Unit 1 Organisation in Life (MYP 4) 2024-25 PDF

Academic Year 2024-25 Unit1: Organization in Life Grade: MYP 4 Key concept: Systems Related concept: Pattern, Function Global context: Identities and relationships Students will explore identity formation. S...

Academic Year 2024-25 Unit1: Organization in Life Grade: MYP 4 Key concept: Systems Related concept: Pattern, Function Global context: Identities and relationships Students will explore identity formation. SOI: Our identity is determined by the relationship between different patterns and functioning of the cells which work together to create a larger, functioning system. Purpose of the Notes: The purpose of giving notes for the above topics is to provide students with a condensed and organized summary of the important information and knowledge covered in the lesson. Notes help students consolidate information, serve as a reference for later review, visually represent complex ideas and support personalized learning. Learning outcomes: ⚫ Identify the structure and function of chromosomes, DNA, and genes, and understand their role in carrying genetic information. ⚫ Explain the process of mitosis and meiosis, including the key events and changes that occur during each phase. ⚫ Compare and contrast the phases of mitosis and meiosis, including interphase, prophase, metaphase, anaphase, and telophase. ⚫ Understand the role of mitosis in asexual reproduction and of meiosis in sexual reproduction. CELL CYCLE, MITOSIS AND MEIOSIS: Introduction: Chromosomes are located in the nucleus of cells. They are thread-like structures of DNA, carrying genetic information in the form of genes. A gene is a short length of DNA found on a chromosome that codes for a specific protein. This could be a structural protein such as collagen found in skin cells, an enzyme or a hormone. Genes control our characteristics as they code for proteins that play important roles in what our cells do. Genes are short lengths of DNA that code for a protein. They are found on chromosomes. source: https://cdn.savemyexams.co.uk/wp-content/uploads/2020/01/DNA-genes-and-chromosomes.png Diploid and haploid nuclei: All humans have 23 different chromosomes in each cell. In most body cells, not including the gametes (sex cells), we have 2 copies of each chromosome, leading to a total of 46 chromosomes. Nuclei with two sets of chromosomes are known as diploid nuclei. The gametes (egg and sperm cells) only have one copy of each chromosome, meaning they have a total of 23 chromosomes in each cell. Nuclei with one set of unpaired chromosomes are known as haploid nuclei. Source: “Diploid versus Haploid | BioNinja.” Bioninja.com.au, 2019, ib.bioninja.com.au/standard-level/topic-3-genetics/32- chromosomes/diploid-versus-haploid.html. CELL CYCLE Cells divide into new (daughter) cells through a series of events that take place in steps. The products formed in each round replicate the process in the next round. A cell cycle is thus a sequence of events that a cell goes through as it grows and divides to produce new cells. Therefore, it can be called the life cycle of a cell. Cell division is responsible for a newborn baby gradually growing into an adult. Similarly, a caterpillar turning into a butterfly. Other living organisms, such as a plant or bacteria, also follow a series of developmental stages following birth until reproduction. Source: Sciencefacts.net. 2021. [online] Available at: It is the first phase of the cell cycle, recognized by the growth period where the chromosome gets duplicated as the cell prepares for division. Interphase happens between one cell division or mitotic (M) phase and the next. It is the longest part of the cell cycle involving three sub-phases. The typical duration of this phase is 23 hours.  a. G1-phase: Also known as the first-gap phase, during this period, the cells grow in size, synthesize cell organelles and other macromolecules such as proteins that serve as the building block of the cell. The cells also accumulate sufficient energy required for division. b. S-phase: Also known as the synthesis phase, the existing DNA is copied within the nucleus. This process of DNA synthesis is also known as DNA-replication. The centrosome is also duplicated during this phase and gives rise to spindle fibers. The entire S-phase requires energy expenditure to proceed. c. G2-phase: This is the second gap phase and is somewhat similar to the G1- phase. During this period, the cells grow further in size, making more proteins and organelles. All preparations for mitosis get completed before the cells enter the mitotic phase. MITOSIS Most body cells have two copies of each chromosome. We describe these cells as diploid. When cells divide their chromosomes double beforehand. This ensures that when the cell splits in two, each new cell still