Biology: Zoology: UPSC Previous Year Questions (Science and Technology)

Explanation

Ticks and mites belong to the class Arachnida making them closely related to spiders and scorpions. They possess eight legs (in their adult stage), two body segments (cephalothorax and abdomen), and lack antennae, distinguishing them from insects. Ticks are primarily ectoparasites, feeding on the blood of vertebrates, while mites can be parasitic, free-living, or plant-feeding. Examples include the Deer Tick (Ixodes scapularis), which spreads Lyme disease, and the Scabies Mite (Sarcoptes scabiei), responsible for scabies.

Explanation

Platelets are more numerous than white blood cells in the bloodstream. The concentration of platelets ranges from 150,000 to 450,000 per microliter of blood whereas white blood cells are present at concentrations of about 4,000 to 11,000 per microliter. Platelets are essential for blood clotting, while WBCs are part of the immune system and are less numerous.

Option (a), (b) and (c) are incorrect:

Veins are more numerous than arteries and hold a significantly larger portion of the body’s blood at any given time. Approximately 70% of the body’s blood volume is found in the venous system at rest, as veins act as capacitance vessels that can expand to store blood. Arteries, on the other hand, carry oxygenated blood away from the heart and are under higher pressure, but they hold a smaller volume of blood compared to veins. Blood is composed of two main components: plasma (the liquid portion) and blood cells (red blood cells, white blood cells, and platelets). Blood cells make up approximately 45% of the total blood volume, a measure known as the hematocrit. The remaining 55% is plasma, which consists of water, proteins, electrolytes, and other dissolved substances. White blood cells (WBCs) are produced primarily in the bone marrow, not exclusively in lymph nodes. Lymph nodes play a role in the maturation and activation of certain types of WBCs, such as lymphocytes, but they are not the primary site of WBC production. Other organs, such as the spleen and thymus, also contribute to the development and function of WBCs.

Explanation

In eye donation, the part of the eye that is transplanted is the cornea. The cornea is the clear, dome-shaped front surface of the eye that allows light to enter and is responsible for focusing light onto the retina. It can become damaged due to injury, disease, or aging. A corneal transplant replaces the damaged cornea with healthy tissue from a deceased donor.

Option (b) is incorrect: The lens is located behind the cornea and focuses light onto the retina. It is not transplanted during eye donation, as it can be replaced with an artificial lens in procedures like cataract surgery.

Option (c) is incorrect: The retina is a sensitive tissue lining the back of the eye that converts light into neural signals. Retinal damage cannot currently be treated through transplantation during eye donation.

Option (d) is incorrect: The whole eye is not transplanted due to the complexity of the organ and the high risk of rejection.

Explanation

Option (a) is correct: O, Rh- blood group is known as the universal donor because it does not have A, B, or Rh antigens. If the patient’s blood type is not O, receiving blood with A or B antigens can trigger an immune response, leading to serious complications. If the patient is Rh-, receiving Rh+ blood can lead to the development of Rh antibodies, which can cause problems in future pregnancies or transfusions. Therefore, O, Rh- blood group will be safe for transfusion if the blood group of the patient is not known.

Option (b) is incorrect: If the recipient is Rh-negative, transfusion of Rh+ blood can cause an immune reaction, leading to complications like hemolysis or sensitization.

Option (c) is incorrect: AB, Rh- has both A and B antigens, which can trigger an immune response in individuals with A, B, or O blood groups.

Option (d) is incorrect: AB, Rh+ blood group is highly specific and can only be safely given to individuals with the AB, Rh+ blood group. It is not suitable for transfusion in emergencies where the recipient’s blood group is unknown.

Explanation

A is matched with 3: Lederberg discovered bacterial conjugation (exchange of genetic material between bacteria) and transduction (transfer of DNA between bacteria via viruses). B is matched with 4: Thomas Hunt Morgan’s work with fruit flies (Drosophila) provided strong evidence for the chromosomal theory of inheritance and firmly established the concept of sex-linked genes. C is matched with 2: Kornberg isolated DNA polymerase I from Escherichia coli, which was crucial for understanding DNA replication. D is matched with 1: Har Gobind Khorana played a significant role in deciphering the genetic code, which specifies how the sequence of nucleotides in DNA translates into the sequence of amino acids in proteins.

