NCERT Class 11 Biology Chapter 8 Notes Cell The Unit Of Life- Download PDF Notes

The NCERT Chapter 8 cell the unit of life, discusses the basic form of life, the cell. The NCERT Class 11 Biology chapter 8 notes cover a brief outline of the chapter cell: the unit of life. The main topics covered in NCERT Class 11 Biology Notes are definitions and types of living and non-living creatures on Earth, characteristics of cells, types of cells, prokaryotic and eukaryotic cells, cell theory, and components or organelles of cells. Class 11 Biology chapter 8 notes cover all the important concepts of this chapter in simple language that makes them easy-to-understand. Having revision notes and NCERT Solutions for Class 11 Biology Chapter 8 handy, provided by careers360, is beneficial to save you time. The NCERT Class 11 Biology chapter 8 notes PDF can be downloaded through the link given below.

Cell: The Unit of Life Class 11 notes Biology Chapter 8 also covers all the important headings of the NCERT Book that are useful in various competitive exams. Chapter 8 Cell The Unit of Life Notes help you revise these major concepts given in the NCERT Book in a short period of time during CBSE Board exam preparation. Download the CBSE Notes for Class 11 Biology Chapter 8 PDF to use them offline anywhere. Notes can be downloaded through the link. Students must go through each topic in the cell the unit of life in Class 11 Notes Biology, in the easiest and most effective way possible with the help of NCERT Notes for Class 11. Check the given Class 11 Biology Notes Chapter 8 Cell The Unit of Life PDF for quick revision.

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NCERT Class 11 Biology Chapter 8 Notes

We can see both living and non-living objects when we glance around. We may have thought and asked ourselves, what makes an organism live? The presence of the basic unit of life, the cell, in all living things is the answer.

Cells make up every living thing. Unicellular species are made up of just one cell, whereas multicellular organisms, like ourselves, are made up of numerous cells.

Cell:

• Unicellular organisms may exist on their own and fulfill all of life's core activities. A cell's structure must be complete in order for it to live on its own. As a result, all living things' cells are the primary structural and functional unit.
• The first living cell was seen and described by Anton Von Leeuwenhoek. The nucleus was later found by Robert Brown.
• The creation of the microscope, and subsequent advancements that led to the development of the electron microscope, revealed all of the cell's structural features.

Cell Theory

In 1838, a German botanist named Matthias Schleiden studied a large number of plants and determined that all plants are made up of several sorts of cells that form the plant's tissues.

Around the same time, a British zoologist named Theodore Schwann (1839) researched many types of animal cells and discovered that they possessed a thin outer covering that is now known as the 'plasma membrane.'

He also came to the opinion that the presence of a cell wall is a distinguishing property of plant cells based on his studies on plant tissues. Schleiden and Schwann collaborated on cell theory.

However, this idea could not explain how additional cells were produced. Cells divide and new cells are created from pre-existing cells, according to Rudolf Virchow (1855). To give the cell theory a final shape, he amended Schleiden and Schwann's idea.

The current understanding of cell theory is that

• All living entities are made up of cells and cell products.

• All cells develop from pre-existing ones.

Prokaryotic Cells

• They are smaller than eukaryotic cells and multiply more quickly. In terms of shape and size, they can be rather varied. Bacillus (rod-shaped), coccus (sphere), vibrio (comma-shaped), and spirillum (spiral) are the four fundamental forms of bacteria (spiral).
• Despite the fact that prokaryotes come in a vast range of forms and functions, the organization of their cells is fundamentally identical.
• With the exception of mycoplasma, every prokaryote has a cell wall that surrounds the cell membrane.
• The cytoplasm is the fluid matrix that fills a cell. The nucleus isn't properly delineated. Because the genetic material is not encased by a nuclear membrane, it is almost bare.
• Many bacteria have tiny circular DNA outside of their genomic DNA (the single chromosome/circular DNA). These tiny DNAs are called Plasmids.
• Bacteria with plasmid DNA have distinct phenotypic characteristics. Antibiotic resistance is one such characteristic. This plasmid DNA is utilized to monitor bacterial transformation with foreign DNA.
• Eukaryotes have a nuclear membrane. Except for ribosomes, prokaryotic cells lack organelles similar to those seen in eukaryotes.

