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Anatomy & Physiology Cell Structure & Function Quiz

This Anatomy & Physiology (A&P)  quiz is designed to test your knowledge of the basic cell structure and function. You will be asked questions that pertain to the mitochondria, nucleolus, nuclear membrane, ribosomes, lysosome, and much more.

This practice test for the cell function and structure for Anatomy & Physiology, is designed to help you for your exam by concentrating on the important facts you may see again on an exam.  The human body is made up of 50 to 100 trillion cells and each cell is designed to perform a variety of functions to keep your body is functioning shape.

Along with the Anatomy & Physiology quiz, we have developed many other quizzes to help you study. After you take the quiz, the page will refresh and you will need to scroll down to see your results with your answers.

Teaching Video on Cell Structure

Quiz for Anatomy & Physiology for Cell Structure & Function

Anatomy & physiology quiz on cell structure.

This quiz is to test your knowledge of the cell structure for Anatomy & Physiology.

• a. Organelles
• c. Plasma membrane
• d. Phagocytosis
• a. Plasma membrane
• b. Cytoplasm
• a. Chromatin
• b. Glycosomes
• d. Plasma membrane
• b. Glycosome
• b. Centrioles
• c. Centrosome Matrix
• d. Microfilament
• a. Ribosome
• c. Mitochondria
• d. Endoplasmic reticulum
• a. Filaments
• b. Microfilament
• c. Microtuble
• d. Microvilli
• b. Mitochondria
• c. Microfilaments
• d. Nuclear Envelope
• a. Microtubles
• b. Intermediate filaments
• c. Chromatin
• d. Nuceloli
• a. mobilize, cytokines
• b. detoxify, free radicals
• c. destory, water
• d. break down, lipids
• a. exocytosis
• b. ribosomes
• c. Golgi apparatus
• d. Lysosomes
• a. Small, dark staining granules, RNA
• b. large, dark staining granules, DNA
• c. tiny-finger-like extensions, and lysosomes
• d. None of the above
• b. Nucleolus
• d. Peroxisome
• a. Peroxisome
• b. Plasma membrane
• d. Nucleolus
• d. Centrosome
• a. mitochondria
• b. chromatin
• c. microtubules
• d. nuclear envelope

Cell Structure Quiz

1. What part of the cell’s subunit is responsible for disposal of waste, maintaining its shape/integrity, and replicating itself? a. Organelles b. Enzymes c. Plasma membrane d. Phagocytosis The answer is a. Organelles.

2. The outer boundary of the cell which makes up the three main parts of the human cell is the? a. Plasma membrane b. Cytoplasm c. Nucleus d. Enzymes The answer is a. Plasma membrane.

3. The nucleus is found in the center of the cell and controls cell activity. True False The answer is True.

4. What structure is responsible for storing glycogen for the cell’s main energy source? a. Chromatin b. Glycosomes c. Nucleus d. Plasma membrane The answer is b. Glycosomes.

5. What structure of the cell is responsible for packaging DNA, reinforcing mitosis, preventing DNA damage, and controlling DNA replication? a. Chromatin b. Glycosome c. Nucleus d. Plasma membrane The answer is a. Chromatin.

6. Smooth endoplasmic reticulum is responsible for fat metabolism. True False The answer is True.

7. The liquid found inside a cell is? a. Cytosol b. Centrioles c. Centrosome Matrix d. Microfilament The answer is a. Cytosol.

8. The lysosomes perform intracellular replication. False True The answer is false. It performs intracellular DIGESTION.

9. This structure is called the power-house of the cell because it generates the cell’s energy? a. Ribosome b. ATP c. Mitochondria d. Endoplasmic reticulum The answer is c. Mitochondria.

10. The centrioles are found in the cytoplasm. False True The answer is false. They are found in the centrosome matrix.

11. What structure of the cell is like tiny, finger-like extensions of the plasma membrane that increases cell’s surface area? a. Filaments b. Microfilament c. Microtuble d. Microvilli The answer is d. Microvilli.

12. The ( ______) helps form the cytoskeleton of the cell? a. Vaults b. Mitochondria c. Microfilaments d. Nuclear Envelope The answer is c. Microfilaments.

13. The (______) is responsible for supporting the cell and giving it shape. a. Microtubles b. Intermediate filaments c. Chromatin d. Nuceloli The answer is a. Microtubles.

14. Intermediate filaments are cytoskeletal elements that help the cell resist tension. True False The answer is true.

15. Peroxisomes use oxidases and catalase to (_______) the body from (_______). a. mobilize, cytokines b. detoxify, free radicals c. destory, water d. break down, lipids The answer is b. detoxify, free radicals.

16. This structure is a stack of three to ten disc-shaped envelopes bound by a membrane that sorts, processes, and packages proteins and membranes? a. exocytosis b. ribosomes c. Golgi apparatus d. Lysosomes The answer is c. Golgi apparatus.

17. Ribosomes have the appearance of _______ and are constructed of _______? a. Small, dark staining granules, RNA b. large, dark staining granules, DNA c. tiny-finger-like extensions, and lysosomes d. None of the above The answer is a. Small, dark staining granules, RNA.

