3.4 Diffusion and Osmosis, Summaries of Chemistry

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KEY CONCEPT Materials move across membranes because of concentration differences.

3.4 Diffusion and Osmosis

Passive transport does not require energy input from a cell.

• Molecules can move across the cell membrane through passive transport.
• There are two types of passive transport.
  • osmosis
  • diffusion

3.4 Diffusion and Osmosis

Diffusion and osmosis are types of passive transport.

• Osmosis is the diffusion of water molecules across a semipermeable membrane.

3.4 Diffusion and Osmosis

Diffusion and osmosis are types of passive transport.

• There are three types of solutions.
  • isotonic

3.4 Diffusion and Osmosis

• hypotonic
• hypertonic

KEY CONCEPT Cells use energy to transport materials that cannot diffuse across a membrane.

3.5 Active Transport, Endocytosis, and Exocytosis

Active transport requires energy input from a cell and enables a cell to move a substance against its concentration gradient.

• Passive transport requires no energy from the cell.
• Active transport is powered by chemical energy (ATP).

3.5 Active Transport, Endocytosis, and Exocytosis

• Cells use active transport to maintain homeostasis.
• Active transport occurs through transport protein pumps.

A cell can import and export large materials or large amounts of material in vesicles during the processes of endocytosis and exocytosis.

• Cells use energy to transport material in vesicles.
• Exocytosis is the process of expelling material from the cell.

3.5 Active Transport, Endocytosis, and Exocytosis