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Some practice questions for the biological science section of the MCAT.

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MCAT - Biological Science Practice

Pregunta 1 de 5

1

The most widely-used differential stain for bacteria is:

Selecciona una de las siguientes respuestas posibles:

  • the capsule stain

  • the Gram stain

  • the endospore stain

  • the flagella stain

Explicación

Pregunta 2 de 5

1

All of the following are true statements about the brain EXCEPT:

Selecciona una de las siguientes respuestas posibles:

  • The pons functions to link the cerebellum with the higher conscious centers

  • The limbic system alerts the cortex of incoming stimuli.

  • The limbic system is associated with emotional responses.

  • The nuclei of cranial nerves 5, 6, 7, and 8 are located in the pons.

Explicación

Pregunta 3 de 5

1

Microfilaments and microtubules form a complex network of fibers within the eukaryotic cell that can be disassembled and reassembled. If this were to occur, what is likely to be the immediate result?

Selecciona una de las siguientes respuestas posibles:

  • Depolarization

  • Protein synthesis

  • Absorption

  • Change in cell shape

Explicación

Pregunta 4 de 5

1

The small intestine is one of many organs that has endocrine functions in addition to its more familiar roles in the body. By producing such hormones as intestinal gastrin, gastric inhibitory peptide (GIP), secretin, and cholecystokinin, the small intestine regulates the activities of neighboring digestive organs and their secretions.
The thymus gland secretes thymosin, a protein hormone that stimulates the maturation and differentiation of T-lymphocytes. These cells of the immune system provide cell-mediated immunity, which not only includes attacks on infectious agents, but on infected cells as well.
Other endocrine-producing structures include the pineal gland, the kidney, and the heart. In response to light stimuli entering the eye, the pineal gland (located in the brain) releases melatonin, which is believed to play a role in regulating daily circadian rhythms. The kidney regulates red blood cell production through the secretion of erythropoietin. The heart, by secreting atrial natriuretic factor (ANF), helps regulate blood pressure, salt, and water balance.

Thymosin can directly _____.

Selecciona una de las siguientes respuestas posibles:

  • respond to specific foreign antigens and bind to receptors on invading organisms.

  • destroy infected host cells.

  • produce chemical (humoral) antibodies.

  • None of the above.

Explicación

Pregunta 5 de 5

1

Phenylalanine is an amino acid that is necessary in small amounts for proper human nutrition. The normal metabolism of this substance requires the enzyme phenylalanine hydroxylase. The ability to produce the enzyme is controlled by an autosomal dominant trait. Approximately one in 15,000 whites in the United States is born without the capacity to produce the enzyme due to a homozygous recessive condition called phenylketonuria (PKU). In people with PKU, phenylalanine accumulates in the blood, and phenylpyruvic acid accumulates in the urine-giving it a distinctive odor. High levels of phenylalanine in the brain and spinal fluid during the first weeks after birth causes mental retardation in PKU individuals. Since PKU can be identified by a blood test at birth, dietary treatment can be administered to prevent this damage. If placed on a 1owphenylalanine diet for the first few years of life, symptoms can be avoided.

A woman, homozygous for PKU, was successfully treated after birth to avoid symptoms of the disorder. If she becomes pregnant, why must similar precautions be taken to control her diet again?

Selecciona una de las siguientes respuestas posibles:

  • The fetus must have the genotype for the disorder.

  • High levels of phenylalanine in her blood can cause brain damage in the fetus, regardless of its genotype.

  • High levels of phenylalanine in her blood can stimulate her body to overproduce phenylalanine hydroxylase, which causes damage in the fetus.

  • Phenylpyruvic acid in her urine can cause damage to the fetus.

Explicación

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