IB Biology 2025 · Theme B · Form and function

B3.3 Muscle and motility (HL). Practice questions with markscheme.

67 original IB-style questions on B3.3, written from the 2025 guide: 31 multiple-choice, 24 short-answer, 6 data-based, 3 extended-response parts, 2 drawing, 1 labelling. This subtopic is additional higher level in its entirety, so below is a 21-mark higher-level practice paper built from them. Hand one out as a class quiz or homework, or sit it yourself and mark against the scheme. Print it, project it, or build a fresh one on the same topic.

What the guide asks for

All 10 statements are additional higher level, so this subtopic is HL only.

B3.3.1HL Adaptations for movement as a universal feature of living organisms
B3.3.2HL Sliding filament model of muscle contraction
B3.3.3HL Role of the protein titin and antagonistic muscles in muscle relaxation
B3.3.4HL Structure and function of motor units in skeletal muscle
B3.3.5HL Roles of skeletons as anchorage for muscles and as levers
B3.3.6HL Movement at a synovial joint
B3.3.7HL Range of motion of a joint
B3.3.8HL Internal and external intercostal muscles as an example of antagonistic muscle action to facilitate internal body movements
B3.3.9HL Reasons for locomotion
B3.3.10HL Adaptations for swimming in marine mammals

In the bank for B3.3

31 multiple-choice
24 short-answer
6 data-based
3 extended-response parts
2 drawing
1 labelling
67 higher level only

Every question is original and tagged to a guide statement. See the whole bank →

Make your own

The practice paper

Additional higher level only · 21 marks

Take it online → Build a fresh paper Paper code BbB-EAEAAAEAABQAOrOA

Biology · topic quiz

Higher level · topic practice, not an exam format

30 minutes21 marks

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Covers B3.3 Muscle and motility · HL

Name:

The table shows measurements made on one sarcomere when relaxed and when contracted. What is the combined width of the light (I) band regions in the contracted sarcomere?

[1]

State	Sarcomere length / µm	Dark (A) band width / µm
relaxed	2.6	1.6
contracted	2.2	not measured

0.6 µm
1.0 µm
0.4 µm
0.3 µm

Relaxed muscle fibres were stretched and the force resisting the stretch was measured. The fibres were then treated with an enzyme that cuts titin molecules but leaves actin and myosin intact. When stretched again, the treated fibres offered far less resistance. What would be expected in a living muscle with its titin damaged in this way, when its antagonistic muscle contracted strongly?

[1]

Its sarcomeres could be overstretched until actin and myosin no longer overlap
It would contract to resist the pull, as titin normally stops it from contracting
Its myosin filaments would be stretched so that they became longer than normal
It could not relax, because titin normally detaches the myosin heads from actin

Fine electrodes were used to record the electrical activity of the external and internal intercostal muscles of eight volunteers. Electrical activity shows that a muscle is contracting. Recordings were made during quiet breathing at rest and during deep, rapid breathing during exercise. The table shows the mean activity in each phase of breathing.

Breathing	Phase	External intercostals: activity / arbitrary units	Internal intercostals: activity / arbitrary units
At rest	Inhalation	18	2
At rest	Exhalation	1	3
Exercise	Inhalation	64	4
Exercise	Exhalation	3	52

(a)Compare the activity of the two layers of intercostal muscles during exercise.[2]

(b)At rest, the internal intercostals show almost no activity, yet the ribcage still moves down and in during exhalation. Explain how.[2]

(c)Suggest why the internal intercostals contract during exhalation in exercise.[2]

Draw a labelled diagram of the human hip joint to show the structures that allow controlled movement.

[4]

A student compared the range of motion of the hip joint and the shoulder joint of one volunteer. The volunteer was photographed at the limit of each movement and the joint angle was measured from the image using computer analysis software. Each movement was repeated three times. The table shows the range of motion for three types of movement at each joint: flexion (bending the limb forwards), extension (bending it backwards) and abduction (moving it sideways away from the midline of the body).

Joint	Movement	Trial 1 / °	Trial 2 / °	Trial 3 / °
Hip	Flexion	118	122	120
Hip	Extension	18	22	20
Hip	Abduction	42	44	40
Shoulder	Flexion	176	180	178
Shoulder	Extension	58	60	62
Shoulder	Abduction	170	174	178

(a)Calculate the mean range of motion for abduction of the hip.[1]

(b)Compare and contrast the range of motion of the hip and shoulder joints.[2]

(c)Suggest one advantage of measuring joint angles by computer analysis of images rather than with a goniometer held against the limb.[1]

(d)Identify two variables that should be controlled when comparing the two joints.[2]

(e)Movement of the hip requires antagonistic muscles. Explain how antagonistic muscles produce flexion and then extension of the hip.[3]

Original practice questions © Biology by Bradford · CC BY-NC-SA 4.0 · Not affiliated with or endorsed by the International Baccalaureate Organization.
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Markscheme BbB-EAEAAAEAABQAOrOA

One mark per point; / separates alternative wording within a point, OR separates alternative answers, words in brackets are not required, underlined words are essential. OWTTE = or words to that effect.

