Biology Leaving Cert2.3 Cell continuity

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 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

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.

Biology Leaving Cert2.3 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