2.1 Cell — Structure, Function, and Organization
A cell is the basic unit of life. All living organisms are made up of cells that carry out life processes such as respiration, excretion, growth, and reproduction.
Structures and Functions of Animal and Plant Cell Components
- Cell Membrane: Controls the movement of substances in and out of the cell. (Present in both)
- Cytoplasm: A jelly-like medium where biochemical reactions occur. (Present in both)
- Nucleus: Controls all cell activities and contains genetic material (DNA/chromosomes). (Present in both)
- Mitochondria: Site of cellular respiration to generate energy (ATP). (Present in both)
- Cell Wall: Made of cellulose; provides structural support and fixed shape to plant cells. (Plant cells only)
- Chloroplast: Contains chlorophyll to absorb light energy for photosynthesis. (Plant cells only)
- Vacuole: Stores cell sap (water, dissolved nutrients, and waste products) and maintains turgidity. (Plant cells only; small or absent in animal cells)
Comparison Between Animal Cells and Plant Cells
- Plant Cells: Have a fixed shape, cell wall, chloroplasts, and large central vacuole.
- Animal Cells: Have no fixed shape, no cell wall, no chloroplasts, and small or no vacuoles.
Unicellular and Multicellular Organisms
- Unicellular Organisms: Made of a single cell (e.g., Amoeba, Paramecium, Euglena, Chlamydomonas, yeast, bacteria).
- Multicellular Organisms: Made of more than one cell (e.g., Spirogyra, Mucor, hydra, plants, animals, humans).
Organization of Cells in the Human Body
Cells organize systematically to form complex living organisms:
$$\text{Cell} \longrightarrow \text{Tissue} \longrightarrow \text{Organ} \longrightarrow \text{System} \longrightarrow \text{Organism}$$
- Cell: Basic unit (e.g., Muscle cell, Nerve cell, Red blood cell).
- Tissue: Group of similar cells working together to perform a specific function (e.g., Epithelial tissue, Muscle tissue).
- Organ: Group of different tissues working together (e.g., Heart, Stomach, Lungs, Kidney, Leaf).
- System: Group of different organs working together for a primary body function (e.g., Digestive system, Blood circulatory system, Respiratory system).
- Organism: An entire living entity composed of integrated systems.
2.2 Cellular Respiration and Photosynthesis
Cellular Respiration
Cellular respiration is the process of breaking down glucose in the presence of oxygen to release energy, carbon dioxide, and water.
$$\text{Glucose} + \text{Oxygen} \longrightarrow \text{Carbon Dioxide} + \text{Water} + \text{Energy}$$
Photosynthesis
Photosynthesis is the process by which green plants synthesize glucose from carbon dioxide and water using light energy absorbed by chlorophyll, releasing oxygen as a byproduct.
$$\text{Carbon Dioxide} + \text{Water} \xrightarrow[\text{Chlorophyll}]{\text{Light Energy}} \text{Glucose} + \text{Oxygen}$$
Interdependence of Cellular Respiration and Photosynthesis
- Respiration uses oxygen and glucose produced during photosynthesis.
- Photosynthesis uses carbon dioxide and water produced during cellular respiration.
- This complementary cycle maintains the balance of oxygen and carbon dioxide in the atmosphere.