FINAL EXAM

MULTIPLE CHOICE [3 points/question]

1. At rest, a winter moth is the same temperature as its environment. Prior to flight, the moth contracts its wing muscles so that their temperature rises 10û C. This behavior indicates that the winter moth is

A) endothermic

B) ectothermic

C) heterothermic

D) homeothermic

2. Which part of a neuron receives most of the incoming signals?

A) myelin

B) cell body

C) dendrite

D) axon

3. The Na/K pump in the cell membrane of animal neurons transports ions in which direction?

A) Na⁺ into the cell; K⁺ into the cell

B) Na⁺ into the cell; K⁺ out of the cell

C) Na⁺ out of the cell; K⁺ into the cell

D) Na⁺ out of the cell; K⁺ out of the cell

4. Following neural stimulation, a skeletal muscle fiber contracts in response to Ca⁺² ions entering its cytoplasm. To which of these muscle proteins does the Ca⁺² ion bind directly?

A) actin

B) myosin

C) tropomyosin

D) troponin

5. When a cell membrane is at its K+ equilibrium potential, which of the following is true?

A) Fifty-percent of the K-channels are open; fifty-percent are closed.

B) The K⁺ concentration gradient and the Na⁺ concentration gradient exert equal and opposite forces.

C) The K⁺ concentration gradient and the electrical gradient exert equal and opposite forces.

D) The K⁺ concentration gradient and the electrical gradient exert equal forces in the same direction.

6. The undershoot at the end of an action potential is hyperpolarized relative to the resting potential. The primary reason for this hyperpolarization is

A) Na/K pumps are active.

B) An inhibitory postsynaptic potential (IPSP).

C) Voltage-gated K-channels are open.

D) Voltage-gated Na-channels are open.

7. At a chemical synapse, which event immediately precedes the fusion of the synaptic vesicles with the cell membrane?

A) postsynaptic potential (PSP)

B) action potential

C) release of neurotransmitter into the interstitial fluid ('synaptic cleft')

D) influx of Ca⁺² ions into the presynaptic cytoplasm

8. The term 'motor unit' refers to

A) a pair of muscles that produce opposite movements at a given joint

B) the unitary contraction ('twitch') produced by a single action potential

C) a single motor neuron and the muscle fibers it innervates

D) the contractile unit of the muscle fiber's cytoskeleton

9. In plants, which of the following tissue types is primarily involved in metabolism and structural support?

A) connective tissue

B) vascular tissue

C) ground tissue

D) epidermis

10. Which of the following statements is not correct?

A) Fruit provides the sporophyte embryo with nutrients prior to germination.

B) The pulp or edible part of a fruit is composed of diploid tissue.

C) Fruit is an evolutionary adaptation that promotes the dispersal of seeds.

D) Only flowering plants produce fruit.

11. In a growing plant, the mitotic activity of an apical meristem is directly responsible for all of the following except

A) elongation of roots

B) elongation of shoots

C) elongation of side branches

D) thickening of shoots or roots

12. Which of the following statements most accurately describes the membrane transport of a guard cell after it has been exposed to the first light of dawn?

A) H₂O flows into the cell; K⁺ ions and H⁺ ions flow out of the cell.

B) K⁺ ions and H₂O flow into the cell; H⁺ ions flow out of the cell.

C) K⁺ ions flow into the cell; H⁺ ions and H₂O flow out of the cell.

D) H⁺ ions and H₂O flow into the cell; K⁺ ions flow out of the cell.

13. During transpiration, why is there a net flow of water towards the leaves?

A) Leaves are hypertonic to the remainder of the plant's body.

B) Leaves experience more evaporation than the remainder of the plant's body.

C) Leaves are the most turgid portion of the plant.

D) Leaves are a 'sugar source' due to photosynthesis.

14. All of the following cell types can be found in the loose connective tissue of humans. Which of these cells synthesizes the extracellular matrix (ECM) protein collagen?

