bio unit 7
Cells transport substances across their membranes. Choose THREE of the following four types of cellular transport. -osmosis -active transport -facilitated diffusion -endo/exocytosis For each of the three types you choose, a. Describe the transport process and explain how the organization of cells membranes functions in the movement of specific molecules across the membrane b. Explain the significance of each type of transport to a specific cell.
Osmosis: a) Is the movement of water from higher concentration to lower concentration. Water molecules are small enough to diffuse through the semi-permeable cell membrane, and so it requires no energy from the cell. b) Osmosis is used in every cell of your body to bring water in and get it out. If placed in a pure water (hypotonic solution) cells would burst because water would continually come in. (Red blood cells must maintain their turgor pressure/shape by having the right amount of water) Active Transport: a) Is transport of substances in and out of cells that requires energy from the cell because it goes against the concentration gradient. Proteins on the membrane help in active transport b) The sodium-potassium pump is the classic example, and is in every cell. The membrane has proteins in it onto which 3 Na ions attach from inside, and 2 K ions from outside. Using the cells energy the protein changes shape and throws the Na out and brings the K in. Facilated Diffusion a) Not all molecules are small enough or have the right charge (polar) to go through the membrane. Proteins on the cell membrane help in transporting larger substances in and out. But unlike the active transport, no energy is used because the diffusion still occur down the concentration gradient. b) Helps carry glucose into cells for them to use it as energy.
Describe the fluid mosaic model of the plasma membrane. Discuss the role of the membrane in the movement of materials through by each of the processes a. Active transport b. Passive transport
The fluid-mosaic model of a plasma membrane describes the bilayer of phospholipids in cellular membranes. This bilayer consists of two layers of phospholipids with the tails facing inward toward each other and the heads facing to the outside of the membranes. The term "fluid" relates to the observation that the components of the membrane, like the phospholipids and proteins, are constantly moving. This is basically explaining that the membrane is not solid or stable, but is always flowing and changing. The term "mosaic"explains that membranes are made of many different types of molecules including proteins, phospholipids, glycoproteins, and glycolipids. Just like mosaic painting, plasma membranes are made of various compounds with different sizes and functions. The plasma membrane of cells regulates the movement of all compounds into and out of the cell. In all types of transport involving the cell, this selective permeable membrane controls everything that can enter and exit the cell. a. Certain small compounds lacking a charge like O2, N2, H2O, and CO2 can easily pass through the phospholipid bilayer. These can move through passive transport, which is a type of transport that does not need energy to move. b. Other larger compounds or compounds that have charge such as glucose, sucrose, H+, K+, or Na+ cannot move through the membrane easily. These can move through active transport, which requires a protein and energy. Active transport is the process of moving particles across the membrane against the concentration gradient. This means that the particles are being transported from a high concentration to a low concentration.
Describe a model of the cell membrane of a eukaryotic cell and discuss different ways in which substances move across the membrane.
The fluid-mosaic model of a plasma membrane describes the bilayer of phospholipids in cellular membranes. This bilayer consists of two layers of phospholipids with the tails facing inward toward each other and the heads facing to the outside of the membranes. The term "fluid" relates to the observation that the components of the membrane, like the phospholipids and proteins, are constantly moving. This is basically explaining that the membrane is not solid or stable, but is always flowing and changing. The term "mosaic"explains that membranes are made of many different types of molecules including proteins, phospholipids, glycoproteins, and glycolipids. Just like mosaic painting, plasma membranes are made of various compounds with different sizes and functions. The plasma membrane of cells regulates the movement of all compounds into and out of the cell. In all types of transport involving the cell, this selective permeable membrane controls everything that can enter and exit the cell. Passive Transport: Passive transport is the transport of substances across a membrane by a trans-membrane protein molecule. The transport proteins tend to be specific for one molecule (a bit like enzymes), so substances can only cross a membrane if it contains the appropriate protein. As the name suggests, this is a passive diffusion process, so no energy is involved and substances can only move down their concentration gradient. Active Transport: Active transport is the pumping of substances across a membrane by a trans-membrane protein pump molecule. The protein binds a molecule of the substance to be transported on one side of the membrane, changes shape, and releases it on the other side. The proteins are highly specific, so there is a different protein pump for each molecule to be transported. Active transport allows substances to move across the concentration gradient- areas of low concentration to areas of high
Describe and give an example for each of the following: a. A bulk transport system b. Facilitated diffusion c. Active transport
a. The movement of macromolecules such as proteins or polysaccharides into or out of the cell is called bulk transport. There are two types of bulk transport, exocytosis and endocytosis, and both require the expenditure of energy (ATP). In exocytosis, materials are exported out of the cell via secretory vesicles and endocytosis allows materials into the cell. b. Facilitated diffusion is the process of spontaneous passive transport of molecules or ions across a biological membrane via specific transmembrane integral proteins. The molecules may be too large or have a charge which does not allow them to pass through the membrane via simple diffusion which is why a protein is needed, however no energy is needed since the molecule is still flowing with the concentration gradient. An example is glucose or sucrose moving in and out of cells. c. Active transport is the movement of molecules across a cell membrane in the direction against the concentration gradient. An example of active transport is the sodium-potassium pump.
Water potential (Ψ) is described by the following formulas. Ψ = Ψp + Ψs Ψ = -iCRT Discuss the variables in both formulas and how they affect water potential.
Ψp Pressure potential. Water will move from the area of high pressure to the area of low pressure. Ψs Solute potential. Water will move from the area of high solute potential (low solute concentration) to the area of lower solute potential (higher solute concentration). i Ionization constant. Greater ionization decreases water potential/increases water movement, OR Decrease in ionization increases water potential/decreases water movement. C Concentration. Increase in concentration decreases water potential/increases water movement, OR Decrease in concentration increases water potential/decreases water movement. R Pressure constant. No change in water potential/movement. T Temperature. Increase in temperature decreases water potential/increases water movement, OR Decrease in temperature increases water potential/decreases water movement. The formulas allow osmotic potential or water movement to be calculated or predicted
