General Biology 1 PDF Notes - Cell Division

GENERAL BIOLOGY 1 Charlyn Aquino Rizzandra Manubay Reynie Ann Juanito June Dexter Martinez Nur-Aina Kuram Shema Mohammad  Evaluation Activity 1.4: Dear _________, Instructions: On a ¼ sheet of paper, write a note or letter to your classmate who is absent about the important thi...

GENERAL BIOLOGY 1 Charlyn Aquino Rizzandra Manubay Reynie Ann Juanito June Dexter Martinez Nur-Aina Kuram Shema Mohammad  Evaluation Activity 1.4: Dear _________, Instructions: On a ¼ sheet of paper, write a note or letter to your classmate who is absent about the important things that s/he missed during our class discussion. LESSON 2: CELL DIVISION Context Learning Competency At the end of the lesson, I can: a. describe the stages of mitosis/meiosis and their control points given 2n=6; b. discuss crossing over and recombination in meiosis; and c. explain the significance of the given disorders and diseases that result from the malfunction of the cell during the cell cycle. Values Integration: I can demonstrate my concern for creation by being aware of the complexity of life through understanding and appreciating the beauty of one of the complex processes it has, as well as show my respect for life by recognizing the important role of cell division as a basic function of life. Essential Understanding: Cell division is the fundamental process by which organisms grow and reproduce. This complex process is essential for numerous function s, including the development of an organism from a single fertilized egg, the replacement of worn-out cells, and even the repair of wounds. There are two main types of cell division: mitosis, which is responsible for growth and repair, and meiosis, which is essential for sexual reproduction. Pre-lection Activity 2.1: Think Pair and Share Instruction: Look for a pair. With your partner, discuss the question below. A stopwatch or other timing device will be used to time the discussion for 2 minutes. After 2 minutes, look for another partner to discuss the answer to the same question. Randomly, someone from the class will be called to share their discussions. Question: What is a Cycle? Give an example. 17 Experience Concept Notes Cell Division: Mitosis and Meiosis The continuity of life, from one cell to another has its foundation in the production of cells by way of the cell cycle. The cell cycle is an orderly sequence of events that describes the stages of a cell’s life from the division of a single parent cell to the production of two new daughter cells. Mitosis is part of a cell cycle that results in identical daughter nuclei that are also genetically identical to the original parent nucleus. In mitosis, both the parent and the daughter nuclei are at the same ploidy level – diploid for most plants and animals. Meiosis employs many of the same mechanisms as mitosis. However, the starting nucleus is always diploid and the nuclei that result at the end of a meiotic cell division are haploid. Figure 2.1 Mitosis vs Meiosis 18 The Cell Cycle: Mitosis The cell cycle is an ordered series of events involving cell growth and cell division that produces two new daughter cells. Cells on the path to cell division proceed through a series of precisely timed and carefully regulated stages of growth, DNA replication, and cell division that produce two identical (clone) cells. The cell cycle has two major phases: the Interphase and the Mitotic Phase. During interphase, the cell grows and DNA is replicated. During the mitotic phase, the replicated DNA and cytoplasmic contents are separated, and the cell divides. Figure 2.2 Cell division 19 During interphase, the cell undergoes normal growth processes while also preparing for cell division. In order for a cell to move from the interphase into the mitotic phase, many internal and external conditions must be met. The three stages of interphase are called G1, S, and G2. The eukaryotic cell cycle is divided into 2 major phases: 1. Interphase a. Divided into 3 stages – G1, S, G2 b. DNA Uncondensed 2. Mitotic Phase b. 4 stages + Cytokinesis c. Prophase, Metaphase, Anaphase, Telophase, Cytokinesis (PMAT) d. Nuclear division & division of cytoplasm e. DNA condensed Table 2.1 Three stages of interphase Cell grows in size: The cell undergoes rapid growth and metabolic activity. Gap 1 Organelles are replicated: Organelles such as mitochondria and ribosomes are (G1) Phase duplicated. Replication of DNA: The cell's DNA is replicated, ensuring each daughter cell Synthesis receives a complete set of genetic information. (S) Phase Synthesis of proteins associated