Science

Science
-Biology
-Chemistry
-Physics

Biology
Cells
There are many types of cells. For example : Squamous and cuticle in plants.
Q : Are cells smaller than atoms?
A : No! In fact, atoms are much smaller than cells and they itself contains them.
Definition of cell : the basic unit of life of all living things.
Parts of cell :
Plasma membrane
-made up of proteins and phospholipids ( Chemistry- Form 4 Chapter 3)
-semi-permeable to ions and organic molecules Example: OXYGEN, CARBON DIOXIDE 
-protects the cell from external environment.                

                                                                                                                       

-Regulate the movement of selective substances in and out of the cell.

Cell wall
-ONLY FOUND in plant cells.
-A rigid layer which surrounds the plasma membrane
-permeable
-Made up of CELLULOSE.
-Maintains shape
-Mechanical support
-plant cell will burst when excess water enters the cell without cell wall.

Mitochondria
-where oxidation of glucose takes place.
-Glucose transforms into ATP(Adenosine triphosphate) which is an energy.

Cytoskeleton
-a network of cisternae that holds together components of the cell.
-within the cytoplasm.

Cell reproduction
-Mitosis
-Meiosis

MITOSIS
-do not occur in gametes and spores(they take part in meiosis)
-occurs every 24 hours
-important to replace old cells in one's body.
-after division, both cells has 46 chromosomes (structures that are made up from DNA( deoxyribonucleic acid )
-only a part of the cell cycle( includes Mitotic phase and interphase)
-every mitotic phase takes about 80 minutes.

Stages of Mitosis
1)Prophase - the DNA condenses, organizes and the classic chromosomes' structure appear.
2)Prometaphase -microtubules attach themselves to the chromosomes.
3)Metaphase - the chromosomes align at the equator of the cell.
4)Anaphase - the chromatids are pulled away from its original form(chromosomes) by the microtubules   towards the poles( centrosomes ).
5)Telophase - the nuclear membrane forms around the newly formed chromosomes. Two nucleus forms
6)Cytokinesis - The cell separates into two daughter cells.



INTERPHASE (A part of the cell cycle)
-Separated into three parts:       G1------S------G2
o G1 (Gap 1) - Cell becomes active, parts of cell ( exp: Mitochondria ) doubles.
o S ( Synthesis phase ) - DNA( forms the chromosomes ) in the cell replicates.
o G2 ( Gap 2 ) - The cell finishes replicating. Two centrosomes appeared in the cytoplasm of the cell.

( Mitosis can start )