A) fibroblast

B) adipocyte

C) macrophage

D) neutrophil

15. In animals, which of the following statements accurately defines 'digestion'?

A) transfer of food from the external environment into the digestive tube

B) polymerization of carbon skeletons to build the body's own macromolecules

C) breakdown of food to release energy for ATP synthesis

D) breakdown of food into subunits that can cross cell membranes

16. In mammals, which of the following occurs when the diaphragm relaxes?

A) alveoli increase in volume

B) air pressure in the lungs becomes more positive

C) diaphragm flattens

D) air is inhaled

17. Which of the following statements accurately describes the blood pressure within the systemic circuit of a mammal?

A) blood pressure decreases as blood travels from arteries to capillaries, and increases again as it travels from capillaries to veins

B) blood pressure increases as blood travels from arteries to capillaries, and decreases again as it travels from capillaries to veins

C) blood pressure steadily decreases as the blood travels further away from the heart

D) blood pressure is constant throughout the circuit (= Law of Continuity)

18. Catecholamines alter the blood flow to many different organs. Which of the following does not occur in response to the secretion of catecholamines?

A) increase in blood flow to kidneys

B) increase in blood flow to muscles

C) increase in blood flow to the brain

D) decrease in blood flow to the digestive system

19. In humans, which of the following is brought on by the secretion of corticosteroid hormones?

A) synthesis of glucose by degradation of the body's own proteins

B) maturation of ovarian follicles in females; formation of sperm in males

C) decrease in blood pressure

D) inflammatory response

20. Chorionic villi perform which of the following functions?

A) absorb water from the renal filtrate

B) absorb waste products from renal blood

C) absorb nutrients from partially digested food

D) absorb nutrients from maternal blood

21. Shivering differs from typical muscular contractions in which of the following ways?

A) Shivering converts some of the chemical energy from ATP into heat.

B) Shivering converts all of the chemical energy from ATP into heat.

C) During shivering, skeletal muscles contract without signals from the nervous system.

D) During shivering, the contraction of the individual muscle fibers is asynchronous.

22. Human chorionic gonadotropin (HCG) is a peptide hormone secreted by the

A) hypothalamus

B) pituitary gland

C) corpeus luteum

D) implanted embryo

23. If a finger were injured and became inflamed, it would swell, turn red, and be painfully tender. Which aspect of the inflammatory response accounts for the reddening of the injured tissue?

A) flow of water and proteins from the blood to the interstitial fluid

B) accumulation of phagocytes (= chemotaxis)

C) vasodilation of blood vessels

D) hypersensitivity of sensory nerves

24. In a normal, healthy human adult, what feature of the immune system accounts for self-tolerance?

A) Lymphocytes that respond to 'self' antigens have all completed their primary immune response.

B) Self-tolerance is not 'normal'; it only occurs following the transplantation of blood or an organ from another individual.

C) There are no lymphocytes that synthesize 'self' antigens.

D) There are no immunoglobulins capable of binding to 'self' antigens.

25. All of the following processes affect the water balance of the human body. However, only one of these processes increases the osmolarity of the bodily fluids. Which one is it?

A) evaporation of water from the lungs

B) secretion of salt ions into the kidney filtrate

C) reabsorption of water from the kidney filtrate

D) reabsorption of water by the digestive tube

Short-Answer Questions - correct answers in italics.

26. Hormonal regulation of the menstrual cycle

The graph above shows the blood plasma concentrations of four different hormones as they change during the menstrual cycle of a human female.

A. [4 pts]

What organ or tissue synthesizes and secretes the gonadotropins FSH and LH? Be specific.

anterior pituitary gland

B. [4 pts]

The concentrations of FSH and LH peak sharply on Day 13. What event is triggered in the reproductive system at the peak concentrations of these hormones?

ovulation

C. [7 pts]

Why do the blood plasma concentrations of FSH and LH drop sharply following this peak?

