DAT Question of the Day

Correct Answer: C. Salt glands secrete the excess salt.

This is a great DAT comprehension question. Let’s run through the answer choices and see what we can eliminate. Choice [A] is wrong because there is no structure in the intestine that can physically eliminate salt. Choice [B] is wrong because most chordates have similar osmolarities. Choice [D] is incorrect because nephrons become longer to resorb MORE ions and water, not less. A classic example are rodents in the desert that have very long loops of Henle to resorb as much water and ions as possible. Lastly, specialized bacteria will still eliminate the salts after they’ve used them, so it does not solve the problem of excessive salt. Choice [C] is correct, sea birds have supraorbital glands, or salt glands, above their eyes, which secrete excess salt from their blood. It functions similar to a kidney, but is much more efficient at excreting salt.

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Correct Answer: B. Transport proteins are often used by many substrates while channel proteins are generally used by ions.

Both of these types of proteins have a large variety in their shapes, sizes, and complexities. Therefore, no generalization can be made about them, and [C], [D], and [E] can be eliminated. Many transport proteins can use passive transport as well via uniport, for example, so [A] can be eliminated too. This leaves [B], where it states that channel proteins are used generally by ions. They aren’t called “ion channels” for nothing!

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Correct Answer: C. methylation.

The bacterial DNA contains numerous methylated adenines and cytosines. This methylation allows restriction endonucleases to discriminate between the host and viral DNA. Bacterial DNA don’t have nucleosomes and don’t coil.

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Correct Answer: E. Merkel cells.

Merkel cells are oval shaped and usually can be found in clusters under ridged epidermal areas. These are the cells responsible for fine-touch differentiation. Keratinocytes produce keratin and are the cells responsible for creating the skin barrier against infection. Fibroblasts manufacture collagen and are found in the dermal layer since collagen is one of the connective tissues. Melanin, the pigment responsible for skin color, is produced by melanocytes. The function of the Langerhans’ cell is to fight against skin infection by processing microbial antigens.

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Correct Answer: A. NADH and FADH2 are oxidized, hydrogen ions move into the intermembrane space, ATP is generated.

In animal cells the electron transport chain (commonly referred to as the ETC) is instrumental in cellular respiration. During the ETC, the two energy carriers, NADH and FADH2, are oxidized. Their electrons are transferred to the cytochromes embedded in the intermembrane of the mitochondria. As the electrons “jump” along the ETC, hydrogen ions are pumped out of the matrix into the intermembrane space. As a result of the hydrogen ion gradient (an electrochemical gradient), the hydrogen ions move through the ATP synthase out of the intermembrane space back into the matrix, thereby making ATP for the cell. The only answer option that details this process accurately is [A]. Note: NADPH, is an energy carrier in photosynthesis. You can think that the “P” is for plants to help remember, but it is really for phosphorus.

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Correct Answer: D. Stimulate sodium reabsorption by the kidneys.

When the adrenal cortex secretes glucocorticoids, many actions are initiated. Cortisol, for example, is released during times of stress. Gluconeogenesis (the process of creating glucose from non-carbohydrates) and lipolysis (the breakdown of fats) are both activated to generate more energy for the both during times of stress. Immunologic response, inflammatory response, glucose uptake by muscle and fat tissues, and protein construction are all restricted as these are energetically expensive and the body needs to place its energy reserves into other areas. Sodium reabsorption by the kidneys is regulated by secretion of mineralocorticoids of the adrenal cortex, such as aldosterone.

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Correct Answer: D. Obligate Anaerobes

The term obligate means that this is a required condition that has to be met to ensure the viability of the organism. An obligate aerobe has to have oxygen present to be able to survive, like humans. Likewise, an organism that cannot live in the presence of oxygen would be an obligate anaerobe. Facultative anaerobes can survive in the presence of oxygen, but prefer aerobic environments. Permissive anaerobe is a term that does not exist in biology. Aerotolerant organisms do not require oxygen, but they are not poisoned by it either.

1. Obligate aerobes need oxygen to survive because they rely on aerobic respiration.
2. Obligate anaerobes cannot survive with oxygen.
3. Facultative anaerobes grow with or without oxygen, but prefer oxygen environments because they can generate more ATP through aerobic respiration.
4. Microaerophiles need oxygen to survive, but they are poisoned by high concentrations of oxygen.
5. Aerotolerant organisms do not require oxygen, but they are not poisoned by it either.
Source from Wikipedia

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Correct Answer: B. The gap between the myelin sheath segments

The correct answer is B. The gap between the axon terminal and dendrite of the next neuron is called the synaptic cleft. The lipid-based coating that covers the neurons is the myelin sheath, and this sheath covers segments along the axon called internodes and the gaps between these internodes are called the Nodes of Ranvier.

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Correct Answer: D. enteropeptidase and trypsin

After releasing trypsinogen from the pancreas, enteropeptidase cleaves the inactive protein at specific sites. As a consequence of this action trypsin is generated. This enzyme has ability to generate trypsinogen on its own and to release an active enzyme.

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Correct Answer: B. They are responsible for the supercoiling of DNA.

Histones are not responsible for methylating DNA(A) or helping topoisomerase enzymes bind. Histones interact with DNA through ELECTROSTATIC interactions, and an octet of histones plus a length of DNA forms a NUCLEOSOME and causes the DNA to form its tertiary structure and become supercoiled.

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