Anatomy and Physiology Answer Key

F motor neuron features cell body with a long

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Unformatted text preview: 2009 Photocopying Prohibited Many cells are specialized to carry out a particular role and have organelles and structures specifically associated with that role, while lacking others that are not relevant or useful. For example, red blood cells lack a nucleus and most organelles, and are thus short lived, but this gives room inside the cell for them to carry a lot of hemoglobin, the oxygen-carrying pigment that enables them to fulfill their role in oxygen transport. Similarly, neutrophils have most organelles, (including many lysosomes), and are very motile with the ability to engulf material. This is associated with their functional role of phagocytosis and destruction of foreign material. The Structure of Membranes (page 19) 1. (a) Phospholipids are amphipathic, meaning they are molecules that are mostly lipid-like (hydrophobic) in structure, but at one end have a region that is polar or ionic (hydrophilic). The hydrophilic region is usually referred to as the head group, and the lipid portion is know as the tail(s). Because of this property, they tend to organize themselves into a bilayer so that the hydrophilic heads face outwards and the hydrophobic tails point in towards each other (away from the aqueous environment both outside and inside the cell). (b) This model accounts for the properties we observe in cellular membranes: its fluidity (how its shape is not static and how its components move within the membrane, relative to one-another) and its mosaic nature (the way in which the relative proportions of the membrane components, i.e. proteins, glycoproteins, glycolipids etc, can vary from membrane to membrane). The fluid mosaic model also accounts for how membranes can allow for the selective passage of materials (through protein channels for example) and how they enable cell-cell recognition (again, as a result of membrane components such as glycoproteins). 2. Membrane surface area is increased by the presence of microvilli and other types of surface projections (and invaginations). 3. (a) High surface area: provides greater surface over which substances can move across (by diffusion or active transport) and a greater surface area over which membran...
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