Chapter 18 Cell Division Mitosis Meiosis 2 n

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Chapter 18: Cell Division • Mitosis • Meiosis

Chapter 18: Cell Division • Mitosis • Meiosis

(2 n) mitosis (2 n) Meiosis (in testes) puberty Meiosis (in ovaries) puberty

(2 n) mitosis (2 n) Meiosis (in testes) puberty Meiosis (in ovaries) puberty

pollen grains (n) meiosis Anther cells (2 n) Section of an anther Ovum (n)

pollen grains (n) meiosis Anther cells (2 n) Section of an anther Ovum (n)

Where are the gametes formed in animals and plants? Animals Plants Gonads (reproductive organs)

Where are the gametes formed in animals and plants? Animals Plants Gonads (reproductive organs) Gametes (reproductive cells) Male gonads = Testes Male gametes = sperms Female gonads = Ovaries Female gametes = eggs or ova (singular: ovum) Male gonads = Anthers Male gametes = pollen grains Female gonads = Ovules Female gametes = eggs/ova

Mitosis 1 Parent cell (2 n) 2 identical daughter cells (2 n) Meiosis 1

Mitosis 1 Parent cell (2 n) 2 identical daughter cells (2 n) Meiosis 1 Parent cell (2 n) 4 gametes (n)

18. 2 Mitosis centrioles nuclear envelope Interphase • = ‘resting’ or non-dividing stage of

18. 2 Mitosis centrioles nuclear envelope Interphase • = ‘resting’ or non-dividing stage of cell. • Cells spend most of their time at interphase. • Cells still carry out absorbing nutrients and building up protoplasm. • Chromosomes appear as long thin threads called chromatin. The chromatin threads cannot be distinguished individually. • Centrioles divide ( animal cell only). chromatin • Chromatin threads replicate. cytoplasm An animal cell at interphase Copyright © 2006 -2011 Marshall Cavendish International (Singapore) Pte. Ltd. 2/24/2021 6

Chromatin threads (DNA) replicates Sister chromatids Chromatin thread DNA replication centromere Chromatin threads Coil

Chromatin threads (DNA) replicates Sister chromatids Chromatin thread DNA replication centromere Chromatin threads Coil & shorten One chromosome

DNA replication and mitosis must be precisely controlled DNA replication • copies all information

DNA replication and mitosis must be precisely controlled DNA replication • copies all information in the chromosomes to ensure daughter cells produced are genetically identical cells. • If an error occurs during DNA replication, it will be passed to the daughter cells. This leads to harmful changes to the genes and affect how the cells function. Mitosis • Uncontrolled cell division leads to cancer. • The tissue will not perform its proper function eg • cancerous growth in alveoli – reduce surface area for gas exchange

The Cell Cycle mitosis The cell cycle: • is the order of events between

The Cell Cycle mitosis The cell cycle: • is the order of events between one cell division and the next. • cytokinesis interphase consists of : 1. Interphase or ‘resting stage’ 2. Mitosis, a nuclear division - the daughter nuclei produced contain the same number of chromosomes as the parent nucleus. 3. Cell division, which is division of the cytoplasm or cytokinesis Copyright © 2006 -2011 Marshall Cavendish International (Singapore) Pte. Ltd. 2/24/2021 11

The Cell Cycle Stages of mitosis • Mitosis can be divided into four stages:

The Cell Cycle Stages of mitosis • Mitosis can be divided into four stages: 1. Prophase Metaphase Anaphase 2. 3. 4. Telophase Copyright © 2006 -2011 Marshall Cavendish International (Singapore) Pte. Ltd. 2/24/2021 13

Stages of Mitosis aster centrioles 1 Prophase • Chromatin threads condense, coil and shorten

Stages of Mitosis aster centrioles 1 Prophase • Chromatin threads condense, coil and shorten to become chromosomes. • Each chromosome consists of two sister chromatids attached at the centromere. sister chromatids (one chromosome) centromere nuclear envelope • The chromosomes are now visible under a microscope. Copyright © 2006 -2011 Marshall Cavendish International (Singapore) Pte. Ltd. 2/24/2021 14

The Cell Cycle aster centrioles 1 Prophase: - Early prophase • In animal cells,

The Cell Cycle aster centrioles 1 Prophase: - Early prophase • In animal cells, structures called asters form around the centrioles. Asters are made of microtubules. • The two pairs of centrioles move to opposite poles or ends of the cell. • The nucleolus disappears. sister chromatids (one chromosome) centromere nuclear envelope Copyright © 2006 -2011 Marshall Cavendish International (Singapore) Pte. Ltd. 2/24/2021 15

The Cell Cycle nuclear envelope breaks up 1 Prophase - Late prophase • The

The Cell Cycle nuclear envelope breaks up 1 Prophase - Late prophase • The nuclear envelope disappears. • A spindle forms with the spindle fibres extending from one pole of the cell to the other. spindle fibres forming Copyright © 2006 -2011 Marshall Cavendish International (Singapore) Pte. Ltd. 2/24/2021 16

Stages in Mitosis 2 centromere Metaphase • Chromosomes line up around the equator of

Stages in Mitosis 2 centromere Metaphase • Chromosomes line up around the equator of the spindle. • The centromere of each chromosome is attached to a spindle fibres attach to centromere Copyright © 2006 -2011 Marshall Cavendish International (Singapore) Pte. Ltd. 2/24/2021 17

Stages in Mitosis daughter chromosomes 3 Anaphase • Each centromere splits. • The spindle

Stages in Mitosis daughter chromosomes 3 Anaphase • Each centromere splits. • The spindle fibres pull the chromatids apart to opposite poles of the cell. • Once the chromatids are separated, they are called daughter chromosomes. Copyright © 2006 -2011 Marshall Cavendish International (Singapore) Pte. Ltd. 2/24/2021 18

Stages in Mitosis chromatin threads nuclear envelope 4 Telophase • Spindle fibres break down.

Stages in Mitosis chromatin threads nuclear envelope 4 Telophase • Spindle fibres break down. • A nuclear envelope forms around the chromosomes at each pole of the cell. • A nucleolus forms and the chromosomes uncoil and lengthen to become thin chromatin threads. nucleolus furrow Copyright © 2006 -2011 Marshall Cavendish International (Singapore) Pte. Ltd. 2/24/2021 19

Stages in Mitosis Cytokinesis identical daughter cells • This is the division of the

Stages in Mitosis Cytokinesis identical daughter cells • This is the division of the cytoplasm. • In animal cells, cleavage or furrows appear in the cytoplasm between the two nuclei. • The furrows deepen and two identical cells are finally produced. Copyright © 2006 -2011 Marshall Cavendish International (Singapore) Pte. Ltd. 2/24/2021 20