with DNA: Histones and other proteins necessary for DNA packaging and replication are synthesized. Synthesis of proteins associated with mitosis: Proteins necessary for the upcoming process of mitosis are synthesized. Gap 2 Double-checks the replicated chromosomes: The cell undergoes a quality (G2) Phase control check to ensure DNA replication was accurate. Repairs errors: Any mistakes or damage to DNA are repaired to maintain genomic integrity before proceeding to mitosis. Figure 2.3 Phases of cell division 20 Cyclins regulate the cell cycle only when they are tightly bound to Cdks. To be fully active, the Cdk/cyclin complex must also be phosphorylated in specific locations. Like all kinases, Cdks are enzymes (kinases) that phosphorylate other proteins. CDKs (Cyclin-dependent kinase) A family of protein kinases that are involved in regulating transcription, mRNA processing, and the differentiation of nerve cells Cyclins A group of proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinase (CDK) enzymes Figure 2.4 Cell cycle checkpoints 21 Stages of Mitotic Phase Karyokinesis, also known as mitosis, is divided into a series of phases – prophase, prometaphase, metaphase, anaphase, and telophase – that result in the division of the cell nucleus. Figure 2.5 Stages of mitotic phase Prophase Chromatin fibers condense into discrete chromosomes visible under a light microscope. Nucleoli disappear. Each chromosome, now duplicated, consists of two identical sister chromatids joined at their centromeres. The mitotic spindle begins to form, composed of centrosomes and microtubules extending from them. Shorter microtubules extending from the centrosomes are called asters. Centrosomes move apart from each other as microtubules lengthen between them, contributing to spindle formation. Metaphase The centrosomes have moved to opposite ends (poles) of the cell. The chromosomes have aligned along the metaphase plate, an imaginary plane equidistant between the spindle poles. Each chromosome centromeres are positioned precisely on this plate. Each chromosome's sister chromatids are attached to kinetochore microtubules originating from opposite spindle poles. 22 Anaphase ▪ Anaphase is the shortest stage of mitosis, often lasting only a few minutes. ▪ Each pair of sister chromatids separates, becoming individual chromosomes. ▪ The newly formed daughter chromosomes move towards opposite ends of the cell as their kinetochore microtubules shorten. This movement pulls the centromeres ahead of the chromosome arms, progressing at a rate of approximately 1 micron per minute. ▪ By the end of anaphase, both ends of the cell contain identical and complete sets of chromosomes. Telophase ▪ Two daughter nuclei form within the cell. ▪ Nuclear envelopes are created from fragments of the parent cell's nuclear envelope and other parts of the endomembrane system. ▪ Nucleoli reappear within the newly forming nuclei. ▪ Chromosomes begin to decondense, returning to their less condensed chromatin state. ▪ Any remaining spindle microtubules are depolymerized. ▪ Telophase marks the completion of mitosis, where one nucleus divides into two genetically identical nuclei. Cytokinesis ▪ Cytokinesis, or “cell motion,” is the second main stage of the mitotic phase during which cell division is completed via the physical separation of the cytoplasm components into two daughter cells. ▪ Animal cells undergo cytokinesis through the formation of a cleavage furrow. A ring of microtubules contracts, pinching the cell in half. ▪ Plant cells undergo cytokinesis by forming a cell plate between the two daughter nuclei. Figure 2.6 Cytokinesis 23 Uncontrolled Mitosis Cancer cells defy normal cell cycle regulations, persistently dividing even in the absence of growth factors. This disregard often stems from genetic mutations altering protein functions involved in cell cycle control or signaling pathways. Unlike normal cells, cancer cells may divide indefinitely, exhibiting random cell cycle checkpoint bypassing. They also evade apoptosis and can transform into tumors, some of which become malignant and spread through metastasis.. ▪ Malignant tumors metastasize, or break away, and can form more tumors. ▪ Benign tumors remain clustered and can be removed Oncogenes are special proteins that increase the chance that a normal cell develops into a tumor cell. Oncology is the study of cancer Cell checkpoints are times when the cell is supposed to stop and check itself, these are disabled in cancer cells. Figure 2.7 Uncontrolled Mitosis The cell cycle: Meiosis Sexual reproduction requires fertilization, the