Biology subject test (2)

Answer choice A is incorrect; a portal system may receive blood from the aorta, but this is not its definition.. Answer choice C is incorrect; a portal system may involve the liver, but

MCAT Subject Tests

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Biology Subject Test 2

1 Which of the following is in a different chemical

category than the others?

A Cytosine

B Thymine

C Arginine

D Guanine

E Uracil

2 A portal system

A receives blood directly from the aorta

B carries blood from one set of capillaries through a

vein to another set of capillaries

C always empties into the liver

D is present in the walls of the ventricles

E links the small intestine and kidney

3 The contractile vacuole of Euglena decreases its rate of

contraction when the organism is transferred from fresh

water to sea water This is explained by

A an increase in the osmotic pressure of the

environment

B a decrease in the osmotic pressure of the

environment

C the nitrogenous wastes can remain in the cell

because of a higher salt concentration outside the

cell

D excess salts are eliminated without the loss of water

E salt inhibits the contractile apparatus

4 The chromosome number remains unchanged as a result

of

A meiosis

B mitosis

C fertilization

D non-disjunction in all gametes formed

E None of the above

5 Which of the following is a correct association?

A Mitochondria : transports materials from the nucleus to the cytoplasm

B Golgi apparatus : modification and glycosylation of proteins

C Endoplasmic reticulum : selective barrier for the cell

D Ribosome : digestive enzymes most active at an acid

pH

E Lysosomes : membrane-bound organelles which convert fat into sugars

6 The distance between linked genes is often measured by

A probability of crossing over

B frequency of silent mutations

C histone concentrations

D distance between ribosomes on mRNA

E AT/GC ratio

7 Disjunction is defined as

A when the paternal chromosomes separate from the maternal chromosomes

B when homologous pairs of chromosomes recombine

C when the spindle apparatus is formed from the centrioles

D when the cell membrane invaginates to form two daughter cells

E None of the above

Questions 8-12 refer to the choices below

A Copulation

B Fertilization

C Meiosis

D Mitosis

E Gastrulation

8 Method of replication for epithelial cells

9 Tetrads are formed in this process

10 Fusion of the nuclei of two gametes

11 May result in the formation of polar bodies

12 Results in archenteron formation

13 Which of the following is (are) derived from the

mesoderm?

A Heart

B Lung epithelium

C Intestinal mucosa

D Nerve

E Two of the above

14 Which of the following is NOT a steroid?

A Cholesterol

B Vitamin D

C Testosterone

D Thyroxine

E Cortisol

15 Which of the following cells produce antibodies?

A Macrophages

B B cells

C T cells

D Neurons

E Natural Killer cells

16 The rate of an enzyme catalyzed reaction can be

influenced by all of the following EXCEPT

A Substrate concentration

B Temperature

C Enzyme concentration

D Rate constant

E pH

17 What is the probability of a white, long tailed mouse

from the cross of a heterozygous black, heterozygous

long-tailed mouse with a homozygous recessive white,

homozygous recessive short tailed mouse?

A 0%

B 25%

C 50%

D 75%

E 100%

18 PGAL

A is considered the prime end product of photosynthesis

B can be used immediately as food

C can be combined and rearranged to form glucose

D can be stored as insoluble polysaccharides such as starch

E All of the above

19 During what stage of meiosis does crossing over occur?

A Prophase I

B Metaphase I

C Anaphase I

D Telophase I

E Interkinesis

20 The blood group antigens are an example of

A pleiotropy

B incomplete dominance

C codominance

D epistasis

E incomplete penetrance

21 Sex-linked traits such as hemophilia and colorblindness

A are located on autosomes

B are always dominant

C are found in genetic bottlenecks

D have been selected out of the population

E are rarely seen in females

22 Cell division

A is a mechanism by which a cell halves its organelles and cytoplasm

B does not involve DNA replication

C is a way for multicellular organisms to grow, develop, and repair

D is also known as mitosis

E None of the above

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23 In Drosophila, the gene for red eyes (w+) is dominant

over the gene for white eyes (w) Round eye (B+) is

dominant to Bar eye (B) A fly of an unknown genotype

is crossed against a white bar eyed fly The phenotypic

ratio of the offspring is

25% Red, round eyed

25% Red, bar eyed

25% White, round eyed

25% White, bar eyed

What is the genotype of the unknown parent?

