BIOGENESIS vs. ABIOGENESIS

Biology Evolves Into A Science

BIOGENESIS vs. ABIOGENESIS

• From Ancient times up to the 19th century,

living organisms were believed to arise

from nonliving matter.

• This belief is known as abiogenesis or

spontaneous generation.

BIOGENESIS vs. ABIOGENESIS

• The belief in abiogenesis was based on

observations:

– Snakes and frogs arising from the mud of river

banks.

– Mice and rats appearing in garbage.

– Worms appearing in stored grains and other foods.

BIOGENESIS vs. ABIOGENESIS

• In middle 1600’s, Italian physician Francesco

Redi was first to challenge abiogenesis.

• Many believed maggots were a type of worm

that ‘arose’ from rotting meat.

• Redi made careful and detailed observations of

rotting meat and believed the maggots were

actually the larvae of flies that laid eggs on the

meat.

BIOGENESIS vs. ABIOGENESIS

• Redi’s Hypothesis: maggots arose from fly

eggs. If flies were deprived of chance to lay

eggs on raw meat, no larvae would arise.

• Exp 1: Raw meat placed in open jars (control)

and in sealed jars.

• Results: maggots found on exposed meat only.

• Conclusion: Maggots arose from flies.

BIOGENESIS vs. ABIOGENESIS

BIOGENESIS vs. ABIOGENESIS

• Some argued that fresh air was required for

spontaneous generation and the sealed jars

prevented this.

• Revised Hypothesis: meat isolated from flies

but not fresh air would not product maggots.

• Exp 2: Raw meat placed in open jars (control)

and in jars covered with gauze.

BIOGENESIS vs. ABIOGENESIS

• Results: Maggots found on meat of open jars.

No maggots found on meat in gauze covered

jars but flies did lay eggs on the gauze which

eventually hatched into maggots.

• Redi’s Conclusion: life arises from life

(Biogenesis).

BIOGENESIS vs. ABIOGENESIS

BIOGENESIS vs. ABIOGENESIS

• In 1745, English scientist John Needham

boiled different types of meat broth then sealed

them

• Several days later, he observed

microorganisms which he believed arose from

the broth (abiogenesis).

BIOGENESIS vs. ABIOGENESIS

• In 1860, French chemist/microbiologist Louis Pasteur signaled the final demise of abiogenesis.

• Hypothesis: Nedhams broth had been exposed to microorganisms from the air. If broth had no contact with these microorganisms, it would remain sterile.

• Experiment: Broth boiled in flask with a bent neck.

BIOGENESIS vs. ABIOGENESIS

• Results: air-born microorganisms were

trapped in neck of flask - broth remained

sterile for months.

• Conclusion: Life arises only from life

(biogenesis).

BIOGENESIS vs. ABIOGENESIS

MODERN CELL THEORY

MODERN CELL THEORY

1. All organisms are composed of one or more

cells and the products of these cells. All the

life process of metabolism and heredity take

place in the cell.

• Some organisms consists of a single cell.

• In multi-celled organisms, there may be

intercellular material produced by cells.

MODERN CELL THEORY

2. Cells are the smallest unit (division) of life - the

basic unit of organization of all living organisms.

• Cells can be divided into smaller parts but these

components are not considered living.

• Unit of Function: cells carry out ALL life

functions.

• Unit of Growth: all organisms begin as single

cell - # cells determines size.

• Unit of Heredity: all cells are identical to

preexisting cells.

MODERN CELL THEORY

3. All cells arise from living cells by the

process of cell division.

• Single cells reproduce by dividing into two

cells.

• Cell division in multi-celled organisms =

GROWTH.

MODERN CELL THEORY

4. All cells carry out their own life activities -

the life activities of multi-celled organisms

is the combined effect of the life activities

of all its individual cells.

• Nutrition

• Transport

• Respiration

MODERN CELL THEORY

4. All cells carry out their own life activities

• Synthesis & Assimilation

• Growth

• Excretion

• Regulation

• Reproduction

• Metabolism