Cell division. Diploma in Veterinary Nursing Key points for consolidation and revision. Pack Code: VET7

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1 Diploma in Veterinary Nursing Key points for consolidation and revision Cell division Pack Code: VET7 RCVS VN3 Comparative anatomy for veterinary nursing practice LO3: Understand the normal form and function of body systems in a range of mammalian species AC3.1: Explain basic cell structure, physiology and division.

2 Introduction Cells divide to allow growth and to replace worn out or damaged cells. Somatic cells are all the body s cells, such as blood or muscle cells, apart from cells involved in reproduction. These cells divide by the process of mitosis. Mitosis enables the cells to make identical copies of themselves. They do this by dividing in two this is called binary fission. The process of division for the cells involved in reproduction is called meiosis. Cells for reproduction are found in ovaries (ova) and the testes (spermatozoa). These are called germ cells. Meiosis must occur before fertilisation. How mitosis works: One cell the parent cell divides into two daughter cells. The two daughter cells are identical to the parent cell. They have the diploid number of chromosones. This means that the DNA of the daughter cells is also identical. The process is sometimes called replication. The diagram below shows what happens. Cell division 2

3 During mitosis a cell cannot function as usual. This is because, to move more easily, the DNA coils around proteins to form chromosomes. However, in its coiled form it is not able to tell the cell what to do. The four stages of mitosis There are four active stages in mitosis. A number of activities take place during each phase. These have to be completed before the next stage can start. Stage 1 Stage 2 Stage 3 Stage 4 Prophase Metaphase Anaphase Telophase This is followed by a resting stage called interphase when the new daughter cells grow and get ready for the next cell division. Cell division 3

4 Revision 1 1. The process of division for somatic cells is called: a) binary fission b) meiosis c) mitosis d) reproduction 2. In mitosis the parent cell divides into: a) 2 daughter cells b) 4 daughter cells c) 6 daughter cells d) 8 daughter cells 3. Cells involved in reproduction are called: a) somatic cells b) blood cells c) daughter cells d) germ cells 4. The first stage of mitosis is: a) anaphase b) interphase c) telephase d) prophase 5. Are the following statements true or false? True False a) In mitosis daughter cells are identical to the parent cell!! b) Meiosis occurs after fertilisation!! c) The 4 th stage of mitosis is metaphase!! d) Germ cells are found in the testes!! Cell division 4

5 (Stage1) Prophase At the prophase stage a number of changes take place in the cell. Two centrosomes (pairs of centrioles) start to move into position at opposite ends of the cell. Chromatin condenses to form chromosomes. The membrane round the nucleus starts to break down and disappear. (Stage 2) Metaphase During metaphase the chromosomes move to the centre of the cell. Each chromosome is made up of two identical halves called chromatids. The chromosomes are now in between the centrosomes. Cell division 5

6 (Stage 3) Anaphase During anaphase the chromosomes split. One chromotid from each chromosome starts to move towards one of the centrosomes, At the same time the other chromotid moves in the opposite direction. The number of chromosomes has doubled. (Stage 4) Telophase During telophase, the reverse of prophase takes place. There are now two nuclei, and a membrane reappears round each one. The chromosomes uncoil so that the DNA can function again. The cell divides into two, resulting in two daughter cells. Cell division 6

7 The end of mitosis At the end of mitosis, two identical cells have been formed. The DNA is now uncoiiled. The cell can issue instructions to the cell again, and function normally. Interphase The four active phases of mitosis are followed by a resting phase called interphase. The daughter cells grow and carry on doing the jobs they are designed to do, until the time comes for them to divide in turn. At the start of interphase, each chromosome has a single chromatid. Before the next cell division can take place, each chromosome has to produce a second chromatid. This process is called DNA synthesis. At the same time, the cell changes from having one centrosome to two. It is then ready to divide again. Meiosis Meiosis is cell division which occurs in the gonads. It is the process in which the gametes (sperm and ova) are produced. It involves two rounds of cell division. Which result in four daughter cells. Each daughter cell has half the number of chromosomes as the parent cell. They have the haploid number of chromosomes. This means that during conception, there is the correct number of chromosomes for the species. In the female, only one of the 4 daughter cells will become an ovum. Cell division 7

8 Revision 2 1. At which stage does the nuclear membrane start to disappear? a) Prophase b) Telophase c) Metaphase d) Anophase 2. During anaphase: a) chomatin condenses b) the chromosomes split c) the chromosomes move to the centre of the cell d) there are two nuclei 3. At which stage does the cell divide, resulting in two daughter cells? a) Telophase b) Anaphase c) Metaphase d) Prophase 4. During the interphase: a) the DNA is uncoiled b) each chromosone produces a second chromatid c) four daughter cells are produced d) the nuclear membrane reappears 5. Meiosis is cell division which happens in: a) all body cells b) blood cells c) the male gonads only d) the gonads 6. Are the following statements true or false? True False a) Mitosis results in two daughter cells with a diploid number of chromosones.!! b) Mitosis results in two daughter cells with a haploid number of chromosones!! c) Meiosis results in four daughter cells with a diploid number of chromosones!! d) Meiosis results in four daughter cells with a haploid number of chromosones!! 7. Decide at which stage (1) prophase, (2) metaphase (3) anaphase and (4) telophase each of the following takes place and put them in the correct order. Membrane around nucleus disappears Membrane reappears around nuclei The chromosomes split The chromosomes move to the centre of the cell Check your answers at the end of this pack. Cell division 8

