Identify the parts of the human brain and their functions, and explain how biceps and triceps muscles work for arm extension.

here are the answers to the next set of questions:

21. The diagram shows the human brain.

• A is the cerebrum, responsible for voluntary actions, thought, and memory.
• B is the cerebellum, which coordinates voluntary movements such as posture, balance, coordination, and speech, resulting in smooth and balanced muscular activity.
• C is the medulla oblongata, which controls vital involuntary functions like breathing and heart rate.
• D is the pituitary gland, an endocrine gland. The part responsible for coordinating all body movements is the cerebellum.

Therefore, the correct option is B.
$\boxed{\text{B}}$

22. The diagram shows an eye accommodated for nearby objects.
When the eye accommodates for near objects, the ciliary muscle contracts. This reduces the tension on the suspensory ligaments, allowing the lens to become thicker and more convex, which increases its refractive power to focus light from nearby objects onto the retina.

Therefore, the correct option is A.
$\boxed{\text{A}}$

23. How do the biceps and triceps muscles work in straightening the arm?
The biceps and triceps are antagonistic muscles. To straighten the arm (extend the elbow), the triceps muscle contracts while the biceps muscle relaxes.

Therefore, the correct option is D.
$\boxed{\text{D}}$

24. The diagram shows potted seedlings placed under a cardboard box with a window cut on one side so that light reaches the shoot from one direction. The seedlings are bending towards the light source.
This response of a plant growing or bending towards a light source is known as positive phototropism.

Therefore, the correct option is D.
$\boxed{\text{D}}$