A w+w+ B+B+

B w+w B+B+

C w+w BB

D ww B+B

E w+w B+B

24 How many ATP are produced from 2 molecules of

glucose using only substrate level phosphorylation?

A 4

B 8

C 36

D 38

E 40

25 In the DNA of C elegans, 15% of the bases are

guanine, what percentage are thymines?

A 15%

B 20%

C 35%

D 70%

E 85%

26 Which of the following does not secrete a hormone?

A pituitary gland

B salivary gland

C hypothalamus

D heart

E kidney

27 In pedigree analysis, which of the following would lead

you to assume autosomal dominance?

A The trait skips every other generation

B The trait shows up in every generation

C The trait shows up mainly in females

D The trait shows up mainly in males

E The trait is always masked by another allele

28 Very early in embryonic development, each cell still has the ability to develop into a complete organism This is known as

A indeterminate cleavage

B determinate cleavage

C blastulation

D gastrulation

E None of the above

29 The insertion or deletion of a single nucleotide base in a cell’s DNA results in a

A thymine dimer

B missense mutation

C frameshift mutation

D nonsense mutation

E degenerate genetic code

30 According to the theory of blood groups, which of the following statements is false?

A Type O blood contains no agglutinins

B Agglutinins are antibodies

C Type A blood contains agglutinins for type B agglutinogens

D Agglutinogens are antigens

E Rh factor is a type of agglutinogen found in human blood

31 During what stage of cell division do chromosomes go from single-stranded to double-stranded?

A Interphase

B Prophase

C Metaphase

D Anaphase

E Telophase

32 What level(s) of protein structure is characterized by α -helices and β-sheets?

A Primary

B Secondary

C Tertiary

D Quaternary

E Secondary and tertiary

33 Axons are sheathed in myelin which

A allows faster conduction of impulses

B maintains the resting potential

C allows the pumping of Na+ out of the cell

D initiates the action potential

E determines the threshold of the neuron

34 How many genetically different gametes can be formed

by a mouse that is genotypically AABbCc? (Assume no

linkage between these genes and that none are lethal.)

A 4

B 6

C 7

D 8

E 9

35 Active transport is best defined as

A diffusion of soluble substances across a membrane

from a region of high concentration to low

concentration

B osmosis of water across a semi-permeable

membrane involving the hydrolysis of polypeptides

C the movement of materials across a semipermeable

membrane against an electrochemical gradient

D the movement of materials across a semipermeable

membrane with an electrochemical gradient

E the movement of substances across a membrane in

accordance with the Donnan equilibrium

36 Which of the following cells does not have DNA?

A Phagocyte

B Epithelial cell

C Erythrocyte

D Osteocyte

E Sperm

37 Continuous muscle contraction causes a buildup of lactic

acid because

A it is a breakdown product of ADP

B it is a degredation product of phosphocreatine

C it is a metabolic end-product of anaerobic

metabolism

D it is a breakdown product of fatty acid degradation

E actomyosin contraction releases cross-links of

lactate

38 What is the major difference between prokaryotes and eukaryotes?

A Only eukaryotes have a cell wall

B Eukaryotes are all autotrophic

C Eukaryotes lack ribosomes

D Prokaryotes have no nuclear membrane

E Prokaryotes have mitochondria

39 In which of the following would you find cristae?

A Endoplasmic reticulum

B Mitochondria

C Nucleus

D Nucleolus

E Ribosomes

40 Which of the following is not a necessary condition for the Hardy-Weinberg equilibrium?

A Random mating

B Large gene pool

C Random emigration and immigration

D Forward mutation rate equals backward mutation rate

E No inbreeding

STOP! END OF TEST

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THE ANSWER KEY AND EXPLANATIONS BEGIN ON THE FOLLOWING PAGE

BIOLOGY SUBJECT TEST 2

ANSWER KEY

1 C

2 B

3 B

4 B

5 B

6 A

7 A

8 D

9 C

10 B

11 C

12 E

13 A

14 D

15 B

16 D

17 B

18 E

19 A

20 C

21 E

22 C

23 E

24 B

25 C

26 B

27 B

28 A

29 C

30 A

31 A

32 B

33 A

34 A

35 C

36 C

37 C

38 D

39 B

40 C

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EXPLANATIONS

1 C

Of the compounds listed, answer choices A, B, D, and E are all nitrogenous bases They are present in such

