The O word!

This week in AP Biology we did a lab over osmosis. Last week we learned osmosis is a type of diffusion, but it only applies to water. The definition of osmosis is the diffusion of water across a selectively permeable membrane.

There are three terms often mentioned when dealing with osmosis and they are hypertonic, hypotonic, and isotonic. Hypertonic is the solution when comparing two solutions has the higher concentration gradient. When cells are placed in hypertonic solutions the water in the cell will rush out of the cell, and the cell will start to shrivel up. In plants this causes plasmolysis, which is when the plasma membrane detaches from the cell wall. Salt water is hypertonic to the cell in our bodies, so if you are ever dehydrated salt water will not hydrate you but will dehydrate you faster.  A hypotonic solution is the solution when comparing two solutions has the lower gradient concentration. Cell placed in a hypotonic solution will most likely bust because the water rushes into the cell because of osmosis, except in plant cells. The cells in plants like to be in a hypotonic solution because it keeps the cell turgid. An isotonic solution is when comparing two solutions and them having the same concentration gradient. This is how people want their cells to be at most times. In plant cells though, this is not the prime environment for the cells. Plant cells in an isotonic solution become flaccid which causes the plant to look wilted. 

 The lab we did was centered around these terms and how the solutions affect cells.

The Gatekeeper

  This week in AP Bio we learned about the gatekeeper of the cell. This guardian of the cell is called the plasma membrane. The plasma membrane is made of a phospho-lipid bi-layer and proteins. The phospho head of the bi-layer is hydrophillic, while the lipid tail is hydrophobic this characteristic of  is called amphipathic. The along with proteins embedded in membrane allows the cell to be selectively permeable. The function of the plasma membrane is to maintain homeostasis by controlling what goes in and out of the cell.
  There is two different ways the plasma membrane diffuses what goes in and out of the cell. One is passive transport that requires no energy; there is two types of passive transport diffusion and facilitated diffusion. Diffusion is when molecules move from a high concentration gradient to a low concentration gradient. Osmosis is also diffusion, but it is when water diffuses across the plasma membrane. Facilitated Diffusion is when molecules move from an are of high concentration to an area of low transportation using a transport protein. The other type of transport that the plasma membrane uses is active transport, and it does require energy. The molecules are moving from an area of low concentration to high concentration, and the cell uses energy from the mitochondria called ATP.
  When cells require to move large particles into or out of the cells they use endocytosis ans exocytosis. Endocytosis is when when the membrane is taking the particles into the cell by vesicles created by the membrane. Once the particles are taken to their destination the membrane is reabsorbed by the cell. There are three types of endocytosis. Phagocytosis although it is also called cell eating; it is when the vacuole or vesicle the material is contained in is sent to the lysosomes to be digestive. In pinocytosis, when the plasma membrane engulfs the materials is also takes in the extracellular fluid this is very important in red blood cells. The third type of endocytosis is receptor-mediator endocytosis it is when the cell binds itself to specific particles. Exocytosis is used when the cell is moving molecules out of the cell. The large particle exiting the cell is enveloped by a vesicle that is fused with the membrane once it's materials exit.
  Each of our cells have a surrounding plasma membrane, even prokaryote cells have one. Is is very crucial to all organisms in maintaining homeostasis.

The Endomembrane System!!!

  The Endomembrane System is very important in our cells. Eukaryotic cells are the only cells that have the endomembrane system. It consists of the the nuclear envelope, the endoplasmic reticulum (smooth and rough), the golgi apparatus, lysosomes, different types of vesicles and vacuoles, and the plasma membrane. The function of the Endomembrane System deals mostly with proteins. It includes the making, modification, sorting, and transport of proteins. All of the Endomembrane System is related by either physically touching or by vesicles transferring between the related organelles.
  Within the Endomembrane System there are many different organelles that have certain responsibilities in the cell. The nuclear envelope is a bi-layer membrane that encompasses the nucleus of cells. The endoplasmic reticulum is the place that proteins are synthesized and transported. Proteins are modified and also transported to other parts of the cell in the golgi apparatus. Lysosomes have a digestive enzyme that allows them to digest macromolecules in the cell. Vesicles are small bits of membranes that are used to transport substances in the cell. Vacuoles are used to store waste products and maintaining the shape of cells. The gatekeeper or plasma membrane of the the cell is used to regulates what enters and exit the cells.
  Endomembrane System consists of most of the membranes in the cells and has many different resposibilities in our cells that are imperative to our bodies.