← Back to 1. Evolution and the theme of Biology and Scientific Inquiry

📝 Positive feedback biology examples (11 MCQs)

📖 From Campbell Biology • 1. Evolution and the theme of Biology and Scientific Inquiry • 11 questions available

←Previous Topic:Negative feedback biology examples📝 Positive feedback biology examplesOrganism interactions with environment ecology:Next Topic→

What is Positive feedback biology examples?

Definition:
Positive feedback is a biological mechanism where a change in a physiological variable triggers a response that amplifies or reinforces the initial change, moving the system further away from its original state, often leading to a rapid and decisive outcome, and it is less common than negative feedback but is crucial for processes that require a swift, self-perpetuating response.

Working:
This mechanism works through a cascade where the response enhances the stimulus, creating a loop that continues until the process is completed or an external factor intervenes, with the amplification often described by an exponential increase, represented by $\frac{dX}{dt} = kX$ , where $X$ is the variable being amplified, $k$ is the rate constant, and $t$ is time, leading to a rapid escalation of the response until a termination point is reached.

Example:
A classic example is blood clotting, where a tear in a blood vessel activates platelets to release chemicals that attract more platelets, which in turn release more chemicals, rapidly forming a clot to seal the wound, but this process is self-limiting as the clot itself eventually stops the cascade, demonstrating the role of positive feedback in achieving a critical outcome.

Reason:
Positive feedback is important for processes that need to be completed quickly and decisively, such as childbirth (oxytocin release enhances uterine contractions), lactation, and nerve impulse generation, but it requires careful regulation to avoid harmful over-amplification, making its study crucial in physiology and pathophysiology.

Easy

Medium

Hard

📝 All Positive feedback biology examples MCQs

Q1. A biochemical pathway produces molecule $P$ , and $P$ activates an enzyme that increases production of more $P$ . If the initial amount of $P$ suddenly rises, what is the most likely immediate system response?

A.Production of

P

decreases because

P

inhibits its enzyme

B.Production of

P

increases, causing further activation of the pathway ✅

C.Production of

P

remains unchanged because feedback cannot alter enzyme activity

D.Production of

P

stops until

P

is completely removed

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: Positive feedback occurs when an increase in an end product strengthens the process producing that same product. Therefore, increased $P$ activates the pathway further, creating additional $P$ and amplifying the original change.

Q2. A student claims that every feedback mechanism automatically stabilizes a biological system. Which observation would most directly challenge this claim?

A.A response becomes progressively stronger after the original stimulus ✅

B.A response eventually returns a variable toward its previous level

C.A response reduces the effect of the initial disturbance

D.A response maintains a variable near a preferred range

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: Positive feedback does not necessarily stabilize a system. When the response reinforces the original stimulus, the change can become progressively larger. This distinguishes amplification from mechanisms that counteract disturbances.

Q3. In a pathway, enzyme $E_1$ produces intermediate $X$ , while $X$ activates $E_1$ . Initially, $X$ is low. A small increase in $X$ activates more $E_1$ , which produces additional $X$ . What best predicts the pathway behavior?

X

should decline steadily because activation consumes

X

X

should remain constant because enzyme activity is independent of product concentration

X

may increase rapidly because each increase in

X

promotes additional production ✅

X

must immediately reach zero because positive feedback prevents accumulation

💡 Difficulty: medium | ✅ Correct: C

📖 Explanation: Because $X$ activates the enzyme responsible for producing it, an increase in $X$ creates an additional increase in production. This self-reinforcing relationship can produce rapid amplification rather than stabilization.

Q4. A cell contains two otherwise identical pathways. In pathway A, the end product activates its own production. In pathway B, the end product inhibits its own production. Both pathways experience the same small increase in end product. Which comparison is most accurate?

A.A increases the disturbance while B tends to oppose it ✅

B.Both pathways necessarily produce identical responses

C.A opposes the disturbance while B amplifies it

D.Neither pathway changes because feedback begins only after complete product accumulation

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: Pathway A contains self-reinforcement, so an increase in product promotes additional production and amplifies the change. Pathway B uses self-inhibition, which tends to counteract an increase and reduce further production.

Q5. A researcher blocks the receptor through which an end product normally stimulates its own synthesis. The starting concentration of the end product is unchanged. Which result would provide the strongest evidence that the receptor participates in positive feedback?