18. This area of the cell is a thin flexible layer that separates fluid into intracellular and extracellular fluid? a. Plasma membrane b. Nucleolus c. Chromatin d. Peroxisome The answer is a. Plasma membrane.

19. This site serves as the synthesis and assembly of ribosomes? a. Peroxisome b. Plasma membrane c. Chromatin d. Nucleolus The answer is d. Nucleolus.

20. This structure is the central core of the cell and it’s genetic material is DNA? a. Nucleus b. Glycosome c. Mitochondria d. Centrosome The answer is a. Nucleus.

21. This area of the cell surrounds the nucleus and regulates passage of substances to and from the nucleus? a. mitochondria b. chromatin c. microtubules d. nuclear envelope The answer is d. nuclear envelope .

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3.1 The Cell Membrane

Learning objectives.

By the end of this section, you will be able to:

• Describe the molecular components that make up the cell membrane
• Explain the major features and properties of the cell membrane
• Differentiate between materials that can and cannot diffuse through the lipid bilayer
• Compare and contrast different types of passive transport with active transport, providing examples of each

Despite differences in structure and function, all living cells in multicellular organisms have a surrounding cell membrane. As the outer layer of your skin separates your body from its environment, the cell membrane (also known as the plasma membrane) separates the inner contents of a cell from its exterior environment. This cell membrane provides a protective barrier around the cell and regulates which materials can pass in or out.

Structure and Composition of the Cell Membrane

The cell membrane is an extremely pliable structure composed primarily of back-to-back phospholipids (a “bilayer”). Cholesterol is also present, which contributes to the fluidity of the membrane, and there are various proteins embedded within the membrane that have a variety of functions.

A single phospholipid molecule has a phosphate group on one end, called the “head,” and two side-by-side chains of fatty acids that make up the lipid tails ( Figure 3.2 ). The phosphate group is negatively charged, making the head polar and hydrophilic—or “water loving.” A hydrophilic molecule (or region of a molecule) is one that is attracted to water. The phosphate heads are thus attracted to the water molecules of both the extracellular and intracellular environments. The lipid tails, on the other hand, are uncharged, or nonpolar, and are hydrophobic—or “water fearing.” A hydrophobic molecule (or region of a molecule) repels and is repelled by water. Some lipid tails consist of saturated fatty acids and some contain unsaturated fatty acids. This combination adds to the fluidity of the tails that are constantly in motion. Phospholipids are thus amphipathic molecules. An amphipathic molecule is one that contains both a hydrophilic and a hydrophobic region. In fact, soap works to remove oil and grease stains because it has amphipathic properties. The hydrophilic portion can dissolve in water while the hydrophobic portion can trap grease in micelles that then can be washed away.

The cell membrane consists of two adjacent layers of phospholipids. The lipid tails of one layer face the lipid tails of the other layer, meeting at the interface of the two layers. The phospholipid heads face outward, one layer exposed to the interior of the cell and one layer exposed to the exterior ( Figure 3.3 ). Because the phosphate groups are polar and hydrophilic, they are attracted to water in the intracellular fluid. Intracellular fluid (ICF) is the fluid interior of the cell. The phosphate groups are also attracted to the extracellular fluid. Extracellular fluid (ECF) is the fluid environment outside the enclosure of the cell membrane. Interstitial fluid (IF) is the term given to extracellular fluid not contained within blood vessels. Because the lipid tails are hydrophobic, they meet in the inner region of the membrane, excluding watery intracellular and extracellular fluid from this space. The cell membrane has many proteins, as well as other lipids (such as cholesterol), that are associated with the phospholipid bilayer. An important feature of the membrane is that it remains fluid; the lipids and proteins in the cell membrane are not rigidly locked in place.

Membrane Proteins

The lipid bilayer forms the basis of the cell membrane, but it is peppered throughout with various proteins. Two different types of proteins that are commonly associated with the cell membrane are the integral proteins and peripheral protein ( Figure 3.4 ). As its name suggests, an integral protein is a protein that is embedded in the membrane. A channel protein is an example of an integral protein that selectively allows particular materials, such as certain ions, to pass into or out of the cell.

Another important group of integral proteins are cell recognition proteins, which serve to mark a cell’s identity so that it can be recognized by other cells. A receptor is a type of recognition protein that can selectively bind a specific molecule outside the cell, and this binding induces a chemical reaction within the cell. A ligand is the specific molecule that binds to and activates a receptor. Some integral proteins serve dual roles as both a receptor and an ion channel. One example of a receptor-ligand interaction is the receptors on nerve cells that bind neurotransmitters, such as dopamine. When a dopamine molecule binds to a dopamine receptor protein, a channel within the transmembrane protein opens to allow certain ions to flow into the cell.

