Cell Introduction YouTube Lecture Handouts

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Cell Introduction YouTube Lecture Handouts

Cell: An Introduction

Structure of Cell For Cell Introduction of Image -1

Structure of Cell for Cell Introduction of Image -1

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  • Lamarck: no body can have life, if no cells

  • Cytology: Study of form, structure & composition of cell

  • Cell Biology: Deals with structure, chemistry & functioning of cell

  • Unicellular: Amoeba, bacteria, yeast, acetabularia – independent existence & perform all essential functions

  • Multicellular: made of many cells (new born infant - cells to 100 trillion in 60 kg man)

  • Large organism – not have large-sized cells but more cells


  • Structural unit

  • Functional Unit

  • Building blocks

  • Smallest unit capable of independent existence

  • Totipotent: Single cell can form whole organism

  • Cell Tissue Organ Organ System (division of labour)

  • Pasteur – life originates from life

  • Haeckel – nucleus stores and transmits hereditary


  • 1st by Zacharias Janssen – 1590

  • Modified by Galileo

  • Then by Robert Hooke – new microscope – study of cork cells

  • Hooke – book – Micrographia- honey comb structure called it cellula

  • Malphighi – called it saccules & utricles

  • Leeuwenhoek – 1st to observe, describe & sketch free living cell

  • Robert Brown – disc. nucleus in cell

  • Dujardin – living semifluid substance as sarcode

  • Purkinje & von Mohl – called sarcode as protoplasm

  • Schwann – disc. cell membrane

  • Nageli & Cramer – named it as cell membrane

Cell Theory

  • By Schleiden & Schwann

  • Schwann – animal cells don’t have cell wall

  • Organism made of cells

  • Cells are units of structure and function of living organisms

  • New cells from pre-existing cells

  • Each cell has protoplasm

  • All cells are alike in chemistry & physiology

  • Activity of organism are sum total of activities of cell

Modern Cell Theory or Cell Doctrine

  • All living beings have cells

  • Cells are units of structure & function

  • Cell can survive independently, organelle cannot

  • Cells have fundamental similarity

  • Life exists in cells

  • Cells can be modified (elongated in muscle & nerve cell)

  • Cell grows & multiplies

  • Life passes to next generation as cell

  • New cells from pre-existing cells

  • All cells have common ancestry

  • Cells are totipotent

  • No organism can have activity that is absent in its cell

Objections to Modern Cell Theory

  • Virus are a cellular

  • Some organisms – body is not differentiated in cells (e.g. rhizopus)

  • Protozoa have uninucleate differentiated body

  • Bacteria & cyanobacteria don’t have nucleus

  • RBCs & sieve tube cells are without nucleus

  • In skin & cork – protoplasm is replaced by nonliving material

Surface Volume Ratio

  • Small cells – higher surface volume ratio

Surface Volume Ratio of Image - 1 For Cell Introduction

Surface Volume Ratio of Image - 1 for Cell Introduction

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Surface Volume Ratio of Image - 2 For Cell Introduction

Surface Volume Ratio of Image - 2 for Cell Introduction

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Surface Volume Ratio of Image - 3 For Cell Introduction

Surface Volume Ratio of Image - 3 for Cell Introduction

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Types of Cells

  • Undifferentiated / Stem Cells: Unspecialized and have power of division – stem apical meristem

  • Differentiated / Post-mitotic Cells: Specialized for better organization and avoid duplication

  • Dedifferentiated Cells: Differentiated cell which revert to undifferentiated state and loose specialization - cork cambium of plant, healing of wound, regeneration in animals and vegetative propagation in plants

Compartmentalization of Cellular Life

  • Separation from extracellular medium

  • Selective permeability

  • Accumulation

  • Interconnections

  • Recognition

  • Communication & exchange

  • Intracellular compartmentalization

Cell Sizes

  • Smallest cell – Mycoplasma

  • RBC is 7 in diameter

  • Lymphocytes are 6

  • Kidney, liver and intestine are 20-30

  • Longest human cell – nerve cell of 90 cm

  • Egg cells are large sized cells – store food for embryo

  • Avian eggs are largest

Cell Shapes

  • Surface cells – flat

  • Cortex – polygonal

  • RBC – biconcave

  • Nerve cells – long

  • Sperms – tail for mobility

Prokaryotic & eukaryotic cells (to be discussed in next lesson)