NEW UNIT!!!! REPRODUCTION

this week we started a new unit: reproduction!!!! We started the new unit with a few questions.....

1. How do organisms reproduce??

I said: Organisms reproduce by when a male and female have sexual contact. A sperm needs to fertilize the ova or egg to reproduce. Males identify if the

organism is male or female. Females only have X chromosomes males xan have X or Y. If a X matches up with an X then the organism is a female if an X matches up with a Y then the organism is a male.

2. How do cells reproduce?

I said cells reproduce by splitting in half, this process is called mitosis. Mitosis is a process of cell division which results in the production of two daughter cells from a single parent cell. The daughter cells are identical to one another and to the original parent cell.

Mitosis has a process or steps:

The steps to mitosis:

Interphase: Cells may appear inactive during this stage, but they are quite the opposite. This is the longest period of the complete cell cycle during which DNA replicates, the centrioles divide, and proteins are actively produced. For a complete description of the events during Interpha

se, read about the Cell Cycle.

Prophase: During this first mitotic stage, the nucleolus fades and chromatin (replicated DNA and associated proteins) condenses into chromosomes. Each replicated chromosome comprises two chromatids, both with the same genetic information. Microtubules of the cytoskeleton, responsible for cell shape, motility and attachment to other cells during interphase, disassemble. And the building blocks of these microtubules are used to grow the mitotic spindle from the region of the centrosomes.

Prometaphase: In this stage the nuclear envelope breaks

down so there is no longer a recognizable nucleus. Some mitotic spindle fibers elongate from the centrosomes and attach to kinetochores, protein bundles at the centromere region on the chromosomes where sister chromatids are joined. Other spindle fibers elongate but instead of attaching to chromosomes, overlap each other at the cell center.

Metaphase: Tension applied by the spindle fibers aligns all chromosomes in one plane at the center of the cell.

Anaphase: Spindle fibers shorten, the kinetochores separate

, and the chromatids (daughter chromosomes) are pulled apart and begin moving to the cell poles.

Telophase: The daughter chromosomes arrive at the poles and the spindle fibers that have pulled them apart disappear.

Cytokinesis: The spindle fibers not attached to

chromosomes begin breaking down until only that portion of overlap is left. It is in this region that a contractile ring cleaves the cell into two daughter cells. Microtubules then reorganize into a new cytoskeleton for the return to interphase.

January 7th, 2010

i think the second day of our new unit we started to look at a slice of an onion root under a microscope.

We saw a few interesting things under the microscope. A few cells had two nuclei in 1 cell, some would have a bunch of little dots in 1 cell, others would have just 1 nuclei in a cell.