NAME: OPTION GROUP: CELL DIVISION MITOSIS WORKBOOK 1
STUDY CHECKLIST AND ASSESSMENT OBJECTIVES Instructions Regular revision throughout the year is essential. It s vital you keep a track of what you understand and what you don t understand. This booklet is designed to help you do this. Use the following key to note how well you understand the work after your revision. Put the letter R, A or G in the table. If you place an R or an A then you should make a note of what you are struggling with and the end of this book under the relevant section and seek help with this. Key R = Red. I am not confident about my knowledge and understanding A = Amber. I am fairly confident about my knowledge and understanding G = green. I am very confident about my knowledge and understanding 2
The following points are what you need to know, revise and answer questions on. Cell Division Mitosis 1. Can you describe the stages of the cell cycle. 2. Can you recognise the cell cycle as shown as a pie graph and an X-Y (line) graph. 3. Can you state the stages of mitosis in the correct order. 4. Can you describe what occurs during the stages of the cell cycle. 5. Can you recognise a cell in each of the stages of the cell cycle from a drawing and microscope images. 6. Do you know the significance of mitosis. 7. Can you state where mitosis occurs in both plants and animals. 8. Can you calculate the mitotic index. Place an R, A or G when you have revised and make notes of what you do not understand. Assessment Objective AO1 AO2 AO3 Description Demonstrate knowledge and understanding of scientific ideas, processes, techniques and procedures. Apply knowledge and understanding of scientific ideas, processes, techniques and procedures: In a theoretical context In a practical context When handling qualitative data When handling quantitative data Analyse, interpret and evaluate scientific information, ideas and evidence, including in relation to issues, to: Make judgments and reach conclusions Develop and refine practical design and procedures 3
WORD BANK Below is a list of some key words and phrases you will need to learn and understand in this water topic. 1. Anaphase 2. Cell cycle 3. Centromere 4. Centromere 5. Cytokinesis 6. Diploid 7. Equator 8. Homologous chromosomes 9. Meiosis 10. Metaphase 11. Mitosis 12. Mitotic Index 13. Pole 14. Prophase 15. Sister chromatids 16. Spindle fibres 17. Telophase 4
1.0 THE CELL CYCLE AND CHROMOSOMES 1.0.1 1.0.2 The Cell Cycle 1.0.1 Concept. The cell cycle is the sequence of events that prepares the cell for division and the actual process of the cell dividing. The preparation stage is called interphase and usually lasts for 23 hours. Interphase can be divided into three parts called G1, S and G2. The process of division is called mitosis and has the following stages: Prophase, metaphase anaphase telophase and cytokinesis. The cell cycle can be represented as a pie chart as shown below. The arrow shows the direction of the cell cycle. G2 Mitosis S G1 1.0.2 Concept During S phase of interphase the DNA is replicated. This means the DNA content of the nucleus has doubled. This can be used to plot a graph showing the cell cycle as shown below: 5
1.0.3 1.0.4 Chromosomes 1.0.3 Concept. A chromosome is a molecule of DNA. In humans the DNA is organized into 46 chromosomes. Because humans obtain one chromosome from the father and one chromosome from the mother the 46 human chromosomes are organized in pairs. These pairs are called homologous pairs of chromosomes as they are identical in size and the genes they contain. When the chromosomes are in pairs the cell is said to be diploid (abbreviated to 2n) and in humans the diploid number of chromosomes is 46. The 46 human chromosomes are shown below in their homologous pairs. 1.0.4 Concept The structure of a chromosomes depends on whether it has been replicated during S phase of interphase or not. Centromere Non-replicated chromosome in an homologous pair as they have come to lie close together. Maternal and paternal nonreplicated chromosomes Homologous pair of non-replicated chromosomes 6
Centromere Replicated maternal and paternal chromosomes not in homologous pairs. The chromosome has an X shape and is made up of two sister chromatids joined at the centromere. Sister chromatids Replicated maternal and paternal chromosomes in homologous pairs as they have come to lie close together. Homologous Pair of chromosomes 7
