NCERT Biology Class XI: Cell-The Unit of Life

Cell

the fundamental structural and functional unit of all living organisms.

Unicellular Organisms

Organisms consisting of a single cell.

Multicellular Organisms

Organisms composed of multiple cells.

Plasma Membrane

Semipermeable boundary structure for cell, facilitates exchange

Cytoplasm

Semi-fluid matrix for cellular activities and main area for all cellular activites

Genetic Material

DNA containing genetic information.

Ribosomes

non-membrane bound granular structures found in all cells both eukaryotic as well as prokaryotic cell, composed of RNA and proteins.

Cell Theory

Cells are the basic units of life, all living organisms are composed of cells and products of cells. and all cells arise from pre-existing cells (Omnis cellula-e cellula)

Eukaryotic Cells

Cells with membrane-bound nuclei.

Prokaryotic Cells

Cells lacking membrane-bound nuclei.

Organelles

Distinct structures within eukaryotic cells.

Mycoplasmas

Smallest known cells, 0.3 μm in length.

Ostrich Eggs

the largest isolated single cell

Plasmids

Small circular DNA in bacteria which confers certain unique phenotypic characters to such bacteria such as resistance

to antibiotics. Also used to monitor bacterial transformation with foreign DNA.

Cell Wall

Rigid outer layer in plant cells.

Division of Labour

differentiation of certain parts of the cell to carry out different functions for increased efficiency and higher survival

Mathias Scheliden

observed that all plants are composed of different kinds of cells which form the tissues of the plant.

Theodore Schwann (1839)

studied different types of animal cells and reported that cells had a thin outer layer which is today known as the plasma membrane, the presence of cell wall is a unique character of the plant cells, and proposed the hypothesis that the bodies of animals and plants are composed of cells and products of cells.

Rudolf Virchow

Proposed cells arise from pre-existing cells.

Robert Hooke

First to observe and name cells.

Anton Von Leeuwenhoek

Described live cells, including bacteria.

PPLO (Pleuro Pneumonia Like Organisms)

subtype of mycoplasma

Prokaryotic DNA

naked DNA which is not associated with histones or proteins

Murein

another name for prokaryotic cell walls due to excess muramic acid

Prokaryotic Periplasmic Space

space between the prokaryotic cell membrane and cell wall

Prokaryotic Inclusions

prokaryotic membrane-less storage found in cytoplasm

Cell Size

Varies from 0.1 μm to several μm.

Coccus

Spherical shape of bacteria.

Bacillus

Rod-like shape of bacteria.

Vibrio

Comma-shaped bacteria.

Spirillum

Spiral-shaped bacteria.

Centrioles

Non-membrane organelles aiding cell division and absent in all higher plants

Cytoplasmic Matrix

Fluid filling the cell, site of reactions.

Microscope

Instrument that magnifies small objects.

Cellular Metabolism

Chemical processes maintaining cell's living state.

Human Red Blood Cells

About 7.0 μm in diameter.

Nerve Cells

Some of the longest cells in humans.

Prokaryotic Cell Envelope

Three-layered structure: glycocalyx, cell wall, plasma membrane.

Gram Positive Bacteria

bacteria that remain the gram stain and observable as purple due to a thick layer of peptidoglycans and thick cell wall

Gram Negative Bacteria

Bacteria that do not retain the Gram stain and observable as pink due to a thin layer of peptidoglycans, thin cell wall, and contain lipopolysaccharides.

Lipopolysaccharides

main component of glycocalyx

Glycocalyx

Outermost layer of cell envelope consisting of lipopolysaccharides.

Capsular glycocalyx

type of glycocalyx which is thick and tough

slime layer glycocalyx

type of glycocalyx which is a loose sheath

Mesosomes

Invaginations of the plasma membrane into the cell in the form of vesicles, tubules, and lamallae.

Functions of Mesosomes

cell wall formation, DNA replication, distribution of DNA to

daughter cells, respiration, secretion processes, increase the surface area of the plasma membrane, and contain enzymatic content.

Chromatophores

membranous extensions into the cell wall that contain pigments vital for photosynthesis in bacteria, such as cyanobacteria.

