: It is the powerhouse of the cell. The cellular energy called ATP is produced by mitochondria.
d) Plastids: Plastids are present in plant cells. They can be categorized as chloroplasts, chromoplasts and leucoplasts.
Apart from the above-mentioned components, you will find in Class 11th Biology Chapter 8 notes that many other components are also present in the cell such as Ribosomes, Cytoskeleton, Cilia and Flagella, Centrosome and Centrioles and Nucleus.
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Conclusion:
The Class 11 CBSE Biology Chapter 8 notes on "Cell: The Unit of Life" provided by Vedantu serve as an invaluable resource for students. These notes comprehensively cover the fundamental aspects of cell biology, highlighting the significance of cells as the building blocks of life. With detailed explanations and diagrams, the notes elucidate cell structure, organelles, and their functions, emphasizing key concepts such as cell division and cell cycle. By studying these notes, students can develop a strong foundation in understanding cellular processes and their role in biological systems. Vedantu's Class 11 Biology Chapter 8 notes enable students to grasp complex topics effectively, aiding in their academic success and overall understanding of cell biology.
FAQs on Cell the Unit of Life Class 11 Notes CBSE Biology Chapter 8 (Free PDF Download)
1. What are centrosomes and centrioles?
The centrosome is an organelle that generally consists of two cylindrical structures known as centrioles. Several amorphous pericentriolar materials surround the centrosome.
2. What do you know of microbodies?
From the NCERT Biology Class 11 Chapter Notes, you will get the perfect idea about the Microbodies. Microbodies are the membrane-bound minute vesicles. Those minute vesicles contain different enzymes. Microbodies are present in both the plant and animal cells.
3. Why is Mitochondria called the ‘powerhouse’ of the cell?
According to Cell the Unit of Life Class 11 notes, mitochondria is called the powerhouse of a cell as it produces cellular energy in the form of ATP.
4. What are the fundamentals of Histology?
Histology is the study of cells which can be defined as the structural and functional unit of life. In Biology, a cell can be defined as the smallest unit that can exist on its own and it makes up all the tissues and organs of a living organism. In order to understand the chapters in this topic, it is important to get through with the basics. The notes curated by Vedantu would help you in not only understanding the concepts but also in revisions.
5. How do I make a study plan for Chapter 8 of Class 11 Biology?
Drafting a study plan for Class 11 Biology is actually an easy task. Start by making a list of the chapters that are in your curriculum. Mark out the chapters that you find difficult. Start by studying these chapters first then gradually move towards the topics that you are confident in. When it comes to Chapter 8, it is exceptionally important that you comprehend the concept of the chapter rather than just memorizing it. Always write and practise to ensure you understand as you go.
6. How do I prepare my notes for Class 11 Biology for Chapter 8?
Make sure your answers are legible.
Underline keywords and important terminologies.
Frame your answers in a pointwise format as opposed to paragraph format as this makes it easier for you to understand your words later too.
Draw neat and labelled diagrams wherever necessary. Make sure the diagram is labelled accurately. Colours can be used to distinguish between different parts of the diagram.
Draw margins and underline the headings if any in each answer.
Ideally, start each answer on a fresh page.
7. Is Chapter 8 of Class 11 Biology hard?
Class 11 Biology Chapter 8 may be a challenge for a few. But with the help of a clear mind and organised study plan, it can be one of the easiest subjects. Here are some pointers that can help make the process of understanding easier:
1. Make sure you are at par with the lesson being taught at school.
2. Have discussions with friends and teachers about the chapter.
3. Use a separate notebook to jot down important points and diagrams. This would make last-minute revisions easier.
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8. Where can I find answers online for NCERT Chapter 8 of Class 11 Biology?
You can find lesson wise notes prepared by experienced faculty on the Vedantu website. These notes are easily understandable with diagrams and accurate facts. The notes found on the website can not only be used to understand the topic but can also help you in last-minute revisions before the exam. Make use of Vedantu for comprehensive Biology notes for Chapter 8 Class 11 by downloading the notes free of cost.