Final answer:
Hypothyroidism can cause weight gain, sensitivity to cold, and reduced mental activity, while hyperthyroidism can cause weight loss, increased heart rate, and profuse sweating.
Step-by-step explanation:
Hypothyroidism, which is the underproduction of thyroid hormones, can cause weight gain, sensitivity to cold, and reduced mental activity among other symptoms. On the other hand, hyperthyroidism, the overproduction of thyroid hormones, can lead to weight loss, increased heart rate, profuse sweating, and other symptoms. Thyroid hormones play a crucial role in the body's metabolism, and imbalances can have various adverse effects.