Chapter 3 (Questions)

Which of the following organelles is not present in animal cells? A. rough endoplasmic reticulum B. Golgi apparatus C. chloroplast D. lysosome E. mitochondrion

C

Every cell in your body has a "fingerprint" made from a variety of molecules on the outside-facing surface of the cell membrane. This molecular fingerprint is key to the function of your immune system. What are "molecular fingerprints"? Why do they explain the fact that one cannot catch HIV through casual contact?

"Molecular fingerprints" are molecules on the outside-facing surface of the cell membrane of every cell in your body. The molecular fingerprints common to all cells signal to the immune system that the cells "belong." Any cells with an unrecognized fingerprint are considered foreign and are attacked. The HIV virus uses molecular fingerprints on plasma membranes to infect an individual's cells. But because the particular molecular fingerprints that HIV interacts with (called CD markers) occur only in cells deep within the body and in the bloodstream, it is virtually impossible for casual contact, such as shaking hands or touching, to lead to HIV infection.

If a cell is put into a solution with a higher concentration of solute than is present inside the cell, the solution is ____________. The cell will __________. If a cell is put into a solution with a lower concentration of solute than is present inside the cell, the solution is _____________. The cell will _________. A. hypertonic; shrink; hypotonic; swell B. hypotonic; shrink; hypertonic; swell C. hypotonic; swell; hypertonic; shrink D. hypertonic; swell; hypotonic; shrink E. None of the above is correct.

A

What cellular structure makes it possible for a cell to differ structurally and biochemically from its surroundings? A. plasma membrane B. phospholipid C. nucleus D. endoplasmic reticulum E. cell wall

A

The transport of large molecules into the cell, across the membrane is accomplished via: A. active transport. B. passive transport. C. endocytosis. D. exocytosis. E. facilitated diffusion.

C

The cell wall is an organelle found in plants (and in some other non-animal organisms). It is made primarily from the carbohydrate cellulose, and it surrounds the plasma membrane of the cell. The cell wall confers tremendous structural strength on plant cells, gives plants increased resistance to water loss, and provides some protection from insects and other animals that might eat the plant. In plants, plasmodesmata connect cells and enable communication and transport between them. List three functions of a plant's cell wall.

A plant's cell wall provides structural strength to the cell, makes the cell more water resistant, and provides some protection from insects and other animals.

The Golgi apparatus—another organelle within the endomembrane system—processes molecules synthesized in the cell and packages those that are destined for use elsewhere in the body. Give two examples of ways in which proteins are modified within the Golgi apparatus.

A protein may be modified within the Golgi apparatus by the addition or removal of a phosphate group or a sugar group.

In active transport, movement of molecules across a membrane requires energy. Active transport is necessary if the molecules to be moved are very large or if they are being moved against their concentration gradient. Proteins embedded in the plasma membrane act like motorized revolving doors to actively transport (pump) the molecules. Why does it sometimes cost energy to move molecules across a membrane?

Active transport, in which energy is spent to move molecules across a membrane, is necessary when the molecules are large and when the molecules are being moved up (against) their concentration gradient.

The most basic unit of any organism is the cell, the smallest unit of life that can function independently and perform all of the necessary functions of life, including reproducing itself. All living organisms are made up of one or more cells, and all cells arise from other, preexisting cells What two facts form the foundation of cell theory?

All living things are made up of one or more cells, and all cells arise from preexisting cells.

The function of cholesterol in membranes is: A. There is no function of cholesterol; it is tolerated in low amounts in mammalian cells. B. to reduce membrane fluidity at higher temperatures. C. to increase membrane fluidity at higher temperatures. D. to reduce membrane fluidity at lower temperatures. E. to increase membrane permeability at lower temperatures.

B

Eukaryotes are single-celled or multicellular organisms consisting of cells with a nucleus that contains linear strands of genetic material. The cells also commonly have organelles throughout their cytoplasm; these organelles may have originated evolutionarily through endosymbiosis or invagination, or both. Compare and contrast the theory of endosymbiosis with the theory of invagination.

Both theories attempt to explain how intracellular structures came to be within eukaryotic cells as well as how these intracellular "compartments" subsequently became modified and specialized over time. Endosymbiosis involves an ancestral eukaryote engulfing an ancestral prokaryote. In time, both cells became mutually dependent upon one another to function and survive, and they became a single, more complex organism. Invagination involves one cell's plasma membrane folding in on itself to form the cell's inner compartments. Organelles that arose from endosymbiosis have their own ribosomes, similar to those found in bacteria, which allow them to synthesize some of their own proteins. Organelles stemming from invagination do not contain ribosomes.

In eukaryotes where can the organism's complete set of DNA be found? A. the Golgi apparatus B. the rough ER C. the nucleus D. the gametes E. the cytoplasm

C

Which of the following statements about prokaryotes is INCORRECT? A. Prokaryotes contain ribosomes. B. Prokaryotes appeared on earth prior to eukaryotes. C. Prokaryotes have circular pieces of DNA within their nuclei. D. Prokaryotes contain cytoplasm. E. Some prokaryotes can conduct photosynthesis.

C

The chloroplast is the organelle in plants and algae that is the site of photosynthesis—the conversion of light energy into chemical energy, with oxygen as a by-product. Chloroplasts may originally have been bacteria that were engulfed by a predatory cell by endosymbiosis. What is the main function of chloroplasts?

Chloroplasts are the site of photosynthesis, where light energy is converted into chemical energy of food molecules.

. The inner scaffolding of the cell, made from proteins, is: A. the cell wall. B. the Golgi apparatus. C. the endoplasmic reticulum. D. the cytoskeleton. E. the cytoplasm.

D

A unique characteristic of mitochondria is that they are inherited from the female parent only. Select the correct explanation for this phenomenon from the choices below. A. Mitochondria are only found in the female's egg cells and do not occur in male sperm cells. B. Mitochondria are found in both female egg cells and the male sperm cells, but after fertilization the female mitochondria outcompete the male mitochondria, which then die off. C. Mitochondria are found in both the female's egg cells and the male sperm cells, but the sperm exhaust their mitochondria during their swim up the female's fallopian tubes and are not viable upon fertilization. D. Male sperm cells have mitochondria, but because the sperm contributes DNA but no cytoplasm, no mitochondria are contributed to the egg at fertilization. E. None of the above is correct.

D

Mammalian cells take in many molecules including hormones, antibodies, and blood proteins. This process is coordinated by proteins that recognize their specific target molecule. This process is best described as: A. cell inclusion. B. cohesion. C. diffusion. D. receptor-mediated endocytosis. E. cell absorption. Submit

D

The role of cholesterol in the plasma membrane of animal cells is to: A. act as a receptor for hormones such as estrogen and testosterone. B. help cells recognize each other, acting as a "fingerprint" on the outside of the cell. C. help transport polar molecules across the plasma membrane. D. keep the plasma membrane flexible, especially at low temperatures. E. form thickened membranes that are stronger and less easily punctured

D

What makes the rough endoplasmic reticulum rough? A. It is covered with microvilli. B. It has a high density of receptor proteins in its membrane. C. Its surface is highly folded to increase surface area. D. It is covered with tiny flagella. E. It is covered with ribosomes.

E

Which of the following facts supports the claim that mitochondria developed from bacteria that were long ago phagocytosed into eukaryotic cells? A. Mitochondria are the "powerhouses" of the cell. B. Mitochondria have several of the proteins necessary for photosynthesis. C. Mitochondria have flagella for motion. D. Mitochondria frequently exchange DNA with intracellular bacteria. E. Mitochondria have their own DNA.

E

Which of the following is an INCORRECT comparison between facilitated and simple diffusion? A. Facilitated diffusion uses a facilitated diffusion carrier, while simple difussion uses a simple diffusion carrier. B. Facilitated diffusion uses transport proteins on the membrane's surface, while simple diffusion uses transport lipids. C. Facilitated diffusion is necessary to maintain an equilibrium inside the cell, while simple diffusion is not necessary for cellular function. D. Facilitated diffusion can function at a very high rate, while simple diffusion is always relatively slow. E. All of the above are INCORRECT comparisons between facilitated and simple diffusion.

E

Which of the following is an example of osmosis? A. flow of water out of a cell B. pumping of water into a cell C. flow of water between cells D. Both A and B are correct. E. Both A and C are correct.

E

Which of the following statements about cell theory is CORRECT? A. All living organisms are made up of one or more cells. B. All cells arise from other pre-existing cells. C. All eukaryotic cells contain symbiotic protists. D. All cells have nuclei. E. Both A and B are correct.

E

Every cell on earth is either a eukaryotic or a prokaryotic cell. Prokaryotes, which have no nucleus, were the first cells on earth. They are single-celled organisms. Prokaryotes include the bacteria and archaea and, as a group, are characterized by tremendous metabolic diversity. How is the location of the DNA in a prokaryotic cell different from that of a eukaryotic cell?

In a eukaryotic cell, DNA is contained within an internal structure called a nucleus. Prokaryotic cells do not have a nucleus, and their DNA simply is located in the cytoplasm

Normal cell functioning can be disrupted when cell membranes—particularly the proteins embedded in them—do not function properly. Such malfunctions can cause health problems, such as cystic fibrosis. But intentional disruption of normal cell membrane function can have beneficial, therapeutic effects, such as in the treatment of high blood pressure and anxiety. In what way does a membrane function improperly in an individual with cystic fibrosis? What are the key symptoms of this disorder?

Individuals with the genetic disorder cystic fibrosis do not produce a functional chloride ion transport protein that is important in the lungs and digestive tract. As a result, chloride ions accumulate within cells, and overly thick and sticky mucus collects in the lungs, impairing lung function and increasing the risk of bacterial infections.

In mitochondria, which are found in nearly all eukaryotic cells, the energy contained in the chemical bonds of carbohydrate, fat, and protein molecules is converted into carbon dioxide, water, and ATP, the energy source for all cellular functions and activities. Mitochondria may have their evolutionary origins as symbiotic bacteria living inside other cells. What is the function of mitochondria? What evidence suggests that mitochondria were separate, bacteria-like organisms billions of years ago?

Mitochondria function within the cell as energy converters. The energy contained in the chemical bonds of carbohydrates, fats, and proteins is converted into energy stored in carbon dioxide, water, and ATP, with some energy lost as heat. (You'll learn more about this process in Chapter 4.) There are several pieces of evidence that suggest mitochondria existed billions of years ago as separate, single-celled bacteria-like organisms. First, mitochondria are similar to bacteria in size and shape. Mitochondria have their own DNA that is highly related to bacterial DNA. Mitochondria divide by fission. Also, mitochondria have ribosomes, similar to those found in bacteria, allowing them to synthesize some of their own proteins.

The diffusion of water across a membrane is a special type of passive transport called osmosis. Water moves from an area with a lower concentration of solutes to an area with a higher concentration of solutes. Water molecules move across the membrane until the concentration of water inside and outside the cell is equalized. Compare and contrast what would happen to a plant cell versus an animal cell (such as a human red blood cell) when placed in a hypotonic solution, a hypertonic solution, and an isotonic solution.

Placing a plant cell and a red blood cell in a hypotonic solution would cause both cells to gain water. The red blood cell would swell and potentially burst as it filled with water, whereas the plant cell's cell wall would prevent it from bursting (although, it would experience turgor pressure and swell slightly). When placing these cells in a hypertonic solution, both would lose water to the solution, causing them to shrink/shrivel; the plant cell would shrink only to a point, limited by its cell wall. In an isotonic solution, both types of cells will have water diffusing into and out of them at equal rates, and the cells will neither burst nor shrink.

In plants, vacuoles can occupy most of the interior space of the cell. Vacuoles are also present in some other eukaryotic species. In plants, they function as storage spaces and play a role in nutrition, waste management, predator deterrence, reproduction, and physical support. What are the five key functions of plant vacuoles?

Plant vacuole functions include nutrient storage, waste management, predator deterrence, sexual reproduction, and physical support

For proper functioning, cells must acquire food molecules and/or other necessary materials from outside the cell. Similarly, metabolic waste molecules and molecules produced for use elsewhere in the body must move out of the cell. In passive transport—which includes simple and facilitated diffusion and osmosis—the molecular movement occurs spontaneously, without the input of energy. This generally takes place as molecules move down their concentration gradient. Why can some molecules diffuse directly across a phospholipid bilayer, while other molecules can only cross the membrane with the assistance of a transport protein?

Small molecules carrying no charge are able to pass directly through a phospholipid bilayer. Molecules with a charge are repelled by the hydrophobic middle region of the membrane, and larger molecules are unable to squeeze through the membrane. These molecules unable to cross the phospholipid bilayer directly still can pass through the membrane with the assistance of a transport protein.

Which cells contain the highest Mitochondria count?

The cells that use the most energy, of course. Such as Liver cells and Muscle cells

The inner scaffolding of the cell, which is made from proteins, is the cytoskeleton. Consisting of three types of protein fibers—microtubules, intermediate filaments, and microfilaments—the cytoskeleton gives animal cells their shape and support, gives cells some ability to control their movement, and serves as a series of tracks on which organelles and molecules are guided across and around the inside of the cell. What are the three chief purposes of the cytoskeleton?

The cytoskeleton gives animal cells shape and support, controls the flow of molecules and organelles within the cell, and gives cells the ability to control their movement.

The nucleus is usually the largest and most prominent organelle in the eukaryotic cell. It directs most cellular activities by controlling which molecules are produced and in what quantity. The nucleus is the storehouse for hereditary information. How does the nuclear membrane differ from the plasma membrane?