union of two cells from two individual organisms. If those two cells each contain one set of chromosomes, then the resulting cell contains two sets of chromosomes. Haploid cells contain one set of chromosomes. Cells containing two sets of chromosomes are called diploid. The number of sets of chromosomes in a cell is called ploidy level. Figure 2.8 Union of two cells from two individual organisms 24  If the reproductive cycle is to continue, then the diploid cell must somehow reduce its number of chromosome sets before fertilization can occur again, or there will be a continual doubling in number of chromosome sets in every generation. So, in addition to fertilization, sexual reproduction includes a nuclear division that reduces the number of chromosome sets. A single cell divides into four unique daughter cells. Daughter cells have half the # of chromosomes as parent cell, so they are considered haploid. Ploidy - Refers to the number of sets of chromosomes in cells. ▪ Haploid - one copy of each chromosome - designated as “n”, the number of chromosomes in one “set” - gametes ▪ Diploid - two sets of chromosomes - two of each chromosome - designated as “2n” - somatic cells - organisms receive one of each type of chromosome from female parent (maternal chromosomes) and one of each type of chromosome from male parent (paternal chromosomes) Figure 2.9 Difference between haploid and diploid chromosomes 25 Homologues = Chromosomes exist in homologous pairs in diploid (2n) cells. Exception: Sex chromosomes (X, Y). Other chromosomes, known as autosomes, have homologues. Autosomes = An autosome is any of the numbered chromosomes, as opposed to the sex chromosomes. Humans have 22 pairs of autosomes and one pair of sex chromosomes (the X and Y). Figure 2.10 Autosomes and sex chromosomes At fertilization, 23 chromosomes are donated by each parent. Total = 46 or 23 pairs Gametes (sperm/ova): ▪ Contain 22 autosomes and 1 sex chromosome. ▪ Are haploid (haploid number “n” = 23 in humans) Fertilization results in diploid zygote. ▪ Diploid cell; 2n = 46. (n = 23 in humans) Stages of Meiosis Phase Figure 2.11 Stages of Meiosis 26 Meiosis I During DNA duplication in the S phase, each chromosome is replicated to produce two identical copies, called sister chromatids, that are held together at the centromere by cohesin proteins. Cohesin hold the chromatids together until anaphase II. The centrosomes, which are the structures that organize the microtubules of the meiotic spindle, also replicate. This prepares the cell to enter prophase I, the first meiotic phase. Prophase I ▪ Centrosome movement, spindle formation, and nuclear envelope breakdown occur, similar to mitosis. ▪ Chromosomes progressively condense. ▪ Early in prophase I, chromosomes pair with their homologs and undergo crossing over, where DNA segments exchange between nonsister chromatids. ▪ By the stage shown, homologous pairs exhibit X-shaped regions called chiasmata, marking sites of crossover events. ▪ Later in prophase I, microtubules from opposite poles attach to kinetochores on each homologous pair, moving them towards the metaphase plate for alignment in metaphase I. Metaphase I ▪ Homologous chromosomes are aligned at the metaphase plate, with one chromosome of each pair facing each pole of the cell. ▪ Each pair of homologous chromosomes has independently lined up, a process known as independent assortment. ▪ Kinetochore microtubules from one pole attach to both chromatids of one homolog, while microtubules from the opposite pole attach to the chromatids of the other homolog. Anaphase I ▪ Proteins responsible for sister chromatid cohesion along chromatid arms break down, allowing homologous chromosomes to separate. ▪ The separated homologous chromosomes move towards opposite poles of the cell, guided by the spindle apparatus. ▪ Despite the breakdown of cohesion along the arms, cohesion at the centromere persists. This causes the two chromatids of each chromosome to move together toward the same pole, ensuring each daughter cell receives a complete set of chromosomes during meiosis I. Telophase I ▪ Each half of the cell now contains a complete haploid set of duplicated chromosomes, with each chromosome consisting of two sister chromatids, some of which may have regions of nonsister chromatid DNA. Cytokinesis ▪ Cytokinesis, the division of the cytoplasm, typically occurs concurrently with telophase I, resulting in the formation of two haploid daughter cells. ▪ In animal cells, a cleavage furrow forms to divide the cytoplasm, whereas in plant cells, a cell plate forms. ▪ In some species, chromosomes decondense, and nuclear envelopes reassemble around the separated chromosomes. ▪ Importantly, there is no duplication of chromosomes between meiosis I and meiosis II, ensuring that each daughter cell from meiosis I enters meiosis II with a haploid set of chromosomes. 