Biology Leaving Cert
2.3 Cell continuity
Cell continuity
Biology Leaving Cert
2.3 Cell continuity
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 Cert
2.3 Cell continuity
Cell continuity
Cell 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 cell
3. Cell reproduction
Biology Leaving Cert
2.3 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
Nuclear pore
Chromatin
Biology Leaving Cert
2.3 Cell continuity
Haploid cells
A haploid cell has only one of each type of
chromosome.
• 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.
Biology Leaving Cert
2.3 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.
Biology Leaving Cert
2.3 Cell continuity
Check your learning..
1.What cell continuity is
2.The difference between haploid and
diploid cells
Biology Leaving Cert
2.3 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 Cert
2.3 Cell continuity
The Cell Cycle
Dividing stage
Mitosis
Interphase
Non dividing stage
The Cell Cycle is the sequence of events in a cell which
includes a state of non division and division.
Biology Leaving Cert
2.3 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
Mitosis
Interphase
Biology Leaving Cert
2.3 Cell continuity
Mitosis
2.3.4 Mitosis
Interphase
• 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
Biology Leaving Cert
2.3 Cell continuity
Learning check…
• What does cell continuity mean?
• Distinguish between haploid and diploid
• Define mitosis
Biology Leaving Cert
2.3 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 Cert
2.3 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
Cell membrane
Double stranded
chromosomes
Fibres
Nucleus
Nuclear
membrane
Biology Leaving Cert
2.3 Cell continuity
Mitosis: Stage 2
• Fibres attach to the chromosomes.
• The chromosomes line up along the centre of the cell.
Biology Leaving Cert
2.3 Cell continuity
Mitosis: Stage 3
• Chromosomes are pulled apart to opposite ends of the cell
Chromosomes
pulled apart
Biology Leaving Cert
2.3 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 Cert
2.3 Cell continuity
Mitosis
Mitosis – stage 2
Interphase
Mitosis – stage 1
Mitosis – stage 4
Mitosis – stage 3
• The end result of mitosis is two new
daughter cells – each with the same
number of chromosomes as the parent cell
Biology Leaving Cert
2.3 Cell continuity
H 2.3.8
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
Cell membrane
Double stranded
chromosomes
Spindle Fibres
Nucleus
Nuclear
membrane
Biology Leaving Cert
2.3 Cell continuity
H 2.3.8
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.
Centromere
Chromosomes line up on
the equator line
Spindle Fibre
Biology Leaving Cert
2.3 Cell continuity
H 2.3.8
Mitosis: Stage 3 - Anaphase
• Spindle fibres contract and chromosome pairs are pulled
apart at the centromere
• Chromosomes are pulled to opposite ends of the cell
Chromosomes
pulled apart
Centromere
Biology Leaving Cert
2.3 Cell continuity
H 2.3.8
Mitosis: Stage 4 - Telophase
• A nuclear membrane forms around each set of new
chromosomes and the cell divides in two
Cell divides in two
Biology Leaving Cert
2.3 Cell continuity
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 Cert
2.3 Cell continuity
H 2.3.8
Mitosis: Stage 4 - Telophase
• Cell division
in an animal cell involves cleavage furrow formation
Chromosomes
appear as
chromatin again
Biology Leaving Cert
2.3 Cell continuity
Mitosis: Stage 4 - Telophase
• Cell division
in a plant cell involves cell plate formation
Biology Leaving Cert
2.3 Cell continuity
Mitosis - PMAT
Telophase
Metaphase
Interphase
Anaphase
Prophase
• The end result of mitosis is two new
daughter cells – each with the same
number of chromosomes as the parent cell
Biology Leaving Cert
2.3 Cell continuity
Biology Leaving Cert
2.3 Cell continuity
Function of Mitosis
1. 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 Cert
2.3 Cell continuity
If living organisms are composed of
cells, what do they need in order to
grow bigger? …
…MORE CELLS !!
Biology Leaving Cert
2.3 Cell continuity
2.3.5 Function of Mitosis
• 2. A method of growth for multicellular organisms
.
Biology Leaving Cert
2.3 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
Biology Leaving Cert
2.3 Cell continuity
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 Cert
2.3 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 Cert
2.3 Cell continuity
2.3.7 Function of Meiosis
1. Sexual reproduction in Multicellular organisms
Meiosis produces haploid cells with half the number of chromosomes
as body cells.
Biology Leaving Cert
2.3 Cell continuity
2.3.7 Function of Meiosis
• 2. Meiosis produces variation
through the random sorting of genetic material which takes
place during meiosis.
• The cells resulting from meiosis are not identical to the parent
cell