Which of the following is the approximate threshold value for mammalian neurons?

A. Aids in the maturation of sex cells

B. Carries electrical impulses

C. Develops into any kind of cell

D. Fights infectious diseases

A totipotent cell is a type of stem cell that has the ability to develop into any kind of cell in the body, including the cells that make up the placenta and the umbilical cord. This means that a totipotent cell can generate a complete organism from a single cell. The only natural example of totipotent cells are the fertilized egg and the cells produced by the first few divisions of the egg. Totipotent cells are different from other types of stem cells, such as pluripotent cells, which can develop into any cell type except for the placenta and the umbilical cord, and multipotent cells, which can only develop into a limited range of cell types. 

A. Carbohydrates

B. Nucleic acids

C. Proteins

D. Lipids

The cytoskeleton of a cell is a complex network of filaments and tubules that provides structural support, shape, movement, and organization to the cell and its components.

The cytoskeleton is composed mainly of proteins, which are macromolecules made of amino acids linked by peptide bonds. The three main types of proteins that form the cytoskeleton are microtubules, microfilaments, and intermediate filaments. Each type has a different structure, function, and distribution within the cell. 

A. Sodium bicarbonate inhibits peristalsis.

B. Sodium bicarbonate stimulates the pyloric sphincter.

C. Sodium bicarbonate is a protease that digests carbohydrates.

D. Sodium bicarbonate neutralizes the acidity of chyme.

The pancreas releases sodium bicarbonate into the duodenum, the first part of the small intestine. The main function of sodium bicarbonate is to neutralize the acidity of chyme, the semi-digested food that comes from the stomach. By doing so, sodium bicarbonate creates a more alkaline environment that is suitable for the action of pancreatic enzymes. Sodium bicarbonate does not affect peristalsis, the rhythmic contraction of the intestinal muscles, nor does it stimulate the pyloric sphincter, the valve that controls the passage of food from the stomach to the duodenum. Sodium bicarbonate is not a protease, an enzyme that digests proteins, nor does it digest carbohydrates. 

A. Filtration

B. Spectrophotometry

C. Titration

D. Electrophoresis

One of the most common techniques for separating DNA fragments by size is electrophoresis. Electrophoresis is a process that uses an electric field to move charged molecules through a porous gel matrix. The gel acts as a sieve, allowing smaller molecules to move faster and farther than larger ones. By applying a dye to the DNA samples and loading them into wells at one end of the gel, the DNA fragments can be visualized as bands after electrophoresis. The distance of each band from the well indicates the size of the corresponding DNA fragment.

A. Lysozymes

B. Perforin

C. Cytokines

D. Granzymes

Cytokines are small proteins that act as chemical messengers between different types of immune cells. They can stimulate or inhibit the activation, proliferation, differentiation, and migration of immune cells. For example, interleukins are a type of cytokine that is produced by one type of white blood cell and can affect the behavior of another type of white blood cell. Lysozymes, perforin, and granzymes are all molecules that are involved in killing pathogens or infected cells, but they do not directly activate other immune cells.

A. Progestin

B. Androgen

C. Aldosterone

D. Estrogen

Testosterone is a hormone that belongs to the class of androgens, which are responsible for the development and maintenance of male characteristics. Androgens are synthesized from cholesterol and can be converted into other types of hormones, such as estrogens and progestins. Aldosterone is a different type of hormone that regulates the balance of salt and water in the body. 

A. Osmosis

B. Diffusion

C. Facilitated diffusion

D. Active transport

One of the ways that cells regulate their water balance is by adjusting to different solute concentrations in their environment. When a cell is placed in a solution that has a higher concentration of solutes than the cell itself, the solution is called hypertonic. In this case, water will tend to move out of the cell through special channels called aquaporins, which are embedded in the plasma membrane. This movement of water across a selectively permeable membrane is a type of passive transport called osmosis. Osmosis does not require any energy input from the cell, unlike other forms of transport such as diffusion, facilitated diffusion, or active transport. 

A. Sodium

B. Potassium

C. Calcium

D. Phosphorus

When a muscle cell is stimulated by a nerve impulse, calcium ions are released from the sarcoplasmic reticulum into the cytoplasm. The calcium ions bind to the troponin complex, which is a protein that regulates the interaction between actin and myosin filaments. The binding of calcium to troponin causes a conformational change that exposes the binding sites for myosin on the actin filaments. This allows the myosin heads to attach to the actin and pull the filaments past each other, resulting in muscle contraction.

A. The reaction is completed in a shorter amount of time.

B. The yield of product is increased.

C. A greater amount of heat energy is released by the reaction.

D. A more desirable product is often formed.

A catalyst is a substance that lowers the activation energy of a chemical reaction, which means that it allows the reaction to proceed faster without being consumed or changed itself. A catalyst does not affect the equilibrium of a reaction, so it does not change the amount or the type of product that is formed.

A. ffx ff

B. Ffx Ff-

C. Ff x ff

D. FFX FF

To produce only offspring with smooth leaves, the parents must both have two copies of the recessive allele (f) for this trait.