Biology Archives

21. Which one among the following animals can perform respiration either t

Which one among the following animals can perform respiration either through gills or through lungs ?

[amp_mcq option1=”Fish” option2=”Frog” option3=”Snake” option4=”Cow” correct=”option2″]

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UPSC CISF-AC-EXE – 2021

Amphibians, like frogs, typically undergo metamorphosis. Their larval stage (tadpole) is usually aquatic and respires through gills. The adult stage is often terrestrial or semi-aquatic and respires primarily through lungs and also through their moist skin. Fish respire only through gills. Snakes (reptiles) and Cows (mammals) respire only through lungs.

Respiration is the process of gas exchange (oxygen intake and carbon dioxide release). Different animals have evolved various respiratory organs depending on their environment. Gills are specialized structures for extracting oxygen from water, while lungs are adapted for gas exchange in air. Amphibians exhibit a dual mode of respiration, reflecting their transition from aquatic to terrestrial life.

The ability to respire through both gills and lungs is characteristic of the life cycle of many amphibians. Besides gills and lungs, cutaneous respiration (through the skin) is also significant in adult frogs, contributing substantially to their overall gas exchange, especially when submerged.

22. Which one of the following is a plant hormone ?

Which one of the following is a plant hormone ?

[amp_mcq option1=”Oestrogen” option2=”Cytokinin” option3=”Insulin” option4=”Thyroxin” correct=”option2″]

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Cytokinin is one of the major classes of plant hormones. Plant hormones (or phytohormones) are signaling molecules produced within plants that occur in extremely low concentrations. Hormones regulate various aspects of plant growth and development. Oestrogen, Insulin, and Thyroxin are animal hormones.

Cytokinins are a group of plant hormones that promote cell division (cytokinesis) in plant roots and shoots. They are involved in various processes such as cell growth, differentiation, apical dominance, and delaying senescence (aging) of leaves.

Major classes of plant hormones include auxins, gibberellins, cytokinins, abscisic acid (ABA), and ethylene. These hormones interact with each other in complex ways to regulate plant development. Oestrogen is a primary female sex hormone in animals. Insulin is a peptide hormone produced by the pancreas that regulates blood sugar levels in animals. Thyroxin is a thyroid hormone produced by the thyroid gland in animals that regulates metabolism.

23. The two elements which are present in proteins but generally absent in

The two elements which are present in proteins but generally absent in carbohydrates are

[amp_mcq option1=”Carbon and Hydrogen.” option2=”Carbon and Nitrogen.” option3=”Nitrogen and Sulphur.” option4=”Sulphur and Hydrogen.” correct=”option3″]

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Proteins are complex organic molecules that always contain carbon, hydrogen, oxygen, and nitrogen. Many proteins also contain sulphur (due to the presence of amino acids like cysteine and methionine). Carbohydrates are primarily composed of carbon, hydrogen, and oxygen, usually in a ratio of CnH2nOn or similar forms. Therefore, nitrogen and sulphur are elements typically found in proteins but generally absent in carbohydrates.

Proteins are polymers of amino acids. Each amino acid contains an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a side chain (R-group) attached to a central alpha carbon. The nitrogen atom is a defining component of the amino group. Carbohydrates, such as sugars and starches, are primarily composed of carbon, hydrogen, and oxygen atoms, often in a 1:2:1 ratio for H:O.

While nitrogen is a constituent of proteins and nucleic acids (DNA, RNA), it is not found in carbohydrates or typical lipids. Sulphur is present in some amino acids (cysteine, methionine) and therefore in many proteins, as well as in some vitamins, but it is not a component of carbohydrates. Carbon and hydrogen are fundamental elements present in all organic molecules, including both proteins and carbohydrates.

24. Tigers have a shorter small intestine compared to cows. The length of

Tigers have a shorter small intestine compared to cows. The length of the small intestine differs in various animals depending on the

[amp_mcq option1=”availability of water in their habitat.” option2=”size of their mouth cavity.” option3=”kind of habitats where they live.” option4=”kind of food they eat.” correct=”option4″]

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Tigers are carnivores and cows are herbivores. The length of the small intestine in animals is primarily adapted to the type of food they eat. Carnivores eat meat, which is relatively easy to digest and absorb, thus requiring a shorter digestive tract. Herbivores eat plant material, which is rich in cellulose and requires a longer, more complex digestive process, often involving fermentation by symbiotic microorganisms. A longer small intestine provides more surface area and time for the digestion and absorption of nutrients from plant matter.

The digestive system, including the length of the small intestine, is adapted to the diet of the animal. Herbivores have longer intestines than carnivores due to the difficulty in digesting plant cellulose.

The digestion of cellulose in herbivores often occurs in specialized chambers (like the rumen in cows) or in the hindgut, requiring a slower passage rate and a larger surface area for absorption, which is facilitated by a longer small intestine and overall digestive tract.

