Summary
Highlights
All living things are made of cells, the smallest living part of an organism capable of performing life activities like growth, reproduction, excretion, and nutrition. Organisms can be unicellular (e.g., bacteria, amoeba) or multicellular (e.g., humans, plants, animals). Cells are microscopic, and their discovery is credited to Robert Hooke in 1665, who named them based on their resemblance to small rooms.
All cells (animal, plant, bacteria) share three basic parts: the cell membrane, nucleus, and cytoplasm. The cell membrane, or plasma membrane, is the outer covering that controls substance entry and exit, protecting the cell. The nucleus, often circular or oval, contains DNA, the hereditary material, and acts as the 'brain' of the cell, controlling all activities. The cytoplasm is the jelly-like substance inside the cell, outside the nucleus, containing various organelles.
Organelles are specialized parts within the cytoplasm, each with a specific function. Mitochondria are the 'powerhouses' of the cell, releasing energy (ATP) through cellular respiration. Ribosomes are 'protein factories' that synthesize proteins based on instructions from the nucleus. The nucleolus, found within the nucleus, is where ribosomes are produced. The Endoplasmic Reticulum (ER) comes in two forms: rough ER (with ribosomes) involved in protein production and transport, and smooth ER (without ribosomes) involved in synthesizing lipids and carbohydrates for the cell membrane.
The Golgi apparatus, nicknamed the 'mailman of the cell,' modifies, transports, and packages proteins and lipids into vesicles for delivery. Vacuoles serve as 'storage rooms' for food, water, and waste. Lysosomes are the 'suicide bags' or 'waste disposal system' of the cell, digesting unneeded materials. Centrioles, found only in animal cells, are cylindrical structures crucial for cell division, which is essential for producing new cells for growth, maintenance, and reproduction.
Plant cells have additional structures not found in animal cells. Chloroplasts contain chlorophyll, capturing sunlight for photosynthesis, the process by which plants produce their own food. The cell wall is an outer covering made of cellulose, providing protection, support, and shape to plant cells, fungi, bacteria, algae, and some archaea. These parts, along with the others, collectively enable the cell to perform its specific functions.