AP Biology Practice Test 7: Feedback Mechanisms

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Question 1
Insulin is secreted by the pancreas, and controls blood sugar levels. When blood sugar level rises, the body responds by secreting insulin into the blood to lower blood sugar levels. When the blood sugar level reaches homeostasis, the pancreas stops releasing insulin. This system is an example of:

A
Positive feedback
B
Negative feedback
C
Allosteric regulation
D
Acceleration
Question 1 Explanation: 
The correct answer is (B). Negative feedback is the most common type of regulation in which the accumulation of the end product slows the process of producing more.
Question 2
If a mammal such as an elk migrates from sea level to an area of high altitude, changes occur to accommodate activity at lower oxygen concentrations. These changes include an increased production of red blood cells and an increase in blood flow to the lungs. These changes are an example of:

A
Adaptations
B
Natural selection
C
Acclimatization
D
Positive feedback
Question 2 Explanation: 
The correct answer is (C). One way in which an animal adjusts to changes in their external environment within the normal range of homeostasis is known as acclimatization. Acclimatization is a temporary change.
Question 3
Which type of heat exchange involves the direct transfer of heat between molecules of objects in direct contact with each other?

A
Radiation
B
Evaporation
C
Convection
D
Conduction
Question 3 Explanation: 
The correct answer is (D). Conduction takes place when heat moves between two objects that are touching each other, such as a snake basking on a rock.
Question 4
Which types of animals utilize the countercurrent exchange of heat as a means of maintaining homeostasis?

A
Terrestrial mammals
B
Amphibians
C
Tropical birds
D
Waterfowl
Question 4 Explanation: 
The correct answer is (D). Countercurrent exchange reduces heat loss when arteries carrying warm blood down the legs of waterfowl are in close contact with veins returning cold blood from cold lakes or ponds. This allows the heat from the blood in the arteries to warm the cold blood returning in the veins. When the blood from the veins reaches the body core, it is almost as warm as the body.
Question 5
Which types of animals would most likely include osmoconformers?

A
Sea stars
B
Marine mammals
C
Freshwater fish
D
Seabirds
Question 5 Explanation: 
The correct answer is (A). The osmolarity of the body fluids of sea stars (starfish) conforms to that of marine waters in which they are found.
Question 6
How does physical or emotional stress affect blood pressure?

A
Smooth muscles relax
B
Blood pressure decreases
C
Arterioles narrow, increasing blood pressure upstream in the arteries
D
Arterioles increase in diameter
Question 6 Explanation: 
The correct answer is (C). When there is physical or emotional stress, nervous and hormonal responses trigger smooth muscles in arteriole walls to contract. This causes the arterioles to narrow, increasing blood pressure in the upstream arteries.
Question 7
When a young seed is germinating, what environmental cue does it use to grow its leaves upward and roots downward when sunlight is not available (as in, when it is buried in the soil)?

A
Photomorphogenesis
B
Photoperiodism
C
Gravity
D
Thigmotropism
Question 7 Explanation: 
The correct answer is (C). Gravity provides the environmental cue signaling for the roots display positive gravitropism (growing downward) and the shoots to display negative gravitropism (growing upward). Photomorphogenesis describes the effects of sunlight on plant growth. Photoperiodism is the physiological response to a photoperiod (relative lengths of day and night), such as long-day and short-day plants. Thigmotropism is directional growth in response to touch, such as a vine wrapping its tendrils around another plant’s stem.
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