1. B3.3.2 [1]

A: the dark (A) band is the length of the thick filaments, which do not shorten, so it stays 1.6 µm and the light band is 2.2 − 1.6 = 0.6 µm; 1.0 µm is the relaxed value (B), 0.4 µm is the shortening of the sarcomere (C), and 0.3 µm is only one of the two light-band regions (D);

2. B3.3.3 [1]

A: titin resists stretching and so prevents overstretching of the sarcomere; without it, the pull of the antagonist could draw the thin filaments out beyond the ends of the thick filaments, so no cross-bridges could form;

3. B3.3.8

(a) [2 max]
- the external intercostals are active during inhalation (64), whereas the internal intercostals are active during exhalation (52);
- each layer shows (almost) no activity while the other is active / activity alternates between the layers;
- the two layers reach similar peak levels of activity (64 and 52), OWTTE;
Award marks only for statements that compare the two layers.
(b) [2 max]
- the external intercostals relax (activity falls from 18 to 1), so they no longer pull the ribcage up and out;
- during inhalation, contraction of the external intercostals stretched the internal intercostals;
- the stretching stored (elastic) potential energy in titin in the sarcomeres of the internal intercostals;
- this energy is released as the internal intercostals recoil, returning the ribcage down and in without contraction, OWTTE;
Beyond this subtopic. Award if given; the marks above can be earned without it.
- B3.1 the stretched lungs recoil elastically / the relaxed diaphragm is pushed back up;
(c) [2 max]
- exhalation must be faster / more forceful / deeper than recoil alone can achieve;
- contraction of the internal layer actively pulls the ribcage down and in (further), because its fibres run in a different direction from those of the external layer;
- their contraction also stretches the external intercostals, storing energy in titin that aids the next inhalation, OWTTE;
Beyond this subtopic. Award if given; the marks above can be earned without it.
- B3.1 this reduces the volume of the thorax further / raises the pressure in the lungs, so more air is expelled quickly;

4. B3.3.6 [4 max]

pelvis with a cup-shaped socket and the rounded head of the femur fitting into it, both bones labelled;
cartilage drawn as a layer covering the surfaces of both bones where they meet, and labelled;
synovial fluid drawn filling the joint cavity between the cartilage surfaces (inside a joint capsule), and labelled;
ligament(s) drawn connecting the pelvis to the femur across the joint, and labelled;
a muscle attached to the bones by tendons and spanning the joint, labelled;

Award marks only for structures that are both drawn and labelled. Names of individual muscles and ligaments are not required.

5. B3.3.7, B3.3.3

(a) [1]
- 42 (°);
Units not required.
(b) [2 max]
- the shoulder has a greater range of motion than the hip for all three movements / in every dimension;
- both joints show the greatest range in flexion and the smallest range in extension;
- the difference between the joints is greatest for abduction (174° vs 42°) and smallest for extension (60° vs 20°), OWTTE;
Award marks only for explicitly comparative statements.
(c) [1]
- the image can be stored and re-measured / checked by another person, so results are more repeatable, OWTTE; OR no instrument needs to be aligned against the body, so the measurement does not interfere with the movement / reduces observer error, OWTTE; OR several angles can be measured from one image at the exact moment of maximum movement, OWTTE;
(d) [2]
- the same volunteer (age / sex / training) for both joints;
- the same warm-up / time of day / temperature;
- the same starting (anatomical) position and camera position/angle for each measurement;
- movement performed actively by the volunteer (not pushed by another person) in every trial, OWTTE;
Mark the first two answers only. Do not accept the independent variable (joint or movement type).
(e) [3 max]
- muscles can only exert force when they contract / can pull but not push;
- the flexor (at the front of the hip) contracts, pulling the femur forwards, whereas the extensor relaxes and is stretched;
- to extend the hip, the extensor (at the back of the hip) contracts and the flexor relaxes and is stretched, OWTTE;
- muscles are attached to the femur and pelvis by tendons / the bones act as levers with the joint as the pivot;
- titin in the stretched muscle stores potential energy and prevents overstretching (aiding recoil), OWTTE;
Content pivot. Names of individual muscles are not required.