Following ovulation, the corpus luteum secretes the hormone progesterone. The presence of progesterone in the blood inhibits the secretion of Gonadotropin Releasing Hormone (GnRH) by the hypothalamus. GnRH stimulates the secretion of FSH and LH by the anterior pituitary. Thus, the inhibition of GnRH secretion results (indirectly) in an inhibition of FSH and LH secretion.

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27. Homeostasis

A. [9 pts]

Saltwater fish maintain an optimal blood osmolarity of approximately 350 mosm/L, even though they live in sea water that is 1200 mosm/L. Describe three (3) physiological or behavioral processes that help the saltwater fish to maintain its internal water balance.

1. A saltwater fish ingests large quantities of water.

2. A saltwater fish excretes small quantities of highly concentrated urine.

3. The gills of a saltwater fish secrete salt ions into the surrounding water.

B. [6 pts]

Joan Jetsetter takes an airplane from New York City to Honolulu, Hawaii, where she eats dinner and goes to bed.

But Joan discovers that she has 'jet lag'. Instead of waking up at 8AM the next morning, she wakes up at 3AM and can't get back to sleep. And she becomes sleepy at 6PM, even though it is still bright and sunny on the beach!

Explain in biological terms what is causing Joan to experience jet lag.

Joan's urges to sleep and wake up are brought about by the 'biological clock' in her brain. Her biological clock is appropriate for the New York time zone (Eastern Standard Time), so when she first arrives in Hawaii her biological clock is several hours out of phase with the days and nights of her new environment.

What must happen in order for Joan to get over her jet lag? [Assume that she remains in Hawaii for some time.]

Joan's biological clock must be entrained by the cycle of days and nights she experiences in Hawaii. This will cause her clock to shift phase until her periods of activity and sleep have become synchronized with the days and nights of her new environment.

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28. Plant biology

A. [5 pts]

What is the tradeoff between opening vs. closing stomata with regard to the health and survival of a plant?

In order to photosynthesize its own organic molecules, a plant must open its stomata so that its mesophyll cells have access to atmospheric CO₂.

However, opening the stomata also results in transpiration, i.e. loss of water by evaporation into the atmosphere. Too much water loss is deleterious, leading to desiccation and possibly death.

B. [5 pts]

What is the endodermis, and where is it located in a plant? Be specific.

The endodermis is a part of the ground tissue within the roots of a plant. The endodermis is cylindrical in shape, one cell in thickness, and located between the cortex (on its outer side) and the vascular tissue (on its inner side).

C. [5 pts]

How does the endodermis control the transport of water and minerals to the shoot?

Water and minerals from the soil must cross the endodermis in order to enter the vascular system and travel to the shoot. Each cell in the endodermis is surrounded by a ring of hydrophobic material - the Casparian strip - located in its cell wall, and the Casparian strip blocks the flow of water and minerals through the apoplastic (= extracellular) pathway. As a result, water and minerals can only cross the endodermal cell through its cytoplasm (= symplastic pathway).

Thus, the endodermis controls the transport of water and minerals to the shoot by insuring that they must be transported across cell membranes before they can enter the vascular system.

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29. Bioenergetics

A. [10 pts]

In a contracting muscle fiber, the proteins actin and myosin convert the chemical energy of ATP into a mechanical force that shortens the long-axis of the fiber. Describe the way in which these two proteins and the ATP molecule interact to generate force.

Each myosin protein has 'head' domains that extend outward from the thick filament. Each myosin head binds and hydrolyzes ATP to obtain the energy for muscle contraction:

1. The binding and hydrolysis of ATP 'cocks' the myosin head, i.e. causes it to swing outward into a high-energy configuration.

2. Once the myosin head is cocked, it releases the ADP and phosphate (products of ATP hydrolysis) and binds to an actin protein in the adjoining thin filament.

3. The myosin head falls from the cocked high-energy configuration to a relaxed low-energy configuration. In doing so, it swings through an arc and pulls the bound actin filament along with it.

