Test: Biology - 3 - MCAT MCQ

Diphyodonts are organisms that have two sets of teeth, known as deciduous teeth (also called baby teeth or milk teeth) and permanent teeth. The deciduous teeth are gradually replaced by the permanent teeth as the organism grows and develops.

On the other hand, monophyodonts are organisms that have only one set of teeth, which are not replaced at later stages of life. They do not undergo a process of tooth replacement or continuous growth.

Heterodonts are organisms that possess different types of teeth specialized for various functions. They have distinct tooth types such as incisors, canines, premolars, and molars, each serving a specific purpose in the oral cavity.

Polyphodonts are organisms whose teeth are continuously replaced throughout their lives. As their teeth wear out or become damaged, new teeth continuously grow and replace the old ones, ensuring a functional dentition is maintained. This process of tooth replacement is observed in certain species such as sharks and reptiles.

Savanna is the term used to describe tropical grasslands, which are primarily located near the equator. These regions are characterized by a combination of grasses, scattered shrubs, and isolated trees. Savannas cover approximately 20% of the Earth's land area, making them a significant biome on a global scale.

Certain species of animals exhibit sex determination that is influenced by environmental factors rather than solely relying on genetic chromosomes. Crepidula fornicata is an example of such a species, where the location plays a significant role in determining their sex. In other cases, temperature-dependent sex determination is observed, particularly in reptiles such as crocodiles and turtles. In these species, the temperature experienced during critical periods of development determines whether an individual will develop as male or female.

Azotobacter, Anabaena, Nostoc, and Calothrix are examples of free-living nitrogen-fixing bacteria. Azotobacter is commonly found in the soil environment. On the other hand, Anabaena, Nostoc, and Calothrix can be found in water bodies and also thrive on moist rocks. These bacteria have the ability to convert atmospheric nitrogen into a usable form, such as ammonia, through the process of nitrogen fixation. This adaptation allows them to contribute to the nitrogen cycle and provide a vital source of nitrogen for other organisms in their respective habitats.

Glucocorticoids are synthesized and secreted by the adrenal cortex, a part of the adrenal glands. They belong to a class of steroid hormones and exert their effects by binding to specific receptors called glucocorticoid receptors. Glucocorticoids have various physiological functions, including the regulation of carbohydrate metabolism. One of their prominent actions is the stimulation of gluconeogenesis, a process that leads to the production of glucose from non-carbohydrate sources such as amino acids and fatty acids. This results in an increase in blood glucose levels, which is important for providing energy to the body during times of stress or fasting.

Mutualism is a symbiotic relationship between two organisms in which both organisms benefit from the association. An example of mutualism is the relationship between Rhizobium bacteria and leguminous plants. Rhizobium forms nodules in the roots of legumes and helps to fix atmospheric nitrogen, making it available for the plants as a nutrient source. In return, the plants provide carbohydrates and a suitable environment for the bacteria to thrive.

Early biologists categorized organisms into three primary domains: bacteria, archaea, and eukarya. The eukarya domain encompasses a wide range of organisms, including protists (which can be unicellular or multicellular, exhibiting diverse reproductive cycles), fungi (multicellular or unicellular, decomposers, with unique reproductive cycles), plantae (multicellular photosynthetic autotrophs with a cell wall), and animalia (chemoheterotrophs lacking a cell wall).

Nematocysts are a characteristic feature of cnidarians. Cnidarians are a group of animals that includes jellyfish, corals, sea anemones, and hydras. Nematocysts are specialized stinging cells found in cnidarians. They are used for prey capture, defense, and movement. Nematocysts contain a coiled thread-like structure called a cnidocyst, which is expelled when triggered by touch or chemical stimuli. The cnidocyst delivers a toxin or venom to immobilize or kill prey, deter predators, or for self-defense. Nematocysts are unique to cnidarians and play a crucial role in their survival and interaction with the environment.

A catchment area, also known as a watershed or drainage basin, is the geographical area where all the surface water runoff converges into a single point, such as a river, lake, or reservoir. In a catchment area, the movement of water is from the surface to the groundwater system as it infiltrates the soil and recharges the underlying aquifers.

The primary structure of a protein refers to the linear sequence of amino acids that make up the protein chain. It is the most basic level of protein structure and is determined by the specific arrangement of amino acids in the polypeptide chain. The sequence of amino acids is encoded by the genetic information in DNA.

Secondary structure (B) refers to the local folding patterns that result from hydrogen bonding between nearby amino acids. Examples of secondary structures include alpha helices and beta sheets.

Tertiary structure (C) is the three-dimensional folding of the entire protein molecule, including interactions between amino acid side chains. It determines the overall shape and functional properties of the protein.

Quaternary structure (D) is the arrangement of multiple protein subunits in a multisubunit complex. It describes the interactions between different protein chains or subunits.

Therefore, the structure of a protein with a linear sequence of amino acids is referred to as the primary structure (A).

Plasma is the liquid portion of blood and makes up the largest portion of blood volume. It is responsible for transporting various substances, including dissolved nutrients, hormones, gases, and waste products throughout the body. While red blood cells, white blood cells, and platelets have important roles in blood function, it is the plasma that carries dissolved nutrients.

An irreversible inhibitor permanently inactivates an enzyme by causing changes to its structure that prevent it from functioning properly. This can occur through covalent modification or binding to essential functional groups within the enzyme. Once the irreversible inhibitor binds to the enzyme, it cannot be easily removed, and the enzyme is permanently inactivated.

Feedback inhibitors, competitive inhibitors, and allosteric inhibitors are reversible inhibitors that can be overcome or reversed under certain conditions. They do not permanently denature the enzyme.

Nissl's granules, also known as Nissl bodies or Nissl substance, are specialized structures found in the cell bodies of neurons. They consist of clusters of rough endoplasmic reticulum (ER) and are involved in protein synthesis within the neurons. Nissl's granules stain darkly with certain dyes and can be observed under a microscope. They play an essential role in the function and metabolism of neurons.

The ear ossicles are a chain of three small bones located in the middle ear. They are the malleus (hammer), incus (anvil), and stapes (stirrup). These bones are connected to each other and transmit sound vibrations from the eardrum to the inner ear. They play a crucial role in the amplification and transmission of sound waves, allowing us to hear.

The pancreas secretes multiple enzymes involved in the digestion of various macromolecules. Among them are elastase, carboxypeptidase, amylase, and ribonuclease. Elastase is an enzyme that breaks down elastin, a protein found in connective tissues. Carboxypeptidase is involved in the digestion of proteins by breaking peptide bonds at the carboxyl end. Amylase is responsible for the digestion of starch and glycogen, breaking them down into smaller sugar molecules. Ribonuclease is an enzyme that hydrolyzes RNA, breaking it down into nucleotides. All of these enzymes are produced and secreted by the pancreas to aid in the digestion of different types of macromolecules.