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Use the provided reading to help you with the questions.
Your score will be shared with you after you submit this.
You can do this up to four times - if you scored below a 70%, do it again.
Your correct answers will be preserved from the previous attempt.
If you do this multiple times (more than once), your highest score is capped at a 70%.
The cell membrane is also known as the plasma membrane, and we use the terms interchangeably. The cell membrane is responsible for bringing essential materials into the cell and excreting metabolic waste products. In this reading, we will be examining some of the components of the membrane. You should keep in mind that other membranes such as the endoplasmic reticulum and the nuclear membrane are similar to the cell membrane.
The cell membrane is made up of proteins and carbohydrates as well as a phospholipid bilayer. It is an extremely thin structure that measures about 5 to 10 nanometers (nm) in thickness, and it can be seen clearly only through an electron microscope. The currently accepted hypothesis of membrane structure is referred to as the fluid mosaic model, and was proposed by Singer and Nicholson in 1976.
a.) The cell membrane is also known as the
b.) The cell membrane is responsible for bringing
c.) The cell membrane is made up of
d.) Singer and Nicholson proposed a model of the cell membrane that is known as the
The most prominent element of the cell membrane is a bilayer of phospholipids, in which a number of proteins are embedded. In the model associated with this article, the bracket outlines the lipid bilayer (A), in which you can see individual phospholipids (B). A phospholipid consists of a somewhat circular phosphate group head, and two long, fatty acid chain tails. The head region is said to be hydrophilic and polar (C) because it is water-soluble, while the tail portions are hydrophobic and nonpolar (D) because they are not water-soluble. Notice that the hydrophilic heads of the lipid bilayer point toward the cell’s exterior and interior, while the hydrophobic tails point inward.
a.) The cell membrane is a bilayer primarily composed of
b.) Each phospholipid is made up of a somewhat circular
c.) The head region is described as
d.) The tail sections are
e.) The hydrophilic heads of the lipid bilayer are oriented toward the cell’s
Another type of lipid within the lipid bilayer is the cholesterol molecule (E). Cholesterol helps to maintain the fluid condition of the bilayer by breaking up the closely associated phospholipids and maintaining space between them. The number of cholesterol molecules within the lipid bilayer changes depending on the environmental conditions related to the temperature. For instance, as the temperatures remain low the cell membrane is at risk of becoming too solid; therefore, the amount of cholesterol molecules in the lipid bilayer will increase, which creates more space between the phospholipids maintaining the fluidity of the membrane. Inversely, as the temperatures remain high the cell membrane is at risk of becoming too fluid; therefore, the amount of cholesterol molecules in the lipid bilayer will decrease, which decreases the space between the phospholipids maintaining the amount of normal-fluidity in the membrane. Therefore, cholesterol is used to maintain the stability of the membrane.
a.) The lipid bilayer has a second type of lipid called
b.) The role of this second lipid is keeping the lipid bilayer fluid-like by preventing
c.) There will be more of this type of lipid in the bilayer when temperatures are
d.) The purpose of this lipid is to keep the membrane's fluidity
Proteins that are embedded in the cell membrane carry out various cell functions such as nutrient and energy transport and message transmission. One type of protein is the integral protein (F), which spans the entire width of the lipid bilayer and protrudes at both sides. These proteins function as channels through which ions and molecules can travel into and out of the cell.
Other membrane proteins include peripheral proteins (G), which are not embedded in the lipid bilayer, but sit on the surface of the membrane. Peripheral proteins are often connected to cytoskeleton filaments (H) on the cell’s interior. Several filaments are shown on the model. These proteins are generally used to help identify the cell, especially within multicellular organisms, which would prevent the immune system from attacking and destroying the cell.
a.) There are two types of proteins in the cell membrane:
b.) The first type of protein mentioned here are used as
c.) The peripheral proteins are not
d.) The peripheral proteins serve to help
Glycoproteins (J) are carbohydrates attached to a membrane protein. Glycolipids are an identical type of carbohydrate but are attached to the head of a phospholipid. In the diagram, a string of hexagonal molecules that represent glucose molecules in a polysaccharide. The carbohydrate molecules are involved in cell recognition as receptors, and they also aid in the cell’s adhesion to other cells. For example, hormones attach to the carbohydrates on the membranes of target cells.
a.)
b.) A similar type of carbohydrate is known as
c.) These carbohydrate molecules play a role in