The Cell TheoryThe cell theory is a contribution of several different scientists over a long period of time, and applies to all living things. As any other theory, it takes time to gather sufficient evidence to support the scientist's claims, obtained from observations, investigations, experimentation, readings, discussions, and research, thus it generally takes time for any THEORY to be widely accepted.
REMEMBER: Scientific theories are well-tested explanations,while scientific laws are well-tested descriptions of natural phenomena, one cannot become the other, like oranges will never become bananas!
German zoologist
Students will:
Benchmark Clarifications Students will:
REMEMBER: Scientific theories are well-tested explanations,while scientific laws are well-tested descriptions of natural phenomena, one cannot become the other, like oranges will never become bananas!
- All organisms are made up of cells. (To disprove this part of the theory, scientists would have to find organisms made of something else other than cells)
- The cell is the basic unit of structure and function of all living things. (Organisms can be unicellular_one cell, or multicellular _many cells, but the cell is the smallest thing that is alive. To disprove this part of the theory, scientists would have to find that something smaller that a cell shares the characteristics of life)
- All cells come from pre-existing cells. (Some organisms reproduce sexually, and others asexually. All cells reproduce by cell division: mitosis, meiosis, of binary fission. In order for scientists to disprove this part of the theory, they would have to find a cell that comes to exist spontaneously.) Note: Viruses are NOT considered livingbecause they are unable to reproduce on their own, but need a living cell as a host to make more viruses.
- Dutch lens grinders, father and son
- produced first compound microscope (2 lenses)
- English scientist
- looked at a thin slice of cork (oak cork) through a compound microscope
- observed tiny, hollow, room like structures
- called these structures 'cells' because they reminded him of the rooms that monks lived in
- only saw the outer walls (cell walls) because cork cells are not alive
- looked at blood, rainwater, scrapings from teeth through a simple microscope (1 lens)
- observed living cells; called some 'animalcules' now called bacteria
- German botanist
- viewed plant parts under a microscope
- discovered that plant parts are made of cells
German zoologist
- viewed animal parts under a microscope
- discovered that animal parts are made of cells
- he showed that mature tissues of animals were traceable to embryonic cells, which provides evidence that all cells come from other cells.
- German physician
- stated that all living cells come only from other living cells
Students will:
- describe and/or explain the cell theory.
- describe how continuous investigations and new scientific information influenced the development of the cell theory.
- identify ways in which a scientific claim is evaluated (e.g., through scientific argumentation, critical and logical thinking, and consideration of alternative explanations).
- identify the criteria that differentiate science from nonscience and pseudoscience.
- explain the development of a theory.
- recognize the differences between theories and laws.
Benchmark Clarifications Students will:
- understand that the quality of a microscope and its ability to magnify depend on its resolving power;
- recognize that compound microscopes use visible light that is passed through the object and then a series of lenses to magnify the object;
- calculate the total magnifying power of a typical light microscope when given the magnification of the objectives;
- recognize that electron microscopes use electrons rather than light to pass over or through an object in a vacuum;
- associate the electron microscope with having greater resolution because it uses a beam of electrons that have a much shorter wavelength than that of light;
- understand that because electron microscopes require specimens to be in a vacuum, only dead cells or organisms can be viewed; and
- identify different types of electron microscopes such as the transmission electron microscope (TEM), scanning electron microscope (SEM), and scanning tunneling microscope (STM).
- require students to recall names of scientists involved in the development of the microscope;
- assess the definitions of prokaryotic, eukaryotic, unicellular, and/or multicellular organisms, but items may refer to those terms.