are the basic building blocks of all living things.
Cells
The Cell Theory states that:
•All living organisms are composed of cells. They may be unicellular or multicellular.
•The cell is the basic unit of life.
•Cells arise from pre-existing cells.
Twenty years later, in 1858, a German biologist, ________, theorized that all living cells come from preexisting living cells. His
conclusion arose from observing dividing cells while he was at work.
Rudolph Virchow
In 1839, a German zoologist, concluded that all animals are composed of cells. Jointly, Schleiden and Schwann came out with the theory that all living things are composed of cells.
Theodore Schwann
In 1838,a German botanist, stated that all plants are composed of cells.
Matthias Schleiden
Over the next 200 years after Hooke, another scientist. a Scottish botanist named ________, made a general conclusion in 1831. He discovered the nucleus and theorized that this structure is a fundamental and a constant component of the cell.
Robert Brown
-In 1674, the Dutch inventor, observed red blood cells, sperms and a myriad of single-celled organisms in pond water.
- ________was a contemporary of Robert Hooke.
- He had more success in living cells in action despite his smaller, simpler, handled microscopes.
Antonie Van Leeuwenhoek
- In 1665, an English scientist, examined a thin slice of cork under the microscope.
- He observed that the piece of cork was composed of many tiny compartments which resembled little rooms with surrounding wall.
- Hooke named these compartments cells
Robert Hooke
The discovery of cells was made possible by the development of the ______ in the 17th century.
Microscope
a prominent French chemist who had been studying microbial fermentation and the causes of wine spoilage, accepted the challenge.
- In 1858, Pasteur filtered air through a gun-cotton filter and, upon microscopic examination of the cotton, found it full of microorganisms, suggesting that the exposure of a broth to air was not introducing a “life force” to the broth but rather airborne microorganisms.
- Later, Pasteur made a series of flasks with long, twisted necks (“swan-neck” flasks), in which he boiled broth to sterilize it.
Louis Pasteur
-To settle the debate, the _____ offered a prize for resolution of the problem.
Paris Academy of Sciences
who demonstrated that maggots were the offspring of flies, not products of spontaneous generation.
Francesco Redi
who argued that microbes arose spontaneously in broth from a “life force.”
John Needham
whose experiments with broth aimed to disprove those of Needham.
Lazzaro Spallanzani
- did not agree with Needham’s conclusions, however, and performed hundreds of carefullv executed experiments using heated broth.
- In response to Spallanzani’s findings, Needham argued that life originates from a “life force” that was destroyed during Spallanzani’s extended boiling.
- Any subsequent sealing of the flasks then prevented new life force from entering and causing spontaneous generation
Lazzaro Spallanzani (1729-1799)
- In 1745, published a report experiments,
of his Own
in which he briefly boiled broth
infused with plant or animal matter, hoping to kill all pre-existing microbes. - He then sealed the flasks.
- After a few days, Needham observed that the broth had become cloudy and a single drop contained numerous microscopic creatures.
- He argued that the new microbes must have arisen spontaneously.
- In reality, however, he likely did not boil the broth enough to kill all pre-existing microbes.
John Needham (1713-1781)
experimental setup consisted of an open container, a container sealed with a cork top, and a container covered in mesh that let in air but not flies. Maggots only appeared on the meat in the open container. However, maggots were also found on the gauze of the gauze.
coverea container.
Francesco Redi
- performed an experiment in 1668 that was one of the first to refute the idea that maggots (the larvae of flies) spontaneously generate on meat left out in the open air.
- He predicted that preventing flies from having direct contact with the meat would also prevent the appearance of maggots.
- Redi left meat in each of six containers
- Two were open to the air, two were covered with gauze, and two were tightly sealed
Francesco Redi (1626-1697)
- a seventeenth century Flemish scientist, proposed that mice could arise from rags and wheat kernels left in an open container for 3 weeks.
Jan Baptista van Helmont
- one of the earliest recorded scholars to articulate the theory of spontaneous generation.
- He believes in the notion that life can arise from nonliving matter
-he noted several instances of the appearance of animals from environments previously devoid of such animals, such as the seemingly sudden appearance of fish in a new puddle of water.
- This theory persisted into the seventeenth century, when scientists undertook additional experimentation to support or disprove it.
- By this time, the proponents of the theory cited how frogs simply seem to appear along the muddy banks of the Nile River in Egypt during the annual flooding. Others observed that mice simply appeared among grain stored in barns with thatched roofs. When the roof leaked and the grain molded, mice appeared.
Aristotle (384-322 BC)
