Directions: In this module you read about specialized cell types called guard cells. These cells are usually found on the bottom side of the leaf and control the size of stomata (“holes” in the leaf where gas exchange occurs). Think about the following questions in regards to these structures:

1)What is the purpose of having these “holes”? What gases enter/ exit this hole? The guard cells control the size of the stomata by swelling and shrinking.

2) What is the mechanism for the swelling and shrinking that take place here? (Hint: Guard cells are specialized cells that have a plasma membrane barrier and the ability to control the solute level inside/ outside of the cell.)

Directions:  In this module, you are learning about the cell cycle, mitosis and meiosis. While the chapter describes how meiosis normally proceeds, it is important to note that mistakes can happen. Let’s look at the animal life cycle for example. Sometimes mistakes can happen in the way the duplicated chromosomes are separated and this can lead to gametes (sex cells: eggs and sperm) that contain more or less of a particular chromosome. Non-disjunction is the failure of chromosome pairs or sister chromatids to separate properly.

As you can imagine whether this happens during the first division of meiosis or the second, the event changes the total chromosome number for a given gamete. An example of one syndrome related to chromosome number abnormality is Down Syndrome and there are others as well. For this discussion board, address the following components:

1)    Describe the effect of a nondisjunction event in the first division and one in the second in your own words.

2)    Choose a syndrome that  results from nondisjunction.

3)    For the syndrome: Describe the specific anomaly, the affects that are known, any factors that may increase the occurrence of this abnormality, and the percent of the population that demonstrate this chromosome number abnormality