• In prokaryotes, the cell has the following characteristics. Its protective cell envelope is chemically complicated. It, on the other hand, lacks a well-defined nucleus and other membrane-bound cell organelles.
• The outer glycocalyx, middle cell wall, and inner plasma membrane form the three-layered structure of the cell envelope. Glycocalyx can be found in two forms: a slime layer (loose sheath) and a capsule (tough). When bacteria are stained, it makes them easier to see. 'Gram staining,' developed by Danish bacteriologist Hans Christian Gram, is the most widely used staining procedure. Gram positive bacteria have peptidoglycan cell walls, while Gram negative bacteria have murein cell walls. It provides the cell with mechanical strength.
• Phospholipid bilayers form the cell membrane. All of these structures protect the cell and aid in intercellular communication.
• Cilia and flagella can both be present in motile bacteria. Both are propelled by the basal body's rotatory action. filament and hook are the other components.
• Tubular pili and fimbriae are two more surface projections. Mesosomes are infoldings in the cell membrane that aid in cell wall construction and DNA replication.
• Some bacteria, particularly photosynthetic cyanobacteria, have more chromatophores. Photosynthetic pigments are carried by them.
• Ribosomes are compact particles found in the cytoplasm that aid in protein synthesis. The sedimentation rate of ribosomes in Svedberg units is used to classify them.

Eukaryotic Cells

• Protists, plants, animals, and fungi are all classified as eukaryotes. The existence of membrane-bound organelles in eukaryotic cells allows for substantial cytoplasm compartmentalization.
• Eukaryotic cells have a nuclear envelope and a well-organized nucleus. Eukaryotic cells also feature a wide range of complicated locomotory and cytoskeletal structures.
• Their genetic material is arranged in the form of chromosomes.
• There are differences among eukaryotic cells. Plant cells have cell walls, plastids, and a big central vacuole, whereas animal cells lack these features. Animal cells, on the other hand, have centrioles, but plant cells do not.

Plant Cell VS. Animal Cell

Cell Organelles

Eukaryotes have a variety of cellular organelles that serve a wide range of activities. Some of these organelles are unique to plant cells, such as the cell wall.

Cell Wall:

• The cell wall of plant cells, fungi, and some protists are stiff, supporting, and has a protective outer coating of the plasma membrane.
• The cell walls of algae contain cellulose, galactans, mannans, and minerals such as calcium carbonate. It is composed of hemicelluloses, pectin, lipids, and protein in other plants.
• Plant cell wall microfibrils demonstrate the existence of cellulose, which is responsible for stiffness. Silica, cutin, suberin, wax, and lignin are some of the cell wall depositions.
• Cell walls in plants have three layers: middle lamella, primary wall, and secondary wall.

Middle lamella: It is thin and is located between two adjacent cells. During cytokinesis, it is the first structure formed from the cell plate. It is primarily composed of calcium pectate. The softening of ripe fruit is caused by pectin solubilization.

Primary wall: It can grow in a young plant cell. It is put inside the middle lamella. It is the sole wall found in meristematic tissue, mesophyll, pith, and so on.

Secondary wall: It can be found from the inner to the primary wall. When the primary wall's growth is complete, the secondary wall is built.

Cell Membrane:

• Lipids and proteins form the majority of the cell membrane. Phospholipids, which are organized in a bilayer, make up the majority of the lipids. The lipids are also distributed within the membrane with the polar heads on the outside and the hydrophobic tails on the inside.
• This guarantees that saturated hydrocarbons' nonpolar tails are protected from the aqueous environment.
• Membranes include cholesterol in addition to phospholipids. Protein and carbohydrates are also present in cell membranes.
• The protein-to-lipid ratio varies significantly between cell types. The erythrocyte membrane in humans has around 52% protein and 40% lipids.
• Membrane proteins are classed as integral or peripheral based on the ease with which they can be extracted. Peripheral proteins are found on the membrane's surface, whereas integral proteins are partially or completely buried in the membrane.
• Singer and Nicolson (1972) proposed the fluid mosaic model, which is widely accepted as a better model of cell membrane structure.
• The quasi-fluid nature of lipids, according to this theory, allows for lateral protein movement within the overall bilayer. The fluidity of a membrane refers to its ability to move within it.
• Cell growth, formation of intercellular junctions, secretion, endocytosis, cell division, and other functions all benefit from the fluid nature of the membrane.
• Transporting molecules through the plasma membrane is one of the plasma membrane's most significant tasks.
• Some molecules on each side of the membrane can pass through the membrane preferentially. The term "passive transport" refers to the ability of several molecules to travel across a membrane without consuming any energy.
• Simple diffusion along a concentration gradient, i.e., from a higher concentration to a lower concentration, can transport neutral solutes across the membrane. Water can also flow from a greater to a lower concentration over this membrane. Osmosis is the process of moving water by diffusion.
• A few ions or molecules are transported across the membrane in the opposite direction of their concentration gradient, that is, from lower to higher concentrations. This type of transport, known as active transport, is an energy-dependent mechanism that makes use of ATP.

