Day 3 Notes: Cell Structure and Biological Diversity
1. The Fundamental Unit of Life: The Cell
All living organisms are made up of basic structures called cells. Understanding the cell is the starting point for investigating living creatures.
| Concept | Detail | Source Integration |
|---|---|---|
| Discovery | Cells were first observed by Robert Hooke in 1665 when examining a thin slice of cork using a self-designed microscope. He called these boxes "cells" (Latin for 'a little room'). | — |
| Structure | Cells have three main parts: a thin outer lining (cell membrane), a central region (cytoplasm), and a small round structure in the middle (nucleus). The cytoplasm is the jelly-like substance located between the cell membrane and the nucleus. | — |
| Size Variation | Most microorganisms are so small they cannot be seen with the naked eye. Conversely, the yolk (yellow part) of an ostrich egg is a single, large cell, measuring about 130 mm to 170 mm in diameter—the largest known cell. | — |
Simulated Infographic: Plant Cell vs. Animal Cell
Cells of plants and animals share similarities but also differ in structure and shape.
| Feature | Plant Cell (e.g., Onion Peel) | Animal Cell (e.g., Human Cheek Cell) |
|---|---|---|
| Outer Boundary | Has a rigid Cell Wall outside the cell membrane. | Only has the Cell Membrane (thin outer lining). |
| Shape | Generally observed as nearly rectangular structures. | Observed as polygon-shaped structures. |
2. Levels of Biological Organization
Cells rarely exist in isolation; they organize themselves to perform complex functions.
- Cell: The smallest unit of life.
- Tissue: A group of cells that are similar in structure and function.
- Examples of specialized animal cells that form tissues include muscle cells (contraction and relaxation cause movement) and cells of the nervous tissue (highly specialized for being stimulated and responding to stimuli).
- Examples of specialized plant cells include Apical meristem (located at growing tips, increases length of stem and root) and Lateral meristem or cambium (increases the girth of the stem or root).
- Organ: (E.g., Heart, Stomach).
- Organ System: (E.g., Digestive System).
- Organism.
3. Diversity and Classification in Plants
The immense variety in nature—called diversity—is explored by classifying organisms based on similarities and differences.
Classification by Stem/Height
| Group | Characteristics | Example |
|---|---|---|
| Herbs | Typically small with soft and green stems. | Tomato plant, Common grass. |
| Shrubs | Many brown woody stems branching close to the ground. Stems are hard but not as thick as a tree stem. | Rose plant, Tulsi. |
| Trees | Generally tall with hard and thick brown stems. | Neem. |
| Climbers/Creepers | Plants with weak stems that need support to climb (Climbers) or creep along the ground (Creepers). | — |
Classification by Leaf and Root Structure
The structure of the leaf is related to the structure of the root:
- Leaf Venation:
- Reticulate Venation: Net-like pattern of veins on the leaf. (e.g., Hibiscus).
- Parallel Venation: Veins run parallel to each other. (e.g., Grass, Banana leaf).
- Root Type: Plants can have fibrous roots or tap roots. (For instance, radish is a kind of root.)
4. Diversity and Movement in Animals
Animals show great diversity in their movement and habitat.
- Movement: Animals use different body parts for movement. They can fly, run, crawl, walk, hop or jump. Examples include fish swimming with fins and birds flying with wings.
- Habitat: Organisms require specific conditions to survive, and different habitats offer different living conditions.
- The variety of plants and animals found in one kind of region, like a desert or a mountain, is different from those found in another kind of region.
- Plants like cactus (thick, fleshy stems) are adapted to deserts, while deodar trees (conical shape, sloping branches) are adapted to mountains.
- Animals can be grouped based on their habitats, such as aquatic (living in water, e.g., Dolphin, Whale) or terrestrial (living on land, e.g., Horse, Lion). Some animals (e.g., Frog, Crocodile, Tortoise) live in both habitats.
💡 Analogy for Biological Diversity:
Biological diversity in nature is like a large orchestral score. While the basic framework of all life is the cell (the fundamental note or structure that makes up every instrument), the way these notes are organized creates wildly different instruments and melodies. The different types of cells combine to form specialized tissues (the strings, brass, or percussion sections). These sections then combine to form vast differences in form, movement, and habit—from the tiny microbe (a single flute) to the soaring eagle (a massive ensemble), each element is unique but indispensable to the symphony of life.