44. If a human female begins taking estradiol and progesterone immediately after the start of a new menstrual cycle, how will ovulation be affected?
(A) Ovulation will be stimulated early in the cycle.
(B) Ovulation will be delayed or inhibited.
(C) Ovulation will occur normally, but fertilization will be prevented.
(D) Ovulation will become irregular, but not necessarily inhibited.

40. If a complete ring of bark is removed from around a tree trunk (a technique called girdling), the tree will die, but typically slowly (in weeks) rather than quickly (in days). Which of the following best explains this observed timeframe?(A) Girdling only disrupts the xylem, and the tree's roots can store enough water to survive for a few days.(B) Girdling severs the phloem, cutting off sugar transport to the roots, which leads to root starvation and eventual death, a process that takes weeks.(C) Girdling directly kills all the living cells in the trunk, but the leaves can continue photosynthesis until stored carbohydrates are depleted.(D) The tree can regenerate the phloem within days, thus preventing rapid death, but the energy cost is high.

41. Which type of plant supplements its mineral nutrition by digesting animals?(A) Epiphytes (B) Parasitic plants(C) Carnivorous plants (D) Nitrogen-fixing plants

42. In mammalian circulation, oxygen-rich blood returns from the lungs to the heart via the:(A) Pulmonary arteries (B) Aorta (C) Venae cavae (D) Pulmonary veins

43. A plant has a double mutation: ctr (constitutive triple response, meaning it always shows the triple response regardless of ethylene) and ein (ethylene insensitive, meaning it cannot respond to ethylene). What would be its triple-response phenotype?(A) It would display a normal triple response, as the mutations compensate for each other.(B) It would not display the triple response, as the ein mutation makes it insensitive to ethylene.(C) It would constitutively display the triple response, because the ctr mutation is dominant.(D) Its phenotype would be intermediate between a wild-type plant and a ctr mutant.

45. Which of the following is a direct consequence of biological magnification?(A) Ecosystems with higher primary productivity support larger populations of herbivores.(B) Toxic chemicals, such as PCBs, become more concentrated in organisms at higher trophic levels.(C) The total biomass decreases as you move up trophic levels in an ecosystem.(D) Species with narrow habitat requirements are more vulnerable to extinction.

46. Ruminant animals, such as cows, have specialized digestive systems that allow them to obtain significant nutrients from cellulose-rich plant material. Which of the following best describes the key adaptation responsible for this ability?(A) They have an extended small intestine for increased absorption surface area.(B) Their stomach has four chambers, with mutualistic microorganisms digesting cellulose in the rumen and reticulum.(C) They produce unique enzymes in their abomasum that directly break down cellulose.(D) They re-ingest their feces to re-process undigested plant matter, similar to coprophagous animals.

47. Which of the following is a less toxic nitrogenous waste product that mammals and most adult amphibians convert ammonia into, requiring a moderate amount of water for excretion?(A) Ammonia (B) Urea (C) Uric acid (D) Creatinine

48. During the rising phase of an action potential, what is the primary event that causes the rapid depolarization of the neuron's membrane?(A) Outflow of potassium ions (K+)(B) Inflow of chloride ions (Cl-)(C) Rapid opening of voltage-gated sodium channels (Na+) allowing Na+ to diffuse into the cell(D) Active transport of sodium and potassium ions by the Na+/K+ pump

49. The production of offspring without the fusion of gametes is known as:(A) Sexual reproduction (B) Parthenogenesis(C) Hermaphroditism (D) Asexual reproduction

50. What is the process by which an encounter with an antigen selects which lymphocyte will divide to produce a clonal population of thousands of cells specific for a particular epitope?(A) Immunological memory (B) Antigen presentation(C) Clonal selection (D) Self-tolerance