Cell membranes are critical to the survival and function of all cells; they keep cells isolated from
the external environment and from other cells. The plasma membrane is said to be differentially
or selectively permeable.
1. What does it mean for a membrane to be selectively permeable?
A membrane that is selectively permeable only allows certain substances to pass through.
(Simon, E.J., J.L. Dickey and J.B. Reece. 2013, pg 84) A cell is a living thing and needs
just the right balance of nutrients and water, called homeostasis. The selective
m
er as
permeability of the membrane allows the cell to stay in homeostasis. The components
co
eH w
that make up the cell membrane allow it to be selectively permeable. The cell membrane
o.
rs e
is made of proteins and a special type of fat called phospholipids . The phospholipids
ou urc
form a bilayer, or double layer. A phospholipid has two parts: the head, which likes water
o
(hydrophilic) and the tail, which doesn't like water (hydrophobic). The phospholipid tails
aC s
vi y re
come together, protecting themselves from the water, leaving the heads on the outside.
2. Select two specific components of the cell membrane and explain how each affects the
ed d
ar stu
permeability of the cell membrane. Meaning, what specific materials are regulated by the
given component and how.
is
Th
Carbohydrates and the phospholipid bilayer are two specific components of the cell
membrane that affect the permeability of the cell membrane. Carbohydrates attach to
sh
proteins and lipids creating glycocalyx. Glycocalyx adds to the protective layer of the cell
membrane and also serves as a recognition mechanism. It acts as a glue to attach cells
together.
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