Untitled Notes

Robert Hooke's discovery of cells occurred in 1665 while observing cork through a self-designed microscope.
The structure of cork resembled that of honeycomb, consisting of many compartments called cells.
The term 'cell' comes from the Latin word for 'a little room', marking a significant event in the history of science.
This observation was crucial as it was the first evidence that living organisms are composed of separate units, which is a foundational concept in biology.

Materials Needed:
- Onion bulb, forceps, watch-glass, glass slide, drop of water, safranin solution, cover slip, mounting needle.
Procedure:
  1. Peel off the epidermis (skin) from the concave side of the onion bulb.
  2. Place the peel in water to keep it flat and prevent drying.
  3. Transfer the peel to a glass slide, add a drop of water and a drop of safranin solution, then apply a cover slip ensuring no air bubbles.
  4. Observe the slide under a compound microscope at low and high power.
Expected Observations:
- Microscopic structures resembling Fig. 5.2 where individual cells of the onion peel can be seen.

Unicellular Organisms:
- Organisms made up of a single cell (e.g., Chlamydomonas, Paramecium, bacteria).
Multicellular Organisms:
- Organisms with multiple cells working together (e.g., fungi, plants, animals).
All multicellular organisms originate from a single cell; cells divide to reproduce their kind.

Experiment with temporary mounts of leaf peels and root tips from onions.
Questions to Consider:
  - Do all cells look alike in shape and size?
  - Are there structural differences among cells?
  - How do cells from different parts of a plant body compare?
Expected Conclusion:
- Even different sized onion bulbs consist of similar cells that act as the building blocks.

Robert Hooke (1665): Discovered cells in cork.
Leeuwenhoek (1674): Discovered free-living cells in pond water.
Robert Brown (1831): Discovered the nucleus in cells.
Purkinje (1839): Coined 'protoplasm' for the fluid substance of cells.
Cell Theory (1838-1839): Proposed by Schleiden and Schwann, stating that all living things are composed of cells, and cells are the basic unit of life.
Virchow (1855): Expanded the cell theory by stating that all cells arise from pre-existing cells.
Electron Microscope (1940): Enabled detailed observation of cellular structures and organelles.

The shape and size of cells are functionally related.
Examples:
- Amoeba: Variable shape due to changing cellular structure.
- Nerve Cells: Fixed and characteristic shapes
Multicellular organisms exhibit division of labor, whereby specialized components perform distinct functions.

Plasma Membrane:
   - The outermost covering of the cell, separates the cell's interior from the external environment.
   - Functions:
     - Selectively permeable to various molecules.
     - Facilitates diffusion (e.g., CO2 and O2) and osmosis (movement of water across the cell membrane).

Diffusion: Movement of molecules from high to low concentrations.
Osmosis: Movement of water through a selectively permeable membrane toward a higher solute concentration.
  - Types of Solutions:
    1. Hypotonic Solution: Higher water concentration outside the cell; cell swells.
    2. Isotonic Solution: Equal water concentration; no net movement of water; cell maintains size.
    3. Hypertonic Solution: Lower water concentration outside the cell; cell shrinks.

Demonstrate osmosis by placing a deshelled egg in pure water and salt solutions.

Present in plant cells, composed mainly of cellulose.
Provides structural strength and enables plant cells to withstand hypotonic environments without bursting.
Plasmolysis: Occurs when plant cells lose water and shrink away from the cell wall.

Observe plasmolysis in Rhoeo leaves by mounting leaf samples in different solutions.

Contains the cell's genetic material in the form of chromosomes, which are made of DNA.
The nuclear membrane has pores for material exchange between the nucleus and cytoplasm.
Nucleoid: In prokaryotic cells, genetic material is located in an undefined area without a membrane-bound nucleus.

Fluid content within the cell membrane containing organelles.
The cytoplasm is involved in various cellular processes and does not take stain easily.

A network of membrane-bound tubes and sheets.
Types of ER:
- Rough ER (RER): Studded with ribosomes; involved in protein synthesis.
- Smooth ER (SER): Involved in synthesis of lipids and detoxification processes.

Membrane-bound sacs containing digestive enzymes.
Act as the cell's waste disposal system and are sometimes referred to as "suicide bags" due to their ability to digest damaged cells.

Known as the powerhouses of the cell; responsible for ATP production through nutrient breakdown.
Has its own DNA and ribosomes, allowing it to synthesize some proteins independently.

Found only in plant cells; include chloroplasts (for photosynthesis) and leucoplasts (for storage).

Cell division is critical for growth, tissue repair, and reproduction.
Types of Cell Division:
- Mitosis: Involves one division resulting in two identical daughter cells; essential for growth.
- Meiosis: Involves two consecutive divisions producing four cells with half the chromosome number; crucial for gamete formation.