Some integral membrane proteins are glycoproteins. A glycoprotein is a protein that has carbohydrate molecules attached, which extend into the extracellular matrix. The attached carbohydrate tags on glycoproteins aid in cell recognition. The carbohydrates that extend from membrane proteins and even from some membrane lipids collectively form the glycocalyx. The glycocalyx is a fuzzy-appearing coating around the cell formed from glycoproteins and other carbohydrates attached to the cell membrane. The glycocalyx can have various roles. For example, it may have molecules that allow the cell to bind to another cell, it may contain receptors for hormones, or it might have enzymes to break down nutrients. The glycocalyces found in a person’s body are products of that person’s genetic makeup. They give each of the individual’s trillions of cells the “identity” of belonging in the person’s body. This identity is the primary way that a person’s immune defense cells “know” not to attack the person’s own body cells, but it also is the reason organs donated by another person might be rejected.

Peripheral proteins are typically found on the inner or outer surface of the lipid bilayer but can also be attached to the internal or external surface of an integral protein. These proteins typically perform a specific function for the cell. Some peripheral proteins on the surface of intestinal cells, for example, act as digestive enzymes to break down nutrients to sizes that can pass through the cells and into the bloodstream.

Transport across the Cell Membrane

One of the great wonders of the cell membrane is its ability to regulate the concentration of substances inside the cell. These substances include ions such as Ca ++ , Na + , K + , and Cl – ; nutrients including sugars, fatty acids, and amino acids; and waste products, particularly carbon dioxide (CO 2 ), which must leave the cell.

The membrane’s lipid bilayer structure provides the first level of control. The phospholipids are tightly packed together, and the membrane has a hydrophobic interior. This structure causes the membrane to be selectively permeable. A membrane that has selective permeability allows only substances meeting certain criteria to pass through it unaided. In the case of the cell membrane, only relatively small, nonpolar materials can move through the lipid bilayer (remember, the lipid tails of the membrane are nonpolar). Some examples of these are other lipids, oxygen and carbon dioxide gases, and alcohol. However, water-soluble materials—like glucose, amino acids, and electrolytes—need some assistance to cross the membrane because they are repelled by the hydrophobic tails of the phospholipid bilayer. All substances that move through the membrane do so by one of two general methods, which are categorized based on whether or not energy is required. Passive transport is the movement of substances across the membrane without the expenditure of cellular energy. In contrast, active transport is the movement of substances across the membrane using energy from adenosine triphosphate (ATP).

Passive Transport

In order to understand how substances move passively across a cell membrane, it is necessary to understand concentration gradients and diffusion. A concentration gradient is the difference in concentration of a substance across a space. Molecules (or ions) will spread/diffuse from where they are more concentrated to where they are less concentrated until they are equally distributed in that space. (When molecules move in this way, they are said to move down their concentration gradient.) Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration. A couple of common examples will help to illustrate this concept. Imagine being inside a closed bathroom. If a bottle of perfume were sprayed, the scent molecules would naturally diffuse from the spot where they left the bottle to all corners of the bathroom, and this diffusion would go on until no more concentration gradient remains. Another example is a spoonful of sugar placed in a cup of tea. Eventually the sugar will diffuse throughout the tea until no concentration gradient remains. In both cases, if the room is warmer or the tea hotter, diffusion occurs even faster as the molecules are bumping into each other and spreading out faster than at cooler temperatures. Having an internal body temperature around 98.6 ° F thus also aids in diffusion of particles within the body.

Interactive Link

Visit this link to see diffusion and how it is propelled by the kinetic energy of molecules in solution. How does temperature affect diffusion rate, and why?

Whenever a substance exists in greater concentration on one side of a semipermeable membrane, such as the cell membranes, any substance that can move down its concentration gradient across the membrane will do so. Consider substances that can easily diffuse through the lipid bilayer of the cell membrane, such as the gases oxygen (O 2 ) and CO 2 . O 2 generally diffuses into cells because it is more concentrated outside of them, and CO 2 typically diffuses out of cells because it is more concentrated inside of them. Neither of these examples requires any energy on the part of the cell, and therefore they use passive transport to move across the membrane.

Before moving on, you need to review the gases that can diffuse across a cell membrane. Because cells rapidly use up oxygen during metabolism, there is typically a lower concentration of O 2 inside the cell than outside. As a result, oxygen will diffuse from the interstitial fluid directly through the lipid bilayer of the membrane and into the cytoplasm within the cell. On the other hand, because cells produce CO 2 as a byproduct of metabolism, CO 2 concentrations rise within the cytoplasm; therefore, CO 2 will move from the cell through the lipid bilayer and into the interstitial fluid, where its concentration is lower. This mechanism of molecules moving across a cell membrane from the side where they are more concentrated to the side where they are less concentrated is a form of passive transport called simple diffusion ( Figure 3.5 ).

