Biology Chapter 3: Cells and Tissue

Cells and Tissue

• Cells are the structural units of all living things, and the human body has 50 to 100 trillion cells.
• The word "cell" comes from the Latin word "cella", meaning "small room".
• Cells are the basic building blocks of all living things, providing structure, taking in nutrients, converting nutrients into energy, and carrying out specialized functions.

Cell Types

• There are two types of cells: Eukaryotic and Prokaryotic.
• Eukaryotic cells have a nucleus and can be single-celled or multicellular, while Prokaryotic cells do not have a nucleus and are single-celled organisms.

Cellular Basis of Life

• The cell theory states that:
  • A cell is the basic structural and functional unit of living organisms.
  • The activity of an organism depends on the collective activities of its cells.
  • According to the principle of complementarity, the biochemical activities of cells are dictated by their structure (anatomy) which determines their function (physiology).
  • Continuity of life has a cellular basis.

Cellular Composition

• Most cells are composed of four elements: carbon, hydrogen, oxygen, and nitrogen.
• Inclusions are chemical substances, such as stored nutrients or cell products, that float in the cytosol.
• Organelles are the metabolic machinery of the cell, performing functions for the cell, and many are membrane-bound, allowing for compartmentalization of their functions.

Cell Regions

• There are three regions of the cell:
  • Nuclear envelope (membrane) and cytosol: fluid that suspends other elements and contains nutrients and electrolytes.
  • Rough endoplasmic reticulum (ER): studded with ribosomes, synthesizes proteins, and transports vesicles within the cell.
  • Smooth endoplasmic reticulum (ER): lacks ribosomes, functions in lipid metabolism, and detoxifies drugs and pesticides.

Cytoskeleton

• The cytoskeleton is a network of protein structures that extends throughout the cytoplasm, providing the cell with an internal framework, determining cell shape, supporting organelles, and providing the machinery for intracellular transport.
• There are three types of elements that form the cytoskeleton: flagellum, microtubules, and microfilaments.

Cell Physiology

• Cells have the ability to metabolize, digest food, dispose of wastes, reproduce, grow, move, and respond to a stimulus.

Passive Processes

• Diffusion: the movement of molecules from high concentration to low concentration, down a concentration gradient.
• Osmosis: the movement of water across a selectively permeable membrane, from high concentration to low concentration.
• Filtration: the movement of water and solutes through a membrane by fluid or hydrostatic pressure.

Active Processes

• Active transport: the movement of substances across a membrane, using ATP energy, against a concentration gradient.
• Vesicular transport: the movement of substances across the membrane in bulk, without actually crossing the plasma membrane.

Types of Vesicular Transport

• Exocytosis: the secretion of substances from the cell, using vesicles that migrate to the plasma membrane.
• Endocytosis: the engulfment of extracellular substances by a membranous vesicle, which then fuses with a lysosome.
• Phagocytosis: the engulfment of large particles, such as bacteria or dead cells, by a membranous vesicle.
• Pinocytosis: the engulfment of fluids and dissolved substances by a membranous vesicle.

Tissue Repair

• The process of tissue repair involves inflammation, granulation tissue formation, and regeneration or fibrosis.
• Whether regeneration or fibrosis occurs depends on the type of tissue damaged and the severity of the injury.
• Tissues that regenerate easily include epithelial tissue, fibrous connective tissues, and bone.
• Tissues that regenerate poorly include skeletal muscle.
• Tissues that are replaced largely with scar tissue include cardiac muscle and nervous tissue within the brain and spinal cord.