NOTES – The Cell Membrane

All Cells Have a Cell Membrane Cells are the basic units of structure and function in living things, which means, they have all the characteristics of life The cell membrane allows the cell to adjust to its environment by using energy to control what comes in and what goes out By doing this the cell maintains homeostasis, or a stable internal environment, which it needs to survive

What are cell parts made of? Proteins (C,H,O,N,S) – building materials, messengers, speed things up Lipids (C,H,O) – store energy, form membranes, insulation Carbohydrates (C,H,O) – energy source for cells, building material Nucleic Acids (C,H,O,N,P) – store and carry information Water (H2O) 97% of an organism’s body weight is the elements C,H,O,N Organic Molecules

Why does the cell need to control what comes in and what goes out? The cell needs to keep a certain amount of substances in its cytoplasm The cell has to take in what it needs and let out what it doesn’t need

Cell Membrane Structure

Structure of the Cell Membrane The cell membrane is arranged in a bi-layer There are 2 layers of phospholipids A phospholipid is made up of a phosphate head (polar) and a lipid tail (non-polar) There are protein molecules spread throughout cell membrane Cholesterol molecules are found in the middle of the bi-layer

Function of Individual Parts Phospholipids: make up a majority of the flexible inner and outer layer of the cell membrane The phosphate head is polar (charged) and is attracted to water (hydrophilic) The lipid tail is non polar (no charge) and is not attracted to water (hydrophobic) Protein molecules: act as a gates that let certain substances in and out, also act as cell identifiers Cholesterol: keeps the lipid tails from sticking together

Cell Membrane Structure Cholesterol Protein Molecules Phospholipid

Fluid Mosaic Model The Cell Membrane is often described as a Fluid Mosaic because A. The membrane moves in a fluid-like motion B. The membrane is made up of many different parts like an art mosaic

Selective Permeability The cell membrane is selectively permeable, which means it allows some substances to pass through while holding other substances back

What are solutions and how do they affect cells? Cells are filled with solution and surrounded by solution A solution is a mixture of solvent (water) and a solute (salt, sugar, calcium, etc.) Cytoplasm is a solution of water and many different solutes (amino acids, oxygen, carbon dioxide, sugars, proteins, organelles, etc.)

Concentration is the amount of solute in a certain amount of solvent High concentration means there is a lot of solute compared to the amount of solvent (Ex. Strong Kool Aid – 4 Tsp sugar to 8 oz water) Low concentration means there is a little solute compared to the amount of solvent (Ex. Weak Kool Aid – 1 Tsp sugar to 8 oz water)

What are the three types of solutions What are the three types of solutions? When you compare the solution outside of a cell to the inside of the cell (cytoplasm), there are 3 possibilities: Hypotonic Solution – has a lower concentration of solute than the cytoplasm of the cell

What are the three types of solutions What are the three types of solutions? When you compare the solution outside of a cell to the inside of the cell (cytoplasm), there are 3 possibilities: Isotonic Solution – has an equal concentration of solute to the cytoplasm of the cell

What are the three types of solutions What are the three types of solutions? When you compare the solution outside of a cell to the inside of the cell (cytoplasm), there are 3 possibilities: Hypertonic Solution – has a higher concentration of solute than the cytoplasm of the cell

Comparing Concentration of the Cytoplasm to the Concentration of the Solution Outside of the Cell The outside has a lower concentration than Cell A (hypotonic) The outside has a higher concentration than Cell B (hypertonic) The outside has an equal concentration to Cell C (isotonic)

Where will substances move? If nothing prevents them from doing so, substances in solution will always move from areas of high concentration to areas of low concentration