Ms. Aseel Samaro

Historical ideas about living things

Cells: The Building Blocks of Life!

What makes the dog alive ?

Movement : This allows a response to changes

Respiration: the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction

Sensitivity : Detecting changes around it

Growth : The ability to replace damaged or lost cells

Reproduction: The ability to produce new organisms.

Excretion : getting rid of waste

Nutrition : taking food

To be considered an organism (a living thing), like the dog,

It must be able to do all of these seven processes

What are four living and four nonliving things that you interact with or see

everyday?

From the time of Aristotle (384–322 BCE) to the 1600s most people believed in the idea of spontaneous generation

they thought that many organisms (living things) came from inanimate objects (non-living things).

For example, observing mice coming out from a stack of corn, they would draw the conclusion that the corn had produced the mice.

History of living things

Spontaneous Generation

The idea that organisms originate directly from non-living matter.

"life from nonlife"

Redi’s experiment to disprove the idea of spontaneous generation

Redi’s Expirement The sealed jar had no maggots.

The opened jar had maggots on the meat.

The mesh covered jar had maggots on the mesh because the flies could smell the rotting meat and laid their eggs there.

Fly Maggot

Redi’s Expirement

People used to think maggots came from meat, not from flies.

Redi proved that maggots came from eggs laid by flies, not from the meat itself.

Redi’s Expirement

In 1864, the scientist Louis Pasteur added the same amount of boiled broth to specially designed bottles.

He sealed some bottles and removed the tops from the rest, then left them for a long time.

He observed no life in any of the bottles that had been sealed, but the open bottles were teeming with life.

Disproving spontaneous generation

With the invention of the microscope in 1590 scientists observed that living things were complex structures, which could not have possibly been formed from inanimate objects.

From studying samples of cork bark, Robert Hooke discovered that organisms were made from simple building blocks.

We call these individual building blocks cells. They are too small to be seen with the unaided eye.

Microscope

In 1665, an Englishman called Robert Hooke first discovered the cell

He looked down at some cork with one of the world's first compound light microscope, which he built himself

He saw many small units, which looked like the small rooms, called cells.

This view into unknown ‘micro’ world was a great jump forward in understanding how life works

Some History

In 1839, two German biologists, Matthias Jakob Schleiden and Theodor Shwann, declared that all living things where made of cells.

Cells are considered ‘the building blocks of life’

Scientists thought that cells must hold the secret to understanding life

Some History

A huge breakthrough in biology occurred in 1859 with a book by Charles Darwin: ‘On the Origin of species’.

He described, with large amounts of scientific evidence, how life changed over time on earth

Darwin’s ideas are now widely accepted in the scientific community, but at the time he was laughed at by many scientists and general public

Some History