Cells and Their Environment Transporting Materials across Cell Membranes

4 lessons – 4 labs  Cells and their Environment  Models of Membranes  Lab  Osmosis + Lab  Lab  Quiz  Relating cells to Society  Lab - Debate

Salmon Run  Most Canadians are familiar with the salmon returning from the ocean to the streams they were born in.  How do they survive the change in the environment?  If you were to place most salt-water organisms in fresh water they would soon bloat and die.  How can salmon survive in both fresh and salt water?

Cells and Their Environment

Bubble Boy!  Imagine if you had to live inside a sealed plastic bag. How long would you survive?  Not long without holes so oxygen could enter.  You need a way to get water and food through the plastic.  You would also need a way of removing wastes, such as carbon dioxide and urine.

Cell Membrane  Cell membrane is like a plastic bag.  However, it is much more complex  Draw a sketch of the following slide – label the parts of a cell membrane

The Cell Membrane

Cell Membranes  The cell membrane has two layers of fat( lipid). Embedded in the fat layers are protein molecules (coloured blobs) and pores made of protein. There are pores of several different sizes

Cell Membrane  Cells allow some materials to enter or leave, but not others. They are said to be permeable to some materials and impermeable to others.  Permeable means permitting passage  Impermeable means not permitting passage.

Cell Membranes  In general, small molecules pass easily through the cell membrane, medium – sized molecules move through less easily, and large ones cannot pass through without help from the cell.  Because it allows certain substances to enter or leave, but not others, the cell membrane is said to be Selectively permeable.

Diffusion  How do substances move from one place to another?  Why doesn’t the ink remain as a small blob?  Molecules are constantly moving and colliding with other molecules. When they collide, they bounce off each other.  This causes molecules concentrated in one area to spread outward.  Diffusion is the movement of molecules from an area of high concentration to an area of lower concentration.

Diffusion  Diffusion is one of the ways substances move into and out of cells.  Substances that a cell uses, such as oxygen, are found in low concentrations inside the cell.  When the concentrations of these substances are higher outside the cell, the molecules will diffuse across the cell membrane in to the cell.  Diffusion will continue until the concentration s the same both inside and outside the cell.

Models of Membranes  Purpose: Comparing the permeability of the three materials – Plastic, a screen, cloth – covering the jars.  What will happen if you pour water, sugar alone, and sugar water solution over each jar?  Which jars are permeable to all three substances. Which is impermeable to some substances but permeable to others?

Assignment  Write up the lab you are doing – follow the scientific report given to you.  Answer the following questions 1. Define diffusion. 2. Explain what is meant by an impermeable material, a permeable material, and a selectively permeable material. 3. What type of membrane do cells have: impermeable, permeable, or selectively permeable?