27. Countercurrent exchange in the gills of a fish
(A) maintains a gradient that enhances diffusion.
(B) speeds up the flow of water through the gills.
(C) interferes with the efficient absorption of oxygen.
(D) means that blood and water flow in the same direction.
(E) enables the fish to obtain oxygen while swimming backward.

23. Which of the following is not directly associated with photosystem II? (A) photophosphorylation (B) splitting water (C) release of oxygen (D) harvesting light energy by chlorophyll (E) P680

24. A man who carries an X-linked allele will pass it on to (A) all of his sons. (B) half of his sons. (C) all of his daughters. (D) half of his daughters. (E) all of his children.

25. Which of the following best illustrates homeostasis? (A) All the cells of the body are about the same size. (B) Most adult human beings are between 5 and 6 feet tall. (C) The lungs and intestines have large surface areas for exchange. (D) When oxygen in the blood decreases, you may feel light-headed. (E) When blood salt concentration goes up, the kidney expels more salt.

26. A technique used in molecular systematics relies on the comparison of cytochrome c in different animals. This technique is referred to as (A) DNA-DNA hybridizatioin. (B) protein comparison. (C) restriction mapping. (D) electron transport. (E) gene cloning.

28. Which of the following is a characteristic of all organisms, but not of viruses? (A) genetic information stored as nucleic acid (B) ability to control metabolism (C) ability to reproduce (D) structure includes proteins (E) plasma membrane

29. Researchers suspect that cytotoxic T cells are usually able to find and attack cancer cells because (A) B cells help them. (B) cancer is induced by bacteria. (C) cancer is an autoimmune disease. (D) cancer cells release antibodies into the blood. (E) cancer changes the surfaces of cancerous cells.

30. Which of the following statements is not true? (A) Chloroplast and mitochondria generate ATP by the same mechanism: chemiosmosis (a H+ gradient across the membrane). (B) The inner membrane of the mitochondria translocate H+ from the intermembrane space to the matrix. (C) Phosphorylation of ADP occurs as the H+ flow back across the membrane through the ATP synthase. (D) ATP is made on the matrix side of the mitochondrial membrane. (E) When ATP synthesis in chloroplast, things occur in the stroma is similar to that occurs in the matrix of mitochondria.

31. The extinction of plants has severe consequences because: (A) plants do not have the extensive ranges that animals do. (B) plants require more nutrients than animals. (C) plants require longer periods of time to reproduce than animals. (D) plants are more susceptible to environmental changes than animals. (E) plants are bases of foundations of food webs.

32. A woman had several miscarriages. Her doctor suspected that a hormonal insufficiency was causing the lining of the uterus to break down, as it does during menstruation, terminating her pregnancies. Treatment with which of the following might help her remain pregnant? (A) prolactin (B) oxytocin (C) testosterone (D) luteinizing hormone (E) follicle-stimulating hormone

33. In eukaryotes, what is the active transcription generally associated with? (A) Euchromatin only (B) Heterochromatin only (C) Highly methylated DNA only (D)Very tightly packed DNA only (E) Both euchromatin and highly methylated DNA