Cell and Transport Study Guide Part II

This page provides an in-depth overview of passive transport mechanisms in biological cells, including simple diffusion, facilitated diffusion, and osmosis. It also introduces the concept of osmoregulation and explains the importance of tonicity in cellular processes.

Passive Transport

Passive transport encompasses three main mechanisms:

1. Simple Diffusion: This process involves the movement of molecules from areas of high concentration to low concentration, following the concentration gradient.

2. Facilitated Diffusion: Similar to simple diffusion, but molecules move with the assistance of proteins, still following the concentration gradient.

3. Osmosis: The movement of water molecules from areas of high concentration to low concentration. While water can move through the phospholipid bilayer, it is a very slow process.

Vocabulary: Osmoregulation is the ability of cells to maintain water balance, preventing excessive uptake or loss of water.

Tonicity

Tonicity refers to the effectiveness of a solution in causing a cell to gain or lose water. There are three types of tonicity:

1. Hypertonic: A solution with a higher solute concentration and lower solvent concentration compared to another solution. This causes water to diffuse out of the cell.

   Example: In a hypertonic environment, plant cells become plasmolyzed, while animal cells crenate.

2. Hypotonic: A solution with a higher solvent concentration and lower solute concentration compared to another solution. This causes water to diffuse into the cell, potentially leading to swelling or bursting.

   Example: In a hypotonic environment, plant cells become turgid, while animal cells may lyse.

3. Isotonic: A solution where water and dissolved solutes diffuse into and out of the cell at the same rate.

   Example: In an isotonic environment, plant cells become flaccid, while animal cells remain normal.

Highlight: Turgor pressure is experienced by plant cells in hypotonic environments, preventing them from bursting due to their cell walls.

Factors Affecting Passive Transport

The rate of passive transport is influenced by:

• Concentration gradient
• Size of molecules
• Temperature

Definition: Dynamic equilibrium is reached when the rate of molecules moving into and out of the cell are equal.

Active Transport

Active transport is introduced as the movement of molecules against the concentration gradient, requiring energy input.