Biology Today — December 2017

Theory of Biogenesis

(a) Redi’s experiment: Francesco Redi (1668) cooked the flesh until no organisms were left alive and placed it in three separate
containers.

Flies entered and laid eggs

that hatched maggots in meat.

Open container

Maggots

Meat

No flies entered and thus no eggs,no

formation of maggots in meat.

Cork-sealed container

No flies entered, no egg and no

formation of maggots in meat.

Maggots

Gauze-covered container

This experiment confirmed that maggots arise from eggs and not from decaying meat.

(b) Spallanzani’s experiment : Spallanzani (1765) disproved the spontaneous generation of microorganisms.

Infusion is boiled for many

hours to kill all microbes

Flask is open

Flask is sealed

Air with microorganisms

entered the flask

No living organisms appeared

(c) Pasteur’s experiment: Louis Pasteur (1822-1895) performed an experiment that discredited the theory of spontaneous
generation.

Air forced out

from open end

Open end

After long time

Dust and microorganisms

trapped in bent neck

Liquid broth

cooled slowly

Liquid broth remains

sterile indefinitely

Liquid broth is

sterilised

by heating

Neck of flask bent

into S-shaped

curve

Non-sterile broth

poured into flask

with long neck

Liquid broth contaminated

with bacteria

Neck was broken off

Open flask allowed air

and any bacteria present

in the air to enter the broth

• This experiment proved that the source of microorganisms for fermentation or putrefaction is air. The organisms or life cannot
  arise spontaneously from nutrient media.

Theory of Panspermia or Cosmozoic or Extraterrestrial

• It was proposed by Richter (1865). It states that life came on earth from some other planet in the form of seed or spore
  called panspermia or cosmozoans hence, it is also called spore theory.