1. THE FUNDAMENTAL UNIT OF LIFE Discovery of Cells (1665): Robert Hooke discovered cells in a thin slice of cork using a self- designed microscope. This observation marked the first identification of cells, resembling compartments in a honeycomb. Fundamental Units of Life: Cells are the fundamental units of life. They can be unicellular (single-celled organisms) or multicellular (organisms with many cells). Cell Division and Origin: Cells divide to produce more cells of their kind. Every multicellular organism originates from a single cell. Specific Organelles: Cells have specific organelles that perform distinct functions. These organelles contribute to the cell's overall functionality. Division of Labor: Within cells, there is a division of labor where organelles perform specific functions. This specialization allows cells to efficiently carry out various tasks. Main Components of Cells: Cells consist of three main components: plasma membrane, nucleus, and cytoplasm.

2. These features facilitate cell activities and interactions with the environment. Uniformity of Organelles: All cells, regardless of their function or the organism they belong to, have the same organelles. This uniformity is observed in the basic structure of cells. Central Role of Organelles: All cellular functions occur within organelles. Organelles collectively constitute the basic unit of life, the cell. PLASMA MEMBRANE Plasma Membrane Function: The plasma membrane is the outermost covering of a cell, separating its contents from the external environment. It regulates the entry and exit of materials in and out of the cell. Selective Permeability: The membrane allows certain materials to pass through while restricting others. Examples include the passage of carbon dioxide, oxygen, and water. Diffusion and Gaseous Exchange: Diffusion, a fundamental process, facilitates the movement of gases like carbon dioxide and oxygen. Gaseous exchange between cells and the environment relies on this process. Osmosis:

3. Osmosis is a specific type of diffusion through a selectively permeable membrane. It involves the net movement of water across the membrane toward higher solute concentration. Effects of Osmosis on Cells: Placing cells in a solution can result in gaining water (hypotonic), becoming isotonic, or losing water (hypertonic) by osmosis. Examples include gaining water by an egg or water absorption by plant roots. Importance of Diffusion: Diffusion is essential for exchanging gases and water within a cell. It plays a crucial role in obtaining nutrition from the cell's environment. Composition of Plasma Membrane: The plasma membrane is flexible and composed of lipids and proteins. Observation of its structure requires an electron microscope. Endocytosis: The flexibility of the cell membrane enables endocytosis, a process where the cell engulfs food and materials from the external environment. Amoebas use endocytosis for acquiring nutrients. Electron Microscope Visibility: The organic molecules, lipids, and proteins making up the membrane can only be observed through an electron microscope.

4. Characteristic Osmosis Diffusion Definition Net movement of water across a selectively permeable membrane towards higher solute concentration. Movement of particles from an area of higher concentration to an area of lower concentration. Medium of Movement Specifically involves the movement of water molecules. Involves the movement of various substances, including gases and solutes. Type of Process A specialized type of diffusion. A general process that can involve various substances. Selectively Permeable Membrane Requires a selectively permeable membrane. Can occur through any permeable membrane. Direction of Movement Towards higher solute concentration. From an area of higher concentration to an area of lower concentration. Involvement in Gaseous Exchange Not directly involved in exchanging gases. Crucial for exchanging gases such as oxygen and carbon dioxide. Examples - Gaining water by an egg in a hypertonic - Movement of oxygen into cells and carbon

5. solution. dioxide out of cells. Cell Effects Can cause cells to gain water (hypotonic), become isotonic, or lose water (hypertonic). Essential for nutrient absorption, waste removal, and maintaining cellular balance. Importance Critical for maintaining water balance in cells and biological systems. Fundamental for various physiological processes, including nutrient transport and waste elimination. Cell Wall: Composition: Mainly composed of cellulose. Function: Provides structural strength to plant cells. Response to Osmosis: When a plant cell loses water through osmosis, it undergoes plasmolysis, shrinking away from the cell wall. Importance: Allows plant cells, as well as cells in fungi and bacteria, to withstand dilute external media without bursting. Tolerance to Changes: Can endure greater changes in the surrounding medium compared to animal cells. Nucleus: Appearance: Darkly colored, spherical or oval dot-like structure near the center of the cell. Role: Plays a central role in cellular reproduction and determines the cell's development and form at maturity.

6. Contents: Contains chromosomes, visible as rod-shaped structures during cell division. Chromosomes: Carry information for the inheritance of traits from parents to the next generation in the form of DNA molecules. Nuclear Structure (Prokaryotes vs. Eukaryotes): Prokaryotes: Lack a defined nuclear membrane. Examples include bacteria. Eukaryotes: Have a nuclear membrane. Examples include plant and animal cells. Organelles: Prokaryotic cells lack most cytoplasmic organelles present in eukaryotic cells. Chromosomal Structure: Chromosomes in eukaryotes are enclosed in a nucleus, while in prokaryotes, the nuclear region is poorly defined.