The Endoplasmic Reticulum (ER):

• The existence of an endoplasmic reticulum, which is a network or reticulum of small tubular structures dispersed throughout the cytoplasm.
• Ribosomes adhering to the outer surface of the ER are frequently seen. Rough endoplasmic reticulum (RER) is a type of endoplasmic reticulum that has ribosomes on its surface.
• They're called smooth endoplasmic reticulum since they don't have any ribosomes (SER).
• RER is commonly found in cells that are active in protein synthesis and secretion.
• They are long and continuous with the nucleus' outer membrane.

Golgi Apparatus:

• Camillo Golgi identified the first brightly pigmented reticular structures around the nucleus in 1898. The bodies were given the name Golgi after him. These formations are made up of many flat, disc-shaped sacs or cisternae with sizes ranging from 0.5m to 1.0m.
• These are arranged in a straight line on top of one another. The number of cisternae in a Golgi complex varies.
• The Golgi cisternae are organized concentrically towards the nucleus, with distinct convex cis and concave trans faces. The organelle's cis and trans faces are completely distinct, although they are linked together.
• The primary function of the Golgi apparatus is to package materials for delivery to intracellular destinations or for secretion outside the cell.
• The materials from the ER that will be packed as vesicles fuse with the Golgi apparatus's cis face and travel towards the developing face. This helps to explain why the Golgi apparatus and the endoplasmic reticulum are so closely linked.

Lysosomes:

• The packaging process in the Golgi apparatus results in membrane-bound vesicular structures called lysosomes.
• The segregated lysosomal vesicles were discovered to be extremely rich in nearly all forms of hydrolytic enzymes (hydrolases, lipases, proteases, and carbohydrates) that are ideally active at an acidic pH.

Vacuoles:

In the cytoplasm, the vacuole is a membrane-bound space. It's made up of water, sap, excretory product, and other substances that are useless for the cell. A single membrane, termed tonoplast surrounds the vacuole. The vacuoles in plant cells can take up to 90% of the cell's volume. The tonoplast in plants helps the movement of a number of ions and other materials against concentration gradients into the vacuole, so their concentration is much higher in the vacuole than in the cytoplasm. The contractile vacuole is critical for osmoregulation and excretion in Amoeba.

Mitochondria:

• Mitochondria are difficult to see under a microscope unless they are stained. The number of mitochondria per cell varies according to the cells' physiological activity.
• There is a great deal of variation in terms of shape and size as well. It has a diameter of 0.2-1.0 micrometer (average 0.5m) and a length of 1.0 - 4.1micrometer and is sausage-shaped or cylindrical.
• Each mitochondrion is a double membrane-bound structure, with the outer and inner membranes dividing the lumen into two aqueous compartments, the outer and inner compartments, respectively. The matrix is a dense homogenous material that fills the interior compartment. The continuous limiting border of the organelle is formed by the outer membrane. In the direction of the matrix, the inner membrane creates a series of infoldings known as cristae. The cristae expand the surface area.
• Aerobic respiration takes place in mitochondria. They generate cellular energy in the form of ATP and are so known as the cell's "powerhouses."
• The matrix also contains a single circular DNA molecule, a few RNA molecules, ribosomes (the 70S), and components that are used for protein synthesis.

Plastids:

• All plant cells including euglenoids include plastids. Because they're so big, they're easy to spot under a microscope.
• They contain a variety of pigments that give the plants distinct colors. Plastids are classed as chloroplasts, chromoplasts, or leucoplasts depending on the type of pigment they contain.
• Chlorophyll and carotenoid pigments are found in chloroplasts, and they are responsible for capturing light energy for photosynthesis.
• Fat-soluble carotenoid pigments like Carotene, xanthophylls are found in chromoplasts.
• Colorless plastids of various forms and sizes with stored nutrients are known as leucoplasts. Amyloplasts store carbohydrates (starch), such as potato, whereas elaioplasts store oils and lipids, and aleuroplasts store proteins.
• The mesophyll cells of the leaves contain the majority of the chloroplasts in green plants. These organelles are lens-shaped, oval, spherical, discoid, or even ribbon-like, with varying lengths (5–10 m) and widths (2-4m).
• Their numbers range from one per cell in the green alga Chlamydomonas to 20–40 per cell in the mesophyll. The chloroplasts, like mitochondria, are double membrane-bound. The inner chloroplast membrane is the least permeable of the two.
• The stroma is the space enclosed by the chloroplast's inner membrane. The stroma contains a number of organised, flattened membranous sacs known as thylakoids.
• Thylakoids are organized in stacks similar to grana (coin piles) or intergranal thylakoids. In addition, the stroma lamellae are flat membranous tubules that connect the thylakoids of the various grana. Thylakoid’s membrane encloses a space known as a lumen.

