Which of the following is the number of protons in a lithium atom?

Plasma B cells.

Antibodies are produced by specialized white blood cells called B lymphocytes (or B cells).

When an antigen binds to the B-cell surface, it stimulates the B cell to divide and mature into a group of identical cells called a clone.

The mature B cells, called plasma cells, secrete millions of antibodies into the bloodstream and lymphatic system.

Choice A, Natural killer cells, is not the correct answer because natural killer cells are a type of white blood cell that play a major role in the host-rejection of both tumors and virally infected cells.

Choice B, Cytotoxic T-cells, is not the correct answer because cytotoxic T-cells are a type of white blood cell that kills cancer cells, cells that are infected (particularly with viruses), or cells that are damaged in other ways.

Choice D, Helper T-cells, is not the correct answer because helper T-cells are a type of white blood cell that play an important role in the immune system by helping other white blood cells fight infections.

Carbonic acid.

In the human body, maintaining the pH of the blood within a narrow range is critical for proper physiological functioning.

One of the buffering systems that helps to regulate blood pH involves the conversion of carbon dioxide (CO2) and water (H2O) into carbonic acid (H2CO3), which then dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-).

Carbonic acid (H2CO3) is responsible for donating H+ ions to act as a buffer when blood pH rises.

When blood pH rises (becomes more alkaline), carbonic acid dissociates, and the H+ ions combine with bicarbonate ions to form more carbonic acid.

This helps to remove excess H+ ions from the blood and prevent the pH from rising too much.

Option A, carbon dioxide, is involved in the buffering system through its conversion to carbonic acid.

However, it does not directly donate H+ ions to act as a buffer when blood pH rises.

Option B, carbon monoxide, is a toxic gas that binds to hemoglobin in red blood cells, preventing them from carrying oxygen.

It is not involved in the buffering system and does not donate H+ ions.

Option D, oxygen, is carried by hemoglobin in red blood cells and is essential for respiration.

It is not involved in the buffering system and does not donate H+ ions.

Testosterone is classified as an androgen hormone.

Androgens are a type of sex hormone that primarily regulates the development and maintenance of male characteristics, such as body hair growth, muscle mass, and deepening of the voice.

Testosterone is produced primarily in the testes in males and in smaller amounts in the ovaries and adrenal glands in females.

Option A, estrogen, is a female hormone that regulates the development of female sexual characteristics, such as breast growth and menstruation.

While estrogen and testosterone are both steroid hormones and can be converted to one another in the body, testosterone is not categorized as estrogen.

Option B, progestin, is a synthetic form of the hormone progesterone.

Progesterone is a female hormone that plays a role in the menstrual cycle and pregnancy.

Testosterone and progestin are not related, and testosterone is not categorized as progestin.

Option C, aldosterone, is a mineralocorticoid hormone that regulates salt and water balance in the body.

It is produced in the adrenal gland and plays a role in regulating blood pressure.

Testosterone and aldosterone are not related, and testosterone is not categorized as aldosterone.

The cytoskeleton of a cell is comprised of protein fibers that provide structural support and help maintain the shape of the cell.

These protein fibers include microfilaments, intermediate filaments, and microtubules.

Choice A.

Carbohydrates is not the correct answer because carbohydrates are a type of macromolecule that provides energy to cells and are not a component of the cytoskeleton.

Choice B.

Nucleic acids is not the correct answer because nucleic acids are macromolecules that store and transmit genetic information and are not a component of the cytoskeleton.

Choice C.

Lipids is not the correct answer because lipids are a type of macromolecule that makes up cell membranes and are not a component of the cytoskeleton.

Microtubule organization.

Centrosomes are organelles that serve as the main microtubule-organizing centers for animal cells.

They regulate the movement of microtubules and other cytoskeletal structures, thereby facilitating changes in the shapes of the membranes of animal cells.

Choice A, Organelle trafficking, is not the correct answer because while centrosomes do play a role in intracellular trafficking during interphase by organizing an astral ray of microtubules, their main function is microtubule organization.

Choice B, Pathogen digestion, is not the correct answer because centrosomes do not play a direct role in pathogen digestion.