25. Which one of the following nutrients is not available in

Which one of the following nutrients is *not* available in fertilizers?

[amp_mcq option1=”Iron” option2=”Nitrogen” option3=”Phosphorus” option4=”Potassium” correct=”option1″]

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UPSC CISF-AC-EXE – 2020

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The question asks which nutrient is *not* available in fertilizers among the given options. All listed options (Iron, Nitrogen, Phosphorus, Potassium) are essential plant nutrients and are available in various types of fertilizers. Nitrogen, Phosphorus, and Potassium are primary macronutrients commonly found in NPK fertilizers, which form the bulk of the fertilizer industry. Iron is a micronutrient, required in smaller quantities, but is also available in specific micronutrient fertilizers (e.g., iron chelates) and is often included in complete fertilizer blends.

While all options are plant nutrients and can be found in fertilizers, Nitrogen, Phosphorus, and Potassium are the primary macronutrients (needed in large quantities) and form the basis of most common fertilizers. Iron is a micronutrient (needed in smaller quantities).

The phrasing of the question is potentially misleading, as Iron is indeed available in fertilizers. However, in the context of multiple-choice questions where one option must be selected, and considering the prominence of N, P, and K as the main components of standard fertilizers compared to Iron which is a micronutrient supplement, Iron might be considered the intended answer if the question is implicitly distinguishing between macronutrients and micronutrients in the context of bulk fertilization, despite the poor wording. Given the options, Iron is the least likely to be a major component of a general fertilizer compared to N, P, and K.

26. During photosynthesis, O₂ of the atmosphere is fixed with the help of

During photosynthesis, O₂ of the atmosphere is fixed with the help of H₂O and sunlight to synthesize carbohydrate and O₂ is evolved by the splitting of

[amp_mcq option1=”CO₂” option2=”H₂O” option3=”NO₃⁻” option4=”PO₄³⁻” correct=”option2″]

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During photosynthesis, $O_2$ is evolved by the splitting of H₂O.

– Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll pigment.
– The overall equation for photosynthesis is $6\text{CO}_2 + 6\text{H}_2\text{O} + \text{Light Energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$.
– The process occurs in two main stages: the light-dependent reactions and the light-independent reactions (Calvin cycle).
– The light-dependent reactions take place in the thylakoid membranes of chloroplasts. In this stage, light energy is absorbed by chlorophyll, leading to the splitting of water molecules ($H_2O$). This process is called photolysis.
– Photolysis of water ($2H_2O \rightarrow 4e^- + 4H^+ + O_2$) releases electrons (used in the electron transport chain to produce ATP and NADPH), protons ($H^+$), and oxygen gas ($O_2$) as a byproduct. This oxygen is released into the atmosphere.
– The light-independent reactions (Calvin cycle) take place in the stroma of chloroplasts and use the ATP and NADPH produced during the light reactions to fix carbon dioxide ($CO_2$) from the atmosphere and synthesize carbohydrates.
– The question contains a slight inaccuracy by stating “$O_2$ of the atmosphere is fixed with the help of $H_2O$ and sunlight…”. It should be “$CO_2$ of the atmosphere is fixed…”. However, the second part of the sentence correctly asks what $O_2$ is evolved from.
– Based on the mechanism of photosynthesis, the oxygen gas evolved comes directly from the splitting of water molecules during the light-dependent stage.

The origin of oxygen produced during photosynthesis was a significant scientific question. Experiments using isotopic tracers ($^{18}O$) demonstrated that the oxygen evolved comes from water and not from carbon dioxide.

27. Which of the following organelle(s) in an animal cell would have DNA a

Which of the following organelle(s) in an animal cell would have DNA and RNA?

[amp_mcq option1=”Nucleus only” option2=”Nucleus and mitochondria only” option3=”Nucleus, mitochondria and ribosomes” option4=”Mitochondria only” correct=”option2″]

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In an animal cell, the Nucleus and mitochondria only would have DNA and RNA.

– DNA (Deoxyribonucleic Acid) is the primary genetic material in most organisms. In eukaryotic cells, the majority of DNA is found in the nucleus (nuclear DNA), forming chromosomes.
– Eukaryotic cells also contain DNA in certain organelles: mitochondria (mitochondrial DNA or mtDNA) and, in plant cells and some other eukaryotes, chloroplasts (chloroplast DNA or cpDNA). Animal cells lack chloroplasts.
– RNA (Ribonucleic Acid) is involved in protein synthesis and other cellular processes. Various types of RNA (mRNA, tRNA, rRNA) are transcribed from DNA.
– In animal cells:
– Nucleus: Contains the main genome (DNA) and is where transcription occurs, producing various types of RNA. Thus, the nucleus has both DNA and RNA.
– Mitochondria: Contain their own circular DNA (mtDNA) and also have ribosomes (mitoribosomes) made of ribosomal RNA (mt-rRNA) and proteins, and produce their own mRNA and tRNA. Thus, mitochondria have both DNA and RNA.
– Ribosomes: Are complex molecular machines responsible for protein synthesis. They are composed of ribosomal RNA (rRNA) and proteins. Ribosomes themselves do not contain DNA. They read mRNA to build proteins.
– Therefore, in an animal cell, the nucleus and mitochondria are the organelles that contain both DNA and RNA.