4. When the myosin head pulls on the adjoining thin filament, the thick and thin filaments slide past one another. This sliding is oriented in such a way that it contracts (= shortens) the muscular fiber.

B. [6 pts]

Muscle contraction generates heat, and a human being uses that heat to raise his or her body temperature above the ambient temperature of the environment.

Describe two (2) structural or functional adaptations of the human body that help to prevent this heat from being lost to the environment.

1. A layer of subcutaneous fat provides thermal insulation between the warm body tissues and the external environment.

2. Humans can vasoconstrict the arteries that blood (which is warm) close to their skin. The vasoconstriction of these cutaneous arteries decreases blood flow near the body surface, and thereby reduces heat loss to the surrounding environment.

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30. Electrophysiology

A. [8 pts]

The drawing above represents an action potential occuring in a nerve cell membrane.

A critical part of the action potential is the opening and closing of the activation and inactivation gates on Na-channel proteins. At each of the marked time-points, the two gates are predominately in either the open or closed position.

Use the table below to show whether each gate is open or closed at these 4 time-points.

Correct answers marked in bold.

B. [7 pts]

Describe the sequence of cellular events that are responsible for the knee-jerk reflex, starting with transduction of the stimulus and ending with the contraction of the quadriceps muscle. Be sure to name or describe [i] the cells and [ii] the general location in the body where each event occurs.

1. The stimulus (stretching of the quadriceps muscle and its tendon) is initially transduced into an action potential by sensory neurons whose axons innervate the quadriceps.

2. The action potential is conducted to the spinal cord along the axons of these sensory neurons.

3. In the spinal cord, the sensory axons have synapses onto motor neurons. Action potentials in the presynaptic sensory axons produce EPSPs - leading to action potentials - in the postsynaptic motor neurons.

4. The action potential is conducted from the spinal cord to the quadriceps muscle along the axons of these motor neurons.

5. The motor axons have synapses with the muscle fibers of the quadriceps muscle. Action potentials in the presynaptic motor axons produce EPSPs - leading to action potentials - in the postsynaptic muscle fibers.

6. Those muscle fibers that experience action potentials contract in response to them.

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31. Immunity

Tiger and Furball are house cats. Tiger was immunized with 'heat-killed' feline leukemia virus (FeLV) as a kitten. Furball never received an immunization against FeLV.

The two cats are exposed to live FeLV as adults, and they both mount an immune response against it. Tiger remains healthy, but Furball becomes infected with the virus, sickens, and eventually dies.

A. [6 pts]

Both Tiger and Furball produced antibodies that attack the live virus. Why were Tiger's antibodies more effective at fighting off the virus?

Because of his immunization against FeLV, Tiger experiences a secondary immune response when he is exposed to the live virus. During a secondary immune response, the immune system (1) generates a higher concentration of antibodies and (2) generates antibodies more rapidly than during a primary immune response.

Furball's immune system had not previously encountered the virus, and therefore can only mount a primary (less effective) immune response against it.

B. [4 pts]

Tiger was able to fight off the live virus because his immune system has a particular class of lymphocyte that Furball was lacking. Name or describe the class of lymphocytes that gave Tiger his added protection.

memory cells

C. [5 pts]

Will immunization against FeLV protect Tiger from rabies or other unrelated viruses? Explain your reasoning in terms of the cellular and molecular properties of the immune system.

Immunization against FeLV should not protect Tiger against an unrelated virus.

Immunization with FeLV produces memory cells whose immunoglobulins specifically bind to that particular virus. Since each lymphocyte can only synthesize one kind of immunoglobulin binding-site, the memory cells produced by FeLV immunization will not respond to other antigens. If Tiger encounters an unrelated virus, he will not have protective immunity and will have to undergo a primary immune response against it.

[Note: in theory, immunization with FeLV could protect Tiger against a virus that shares a molecular epitope with FeLV. But the chance of two unrelated viruses having the same molecular epitope is vanishingly small.]