Test: Biology - 1 - MCAT MCQ

Phytochrome is a light sensitive pigment in plants and some bacteria and fungi. It exists in two interconvertible forms- Pr and Pfr. Pfr absorbs far red light of 730 nm wavelength. When it absorbs far red light, it converts to its original form, Pr. Thus Pfr is the active form of phytochrome which inhibits flowering.

Follicle stimulating hormone (FSH) is secreted by the anterior pituitary gland. In males, FSH plays a crucial role in stimulating spermatogenesis, the production of sperm cells. In females, FSH stimulates the growth and development of ovarian follicles, which contain the eggs. Besides FSH, the anterior pituitary gland also secretes several other hormones including luteinising hormone, prolactin, thyroid stimulating hormone, adrenocorticotrophic hormone, and growth hormone.

Crossing over, a phenomenon that takes place during meiosis, involves the exchange of genetic material between paired chromosomes. Mitosis, on the other hand, is a stepwise process of cell division that occurs in somatic cells. Mutations arise from alterations in the sequence of nucleotides. Transduction denotes the transfer of DNA from one bacterium to another facilitated by bacteriophages. Transformation, meanwhile, pertains to the modification of DNA resulting from the incorporation of foreign genetic material.

The lymphatic system plays a crucial role in maintaining the body's fluid balance and is closely intertwined with the immune system to combat infections. Its key components include the thymus, bone marrow, spleen, lymph nodes, and lymphatic vessels. Within the spleen, a lymphatic organ, B-lymphocytes, which are involved in the body's defense mechanisms, gather and undergo maturation processes.

G protein-coupled receptors (GPCRs) have a characteristic structure with 7 transmembrane alpha helices that span the plasma membrane. These helices are connected by loops of varying lengths. The carboxy-terminus of the receptor is located on the inside of the cell, while the amino terminus is positioned outside of the cell. This structural arrangement allows GPCRs to interact with extracellular ligands and transmit signals across the cell membrane to activate intracellular signaling pathways.

Angiotensinogen is indeed a serum globulin that is primarily synthesized by the liver. It serves as the precursor molecule for angiotensin, an oligopeptide that plays a crucial role in the regulation of blood pressure. Angiotensin acts by promoting vasoconstriction, which leads to an increase in blood pressure.

However, angiotensinogen does not belong to the serpin family. Serpins (serine protease inhibitors) are a distinct group of proteins that function as inhibitors of serine proteases, regulating various physiological processes. While angiotensinogen is a globulin, it is not classified as a serpin. Instead, it is a glycoprotein belonging to the larger family of alpha-2 globulins.

The inactivated X chromosome in females is commonly referred to as the Barr body. It was named after Dr. Murray L. Barr, who first observed it in the nuclei of cells. Inactivation of one of the X chromosomes in females is a process known as X-chromosome inactivation or Lyonization, and it serves as a mechanism for dosage compensation. By inactivating one X chromosome, female cells ensure that the gene expression from the X chromosome is equalized with male cells, which only have one X chromosome. This process helps to balance the gene dosage between males and females.

During the process of fossil formation, petrification occurs when dissolved minerals replace the organic remains of deceased organisms. Petrification takes on different forms depending on the specific mineral involved. Silicification, for example, entails the substitution of original organic matter with silica. Pyritization, on the other hand, involves the replacement of organic material with iron pyrites. Carbonization refers to the deposition of carbon compounds, while in dolomitization, magnesium carbonate replaces previously deposited calcium carbonate within the decaying organic matter.

Denitrification is indeed a microbial process where nitrate (NO^3-) is reduced to molecular nitrogen (N₂). Denitrifying bacteria, such as Pseudomonas species, are capable of carrying out this conversion.

On the other hand, nitrifying bacteria play a role in the nitrogen cycle by oxidizing ammonia (NH₃) to nitrite (NO^2-) and then further oxidizing nitrite to nitrate. Nitrosomonas species are examples of bacteria involved in the first step of nitrification, converting ammonia to nitrite. Nitrobacter species are responsible for the second step, oxidizing nitrite to nitrate.

Lastly, nitrogen-fixing bacteria, such as Rhizobium species, have the ability to convert atmospheric nitrogen (N₂) into a form that can be utilized by plants. This process is important for nitrogen fixation in the soil and often occurs in symbiosis with leguminous plants, forming nodules on their roots.

