High School Biology Help » Cell Biology » Cell Structures and Organelles » Common Cell Structures » Understanding the Cell Membrane and Cell Wall
Explanation:

Bacteria and plant cells both have cell walls, although the cell walls are composed of different macromolecules in different cell types. Plants use the protein chitin, while bacteria use peptidoglycan. Bacteria are a certain class of prokaryotes.

You are watching: No cell wall only plasma membrane

Animal cells only have a plasma membrane, and do not have cell walls.


Explanation:

Two general concepts allow you to predict how easily a molecule is able to cross the plasma membrane.

1. The smaller the molecule, the more permeable the membrane is to it. Large molecules have a harder time crossing the membrane.

2. Polar and charged molecules have a very hard time crossing the membrane. Nonpolar molecules can cross the membrane much more easily.

As a result, small, nonpolar molecules are ideal for crossing the membrane easily. Larger molecules do not fit through the membrane gaps, and polar molecules are repelled by the hydrophobic interior of the membrane.


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Example Question #3 : Understanding The Cell Membrane And Cell Wall


An animal cell is placed into a solution of salt water. The salt is unable to cross the membrane. What will most likely happen to the cell?


Possible Answers:

The cell will shrivel


The cell will break open


The cell will swell


The cell will remain the same


Correct answer:

The cell will shrivel


Explanation:

Since salt is unable to pass the membrane, the animal cell will attempt to equalize the salt concentrations on both sides by expelling water into the solution. The concentration of salt outside the cell is higher than the concentration inside the cell. This means that water itself is more concentrated inside the cell than outside. The water will flow down its gradient from high solvent concentration (in the cell) to low solvent concentration (outside the cell) via the process of osmosis. As the water exits the cell, it will lose volume and shrivel.


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Example Question #4 : Understanding The Cell Membrane And Cell Wall


The cell walls of plant cells and bacteria allow them to __________.


Possible Answers:

move water into the surrounding environment


endure hypertonic solutions better than animal cells


maintain less intracellular pressure


endure hypotonic solutions better than animals cells


Correct answer:

endure hypotonic solutions better than animals cells


Explanation:

The cell wall is a very tough structure that is able to help the cell withstand extracellular stressors. A plant cell or bacterium can survive hypotonic solutions better than an animal cell due to protection from the cell wall. As water flows into the cell, but the cell wall will keep the cell from bursting.

The cell wall does not protect well against hypertonic environments, however. As water exits the cell, the plasma membrane pulls away from the cell wall. The cell shrinks within the cell wall, which maintains its original size and does not prevent cellular damage.


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Example Question #5 : Understanding The Cell Membrane And Cell Wall


Which of the following has a cell wall composed of peptidoglycan?


Possible Answers:

Plant cells


Bacteria


Animal cells


Archaea


Correct answer:

Bacteria


Explanation:

Peptidoglycan is found in the cell walls of bacteria. Plant cells have cell walls made of cellulose, and animal cells lack a cell wall entirely. Archaea are a class of prokaryote, but have cell walls that differ from those of bacteria. Archaea cell walls do not contain peptidoglycan.


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Example Question #6 : Understanding The Cell Membrane And Cell Wall


Which of the following types of cellular transport requires the expenditure of energy in order to take place?


Possible Answers:

Facilitated diffusion


Passive diffusion


Osmosis


Active transport


Correct answer:

Active transport


Explanation:

Diffusion and osmosis are both used in order to equalize the concentrations of solutes on both sides of a membrane. This act requires no energy to take place, as solutes will passively flow from regions of high concentration to areas of low concentration. Facilitated diffusion requires a channel protein to allow substances to cross the membrane, but also allows flow down a concentration gradient and does not require energy.

Active transport is needed in order to accumulate solutes on one side of a barrier against their concentration gradient. This requires ATP in order to take place, as the solutes will not flow in this direction naturally.


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Example Question #7 : Understanding The Cell Membrane And Cell Wall


What does it mean when a cell membrane is "selectively permeable?"


Possible Answers:

The shape of the membrane will change, depending on the environment


Some compounds can cross the membrane, while others cannot


Compounds can only enter the cell through channels


Harmful compounds cannot enter the cell


Correct answer:

Some compounds can cross the membrane, while others cannot


Explanation:

The cell membrane is composed of a phospholipid bilayer. Polar regions of the membrane face outward and shield a hydrophobic interior. Only certain compounds can cross both regions of the membrane. Polar compounds and ions will be able to interact with the polar regions of the membrane, but be unable to cross the hydrophobic interior. Similarly, large compounds will be unable to fit between the phospholipids. Only small, nonpolar molecules can cross the membrane freely.

Protein channels are placed in the membrane to allow polar and large molecules to cross, further adding to the selective nature of the membrane. Harmful compounds can still enter the cell from time to time, but the selectivity of the membrane helps prevent the potency of these attacks.


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Example Question #8 : Understanding The Cell Membrane And Cell Wall


Which of the following does not contain a cell wall?


Possible Answers:

Plant cells


Some fungi


All cells have a cell wall


Some protists 


Animal cells


Correct answer:

Animal cells


Explanation:

A cell wall is a tough, and rigid layer of polysaccharides lying outside of the plasma membrane in plants, some fungi, and some protists. The cell wall provides these cells with structural support and protection. It also prevents over-expansion when water enters the cell. Animal cells lack a cell wall, and only have a plasma membrane.


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Example Question #9 : Understanding The Cell Membrane And Cell Wall


Which of the following controls what enters and leaves the cell?


Possible Answers:

Nucleus


DNA


Cytoplasm


Cell membrane


Correct answer:

Cell membrane


Explanation:

The cell membrane controls what enters and leaves the cell. The cell membrane is a selectively permeable phospholipid bi-layer, which admits molecules by passive and active transport into the interior of the cell. The DNA is the genetic code found in the nucleus while cytoplasm is the liquid inside the cell.


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Example Question #10 : Understanding The Cell Membrane And Cell Wall


What is the best description of the fluid-mosaic model for a cell"s membrane?


Possible Answers:

A single layer of phospholipids with embedded proteins


A single layer of phospholipids


A double layer of phospholipids


A double layer of phospholipids with embedded proteins


Correct answer:

A double layer of phospholipids with embedded proteins


Explanation:

The fluid-mosaic model for the cell membrane is a double layer of phospholipids with embedded proteins. The proteins do active transport in pumping molecules across the membrane. The phosphates are on the outside and the lipid chains are on the inside of the membrane.

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