Large polar or ionic molecules, which are hydrophilic, cannot easily cross the phospholipid bilayer. Very small polar molecules, such as water, can cross via simple diffusion due to their small size. Charged atoms or molecules of any size cannot cross the cell membrane via simple diffusion as the charges are repelled by the hydrophobic tails in the interior of the phospholipid bilayer. Solutes dissolved in water on either side of the cell membrane will tend to diffuse down their concentration gradients, but because most substances cannot pass freely through the lipid bilayer of the cell membrane, their movement is restricted to protein channels and specialized transport mechanisms in the membrane. Facilitated diffusion is the diffusion process used for those substances that cannot cross the lipid bilayer due to their size, charge, and/or polarity ( Figure 3.6 ). A common example of facilitated diffusion is the movement of glucose into the cell, where it is used to make ATP. Although glucose can be more concentrated outside of a cell, it cannot cross the lipid bilayer via simple diffusion because it is both large and polar. To resolve this, a specialized carrier protein called the glucose transporter will transfer glucose molecules into the cell to facilitate its inward diffusion.

As an example, even though sodium ions (Na + ) are highly concentrated outside of cells, these electrolytes are charged and cannot pass through the nonpolar lipid bilayer of the membrane. Their diffusion is facilitated by membrane proteins that form sodium channels (or “pores”), so that Na + ions can move down their concentration gradient from outside the cells to inside the cells. There are many other solutes that must undergo facilitated diffusion to move into a cell, such as amino acids, or to move out of a cell, such as wastes. Because facilitated diffusion is a passive process, it does not require energy expenditure by the cell.

Water also can move freely across the cell membrane of all cells, either through protein channels or by slipping between the lipid tails of the membrane itself. Osmosis is the diffusion of water through a semipermeable membrane ( Figure 3.7 ).

The movement of water molecules is not itself regulated by some cells, so it is important that these cells are exposed to an environment in which the concentration of solutes outside of the cells (in the extracellular fluid) is equal to the concentration of solutes inside the cells (in the cytoplasm). Two solutions that have the same concentration of solutes are said to be isotonic (equal tension). When cells and their extracellular environments are isotonic, the concentration of water molecules is the same outside and inside the cells, and the cells maintain their normal shape (and function).

Osmosis occurs when there is an imbalance of solutes outside of a cell versus inside the cell. A solution that has a higher concentration of solutes than another solution is said to be hypertonic , and water molecules tend to diffuse into a hypertonic solution ( Figure 3.8 ). Cells in a hypertonic solution will shrivel as water leaves the cell via osmosis. In contrast, a solution that has a lower concentration of solutes than another solution is said to be hypotonic , and water molecules tend to diffuse out of a hypotonic solution. Cells in a hypotonic solution will take on too much water and swell, with the risk of eventually bursting. A critical aspect of homeostasis in living things is to create an internal environment in which all of the body’s cells are in an isotonic solution. Various organ systems, particularly the kidneys, work to maintain this homeostasis.

Another mechanism besides diffusion to passively transport materials between compartments is filtration. Unlike diffusion of a substance from where it is more concentrated to less concentrated, filtration uses a hydrostatic pressure gradient that pushes the fluid—and the solutes within it—from a higher pressure area to a lower pressure area. Filtration is an extremely important process in the body. For example, the circulatory system uses filtration to move plasma and substances across the endothelial lining of capillaries and into surrounding tissues, supplying cells with the nutrients. Filtration pressure in the kidneys provides the mechanism to remove wastes from the bloodstream.

Active Transport

For all of the transport methods described above, the cell expends no energy. Membrane proteins that aid in the passive transport of substances do so without the use of ATP. During active transport, ATP is required to move a substance across a membrane, often with the help of protein carriers, and usually against its concentration gradient.

One of the most common types of active transport involves proteins that serve as pumps. The word “pump” probably conjures up thoughts of using energy to pump up the tire of a bicycle or a basketball. Similarly, energy from ATP is required for these membrane proteins to transport substances—molecules or ions—across the membrane, usually against their concentration gradients (from an area of low concentration to an area of high concentration).

The sodium-potassium pump , which is also called Na + /K + ATPase, transports sodium out of a cell while moving potassium into the cell. The Na + /K + pump is an important ion pump found in the membranes of many types of cells. These pumps are particularly abundant in nerve cells, which are constantly pumping out sodium ions and pulling in potassium ions to maintain an electrical gradient across their cell membranes. An electrical gradient is a difference in electrical charge across a space. In the case of nerve cells, for example, the electrical gradient exists between the inside and outside of the cell, with the inside being negatively-charged (at around -70 mV) relative to the outside. The negative electrical gradient is maintained because each Na + /K + pump moves three Na + ions out of the cell and two K + ions into the cell for each ATP molecule that is used ( Figure 3.9 ). This process is so important for nerve cells that it accounts for the majority of their ATP usage.

Active transport pumps can also work together with other active or passive transport systems to move substances across the membrane. For example, the sodium-potassium pump maintains a high concentration of sodium ions outside of the cell. Therefore, if the cell needs sodium ions, all it has to do is open a passive sodium channel, as the concentration gradient of the sodium ions will drive them to diffuse into the cell. In this way, the action of an active transport pump (the sodium-potassium pump) powers the passive transport of sodium ions by creating a concentration gradient. When active transport powers the transport of another substance in this way, it is called secondary active transport.

