For each of the questions below, ONE or MORE of the response(s) is (are) correct. Decide which of the response(s) is (are) correct. Then choose:

Step 1: Answer Question 21. 1. Producers are autotrophic organisms (True). 2. Each organism has many food sources (False, this is more characteristic of a food web). 3. Producers release carbon dioxide during photosynthesis (False, they release oxygen and take in carbon dioxide). Only statement 1 is correct. The correct answer is D. D Step 2: Answer Question 22. 1. The biceps muscles contract (True, they are flexors). 2. The triceps muscles relax (True, they are extensors and relax during flexion). 3. The ulna and radius straighten (False, the bones themselves do not straighten; the joint bends). Statements 1 and 2 are correct. The correct answer is B. B Step 3: Answer Question 23. 1. Occurs as a result of the eyeball being large (True, or the cornea is too curved). 2. Near objects are seen clearly (True, distant objects are blurry). 3. Is corrected with the use of concave lenses (True, concave lenses diverge light to focus it on the retina). All three statements are correct. The correct answer is A. A Step 4: Answer Question 24. 1. Sweating is inhibited (False, sweating increases to cool the body). 2. Vasodilation occurs (True, blood vessels dilate to release heat). 3. The hair erector muscles relax (True, hairs lie flat to reduce insulation). Statements 2 and 3 are correct. The correct answer is C. C Step 5: Answer Question 25. 1. They have wings (True, essential for flight). 2. They have hollow bones (True, reduces weight). 3. They have streamline bodies (True, reduces air resistance). All three statements are correct. The correct answer is A. A Step 6: Answer Question 26. First statement: During anaerobic respiration glucose is partially broken down (True). Second statement: Anaerobic respiration occurs in the cytoplasm (True). The second statement is true but does not explain why glucose is partially broken down. The correct answer is B. B Step 7: Answer Question 27. First statement: Arteries have small lumen and thick elastic walls (True, adapted for high pressure). Second statement: Arteries carry blood away from the heart (True, this is their function). The second statement is true but does not explain why arteries have the described structure. The correct answer is B. B Step 8: Answer Question 28. First statement: Fresh water Amoeba* possesses contractile vacuole (True, for osmoregulation). Second statement: The cytoplasm of fresh water Amoeba* is more concentrated than the surrounding water (True, this causes water to enter by osmosis). The second statement correctly explains why the Amoeba needs a contractile vacuole. The correct answer is A. A Step 9: Answer Question 29. First statement: Acid rain results when Sulphur dioxide and nitrogen dioxide are released into the atmosphere (True, these gases form acids). Second statement: Sulphur dioxide and nitrogen dioxide in the atmosphere originate from the burning of fuel (True, fossil fuel combustion is a major source). The second statement correctly explains the origin of the gases mentioned in the first statement. The correct answer is A. A Step 10: Answer Question 30. First statement: The body of most mammals is covered with fur or hair (True, a characteristic feature). Second statement: Fur or hair assist in the control of body temperature (True, by providing insulation). The second statement correctly explains a key function of fur or hair. The correct answer is A. A What's next?