Biology Archives

261. The transfer of electrical signals by nerve cells in human body is ena

The transfer of electrical signals by nerve cells in human body is enabled by

[amp_mcq option1=”sodium” option2=”potassium” option3=”iron” option4=”sodium and potassium” correct=”option4″]

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UPSC NDA-2 – 2022

The transfer of electrical signals by nerve cells in the human body is enabled by sodium and potassium ions.

Nerve impulses (action potentials) are electrical signals that travel along the axon of a neuron. These signals are generated by the movement of ions, primarily sodium (Na+) and potassium (K+), across the cell membrane. Voltage-gated ion channels specific for Na+ and K+ open and close in sequence, causing rapid changes in the membrane potential.

The sodium-potassium pump actively transports Na+ out of the cell and K+ into the cell, maintaining the concentration gradients necessary for the generation of action potentials. While other ions like Calcium (Ca²⁺) are involved in synaptic transmission, sodium and potassium are central to the electrical signal propagation along the neuron itself.

262. Which one of the following hormones is responsible for the development

Which one of the following hormones is responsible for the development of female sexual characters ?

[amp_mcq option1=”Prolactin” option2=”Estrogen” option3=”Oxytocin” option4=”Progesterone” correct=”option2″]

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The correct answer is B) Estrogen.

Estrogen is the primary female sex hormone responsible for the development and maintenance of secondary sexual characteristics in females, such as breast development, widening of the hips, and maturation of the reproductive organs.

Prolactin is involved in milk production. Oxytocin is involved in uterine contractions during childbirth and milk let-down. Progesterone is mainly involved in preparing the uterus for pregnancy and maintaining pregnancy.

263. Intestinal bacteria are main source of which one of the following vita

Intestinal bacteria are main source of which one of the following vitamins ?

[amp_mcq option1=”Vitamin E” option2=”Vitamin C” option3=”Vitamin B₁₂” option4=”Vitamin A” correct=”option3″]

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UPSC NDA-2 – 2021

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The correct answer is C) Vitamin B₁₂.

Bacteria residing in the large intestine (colon) of humans are known to synthesize several vitamins, including Vitamin K and various B vitamins, particularly Vitamin B₁₂ (cobalamin).

While intestinal bacteria produce B₁₂, its absorption primarily occurs in the ileum (part of the small intestine) and requires intrinsic factor produced by the stomach. Dietary intake is the main source of Vitamin B₁₂ for humans, as the bacterial production in the colon might not be sufficient or readily absorbable. However, among the options provided, B₁₂ is the vitamin most notably associated with production by intestinal bacteria.

264. What is the total number of chambers in the stomach of domestic animal

What is the total number of chambers in the stomach of domestic animals like cattle, buffalo, goat and sheep ?

[amp_mcq option1=”Four” option2=”Two” option3=”One” option4=”Three” correct=”option1″]

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The correct answer is A) Four.

Domestic animals like cattle, buffalo, goat, and sheep are ruminants. Ruminants possess a unique digestive system featuring a four-chambered stomach.

The four chambers are the rumen, reticulum, omasum, and abomasum. The rumen is the largest chamber where microbial fermentation of plant material occurs. The abomasum is the true glandular stomach, similar to that of monogastric animals.

265. Cornea in human eye

Cornea in human eye

[amp_mcq option1=”is a light sensitive screen.” option2=”is a muscular diaphragm.” option3=”contains blood vessels.” option4=”is composed of proteins and cells.” correct=”option4″]

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The correct answer is D) is composed of proteins and cells.

The cornea is the transparent outer layer at the front of the eye. It is composed of highly organized layers of collagen proteins and specialized cells, which contribute to its transparency and structural integrity.

The retina (A) is the light-sensitive screen at the back of the eye. The iris (B) is a muscular diaphragm that controls the size of the pupil. The cornea (C) is avascular, meaning it does not contain blood vessels, which is crucial for its transparency.

266. Which one of the following viruses used to be responsible for highly i

Which one of the following viruses used to be responsible for highly infectious disease Smallpox ?

