The Cell Theory

DO NOW (silently, 5 min) Create this chart on pg. 17 and write if you either agree or disagree with it. Be prepared to defend why you agreed or disagreed. BEFORE STATEMENT AFTER All bacteria that are alive today have come from pre-existing bacteria. The smallest unit of life is a carbon atom because all living things are carbon-based life forms. Plants and animals are made of cells but fungi and bacteria are not. All cells are microscopic (you need a microscope to view them). To be considered a cell the only two things it needs are a cell membrane and cytoplasm.

By the end of class, I will be able to… SWBAT: Identify the three components of cell theory SWBAT: Describe how Reddi’s experiment disproved spontaneous generation. SWBAT: Describe how continuous investigations and/or new scientific information influenced the development of cell theory.

By the end of the unit… How does the structure of cells affect the function of the organisms it makes up?

The Cell Theory

Engage: How Small is a Cell? http://learn.genetics.utah.edu/content/begin/cells/scale/

I. What is a cell? A cell is a structure containing cytoplasm enclosed by a cell membrane.

II. What did people believe before cells were discovered? A. Theory of Spontaneous generation = that living things can come from non-living things Ex – maggots from meat; or mice from hay;

How we discovered cells. In 1665 Robert Hook looked under a microscope and this is what he saw This is a picture of what a piece of dead plant looks like under a microscope. What observations can we make? What would you call these?

How we discovered cells. In 1838 Matthias Scheliden looked under a microscope and this is what he saw This is a picture of living plant tissue. What observations can we make? What inference can we make about plants? Are they made of cells?

How we discovered cells. The next year, Theodore Schwann looked under a microscope and this is what he saw This is a picture of living animal tissue. What observations can we make? What inference can we make about animal tissue? Are they made of cells?

III. What is cell theory? A. Cell theory is used to explain what cells are. 3 parts: 1. All cells come from pre-existing cells 2. Cells are the basic unit of life 3. All organisms are made of cells. B. Cell theory was used to disprove spontaneous generation

CELL RECAP!! Write which part of cell theory you think goes with each of the next three slides at the bottom of your notes!

All organisms are made of cells.

All existing cells are produced by other living cells.

The cell is the most basic unit of life. Characteristics of Life Made of cells Need Materials and Energy Respond to surroundings Grow and develop Universal genetic code Reproduce Maintain an Internal Balance Evolve

Independent Practice- Pg. I am going to model #1 for you. A student conducted an experiment in which she placed a piece of meat in three jars. One jar had a sealed lid, a second had a screen, and the third had no top at all. After 20 days of being left out in the same conditions she came back to observe the results. She noticed that the jar without a lid had maggots growing in it while the other two did not. What part of cell theory does this experiment best support? How do you know?

Exemplar Response: The part of cell theory that this best supports is that all cells come from pre-existing cells. This is because the jars with lids did not produce maggots which means the maggots must have come from cells found outside the jars.

Independent Practice Let’s do #2 together. A scientist observes 5,000 different specimens under a microscope. His notes indicate that he described seeing “walled compartments” in all 5,000 of his specimens when viewed under a microscope. What part of cell theory does this best support? How do you know?

Exemplar Response: The part of cell theory this best supports is that all living things are made of cells. This is because thousands of different specimens all contained the same cell-like structure.

Independent Practice 3. A student was looking at a live cell under a microscope and noticed that it was gradually separating into two new cells. His teacher told him that he was observing a process known as mitosis. What part of cell theory does mitosis best support? How do you know? You have 10 minutes to complete your work!

Closing. Let’s Discuss our answers Modify your anticipation guide answers Take our exit ticket! BEFORE STATEMENT AFTER All bacteria that are alive today have come from pre-existing bacteria. The smallest unit of life is a carbon atom because all living things are carbon-based life forms. Plants and animals are made of cells but fungi and bacteria are not. All cells are microscopic (you need a microscope to view them). To be considered a cell the only two things it needs are a cell membrane and cytoplasm.

Question 1 Which of the following statements is true? “All organisms are made up of multiple cells.” “Some cells are microscopic but others can be seen with the naked eye.” “The nucleus is the most basic unit of life.” “All existing cells are produced by other living cells unless it is a bacteria.”

Question 2 Short Answer: What are 2 things all cells have in common?

Question 3 Spontaneous generation was true The theory of spontaneous generation included the idea that simple organisms like worms and flies were created from abiotic (non-living) things like mud. In the 1600’s Francesco Redi performed an experiment. Maggots developed from the eggs laid by flies in the first flask. No maggots were developed in the remaining two flasks. The results of this experiment provided evidence that: Spontaneous generation was true Living things come from non-living things Flies need meat to survive Living things come only from other living things

Question 4 The graphic to the right shows the stages of cellular meiosis which allows two parent cells to combine and form four daughter cells. Which statement best explains this process? All cells come from pre-existing cells Cells appear as walled “rooms” All living things are composed of cells Identification of the microbial agents causing disease

Question 5 The cell theory was first proposed in 1838. Evidence obtained through additional scientific investigations resulted in the current cell theory. Which statement describes a component of the original cell theory that was removed because of new scientific knowledge? All living things are made of cells All cells come from other preexisting cells Cells form through spontaneous generation Cells are the basic structural and functional units of life.

Exit Slip Scoring 1/5= 20% 2/5= 40% 3/5= 60% 4/5= 80% Mastery! 5/5= 100% Biology Beast!