Biology: Passive and Active Transport

Cell Transport Mechanisms

• Diffusion and osmosis are types of passive transport, requiring no energy
• Active transport requires energy to move materials against a concentration gradient
• Factors affecting the rate of diffusion across a cell membrane include:
  • Particle size
  • Temperature
  • Concentration difference
  • Diffusion distance
• Smaller particles move faster than larger particles at a given temperature

Endocytosis and Exocytosis

• Endocytosis involves the uptake of materials into a cell through the formation of vesicles
• Types of endocytosis include:
  • Phagocytosis (uptake of large molecules or cells)
  • Pinocytosis (uptake of fluids and dissolved substances)
  • Receptor-mediated endocytosis
• Exocytosis is the process of cellular secretion of macromolecules, where an intracellular vesicle fuses with the plasma membrane and discharges its contents outside the cell

Osmosis and Cell Environments

• Hypertonic solution: higher concentration of solutes and less water than the cell, causing water to leave the cell
• Isotonic solution: equal concentration of solutes and water as the cell, no net movement of water
• Hypotonic solution: lower concentration of solutes and more water than the cell, causing water to enter the cell

Cell Membrane Structure and Function

• The fluid-mosaic model of the cell membrane consists of:
  • Phospholipid bilayer
  • Embedded proteins
  • Carbohydrate chains attached to proteins (glycoproteins) or lipids (glycolipids)
• The cell membrane is selectively permeable, controlling the passage of materials in and out of the cell

Cell Structures and Their Functions

Cell Membrane

• Selectively permeable to ions and organic molecules
• Controls movement of substances in and out of the cell
• Protects the cell from its surroundings

Mitochondria

• Eukaryotic membranous organelles that break down carbohydrates to produce ATP molecules
• Produce energy for the cell through respiration and regulate cellular metabolism

Endoplasmic Reticulum

• Smooth ER: regulates and releases calcium ions and processes toxins
• Rough ER: has ribosomes for protein synthesis on its surface

Ribosomes

• Composed of two subunits: large and small
• Both subunits are composed of rRNA and protein

Golgi Bodies

• Process and bundle macromolecules like proteins and lipids as they are synthesized within the cell
• Present in most eukaryotic cells and made up of membrane-bound sacs

Vesicles

• Cellular organelles composed of a lipid bilayer
• Function in metabolism and enzyme storage
• Used to transport materials from one place to another

Vacuoles

• Membrane-bound sacs within the cytoplasm of a cell
• Function in several different ways, including:
  • Providing structural support
  • Storage
  • Waste disposal
  • Protection
  • Growth

Lysosomes

• Involved in digestion and waste removal
• Contain digestive enzymes
• Digest excess or worn-out organelles, food particles, and engulfed viruses or bacteria

Nuclear Envelope and Nucleus

• Nuclear envelope: double membrane structure surrounding the nucleus in eukaryotic cells
• Nucleus: contains the majority of the cell's genetic material, organized as DNA molecules and proteins to form chromosomes

Nucleolus

• Made up of proteins and ribonucleic acids (RNA)
• Function is to rewrite ribosomal RNA (rRNA) and combine it with proteins