has two copies of each chromosome (is still diploid). This type of cell division is used for growth, repair of damaged tissues, replacement of cells and asexual reproduction and is known as mitosis Mitosis is defined as nuclear division giving rise to genetically identical cells. Importance: All cells in the body (excluding gametes) are produced by mitosis of the zygote. Mitosis is important for replacing cell eg, skin cells, RBC's and for allowing growth (production of new cells). Occurs in: Growth: Mitosis produces new cells. Repair: To replace damaged or dead cells. Asexual reproduction: Mitosis produces offspring that are genetically identical to the parents. Process: Source: V1.nitrocdn.com. 2021. [online] Available at:https://v1.nitrocdn.com/kDXDIJNDOaszRbpagqNqUtquAQQkiLpO/assets/static/optimized/rev- 0f796fc/wp- content/uploads/2020/01/Mitosis.png Prophase: It is the first and the longest of all phases of mitosis. Prophase shows the following distinct changes within the cell. The beginning is marked by the appearance of thin thread-like condensing X shaped chromosomes. Each chromosome is made of two coiled filaments called sister chromatids. As the stage progresses, the sister chromatids become increasingly shorter and thicker that join at a site called the centromere. The two pairs of centrioles, formed during interphase, move away from each other to the opposite poles of the cell. Spindle fibers formed of microtubules and proteins begin to appear and  gradually extend across the cell between the centrioles as they move towards opposite poles. On reaching the end of this phase, the nuclear envelope starts to break apart thus releasing the chromosome. The nucleolus gradually disintegrates. The chromosomes begin to migrate towards the center of the cell, marking the end of prophase. Source: Sciencefacts.net. 2021. [online] Available at: [Accessed 30 July 2021]. Metaphase: It is the second phase of mitosis and is marked with the complete disappearance of the nuclear envelope that had started during prophase. The chromosomes, which are at their shortest and thickest stage with two sister chromatids, get attached to the spindle fibers present at the opposite poles. They then align end to end along the middle of the cell. The spindle fibers then attach to each of the sister chromatids. Source: Sciencefacts.net. 2021. [online] Available at: Anaphase: It starts by splitting each paired chromosome into two sister chromatids,  now known as daughter chromosomes. The daughter chromosomes are pulled towards the opposite end of the cell due to the contraction of the spindle fibers. At the end of this phase, each pole contains a complete set of chromosomes. Source: Sciencefacts.net. 2021. [online] Available at: Telophase: It is the last recognized phase of mitosis marked by the end of the daughter chromosome’s migration to the opposite poles. Nuclear envelopes redevelop around each group of chromosomes to form daughter nuclei. Mitotic apparatus disappears with a reduction in the viscosity of cytoplasm, followed by the synthesis of RNA. The nucleolus reappears with the chromosomes becoming slender and extended. Source: Sciencefacts.net. 2021. [online] Available at: Cytokinesis: This is the process where the cytoplasm gets divided to produce two independent daughter cells, each containing a complete set of chromosomes.  Cytokinesis begins at the anaphase stage and continues through telophase and into the interphase. In the end, mitosis results in two genetically identical daughter cells, each having diploid (2n) number of chromosomes. Source: Sciencefacts.net. 2021. [online] Available at: The Difference in Cytokinesis between Plant and Animal Cells: In animals, cytokinesis occurs through a constriction of the cell membrane in-plane of the metaphase plate, while in plants the division happens through the formation of the cell plate. MEIOSIS Meiosis is a cell division process where a single (parent) cell divides twice to produce four independent (daughter) cells, each having half the chromosomes as the original cell. The term ‘meiosis’ came from the Greek word ‘meiosis’, meaning ‘lessening’. Meiosis takes place only in the reproductive cell types (sperm and egg cells) of sexually reproducing organisms, including humans. For a cell to undergo meiosis, it must have a diploid (2n) chromosome number. Meiosis involves two successive stages or phases of cell division, meiosis I and meiosis II. Each stage includes a period of nuclear division or karyokinesis and a cytoplasmic division or cytokinesis. Although not a part of meiosis, the cells before entering meiosis I undergo a compulsory growth period called interphase. Steps of meiosis I: Prophase I: It is the longest phase of meiotic division involving a series of events and is divided into the following steps: The