compounds as RNA and DNA The nitrogenous bases guanine and adenine are purines, and the nitrogenous bases

cytosine, thymine, and uracil are pyrimidines Answer choice C, arginine, is an amino acid and not a nitrogenous base Amino acids are the building blocks for proteins

2 B

Portal systems are unusual circulatory arrangements in the body in which there are two interconnected capillary beds

In normal non-portal circulation, blood travels from arteries to a capillary bed and back to a vein In portal systems, however, blood travels from an artery to a capillary bed, to a vein, to a second capillary bed, and back to a second vein The two most well-known portal systems in the human body are the hepatic portal system and the hypothalamic portal system In the hepatic portal system, blood leaving the capillary bed of the small intestine, which has picked up digested food, passes through the hepatic portal vein to a capillary bed in the liver before returning to a normal venous system In the hypothalamic portal system, the two capillary beds are contained in the hypothalamus and the anterior pituitary This portal system brings releasing factors from the hypothalamus to the anterior pituitary Answer choice A is incorrect; a portal system may receive blood from the aorta, but this is not its definition Answer choice C is incorrect; a portal system may involve the liver, but there are other systems as previously described Answer choice D is incorrect; there is no portal system within the ventricles of the heart Answer choice E is incorrect; there is no portal system connecting the small intestine and the kidney

3 B

The contractile vacuole of Euglena removes excess water from the organism after it comes through the cell

membrane osmotically In fresh water, the osmotic pressure drives water inside the organism due to a higher solute

concentration with the Euglena The organism must use energy (ATP) to force the water back out When this organism is

transferred to salt water, the solute concentration is greater outside the cell, thus the osmotic pressure is smaller This

causes water to leave the Euglena The contractile vacuole no longer has to remove water

4 B

Mitosis is cellular division that results in the formation of two daughter cells that are genetically identical to each other and to the parent cell The two daughter cells are also diploid (2n) Answer choice A is incorrect because meiosis results in a reduction of chromosome number from 2n to n It is a process of cell division in which two successive nuclear divisions produce four haploid gametes from one diploid germ cell Answer choice C is incorrect because fertilization is the fusion of two haploid (n) gametes into one diploid (2n) zygote Answer choice D is incorrect because non-disjunction results from the failure of homologous chromosomes to separate during meiosis and has chromosome numbers of n+1 or n–1

5 B

The Golgi apparatus consists of a stack of membrane-enclosed sacs The Golgi receives vesicles and their contents from the ER, modifies them (e.g glycosylation) and repackages them into vesicles, and distributes them Answer choice A

is incorrect because mitochondria are involved in cellular respiration, and answer choice C is incorrect because the ER transports polypeptides around the cell and to the Golgi apparatus for packaging Answer choice D is incorrect because the ribosome is the site of protein synthesis, and answer choice E is incorrect because lysosomes are membrane-bound organelles containing digestive enzymes, and typically have a low pH

6 A

The degree of genetic linkage is a measure of how far apart two genes are on the same chromosome The probability

of a crossover and exchange occurring between two points is generally directly proportional to the distance between the points For example, pairs of genes that are far apart from each other on a chromosome have a higher probability of being separated during crossover than pairs of genes that are located close to each other Thus, the frequency of genetic

recombination between two genes is related to the distance between them Recombination frequencies can be used to construct a genetic map One map unit is defined as a 1 percent recombinant frequency Recombination frequencies are roughly additive

