Overview
This lecture introduces the basics of cell structure and function, focusing on cell theory, cell size and shape, plasma membrane structure and extensions, and mechanisms of membrane transport.
The Cell Theory
- The cell is the fundamental unit of life.
- All organisms are composed of at least one cell (unicellular or multicellular).
- All cells arise from pre-existing cells (no spontaneous generation).
Cell Structure and Size
- Cells remain small to maintain an effective surface area-to-volume ratio for nutrient uptake and waste removal.
- Surface area increases by a factor of four when cell size doubles, but volume increases eightfold.
- Larger cells may be specialized in shape (flattened) to maintain efficient transport.
Basic Components of All Cells
- All cells possess a plasma (cell) membrane that separates internal cytoplasm from external environments.
- Cytoplasm contains organelles like mitochondria, nucleus, rough and smooth endoplasmic reticulum, and Golgi apparatus.
- Presence of a nucleus distinguishes eukaryotic (true nucleus) from prokaryotic (no nucleus) cells.
Plasma Membrane Structure
- Plasma membrane is a phospholipid bilayer with hydrophilic (water-loving) heads facing outward and hydrophobic (water-fearing) tails inward.
- Semi-permeable/selectively permeable barrier regulates what enters and exits the cell.
- Membrane fluidity enables lateral movement of components.
Membrane Extensions
- Microvilli: tiny, numerous extensions that increase surface area for absorption (e.g., intestinal lining).
- Cilia: longer, hair-like structures for movement of substances; can be motile (move mucus/pathogens) or non-motile (sensory).
- Flagella: long, whip-like structures for locomotion; in humans, found only in sperm cells.
- Pseudopods: temporary membrane extensions for engulfing particles or movement (e.g., white blood cells).
Membrane Transport Mechanisms
- Plasma membrane is selectively permeable due to phospholipid bilayer.
- Passive transport: moves substances down concentration gradients (high to low) without ATP; driven by kinetic energy.
- Active transport: moves substances against gradients (low to high) requiring ATP input.
Types of Passive Transport
- Diffusion: movement of solute particles from high to low concentration (e.g., Oâ‚‚, COâ‚‚, glucose).
- Facilitated diffusion: solute movement via membrane proteins from high to low concentration.
- Osmosis: movement of water across a semi-permeable membrane from high to low water concentration; critical for maintaining fluid balance.
Key Terms & Definitions
- Cell Theory — states the fundamental properties of cells in living organisms.
- Plasma (Cell) Membrane — phospholipid bilayer that controls entry and exit of substances.
- Surface Area-to-Volume Ratio — a comparison that influences cell efficiency in exchange.
- Phospholipid Bilayer — double-layered structure forming the cell membrane.
- Microvilli — small projections that increase membrane surface area.
- Cilia — hair-like extensions for movement or sensory purposes.
- Flagella — long, tail-like projections used for cell movement.
- Pseudopod — temporary membrane extension for engulfment/movement.
- Passive Transport — movement of substances without energy use.
- Active Transport — energy-requiring movement of substances against concentration gradients.
- Diffusion — passive movement of solute from high to low concentration.
- Osmosis — passive movement of water from high to low concentration.
Action Items / Next Steps
- Review the PowerPoint slides available on D2L for supplementary images.
- Prepare for Part 2 of Chapter 3, covering tonicity and cell organelles.
- Note any questions for office hours or the D2L discussion board.