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SAJANS E CLASS
Saturday, July 12, 2025
LIBRARY BOOK DATA ENTRY
Saturday, November 16, 2024
CELLDIVISION AND MULTIPLAICATION
Notes on Cell Division and Multiplication
Introduction
Cell division is a fundamental biological process through which a parent cell divides into two or more daughter cells. This process is essential for growth, development, and maintenance of all living organisms. There are two primary types of cell division: mitosis and meiosis.Types of Cell Division
1. Mitosis
- Definition: Mitosis is the process of nuclear division that results in two genetically identical daughter cells, each with the same number of chromosomes as the parent cell.
- Purpose:
- Growth and development
- Tissue repair and regeneration
- Asexual reproduction in some organisms
- Phases of Mitosis:
- Prophase: Chromatin condenses into visible chromosomes; the nuclear envelope begins to break down.
- Metaphase: Chromosomes align at the cell's equatorial plane (metaphase plate).
- Anaphase: Sister chromatids are pulled apart to opposite poles of the cell.
- Telophase: Nuclear envelopes reform around each set of chromosomes; chromosomes begin to de-condense.
- Cytokinesis: The cytoplasm divides, resulting in two separate daughter cells.
2. Meiosis
- Definition: Meiosis is a specialized form of cell division that reduces the chromosome number by half, producing four genetically diverse haploid cells (gametes).
- Purpose:
- Sexual reproduction (formation of sperm and eggs)
- Increases genetic diversity through recombination and independent assortment.
- Phases of Meiosis:
- Meiosis I:Prophase I
- Meiosis II (similar to mitosis):Prophase II, Metaphase II, Anaphase II, Telophase II, and Cytokinesis result in four haplo
id cells.
Importance of Cell Division
- Growth and Development: Mitosis allows organisms to grow from a single fertilized egg into complex multicellular beings.
- Tissue Repair: Mitosis replaces damaged or dead cells, maintaining tissue integrity.
- Genetic Diversity: Meiosis introduces genetic variation essential for evolution and adaptation in populations.
Regulation of Cell Division
- Cell division is tightly regulated by various mechanisms to ensure proper growth and prevent uncontrolled proliferation (cancer). Key regulatory proteins include:
- Cyclins and cyclin-dependent kinases (CDKs)
- Tumor suppressor genes (e.g., p53)
- Oncogenes
Conclusion
Cell division is a critical biological process that underpins growth, reproduction, and maintenance in living organisms. Understanding both mitosis and meiosis is essential for studying biology, genetics, and medicine.ICT TRAINING
Saturday, February 25, 2023
CELL STRUCTURE
LEARNING OUTCOMES
1. Students will understand the structures and purposes of basic components of prokaryotic and eukaryotic cells, especially macromolecules, membranes, and organelles
2. Students will understand how these cellular components are used to generate and utilize energy in cells 3. Students will understand the cellular components underlying mitotic cell division.
4. Students will apply their knowledge of cell biology to selected examples of changes orlosses in cell function. These can include responses to environmental or physiological changes, or alterations of cell function brought about by mutation.
8.1 WHAT IS A CELL?
Unicellular organisms are capable of (i) independent existence and (ii) performing the essential functions of life. Anything less than a complete structure of a cell does not ensure independent living. Hence, cell is the fundamental structural and functional unit of all living organisms. Anton Von Leeuwenhoek first saw and described a live cell. Robert Brown later discovered the nucleus. The invention of the microscope and its improvement leading to the electron microscope revealed all the structural details of the cell.
8.2 CELL THEORY
In 1838, Matthias Schleiden, a German botanist, examined a large number of plants and observed that all plants are composed of different kinds of cells which form the tissues of the plant. At about the same time, TheodoreSchwann (1839), a British Zoologist, studied different types of animal cells and reported that cells had a thin outer layer which is today known as the ‘plasma membrane’. He also concluded, based on his studies on plant tissues, that the presence of cell wall is a unique character of the plant cells. On the basis of this, Schwann proposed the hypothesis that the bodies of animals and plants are composed of cells and products of cells. Schleiden and Schwann together formulated the cell theory. This theory however, did not explain as to how new cells were formed. Rudolf Virchow (1855) first explained that cells divided and new cells are formed from pre-existing cells (Omnis cellula-e cellula). He modified the hypothesis of Schleiden and Schwann to give the cell theory a final shape. Cell theory as understood today is: (i) all living organisms are composed of cells and products of cells. (ii) all cells arise from pre-existing cells.
8.3 AN OVERVIEW OF CELL
You have earlier observed cells in an onion peel and/or human cheek cells under the microscope. Let us recollect their structure. The onion cell which is a typical plant cell, has a distinct cell wall as its outer boundary and just within it is the cell membrane. The cells of the human cheek have an outer membrane as the delimiting structure of the cell. Inside each cell is a dense membrane bound structure called nucleus. This nucleus contains the chromosomes which in turn contain the genetic material, DNA. Cells that have membrane bound nuclei are called eukaryotic whereas cells that lack a membrane bound nucleus are prokaryotic. In both prokaryotic and eukaryotic cells, a semi-fluid matrix called cytoplasm occupies the volume of the cell. The cytoplasm is the main arena of cellular activities in both the plant and animal cells. Various chemical reactions occur in it to keep the cell in the ‘living state’. Besides the nucleus, the eukaryotic cells have other membrane bound distinct structures called organelles like the endoplasmic reticulum (ER), the golgi complex, lysosomes, mitochondria, microbodies and vacuoles. The prokaryotic cells lack such membrane bound organelles. Ribosomes are non-membrane bound organelles found in all cells – both eukaryotic as well as prokaryotic. Within the cell, ribosomes are found not only in the cytoplasm but also within the two organelles – chloroplasts (in plants) and mitochondria and on rough ER. Animal cells contain another non-membrane bound organelle called centrosome which helps in cell division. Cells differ greatly in size, shape and activities (Figure 8.1). For example, Mycoplasmas, the smallest cells, are only 0.3 µm in length while bacteria
Wednesday, February 22, 2023
Wednesday, April 6, 2022
Thursday, February 10, 2022
Thursday, December 2, 2021
KIDNEY FUNCTIONS
Kidneys areexcretory organs they help to remove nitrogenous waste from our body
Saturday, October 9, 2021
Friday, July 2, 2021
Monday, March 8, 2021
SAMPLING
What Is Sampling?
Sampling is a process used in statistical analysis in which a predetermined number of observations are taken from a larger population. The methodology used to sample from a larger population depends on the type of analysis being performed, but it may include simple random sampling or systematic sampling.
KEY TAKEAWAYS
- Certified Public Accountants use sampling during audits to determine the accuracy and completeness of account balances.1
- Types of sampling include random sampling, block sampling, judgement sampling, and systematic sampling.
- Companies use sampling as a marketing tool to identify the needs and wants of their target market.
PLEASE LISTEN THE AUDIO