7 A

Disjunction is defined as the separation of maternal and paternal chromosomes during meiosis Each tetrad is separated into two halves One of each pair of chromosomes, each containing two chromatids, is pulled to opposite ends

of the cell Note that some of the maternal chromosomes can go to one end and some to the other end The distribution homologues between the two resultant nuclei are random

8 D

Epithelial cells are constantly shed from the body and have to be replaced Epithelial cells are indentical to one another, and are produced via mitosis

9 C

During prophase I of meiosis I, homologous chromosomes come together and intertwine in a process called synapsis Since at this stage each chromosome consists of two sister chromatids, each synaptic pair of homologous chromosomes contains four chromatids, and is therefore often called a tetrad

10 B

Fertilization is defined as the fusion of nuclei of two gametes to form a zygote capable of becoming an adult

organism

11 C

Oogenesis is a type of meiosis that produces eggs Meiosis I of this process results in two daughter cells known as the secondary oocyte and a small polar body The polar body is formed by an unequal distribution of cytoplasm during splitting of the primary oocyte

12 E

Gastrulation results in the formation of the tree primary germ layers and the primitive digestive tract, called the archenteron

13 A

The ectodermal germ layers give rise to the epidermis of the skin and also the nervous system The endodermis, or endodermal germ layer, gives rise to the lining of the digestive system, its associated glands and organs (such as the liver and pancreas), and the lungs Most of the other organs and systems of the body are mesodermal, including the excretory system, the reproductive system, the muscular and skeletal systems, and the circulatory system Many of the human body tissues are derived from the mesoderm In answering questions of this type, if you review and eliminate tissues derived

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from the ectoderm and endoderm, you find that the remaining tissues are mesodermal In this question, answer choices B and C are endodermal tissues Answer choice D, nerve, is an ectodermal derivative

14 D

Thyroxine is a hormone released from the thyroid gland It is not a steroid, but a derivative of the amino acid

tyrosine All of the other answer choices are steroids and belong to a class of lipid-derived molecules with a characteristic ring structure Steroid hormones pass through the cell membrane with ease because they are lipid-soluble

15 B

Antibodies are produced as a response to the detection of foreign material (e.g viral coat proteins, bacterial cell walls) in the body These antigens are detected by T cells which set the immune response in motion Among their many actions, T cells stimulate B cells to become antibody producing plasma cells, making choice B the correct answer B cells can also be stimulated to become memory cells, which remain dormant in the interstitial fluid and lymphatics until the same antigen is detected again, upon which they can quickly initiate a humoral response

Choice A is incorrect because macrophages are phagocytic cells that engulf foreign material (such as bacterial cells) and digest it Choice C, T cells, are the immune response organizers They can become cytotoxic cells (which kill invading cells), helper T cells (which recruit other T and B cells into the battle) and suppresser T cells (which turn the response off when the antigen has been cleared) Choice D is a throw away neurons play no role in the immune response Choice E, natural killer cells, are rouge cells that destroy invading cells that they come across

16 D

The rate constant (k) which appears in the rate law is a temperature dependent constant For a given temperature

nothing will change k, so it can have no influence on an enzyme catalyzed reaction

We can eliminate choice A with the understanding that if the substrate concentration increases the reaction rate will also increase, until you hit a maximum rate (at which point the enzymes become saturated with substrate)

Choices B and E are incorrect because all enzymes have an optimal temperature and pH (for most enzymes it is body temperature and plasma pH; 37oC and 7.2 respectively) under which they operate most efficiently If the temperature or

pH is increased or decreased from the optimal point, the reaction rate will decrease

Choice C is incorrect because an increase in enzyme concentration will cause an increase in reaction rate, so we are left with choice D

17 B

Let B = black coat color and b = white coat color and L = long tail and l = short tail So, what is the probability of a white, long-tailed mouse from the cross of BbLl x bbll? Let's construct the Punnett square

bl (only possible gamete)

BbLl (black, long)

Bbll (Black, short)

bbLl (white, long)

bbll (white, short)

So, 25% of the offspring will be black with long tails, 25% of the offspring will be black with short tails, 25% of the offspring will be white with long tails (what we're looking for), and 25% of the offspring will be white with short tails