7. ANSWERS
WHICH CELLS ??
1. Unicellular organisms
(eukaryotes and prokaryotes)
2. Most specialized cells (G0) in
multicelullar organisms, except
some (cardiac muscle, neurons,
gametes…).
3. Stem cells (non-differentiated
cells which divide to produce
different types of cells.)
WHY ??
1. Asexual reproduction of
unicelular organisms
2. Growth multicelullar organisms
3. Increase in the amount of
specific cells.
4. Regeneration or cell
replacement
8. TWO MAIN MOMENTS IN
THE CELL LIFE
Interphase: development Mitotic phase: division
10. INTERPHASE
During this stage the cell grows, develops more organelles, DNA is
duplicated and centrosomes duplicate. The cell becomes ready for
the next division.
It is the longest stage of the cell cycle
The nucleus has the usual structure
There are 3 distinguished phases during Interphase:
G1: Cell growth, organelles and cytoplasm substances duplicate
S: DNA replication
G2: Cell checks for error in replication, finishes duplicating
centrosomes. Ready for division.
G0 is a stage in which the cell stops dividing and is metabolically
active
Images: http://scienceaid.co.uk/biology/cell/cycle.html
11. MITOTIC PHASE
Mitosis: nuclear division
1 cell nucleus divides into 2
identical nuclei. Same DNA.
Cytokinesis: Division of the
cytoplasm
12. EXERCISE 1
How many cells are in Interphase?
How many cells are in the Mitotic phase?
http://www.ncbi.nlm.nih.gov/books/NBK9906/
The cells of adult animals can be grouped into three general categories with respect to cell proliferation. A few types of differentiated cells, such as cardiac muscle cells in humans, are no longer capable of cell division. These cells are produced during embryonic development, differentiate, and are then retained throughout the life of the organism. If they are lost because of injury (e.g., the death of cardiac muscle cells during a heart attack), they can never be replaced.
In contrast, most cells in adult animals enter the G0 stage of the cell cycle but resume proliferation as needed to replace cells that have been injured or have died. Cells of this type include skin fibroblasts, smooth muscle cells, the endothelial cells that line blood vessels, and the epithelial cells of most internal organs, such as the liver, pancreas, kidney, lung, prostate, and breast.
Other types of differentiated cells, including blood cells, epithelial cells of the skin, and the epithelial cells lining the digestive tract, have short life spans and must be replaced by continual cell proliferation in adult animals. In these cases, the fully differentiated cells do not themselves proliferate. Instead, they are replaced via the proliferation of cells that are less differentiated, called stem cells (Figure 14.43). Stem cells divide to produce daughter cells that can either differentiate or remain as stem cells, thereby serving as a source for the production of differentiated cells throughout life.
The dark circles are nucleoulus.
Interphase 31
Mitotic phase 9