27  Meiosis II During meiosis II, the sister chromatids within the two daughter cells separate, forming four new haploid gametes. The mechanics of meiosis II is similar to mitosis, except that each dividing cell has only one set of homologous chromosomes. Therefore, each cell has half the number of sister chromatids to separate out as a diploid cell undergoing mitosis. Prophase II ▪ Sister Chromatids condense. A new spindle begins to form. The nuclear envelope starts to fragment. Prometaphase II ▪ The nuclear envelope disappears, and the spindle fibers engage the individual kinetochores on the sister chromatids. Metaphase II ▪ The sister chromatids are maximally condensed and aligned at the equator of the cell. Anaphase II ▪ The sister chromatids are pulled apart by the kinetochore microtubules and move toward opposite poles. Non-kinetochore microtubules elongate the cell. Telophase II ▪ The chromosomes arrive at opposite poles and begin to decondense. Nuclear envelopes form around the chromosomes. Cytokinesis ▪ Cytokinesis separates the two cells into four unique haploid cells. At this point, the newly formed nuclei are both haploid. The cells produced are genetically unique because of the random assortment of paternal and maternal homologs and because of the recombining of maternal and paternal segments of chromosomes (with their sets of genes) that occurs during crossover. Table 2.2 Different events between Meiosis I and Meiosis II Meiosis I Meiosis II Synapsis occur No synapsis Crossing over occurs No crossing over In Metaphase I, paired homologous In Metaphase II, sister chromatids line up at chromosomes line up at equator equator In Anaphase I, paired homologous In Anaphase II, sister chromatids separate and chromosomes separate and move to opposite move to opposite poles poles At the end of the Meiosis I, 2 haploid cells are At the end of Meiosis II, 4 haploid cells are formed formed 28 Table 2.3 Difference between Mitosis and Meiosis Cell Division MITOSIS MEIOSIS Number of division 1 2 Number of daughter cells 2 4 Genetically identical YES NO Same as parent Half of parent Chromosomes # (Diploid) (Haploid) Somatic Cells Sex Cells Where (Body cells) (Reproductive cells) When Throughout life At sexual maturity Role Growth and repair Sexual reproduction Nondisjunction Nondisjunction means that a pair of homologous chromosomes as failed to separate or segregate at anaphase so that both chromosomes of the pair pass to the same daughter cell. This probably occurs most commonly in meiosis, but it may occur in mitosis to produce a mosaic individual. The cause(s) of nondisjunction is not known; the following are some possibilities. Abortuses and neonates with trisomy 21 and with trisomy 18 are associated with increasing maternal age, suggesting the mother's age may be an important etiological factor. Structural abnormalities of the chromosomes such as translocations and pericentric inversions may interfere with chromosome pairing at meiosis and promote nondisjunction. Some families seem to have an inherited tendency for nondisjunction; for example, they may have several children with trisomy 21 or they may have a child with Klinefelter's syndrome and another with Down's syndrome. Mitotic Nondisjunction occurs during anaphase when sister chromatids fail to separate. Meiotic Nondisjunction is of two types. In the first type, due to nondisjunction during meiosis I, homologous chromosomes fail to segregate at anaphase I and lead to all the haploid cells with an abnormal number of chromosomes. The second type of nondisjunction occurs during meiosis II when sister chromatids fail to segregate. It leads to half of the haploid cells with abnormal chromosomes. Figure 2. 