Chapter 7.3 - Transport of Substances across the Cell Membrane Cell Boundaries Cell Wall Cell Membrane Diffusion & Osmosis Diffusion Osmosis Transport of Substances Passive Transport Active Transport

Cell Walls & Cell Membranes Cell Boundaries Cell Walls & Cell Membranes

Cell Walls Plants, Algae, Fungi, and many prokaryotes have cell walls – Animal cells do not! The cell wall is located outside of the cell membrane and surrounds the cell. The cell wall provides strength, support, shape, and protection to the cell.

Cell Wall Composition The cell wall is porous, which means it easily allows for the transport of water, oxygen, carbon dioxide, and other substances. The cell wall is composed of polysaccharide carbohydrate fibers called “Cellulose”. Wood and paper are made up of these cellulose fibers.

Continuing Research – We are not done!!!

Cell Membranes Definitions Cell membrane = plasma membrane = cytoplasmic membrane Protoplasm = everything within the cell Cytoplasm = everything within the cell except the nucleus Cytosol = everything within the cell except the nucleus and the organelles

Cell Membrane Composition The cell membrane is composed of: Phospholipids Proteins Carbohydrates Cholesterol

Cell Membrane Functions Provide protection and support Separate the cell from its surroundings Communicate with other cells Recognize foreign material Maintains HOMEOSTASIS = Maintenance of an organism’s internal environment

The Cell Membrane Floats The cell membrane is flexible and dynamic. The cell is suspended in fluid surroundings with a fluid interior. The cell membrane is composed of a Lipid Bilayer which is a “waterproof” membrane separating the contents of the cell from its surroundings The cell membrane is selectively permeable, allowing some substances to cross, but not others.

Cell Membrane – Lipid Bilayer Contains two opposing chains of PHOSPHOLIPIDS. Each phospholipid is composed of a phosphate group with two fatty acid tails The phosphate head is HYDROPHILIC = water loving The fatty acid tails are HYDROPHOBIC = water fearing The phospholipids are arranged with the hydrophilic heads facing the fluid in and out of the cell, with the hydrophobic tails to the inside. This arrangement creates a “waterproof” barrier which is difficult to cross.

Cell Membrane – Lipid Cholesterol CHOLESTEROL is a non-polar lipid which helps maintain the fluidity of the cell membrane by keeping the fatty acid tails from sticking together.

Cell Membrane - Proteins Glycoproteins (Marker Proteins) – identifies cell Receptor Proteins – senses environment Aquaporins – water transport Channel/Carrier Proteins – passive transport Protein Pumps – active transport

Cell Membrane - Carbohydrates Cell membrane CARBOHYDRATES are polysaccharides which act as markers for cell recognition. These molecules help white blood cells recognize and attack harmful bacteria. Carbohydrates

Osmosis & Diffusion

Diffusion Molecules move constantly in a random motion = Brownian Motion The molecules bump into each other causing them to move from an area of high concentration to an area of lower concentration = DIFFUSION down a CONCENTRATION GRADIENT No extra energy is needed because the molecules are already in motion (like busy bees). Diffusion will continue until EQUILIBRIUM is reached and particles are spread throughout the container.

Diffusion Across a Semipermeable Membrane Permeable = Allows liquids or gases to pass through => Porous => Penetrable Semipermeable = Allows only certain liquids or gases to pass through The semipermeable membrane above is permeable to small substances, but not large substances.

Osmosis Hypotonic Solution Hypertonic Solution WATER moves across a semipermeable membrane from an area of low solute concentration to an area of high solute concentration until equilibrium is reached. OSMOSIS only applies when solute movement is restricted by a semipermeable membrane. Semipermeable Membrane

How Osmosis Affects our Cells HYPERTONIC solution = water outside of cell has a HIGH solute concentration (salty) which pulls water out of the cell. ISOTONIC solution = solute concentration is the SAME inside the cell as outside of the cell. Water moves back and forth freely. HYPOTONIC solution = water outside the cell has a LOW solute concentration (pure water), water moves into the cell.

Transport of Substances Across a Semipermeable Membrane Passive Transport Simple Diffusion Facilitated Diffusion Channel Proteins Carrier Proteins Active Transport Protein Pumps Vesicles Endocytosis Exocytosis

Passive Transport Across a Cell Membrane – SIMPLE DIFFUSION SMALL – small enough to squeeze through the membrane NON-POLAR – no positive or negative end to the molecule Oxygen Carbon Dioxide Hormones NO ENERGY REQUIRED!

Passive Transport Across a Cell Membrane – Facilitated Diffusion LARGE – too large to squeeze through the membrane POLAR – molecule has a positive end and a negative end The cell membrane allows SPECIFIC molecules to DIFFUSE across the membrane using tunnels (CHANNEL PROTEINS) or gates (CARRIER PROTEINS). Water (Aquaporins) Ions (Na+) Carbohydrates Amino acids NO ENERGY REQUIRED!

Active Transport Across the Cell Membrane - Pumps (like the Na+K+ Pump) use CARRIER PROTEINS & ENERGY to transport molecules AGAINST the CONCENTRATION GRADIENT. ENERGY is REQUIRED!

Active Transport Across the Cell Membrane - Vesicles Endocytosis = the process of taking material into the cell a. Phagocytosis = intake of matter b. Pinocytosis = intake of liquids Exocytosis = the process of removing material from the cell

Phagocytosis