Ribosomes:

• They are made up of ribonucleic acid (RNA) and proteins and are not enclosed by a membrane.
• The 80S ribosomes are found in eukaryotes, while 70S ribosomes are found in prokaryotes. Each ribosome is made up of two subunits: bigger and smaller subunits. The two subunits of 80S ribosomes are 60S and 40S, while those of 70S ribosomes are 50S and 30S.

Cytoskeleton:

The cytoskeleton is a complex network of proteinaceous structures in the cytoplasm that includes microtubules, microfilaments, and intermediate filaments. Many roles of the cytoskeleton in a cell include mechanical support, motility, and cell shape maintenance.

Cilia and Flagella:

• They are fine, hair-like protoplasmic outgrowths on the cell's free surface that are membrane-bound. They create a current in a fluid medium to allow stuff to move through and for locomotion. Cilia are little, yet they are numerous.
• Flagella are longer and fewer in number. Flagella found in prokaryotic bacteria differ structurally from those found in eukaryotic bacteria. Cilium or flagellum is made up of three parts: a basal body, a basal plate, and a shaft.
• The basal body is found in the cytoplasm's outer layer. The centriole is the source of it. It consists of nine peripheral triplets of fibrils.
• The exposed section of the cilia or flagella is called the shaft. It is made up of two parts: the sheath and the axoneme. The sheath covers the cilium or flagellum membrane. The axoneme core has 11 fibrils that run parallel to the long axis. It has nine peripheral doublets and two single-center fibrils (9+2). A central sheath surrounds the central tubules.

Centrosome and Centrioles:

• A centrosome is an organelle that typically contains two cylindrical structures known as centrioles.
• Pericentriolar elements that are amorphous surround them. A centrosome's centrioles are perpendicular to one another and have a cartwheel-like organization.
• They're made up of nine tubulin-protein peripheral fibrils that are evenly spaced. The peripheral fibrils are all triplets. The adjacent triplets are linked as well.
• The central part of the centriole's proximal region, known as the hub, is also proteinaceous and is linked to the tubules of the peripheral triplets via radial spokes made of protein.

Nucleus:

• Robert Brown was the first to characterize the nucleus as a cell organelle in 1831. Flemming later gave the name chromatin to the nucleus material stained with basic dyes.
• Except for RBCs, all eukaryotic cells have a double membrane structure called the nucleus.
• It includes the vast bulk of the genetic material that is passed down from parents to offspring during cell division.
• The DNA in the nucleus is packed in the shape of chromosomes with histone proteins, and it regulates the cell's activity and development. The gene is a piece of DNA that contains the instructions for making a protein.
• There are two kinds of chromosomes: euchromatin and heterochromatin. Euchromatin is a less compact structure that may be transcribed into mRNA. Heterochromatin, on the other hand, is a dense structure that cannot be transcribed into mRNA.
• The nuclear membrane is a two-layered structure that prevents big molecules from passing through. The endoplasmic reticulum and the outer layer are joined. The transport of solutes into and out of the nucleus is regulated by the presence of nuclear pores in the membrane. Between these two layers, there is a region called a perinuclear.
• In eukaryotic cells, the nucleolus is a solid, spherical structure found inside the nucleus. During protein synthesis, it is involved in the assembly of ribosomes. It vanishes during cell division and reappears when the division is completed.

Microbodies:

Both plant and animal cells contain a large number of membrane-bound minute vesicles known as microbodies, which contain different enzymes.

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Significance of NCERT Class 11 Biology Chapter 8 Notes

Cell: The Unit of Life Class 11 notes will be useful in revising the chapter and gaining an understanding of the key topics addressed. These Notes for Class 11 Biology chapter 8 are also beneficial for covering the key themes of the CBSE Biology Syllabus in Class 11 as well as for competitive examinations such as AIPMT, AIIMS, NEET, and others. The Class 11 Biology chapter 8 notes pdf download may be utilized for offline preparation. CBSE Class 11 Biology chapter 8 notes do not include anything about Cell cycle and cell division.

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