Question 1

In which stage of mitosis do the identical sets of chromosomes line up along the midline or equator of the cell?

Accepted Answer

During metaphase, the spindle fibers attach to the centromeres of the chromosomes and align them along the equator or midline of the cell. This is the stage where the chromosomes are most condensed and can be clearly seen under a microscope.

Question 2

Which organelle is responsible for processing and packaging proteins destined for export from the cell?

Accepted Answer

The Golgi apparatus is responsible for processing and packaging proteins for export from the cell. The endoplasmic reticulum is involved in protein synthesis and folding, but the Golgi is responsible for the final modifications and sorting. Peroxisomes are involved in lipid metabolism and detoxification, while lysosomes are involved in intracellular digestion.

Question 3

Which of the following would NOT be restricted (limited) by low levels of ATP?

Accepted Answer

Osmosis does not require ATP as it is a passive movement of water molecules across a selectively permeable membrane from an area of high concentration to an area of low concentration. On the other hand, pinocytosis, phagocytosis, and exocytosis all involve the active transport of substances across membranes and require the use of ATP.

Question 4

A cell engulfing a relatively large particle will likely utilize __________.

Accepted Answer

Phagocytosis is the process of engulfing large particles such as bacteria or cellular debris. Exocytosis is the process of releasing substances out of the cell, receptor-mediated endocytosis is the process of specific molecules being taken up by the cell using receptor proteins, and pinocytosis is the process of taking up small, dissolved substances through invagination of the cell membrane.

Question 5

If active transport establishes a concentration gradient with the use of ATP, then the concentration gradient can be looked at as_________ .

Accepted Answer

The concentration gradient established by active transport is a form of potential energy that can be harnessed when molecules passively diffuse down the gradient. This is the driving force behind facilitated diffusion and allows cells to use the energy from ATP to move molecules against their concentration gradient, ultimately maintaining homeostasis.

Question 6

The functions of centrioles include __________.

Accepted Answer

The primary function of centrioles is to organize the microtubules of the mitotic spindle during cell division.

Question 7

Crenation (shrinking) is likely to occur in blood cells immersed in_________ .

Accepted Answer

Crenation (shrinking) occurs in blood cells when they are immersed in a hypertonic solution, meaning the solution has a higher concentration of solutes (such as salt) than the inside of the cell. This causes water to leave the cell, leading to the cell shrinking and possibly even dying.

Question 8

If a tRNA had an AGC anticodon, it could attach to a(n) _________mRNA codon.

Accepted Answer

A tRNA with an AGC anticodon can pair with an mRNA codon that is complementary in sequence, which in this case would be TCG. The other options have codons that do not match the anticodon sequence.

Question 9

If a human cell were to increase the amount of cholesterol embedded within its plasma membrane, which of the following would most likely happen?

Accepted Answer

Cholesterol has a stabilizing effect on the plasma membrane, making it less fluid and more stable. This would result in a decrease in permeability, making it harder for certain molecules to pass through the membrane. Option B involves the formation of a plaque, which is not a direct consequence of an increase in cholesterol in the plasma membrane. Option C suggests that ions and lipids have the same permeability properties, which is not usually the case. Option D suggests that an increase in cholesterol would make the plasma membrane more fluid, which is opposite to the stabilizing effect of cholesterol.

Question 10

The movement of water across the plasma membrane can be described by all of the following EXCEPT_________ .

Accepted Answer

Water movement across the plasma membrane is primarily through simple diffusion and facilitated diffusion via aquaporins, both of which are passive processes. Carrier-mediated facilitated diffusion typically involves the transport of molecules other than water, making option C the exception.

Question 11

The lungs deliver a regular supply of oxygen to the blood, which is in turn circulated to most all the cells of the body. At the same time oxygen is consumed during aerobic cellular respiration within these cells. This implies that _________.

Accepted Answer

Oxygen will passively diffuse into the cells due to the concentration gradient created by the consumption of oxygen during cellular respiration. As oxygen is used up, the concentration of oxygen is lower inside the cell than outside, allowing for passive diffusion. A is incorrect because the rate of diffusion is dependent on concentration. B is incorrect because the concentration gradient is steeper outside of the cell. D is incorrect because oxygen enters cells through passive diffusion, not active transport.

