Historical ideas about living things
Ms. Aseel Samaro
Cells: The Building Blocks of Life!
What makes the dog alive ?
To be considered an organism (a living thing), like the dog,
It must be able to do all of these seven processes
 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
What are four living and four nonliving
things that you interact with or see
everyday?
History of living things
 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.
Spontaneous Generation
 The idea that organisms originate directly from non-living
matter.
 "life from nonlife"
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.
Redi’s experiment to disprove the idea of spontaneous generation
Redi’s Expirement
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.
Disproving spontaneous generation
 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.
Microscope
 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.
Some History
 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