Biology: Cell Structure and Types

Cells - Basic Units of Life

• Cells are the fundamental structural and functional units of all living organisms.
• All living organisms are composed of one or more cells.
• Cells carry out all life processes, including growth, reproduction, metabolism, and response to stimuli.

Cell Types

• Two main types of cells exist: prokaryotic and eukaryotic.
• Prokaryotic cells are simpler, smaller, and lack a nucleus and membrane-bound organelles. Examples include bacteria and archaea.
• Eukaryotic cells are more complex, larger, and have a nucleus and membrane-bound organelles. Examples include plant and animal cells.

Cell Structure (Eukaryotic Cell)

• Cell Membrane: A thin, flexible barrier surrounding the cell, controlling what enters and leaves. It is selectively permeable.
• Cytoplasm: The jelly-like substance filling the cell, containing organelles and supporting internal transport.
• Nucleus: The control center of the cell, containing DNA enclosed by a nuclear membrane.
• Mitochondria: The "powerhouses" of the cell, producing energy (ATP) through cellular respiration. They have their own DNA.
• Ribosomes: Small structures involved in protein synthesis, either free-floating or attached to the endoplasmic reticulum. They translate genetic information into proteins.
• Endoplasmic Reticulum (ER): A network of membranes involved in protein and lipid synthesis. Rough ER has ribosomes; smooth ER does not. It transports and modifies proteins and lipid synthesis.
• Golgi Apparatus: Processes, packages, and distributes proteins and lipids.
• Lysosomes: Contain digestive enzymes breaking down waste materials and cellular debris, crucial for waste removal.
• Vacuoles: Storage sacs for water, nutrients, or waste products. Plant cells often have a large central vacuole.
• Chloroplasts (Plant Cells Only): Sites of photosynthesis, converting light energy into chemical energy. They contain chlorophyll, giving plants their green color.

Cell Functions

• Transport: Movement of substances across the cell membrane, including passive and active transport.
• Metabolism: All chemical reactions within the cell to sustain life, encompassing both breaking down molecules for energy and building up molecules for structure and function.
• Growth and Reproduction: Cells increase in size and number (cell division) leading to development and repair in multicellular organisms.

Differences between Plant and Animal Cells

• Cell Wall: Plant cells have a rigid cell wall made of cellulose, providing support and protection. Animal cells lack a cell wall.
• Chloroplasts: Plant cells have chloroplasts for photosynthesis. Animal cells do not.
• Vacuoles: Plant cells typically have a large central vacuole. Animal cells have smaller vacuoles.

Importance of Cells

• Cells are fundamental to all life processes.
• Organization of cells into tissues, organs, and organ systems allows complex structure and function in multicellular organisms.