RBSE Class 11 Biology Notes Chapter 8 Cell: The Unit of Life

These comprehensive RBSE Class 11 Biology Notes Chapter 8 Cell: The Unit of Life will give a brief overview of all the concepts.

RBSE Class 11 Biology Chapter 8 Notes Cell: The Unit of Life

→ Cell is the structural and functional unit of all living organisms, which is surrounded by differentially permeable membrane.

→ Cell was discovered by Robert Hooke (1665). He wrote a book ‘Micrographia’ and coined the term cellula which was later changed into cell.

→ The branch of science that deals with the study of cell is called cytology.

→ Schleiden and Schwann (1839) compared their findings and formulated cell theory.

→ Nageli (1846) and Rudolf Vircho modified the cell theory into modern cell theory which states that:

• Cells are structural and functional unit of all living organisms.
• New cells always arise from pre existing cells.

→ Gram Positive Bacteria: Staphylococcus, Streptococcus, Pneumococcus, Bacillus, Clostridium, Mycobacterium, Streptomyces.

→ Gram negative Bacteria: Salmonella, Pseudomonas, Vibrio, Helicobacter, Haemophilus, Escherichia.

→ Virus is the exception of cell because it has protein and nucleic acid but other cell organelles like cell wall, protoplasm, mitochondria etc are absent.

→ Mycoplasma (PPLO) is smallest cell, while the cell of Acetabularia algae is longest cell. In animals, the longest cell is nerve cell while the Ostrich egg is largest cell in diameter.

 

→ The lysozyme present in saliva, tears and gastric juice has similar effect.

→ Mesosomes are convoluted membranous structures formed by invagination of plasma membrane.

→ Ribosomes take part in protein synthesis. 4-8 ribosomes are often found attached to a single m-RNA for forming the copies of the same polypeptide. Ribosome aggregates are called polysomes.

→ Nucleoid is folded, single, circular strand of DNA of prokaryotic cells, also called genophore, prochromosome or chromoneme.

→ Additional or extrachromosomal, small rings of DNA having a few useful but non vital genes are called plasmid in prokaryotic cells.

→ The association of plasmid with nucleoid is called episome.

→ Pili (singular pilus) are 1 to 4, long hollow tubes (18-20 pm long, 30-35 nm diameter), also called sex pili or F-pili, because they take part in conjugation.

→ Middle lamella is the outermost region which functions as cementing layer between two cells, it rupture to create intercellular space.

→ Cell wall possesses minute cytoplasmic bridges between adjacent cells, called plasmodesmata (Strasburger, 1901).

→ Fluid mosaic model of plasma membrane was given by “Singer and Nicolson”. They have described cell membrane as “protein icebergs in sea of lipids”.

→ Desmosomes are just like welded areas between adjacent cells having intercellular thickning material.

→ Passive transport occurs through diffusion and osmosis without expenditure of energy.

→ Active transport occurs with the help of energy, usually against concentration gradient, through the carrier proteins and gated channels.

→ Bulk transport is transport of large quantities of micromolecules, macromolecules and food particles through the membrane. It is accompanied by formation of transport or carrier vesicles.

→ Pinocytosis is called “cell drinking” while phagocytosis is called “cell eating”.

→ Streaming movement of cytoplasm is called cyclosis.

→ A glycoprotein that is attached ribosome on the surface of endoplasmic reticulum is called ribophorin.

→ Magnesium ion is essential for finding the ribosome subunits. The value is 1-2 mM for eukaryotes and 0.5 mM for prokaryotes. The subunits separates below this concentration.

→ Golgi apparatus is also called ‘traffic policeman’. It take part in the formation of lysosomes.-

→ Acentric: The chromosomes without centromere.

→ Apoptosis: A controlled sequence of steps in which cells signal self termination.

→ Capsule: Gelatinous membrane of some cyanobacteria or bacterial cells.

→ Basal body: Rod like, basal part of flagellum which are attached in cell envelope.

→ Cell biology: The sub disciplane of biology that focuses on the study of the basic unit of life, the cell.

→ Cell cycle: The life cycle of a dividing cell, including interphase and the mitotic (M) phase (mitosis and cytokinesis).

→ Cell theory: One of the five basic principles of biology, stating that the cell is basic unit of life and living cells arise from pre-existing cells.