12 Difference between normal chromosome and nondisjunction 29 Types of Chromosomal Aberrations Structural Chromosome Abnormalities 1. Deletion - loss of a portion of one chromosome. When this chromosome is passed onto offspring the result is usually lethal due to missing genes Example: Angelman syndrome Figure 2.13 Deletion 2. Duplication – A portion of a chromosome is duplicated, resulting in extra genetic material. Example: Fragile X syndrome Figure 2.14 Duplication 3. Inversion – A portion of the chromosome has broken off, turned upside down, and reattached. As a result, the genetic material is inverted. Example: Increase the risk of miscarriage Figure 2.15 inversion 4. Translocation – A portion of a chromosome is moved from one chromosome to another Example: Chronic Myelogenous leukemia Figure 2.16 translocation 30 5. Insertion – Is a mutation where one portion of a chromosome is inserted into another. In this case, genetic material is not wrapped; it is just moved to another chromosome. Figure 2.17 insertion Numerical Chromosome Abnormalities 1. Monosomy ( 2n-1)- the term "monosomy" is used to describe the absence of one member of a pair of chromosomes. Therefore, there is a total of 45 chromosomes in each cell of the body, rather than 46. For example, if your baby is born with only one X chromosome, rather than the usual pair (either two X's or one X and one Y chromosome), your baby would be said to have "monosomy X." Monosomy or partial monosomy is the cause of certain diseases. Example: Turner's syndrome Figure 2.18 Turner’s syndrome karyotype 31 2. Trisomy ( 2n +1)–. The term ‘’Trisomy ‘’ is used to describe the presence of 3 chromosomes, rather than the usual pair of chromosomes. For example, if your baby is born with a 3 number 21 chromosome, rather than the usual pair, your baby would be said to have ‘’Trisomy 21” which causes down syndrome. Other examples of trisomy include trisomy 18 or trisomy 13. simply means 3 copies of the there 3 copies of the number 18 chromosome or number 13 chromosome present in each cell of the body, rather than the usual pair. Example: Down’s syndrome Figure 2.19 Down’s syndrome karyotype. 3. Tetrasomy ( 2n +2) – This occurs when four total copies of a chromosome are present. Tetrasomy is extremely rare. Example: Tetrasomy 9p Figure 2.20 Tetrasomy WATCH THE ANIMATION HERE: Gram Positive vs Gram Negative Bacteria https://www.youtube.com/watch?v=Didrc3wJ3E8 Prokaryotic cell: Flagella and Fimbriae https://www.youtube.com/watch?v=VzqC7nag6KM The Secret Life of a Cell, Part 3 - The Nucleus https://www.youtube.com/watch?v=zwA96STHLW8 FURTHER READING: Ayuste, T. D. (2017). General biology 1. Diwa learning systems, Inc. 32  REFERENCES BOOKS ✓ Ayuste, T. D. (2017). General biology 1. Diwa learning systems, Inc. ✓ Belardo, G. M. (2015). General biology 1. Vibal Group. ✓ Cabrido, A. (2016). Biology 1. Books Atbp. Publishing Corp. ✓ Freeman, S. (2002). Biological science. Prentice-Hall, Inc. ✓ Ramos, A. M., Ramos, J. A., & Sabile, M. G. (2006). Exploring life through science – biology. Teacher’s guide. Phoenix Publishing House, Inc. WEBSITE ✓ Jennings, D. (2016). Meiosis illustration identification. Retrieved from, http://www.quia.com/jg/1294967list.html ✓ Meiosis II. (2016). Retrieved from, http://27.109.7.67:1111/econtent/animal- cell/meiosis2.php ✓ Schroer, T.A. (2016). Cell cycle 4: Mitosis. Retrieved from, http://www.pha.jhu.edu/~guzheng/old/webct/note7_6.htm ✓ Blamire, J. (2002). Prophase I. Retrieved from, http://www.Brooklyn.cuny.edu/bc/ahp/LAD/C9/C9_m_prophase.htm IMAGES ✓ Figure 2.1 sciencefacts.net ✓ Figure 2.2 CBSE Neet biology Notes ✓ Figure 2.3 online biology notes ✓ Figure 2.4 diwa learning system inc ✓ Figure 2.5 www2.le.ac.uk ✓ Figure 2.6 differencebetween.com ✓ Figure 2.7 slideplayer.com ✓ Figure 2.8 slideplayer.com ✓ Figure 2.9 geeksforgeeks.com ✓ Figure 2.10 differencebetween.com ✓ Figure 2.11 microbenotes.com ✓ Figure 2.12 Nondisjunction DP IB Biology ✓ Figure 2.13 Yourgenome.com ✓ Figure 2.14 Yourgenome.com ✓ Figure 2.15 Yourgenome.com ✓ Figure 2.16 Yourgenome.com ✓ Figure 2.17 Yourgenome.com ✓ Figure 2.18 Yourgenome.com ✓ Figure 2.19 Yourgenome.com ✓ Figure 2.20 Yourgenome.com 33 Independent Practice Activity 2.2: Mitosis VS Meiosis Venn Diagram Instructions: Below is a list of characteristics regarding cell division arrange them in their respective places in the Venn diagram. Submit your output in a separate sheet of paper. Aims to create gamete Chromosome movement by spindle fibers. Facilitates growth and repair Generates diploid cells Genetically diverse cells Half the DNA content Identical daughter cells Involve stages of prophase, metaphase, anaphase, and telophase. Involves asexual reproduction Involves sexual reproduction Processes end with cytokinesis. Produces haploid cells Resulting in daughter cells. Same DNA content as the parent Spindle fibers attach to kinetochores. 