Movement of Substances in the Cell

Transcription

1 Movement of Substances in the Cell The Marble Memories Biology All cells are surrounded by a plasma membrane (also called cell membrane). This membrane regulates the entry and exit of substances into and out of the cell. The structure of the cell membrane allows it to let some substances pass through it while hinder some. That is why it is described as semipermeable membrane. The illustration below shows the components of the cell membrane. Some substances may pass through the membrane in two ways passive transport and active transport. Passive transport from a higher concentration, tiny molecules pass through the openings in the membrane (including through some proteins) towards the area of lower concentration. In this process, the movement is driven by the difference in concentration. That is why it is from a high concentration to a lower concentration following the concentration gradient (high to low). No energy from the cell (ATP) is used for the movement. Simple diffusion is a passive transport where tiny particles pass through the openings between the phospholipid bilayers.

2 Water, carbon dioxide, and oxygen move in and out of the cell through simple diffusion. Osmosis is a special term that refers to diffusion of water. Simple Diffusion Facilitated diffusion is when larger particles that cannot pass through the small openings are aided by protein channels. The particles will still move from a higher concentration to a lower concentration passing through specific channel proteins. No cell energy (ATP) is required for the process. Water and sugar move in and out of the cell through facilitated diffusion. Active Transport if substances will need to move from a lower concentration to a higher concentration (against the concentration gradient) cell energy (in the form of ATP) is used to fuel the process. Active transports not only move tiny particles against the concentration gradient, it also allows the movement of large particle by engulfing the particles. Sodium-Potassium pump moves potassium and sodium ions across the plasma membrane with the use of cell energy (ATP). Pumps are integral membrane proteins that open and bind with specific substances when activated by cell energy.

3 The Sodium Potassium Pumps Image is modification of work by Mariana Ruiz Villarreal Endocytosis - is a type of active transport (require ATP) that moves particles, such as large molecules, parts of cells, and even whole cells, into a cell. The plasma membrane of the cell forms a pocket around the target particle. The pocket pinches off, resulting in the particle being contained in a pocket then moved into the cell. The different variations are phagocytosis, pinocytosis, and receptor-mediated endocytosis. Phagocytosis membrane engulfs a solid particle

4 Pinocytosis membrane engulfs a small volume of fluid Receptormediated endocytosis uses a single type of substance that binds at the receptor on the external cell membrane

5 Exocytosis - is to expel material from the cell into the outside of the cell. A vesicle migrates to the plasma membrane, binds, and releases its contents to the outside of the cell. Cell and Tonicity Tonicity describes the amount of solute in a solution. Cells are greatly affected by tonicity. In a hypotonic solution, the extracellular fluid has a lower concentration of solutes than the fluid inside the cell, and water enters the cell. In living systems, the point of reference is always the cytoplasm, so the prefix hypomeans that the extracellular fluid has a lower concentration of solutes. This may cause an animal cell to burst, or lyse. In a hypertonic solution, the prefix hyper- refers to the extracellular fluid having a higher concentration of solutes than the cell s cytoplasm. Water will leave the cell and may cause an animal cell to shrivel, or crenate.

6 In an isotonic solution, the extracellular fluid has the same solute concentration as the cell. There is no net movement of water into or out of the cell. Tonicity and Blood Cell Appearance Image is modification of work by Mariana Ruiz Villarreal Tonicity and Plant Cell Appearance Image is modification of work by Mariana Ruiz Villarreal The cell wall prevents the cell from busting.