Symporters are secondary active transporters that move two substances in the same direction. For example, the sodium-glucose symporter uses sodium ions to “pull” glucose molecules into the cell. Because cells store glucose for energy, glucose is typically at a higher concentration inside of the cell than outside. However, due to the action of the sodium-potassium pump, sodium ions will easily diffuse into the cell when the symporter is opened. The flood of sodium ions through the symporter provides the energy that allows glucose to move through the symporter and into the cell, against its concentration gradient.

Conversely, antiporters are secondary active transport systems that transport substances in opposite directions. For example, the sodium-hydrogen ion antiporter uses the energy from the inward flood of sodium ions to move hydrogen ions (H+) out of the cell. The sodium-hydrogen antiporter is used to maintain the pH of the cell's interior.

Other forms of active transport do not involve membrane carriers. Endocytosis (bringing “into the cell”) is the process of a cell ingesting material by enveloping it in a portion of its cell membrane, and then pinching off that portion of membrane ( Figure 3.10 ). Once pinched off, the portion of membrane and its contents becomes an independent, intracellular vesicle. A vesicle is a membranous sac—a spherical and hollow organelle bounded by a lipid bilayer membrane. Endocytosis often brings materials into the cell that must be broken down or digested. Phagocytosis (“cell eating”) is the endocytosis of large particles. Many immune cells engage in phagocytosis of invading pathogens. Like little Pac-men, their job is to patrol body tissues for unwanted matter, such as invading bacterial cells, phagocytize them, and digest them. In contrast to phagocytosis, pinocytosis (“cell drinking”) brings fluid containing dissolved substances into a cell through membrane vesicles.

Phagocytosis and pinocytosis take in large portions of extracellular material, and they are typically not highly selective in the substances they bring in. Cells regulate the endocytosis of specific substances via receptor-mediated endocytosis. Receptor-mediated endocytosis is endocytosis by a portion of the cell membrane that contains many receptors that are specific for a certain substance. Once the surface receptors have bound sufficient amounts of the specific substance (the receptor’s ligand), the cell will endocytose the part of the cell membrane containing the receptor-ligand complexes. Iron, a required component of hemoglobin, is endocytosed by red blood cells in this way. Iron is bound to a protein called transferrin in the blood. Specific transferrin receptors on red blood cell surfaces bind the iron-transferrin molecules, and the cell endocytoses the receptor-ligand complexes.

In contrast with endocytosis, exocytosis (taking “out of the cell”) is the process of a cell exporting material using vesicular transport ( Figure 3.11 ). Many cells manufacture substances that must be secreted, like a factory manufacturing a product for export. These substances are typically packaged into membrane-bound vesicles within the cell. When the vesicle membrane fuses with the cell membrane, the vesicle releases it contents into the interstitial fluid. The vesicle membrane then becomes part of the cell membrane. Cells of the stomach and pancreas produce and secrete digestive enzymes through exocytosis ( Figure 3.12 ). Endocrine cells produce and secrete hormones that are sent throughout the body, and certain immune cells produce and secrete large amounts of histamine, a chemical important for immune responses.

View the University of Michigan WebScope to explore the tissue sample in greater detail.

Diseases of the...

Cell: cystic fibrosis.

Cystic fibrosis (CF) affects approximately 30,000 people in the United States, with about 1,000 new cases reported each year. The genetic disease is most well known for its damage to the lungs, causing breathing difficulties and chronic lung infections, but it also affects the liver, pancreas, and intestines. Only about 50 years ago, the prognosis for children born with CF was very grim—a life expectancy rarely over 10 years. Today, with advances in medical treatment, many CF patients live into their 30s.

The symptoms of CF result from a malfunctioning membrane ion channel called the cystic fibrosis transmembrane conductance regulator, or CFTR. In healthy people, the CFTR protein is an integral membrane protein that transports Cl – ions out of the cell. In a person who has CF, the gene for the CFTR is mutated, thus, the cell manufactures a defective channel protein that typically is not incorporated into the membrane, but is instead degraded by the cell.

The CFTR requires ATP in order to function, making its Cl – transport a form of active transport. This characteristic puzzled researchers for a long time because the Cl – ions are actually flowing down their concentration gradient when transported out of cells. Active transport generally pumps ions against their concentration gradient, but the CFTR presents an exception to this rule.

In normal lung tissue, the movement of Cl – out of the cell maintains a Cl – -rich, negatively charged environment immediately outside of the cell. This is particularly important in the epithelial lining of the respiratory system. Respiratory epithelial cells secrete mucus, which serves to trap dust, bacteria, and other debris. A cilium (plural = cilia) is one of the hair-like appendages found on certain cells. Cilia on the epithelial cells move the mucus and its trapped particles up the airways away from the lungs and toward the outside. In order to be effectively moved upward, the mucus cannot be too viscous; rather it must have a thin, watery consistency. The transport of Cl – and the maintenance of an electronegative environment outside of the cell attract positive ions such as Na + to the extracellular space. The accumulation of both Cl – and Na + ions in the extracellular space creates solute-rich mucus, which has a low concentration of water molecules. As a result, through osmosis, water moves from cells and extracellular matrix into the mucus, “thinning” it out. This is how, in a normal respiratory system, the mucus is kept sufficiently watered-down to be propelled out of the respiratory system.