34  Guide to Writing a Laboratory Report I. Objectives Purpose: Clearly state the goals of the experiment. A concise statement of what you are trying to discover or prove. Laboratory experiments are given to discover concepts or prove/disprove theories/laws. In cases where proving/disproving laws serve as the main purpose of the experiment, objectives should be written where the group's hypothesis is emphasized. (e.g. Compare the calculated and measured total resistance of resistors arranged in series and parallel) Specific outcomes you expect to achieve. You may start your objective using the following adjectives: describe, compare, identify, etc. Refrain from using words such as learn, understand, etc. or any other words that are not measurable II. Introduction Purpose: Provide background information and context for the experiment. A brief overview of the scientific concepts related to the experiment. Limit it to one to two paragraphs only. Each paragraph should only consist of a maximum of five sentences. Any relevant history or prior research. Make sure to cite your sources correctly. Explanation of why the experiment is important or identify the aim of the experiment. III. Data and Results Purpose: Present the raw data collected during the experiment and summarize the findings. Tables, charts, or graphs showing the data from the data/observation sheet Clear photos, labels, and units for all measurements. IV. Analysis Purpose: Interpret the data and explain what it means. All pictures, tables, charts, or graphs must be interpreted. A detailed discussion of the results backed up with facts based on discussion or related literature. Make sure to correctly cite the sources. Possible explanations for any discrepancies. Any sources of error and their potential impact on the results. V. Guide Questions Purpose: Ensures the understanding and articulation of the main goals of the experiment. Ensure your response directly answers the question. Cite the sources correctly. Use appropriate scientific terms to demonstrate your understanding. 35 VI. Conclusion Purpose: Summarize the findings and their implications. A restatement of the experiment's objective and whether it was achieved. A brief restatement on what went wrong on objectives that were not met. A summary of the main findings. The significance of the results. Suggestions for further research or improvements of the experiment. THE USE OF AI Purpose: To regulate the use of AI in creating the laboratory report All laboratory reports will be submitted online (via google classroom) and face- to-face (printed hard copy) AI tools may be utilized ONLY for improving the readability and language of the laboratory report (e.g. grammar and style checking). AI tools must NOT be used to create the content (e.g. results and discussion) of your laboratory report. (Note: This is adapted from the recommendations of UPLB Graduate School regarding the use of AI tools) If the AI tool detects that more than 50% of the output is AI generated, each segment with AI-generated content will have a due deduction of points. If the AI tool detects that the submitted output is 80-100% AI-generated, the group will be given zero (0) as a score for the laboratory report. Some AI tools that can be used are the following but not limited to: turnitin.com, gptzero.me, quillbot.com, and writer.com. Before the Experiment 1. Read the laboratory procedure: Understand the experiment's objectives and the scientific concepts involved. 2. Prepare the borrower’s slip: Take note of the apparatus and reagents that are needed in the experiment. There is an allotted time of 15 minutes for the requisition of materials during the scheduled laboratory experiment. During the Experiment 1. Make sure all necessary materials are ready: You will not be allowed to do the experiment if the materials for each group are not complete. 2. Follow the procedure: Carefully follow the steps outlined in the lab manual. 3. Record data accurately: Ensure all measurements are precise and noted immediately. 4. Observe carefully: Note any unexpected results or observations. After the Experiment 1. Organize your data: Use tables or graphs to make your data clear and understandable. 2. Analyze your results: Discuss what the data means and how it relates to your objectives 3. Write clearly: Ensure each section of your report is concise and well-organized. 4. Review your work: Check for any errors or omissions before submitting your report. 5. Submission of Laboratory Report: On the agreed date, submit the hard copy to your teacher in class and upload the soft copy in Google Classroom. You may opt to have it printed on both sides of the paper for minimal paper consumption. 36 Reflection Topic: Cell Division Date: _________________ 1. How does learning about mitosis and meiosis help me understand the complexity of life? How does it influence my daily actions and commitment to respecting life and caring for others? 