SC.912.L.14.1 Describe the scientific theory of cells (cell theory) and relate the history of its discovery to the process of science.
Students will:
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.
Scientific Theories
A scientific theory is a well- supported explanation of a natural phenomenon. Evidence is required to support the claim, and it is obtained from careful and systematic observations and experimentations. Theories are subject to revision if new scientific evidence is obtained that disproves previous ideas.
The Cell Theory
The cell theory is the 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! |
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1. All organisms are made up of cells.
Evidence:
Evidence:
- If you observe organisms under the microscope, they consistently appear to be made up of cells.
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- Matthias Schleiden (1838), German botanist viewed plant parts under a microscope. He discovered that plant parts are made of cells
- Theodor Schwann (1839), German zoologist viewed animal parts under a microscope. He discovered that animal parts are made of cells.
- To disprove this part of the theory, scientists would have to find organisms made of something else other than cells.
2. The cell is the basic unit of structure and function of all living things.
Evidence:
Evidence:
- 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 all the characteristics of life.
3. All cells come from pre-existing cells.
Evidence:
Evidence:
In the seventeenth century, Francesco Redi performed experiments using raw meat placed in jars.
- Half of the jars were covered, and half were left open.
- Redi noticed that the meat in the sealed jars did not have maggots, but the meat in the open jars did have maggots.
- Redi concluded that only flies could make more flies.
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 living because they are unable to reproduce on their own, but need a living cell as a host to make more viruses.
Sample Questions
Here are some sample questions of how the 3 parts of the cell theory could be tested.
Sample Question1: (Focuses on the first part of the cell theory)
According to cell theory, which of the following best describes the role of cells in living organisms?
A. Cells join together to form multicellular organisms.
B. Cells are the basic operating units of living organisms.
C. Cells make up the soft portions of tissues in living organisms.
D. Cells are responsible for coordinating activities in multicellular organisms.
Sample Question 2: (Focuses on the second part of the cell theory)
When scientists set out to test a hypothesis, it is often most practical to try to prove the hypothesis false rather than to prove it is true in all cases. Scientists place great confidence in cell theory, yet it has not been tested in every living thing on the planet.
What piece of evidence would cause scientists to decide that cell theory would need to be revised?
A. An organism was found with tissues made of something other than cells. B. A cell was found that could continue to divide and reproduce indefinitely.
C. An animal cell was found that could harness solar energy as plant cells do.
D. Cells were found that used something other than DNA as hereditary material.
Sample Question 3: (Focuses on the third part of the cell theory)
According to modern cell theory, how do new cells develop?
A. Cells come from preexisting cells through cell division.
B. The original cell dies and leaves a new one in its place.
C. Cells form by free-cell formation, similar to how crystals are formed.
D. A membrane forms around DNA that is released from a parent cell, and the DNA contains the information needed to produce organelles.
Sample Question1: (Focuses on the first part of the cell theory)
According to cell theory, which of the following best describes the role of cells in living organisms?
A. Cells join together to form multicellular organisms.
B. Cells are the basic operating units of living organisms.
C. Cells make up the soft portions of tissues in living organisms.
D. Cells are responsible for coordinating activities in multicellular organisms.
Sample Question 2: (Focuses on the second part of the cell theory)
When scientists set out to test a hypothesis, it is often most practical to try to prove the hypothesis false rather than to prove it is true in all cases. Scientists place great confidence in cell theory, yet it has not been tested in every living thing on the planet.
What piece of evidence would cause scientists to decide that cell theory would need to be revised?
A. An organism was found with tissues made of something other than cells. B. A cell was found that could continue to divide and reproduce indefinitely.
C. An animal cell was found that could harness solar energy as plant cells do.
D. Cells were found that used something other than DNA as hereditary material.
Sample Question 3: (Focuses on the third part of the cell theory)
According to modern cell theory, how do new cells develop?
A. Cells come from preexisting cells through cell division.
B. The original cell dies and leaves a new one in its place.
C. Cells form by free-cell formation, similar to how crystals are formed.
D. A membrane forms around DNA that is released from a parent cell, and the DNA contains the information needed to produce organelles.
Practice Questions: here and here
Cell Theory Timeline
Hans and Zacharias Janssen
German zoologist
- 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
MICROSCOPES
SC.912.L.14.4 Compare and contrast structure and function of various types of microscopes.
Benchmark Clarifications Students will:
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