cell_transport-lab - Cell Transport page 1 of 5 ANAT 11110...

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Cell Transport page 1 of 5 ANAT 11110 Lab 2 Fall 2011 Cell Transport The cell membrane is both a barrier and a gateway between the cytoplasm and organelles in the interior of the cell and the extracellular environment. On the one hand it must contain the contents of the cell and prevent invasion of the cell by external substances; on the other it must allow certain substances (e.g., nutrients and wastes) to pass through, either from the outside in or from inside out. We speak of the cell membrane as being selectively permeable , meaning that it will allow certain substances through and keep others out (or in, as the case may be). In general, the various ways of moving substances across the cell membrane fall into two categories: active or passive mechanisms. Passive mechanisms do not require any energy expenditure by the cell. Active mechanisms require the expenditure of energy by the cell, depleting its ATP supplies. In this lab, we will look at some of the passive transport mechanisms, which, for the most part, rely on the energy generated by random molecular movement to power movement of a substance across the cell membrane. Station 1: Brownian Motion All molecules vibrate randomly at temperatures above absolute zero (-273 0 C). In general, the smaller the particle, the greater the inherent kinetic energy of the molecule and the faster it moves. This random movement will cause molecules to move across a permeable membrane without the input of energy into the system. This random movement, called Brownian motion , can be detected indirectly by observing a suspension, like milk. The larger particles in the suspension can be seen moving randomly as they are hit and deflected by the smaller, more rapidly moving particles. Place a small drop of milk on a slide and cover carefully with a cover slip. Allow the slide to sit on the microscope stage for a few minutes. As you look through the microscope, what do you see? As the minute water molecules collide with the larger fat globules of the milk, the larger fat globules will ricochet around in an erratic movement. Place the prepared slide on a warm hot plate for a few seconds and then view the slide under the microscope. How has the rate of Brownian motion changed (i.e., are the particles moving faster or slower)? ________________________ ______________________________________________________________ ______________________________________________________________
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Cell Transport page 2 of 5 What is the effect of increased temperature on the kinetic energy of the molecules? Does it increase or decrease the kinetic energy of the particles?
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cell_transport-lab - Cell Transport page 1 of 5 ANAT 11110...

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