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IB DP Biology HL Prediction Paper 2

IB DP Biology HL Prediction Paper 2 for 2025 Exams

IB DP Biology HL Prediction Paper 2- April/May 2025 Exam

IB DP Biology HL Prediction Paper 2: Prepare for the IB exams with subject-specific Prediction questions, model answers. All topics covered.

Prepared by IB teachers: Access our IB DP Biology HL Prediction Paper 2 with model answer. Students: Practice with exam-style papers for IB DP Biology HL Exam

Question 1: Squirrel Defense Mechanisms

California ground squirrels (Otospermophilus beecheyi) chew moulted rattlesnake skins and lick their fur to acquire rattlesnake scent as a defense mechanism. An experiment tested rattlesnake responses to different scents.

a
Calculate the difference in mean time spent studying squirrel-scented filter paper with and without rattlesnake scent.
▶️Answer/Explanation

Correct answer: 80s (accept 75s–85s)

Explanation: From the graph, the difference between pure squirrel scent (≈20s) and mixed scent (≈100s) is approximately 80 seconds.

b
Outline conclusions from the control results.
▶️Answer/Explanation

Correct answer:

  1. Snakes spend minimal time studying control filter paper (water).
  2. Filter paper itself isn’t attractive to snakes.

Explanation: The control establishes baseline behavior, showing snakes aren’t responding to the paper itself but to specific scents.

c
Why were filter paper positions changed for each trial?
▶️Answer/Explanation

Correct answer: To ensure snakes respond to scent rather than position preference.

Explanation: Eliminates potential bias from snakes developing a preference for one side of the chamber.

d
Why does rattlesnake scent lower attack chances?
▶️Answer/Explanation

Correct answer: Masks squirrel scent/suggests presence of rival snake.

Explanation: Snakes may avoid areas with other snakes’ scents to prevent conflict.

Tail-flagging Behavior Graph

 

Key: ▲ Tail-flagging squirrels ◆ Non-tail-flagging squirrels
Source: Adapted from Barbour & Clark (2012)

e
Compare tail-flagging vs non-tail-flagging strike probability.
▶️Answer/Explanation

Correct answer:

  1. Both have high strike probability at short distances (<10 cm).
  2. Tail-flagging squirrels have lower strike probability at greater distances (e.g., 20 cm: ≈0.2 vs. 0.8 for non-tail-flagging).

Explanation: Tail-flagging deters attacks beyond close range, signaling alertness to the snake.

f
Estimate the distance for 50% strike probability at tail-flagging squirrels.
▶️Answer/Explanation

Correct answer: 14 cm (accept 12–16 cm).

Explanation: The tail-flagging curve intersects the 0.5 probability line at ~14 cm on the x-axis.

g
Suggest why snakes avoid tail-flagging squirrels.
▶️Answer/Explanation

Correct answer: Tail-flagging signals alertness, making successful strikes unlikely.

Explanation: Snakes conserve energy by avoiding prey that is aware of their presence.

Hawk Sound Experiment

Grey squirrels (Sciurus carolinensis) were exposed to hawk sounds and bird chatter. Their vigilance was measured:

 

h
State conditions for least squirrel lookups.
▶️Answer/Explanation

Correct answer: With bird chatter AND 3 minutes after hawk sounds.

Explanation: Chatter signals safety, and time reduces perceived threat.

i
Does bird chatter significantly affect immediate vigilance?
▶️Answer/Explanation

Correct answer:

  1. No significant difference immediately after hawk sounds (bars overlap).
  2. Chatter’s effect becomes apparent after 3 minutes.
j
Analyze bird chatter’s effect on squirrel behavior.
▶️Answer/Explanation

Correct answer:

  1. Chatter reduces vigilance over time (lower lookups and % vigilance after 3 minutes).
  2. Squirrels interpret chatter as an “all clear” signal.
  3. Immediate response to hawk sounds dominates initial behavior.
Complete DP Biology HL Paper 2- 2025- Prediction Questions..
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