NCERT Solutions for Class 11 Biology Chapter 8 – Cell The Unit of Life
NCERT Solutions for Class 11 Biology Chapter 8 are prepared to help you understand the topics of the chapter easily. Providing extensive knowledge on the Biology subject, chapter 8 discusses the concept of cells. It deals with topics such as- cell theory, the structure of a cell, and a detailed account of prokaryotic and eukaryotic cells. There are 14 questions in this chapter of NCERT Solutions.
Instasolv not only simplifies complex issues with its lucid explanation but also highlights key features essential from the examination point of view. To meet your competency level, easy language has been used to explain the intricate topics in NCERT Solutions for Class 11. We are sure that with the help of these solutions, you will be able to enhance your academic knowledge in the subject.
Important Topics for NCERT Solutions for Class 11 Biology Chapter 8- Cell: The Unit of Life
What is a Cell?
In all the living organisms the structural and the fundamental unit is called the cell. To first see and describe a living cell was Anton Van Leeuwenhoek. Later, the nucleus was discovered by Robert Brown.
Theodore Schwann, a British zoologist in 1839 reported that the cells had a thin outer layer called the ‘plasma membrane’. Cell theory was formulated by Schleiden and Schwann but their theory did not explain how the new cells are formed. It was Rudolf Virchow, who gave the final shape to the cell theory. According to the cell theory-
- All the living organisms are composed of cells and products of cells
- All cells arise from pre-existing cells.
An Overview of Cell
The nucleus is the dense membrane-bound structure present inside the cell and it contains chromosomes. It contains genetic material called DNA. In Eukaryotic cells, membrane-bound nuclei are present in the cell and in prokaryotic cells, no membrane-bound nucleus is present. In both plant and animal cell cytoplasm i.e. the semi-fluid matrix is present. In Eukaryotic cells, organelles are found but are found in prokaryotic cells.
These cells are usually small and grow fast. E.g. are bacteria, blue-green algae, mycoplasma, and PPLO. A bacterium has four basic shapes- bacillus (rod), coccus (spherical), vibrio (comma), and spirillum (spiral). In prokaryotes, the cell membrane is surrounded by the cell wall. Cytoplasm with a not well-defined nucleus is present. There is no nuclear membrane.
- Cell Envelope and its modifications
Cell envelope consists of three tightly bound layered structures- glycocalyx (outermost), cell wall, and the plasma membrane. These together act as a single unit. Bacteria can be gram-positive and negative. Glycocalyx can be a slime layer when it is in the form of the loose sheath and it could be in capsule form when it is thick and tough. The cell wall provides structure and shape to the cell. The semi-permeable plasma membrane is there. Mesosomes, formed by the extension of the plasma membrane into the cell, are present and their form can be vesicles, tubules, and lamellae.
- Ribosomes and Inclusion bodies
In prokaryotes, ribosomes are connected with the plasma membrane. They perform protein synthesis. Polyribosome or polysome is the chain of various ribosomes attached to a single mRNA. Inclusion bodies store the reserve material in the cytoplasm.
The presence of membrane-bound organelles results in the extensive compartmentalisation of the cytoplasm. It has an organised nucleus in a nuclear envelope. Plants cells and animal cells are different, as the former has a cell wall, plastids, central vacuole but the latter has only centrioles.
- Cell Membrane
The membrane is made of lipids arranged in a bilayer. Phosphoglycerides constitute the lipid component. They possess protein and carbohydrates. Membrane proteins can be integral and peripheral. Singer and Nicolson proposed the fluid mosaic model. The plasma membrane transports the molecules and is selectively permeable. Passive transport refers to the movement of molecules without the requirement of energy. Water also moves across this membrane and the movement of water by diffusion is known as osmosis.
- Cell Wall
It is the outer cover of the plasma membrane in fungi and plant cells. It gives shape to the cell, protects the cell from damage, helps in cell-to-cell interaction, and also provides a barrier to undesirable macromolecules.
- Endomembrane System
It includes the endoplasmic reticulum, Golgi complex, lysosome, and vacuoles.
- Endoplasmic Reticulum
They are the tiny tubular structures present in the cytoplasm, dividing the intracellular space into- luminal and extraluminal compartments.
- Golgi Apparatus
Flat, disc-shaped sacs or cisternae are present in the Golgi apparatus. Its function is to pack materials for intracellular targets or to be secreted outside the cell. The formation of glycoproteins and glycolipids occurs here.
Formed by the process of packaging in the Golgi apparatus, these are membrane-bound vesicular structures. They produce enzymes that are capable of digesting carbohydrates, proteins, lipids, and nucleic acids.
They are formed by a single membrane called tonoplast, these are spaces found in the cytoplasm. Water, soap, and other useful materials for the cell are found here.
It is a double membrane-bound structure, each membrane dividing its lumen into two aqueous compartments. Matrix is the inner compartment. It is a site for aerobic respiration. They are called ‘powerhouses’ as they produce ATP, a form of cellular energy.
On the basis of the type of pigments, plastids are divided into chloroplasts, chromoplasts, and leucoplasts. The chloroplast contains chlorophyll, essential for photosynthesis. Chloroplasts contain fat-soluble carotenoid pigments. Leucoplasts are colourless and store nutrients like amyloplasts, elaioplasts, and aleuroplasts.
They are granular structures composed of ribonucleic acid and proteins. They do not have any membrane.
In the cytoplasm, a filamentous proteinaceous network is presently called the cytoskeleton. It provides mechanical support, mobility, and shape to the cell.
- Cilia and Flagella
They are hair-like outgrowths on the cell membrane. They are responsible for the cell movement. Emerging from a centriole-like structure called the basal bodies; they are covered with the plasma membrane. Their core is known as axoneme, containing many microtubules.
- Centrosome and Centrioles
The centrosome contains two cylindrical structures called the centrioles, which are surrounded by amorphous pericentriolar materials. The centrioles form the basal body of cilia or flagella.
The interphase nucleus contains chromatin, nuclear matrix, and nucleoli. Perinuclear space is the space between the membranes in the nuclear envelope. The nuclear matrix or the nucleoplasm has nucleolus and chromatin. Chromatin contains DNA, histones, non-histone proteins, and RNA. The chromosome has centromere. Based on the location of the centromere, chromosomes are of four types- metacentric, sub-metacentric, acrocentric, and telocentric.
In both plant and animal cells, these are minute vesicles on the cell membrane containing various enzymes.
Discussion of Exercises of NCERT Solutions for Chapter 8- Cell: The Unit of Life
- The first-four questions are objective types which include picking the correct answer and matching the following type of questions.
- Fifth to eleventh questions are definition based. They are related to prokaryotic and eukaryotic cells.
- Few questions deal with cells and their structure.
- In some questions, you have to draw diagrams of the cell. We have included clear diagrams for your reference.
The NCERT Solutions for Class 11 Biology Chapter 8- Cell: The Unit of Life by Instasolv will expand your understanding of these very fundamental yet vital concepts of biology. Grab the opportunity and have it for a better score in your CBSE exams.