Embedded Files
Learning Outcomes
Learning Outcomes
State the importance of mitosis in growth, repair and asexual reproduction.
Explain the need for the production of genetically identical cells and fine control of replication.
Identify, with the aid of diagrams, the main stages of mitosis.
State what is meant by homologous pair of chromosomes.
Identify, with the aid of diagrams, the main stages of meiosis.
Define the terms haploid and diploid, and explain the need for reduction division process prior to fertilisation in sexual reproduction.
State how meiosis and fertilisation can lead to variation.
🕜Estimated Time: 2 hours
Cell Cycle
Cell Cycle
Cell cycle refers to the life of a cell from the time it is first formed from a dividing parent cell until its own division into two cells.
The cell cycle is divided into 3 stages
Interphase
Period of synthesis and growth where the cell prepares for division.
DNA replication takes place.
Nuclear division - mitosis or meiosis
Division of nuclear content
Cytokinesis
Division of the cytoplasm into two daughter cells
Interphase (non-dividing stage)
Interphase (non-dividing stage)
The cell spends the majority of time during cell cycle in the interphase stage.
The cell is not undergoing any division.
The role of interphase is to prepare for division.
The role of interphase is to prepare for division.
Absorb nutrients, building up protoplasm and increasing in size.
DNA replication
At interphase, the DNA appears as long thin threads called chromatin.
Each chromatin thread replicates and produces two identical chromatin threads.
Nuclear Division: Mitosis
Nuclear Division: Mitosis
Mitosis refers to nuclear division in which a cell nucleus divides to produce two daughter nuclei with the same set of chromosome as the parental nucleus.
Prophase
Prophase
Chromatin thread condenses, coil and shorten to become chromosome.
Each chromosome consists of 2 sister chromatids attached at the centromere.
Spindle fibres form and extend from one pole to another.
Metaphase
Metaphase
The chromosome line up at the equator of the spindle.
The centromere of each chromosome is attached to a spindle fibre.
Anaphase
Anaphase
Each centromere splits.
The spindle fibres pull the chromatids to opposite poles of the cells.
Once the chromatids are separated, each of them is now known as daughter chromosome.
Telophase
Telophase
The chromosomes uncoil and lengthen into thin chromatin threads.
The spindle fibres disintegrate.
Cytokinesis
Cytokinesis
In animal cells
In animal cells
Cleavage (furrow) appears in the cytoplasm between the two nuclei.
The cleavage deepen and two identical daughter cells are produced (in mitosis)
In plant cells
In plant cells
A cell plate is formed between the two daughter nuclei. (instead of cleavage)
Small fluid-filled vesicles produced by the Golgi apparatus fuse at the equator to form the cell plate.
Importance of Mitosis
Importance of Mitosis
Growth of an organism
Growth of an organism
New cells must be produced by mitosis for multicellular organism (e.g. human) to grow.
Repair of worn-out part
Repair of worn-out part
Dead or worn-out cells are replaced by new cells through mitosis.
Asexual reproduction
Asexual reproduction
For shoot and root formation in storage organs (vegetative reproduction).
Nuclear Division: Meiosis
Nuclear Division: Meiosis
Meiosis refers to nuclear division in which a cell nucleus divides to produce four daughter nuclei with half the number of chromosome as the parental nucleus.
During fertilisation,
Two gametes (1 egg and 1 sperm) fuse to form a zygote.
The zygote then undergoes mitosis repeatedly to form a new organism.
This implies that gametes only have half the number of chromosome as the zygote.
Gametes are haploid (n) cells – Cells with half the number of chromosome.
Other body cells, including the cells that form the gametes, are diploid (2n) (full 2 sets of chromosomes).
Meiosis consists of two divisions – meiosis I and meiosis II.
Each division consists of four stages – prophase, metaphase, anaphase and telophase.
Meiosis I
Meiosis I
Prophase I
Prophase I
Chromatin thread condenses, coil and shorten to become chromosome.
Each chromosome consists of 2 sister chromatids attached at the centromere.
Chromatid of homologous chromosome may cross and twist around each other at points called chiasmata (singular chiasma).
The strength of this coiling may cause the chromatid to break and exchange part – process known as crossing over.
Crossing over produced new combination of genes – genetic variation.
Spindle fibres form and extend from one pole to another.
During prophase of meiosis I, homologous chromosomes pair up through the process known as synapsis.
One homologous chromosome comes from the male parent, while the other comes from the female parent.
Homologous chromosomes have the same shape, length, position of centromere and genes.
Metaphase I
Metaphase I
Pairs of homologous chromosome arrange themselves along the equator of the cell.
Anaphase I
Anaphase I
Homologous chromosome separate and move to opposite poles of the cell.
The resulting chromosome is made up of 2 chromatids.
Telophase I
Telophase I
The chromosomes uncoil and lengthen into thin chromatin threads.
The spindle fibres disintegrate.
Cytokinesis
Cytokinesis
The cytoplasm cleaves into two daughter cells with haploid number of chromosome.
Meiosis II
Meiosis II
Prophase II
Prophase II
Chromatin thread condenses, coil and shorten to become chromosome.
Spindle fibres form and extend from one pole to another.
Metaphase II
Metaphase II
The chromosome line up at the equator of the spindle.
The centromere of each chromosome is attached to a spindle fibre.
Anaphase II
Anaphase II
Each centromere splits.
The spindle fibres pull the chromatids to opposite poles of the cells.
Once the chromatids are separated, each of them is now known as daughter chromosome.
Telophase II
Telophase II
The chromosomes uncoil and lengthen into thin chromatin threads.
The spindle fibres disintegrate.
Cytokinesis
Cytokinesis
The cytoplasm cleaves into four daughter cells with haploid number of chromosome.
Importance of Meiosis
Importance of Meiosis
Produces haploid gametes
Produces haploid gametes
When male gamete fuses with female gamete, the diploid number of chromosome is restored. (Maintenance of diploidy)
When male gamete fuses with female gamete, the diploid number of chromosome is restored. (Maintenance of diploidy)
Results in variation in gametes produced
Results in variation in gametes produced
Due to crossing over in prophase I
Independent assortment of chromosomes
Each pair of chromosome can combine with either chromosome of the other pair.
Biology Resources Main Page
Test Your Understanding!
Test Your Understanding!
Fill out the form below to test your understanding on the topic of Cell Cycle. Remember to click 'View responses' to see the correct answers.
Page updated
Google Sites
Report abuse