DAT Question of the Day

Correct Answer: B. Blood

The three primary germ layers of the embryo include: the ectoderm, endoderm, and mesoderm. The endoderm differentiates to form the gastrointestinal tract, the lungs, the pharynx and parts of the urinary system. The ectoderm is the outer layer of the three germ layers and results in the formation of the epidermis and related structures like hair, nails, and external sense organs. The ectoderm also forms the spinal cord and the brain. The mesoderm is the middle layer of the three germ layers and eventually develops into connective tissues (including bone), cartilage, muscle, and the blood vessels. Blood is considered a type of connective tissue, thus the correct answer is [B].

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Correct Answer: C. Cellular slime molds

Bryophytes are a type of plant and can be eliminated. While the rest of the choices are unicellular protists, only cellular slime molds exhibit an amoeboid characteristic and “slug stage”, when many cells combine in a mass.

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Correct Answer: A. Prophase I

The process described is crossing over. Crossing over occurs during the first stage of meiosis called prophase I. In this stage the homologous chromosomes begin to come together and they form tetrads. The homologous chromosomes are able to “cross over” sections of the chromosome between the homologous pair. The point at which the new chromosomal pieces attach is referred to as the chiasmata.

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Correct Answer: B. Golgi apparatus.

The Golgi apparatus is an organelle which somewhat resembles a stack of pita bread or pancakes. Its purpose is to modify proteins that are manufactured by the endoplasmic reticulum. Within the Golgi are resident enzymes, which catalyze the cargo proteins. The modification processes are glycosylation – the adding or removing of sugars from the protein, sulfation – addition of sulfate groups and phosphorylation – adding phosphate groups.

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Correct Answer: B. perforin

Cytotoxic T-cells are able to rid the body of infections that have spread to cells. To do this, cytotoxic T-cells release perforin, which disintegrates the cell membrane, causing the infected cell to lyse and then be engulfed by macrophages. Antibodies are released from B-cells that then aggregate to an antigen, tagging it to be eaten by macrophages. Actin and tubulin are proteins present in the cytoskeleton and histamine is a chemical released during an allergic reaction or to initiate an inflammatory response.

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Correct Answer: C. pH levels

The brain triggers the diaphragm to contract and lower to spur inhalation when the pH levels begin to drop. In the presence of high amounts of CO2, the blood’s pH begins to become acidic, which is detected by chemoreceptors. This will initiate inhalation, where CO2 will be expelled and oxygen will be absorbed into the capillaries in the alveoli, thereby restoring blood’s neutral pH.

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Correct Answer: B. mycorrhizae

The mycorrhizae inhabit the roots of vascular plants and help to increase the surface area of the roots leading to higher rates of nutrient and water absorption. Rhizomes are underground stems that can sprout to produce new shoots and roots for the plant. Likewise, the apical meristem is the portion on the stem that enables upward growth of the stem. The vascular cambium produces secondary xylem and phloem that help sustain the plant as it grows laterally each year. In addition, the cork cambium forms the “woody” part of the plant helping to provide the plant with structure and support as it grows laterally.

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Correct Answer: B. recombinant DNA

The phenotype of the offspring is a mixture of the two parents’ phenotype. This would be due to recombinant DNA, specifically crossing over that likely occurred during meiosis I (prophase I). Restriction enzymes cut the DNA at specific sequences and would not be the direct cause of the change in phenotype observed. Genetic drift describes the change in allele frequency over time not in one generation. Genetic mutations can lead to different features in an offspring than what was present in the parents, however the offspring resemble the parents, with one phenotypic characteristic from each parent expressed.

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