2. Rest of month assessments (including first big lab)
3. Chapter 1.1
Lesson Objectives: You should be able to...
1. Describe and explain the evolution of a multicellular organism.
2. Compare and contrast the cell structures of eukaryotes and prokaryotes.
3. Explain the purpose of the plasma membrane and describe its structure.
1.1: The evolution of multicellular organisms allowed cell specialization and cell replacement.
1.2: Eukaryotes have a much more complex cell structure than prokaryotes.
1.3: The structure of biological membranes makes them fluid and dynamic.
Links: Cell Theory Ultrastructure Membrane Structure & Transport
Textbook Readings: Chapter 1, section 1.1-1.4
Mission 1: Yeah, yeah...this is a Biology Class. We finish the calendar year with a unit on cells. This is a short TedEd video talking about microscopes, cells and accidental science. What three components make up the foundation of cell theory? How did we get from the rudimentary two-lens scope of the 1500s to now? Do you think science occurs in a vacuum? Why do you think that some scientists couldn't get along? What does this tell you about the nature of scientific discovery?
Essential Idea: 1.1: The evolution of multicellular organisms allowed cell specialization and cell replacement.
Living organisms are composed of cells
· Single-celled organisms carry out all functions of life in that cell.
· Surface area to volume (SA-V) ratio is important in the limitation of cell size.
· Multicellular organisms have properties that emerge from the interaction of their cellular components.
· Specialized tissues can develop by cell differentiation into multicellular organisms.
· Differentiation involves the expression of some genes and not others in a cell’s genome.
· The capacity of stem cells to divide and differentiate along different pathways is necessary in embryonic development and also makes stem cells suitable for therapeutic uses.
We will work through the video to make sure you have an answer or statement for the EI and the Understandings.
From the IB Guides:
Many reactions occur within the cell. Substances need to be taken into the cell to fuel these reactions and the waste products of the reactions need to be removed. When the cell increases in size, so does its chemical activity. This means that more substances need to be taken in and more need to be removed.
The surface area of the cell is vital for this. Surface area affects the rate at which particles can enter and exit the cell (the amount of substances that it takes up from the environment and excretes into the environment), whereas the volume affects the rate at which materials are made or used within the cell, hence the chemical activity per unit of time.
As the volume of the cell increases so does the surface area however not to the same extent. When the cell gets bigger its surface area to volume ratio gets smaller.
Homework: Review the material in Missions 1, 2 & 3. You need practice with SA/V, so here it is: Lesson #3 in the workbook, and this rightchea. Just complete parts I, II & III.
Since one of the skills you have to develop is determining the approximate size of a cell, you need to make sure you know how to do the following:
(1) Formula for magnification: size of image/size of specimen. There is no unit.
(2) Determining total magnification: The ocular lens (the eyepiece) has a magnification of 10X. There are at least 3 objective lenses on the 'scope (X4, X10, X40). Multiply the ocular magnification by the objective magnification and you will get your total magnification.
(3) Determining the field of view: Place a metric ruler (using millimeters) and measure the diameter of the round area above the light. Count how many cells (approximate) cross the diameter. Then divide the diameter of the field of view by the number of cells that cross it.
diameter of field of view
# of cells that cross the diameter
(3) Determining magnification from a sketch: Use the mm side of a metric ruler to draw cells to scale. Divide the drawing size by the actual size of the specimen (as determined from #2).
drawing size (mm)
Below is a short tutorial.