Choice C, Cytoplasm formation, is not the correct answer because centrosomes do not play a direct role in cytoplasm formation.

The pleura is a double-layered serous membrane that covers each lung and lines the thoracic cage

The pleura is a vital part of the respiratory tract.

Its role is to cushion the lung and reduce any friction that may develop between the lung, rib cage, and chest cavity.

Each pleura (there are two) consists of a two-layered membrane that covers each lung.

The layers are separated by a small amount of viscous (thick) lubricant known as pleural fluid.

The pleura is comprised of two distinct layers: the visceral pleura and the parietal pleura.

The visceral pleura is the thin, slippery membrane that covers the surface of the lungs and dips into the areas separating the different lobes of the lungs (called the hilum).

The approximate threshold value for mammalian neurons is -55 mV.

The threshold potential is the critical level to which a membrane potential must be depolarized to initiate an action potential.

Most often, the threshold potential is a membrane potential value between –50 and –55 mV

The membrane potential of a neuron is determined by the distribution of ions across the cell membrane.

At rest, the inside of a neuron is more negative than the outside due to the presence of negatively charged proteins and other molecules.

The movement of ions across the cell membrane can change the membrane potential.

For example, when sodium ions enter the cell, they make the inside of the cell more positive (less negative), causing depolarization.

Choice B is incorrect because -80 mV is below the typical threshold value for mammalian neurons.

Choice C is incorrect because +35 mV is above the typical threshold value for mammalian neurons.

Choice D is incorrect because 0 mV is above the typical threshold value for mammalian neurons.

Triple covalent bonds.

Nitrogen gas (N2) is an extremely stable molecule because it consists of two nitrogen atoms bonded together by a triple covalent bond.

A covalent bond is a type of chemical bond where atoms share electrons to form a molecule.

In a triple covalent bond, three pairs of electrons are shared between the two atoms, resulting in a very strong bond that makes the molecule extremely stable.

Choice A.

Ionic bonds is not correct because ionic bonds involve the transfer of electrons from one atom to another to form ions, which are then attracted to each other due to their opposite charges.

Nitrogen gas does not contain ions and is not held together by ionic bonds.

Choice B.

Hydrogen bonds is not correct because hydrogen bonds are weak electrostatic attractions between molecules that contain hydrogen atoms bonded to highly electronegative atoms such as oxygen or nitrogen.

Nitrogen gas does not contain hydrogen atoms and is not held together by hydrogen bonds.

Choice C.

Resonance bonds is not correct because resonance refers to the delocalization of electrons in a molecule where multiple Lewis structures can be drawn to represent the molecule.

Nitrogen gas has a single Lewis structure and does not exhibit resonance.

Osmosis is the movement of water molecules across a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration.

In a hypertonic solution, the concentration of solutes outside the cell is higher than inside the cell, so water flows out of the cell through aquaporins embedded in the plasma membrane to balance the concentration gradient.

Choice A.

Facilitated diffusion is not correct because it is a type of passive transport that involves the movement of molecules across a membrane through specific transport proteins, but it does not specifically refer to the movement of water molecules.

Choice B.

Active transport is not correct because it is a type of transport that involves the movement of molecules against their concentration gradient and requires energy in the form of ATP, but osmosis is a passive process that does not require energy.

Choice D.

Diffusion is not correct because it refers to the movement of molecules from an area of higher concentration to an area of lower concentration, but it does not specifically refer to the movement of water molecules.

Antidiuretic hormone (ADH), also known as vasopressin, is a hormone that helps regulate the amount of water in your body.

It works to control the amount of water your kidneys reabsorb as they filter out waste from your blood.

Choice A is not correct because an increase in the concentration of calcium in the glomerulus is not a physiological response caused by the release of antidiuretic hormone.

Choice C is not correct because a decrease in the concentration of calcium in the glomerulus is not a physiological response caused by the release of antidiuretic hormone.

Choice D is not correct because a decrease in water reabsorption in the collecting duct is not a physiological response caused by the release of antidiuretic hormone.