Flagella

thin filamentous extensions from bacterial cell wall composed of the filament, hook, and basal body for motility purposes in the bacteria

Flagellar filament

the longest portion of the flagella and extends from the cell surface to the outside

Pili

prokaryotic elongated tubular structures made of a special protein and do not play a role in motility

Fimbrae

small bristle like fibers sprouting out of prokaryotic bacteria which attach to the environment and do not play a role in motility

Prokaryotic ribosomes

Made of 70S Ribosomes (50S and 30S ribosomal subunits)

Polyribosomes

Chains of ribosomes attached to a single mRNA which translate the mRNA into proteins

Inclusion Bodies

Free-floating reserve material in prokaryotic cells found in the cytoplasm. E.g. phosphate granules, cyanophycean granules, and glycogen granules.

Gas vacuoles

inclusion vacuoles found in blue green, purple, and green photosynthetic bacteria

Cell Wall (Plant Cells)

Present in plant cells, absent in animal cells.

Contents of the Human erythrocyte

composed of approx. 52% protein and 40% lipids

Fluid Mosaic Model

the plasma membrane consists of fluid phospolipids allowing for lateral movement and different proteins, lipids, and carbohydrates.

Phospholipids

the main component of cell membrane formed by a hydrophilic "head" made up of a phosphate group attached to a glycerol molecule, and two hydrophobic "tails" made up of fatty acid chain

Functions of the Cell Membrane

Cell growth, intercellular junctions, secretion, endocytosis, and cell division

Hydrophilic head

Water-attracting part of phospholipid molecules consisting of a phosphate group.

Hydrophobic tail

Water-repelling part of phospholipid molecules consisting of a saturated and unsaturated fatty acid chain

Cholestrol in the Cell Membrane

Helps in membrane stability and fluidity

Quasifluid Nature

enables lateral movement of protein within the overall bilayer for various functions

Extrinisic proteins

proteins that are loosely attachIed to the surface of a cell membrane

Intrinsic proteins

proteins that are permanently embedded in the phospholipid bilayer of a cell membrane

Peripheral proteins

proteins that temporarily adhere to the surface of a cell membrane and can be easily removed by changing the pH, ionic strength, or washing the membrane.

Integral proteins

proteins that are permanently attached to a biological membrane and are essential for life.

Partially buried integral protiens

proteins incompletely buried through the thickness of membrane

Totally buried integral protiens

proteins totally bired through the complete thickness of the membrane in the form of carrier proteins or tunnel proteins.

Glycolipids & Glycoprotiens

Carbohydrate bound to either a lipid or a protein; serve to identify cell as part of the body and for cell recognition. Example: fertilization

Ribosomes (Prokaryotic)

70S ribosomes associated with plasma membrane.

Vacuole

Storage organelle, larger in plant cells.

Golgi Apparatus

Organelle involved in modifying and packaging proteins.

Endoplasmic Reticulum

Network of membranes involved in protein and lipid synthesis.

Phospholipid

Molecule forming the plasma membrane's bilayer.

Fluidity

Ability of membrane components to move laterally.

Unsaturated fatty acid

Fatty acid with one or more double bonds.

Saturated fatty acid

Fatty acid with no double bonds, more rigid.

Cholesterol

Steroid that stabilizes plasma membrane structure.

Fluid mosaic model

Describes membrane structure with diverse components.

Peripheral protein

Surface protein, easily separated from membrane.

Integral protein

Protein tightly bound to phospholipid bilayer.

Partially buried protein

Protein incompletely embedded in membrane thickness.

Totally buried protein

Protein fully embedded across membrane thickness.

Oligosaccharides

Short sugar chains on membrane surface.

Passive transport

diffusion of particles along a concentration gradient without the use of energy such as osmosis.

Simple Diffusion

diffusion of neutral and lipid soluble solutes such as O2 and CO2

Active transport

movement of particles against its concentration gradient with the use of energy. Na-K pumps.

Facilitated diffusion

diffusion of large polar molecules such as amino acids via carrier proteins or tunnel proteins

Endocytosis

Process of engulfing substances into the cell.

Pinocytosis

Ingestion of liquid material by plasmalemma in the form of vesicles or pinosomes

Phagocytosis

Ingestion of solid materials by membrane in the form of phagosomes (vesicles)

Exocytosis

Process of expelling materials from the cell.

Cell wall

a non-living rigid structure for the plasma membrane of Bacteria, some Protistan, Fungi, Algae and

Plants.

Algae cell wall

cell will consisting of cellulose, galactans, mannans and minerals like calcium carbonateC

cell wall structure

consisting of cellulose, hemicellulose, cutin, pectin, lignin, suberin, and proteins