2.0 THE STAGES OF THE CELL CYCLE IN DETAIL 2.0.1 2.0.3 Interphase 2.0.1 Concept There are two important locations in a cell during cell division. These are the poles and the equator. Pole Equator Pole 2.0.2 The features of a cell in interphase. A cell in interphase has a clear nucleus with a nucleolus and chromatin threads and two pairs of centrioles. Under the microscope a cell in interphase has a grainy appearance in the nucleus which is the chromatin threads. There are no visible chromosomes at the stage. 2.0.3 The processes that occur during interphase are: 1. Organelles are produced. 2. Mitochondria and chloroplasts replicate. 3. Protein synthesis. 4. Centrioles replicate to form two pairs. 5. ATP produced by respiration. 5. The cell increases in size. 6. DNA replication r the DNA content doubles. 8
2.0.4 2.0.5 Prophase 2.0.4 Concept Prophase is the first stage of mitosis and is the first time that the chromosomes become visible. This occurs due to the chromatin threads shortening and condensing. The chromosomes have the characteristic X shape with two sister chromatids joined at the centromere. In image below, you will see 4 chromosomes. It is customary to use just a small number of chromosomes to aid clarity. There are two homologues pairs indicated by chromosomes of the same size, the different colours represent the maternal and paternal chromosomes. 2.0.5 Features of a cell in prophase. In addition to the chromosomes becoming visible the following features/events occur during prophase: The pairs of centrioles migrate to opposite poles of the cell. Spindle fibres begin to form from the centrioles. The function of the spindle fibres will be covered in metaphase and anaphase stages. An aster is formed which is a star like arrangement of spindle fibres radiating from the centrioles. The nucleolus had disappeared. The nuclear envelope starts to breakdown (as indicated by the dashed line in drawing above) and will be completely gone by the end of prophase. This is essential for metaphase where the chromosomes must be free in the cytoplasm of the cell. A real cell undergoing mitosis has the appearance of that shown above. The chromatin is no longer spread thought the nucleus but has form distinct chromosomes. 9
2.0.6 Metaphase 2.0.6 Features of a cell in metaphase Metaphase is the second stage of mitosis and the chromosomes are now free in the cytoplasm. This permits the chromosomes to align along the equator of the cell in a single row. The spindle fibres have now completely formed and span the cell from pole to pole. The chromosomes are attached to the spindle fibres by the centromere. 2.0.7 Anaphase 2.0.7 Features of a cell in anaphase The sister chromatids are pulled to opposite poles of the cell by shortening of the spindle fibres. The centromere leads the way and the chromatids have the arrow head like appearance indicating the strong pulling force of the spindle fibres. The centromeres divide. 10
2.0.8-2.09 Telophase and cytokinesis 2.0.8 Features of a cell in telophase During telophase the chromatids have reached the poles of the cell. The chromatids are now called chromosomes. The cell will then begin to constrict in the middle. This is cytokinesis and is the cell is beginning to divide into two daughter cells. 2.0.9 Features of a cell in telophase II A new nuclear envelop form around the chromosomes at the poles. Cytokinesis continues are two new daughter cells are form and enter interphase of the cell cycle. 11
3.0 THE MITOTIC INDEX 3.0.1 Concept The mitotic index is the percentage of cells in mitosis. It can be calculated by the equation: number of cells in prophase + metaphase + anaphase + telophase total number of cells 4.0 THE SIGNIFICANCE OF MITOSIS 4.0.1 Concept Mitosis produces genetically identical daughter cells with the same diploid chromosome number. 4.0.2 Concept Mitosis produces new cells so can cause the growth of an organism. Mitosis also repairs damages tissues and replaces worn out cells. 4.0.3 Concept Organisms like bacteria and plants reproduce asexually by mitosis. 4.0.4 Concept mitosis occurs in all body cells of an animal and plant. Mitosis also occurs in the root tip of plants and the meristems. 5.0 THE SQUASHED ROOT TIP PRAC 5.0.1 Concept The squashed root tip prac is used to view cells in all stages of mitosis. The following steps are needed to produce a good squashed root tip: 1. The root tip must be fully squashed. 2. The cells must form a single layer of cells with no overlap of cells. 3. A stain must be used to make the chromosomes visible. 4 A good squashed root tip looks like the image below 12
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