7. Characteristic Prokaryotic Cell Eukaryotic Cell Nuclear Structure Lack a true nucleus; DNA is present in the nucleoid region, not enclosed by a membrane. True nucleus with a nuclear membrane enclosing DNA. Membrane-bound Organelles Lack membrane- bound organelles (except for some membranous structures like ribosomes). Contain membrane- bound organelles (e.g., mitochondria, endoplasmic reticulum, Golgi apparatus). Chromosomes Single, circular chromosome (typically); no histones. Multiple linear chromosomes with histones. Cell Size Generally smaller (1-5 micrometers). Larger (10-100 micrometers). Cell Division Binary fission (simple cell division). Mitosis and meiosis (complex cell division processes). Cytoplasmic Structure Simple cytoplasm with no cytoskeleton. Complex cytoplasm with a well-developed cytoskeleton. Examples Bacteria and Archaea. Protists, fungi, plants,

8. and animals. Flagella Structure Simple, composed of a single protein flagellin. Complex, composed of microtubules in a 9+2 arrangement. Chloroplasts Absent (photosynthesis occurs in the cell membrane). Present in plant cells; site of photosynthesis. Endomembrane System Absence of endoplasmic reticulum, Golgi apparatus. Endoplasmic reticulum, Golgi apparatus present. Nuclear Envelope Absent. Present, separating the nucleus from the cytoplasm. Example Microorganisms Bacteria (e.g., Escherichia coli). Animal cells, plant cells, fungi (e.g., Saccharomyces cerevisiae). Chlorophyll in Prokaryotic Cells: Association: Chlorophyll in photosynthetic prokaryotic bacteria is associated with membranous vesicles. Difference from Eukaryotic Cells: Unlike eukaryotic cells, chlorophyll in prokaryotes is not associated with plastids.

9. Cytoplasm: Fluid content inside the plasma membrane. Contains specialized cell organelles that perform specific functions for the cell. Prokaryotic vs. Eukaryotic Cells: Prokaryotes lack membrane-bound cell organelles. Eukaryotic cells have nuclear membranes and membrane-enclosed organelles. Importance of Cell Organelles: Cell organelles are crucial for carrying out specific functions in cells. Examples of Cell Organelles:

10. Endoplasmic reticulum (ER), Golgi apparatus, lysosomes, mitochondria, and plastids. Endoplasmic Reticulum (ER): Large network of membrane-bound tubes and sheets. Two types: Rough ER (RER) with attached ribosomes for protein manufacture, and Smooth ER (SER) for lipid manufacture andCrucial for detoxifying poisons and drugs. Lysosomes: Membrane-bound sacs filled with digestive enzymes. Made by Rough ER. Digest foreign material and worn-out cell organelles. Made by the Reactive Enzyme Receptor (REER). Break down complex substances into simpler ones. When damaged, lysosomes may burst, and enzymes digest their own cell. Golgi Apparatus: First described by Camillo Golgi. Consists of membrane-bound vesicles arranged in stacks (cisterns). Functions include storage, modification, and packaging of products. Lysosomes may burst if damaged, and enzymes can digest their own cell. Camillo Golgi: Born in 1843, studied medicine, and developed the 'black reaction' staining technique. Golgi apparatus consists of membrane-bound vesicles arranged in stacks (cisterns).

11. Functions include storage, modification, and packaging of products. Functions of Golgi Apparatus: Storage, modification, and packaging of products in vesicles. Some complex sugars may be synthesized from simple sugars. Mitochondria: Powerhouses of the cell. Have two membrane coverings: outer membrane (porous) and inner membrane (deeply folded). Release energy in the form of ATP (energy currency of the cell). Have their own DNA and ribosomes, allowing them to make some of their own proteins. Plastids: Present only in plant cells. Two types: chromoplasts (colored) and leucoplasts (white or colorless). Chloroplasts contain chlorophyll, while leucoplasts store starch, oils, and protein granules. Vacuoles: Storage sacs for solid or liquid contents. Provide turgidity and rigidity to the cell. Cell Functions: Fundamental structural unit of living organisms. Basic functional unit of life. Performs functions like respiration, nutrition, waste clearance, and protein synthesis.

12. Cell Division: Process essential for growth, replacement, and reproduction in organisms. Types of Cell Division: Two main types: mitosis and meiosis. Mitosis:

13. Involves two consecutive divisions. Results in daughter cells with the same number of chromosomes as the mother cell. Meiosis: Also involves two consecutive divisions. Produces four new cells with half the chromosome number as the mother cells. Characteristic Mitosis Meiosis Purpose Growth, repair, and maintenance of somatic cells Formation of gametes for sexual reproduction Number of Divisions One division Two divisions Number of Cells Produced Two genetically identical daughter cells Four non-identical daughter cells Chromosome Number Maintained (2n) Halved (n) Genetic Diversity No crossing over, minimal genetic diversity Introduces genetic diversity through crossing over and random assortment Role in Organisms Occurs in somatic cells for tissue maintenance Occurs in germ cells for sexual reproduction