The Cell in Action

A cell must be able to obtain food and raw materials and get rid of wastes.

What is diffusion?Diffusion = the movement of particles from regions of higher density to regions of lower density

∗ Cells do not need to use energy for diffusion

Section 1: Exchange with the Environment

Diffusion of Ink in Water

∗ The particles of the dye of the ink slowly diffuse through the water

∗ The cells of organisms are surrounded by and filled with fluids that are made mostly of water

∗ Osmosis = the diffusion of water through a semi-permeable membrane

∗ “semi permeable” means that some things, but not all, can get through

Diffusion of Water

Osmosis, continued

∗ Pure water has highest concentration of water molecules

∗ When you mix something with water, you lower the concentration of water molecules.

∗ During osmosis, water particles move to where they are less concentrated

Diffusion in Action

Salt would cause water molecules to travel out of the cell membrane. Water loss equals dead slugs!

The Cell and Osmosis

∗ Osmosis is important to cell functions

∗ Example: red blood cells are surrounded by plasma, which is made up of water, salt, sugars, and other particles. The concentration of these particles is kept in balance by osmosis!

∗Osmosis also occurs in plant cells Example: when a wilted plant is watered, osmosis makes the plant firm again

Osmosis in Plant Cells

∗Why would red blood cells burst if you placed

them in pure water?

Comprehension Question:

Answer:

∗ Red blood cells would burst in pure water because water particles move from outside, where particles are dense, to the inside of the cell, where particles are less dense. This movement of water would cause red blood cells to fill up and burst!

SORRY!

Knowledge does not diffuse

from the pages

of the textbook to your brain!

Moving Small Particles

∗Small particles, like sugar, cross the cell membrane through channels, which are made up of proteins

∗ Passive transport = the movement of substances across the cell membrane without the use of energy by the cell

∗ During passive transport, particles move from an area of high concentration to an area of low concentration

∗ Examples of passive transport : osmosis and diffusion

Passive Transport

Passive Transport

∗ Active transport = the movement of substances across the cell membrane that requires the cell to use energy

∗ Examples of active transport: endocytosis and exocytosis

∗ involves the movement of particles from an area of low concentration to an area of high concentration

Active Transport

Endocytosis:

∗ Endocytosis = the process by which a cell membrane surrounds a particle and encloses the particle in a vesicle to bring the particle into the cell

ENDO = IN and GO

1. The cell comes into contact with a particle

2. The cell membrane begins to wrap around the particle

3. Once the particle is completely surrounded, a vesicle pinches off

4. Endocytosis = “within the cell”

Steps of Endocytosis:

∗Exocytosis = the process in which a cell releases a particle by enclosing the particle in a vesicle that then moves to the cell surface and fuses with the cell membrane

EXO = EXIT THE CELL

Exocytosis:

∗ Large particles that leave the cell must be packaged in vesicles.

∗ Vesicle travels to the cell membrane and fuses with it.

∗ Cell releases the particle to the outside of the cell

∗ Exocytosis = “outside the cell”

Steps of Exocytosis

Endocytosis & Exocytosis

1. What part of the cell do materials pass through to get into and out of the cell?

2. What is osmosis?

3. What are 2 examples of passive transport?

4. Large particles enter the cell by_________ and leave by ______________.

Let’s Review:

1. Cell membrane

1. The diffusion of water through the semi-permeable cell membrane

1. Diffusion and osmosis

1. Endocytosis, exocytosis

Answers: