Question 1

A cell with a predominance of free ribosomes is most likely

Accepted Answer

Free ribosomes produce proteins for use within the cytoplasm of the cell, rather than for secretion or for constructing extracellular structures like cell walls or extracellular matrices. Therefore, a cell with a predominance of free ribosomes is most likely producing primarily cytoplasmic proteins.

Question 2

The fact that the outer membrane of the nuclear envelope has bound ribosomes allows one to most reliably conclude that

Accepted Answer

The fact that ribosomes are bound to the outer membrane of the nuclear envelope suggests that proteins needed for the nuclear envelope's functioning might be synthesized on those ribosomes.

Question 3

Which of the following produces and modifies polysaccharides that will be secreted?

Accepted Answer

The Golgi apparatus is responsible for modifying, sorting, and packaging proteins and lipids that will be secreted or transported to other parts of the cell. This includes polysaccharides that will be secreted as part of the cell's extracellular matrix or as part of the structure of cell walls in plant cells.

Question 4

Which of the following statements correctly describes some aspect of protein secretion from prokaryotic cells?

Accepted Answer

Prokaryotes lack an endomembrane system, but they still have the ability to secrete proteins. Secreted proteins in prokaryotes are synthesized on ribosomes that are bound to the cytoplasmic surface of the plasma membrane.

Answer: B
 The mechanism of protein secretion in prokaryotes is not identical to that in eukaryotes, but there are some similarities. For example, both prokaryotes and eukaryotes use signal sequences to direct proteins to their appropriate location.

Answer: D
 Ribosomes that are used for the synthesis of secreted proteins in prokaryotes are located in the cytoplasm. However, some prokaryotes have specialized structures (such as the type III secretion system) that allow them to secrete proteins directly from the cytoplasm into other cells or the external environment.

Answer: E
 Prokaryotes do not have large pores in their plasma membrane. However, some bacteria have specialized structures (such as pili) that allow them to transport proteins across the membrane and into other cells.

Question 5

Which plant cell organelle contains its own DNA and ribosomes?

Accepted Answer

The mitochondrion is the only cell organelle in plant cells that contains its own DNA and ribosomes. The DNA in the mitochondrion is circular, similar to bacterial DNA, and is believed to have originated from an endosymbiotic event with a bacteria-like organism. The ribosomes in the mitochondrion are smaller than the ribosomes in the cytoplasm and are similar in size to bacterial ribosomes.

Question 6

The liver is involved in detoxification of many poisons and drugs. Which of the following structures is primarily involved in this process and therefore abundant in liver cells?

Accepted Answer

The smooth endoplasmic reticulum (SER) is primarily involved in detoxification of drugs and poisons in liver cells. This is because the SER contains enzymes called cytochrome P450s that can modify and break down many foreign substances. Rough endoplasmic reticulum (RER) is involved in protein synthesis, the Golgi apparatus processes and packages proteins, the nuclear envelope encloses the nucleus, and transport vesicles move molecules between different parts of the cell.

Question 7

Tay-Sachs disease is a human genetic abnormality that results in cells accumulating and becoming clogged with very large and complex lipids. Which cellular organelle must be involved in this condition?

Accepted Answer

Lysosomes are the organelles responsible for breaking down and recycling cellular components, including lipids. In Tay-Sachs disease, a deficiency in the enzyme hexosaminidase A leads to the accumulation of gangliosides (a type of lipid) in the lysosomes of nerve cells, causing neurological symptoms.

Question 8

The Golgi apparatus has a polarity or sidedness to its structure and function. Which of the following statements correctly describes this polarity?

Accepted Answer

All of the statements correctly describe the polarity of the Golgi apparatus. Transport vesicles fuse with one side and leave from the opposite side, and proteins and lipids may be sorted and modified as they move from one side of the Golgi to the other. Soluble proteins in the cisternae of the Golgi may also be sorted and modified as they move through the Golgi apparatus.

Question 9

Which of the following contains hydrolytic enzymes?

Accepted Answer

Lysosomes are organelles that contain hydrolytic enzymes, which are enzymes that break down macromolecules (such as proteins, lipids, and carbohydrates) into smaller molecules. These enzymes work best under acidic conditions, which is why lysosomes have a low pH. Lysosomes function in intracellular digestion, autophagy, and the recycling of cellular components.

Question 10

One of the key innovations in the evolution of eukaryotes from a prokaryotic ancestor is the endomembrane system. What eukaryotic organelles or features might have evolved as a part of, or as an elaboration of, the endomembrane system?

Accepted Answer

The nuclear envelope is a fundamental component of the endomembrane system, as it is a double membrane that surrounds the nucleus and separates it from the cytoplasm. The nuclear envelope evolved from the infolding of the plasma membrane, which allowed for the separation of transcription and translation within the cell.

Answer: A, C
 The plasma membrane and mitochondria are both organelles that are derived from the endomembrane system. The plasma membrane evolved from the ancestral cell membrane, which was then elaborated upon to form the various membranous organelles of the endomembrane system. Mitochondria, which are thought to have evolved from a free-living prokaryote that was engulfed by an ancestral eukaryotic cell, also have a double membrane structure that is similar to that of the nuclear envelope.

Question 11

Which animal cell organelle contains enzymes that transfer hydrogen from various substrates to oxygen?

Accepted Answer

The organelle that contains enzymes that transfer hydrogen from various substrates to oxygen is the peroxisome. These enzymes are called peroxidases and catalase, and they work to detoxify harmful substances in the cell. The other organelles listed do not have this function. Lysosomes contain digestive enzymes, vacuoles store water and nutrients, mitochondria produce energy for the cell, and Golgi apparatus modifies and packages proteins.

Question 12

In a plant cell, DNA may be found

Accepted Answer

DNA is found in the nucleus where it directs the transcription and translation of genes, in mitochondria where it encodes for some of the proteins needed for oxidative phosphorylation, and in chloroplasts where it encodes for some of the proteins needed for photosynthesis. DNA is not typically found in peroxisomes. Therefore, the correct choice is D: in the nucleus, mitochondria, and chloroplasts.

Question 13

Which structure is the site of the synthesis of proteins that may be exported from the cell?

Accepted Answer

The rough endoplasmic reticulum (ER) contains ribosomes that synthesize proteins that are usually targeted for export out of the cell or are embedded in membranes. The rough ER is involved in protein synthesis, folding, and modification. Therefore, it is the structure that is the site of the synthesis of proteins that may be exported from the cell.

Question 14

Which type of organelle or structure is primarily involved in the synthesis of oils, phospholipids, and steroids?

Accepted Answer

The smooth endoplasmic reticulum (SER) is the organelle primarily involved in the synthesis of oils, phospholipids, and steroids. It lacks ribosomes, which are found on the rough endoplasmic reticulum (RER) and are involved in protein synthesis. Lysosomes contain digestive enzymes, mitochondria are involved in ATP production, and contractile vacuoles are found in some protists and participate in osmoregulation.

Question 15

Hydrolytic enzymes must be segregated and packaged to prevent general destruction of cellular components. Which of the following organelles contains these hydrolytic enzymes in animal cells?

Accepted Answer

Lysosomes are organelles found in animal cells that contain hydrolytic enzymes, such as proteases and nucleases, which are important for breaking down waste materials, cellular debris, and foreign substances. These enzymes are highly acidic and could destroy other cellular components if not properly segregated and packaged within the lysosome. Therefore, lysosomes serve as a crucial organelle for maintaining cellular homeostasis and preventing cellular damage.

Question 16

Thylakoids, DNA, and ribosomes are all components found in

Accepted Answer

Thylakoids, DNA, and ribosomes are all components found in chloroplasts, which are the organelles responsible for photosynthesis in plant cells. Vacuoles are large membrane-bound sacs that store water and other molecules, mitochondria are involved in cellular respiration, lysosomes contain digestive enzymes, and nuclei contain the genetic material of the cell.

Question 17

The chemical reactions involved in respiration are virtually identical between prokaryotic and eukaryotic cells. In eukaryotic cells, ATP is synthesized primarily on the inner membrane of the mitochondria. In light of the endosymbiont theory for the evolutionary origin of mitochondria, where is most ATP synthesis likely to occur in prokaryotic cells?

Accepted Answer

Since mitochondria evolved from prokaryotic cells, it is likely that the location of ATP synthesis in prokaryotic cells would be similar to that of the inner membrane of mitochondria. In prokaryotic cells, this would correspond to the plasma membrane.

Question 18

Which organelle is the primary site of ATP synthesis in eukaryotic cells?

Accepted Answer

The mitochondrion is known as the powerhouse of the cell and is responsible for ATP synthesis through cellular respiration. Lysosomes, vacuoles, Golgi apparatus, and peroxisomes have other functions related to cell maintenance and metabolic processes.

Question 19

Which organelle often takes up much of the volume of a plant cell?

Accepted Answer

The vacuole often takes up much of the volume of a plant cell. It stores water, ions, and other nutrients, and can also contribute to the stiffness of the cell. The other organelles listed do not typically take up as much volume in a plant cell.

Question 20

The difference in lipid and protein composition between the membranes of the endomembrane system is largely determined by

Accepted Answer

The Golgi apparatus is responsible for sorting and directing membrane components, which means it plays a key role in determining the lipid and protein composition of the membranes in the endomembrane system. Other factors may also contribute, but C is the most accurate answer.

Quiz 6: A Tour of the Cell