Transport In Cells | COMPLETE NOTES

Diffusion Overview
• Random particle movement from high to low concentration.
• Aims for equilibrium.

Osmosis Overview
• Defined as water diffusion across a semipermeable membrane.
• Movement of water molecules from high to low concentration areas.
• Aims for equilibrium at the end.

Osmosis in Plant and Animal Cells

• Plant cells contain solutes, resulting in a low water potential.
• Cells are surrounded by a dilute solution (hypotonic solution) with few solutes and more water molecules.
• Water molecules osmose from the outer solution with a higher water potential into the cell with a lower water potential, causing ENDOSMOSIS.
• The cell swells and becomes firm (turgid), with the outward pressure being turgor pressure.
• In isotonic liquid, equal water movement into and out of the cells results in no internal pressure and flaccid cell.
• In hypertonic liquid, water moves out of the cells, leading to exosmosis and cell plasmolysis.
• Osmosis in animal cells is crucial for maintaining cell shape, preventing dehydration, and regulating ion and other molecule concentration.
• Animal cells have mechanisms to regulate osmotic balance, such as pumping out excess water or taking in ions.
• In hypertonic solution, water moves out of the cell, leading to cell shrinkage.

Cell Active Transport Overview

• Active transport involves substances moving across a membrane against a concentration gradient, requiring energy (ATP) to move substances across the semi-permeable membrane.
• An example of active transport is in human nerve cells where sodium ions are constantly transported to the external fluid bathing the cell.
• Pinocytosis is the active uptake of large molecules from a solution, requiring energy. It involves invagination of the plasma membrane forming and suspending the particles within small vesicles.
• Phagocytosis is the cellular process of engulfing solid particles by the cell membrane to form an internal phagosome, which is an active uptake across a membrane.
• Lysosomes may fuse with the food vacuole and empty digestive enzymes into it, which digest the food and absorb it into the cytoplasm of the cell.