Overall, denitrification, nitrification, and nitrogen fixation are important microbial processes in the nitrogen cycle, with different bacteria playing specific roles in each process.

The decomposition process in soil encompasses two main processes: humification and mineralization. Humification involves the accumulation of a dark-colored, amorphous substance known as humus. Humus serves as a nutrient reservoir, resisting microbial breakdown and thereby resulting in slow decomposition. Over time, humus can undergo further degradation by microorganisms, leading to mineralization. Mineralization refers to the conversion of organic matter into inorganic forms, releasing nutrients that become available for uptake by plants and other organisms.

Archaeopteryx is a well-known fossil bird that lived during the Jurassic period. It is considered an important transitional fossil, displaying features both of modern birds and ancient reptiles, particularly dinosaurs. Archaeopteryx exhibited several characteristics that were also present in Mesozoic dinosaurs, such as sharp teeth, a long bony tail, and three-fingered hands with claws. These similarities provide evidence of the evolutionary link between dinosaurs and birds, supporting the theory of birds evolving from theropod dinosaurs.

Hotspots are indeed regions characterized by a significant reservoir of biodiversity, often hosting a high number of endemic species. These areas are particularly vulnerable to threats posed by human activities, including habitat destruction, pollution, and climate change.

A botanical garden is a place specifically designed for the cultivation and display of plants. It serves educational, scientific, and ornamental purposes, providing a controlled environment for the study, conservation, and enjoyment of various plant species.

Wildlife sanctuaries, on the other hand, are areas set aside to conserve and protect the natural habitat and wildlife within them. These areas are usually designated with the goal of minimizing human intervention, allowing animal populations to thrive undisturbed. Human activities such as hunting or extraction of resources are generally restricted or prohibited within wildlife sanctuaries.

A zoo is an institution where living animals are kept and often exhibited to the public. Zoos aim to educate the public about different animal species, contribute to conservation efforts, and provide opportunities for research and breeding programs. While zoos can play a role in conservation and education, their ethical practices and treatment of animals have been subject to ongoing discussions and debates.

Overall, these terms describe different aspects of biodiversity conservation, plant cultivation, and the exhibition of animals, each serving unique purposes and facing specific challenges in our interaction with the natural world.

Itai-itai disease is a condition caused by chronic cadmium poisoning. It was first identified in Japan and primarily affected individuals residing near mining areas contaminated with cadmium. The main symptom of the disease is weak and brittle bones, leading to severe pain and fractures. Itai-itai disease is particularly characterized by spinal and leg bone pain in the initial stages. Prolonged exposure to cadmium can also lead to kidney damage and eventually kidney failure, which is a serious complication associated with the disease.

Aggradation refers to the process of sediment accumulation, resulting in the elevation of land. It occurs when the deposition of sediments surpasses the capacity of the system to transport them away. This can happen in various environments, such as rivers, floodplains, or coastal areas, where sediment deposition exceeds erosion.

Biocoenosis, on the other hand, refers to the community of interacting organisms within a particular habitat or ecosystem. It encompasses all living organisms, including plants, animals, and microorganisms, and their interactions with each other and their environment. Biocoenosis focuses on the relationships and dynamics between different species and the roles they play in the functioning of the ecosystem.

The lowest area of a water body, such as an ocean or lake, is known as the benthic zone. Organisms that inhabit this zone are referred to as benthos. The benthic zone is characterized by its proximity to the bottom of the water body.

The littoral zone, on the other hand, refers to the region of a lake, sea, or ocean that is near the shore. It is the shallow, well-lit area where plants are rooted and many organisms live.

The aphotic zone is the portion of a water body that lacks sunlight, usually located below the depth to which sunlight can penetrate. This zone is characterized by a significant reduction in light intensity, and photosynthesis cannot occur here.

In contrast, the photic zone is the upper part of a water body where enough sunlight penetrates to support photosynthesis. This zone typically extends to the depth at which sunlight becomes too weak for photosynthesis to occur effectively.

These terms help describe different regions and characteristics of water bodies, highlighting the varying environmental conditions and habitats within aquatic ecosystems.