A.The product concentration becomes unable to increase rapidly after a small initial increase ✅

B.The product concentration immediately becomes zero

C.The product concentration increases faster than before receptor blocking

D.The pathway becomes completely independent of enzyme concentration

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: If the receptor normally transmits the reinforcing signal, blocking it should weaken amplification. Therefore, a reduced ability of the pathway to accelerate after a small increase supports its role in positive feedback.

Q6. The graph below represents product concentration $P$ over time. Curve A rises slowly and then levels off, while Curve B rises increasingly steeply over the same interval. Which curve is more consistent with strong positive feedback?

A.Curve A, because leveling off proves amplification

B.Curve B, because the increasing slope indicates strengthening production ✅

C.Both curves equally, because feedback cannot be inferred from slope

D.Neither curve, because concentration graphs cannot show feedback

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: Positive feedback can cause the production rate to increase as the product accumulates. On a concentration-versus-time graph, this can appear as an increasingly steep slope, as represented by Curve B.

Q7. A pathway initially produces $10$ units of product per minute. Each increase in product activates additional enzymes, raising production to $15$ , then $22$ , then $31$ units per minute. What conclusion is best supported by this pattern?

A.The product is progressively inhibiting its own synthesis

B.The production rate is being reinforced as product accumulates ✅

C.The pathway is operating independently of product concentration

D.The increasing values prove that the system has reached equilibrium

💡 Difficulty: hard | ✅ Correct: B

📖 Explanation: The production rate itself is increasing as product accumulates, which is characteristic of reinforcement. The sequence $10,15,22,31$ shows increasing output rather than stabilization or self-inhibition.

Q8. A student observes that product concentration increases over time and concludes that positive feedback must be present. Why is this conclusion insufficient?

A.Positive feedback requires the product to reinforce the process producing it ✅

B.Any increasing concentration automatically proves self-amplification

C.Positive feedback occurs only when concentration decreases

D.A product can never increase without positive feedback

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: An increasing concentration alone does not establish positive feedback. The crucial evidence is that the product or its downstream effect enhances its own production, creating a reinforcing relationship.

Q9. Two experimental groups show the following product concentrations: Group 1: $2,4,6,8$ ; Group 2: $2,3,5,9$ , measured at equal time intervals. Which interpretation is most reasonable if the experiment is testing self-amplification?

A.Group 1 more clearly shows a steadily constant production rate

B.Group 2 suggests increasing production rate because successive increases become larger ✅

C.Both groups demonstrate identical positive feedback strength

D.Group 2 must represent negative feedback because its concentration eventually rises

💡 Difficulty: hard | ✅ Correct: B

📖 Explanation: Group 2 has successive increases of $1,2,4$ , indicating that production becomes progressively faster. That pattern is compatible with amplification, whereas Group 1 shows a more constant rate of accumulation.

Q10. A signaling molecule activates production of an enzyme, and the enzyme produces more of the same signaling molecule. A researcher reduces the initial signaling molecule concentration by half. If positive feedback remains intact, what is the most likely qualitative outcome?

A.The pathway can still amplify the remaining signal, although the initial response may be smaller ✅

B.The pathway must immediately stop permanently

C.The pathway becomes negative feedback automatically

D.The enzyme can no longer respond to any signaling molecule

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: Reducing the starting signal does not eliminate the reinforcing relationship. If the feedback mechanism remains functional, the remaining signaling molecule can still activate enzyme production and amplify the response.

Q11. A model predicts that increasing an end product from $P=5$ to $P=10$ causes production rate to rise from $20$ to $45$ units per hour. Another model predicts the rate falls from $20$ to $8$ units per hour. Which conclusion best distinguishes the models?

A.The first model represents reinforcement, whereas the second represents self-limitation ✅

B.The first model represents self-limitation, whereas the second represents reinforcement

C.Both models represent positive feedback because both change production

D.Neither model involves feedback because production rate changes are impossible

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: In the first model, increasing product concentration causes a larger production rate, indicating self-reinforcement. In the second, increasing product reduces production, indicating self-limitation rather than positive feedback.

🔗 Related Topics (MCQs)

📝 The Study of Life Reveals Unifying Themes MCQs 📝 Hierarchical organization of life MCQs 📝 Reductionism in biology MCQs 📝 Emergent properties biology MCQs 📝 Systems biology MCQs

←Previous Topic:Negative feedback biology examples📝 Positive feedback biology examplesOrganism interactions with environment ecology:Next Topic→