(a) List four functions of.the mammalian skeleton and name a particular part of the skeleton which performs each of these functions. (b) Briefly describe ho...

Answer Details

(a) Four functions of the mammalian skeleton and the part that performs each

(b) How muscles and bones bring about movement at the elbow

The elbow is a hinge joint between the humerus (upper arm) and the radius and ulna (forearm). Two muscles act as an antagonistic pair: the biceps (a flexor) on the front and the triceps (an extensor) at the back. To bend (flex) the arm, the biceps contracts and shortens while the triceps relaxes, pulling the forearm up. To straighten (extend) the arm, the triceps contracts and the biceps relaxes, pulling the forearm down. Because each muscle can only pull (not push), the two work in opposition to move the bones about the joint.

(c) Support in plants

(i) Herbaceous plants: support comes mainly from the turgidity of their cells; water in the vacuoles keeps the cells firm, and the collenchyma and turgid parenchyma keep the soft stem upright.

(ii) Woody plants: support comes from the lignified (woody) xylem tissue and sclerenchyma, and from secondary thickening of the stem, which provide rigid mechanical strength.

(d) One vitamin and one mineral for healthy bones

Vitamin: vitamin D. Mineral element: calcium (phosphorus is also acceptable).