[amp_mcq option1=”Adenovirus” option2=”Variola virus” option3=”Aichi virus” option4=”Coxsackie virus” correct=”option2″]

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Smallpox was a devastating infectious disease caused by the Variola virus. It was eradicated globally by 1980 due to a successful vaccination campaign led by the World Health Organization.

The Variola virus is a member of the Orthopoxvirus genus, which also includes vaccinia virus and monkeypox virus. Smallpox caused a characteristic rash, fever, and often led to severe scarring or death.

Adenoviruses cause various illnesses, primarily respiratory infections. Aichi virus is an enterovirus linked to gastroenteritis. Coxsackie viruses are also enteroviruses known for causing hand, foot, and mouth disease, and other conditions.

267. Different varieties of the same gene are called

Different varieties of the same gene are called

[amp_mcq option1=”Genotypes” option2=”Sib pairs” option3=”Alleles” option4=”Isomers” correct=”option3″]

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UPSC NDA-2 – 2021

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Alleles are different versions or forms of the same gene. They arise through mutations and are located at the same position (locus) on homologous chromosomes.

For example, the gene for flower color might have two alleles: one for purple flowers and one for white flowers. These different alleles determine the variation in traits observed within a population.

Genotype refers to the genetic makeup of an organism, i.e., the combination of alleles it possesses for a particular trait or set of traits. Sib pairs are simply siblings. Isomers are chemical compounds with the same molecular formula but different structural formulas.

268. Girth of stem of a plant increases due to division of cells in

Girth of stem of a plant increases due to division of cells in

[amp_mcq option1=”apical meristem only.” option2=”lateral meristem only.” option3=”apical and intercalary meristem.” option4=”both apical and lateral meristem.” correct=”option2″]

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Increase in the girth or diameter of a plant stem or root is called secondary growth. This growth is primarily due to the activity and division of lateral meristems, namely the vascular cambium and the cork cambium.

Apical meristems are located at shoot and root tips and are responsible for primary growth (increase in length). Intercalary meristems are found at the base of nodes and leaves, also contributing to primary growth in certain plants (like grasses). Lateral meristems (vascular and cork cambium) are responsible for secondary growth (increase in thickness).

The vascular cambium produces secondary xylem (wood) and secondary phloem, adding to the stem’s diameter. The cork cambium produces periderm, including cork, which replaces the epidermis as the protective outer layer.

269. Which one of the following tissues is known as basic packing tissue an

Which one of the following tissues is known as basic packing tissue and found in xylem and phloem ?

[amp_mcq option1=”Collenchyma” option2=”Parenchyma” option3=”Sclerenchyma” option4=”Vessels” correct=”option2″]

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Parenchyma tissue is composed of living cells that are typically isodiametric (roughly equal in diameter). These cells form the bulk of ground tissues in plants (cortex, pith) and are also present in xylem and phloem rays and parenchyma. Due to their widespread occurrence and roles in storage, secretion, and basic metabolic functions, they are often referred to as basic packing tissue.

Parenchyma cells are thin-walled and versatile. They are found throughout the plant body and participate in various functions like photosynthesis, storage, and secretion.

Collenchyma is a living support tissue providing mechanical support to growing stems and petioles. Sclerenchyma provides rigid support and strength to mature plant parts using thick, lignified walls (fibers and sclereids). Vessels are conducting elements in xylem responsible for water transport.

270. How are evergreen plants with woody stems having naked seed classified

How are evergreen plants with woody stems having naked seed classified ?

[amp_mcq option1=”Angiosperms” option2=”Monocotyledons” option3=”Pteridophytes” option4=”Gymnosperms” correct=”option4″]

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Gymnosperms are a group of seed-bearing plants that produce “naked” seeds, meaning their seeds are not enclosed within an ovary or fruit. Many gymnosperms, such as conifers, are evergreen trees or shrubs with woody stems.

The defining characteristic of gymnosperms is the presence of naked seeds. They are vascular plants and include forms like conifers, cycads, ginkgo, and gnetophytes.

Angiosperms (flowering plants) have seeds enclosed within a fruit. Pteridophytes (ferns and horsetails) are vascular plants but do not produce seeds; they reproduce via spores. Monocotyledons are a subgroup of Angiosperms.