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Learning objectives
• Today you should learn about
1.What cell continuity is
2.The difference between haploid and diploid cells
3.The two main stages in mitosis
4.What happens during interphase in the cell cycle
Biology Leaving Cert2.3 Cell continuity
Biology Leaving Cert2.3 Cell continuity
Cell continuityCell continuity means that new cells can only be produced by the division of existing live cells.
This requires:
1. Synthesis of materials needed in the cell, 2. Growth of the cell3. Cell reproduction
Biology Leaving Cert2.3 Cell continuity
2.3.1 Chromosomes
• Chromosomes are the structures made of DNA and protein which are located in the nucleus of the cell.
Nuclear membrane
Chromatin
Nuclear pore
Biology Leaving Cert2.3 Cell continuity
Haploid cells
• Def Haploid number is the number of chromosomes in a haploid cell
• Haploid number is represented by the letter n
n = 4 describes a haploid cell that has four chromosomes.
A haploid cell has only one of each type of chromosome.
Biology Leaving Cert2.3 Cell continuity
Diploid cells• A diploid cell has two of each type of chromosome.
Def Diploid number is the number of chromosomes in a diploid cell
Diploid number is represented by the letter 2n
2n = 4 describes a Diploid cell that has four chromosomes.
Check your learning..
1.What cell continuity is
2.The difference between haploid and diploid cells
Biology Leaving Cert2.3 Cell continuity
Learning objectives
1.The two main stages in mitosis
2.What happens during interphase in the cell cycle
3.What mitosis is and how it happens
Biology Leaving Cert2.3 Cell continuity
Biology Leaving Cert2.3 Cell continuity
The Cell Cycle
The Cell Cycle is the sequence of events in a cell which includes a state of non division and division.
Interphase
Mitosis
Non dividing stage
Dividing stage
Biology Leaving Cert2.3 Cell continuity
During Interphase
• The chromosomes:
1. Elongate – as chromatin
2. then make copies of themselves!
• The cell also produces new organelles and makes chemicals, enzymes and proteins
Interphase
Mitosis
Biology Leaving Cert2.3 Cell continuity
2.3.4 Mitosis Interphase
Mitosis
• Def Mitosis is the division of the nucleus to produce two daughter nuclei, containing identical sets of chromosomes.
Daughter nuclei with chromosomes identical to parent cell
Learning check…
• What does cell continuity mean?
• Distinguish between haploid and diploid
• Define mitosis
Biology Leaving Cert2.3 Cell continuity
Today’s objectives
• To learn the names of the four stages of mitosis
• To learn about what happens in each stage of mitosis
Biology Leaving Cert2.3 Cell continuity
Biology Leaving Cert2.3 Cell continuity
Mitosis: Stage 1
:
•The chromatin shortens, thickens and double stranded chromosomes become visible in the nucleus.
•The Nuclear membrane breaks down
•Fibres are formed
Fibres
Double stranded chromosomes
Nucleus
Nuclear membrane
Cell membrane
Biology Leaving Cert2.3 Cell continuity
Mitosis: Stage 2
• Fibres attach to the chromosomes.
• The chromosomes line up along the centre of the cell.
Biology Leaving Cert2.3 Cell continuity
Mitosis: Stage 3
• Chromosomes are pulled apart to opposite ends of the cell
Chromosomes pulled apart
Biology Leaving Cert2.3 Cell continuity
Mitosis: Stage 4• A nuclear membrane forms around each set of new
chromosomes and the cell divides in two
Cell divides in two
Biology Leaving Cert2.3 Cell continuity
Mitosis
• The end result of mitosis is two new daughter cells – each with the same number of chromosomes as the parent cell
InterphaseMitosis – stage 1
Mitosis – stage 2
Mitosis – stage 3
Mitosis – stage 4
Biology Leaving Cert2.3 Cell continuity
Mitosis: Stage 1 - Prophase
:
•The chromatin shortens, thickens and double stranded chromosomes become visible in the nucleus.
•The Nuclear membrane breaks down
•Spindle fibres are formed
Spindle Fibres
Double stranded chromosomes
Nucleus
Nuclear membrane
Cell membrane
H 2.3.8
Biology Leaving Cert2.3 Cell continuity
Mitosis: Stage 2 - Metaphase
• Fully formed Spindle fibres attach to the chromosomes pairs at the centromere.
• The chromosomes line up along the centre of the cell – the equator line.
Spindle Fibre
Chromosomes line up on the equator line
Centromere
H 2.3.8
Biology Leaving Cert2.3 Cell continuity
Mitosis: Stage 3 - Anaphase
Chromosomes pulled apart
• Spindle fibres contract and chromosome pairs are pulled apart at the centromere
• Chromosomes are pulled to opposite ends of the cell
Centromere
H 2.3.8
Biology Leaving Cert2.3 Cell continuity
Mitosis: Stage 4 - Telophase• A nuclear membrane forms around each set of new
chromosomes and the cell divides in two
Cell divides in two
H 2.3.8
Today’s objectives
• Difference in Telophase between plant and animal cells
• Function of mitosis in unicellular organisms
• Function of mitosis in multicellular organisms
Biology Leaving Cert2.3 Cell continuity
Biology Leaving Cert2.3 Cell continuity
Mitosis: Stage 4 - Telophase
• Cell division
in an animal cell involves cleavage furrow formation
H 2.3.8
Chromosomes appear as chromatin again
Biology Leaving Cert2.3 Cell continuity
• Cell division
in a plant cell involves cell plate formation
Mitosis: Stage 4 - Telophase
Biology Leaving Cert2.3 Cell continuity
Mitosis - PMAT
• The end result of mitosis is two new daughter cells – each with the same number of chromosomes as the parent cell
InterphaseProphase
MetaphaseAnaphase
Telophase
Biology Leaving Cert2.3 Cell continuity
Function of Mitosis1. A method of reproduction for single celled organisms
mitosis allows single celled organisms to multiply and produce offspring identical to themselves. E.g. Amoeba
Biology Leaving Cert2.3 Cell continuity
If living organisms are composed of cells, what do they need in order to grow bigger? …
…MORE CELLS !!
Biology Leaving Cert2.3 Cell continuity
2.3.5 Function of Mitosis
• 2. A method of growth for multicellular organisms
.
Biology Leaving Cert2.3 Cell continuity
The Cell Cycle 2.3.4•Def Cancer is a group of disorders in which cells lose the ability to control the number of times that mitosis happens and how fast it happens. It results in uncontrolled multiplication of cells.
Two possible causes of cancer:
Cigarette smoke
Ultraviolet radiation
Check your learning
• How mitosis happens in haploid and diploid cells
• Difference in Telophase between plant and animal cells
• Functions of mitosis
• Cancer – definition and possible causes
Biology Leaving Cert2.3 Cell continuity
Biology Leaving Cert2.3 Cell continuity
2.3.6 Meiosis• Def Meiosis is division of the cell to produce daughter
cekks which contain half the chromosome number of the parent cell.
Diploid cell with 2n = 4
Haploid cells with n = 2
Biology Leaving Cert2.3 Cell continuity
2.3.7 Function of Meiosis1. Sexual reproduction in Multicellular organismsMeiosis produces haploid cells with half the number of chromosomes
as body cells.