Life Science
 






Updated 2/4/2011

I UPDATED THE INFO BELOW. THE LAYOUT IS NOT EXACTLY AS I WOULD LIKE IT, BUT AT THE LEAST THE INFO IS THERE... STILL HATING TECHNOLOGY... : )

Welcome to Team Grizzly's Science Website!
Glad you could stop by!


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Quote:
"POOR IS THE NATION WHICH HAS NO HEROES.
SHAMEFUL IS THE NATION WHO HAS THEM AND FORGETS."



Please remember the men and women, and their families, who have sacrificed for the freedoms we so often take for granted.
If you see a veteran, please thank them for their service. It is the LEAST we can do.

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If a cell maintains homeostasis long enough, it will survive and reproduce.
This brings us to the Cell Cycle which consists of 5 stages:
1. Interphase
2. Prophase
3. Metaphase
4. Anaphase
5. Telophase

Mitosis consists of Prophase through Telophase and is the process by which "body cells" reproduce making two cells identical to the original.

"MY-TOE-SIS, MY-TWO-SIS" makes cells found in your toes-- bone, muscle, skin-- but not blood.

"So what goes on during each of these phases?" you ask.

CELL CYCLE

Interphase- Cell not dividing (growing)
Nuclear membrane visible
Long chromosomes difficult to see
Before cells begin to divide, chromosomes shorten

Mitosis


Prophase- Nuclear membrane disappears
Chromosomes double (2 identical strands)
Chromosomes held together at centromere

Metaphase- Chromosomes line up along the middle of cell
Spindle fibers form across the cell
Spindle fibers form from the poles and attach to centromere

Anaphase- Centromeres split and 2 strands of chromosomes separate
Chromosomes pulled to poles of cell
Cell membrane begins to pinch (furrow)

Telophase- Chromosomes become long and stringy and are no longer visible
Cell cytoplasm divides into 2 cells (cytokinesis)
Nuclear membrane reappears

Cytokinesis- Division of the parent cell’s cytoplasm
Occurs immediatley after mitosis (telophase)

It is when the new cells are pinched apart by a ring of fiber
that starts big and keeps getting smaller and smaller in size until
the 2 new cells are completely separate. It is similar to tying a knot
in a string and continuing to pull both ends of the string until the loop
is completely closed upon itself.

Here is what it looks like between the time the pinching begins and the time the 2 cells are completely apart from each other.



Interphase Key Questions:

How does a cell know when to divide?
When the surface area of the membrane can no longer support the volume
of the cell. Translation: When the cell gets so big that the oxygen and
nutrients can't get to the middle of the cell before they are used up,
so the middle of the cell doesn't have what it needs to maintain homeostasis.

(Check out the drawing in your notes that goes with this Q and A!)

Why do chromosomes shorten and thicken before cell division begins?
1. So there is ENOUGH ROOM. (Remember, you have twice the amount of chromosomes in the cell as you had earlier in interphase!)
2. To reduce the chance of CHROMOSOMES TANGLING AND TEARING (which could result in problems in the new cells.)

(Think pasta!! Spaghetti-long and stringy- and elbow macaroni- short and thick. Which is more likely to tangle and tear?)

Prophase Key Question:
Why must chromosomes double before splitting into 2 new cells?
So that each of the new cells has the same number of chromosomes as the original cell.
Humans have 46 chromosomes in most body cells. Those 46 will double to make 92.
Those 92 will then separate into 2 groups of 46, one set for each of the 2 new cells!

(Check out the drawing in your notes that goes with this Q and A!)

Metaphase Key Question:
Why is it beneficial (good) for the chromosome pairs to line up along the Middle of the cell?
1. So that spindle fibers do not tangle and damage the chromosomes.
2. So that the chromosomes themselves don't tangle and tear.

Anaphase Key Question:
Why are cells with an abnormal chromosome count USUALLY attributed to a mistake during this phase? (If a new cell ends up with the wrong number of chromosomes, why is it usually thought that a mistake happened during anaphase?)
If a centromere ("Velcro" in our classroom example, but you may not write "Velcro" on a test or quiz) does not separate properly, each daughter cell may end up with an abnormal number of chromosomes. To clarify, we have 46 chromosomes which will double to 92. If instead of each pair (the original and its copy) separating the way they shoud, two stay stuck together and are pulled to the same pole, that new cell will end up with 47 and the other will only get 45.

(Check out the drawing in your notes that goes with this Q and A!)



Here it is in an animated format!!! Hold onto your hats, this is exciting!



Science in the News Handout

Science in the News- Due Dates for Periods 1 to 4


Science in the News Due Dates- Period 6




Here are the Random Questions for this week, due Friday, 1/7/11.

Period 1:
Period 2: What happens when you crack your knuckles?
Period 3: How much lead or graphite does the average person use per year in pencils?
Period 4: Why does an atom blow up when split?
Period 6: Why do some people get headaches when the barometric pressure changes ?

Students must write their name, the question, answer, and information source on a slip of paper
and turn it in at the beginning of their class period on the day it is due.




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Last updated  2011/02/04 09:59:53 PSTHits  2473