Biology Chapter 3: Cells and Tissue

Study Notes

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.

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.

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.

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.

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.

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.

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

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 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.

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.

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.