Biology

271. Which one of the following statements about the process of photosynthe

Which one of the following statements about the process of photosynthesis is correct ?

[amp_mcq option1=”Chemical energy is converted into light energy.” option2=”Carbon dioxide is oxidised to form carbohydrate.” option3=”Water molecule splits into hydrogen and oxygen.” option4=”Light energy is directly used to split water.” correct=”option3″]

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UPSC NDA-2 – 2021
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During the light-dependent reactions of photosynthesis, water molecules are split (photolysis) using light energy absorbed by chlorophyll. This process yields oxygen, electrons, and protons (hydrogen ions). Oxygen is released as a byproduct.
Photosynthesis involves two main stages: light-dependent reactions and light-independent reactions (Calvin cycle). The splitting of water occurs in the light-dependent reactions and is crucial for providing electrons and protons for subsequent steps and releasing oxygen.
The overall equation for photosynthesis is $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$. Carbon dioxide is reduced to carbohydrate, not oxidized. Light energy is converted into chemical energy stored in glucose and other organic molecules.

272. Shoots of plant show upward movement and it can be designated to be

Shoots of plant show upward movement and it can be designated to be

[amp_mcq option1=”Negatively phototropic” option2=”Positively chemotropic” option3=”Positively hydrotropic” option4=”Negatively geotropic” correct=”option4″]

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The upward movement of plant shoots is a response to gravity. Since gravity pulls downwards, movement upwards is against the direction of gravity. This response to gravity is called gravitropism (or geotropism).
Plant shoots typically exhibit negative gravitropism (growing away from gravity) and positive phototropism (growing towards light). The question asks about the upward movement, which is primarily defined relative to the gravitational pull.
Positive gravitropism is seen in roots, which grow downwards into the soil. Phototropism is the growth of a plant in response to a light stimulus. Chemotropism is movement in response to chemicals, and hydrotropism is movement in response to water.

273. Which one of the following is NOT a component of human male reproducti

Which one of the following is NOT a component of human male reproductive system ?

[amp_mcq option1=”Cervix” option2=”Urethra” option3=”Seminal vesicle” option4=”Vas deferens” correct=”option1″]

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The human male reproductive system includes organs responsible for producing sperm and male hormones, as well as transporting sperm out of the body. The Urethra is part of both the urinary and reproductive systems, carrying urine and semen. The Seminal vesicle produces fluid that contributes to semen. The Vas deferens is a tube that carries sperm from the epididymis towards the ejaculatory duct. The Cervix is the lower, narrow part of the uterus in the female reproductive system, connecting the uterus to the vagina. Therefore, the cervix is NOT a component of the human male reproductive system.
The cervix is a distinct anatomical structure found in the female reproductive system, not the male.
Key organs of the male reproductive system include the testes, epididymis, vas deferens, seminal vesicles, prostate gland, bulbourethral glands, urethra, and penis. The female reproductive system includes ovaries, fallopian tubes, uterus, cervix, vagina, and external genitalia.

274. The part of the human eye on which the image is formed is

The part of the human eye on which the image is formed is

[amp_mcq option1=”pupil” option2=”cornea” option3=”retina” option4=”iris” correct=”option3″]

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Light enters the human eye through the cornea, passes through the pupil (regulated by the iris), the lens, and then is focused on the retina. The retina is the light-sensitive tissue located at the back of the eye containing photoreceptor cells (rods and cones), where the image is formed and converted into electrical signals that are sent to the brain via the optic nerve.
The retina is the screen at the back of the eye where the image is formed by the lens system.
The cornea and lens are responsible for refracting (bending) light to focus it on the retina. The iris controls the size of the pupil, regulating the amount of light entering the eye. The image formed on the retina is real and inverted.

275. Cartilage is NOT found in

Cartilage is NOT found in

[amp_mcq option1=”larynx” option2=”nose” option3=”ear” option4=”urinary bladder” correct=”option4″]

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Cartilage is a type of flexible connective tissue found in various parts of the body that require support and flexibility. The larynx (voice box), nose, and ear all contain cartilage as a major structural component. The urinary bladder is a hollow muscular organ that stores urine; its wall is primarily composed of smooth muscle tissue, not cartilage.
Cartilage is a structural component of the skeletal system and certain organs, providing support and flexibility. It is different from muscle tissue, which forms the walls of organs like the urinary bladder.
Examples of locations where cartilage is found include joints (articular cartilage), ribs, trachea, bronchi, intervertebral discs, and the structures mentioned in options A, B, and C. The urinary bladder wall consists of the detrusor muscle, a type of smooth muscle.

276. Which one of the following plant tissues has dead cells ?

Which one of the following plant tissues has dead cells ?

