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CELLS. Robert Hooke 1665 coined the word `cell’ for the box-like structures of cork. M J Schleiden a lawyer turned botanist & Theodore Scwann an animal embryologist met at dinner party in 1837 1839 formally espoused cell theory

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Robert Hooke1665

coined the word `cell’ for the box-like structures of cork

  • M J Schleiden

  • a lawyer turned botanist&

  • Theodore Scwann

  • an animal embryologist

  • met at dinner party in 1837

  • 1839 formally espoused cell theory

  • the cells are of universal occurrenceand are

  • the basic units of an organism

  • 1849 Cell division described

  • 1858 Rudolph Virchow forcefully states the paradigm of cell theory

  • ``All cells come from previous cells’’

  • Omnis cellula e cellula

    • Thus: 

    • all individuals derived from a single celled organism are related &

  • all cells in a multi-celled organism are descended from one fertilized egg.

Basics of the cell theory
Basics of the Cell Theory

  • all known living things(systems) arecomposed of cells

  • cells arise only from other cells     (not spontaneously - experiments of Redi and Pasteur)

    • allenergy flow (metabolism & biochemistry) of life occurs within cells

    • cells containDNAas genetic info - (for subsequent generations)

Some important facts about cells:

        - their diversity : many sizes, shapes, and types

(165+ in humans)

        - their similarity: have same basic structural plan

                  - surrounded by cell membrane

                  - contain nuclei     (bacteria = genophore)

                  - similar sub-cell parts (ORGANELLES)

                  - all contain same macromolecules

Why are cells so small
Why are cells so small?

a.Efficiency:  smaller cells have larger surface area

b. Specialization: Having numerous small cells permits specialization

How large cells can be?

  • As an object increases in size its volume increases as the cube of its linear dimensions while surface area increases as the square

  • Surface area = L X B Square of two linear dimensions

  • Volume = L X B X H Cube of three linear dimensions

  • As these cubes illustrate the surface area to volume ratio of a small object is larger than that of a large object of similar shape

  • This ratio limits how large cells can be

Getting around this problem

Divide to become multicelled - Embryo

long and thin or skinny and flat

many protists, nerve cells, muscle cells

Smaller particles react faster than larger particles
Smaller Particles React Faster Than Larger Particles

  • Granular sugar dissolves easier than sugar cubes

  • Everything that the cell needs or has to get rid

    of has to go through the cell membrane, the amount of which relates to the surface area

  • Surface must allow sufficient exchange to support the contents of the cell

  • stops growing when its surface area is insufficient to meet the demands of the cell's volume

Cells have evolved two basic architectural plans
Cells Have Evolved Two Basic Architectural Plans

Cells without a nucleus Cells with a nucleus

“karyon” = kernel or nut; “pro” = before ; “eu” = good or true; • Eukaryotes - “cells with a true nucleus”

• Prokaryotes - “cells with no defined nucleus”


  • Cells whose nucleus

    is not enclosed in a membrane

  • Lack other organelles too

  • First to evolve, The oldest accepted prokaryote fossils date to 3.5 billion years

  • Contain

    a circular chromosome

    Plasmids with satellite DNA


    food storage granules


  • Cells whose nucleus is enclosed in a membrane

  • Evolved later. Eukaryotic fossils date to between 750 million years and possibly as old as 1.2-1.5 billion years.

Organelles microscope studies

  • Mitochondria and chloroplasts are energy-transducing organelles

  • Both seem to share many properties with bacteria:

    • contain 70S ribosomes (whereas rest of eukaryote cells contain 80S ribosomes)

    • divide by binary fission

    • contain circular DNA without nucleus, etc.

Endosymbiont theory symbiosis living together
Endosymbiont Theory microscope studies Symbiosis = "living together“

  • Chloroplasts and Mitochondriaderived from ancient colonization of large bacteria (became the eukaryotic cell) by smaller bacteria

  • Host cells acquired respiration from the precursor of the mitochondrion, and oxygenic photosynthesis from the precursor of the chloroplast

  • Also acquired much of their genetic information

  • Eventually, organelles lost ability to exist as separate organisms, cannot have independent existence from cell

E microscope studies







Some protists

Why double membrane of chloroplast? microscope studies


Outer membrane of organelle originally belonged to the host cell.

Why double membrane? microscope studies

Images with electron microscope microscope studies


Cutaway view of mitochondrion microscope studies

Inner membrane more active

Centrifugation microscope studies

  • A centrifuge is a device for separating particles from a solution according to their size, shape, density, viscosity of the medium and rotor speed

  • In biology, the particles are usually cells, sub cellular organelles, viruses, large molecules such as proteins and nucleic acids

  • Instrumental in working out the functions of organelles

Centrifuge microscope studies