I made these notes with the help of my teacher and obtained 96% (straight 7) on my final IB examinations thanks to these incredibly well-organized and clear notes that include diagrams, images, colours, and much more and exactly match what you will be asked on your IB biology exam.
Why do cells divide:
● Reproduction
● Growth (from fertilized egg to multicellular organism)
● Repair & Renewal
Mitosis:
Mitotic chromosomes:
Duplicated chromosomes:
● 2 sister chromatids
● narrow at centromeres
● contain identical copies of original DNA
Mitosis: Dividing the parent cell’s DNA between 2 daughter nuclei
Interphase:
● Most of a cell’s life cycle (~95%)
● Doing the “everyday job”:
○ Synthesize proteins / enzymes, metabolism, etc.
● Prepare for duplication if signalled to do so (so not
part of mitosis)
● Divided into 3 phases:
○ G1 : 1st gap (growth)
■ Non-dividing life, Cells increase in size,
create new proteins and organelles
○ S : DNA synthesis
■ Chromosomes replication
○ G2 : 2nd gap (Growth)
■ prepares for division
■ produces organelles and molecules needed for division
, ● DNA loosely packed as chromatin fibers in nucleus
● Prepares for mitosis (so not really part of mitosis!)
○ Replicates chromosome
○ Produces proteins & organelles
Prophase:
● Chromatin condenses → visible chromosomes
● Centrioles (they organize microtubules) move to opposite
poles of cell
● Spindle fibers cross cell to form mitotic spindle
○ Microtubules
○ Coordinate movement of chromosomes
● Nuclear membrane breaks down and disappears.
Metaphase:
● Spindle fibers attach to centromeres
● Chromosomes align along middle of cell
○ Metaphase plate
■ Meta = middle
○ Spindle fibers coordinate movement
Anaphase:
● Sister Chromatids separate into individual chromosomes and
are moved apart.
Telophase:
● Chromosomes arrive at opposite poles
● Chromosome unravel and reform chromatin
● 2 new nuclear envelopes form
● Spindle fibers disappear
● Cytokinesis begins
○ Cell division
, Mitotic Index: the percentage of cells undergoing mitosis in a given population of cells
High Mitotic Index suggests cancer (uncontrolled, constant cell division of)
Mitosis and Meiosis on a drawing: What happens to the DNA
Cytokinesis:
Animals:
● Cleavage furrow forms
● Cell membrane is drawn inward
● Splits cell in two
● Like tightening a draw string
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