Biology

Proteins are the chief builders of the body because they are essential for the growth, repair, and maintenance of body tissues. Carbohydrates and fats primarily provide energy, not structural building blocks.

Valine is coded by four DNA codons: GTT, GTC, GTA, and GTG. Among the given options, only option A (GTT) is a valid DNA triplet that codes for valine. The other options code for different amino acids or are RNA codons.

Urine is produced in the kidneys, where blood is filtered to remove waste and excess substances, forming urine. The lungs, large intestine, and liver do not produce urine.

At night, plants do not perform photosynthesis due to lack of sunlight, so they consume oxygen for respiration and release carbon dioxide as a byproduct. Therefore, they intake oxygen and release carbon dioxide at night.

Digestion of food is completed in the small intestine, where enzymes break down nutrients for absorption. The stomach initiates digestion, the large intestine absorbs water, and the liver produces bile but does not digest food directly.

The retina is the sensitive layer of the eye that contains photoreceptor cells responsible for detecting light and sending visual signals to the brain. Other options like choroid, sclera, and cornea serve different functions but are not primarily sensitive layers.

The study of life beyond Earth, including the possibility of extraterrestrial life, is called Exobiology. The other options refer to different biological fields unrelated to life in outer space.

Pyridoxine (Vitamin B6) deficiency leads to decreased hemoglobin production because it is essential for heme synthesis, a component of hemoglobin. Deficiency can cause microcytic anemia due to impaired hemoglobin formation.

Lyme disease is caused by the bacterium Borrelia burgdorferi, which is transmitted to humans through the bite of infected black-legged ticks. The other bacteria listed do not cause Lyme disease.

In photosynthesis, oxygen is released as a byproduct when water molecules are split during the light-dependent reactions. Therefore, water is the source of the oxygen produced.