Zoology Test - 3 (Medical Entrance)

Heparin is an anticoagulant substance produced primarily by mast cells, which are connective tissue cells containing granules with heparin and histamine. Mast cells release heparin as part of the inflammatory response and to prevent blood clotting. Other options are incorrect: fibroblasts produce collagen, plasmocytes are antibody-producing plasma cells, and adipocytes store fat.

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.

Halteres are club-shaped structures formed from the modified hind wings of flies (order Diptera, meaning 'two wings'). They function as gyroscopic sensory organs that help flies maintain balance during flight. The other orders listed (Lepidoptera - butterflies/moths, Orthoptera - grasshoppers/crickets, Hemiptera - true bugs) all have four functional wings and do not have halteres.

Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required for the reaction to proceed. They provide an alternative reaction pathway with a lower energy barrier, allowing reactions to occur faster under physiological conditions. Enzymes do not change the free energy difference between reactants and products, do not primarily work by releasing heat, and do not just increase molecular motion.

ATP (Adenosine Triphosphate) is structurally similar to RNA molecules because both contain a ribose sugar (not deoxyribose like DNA) and the nitrogenous base adenine. ATP can be considered a modified RNA nucleotide with three phosphate groups instead of one. DNA contains deoxyribose sugar, amino acids and fatty acids are completely different molecular structures.

Class Trematoda (flukes) belongs to the phylum Platyhelminthes, which includes flatworms. Trematodes are parasitic flatworms with complex life cycles. Arthropoda includes insects and crustaceans, Mollusca includes snails and clams, and Annelida includes segmented worms - none of these contain trematodes.

Albinism is caused by defective melanin production due to deficiency of the enzyme tyrosinase (also called tyrosine 3-monooxygenase). This enzyme converts tyrosine to DOPA in the melanin synthesis pathway. Without functional tyrosinase, melanin cannot be produced, resulting in absence of pigment in skin, hair, and eyes. The other enzymes listed are involved in different metabolic pathways: homogentisic acid oxidase in tyrosine breakdown, phenylalanine hydroxylase in phenylalanine metabolism, and thiamine pyrophosphate is a coenzyme.

A coadapted gene complex refers to a set of interdependent genes with related functions that have evolved together to work in a coordinated manner. These genes often influence the same trait or set of traits and their effects are interconnected. The other options are incorrect: an inversion is a chromosomal rearrangement, a fitness set refers to possible combinations of traits, and super mutation is not a standard genetic term.

Ascaris (roundworm) has a rhabditiform larval stage in its life cycle. The rhabditiform larva is an early developmental stage with a muscular esophagus characteristic of many nematodes. The other organisms listed do not have rhabditiform larvae: Liver fluke (Trematoda) has miracidium, sporocyst, redia, and cercaria stages; Hydra (Cnidaria) has a planula larva; Taenia (Cestoda) has a hexacanth (oncosphere) larva.

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.

Stratum malpighi (also called stratum basale or basal layer) is the deepest layer of the epidermis where maximum cell division (mitosis) occurs. This layer contains continuously dividing stem cells that continuously produce new keratinocytes. The other layers represent stages of keratinocyte differentiation: stratum spinosum (prickle cell layer), stratum granulosum (granular layer), and stratum corneum (dead, keratinized surface layer) have progressively less mitotic activity.

Acetylcholine is a neurotransmitter that carries nerve signals across the synaptic gap between neurons. The synapse is the specialized junction where transmission occurs, not the dendrites, axons, or cytons which are structural parts of neurons.

UAG, UAA, and UGA are the three stop/termination codons in the genetic code that signal the end of protein synthesis during translation. The other options contain codons that code for specific amino acids.

Alalia is the medical term for loss of speech ability due to physical defects in the vocal organs. The other options are not recognized medical terms for speech disorders.

The tube-within-a-tube body plan refers to organisms with a complete digestive tract having both mouth and anus. Ascaris (a nematode) exhibits this body plan, unlike hydra and planaria which have a single opening (sac-like body plan).

The soma (cell body) contains the nucleus and organelles necessary for basic cellular functions including protein synthesis. Axons and dendrites are specialized for signal transmission, while synaptic knobs are involved in neurotransmitter release.

Lewy bodies are abnormal protein aggregates primarily found in brain cells, associated with Parkinson's disease and Lewy body dementia. They are not found in plasma, lymph, or kidneys.

Secretin is the hormone released from the small intestine that stimulates the pancreas to secrete bicarbonate-rich fluid to neutralize acidic chyme from the stomach. Insulin and glucagon regulate blood sugar, while oxytocin is involved in reproduction.

Tachyglossus (echidna) is a monotreme, which is an egg-laying mammal. Pangolins and porcupines are placental mammals, while bats are also placental mammals that give live birth.

Cross-bridges are formed by myosin heads that bind to actin filaments during muscle contraction. This is the basis of the sliding filament theory. Actin is the thin filament that myosin pulls on, collagen is connective tissue, and creatine phosphate is an energy source.

The alimentary canal contains smooth (unstriated) muscle that is neurogenic, meaning it requires neural stimulation from the autonomic nervous system for contraction. Unlike cardiac muscle, which is myogenic, gut muscle depends on nerve impulses.

Myoglobin is the oxygen-binding protein found in muscle tissue that stores oxygen for use during muscle activity. Myosin is a contractile protein, actomyosin is a complex of actin and myosin, so myoglobin is the correct answer for oxygen storage.

Rod cells contain rhodopsin, a photosensitive pigment that enables vision in low-light conditions. Myelin is a nerve insulation material, keratin is a structural protein in skin/hair/nails, and actin is a muscle contraction protein - none are photosensitive.

Tiedemann's bodies are peculiar structures found in the coelomic fluid of starfish (Asterias), part of the echinoderm group. Sponges have choanocytes, hydra has cnidocytes, and hirudinaria (leech) has different specialized cells.