2. What are the key concepts I have learned in cell division? How does it reinforce my understanding of the importance of complex processes that sustain life? 3. What strategies did I use to understand complex concepts related to cell division? Is it effective? Action Performance Task: Laboratory Activity on Cell Division Perform an experiment on Cell Division and submit a GOAL Laboratory Report ROLE Cytologist AUDIENCE Farmers of Zamboanga City Farmers of Zamboanga City have been struggling with the slow growth of their crops and the abnormal growth of their livestock. As an expert in the field of cytology, you study the SITUATION cellular growth of the onion by investigating its root tip to determine the problem on the crops and to explain how mutation happens by studying the cell division among chickens and cows. PERFORMANCE/ Laboratory Experiment and Laboratory Report PRODUCT Please refer to the rubric for the grading of the Laboratory STANDARD activities on page 99. 37 Laboratory Experiment: Cell Cycle: Mitosis and Meiosis The second cell division in Meiosis is known as Meiosis II. Meiosis II is very similar to Mitosis. In both cases chromosomes line up and sister chromatids are separated by the action of the spindle fibers. The daughter cells are genetically identical to one another. There are some minor differences between Mitosis and Meiosis II. Cells at the start of Mitosis II are haploid. Cells at the start of have the normal ploidy of the organism they are in. Normally we think of Mitosis as occurring in diploid cells but in many organisms, it can occur in haploid cells as well. Materials to be borrowed: Materials to bring: Compound microscope Prepared rooted onion bulb Glass slide Medicine dropper Coverslip Cutter Alcohol lamp Paper towel Ruler Coloring materials Pencil Chemicals: Aceto-alcohol fixative Acetocarmine Stain 0.1M HCl Prepared slides: Allium cepa Procedure: Part 1.1.Preparation and Harvesting of Onion Bulbs 1. Select healthy onion bulbs without any signs of damage or decay and remove any dry outer layers of the onion bulbs. 2. Fill glass jars or beakers with enough distilled water to cover the base of the onion bulbs. 3. Place the onion bulbs root-end down into the jars. Ensure that only the root area is submerged in water and place the jars in a location with indirect sunlight at room temperature. 4. Allow the onions to grow for 4-5 days. 5. Once the roots have grown to about 1-2 cm in length, carefully remove the onion bulbs from the jars. 6. Using forceps, gently cut the root tips (about 1-2 cm from the root end) for staining and transfer them into a freshly prepared aceto-alcohol fixative (1:3 glacial acetic acid:ethanol mixture). 38 Part 1.2 Preparing the Root Tips for Staining 1. Place the root tips on a clean microscope slide and wash then in water. 2. Place one drop of 0.1 M HCl and heat for 5-10 seconds. 3. Allow to cool for 1-2 minutes, Rinse with 2-3 drops of water.Add 2-3 drops of acetocarmine stain onto the root tips. 4. Gently heat the slide over a flame or hot plate for about 30 seconds to intensify the staining, avoiding boiling the stain. 5. Wait for 20-30 minutes to allow it to cool, and cut it longitudinally. 6. Use the eraser of a pencil to gently press down on the coverslip to squash the root tip, spreading the cells into a single layer. 7. Place the slide under a compound microscope. 8. Start with a low magnification to locate the root tip and then switch to higher magnifications to observe the mitotic stages in the cells. Part 2 Examining Prepared Slides 1. Place a prepared slide on the microscope stage. 2. Start with the lowest magnification to locate the cells, then switch to higher magnifications for detailed observation. 3. Observe and note the cell structure, identifying key components such as the cell wall, cell membrane, nucleus, and other organelles. 4. Compare the structures observed in prepared slides with those seen in stained onion and cheek cells. Part 3 Meiosis Diagram the process of meiosis. Label completely the events such as Homologous Chromosomes, Crossing Over, Loci, Centrosomes, and Cleavage Furrow). Use colored pencils/crayons to draw chromosomes (use one color for the parental chromosomes and another color for the maternal chromosomes). 39 Evaluation Activity 2.3: Modified 3,2,1 Instructions: Based on the lesson discussed, complete the given statements. Write your answer on a separate sheet of paper. 3 Things I learned today…. 2 interesting facts about the lesson…. 1 question I have in mind…. I feel….. 40