→ Centrloles: Cylindrical structures that are composed of groupings of microtubules arranged in 9 + 3 pattern.

→ Centromere: A region on chromosome that joins two sister chromatids.

→ Chromatid: One of two identical copies of a replicated chromosome.

→ Chromatin: The mass of genetic material composed of DNA and proteins that condense to form chromosomes during eukaryotic cell division.

→ Chromosome: A long, stringy aggregate of genes that carries heredity information (DNA) and is formed from condense chromatin.

→ Cilia: Small and large number of hair like protrusions arise from cell membrane that aid in cellular locomotion.

→ Cytosol: Semifluid component of a cell’s cytoplasm.

→ Flagella: Long and some hair like protrusions arise from cell membrane that aid in cellular locomotion.

→ Diffusion: Movement of solid/liquid/gases molecules or ions from the region of their higher concentration to the region of their lower concentration is called diffusion.

→ Diploid cell: A cell that contains two sets of chromosomes out of which one set of chromosome is maternal and another is of paternal.

→ Glycocalyx: The dense (capsule) or loose (slimy) gel like covering of the cell wall in bacterial cells. .

→ Glycolipids: The lipids of cell membrane that contains a hydrophillic head and hydrophobic tail.

→ Fluid mosaic model: Singer and Nicolson described the cell membrane as ^protein iceberg in sea of lipids”.

→ Glycoproteins: The proteins attached with polysaccharide chain in the structure of cell membrane.

→ Golgi complex: The cell organelle that is responsible for manufacturing, warehousing and shipping of certain products in the cytoplasm of a cell.

→ Granum: The structure formed by arranging the thylakoids one above the other, (plural grana).

→ Golgisome: A unit of golgi apparatus is known as golgisome.

→ Haploid cell: A cell that contains one complete set of chromosomes.

→ Interphase: The stage in the cell cycle where a cell doubles in size and synthesizes DNA in preparation for cell division.

→ Leucoplasts: Colourless plastids that store starch (amyloplasts), protein (aleuroplasts) and fats (elaioplasts).

→ Lysosomes: The membranous sacs of enzymes that can digest cellular macromolecules, also called as “suicide bags of cell”.

→ Matrix: Semi liquid substance filled in organelles.

→ Mitochondria: It is called “powerhouse of the cell” because it converts energy into forms (ATP) that are unable by the cell.

→ Micrometer: pm = 10^-6 m (10^-3 mm),

→ Microtubules: Fibrous, hollow rods that function primarily to help in support and shape the cell.

→ Nanometer: nm = 10^-9 m (10^-3 pm).

→ Nucleic Acid: Polymers of nucleotides e.g., DNA and RNA.

→ Nucleoid: The genetic material without covering in prokaryotic cell.

→ Nucleolus Roughly rounded, darkly stained structure inside the nuCeus that is the site for elaboration ofrRNA and synthesis of ribosomal units.

→ Nucleoplasm: A colloidal complex that fills the nucleus, also called karyolymph or karyoplasm, contains raw material for synthesis of DNA and RNA.

→ Nucleosome: The DNA is packed with histone protein (octamer) to form a unit called nucleosome. Due to this DNA appears as beads on string,

→ Nucleus: A membrane bound structure that contains the cell’s hereditary information and controls the cell’s growth and reproduction of cell. Also called control centre or Brain of the cell,

→ Organelles: Tiny cellular structures, that carry out specific functions necessary for cellular operation,

→ Peroxisomes: Cell structures that contain enzymes, that produce hydrogen peroxide as a by product,

→ Osmosis: Movement of solvent molecules from their higher concentration to the region of their lower concentration through the semipermeable membrane,

→ Phagocytosis: Ingestion of large particles by living cells through plasma membrane (cell eating).

→ Pinocytosis: Intake of fluid, ions and molecules by living cell through plasma membrane (cell drinking). 

→ RER: The endoplasmic reticulum with ribosomes attached on the surface.

→ SER: The endoplasmic reticulum without ribosome on the surface.

→ Sister chromatids: Two identical copies of a single chromosome that are connected by a single chromosome.

→ Spindle fibres: Aggregates of microtubules that move chromosomes during cell division.