Question 12

Which of the following is NOT a function of lysosomes?

Accepted Answer

Lysosomes do not help in the formation of cell membranes. Their main functions are to break down materials taken in by endocytosis, degrade worn-out or nonfunctional organelles, and recycle cellular components. They are also involved in processes such as programmed cell death and the release of stored nutrients. However, calcium homeostasis is primarily regulated by hormones and other mechanisms unrelated to lysosomes.

Question 13

The myocardium (cardiac muscle tissue) undergoes a significant amount of physical stress due to its contractions. You would expect to see relatively large numbers of which of the following embedded within their plasma membrane?

Accepted Answer

Desmosomes are cell junctions that anchor adjacent cells together, providing mechanical strength to tissues that undergo stress or stretching, such as in the myocardium. Therefore, it is expected to see relatively large numbers of desmosomes embedded within their plasma membrane. Transport proteins and tight junctions are not related to mechanical stress, while glycolipids are not directly involved in cell-cell adhesion.

Question 14

A gene can best be defined as_________ .

Accepted Answer

A gene is defined as a segment of DNA that carries the instructions for one polypeptide chain. This means that a gene contains the information needed to code for a specific protein or part of a protein. Genes are made up of nucleotide sequences and can be transcribed into RNA and then translated into a specific amino acid sequence, which ultimately determines the function of the protein.

Question 15

Which of the following will NOT speed up the net rate of diffusion for glucose into a cell?

Accepted Answer

Decreasing the number of phospholipids in the plasma membrane would actually slow down the rate of diffusion for glucose into the cell, as it would make the membrane less permeable to glucose. Increasing the concentration of glucose outside of the cell, decreasing the concentration of glucose within the cell, and increasing the number of glucose transport proteins within the plasma membrane would all speed up the net rate of diffusion for glucose into the cell.

Question 16

Which of the following statements is most correct regarding the intracellular chemical signals known as "second messengers"?

Accepted Answer

Cyclic AMP and calcium are examples of second messengers that transmit signals within the cell after activation of a receptor by a first messenger such as a hormone or neurotransmitter. Second messengers do not act through K-proteins, inactivate protein kinase enzymes, or remove nitric oxide from the cell.

Question 17

Which of the following is NOT one of the concepts collectively known as the cell theory?

Accepted Answer

The concept that all cells must be motile and divide is not part of the cell theory. The other three concepts (all organisms made of one or more cells, the cell is the smallest unit of life, and cells only arise from other cells) are considered fundamental to the cell theory.

Question 18

Which of the following is a principle of the fluid mosaic model of cell membrane structure?

Accepted Answer

The principle of the fluid mosaic model of cell membrane structure is that the membrane is composed of a phospholipid bilayer that is fluid and allows for the movement of proteins within it. The bilayer is largely impermeable to water-soluble molecules, which is necessary for maintaining cellular integrity and regulating the movement of molecules in and out of the cell. Option A is incorrect because proteins can be embedded within the bilayer, not just in a fluid layer on the outside. Option B is incorrect because the lipid bilayer is fluid at body temperature, not solid. Option C is incorrect because phospholipids have a polar head and a nonpolar tail made of two fatty acid chains, not three.

Question 19

Cancerous cells can divide so rapidly that they will often produce a glycocalyx that is different than the other cells in the body. This may result in _________.

Accepted Answer

The altered glycocalyx on cancerous cells can lead to their recognition as foreign by the immune system, prompting an immune response to destroy them.

Question 20

Some hormones enter cells via __________.

Accepted Answer

Hormones typically cannot enter the cell membrane freely due to their large size and hydrophilic nature. Therefore, they often enter the cell via receptor-mediated endocytosis, in which the hormone binds to a receptor on the cell surface and is then taken up into the cell via an endosome. Primary active transport and exocytosis are not typical pathways for hormone entry into cells. Pinocytosis, while a type of endocytosis, is a non-specific process in which the cell takes up fluid and solutes randomly and is not specific to any particular molecule or hormone.

Quiz 3: Cells: the Living Units