If the CFTR channel is absent, Cl – ions are not transported out of the cell in adequate numbers, thus preventing them from drawing positive ions. The absence of ions in the secreted mucus results in the lack of a normal water concentration gradient. Thus, there is no osmotic pressure pulling water into the mucus. The resulting mucus is thick and sticky, and the ciliated epithelia cannot effectively remove it from the respiratory system. Passageways in the lungs become blocked with mucus, along with the debris it carries. Bacterial infections occur more easily because bacterial cells are not effectively carried away from the lungs.

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• Section URL: https://openstax.org/books/anatomy-and-physiology-2e/pages/3-1-the-cell-membrane

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Cell Structure

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Select a sample cell from an animal, plant, or bacterium and view the cell under a microscope. Select each organelle on the image to learn more about its structure and function. Closeup views and animations of certain organelles is provided.

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6.20: Assignment- Cell Builder

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Create a model of a eukaryotic cell using any material of your choice. In your model be sure to include all the organelles appropriate to your cell (either plant or animal). Once complete, take multiple photographs of your model from all angles. Include these images in a document that also contains the following in table format:

• A detailed key/legend that matches the model;
• Each organelle or part with its basic function;
• A disease or disorder that is associated with the malfunction of each cellular component
• How this organelle is visualized microscopically

Note for the disease information, you can list a disease in either animals or plants, regardless of what type of cell you are modeling. In other words, its okay to discuss a “human” disease even if you are making a plant model, provided the organelle is present in both types of cells.

Some suggestions for 3D models include Legos, a decorated cake with candy toppings, or standard Styrofoam base with appropriate pieces attached. You can also draw or illustrate a model. Here is an example of what you might make.

Basic Requirements (the assignment will not be accepted or assessed unless the follow criteria have been met):

• Assignment has been proofread and does not contain any major spelling or grammatical errors
• Assignment includes appropriate references
• Assignment includes photographs or images of created model from all angles.
• Assignment includes a key documenting how each organelle is represented in the model.
• Assignment includes a completed table such as the one illustrated in the example document.
• Assignment includes a disease caused by malfunction of each identified component in the model.
• Assignment includes at least 7 organelles in the model and table.

Contributors and Attributions

• Performance Assessments: Cell Builder. Authored by : Shelli Carter. Provided by : Columbia Basin College. Located at : https://www.columbiabasin.edu/ . License : CC BY: Attribution

Resources: Course Assignments

Module 4 assignment: cell builder.

Create a model of a eukaryotic cell using any material of your choice. In your model be sure to include all the organelles appropriate to your cell (either plant or animal). Once complete, take multiple photographs of your model from all angles. Include these images in a document that also contains the following in table format:

• A detailed key/legend that matches the model;
• Each organelle or part with its basic function;
• A disease or disorder that is associated with the malfunction of each cellular component
• How this organelle is visualized microscopically

Note for the disease information, you can list a disease in either animals or plants, regardless of what type of cell you are modeling. In other words, its okay to discuss a “human” disease even if you are making a plant model, provided the organelle is present in both types of cells.

Some suggestions for 3D models include Legos, a decorated cake with candy toppings, or standard Styrofoam base with appropriate pieces attached. You can also draw or illustrate a model. Here is an example of what you might make.

Basic Requirements (the assignment will not be accepted or assessed unless the follow criteria have been met):

• Assignment has been proofread and does not contain any major spelling or grammatical errors
• Assignment includes appropriate references
• Assignment includes photographs or images of created model from all angles.
• Assignment includes a key documenting how each organelle is represented in the model.
• Assignment includes a completed table such as the one illustrated in the example document.
• Assignment includes a disease caused by malfunction of each identified component in the model.
• Assignment includes at least 7 organelles in the model and table.
• Performance Assessments: Cell Builder. Authored by : Shelli Carter. Provided by : Columbia Basin College. Located at : https://www.columbiabasin.edu/ . License : CC BY: Attribution

• Biology Article

Cells are the basic, fundamental unit of life. So, if we were to break apart an organism to the cellular level, the smallest independent component that we would find would be the cell.

Explore the cell notes to know what is a cell, cell definition, cell structure, types and functions of cells. These notes have an in-depth description of all the concepts related to cells.

Table of Contents

Cell Definition

What is a cell, characteristics of cells, types of cells, cell structure, cell theory.

• Functions of a Cell

Cells are the fundamental unit of life. They range in size from 0.0001 mm to nearly 150 mm across.

“A cell is defined as the smallest, basic unit of life that is responsible for all of life’s processes.”

Cells are the structural, functional, and biological units of all living beings. A cell can replicate itself independently. Hence, they are known as the building blocks of life . 

Each cell contains a fluid called the cytoplasm, which is enclosed by a membrane. Also present in the cytoplasm are several biomolecules like proteins, nucleic acids and lipids. Moreover, cellular structures called cell organelles are suspended in the cytoplasm.