9 Different types of cell Every mammal begins life as a single cell the fertilised egg. As this cell divides the initial cells are all totipotent they have the potential to produce any kind of cell. After about four days, the cells start to specialise. This process is called cell differentiation It leads to different kinds of cell liver cells, blood cells, muscle cells, etc. There are over 200 different kinds of mammal cells, and each is specialised to carry out particular jobs. Examples of types of cell Type of cell Function Specialisation Red blood cell (erythrocite) Carries oxygen to other cells This membrane allows oxygen to diffuse quickly; contains haemoglobin to carry oxygen White blood cell Fights disease Cytoplasm can engulf bacteria Neuron Sends messages through nerves Connect with other nerve cells to pass messages Muscle cell Helps muscles to contract Long shape so they can slide together. Move mitochondria to create more energy Epithelial cell Covers the surfaces of the body e.g. skin and linings of the throat, lungs, lungs, intestines, etc. Interlocking edges fit closely together Bone cell (Osteocyte) Helps to make bones firm Star-shaped cells bond together strongly Kidney cell (Podocyte) Filters the blood and creates urine Large ER and Golgi apparatus help to filter out proteins Cell division 9

10 Stem cells Stem cells are cells which are not differentiated, but which have the capacity to create more than one cell type. Stem cells are of great medical interest at the moment, because scientists may be able to use them to grow new cells to replace cells that have been damaged by illness. Cell division 10

11 Revision 3 1. Cell differentiation is the process whereby: a) cells divide b) cells start to specialise c) worn out cells die d) cells carry oxygen 2. The cells that fight disease are: a) red blood cells b) white blood cells c) stem cells d) bone cells 3. Muscle cells: a) connect with other nerve cells to pass messages b) contain haemoglobin to carry oxygen c) move mitochrondia to create energy d) help filter out proteins 4. Match the following cells to their functions Type of cell Red blood cell (erythrocite) White blood cell Neuron Muscle cell Epithelial cell Bone cell (Osteocyte) Kidney cell (Podocyte) Function Filters the blood and creates urine Helps to make bones firm Sends messages through nerves Fights disease Carries oxygen to other cells Covers the surfaces of the body e.g. skin and linings of the throat, lungs, lungs, intestines Helps muscles to contract Cell division 11

12 Answers to revision questions Revision 1 1. c) The process of division for somatic cells is mitosis 2. a) In mitosis the parent cell divides into two daughter cells 3. d) Cells involved in reproduction are called germ cells 4. d) The first stage of mitosis is called prophase 5. a) True; b) False; c) False; d) True Revision 2 1. a) The nuclear membrane starts to disappear at the prophase stage 2. b) During anaphase the chromosomes split 3. a) The cell divides, resulting in two daughter cells, during telophase 4. b) During the interphase each chromosone produces a second chromatid 5. d) Meiosis is cell division which happens in the gonads 6. a) True; b) False; c) False; d) True Prophase membrane around the nucleus disappears 2. Metaphase The chromosomes move to the centre of the cell 3. Anaphase The chromosomes split 4. Telophase Membrane appears around the nuclei Revision 3 1. b) Cell differentiation is the process whereby cells start to specialise 2. b) The cells that fight disease are white blood cells 3. c) Muscle cells move mitochondria to create energy 4. Type of cell Red blood cell (erythrocite) White blood cell Neuron Muscle cell Epithelial cell Bone cell (Osteocyte) Kidney cell (Podocyte) Function Carries oxygen to other cells Fights disease Sends messages through nerves Helps muscles to contract Covers the surfaces of the body e.g. skin and linings of the throat, lungs, lungs, intestines Helps to make bones firm Filters the blood and creates urine Cell division 12

13 Acknowledgements This learning pack has been produced by the Land Based Colleges National Consortium Ltd. The LBCNC is a consortium of colleges working in the land-based sector which cooperate in the development and production of quality flexible learning materials which encourage independent learning. We would like to acknowledge the contributions made by the following individuals and colleges in the development of this learning pack. Initial guidance and source material Initial guidance: Gemma Irwen-Porter, Bridgwater College Cover photograph: Steve Watson, Riseholme College, University of Lincoln Developed and produced for LBCNC by Learners First Illustrations: Shevanthi De-Silva Graphic design: Eat Cake Design, Bristol Written July The Land Based Colleges National Consortium Ltd. All rights reserved. Permission to photocopy or adapt the material in this learning pack is granted to members of the Land Based Colleges National Consortium Ltd. only. For further information please contact the LBCNC project management team at 7 Tyne Road, Bishopston, Bristol BS7 8EE. Tel Cell division 13