The nuclear membrane consists of two phospholipid bilayers, while the plasma membrane consists of one bilayer. Also, the nuclear membrane is perforated by numerous pores, which allow large molecules to pass between the nucleus and the cytoplasm.

What does taking a beta-receptor blocker pill do?

The pill dissolves and the chemicals travel throughout your body until they encounter the beta-receptors. They bind to the receptors, hold on, and block the adrenaline from doing its job. This outcome slows your heart rate, causes a reduction in blood pressure, and can bring great relief to those suffering from the sweating and trembling associated with anxiety.

The production and modification of biological molecules in eukaryotic cells occurs in a system of organelles called the endomembrane system, which includes, among other organelles, the rough and smooth endoplasmic reticulum. In rough ER, proteins that will be shipped elsewhere in the body are folded and packaged. In the smooth ER, lipids and carbohydrates are synthesized and alcohol, antibiotics, and other drugs are detoxified. List the two divisions of the endoplasmic reticulum and at least one function of each.

The primary function of the rough endoplasmic reticulum is to fold and package newly produced proteins. The smooth endoplasmic reticulum synthesizes lipids and detoxifies drugs and other toxins.

Form follows function in an organism's cells and reflects their environment. When cells must perform intensive heat production, for example, they significantly increase the number and size of their mitochondria. They also increase the blood supply to the tissue and make use of existing stores of energy. What process did researchers use to investigate how an animal's cells might respond to exposure to colder environments? What did they discover?

The researchers used 15 cats from 5 litters. For the control, one cat from each litter was kept at 20˚ C; for the experimental group, the cats were exposed to -30˚ C for two periods of one hour per day. After one week, fat tissue was collected. Researchers measured the number and size of mitochondria, the number of capillaries, and the size of fat cells. They found that the fat tissue of the cold-exposed cats essentially had "upgraded" their heat generating system: mitochondria were larger and more plentiful, the number of blood vessels had doubled, and the fat cells had shrunk to a quarter of the size of those in the control group.

When materials cannot get into a cell by diffusion or through a pump (for example, when the molecules are too big), cells can engulf the molecules or particles with their plasma membrane in a process called endocytosis. Similarly, molecules can be moved out of a cell by exocytosis. In both processes, the plasma membrane moves to surround the molecules or particles and forms a little vesicle that is pinched off inside the cell (endocytosis) or fuses with the plasma membrane and dumps its contents outside the cell (exocytosis). Give two examples of cases in which cells of your body use endocytosis.

The textbook describes white blood cells consuming foreign cells through phagocytosis, as well as the uptake of cholesterol-containing LDL particles by receptor-mediated endocytosis in liver cells.

Every cell of every living organism is enclosed by a plasma membrane, a two-layered membrane that holds the contents of a cell in place and regulates what enters and leaves the cell. Describe the structure of a phospholipid. How do its two main regions interact with water? How are phospholipids arranged in two layers to form a plasma membrane that interacts with water on both surfaces?

The two regions of a phospholipid are its hydrophilic head, which interacts very well with water, and its hydrophobic tails, which interact very poorly with water. A plasma membrane consists of two layers of phospholipids, arranged so that the hydrophilic heads point toward the watery solutions inside and outside a cell and the hydrophobic tails point toward each other within the membrane, away from these watery fluids.

Lysosomes are round, membrane-enclosed, acid-filled organelles that function as a cell's garbage disposals. They are filled with about 50 different digestive enzymes and enable a cell to dismantle macromolecules, including disease-causing bacteria. What is the fate of a bacterium engulfed by a white blood cell through phagocytosis?

The vacuoles enclosing the engulfed bacteria can be fused with a lysosome, where the lysosomal enzymes will break down the various proteins, lipids, and other molecules of this bacterium, making these nutrients available to the cell.

The plasma membrane is a fluid mosaic of proteins, lipids, and carbohydrates. Proteins found in the plasma membrane enable it to carry out most of its gatekeeping functions. The proteins act as receptors, help molecules enter and leave the cell, and catalyze reactions on the inner and outer cell surfaces. In conjunction with carbohydrates, some plasma membrane proteins identify the cell to other cells. And, in addition to the phospholipids that make up most of the plasma membrane, cholesterol is an important lipid in some membranes, influencing fluidity. List the four primary types of membrane proteins and their function.

the four primary types of membrane proteins are receptor proteins, recognition proteins, transport proteins, and membrane enzymes. Receptor proteins regulate certain processes within the cell by binding to chemicals in the cell's external environment. Recognition proteins give each cell a "fingerprint" to identify the cell. Transport proteins help large or strongly charged molecules pass through the membrane. Membrane enzymes accelerate chemical reactions on the plasma membrane's surface.