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

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Sclerenchyma is a plant tissue that provides mechanical support and strength to the plant. Sclerenchyma cells typically have thick, lignified secondary cell walls and are often dead at maturity, their function being purely mechanical support provided by their rigid walls. Examples include fibers (long, slender cells) and sclereids (variously shaped cells found in fruits, seeds, etc.).
Plant tissues can be broadly classified into meristematic (dividing cells) and permanent (differentiated cells). Permanent tissues can be simple (made of one type of cell) or complex (made of more than one type of cell). Parenchyma, Collenchyma, and Sclerenchyma are simple permanent tissues. Parenchyma and Collenchyma are composed of living cells.
– Epidermis is the outermost protective layer of cells, usually living.
– Parenchyma cells are living, thin-walled cells involved in photosynthesis, storage, secretion, etc.
– Collenchyma cells are living cells with unevenly thickened primary cell walls, providing mechanical support to growing stems and petioles.

277. In prokaryotic organisms, nuclear region is not surrounded by a membra

In prokaryotic organisms, nuclear region is not surrounded by a membrane. This undefined nuclear region is known as

[amp_mcq option1=”Nucleic acid” option2=”Nucleoid” option3=”Nucleolus” option4=”Nucleosome” correct=”option2″]

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In prokaryotic organisms (like bacteria and archaea), the genetic material (DNA) is located in a region of the cytoplasm that is not enclosed by a nuclear membrane. This ill-defined, irregularly shaped region where the genetic material is concentrated is called the nucleoid.
Prokaryotes lack membrane-bound organelles, including a true nucleus. Eukaryotic cells, on the other hand, have a membrane-bound nucleus containing their genetic material.
– Nucleic acid refers to the genetic material itself (DNA or RNA).
– Nucleolus is a dense structure found within the nucleus of eukaryotic cells, involved in ribosome synthesis.
– Nucleosome is a structural unit of a eukaryotic chromosome, consisting of a length of DNA coiled around a core of histone proteins.

278. Which one of the following statements is correct about effects of anti

Which one of the following statements is correct about effects of antibiotics on viruses ?

[amp_mcq option1=”Viruses are "non-living" entities but it can interact with antibiotics” option2=”Taking antibiotics cures viral infections” option3=”Viruses do not possess metabolic pathways on which antibiotics can function, whereas bacteria have such pathways” option4=”Viruses are resistant to antibiotics” correct=”option3″]

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Antibiotics are designed to target specific structures or metabolic processes in bacteria, such as cell wall synthesis, protein synthesis (ribosomes), DNA replication, or specific enzymatic pathways. Viruses, being intracellular parasites, lack their own metabolic machinery; they hijack the host cell’s machinery for replication. Therefore, viruses do not possess the metabolic pathways or structures that antibiotics are designed to inhibit, rendering antibiotics ineffective against them.
– Antibiotics target bacterial processes, not viral ones.
– Viruses lack their own metabolic pathways for functions like replication, using host cell machinery instead.
– Taking antibiotics for viral infections is ineffective and contributes to antibiotic resistance in bacteria.
– Viral infections require antiviral medications, not antibiotics.
The misuse of antibiotics for viral infections is a major driver of antibiotic resistance, a growing global health crisis. Antiviral drugs work by targeting different stages of the viral life cycle, such as entry into the host cell, replication of viral genetic material, or assembly and release of new viruses. Examples of viral infections include the common cold, flu, COVID-19, measles, and HIV.

279. Which one of the following cell organelles may play a role in expellin

Which one of the following cell organelles may play a role in expelling excess water and wastes in case of unicellular organisms ?

[amp_mcq option1=”Lysosome” option2=”Vacuole” option3=”Golgi body” option4=”Endoplasmic reticulum” correct=”option2″]

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In many freshwater unicellular organisms like *Paramecium* or *Amoeba*, contractile vacuoles are specialized organelles that collect excess water that enters the cell by osmosis and periodically expel it out. This process is crucial for osmoregulation, preventing the cell from bursting in a hypotonic environment. Wastes can also be expelled via this mechanism or through other means like diffusion or exocytosis.
– Vacuoles in unicellular organisms can include contractile vacuoles, which are vital for maintaining osmotic balance by expelling excess water.
– Lysosomes are involved in intracellular digestion.
– Golgi body (or Golgi apparatus) is involved in modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles.
– Endoplasmic reticulum is involved in protein and lipid synthesis.
Contractile vacuoles are found mainly in protists living in freshwater habitats. Their rate of pulsation is regulated by the osmotic potential of the surrounding medium; they pump faster in more dilute environments. While primarily for water expulsion, they also contribute to the removal of some metabolic wastes.

280. Light enters the eye through a thin membrane called

Light enters the eye through a thin membrane called

[amp_mcq option1=”retina” option2=”cornea” option3=”pupil” option4=”iris” correct=”option2″]

This question was previously asked in
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The correct answer is (B) cornea. The cornea is the transparent outer layer at the front of the eye that covers the iris, pupil, and anterior chamber. It is the first surface that light encounters when entering the eye.
The cornea acts as the eye’s outermost lens, controlling and focusing the entry of light into the eye.
The retina is the light-sensitive tissue lining the back of the eye. The pupil is the opening in the center of the iris that allows light to enter the eye. The iris is the colored part of the eye that controls the size of the pupil.
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