duplicated chromosomes condense, resembling an X-shaped structure with two sister chromatids that become distinctly visible within the nucleus. The homologous chromosome pair (one inherited from each parent) comes closer and associates along the entire chromosome length, forming a tetrad. Each tetrad is composed of four chromatids. The homologous chromosomes exchange parts of DNA with each other; this process is known as crossing over. The points of physical contact from which the genetic materials are exchanged are known as chiasmata. Spindle fibers originate from the centrioles on either side of the cell, getting attached to each chromosome’s centromere. The last step of prophase involves the breakdown of the nuclear envelope. The chromosomes then start moving towards the middle of the cell. Source: Sciencefacts.net. 2021. [online] Available at: Metaphase I: Homologous chromosomes align along the centre of the cell. The centrioles reach the opposite poles of the cell with the spindle fibers extending from them. The centromeres orient themselves towards the opposite poles of the cell. Anaphase I: The chromosomes with two sister chromatids are separated, and they begin to migrate to the opposite poles. This separation is achieved because of the contraction of the spindle fibers attached to each chromosome’s centromere. The homologous chromosomes start to migrate to the opposite poles. Telophase I: The chromosomes stop migrating with each pole containing a haploid number of chromosomes. The nuclear envelope is formed around the chromosome, and the spindle fibers disappear. The chromosomes uncoil and become less dense with the nucleolus appearing within the nucleus. Cytokinesis I: It involves the division of the cytoplasm to produce two individual daughter cells. In animals, cytokinesis occurs by constriction of the cell membrane, while in plants, it happens through the formation of a cell plate. In most cells, cytokinesis occurs at the same time as telophase. Result of meiosis I: At the end of cytokinesis I, two different daughter cells are formed, each with half the number of chromosomes as the parent cell (having 23 chromosomes having 23 pairs of chromatids). Meiosis is thus also called the reduction division. Steps of Meiosis II: The daughter cells produced in meiosis I enters the second round of division called meiosis II. Prophase II: The nuclear membrane initiates to break down, and the spindle fibers appear again. Each centriole divides, forming two pairs of centrioles. Chromosomes do not replicate any further in this phase of meiosis and begin migration towards the centre of the cell. Metaphase II: Chromosomes arrange on the equator of the cell with the help of the spindle fibers. The centrioles are now at opposite poles in each of the daughter cells. Centromere divides, producing two sister chromatids, now known as daughter chromosomes, with the spindle fibers attached to each chromosome. Anaphase II: The daughter chromosomes are pulled towards the opposite poles of the cells with the help of the spindle fibers. At the end of anaphase II, each end of the cell contains a complete set of chromosomes. Telophase II: The nuclear membrane forms around each chromosome with the disappearance of the spindle fibers. Nucleolus reappears as the cell prepares for the second round of cytoplasmic division. Cytokinesis II: This step is identical to cytokinesis I, involving the second cytoplasm division, resulting in the formation of two individual daughter cells. Result of Meiosis: Thus, at the end of meiosis II, four non-identical, haploid daughter cells are formed, each having half chromosome number as the original parent cell. Source: “Meiosis II | Biology.” Wizeprep, www.wizeprep.com/online-courses/16916/chapter/12/core/2/1  Guiding Questions 1. State cell cycle. 2. What are chromosomes, and state their location within a cell? 3. Differentiate between diploid and haploid nuclei. 4. Outline the key events that occur during each phase of mitosis (prophase, metaphase, anaphase, telophase) and cytokinesis. 5. Explain the results of meiosis. Resources: Books: ⚫ MYP Biology 4/5: A Concept Based Approach. By- David Mindorff and Andrew Allott ⚫ MYP by concepts 4 & 5. By- Andrew Davis and Patricia Bibliography: Books: ⚫ Davis, Andrew. MYP by Concept 4&5 Biology. Hodder Education, 2016. ⚫ Mackean, D. G., and Dave Hayward. Cambridge IGCSE Biology. Hodder Education, 2014. ⚫ Prasad, Anita. A Textbook of ICSE Biology. General Printers and Publishers, 2008. Websites: ⚫ https://www.sciencefacts.net/meiosis.html ⚫ https://www.sciencefacts.net/mitosis.html ⚫ https://www.savemyexams.co.uk/notes/igcse-biology-cie-new/17- inheritance/17- 1-inheritance-cell-division/17-1-4-cell-division/ ⚫ https://ib.bioninja.com.au/standard-level/topic-3-genetics/33-meiosis/stages- of- meiosis.html