Download 2-1,2-2 Cell Division - Cell Structures

UNIT 1:
REPRODUCTION
UNIT A IN YOUR GRADE 9 SCIENCE 9 PROBE TEXTBOOK
2.1 The importance of Cell
Division (pg 36)

You have probably encountered the idea that cells
divide to create new cells. This process is called cellular
division and it provides three main functions:
•
Growth – If cell division did not happen all of us would only be
one cell big. From the moment of conception onward our cells
are dividing to help us grow bigger. So why don’t our cells just
get bigger? Why do we need more? As a cell gets bigger it
becomes less efficient. That means being made of many,
smaller, cells is better.
•
Repair – Your cells get damaged all of the time. In order to
deal with these damages your cells divide and produce new
healthy cells to replace the old damaged ones. Old and dead
cells are replaced every second. The cells that you started off
life with are long gone.
•
Reproduction – Unicellular organisms reproduce by growing
larger and then splitting in half. When a bacteria splits in half
it creates two identical copies of the original cell.

Some interesting questions exist around cell division.
Like why do some cells divide more often than others?
3.2 Cell Structures Involved in
Cell Division (Sec 2.2 pg 39)

When a cell undergoes cell division all parts of the cell
get copied so the two new cells will have all the parts
that they need. Some of those parts are more important
to cell division and we will focus on them now:
•
The nucleus – This organelle directs cell division. It also
contains all of the DNA. During cell division the nuclear
membrane dissolves so that the DNA can duplicate and get into
each new cell.
•
Chromosomes – This is the name for the segments of DNA.
Humans typically have 46 (23 pairs) of chromosomes. These get
copied during cell division.
•
Nucleolus – This part of the nucleus creates ribosomes
•
Ribosomes and Endoplasmic Reticulum (ER) – The ribosomes
make proteins which help the cell function properly. The rough
ER folds and transports the proteins to where they are needed
in the cell. The smooth ER manufacturers and transports fats
to where they are needed in the cell.
•
Cytoplasm – This is the fluid that contains all of the organelles
in the cell. The cytoplasm also contains a network of
microtubules that act like a rail system and skeleton for the
cell. During cell division a segment of the microtubules, called
the centrioles, help the cell divide evenly in half.