8.3 Cell Transport, Exercises of Cell Biology

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Lesson Overview

8.3 Cell Transport

Passive Transport

The movement of materials across the cell membrane without using cellular energy is called passive transport.

Diffusion

High Conc. Low Conc.

Diffusion

Facilitated Diffusion

Some molecules that cannot directly diffuse across the membrane pass through special protein channels in a process known as facilitated diffusion.

• protein channels are molecule specific
• form of passive transport
• particles move down concentration gradient

Osmosis: An Example of Facilitated

Diffusion

Osmosis is the diffusion of water through a selectively permeable membrane.

• water moves down concentration gradient
• passive

How Osmosis Works

Hypertonic

Hypotonic

How Osmosis Works

Osmotic Pressure

Because the cell is filled with salts, sugars, proteins, and other molecules, it is almost always hypertonic to fresh water. So if a cell is in fresh water, water tends to move quickly into the cell, causing it to swell or even burst.

Osmotic Pressure

In plants, the movement of water into the cell causes the central vacuole to swell, pushing cell contents out against the cell wall.

In a hypertonic solution, water rushes out of the cell, causing animal cells to shrink and plant cell vacuoles to collapse.

Osmotic Pressure

Active Transport

The movement of materials against or up a concentration difference is known as active transport.

• requires energy (ATP).

Active Transport: Bulk Transport

Bulk Transport moves larger molecules and clumps of material across cell membranes.

• requires energy (ATP)
• forms:
  1. endocytosis a. pinocytosis b. phagocytosis
  2. exocytosis

Endocytosis

process of taking material into the cell by vesicles or vacuoles