Molecular Transport: Cell Membranes and Diffusion

• Cells have membranes that separate the inside from the outside.
• Internal cellular environments differ from external environments.
• Living organisms maintain cellular barriers for growth, reproduction, and homeostasis.
• Homeostasis maintains stable internal conditions despite external changes.
• Cells require protection to perform functions for survival and reproduction.

Molecular Transport

• Eukaryotic cells have a nucleus and organelles.
• Eukaryotic cells include plants, animals, and fungi.
• Plasma membranes regulate the internal cell environment.
• Diffusion is the tendency of particles to spread evenly.
• Molecules move from high to low concentration areas, balancing across the membrane.
• Passive transport requires no cell energy for molecular movement.
• Facilitated diffusion uses transport proteins to create channels for molecule passage.
• Transport proteins allow larger, polar molecules to pass through the membrane.
• Facilitated diffusion is passive transport because the cell does not expend energy.
• Active transport requires energy to move molecules against the concentration gradient.
• Cells actively pump molecules through transport proteins to maintain their environment.
• Exocytosis exports materials out of the cell.
• Endocytosis imports materials into the cell.

Importance of Internal Regulation

• Uncontrolled internal cellular environments prevent cells from functioning properly.
• Cellular processes require specific conditions, like correct sugar level, temperature, oxygen and water balance.
• Metabolism helps maintain body temperature.
• Endotherms generate heat through metabolism, including mammals, birds, and some fishes and insects.
• Cells must remove waste through molecular transport.
• Protein synthesis relies on homeostasis.
• Cells make proteins for DNA, injury recovery, food breakdown, and other functions.
• Without homeostasis, the body cannot make proteins or perform bodily functions.

This lesson explores cell membranes, their role in separating internal and external environments, and the process of diffusion. It covers how cells maintain homeostasis and use passive and facilitated transport to regulate molecular movement across the plasma membrane, crucial for cellular function and survival.