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NEET Biology Cell : The Unit of Life

Cell : The Unit of Life PDF Notes, Important Questions and Synopsis

 

SYNOPSIS

 

  • Kinds of Cells
     

FEATURE

PROKARYOTIC CELL

EUKARYOTIC CELL

Nucleus

Absence of well-defined nucleus

Presence of well-defined nucleus with a nuclear membrane

Nucleolus

Absent

Present

Genetic material

Presence of a single length of only DNA

Presence of several lengths of DNA wound around certain proteins

Ribosomes

Presence of smaller ribosomes

Presence of larger ribosomes

  • Components of Eukaryotic Cell

CHARACTERISTICS

FUNCTIONS

Plasma membrane

  • Very thin, flexible and delicate living semi-permeable membrane
  • Lipid bilayer, integral and peripheral proteins

 

  • Acts as an effective barrier
  • Regulates the entry of certain solutes and ions

Cell wall (only in plant cells)

  • Freely permeable, mainly composed of cellulose
  • Consists of primary and secondary walls and middle lamella

 

  • Gives rigidity and shape to plant cells
  • Provides protection

Cytoplasm

  • Contains a mixture of water and soluble organic and inorganic compounds and various cell organelles

 

  •  Seat of occurrence of glycolysis (production of pyruvic acid)

Endoplasmic reticulum

  • May be smooth (SER) or rough (RER)

 

  • Acts as a supportive framework of the cell
  • RER involved in protein synthesis and secretion
  • SER involved in synthesis of glycogen, cholesterol, fat and oil

Mitochondria

  • Double-walled, inner wall thrown into folds called cristae
  • Known as powerhouses of the cell

 

  • Seat of aerobic respiration
  • Synthesise respiratory enzymes and energy-rich compounds

Golgi apparatus (in animal cells)

Dictyosomes (in plant cells)

  • Consists of a set of membrane-bound, fluid-filled vesicles and vacuoles

  • Synthesis of plasma membrane, cell wall
  • Synthesis and secretion of enzymes and hormones

Ribosomes

  • Single-walled, dense, spherical bodies composed mainly of RNA and proteins
  • Known as protein factories of the cell

 

  •  Synthesis of proteins

Lysosomes

  • Membrane-bound vesicles containing 40 different types of hydrolytic enzymes

  •  Intracellular digestion

Centrosomes

  • Contains one or two centrioles which are surrounded by radiating microtubules to form an aster shape

  •  Initiates and regulates cell division

Plastids

  • Double membrane, proteinaceous matrix containing DNA and disc-like structures called thylakoids containing chlorophyll

  • Chromoplasts: Impart colour to flowers and fruits
  • Chloroplasts: Trap solar energy for photosynthesis
  • Leucoplasts: Store starch

Nucleus

  • Mostly spherical and dense, surrounded by nuclear membrane with pores

  • Nuclear matrix contains nucleolus and chromatin

  • Nucleoli are spherical structures, one or more in number

  • Chromatin fibres are a network of thread-like structures made of DNA

  • Regulates cell cycle and cell functions
  • Nucleolus participates in protein synthesis by forming and storing RNA
  • Chromosomes carry hereditary information or genes

Vacuoles

  • Non-living, membrane-bound structures

 

  • Storage of water and other substances, food, pigments and waste products

Granules

  • Small particles, crystals or droplets

  • Starch (in plant cells), glycogen (in animal cells) and fat-containing granules serve as food for the cell

Cytoskeleton

  • Filamentous proteinaceous structures present in the cytoplasm

  • Mechanical support, motility and maintenance of shape of the cell

Cilia and Flagella

  • Hair-like outgrowths of the cell membrane

  •  Work like oars causing movement

Microbodies

  • Membrane-bound minute vesicles

  •  Contain various enzymes