Biology: Plasma Membrane and Functions

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Questions and Answers

What is the main characteristic of the plasma membrane's selectivity?

It allows all substances to pass freely.

It only allows water and small ions to enter the cell.

It prevents any substances from crossing.

It selectively permits some substances to cross more easily than others. (correct)

What is one of the primary functions of the plasma membrane?

To provide structural rigidity to the cell.

To facilitate intracellular communication.

To control what enters and exits the cell. (correct)

To generate energy for the cell.

What is the approximate thickness of the plasma membrane?

20 nm

5 nm

12 nm

8 nm (correct)

What role does the plasma membrane play in the protection of the cell?

It acts as a barrier against harmful substances. Signup and view all the answers

What internal balance does the plasma membrane help maintain?

Chemical homeostasis. Signup and view all the answers

What is the primary component of cell membranes?

Phospholipids Signup and view all the answers

What characteristic do amphipathic molecules possess?

Both hydrophilic and hydrophobic regions Signup and view all the answers

How does cholesterol affect membrane fluidity at warm temperatures?

Decreases fluidity by restraining phospholipid movement Signup and view all the answers

Which term describes the selective ability of the cell membrane?

Selectively permeable Signup and view all the answers

What structure of phospholipids faces the internal environment of the cell?

Hydrophobic tails Signup and view all the answers

What is the overall shape of the cell membrane described as?

Fluid mosaic Signup and view all the answers

What is the primary role of the proteins in the cell membrane?

To facilitate various cellular processes Signup and view all the answers

What is the polar characteristic of the phosphate head of phospholipids?

It is hydrophilic Signup and view all the answers

What role does cholesterol play in the cell membrane at lower temperatures?

It prevents the membrane from freezing. Signup and view all the answers

How do cells respond to changes in temperature regarding membrane lipid concentration?

By altering membrane lipid concentration. Signup and view all the answers

Which statement is true about integral proteins?

They can span both layers of the phospholipid bilayer. Signup and view all the answers

What characterizes peripheral proteins in the cell membrane?

They are attached only to the membrane surface. Signup and view all the answers

What is the fluidity of the membrane at higher temperatures?

It becomes stiffer. Signup and view all the answers

What is the primary function of membrane proteins?

To determine specific functions of the membrane. Signup and view all the answers

Which feature is NOT characteristic of integral proteins?

They are only present on one side of the membrane. Signup and view all the answers

What is the overall structure of the cell membrane commonly described as?

A mosaic of proteins and phospholipids. Signup and view all the answers

Study Notes

Plasma Membrane

The plasma membrane separates the living cell from its nonliving surroundings.
It is a thin barrier, 8 nm thick, controlling traffic into and out of the cell.
Like other membranes, the plasma membrane is selectively permeable, allowing some substances to cross more easily than others.
All cells have a cell membrane.

Cell Membrane Functions

Controls what enters and exits the cell to maintain internal balance, called homeostasis.
Provides protection and support for the cell.

Membrane Structure

Lipids and proteins are major components, with carbohydrates also playing a role.
Phospholipids are the most abundant lipids in most membranes.
Phospholipids and most membrane proteins are amphipathic molecules.
A membrane is a fluid mosaic of lipids, proteins, and carbohydrate.
The membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids.
The cell membrane only lets certain substances in and out of the cell.

Phospholipid Bilayer

Polar heads are hydrophilic ("water-loving").
Tails (fatty acids) are hydrophobic ("water-fearing") and face inward.

Cholesterol

Found in plasma membranes of eukaryotes.
Modulates membrane fluidity by making the membrane:
- Less fluid at warm temperatures (e.g., 37°C) by restraining phospholipid movement.
- More fluid at lower (cool) temperatures by preventing close packing of phospholipids.
Cells may alter membrane lipid concentration in response to changes in temperature.

Membrane Proteins

Integral proteins span both layers of the phospholipid bilayer.
Peripheral proteins are on either the top or bottom half of the phospholipid bilayer.
Proteins determine most of the membrane's specific functions.
There are two populations of membrane proteins. Peripheral proteins are not embedded in the lipid bilayer. Instead, they are loosely bounded to the surface of the protein, often connected to the other population of membrane proteins.

Membrane Carbohydrates

Important for cell-cell recognition.
The ability of a cell to distinguish one type of neighboring cell from another.
Crucial for organism function.
The basis for sorting cells into tissues and organs in an animal embryo.
The basis for rejection of foreign cells by the immune system, and many other processes.
Usually branched oligosaccharides (<15 monomers).
Some are covalently bonded to lipids, forming glycolipids.
Most are covalently bonded to proteins, forming glycoproteins.

Membrane Functions

Receives signals from outside the cell for internal cellular activities.
Imports and exports molecules.
Movement of the cell.

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Description

This quiz explores the plasma membrane's role in cellular structure and function. It covers the characteristics of the cell membrane, its selective permeability, and the components that make up this vital barrier. Test your understanding of how membranes maintain homeostasis and support cellular activities.