While RNA is widely present in the cytoplasm (as mRNA being translated, tRNA carrying amino acids, and ribosomes containing rRNA), the question asks about *organelles* that contain both DNA and RNA. Ribosomes are technically organelles (or macromolecular machines depending on definition), but they lack DNA. The nucleus and mitochondria fit the criteria.

28. The kingdom Plantae as laid down by R. Whittaker comprises which of th

The kingdom Plantae as laid down by R. Whittaker comprises which of the following group of plants?

[amp_mcq option1=”Bryophyta, Pteridophyta, Protista, Gymnosperms and Angiosperms” option2=”Thallophyta, Pteridophyta, Fungi, Gymnosperms and Angiosperms” option3=”Thallophyta, Bryophyta, Monera, Pteridophyta and Gymnosperms” option4=”Thallophyta, Bryophyta, Pteridophyta, Gymnosperms and Angiosperms” correct=”option4″]

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The kingdom Plantae as laid down by R. Whittaker comprises Thallophyta, Bryophyta, Pteridophyta, Gymnosperms and Angiosperms.

– R.H. Whittaker proposed the five-kingdom classification system: Monera, Protista, Fungi, Plantae, and Animalia.
– According to Whittaker’s system, the kingdom Plantae includes multicellular eukaryotic organisms that are autotrophic (perform photosynthesis) and have cell walls primarily made of cellulose.
– The major groups traditionally placed under Plantae in Whittaker’s system are Algae (specifically multicellular forms), Bryophytes, Pteridophytes, Gymnosperms, and Angiosperms.
– The term ‘Thallophyta’ is an older classification group (or a descriptive term) that included organisms with an undifferentiated body structure (thallus), such as algae, fungi, and lichens. In Whittaker’s system, Fungi were placed in a separate kingdom, and Algae were distributed among Protista (unicellular eukaryotes) and Plantae (multicellular eukaryotes).
– Option D lists Thallophyta, Bryophyta, Pteridophyta, Gymnosperms, and Angiosperms. Given the other options include members of Monera, Protista, and Fungi (separate kingdoms), option D is the most accurate representation of the groups typically included in Whittaker’s Plantae. ‘Thallophyta’ in this context likely refers to the multicellular algae forms included in Plantae by Whittaker, such as some green algae (e.g., Spirogyra, Ulothrix) and brown/red algae.

Whittaker’s five-kingdom system was a significant step in biological classification, separating organisms based on cell structure, mode of nutrition, and ecological role. While ‘Thallophyta’ is somewhat an outdated term as a formal taxon in modern cladistics, its inclusion in Option D reflects the historical context and how these groups were often discussed under the umbrella of Plantae in earlier classification frameworks like Whittaker’s, distinguishing them from Embryophytes (Bryophytes, Pteridophytes, Gymnosperms, Angiosperms).

29. Which one of the following is not a female reproductive organ of

Which one of the following is not a female reproductive organ of flower?

[amp_mcq option1=”Style” option2=”Ovary” option3=”Pollen” option4=”Stigma” correct=”option3″]

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UPSC CISF-AC-EXE – 2019

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Pollen is the male gametophyte of a flower.

The female reproductive part of a flower is called the pistil or carpel, typically consisting of three parts: the stigma (receives pollen), the style (stalk connecting stigma to ovary), and the ovary (contains ovules, which develop into seeds). The male part is the stamen, consisting of the anther (produces pollen) and the filament.

Style, Ovary, and Stigma are all components of the pistil/carpel, which constitutes the female reproductive organ(s) of a flower. Pollen grains are produced by the anthers, which are part of the male reproductive organs (stamens).

30. Which one of the following cell organelles synthesizes its own protein

Which one of the following cell organelles synthesizes its own proteins involving genes present in its DNA?

[amp_mcq option1=”Endoplasmic reticulum” option2=”Plasma membrane” option3=”Plastid” option4=”Lysosome” correct=”option3″]

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Plastids (like chloroplasts) contain their own DNA and ribosomes and can synthesize some of their own proteins.

Mitochondria and plastids are unique among eukaryotic organelles because they possess their own circular DNA (similar to bacterial DNA) and ribosomes (70S type). This allows them to synthesize some of the proteins required for their function, independently of the cell’s nucleus and cytoplasmic ribosomes.

The endoplasmic reticulum is involved in protein synthesis and modification but relies on ribosomes attached to it or free in the cytoplasm. The plasma membrane is a structural component. Lysosomes contain enzymes synthesized elsewhere in the cell.