A cell is the structural and fundamental unit of life. The study of cells from its basic structure to the functions of every cell organelle is called Cell Biology. Robert Hooke was the first Biologist who discovered cells.

All organisms are made up of cells. They may be made up of a single cell (unicellular), or many cells (multicellular).  Mycoplasmas are the smallest known cells. Cells are the building blocks of all living beings. They provide structure to the body and convert the nutrients taken from the food into energy.

Cells are complex and their components perform various functions in an organism. They are of different shapes and sizes, pretty much like bricks of the buildings. Our body is made up of cells of different shapes and sizes.

Cells are the lowest level of organisation in every life form. From organism to organism, the count of cells may vary. Humans have more number of cells compared to that of  bacteria .

Cells comprise several cell organelles that perform specialised functions to carry out life processes. Every organelle has a specific structure. The hereditary material of the organisms is also present in the cells.

Discovery of Cells

Discovery of cells is one of the remarkable advancements in the field of science. It helps us know that all the organisms are made up of cells, and these cells help in carrying out various life processes. The structure and functions of cells helped us to understand life in a better way.

Who discovered cells?

Robert Hooke discovered the cell in 1665. Robert Hooke observed a piece of bottle cork under a compound microscope and noticed minuscule structures that reminded him of small rooms. Consequently, he named these “rooms” as cells. However, his compound microscope had limited magnification, and hence, he could not see any details in the structure. Owing to this limitation, Hooke concluded that these were non-living entities.

Later Anton Van Leeuwenhoek observed cells under another compound microscope with higher magnification. This time, he had noted that the cells exhibited some form of movement (motility). As a result, Leeuwenhoek concluded that these microscopic entities were “alive.” Eventually, after a host of other observations, these entities were named as animalcules.

In 1883, Robert Brown, a Scottish botanist, provided the very first insights into the cell structure. He was able to describe the nucleus present in the cells of orchids.

Following are the various essential characteristics of cells:

• Cells provide structure and support to the body of an organism.
• The cell interior is organised into different individual organelles surrounded by a separate membrane.
• The nucleus (major organelle) holds genetic information necessary for reproduction and cell growth.
• Every cell has one nucleus and membrane-bound organelles in the cytoplasm.
• Mitochondria, a double membrane-bound organelle is mainly responsible for the energy transactions vital for the survival of the cell.
• Lysosomes digest unwanted materials in the cell.
• Endoplasmic reticulum plays a significant role in the internal organisation of the cell by synthesising selective molecules and processing, directing and sorting them to their appropriate locations.

Also Read : Nucleus

Cells are similar to factories with different labourers and departments that work towards a common objective. Various types of cells perform different functions. Based on cellular structure, there are two types of cells:

• Prokaryotes

Explore:   Difference Between Prokaryotic and Eukaryotic Cells

Prokaryotic Cells

Main article: Prokaryotic Cells

• Prokaryotic cells have no nucleus. Instead, some prokaryotes such as bacteria have a region within the cell where the genetic material is freely suspended. This region is called the nucleoid.
• They all are single-celled microorganisms. Examples include archaea, bacteria, and cyanobacteria.
• The cell size ranges from 0.1 to 0.5 µm in diameter.
• The hereditary material can either be DNA or RNA.
• Prokaryotes generally reproduce by binary fission, a form of asexual reproduction. They are also known to use conjugation – which is often seen as the prokaryotic equivalent to sexual reproduction (however, it is NOT sexual reproduction).

Eukaryotic Cells

Main article : Eukaryotic Cells

• Eukaryotic cells are characterised by a true nucleus.
• The size of the cells ranges between 10–100 µm in diameter.
• This broad category involves plants, fungi, protozoans, and animals.
• The plasma membrane is responsible for monitoring the transport of nutrients and electrolytes in and out of the cells. It is also responsible for cell to cell communication.
• They reproduce sexually as well as asexually.
• There are some contrasting features between plant and animal cells. For eg., the plant cell contains chloroplast, central vacuoles, and other plastids, whereas the animal cells do not.

The cell structure comprises individual components with specific functions essential to carry out life’s processes. These components include- cell wall, cell membrane, cytoplasm, nucleus, and cell organelles. Read on to explore more insights on cell structure and function.

Cell Membrane

• The cell membrane supports and protects the cell. It controls the movement of substances in and out of the cells. It separates the cell from the external environment. The cell membrane is present in all the cells.
• The cell membrane is the outer covering of a cell within which all other organelles, such as the cytoplasm and nucleus, are enclosed. It is also referred to as the plasma membrane.
• By structure, it is a porous membrane (with pores) which permits the movement of selective substances in and out of the cell.  Besides this, the cell membrane also protects the cellular component from damage and leakage.
• It forms the wall-like structure between two cells as well as between the cell and its surroundings.
• Plants are immobile, so their cell structures are well-adapted to protect them from external factors. The cell wall helps to reinforce this function.
• The cell wall is the most prominent part of the plant’s cell structure. It is made up of cellulose, hemicellulose and pectin.
• The cell wall is present exclusively in plant cells. It protects the plasma membrane and other cellular components. The cell wall is also the outermost layer of plant cells.
• It is a rigid and stiff structure surrounding the cell membrane.
• It provides shape and support to the cells and protects them from mechanical shocks and injuries.
• The cytoplasm is a thick, clear, jelly-like substance present inside the cell membrane.
• Most of the chemical reactions within a cell take place in this cytoplasm.
• The cell organelles such as endoplasmic reticulum, vacuoles, mitochondria, ribosomes, are suspended in this cytoplasm.
• The nucleus contains the hereditary material of the cell, the DNA.
• It sends signals to the cells to grow, mature, divide and die.
• The nucleus is surrounded by the nuclear envelope that separates the DNA from the rest of the cell.
• The nucleus protects the DNA  and is an integral component of a plant’s cell structure.