Explanation

The complementary nature of the two DNA strands ensures accurate replication and transmission of genetic information. Adenine (A) always pairs with Thymine (T), and Guanine (G) always pairs with Cytosine (C) on the opposite strand. This allows for precise copying of the genetic information during cell division.

Explanation

Metastasis is the process through which cancer cells spread from the primary tumor to distant parts of the body, forming secondary tumors in organs such as the lungs, liver, bones, or brain. This process is responsible for nearly 90% of cancer-related deaths, showcasing the aggressive and life-threatening nature of malignant tumors. The process begins with Epithelial-to-Mesenchymal Transition (EMT), where cancer cells gain the ability to migrate and invade surrounding tissues. These cells then enter the bloodstream or lymphatic system (intravasation) and travel to other parts of the body. While in circulation, they evade immune system attacks and other hostile conditions. Upon reaching a new site, the cells exit blood vessels (extravasation) and adapt to the local environment to form secondary tumors. Interestingly, some metastatic cells can remain dormant for years before becoming active again, contributing to cancer recurrence.

Explanation

Enzymes are biological catalysts, crucial for various biological processes, including digestion, metabolism, and DNA replication. Hormones are chemical messengers produced by endocrine glands which regulate various physiological processes, such as growth, development, metabolism, reproduction, and mood. A is matched with 2: Ptyalin, also known as salivary amylase, is an enzyme present in saliva that breaks down starch into maltose and smaller polysaccharides during digestion. B is matched with 3: Pepsin is a proteolytic enzyme secreted in the stomach. It helps digest proteins into smaller peptides by breaking peptide bonds in acidic conditions. C is matched with 1: Renin is an enzyme secreted by the kidneys in response to low blood pressure. It converts angiotensinogen (produced by the liver) into angiotensin I, which is further converted to angiotensin II, a potent vasoconstrictor. D is matched with 5: Oxytocin is a hormone produced by the hypothalamus and secreted by the pituitary gland. It induces the contraction of smooth muscles, particularly in the uterus during childbirth and in milk ejection during breastfeeding.

Explanation

Antigens are recognized by the immune system as foreign substances, which stimulates the production of specific antibodies by B-cells (a type of white blood cell). Antibodies bind to antigens, marking them for destruction by other immune cells or neutralizing their harmful effects. Antigens can be proteins, polysaccharides, or lipids. For example, the spike protein of the SARS-CoV-2 virus acts as an antigen, triggering an immune response and the production of antibodies in infected individuals or after vaccination. The immune response involves two types of lymphocytes:

1. B-cells produce antibodies that target antigens.

2. T-cells destroy infected cells displaying antigens.

Explanation

Option (d) is correct: Chloroplasts and mitochondria are unique organelles as they contain their own circular DNA, similar to bacterial chromosomes, along with ribosomes and protein synthesis machinery. Mitochondrial DNA (mtDNA), present in all eukaryotic cells, is maternally inherited and essential for ATP production. Chloroplast DNA (cpDNA) is found in photosynthetic eukaryotes. It encodes proteins for photosynthesis. Their extranuclear DNA supports the endosymbiotic theory which suggests that these organelles evolved from free-living bacteria engulfed by ancestral eukaryotes. Despite their partial independence, mitochondria and chloroplasts still rely on nuclear-encoded proteins for various functions, distinguishing them from other organelles that depend entirely on nuclear DNA. Options (a), (b) and (c) are incorrect:

Centrioles are involved in cell division and the formation of spindle fibers but do not contain DNA. They play a structural role and have no genetic material. The Golgi apparatus modifies, packages, and transports proteins but does not contain DNA or protein synthesis machinery, depending entirely on the cell’s nucleus. Lysosomes are enzyme-filled organelles responsible for digesting cellular waste but lack DNA. They function solely under the control of nuclear-encoded proteins.