Aquatic and Marine Biology

Phytoplankton are microscopic marine plants that drift near ocean surfaces and form the base of aquatic food chains. Through photosynthesis, they produce about 50% of Earth's oxygen and support marine ecosystems.

Ducks have webbed feet that are specially adapted for swimming. The webbing between their toes acts like a paddle, increasing surface area and pushing more water with each stroke. Eagles and parrots have talons for perishing and gripping, while crossbills have specialized beaks for opening seeds.

Pinctada is the genus of pearl oysters that are commercially cultured in India for pearl production. These marine bivalve molluscs deposit layers of nacre around foreign particles, forming pearls. The other options are incorrect: Heliotis (abalone), Anodonta (freshwater mussel), and Mytilus (marine mussel) are not used for pearl culture.

Tube feet (podia) are characteristic locomotory and respiratory structures unique to echinoderms, and star fish (asteroids) prominently display these features on their aboral surface. Tube feet operate through a hydraulic water vascular system. The other animals listed are not echinoderms: cuttle fish and jelly fish belong to Mollusca and Cnidaria respectively, and cray fish is a crustacean arthropod.

Heloderma is the genus containing the Gila monster and Mexican beaded lizard, the only venomous lizards in the world. They produce neurotoxic venom in glands in their lower jaws and deliver it through grooved teeth.

Cuttlefish belongs to phylum Mollusca (class Cephalopoda). Globe fish belongs to phylum Chordata (class Actinopterygii - bony fish). Starfish belongs to phylum Echinodermata. Silverfish belongs to phylum Arthropoda (class Insecta). Only cuttlefish is a mollusk.

Fish have a single circulatory system where blood passes through the heart only once in one complete circuit around the body. The heart has two chambers (one atrium, one ventricle) and blood travels from heart → gills → body tissues → back to heart. Humans, amphibians, birds, and mammals all have double circulation (pulmonary + systemic circuits).

This is the correct answer. Whale satisfy all conditions. 

This is the correct answer. Earthworm and frog both breathe through their skin.

This is the correct answer. Streamlined bodies help fish to move easily in water.

The concentration of heavy metals in the body of the organisms increases with the increase in trophic level. Since phytoplanktons are present at the lowermost trophic level, the concentration of heavy metals in phytoplanktons will be the minimum, while the concentration of heavy metals in herring gull will be the highest as it is present at the highest trophic level. Hence, the correct order of organisms with increasing levels of heavy metals is Phytoplankton < Zooplankton < Smelt < Lake trout < Herring gull.

The Wadden Sea Agreement is aimed at the protection of seals.

An iron nail will sink in water because the density of iron is more than the density of water. So, even though the iron nail is smaller than a piece of drift wood or a plank, it will sink in water.

This is the correct option. The biomagnification of mercury in the fishes through a food chain results in 'Minamata disease' in the fish-eating population of the region.