The purpose of this section is for students to explore what the scientists, who helped develop the cell theory, experienced during their cell investigations.
Power of the Microscope
Students will take turns in observing unlabeled prepared slides of both living and non-living things. Students make observations in microscope sketches, circling living or non-living.
1A. oral smear
2A. onion mitosis
2B. fish mitosis
2C. worm mitosis
3A. hand sanitizer
3B. paper cutout of letter A
Students are paired up and if necessary groups of 3 are made. Slides will be numbered with each number indicating what is being observed - 1.animal/plant cells2.dividing cells 3. non-living material I set up the room by having 10 stations each station containing the three type of slides mentioned above.
Probing eliciting questions:
The purpose of these questions is to elicit student responses and most critically, expand on what was learned during the engage part of lesson 1) All new cells come from preexisting cells 2) All organisms are made of one or more cells.
Questions that I ask student during the activity are:
1) Are the specimens on the slide living or non-living? How do you know?
2) What makes something non-living?
3) Is there anything in common between slides that you classify as living? What is it?
4) Why are there so many objects on the slides labeled with a number 2? What do you think these slides show?
5) Do you notice any similarities between the numbered slides?
6) Which slides contain non-living material? How do you know?
7) Based on this investigation, what are living things made of?
8) What can you conclude when comparing non-living material to living material?
9) What did you observe today that tells you not all cells are exactly alike? Do they have anything in common?
10) Where do cells come from? What group of slides show this process?
Timeline Description: Before 330+ years ago, there was no knowledge of cells. Cells were too small to be seen. But with the invention of the microscope, an entirely new world was discovered, where very large objects like humans are in fact made up of billions of tiny individual pieces called cells.
|1665||Cell first observed |
Robert Hooke, an English scientist, discovered a honeycomb-like structure in a cork slice using a primitive compound microscope. He only saw cell walls as this was dead tissue. He coined the term "cell" for these individual compartments he saw.
|1670||First living cells seen |
Anton van Leeuwenhoek, a Dutch biologist, looks at pond water with a microscope he made lenses for.
|1683||Miniature animals |
Anton van Leeuwenhoek made several more discoveries on a microscopic level, eventually publishing a letter to the Royal Society in which he included detailed drawings of what he saw. Among these was the first protozoa and bacteria discovered.
|1833||The center of the cell seen |
Robert Brown, an English botanist, discovered the nucleus in plant cells.
|1838||Basic building blocks |
Matthias Jakob Schleiden, a German botanist, proposes that all plant tissues are composed of cells, and that cells are the basic building blocks of all plants. This statement was the first generalized statement about cells.
|1839||Cell theory |
Theodor Schwann, a German botanist reached the conclusion that not only plants, but animal tissue as well is composed of cells. This ended debates that plants and animals were fundamentally different in structure. He also pulled together and organized previous statement on cells into one theory, which states: 1 - Cells are organisms and all organisms consist of one or more cells 2 - The cell is the basic unit of structure for all organisms
|1840||Where does life come from |
Albrecht von Roelliker discoveres that sperm and eggs are also cells.
|1845||Basic unit of life |
Carl Heinrich Braun reworks the cell theory, calling cells the basic unit of life.
|1855||3rd part to the cell theory added |
Rudolf Virchow, a German physiologist/physician/pathologist added the 3rd part to the cell theory. The original is Greek, and states Omnis cellula e cellula. This translates as all cells develop only from existing cells. Virchow was also the first to propose that diseased cells come from healthy cells.