Cell Organelles

Cells are composed of various cell organelles that perform certain specific functions to carry out life’s processes. The different cell organelles, along with its principal functions, are as follows:

Cell Theory was proposed by the German scientists,  Theodor Schwann, Matthias Schleiden, and Rudolf Virchow. The cell theory states that:

• All living species on Earth are composed of cells.
• A cell is the basic unit of life.
• All cells arise from pre-existing cells.

A modern version of the cell theory was eventually formulated, and it contains the following postulates:

• Energy flows within the cells.
• Genetic information is passed on from one cell to the other.
• The chemical composition of all the cells is the same.

Functions of Cell

A cell performs major functions essential for the growth and development of an organism. Important functions of cell are as follows:

Provides Support and Structure

All the organisms are made up of cells. They form the structural basis of all the organisms. The cell wall and the cell membrane are the main components that function to provide support and structure to the organism. For eg., the skin is made up of a large number of cells. Xylem present in the vascular plants is made of cells that provide structural support to the plants.

Facilitate Growth Mitosis

In the process of mitosis, the parent cell divides into the daughter cells. Thus, the cells multiply and facilitate the growth in an organism.

Allows Transport of Substances

Various nutrients are imported by the cells to carry out various chemical processes going on inside the cells. The waste produced by the chemical processes is eliminated from the cells by active and passive transport. Small molecules such as oxygen, carbon dioxide, and ethanol diffuse across the cell membrane along the concentration gradient. This is known as passive transport. The larger molecules diffuse across the cell membrane through active transport where the cells require a lot of energy to transport the substances.

Energy Production

Cells require energy to carry out various chemical processes. This energy is produced by the cells through a process called   photosynthesis in plants and respiration in animals.

Aids in Reproduction

A cell aids in reproduction through the processes called mitosis and meiosis. Mitosis is termed as the asexual reproduction where the parent cell divides to form daughter cells. Meiosis causes the daughter cells to be genetically different from the parent cells.

Thus, we can understand why cells are known as the structural and functional unit of life. This is because they are responsible for providing structure to the organisms and perform several functions necessary for carrying out life’s processes.

Also Read:  Difference Between Plant Cell and Animal Cell

To know more about what is a cell, its definition, cell structure, types of cells, the discovery of cells, functions of cells or any other related topics, explore  BYJU’S Biology . Alternatively, download BYJU’S app for a personalised learning experience.

Frequently Asked Questions

1. what is a cell, 2. state the characteristics of cells..

• Cells provide the necessary structural support to an organism.
• The genetic information necessary for reproduction is present within the nucleus.
• Structurally, the cell has cell organelles which are suspended in the cytoplasm.
• Mitochondria is the organelle responsible for fulfilling the cell’s energy requirements.
• Lysosomes digest metabolic wastes and foreign particles in the cell.
• Endoplasmic reticulum synthesises selective molecules and processes them, eventually directing them to their appropriate locations.

3. Highlight the cell structure and its components.

The cell structure comprises several individual components which perform specific functions essential to carry out life processes. The components of the cell are as follows:

• Cell membrane
• Nuclear membrane
• Endoplasmic reticulum
• Golgi Bodies
• Mitochondria
• Chloroplast

4. State the types of cells.

Cells are primarily classified into two types, namely

• Prokaryotic cells
• Eukaryotic cells

5. Elaborate Cell Theory.

Cell Theory was proposed by  Matthias Schleiden, Theodor Schwann, and Rudolf Virchow, who were German scientists. The cell theory states that:

6. What is the function of mitochondria in the cells?

7. what are the functions of the cell.

The essential functions of the cell include:

• The cell provides support and structure to the body.
• It facilitates growth by mitosis.
• It helps in reproduction.
• Provides energy and allows the transport of substances.

8. What is the function of Golgi bodies?

9. who discovered the cell and how, 10. name the cell organelle that contains hydrolytic enzymes capable of breaking down organic matter., 11. which cellular structure regulates the entry and exit of molecules to and from the cell.

Register at BYJU’S for cell related Biology notes. Refer to these notes for reference.

Further Reading:  Cell Biology MCQs

Put your understanding of this concept to test by answering a few MCQs. Click ‘Start Quiz’ to begin!

Select the correct answer and click on the “Finish” button Check your score and answers at the end of the quiz

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