Cell

71. Energy is required for maintenance of life. It is obtained by a proces

Energy is required for maintenance of life.
It is obtained by a process called

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Metabolism
Phagocytosis
Photorespiration
Decomposition
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UPSC NDA-1 – 2015
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The correct answer is Metabolism. Metabolism encompasses all the chemical processes that occur within a living organism to maintain life, including those that generate energy.
Metabolism includes catabolic pathways which break down complex molecules (like carbohydrates, fats, proteins) obtained from food, releasing energy in the process (primarily in the form of ATP) that is used for cellular activities and maintenance of life.
Phagocytosis is a process of engulfing particles; Photorespiration is a process in plants that reduces photosynthetic efficiency; Decomposition is the breakdown of dead organic matter. While these processes are related to obtaining or releasing energy in specific contexts, Metabolism is the general term for the sum of biochemical reactions within an organism that yield energy for life functions.

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72. What is the number of chromosomes found in human somatic cell?

What is the number of chromosomes found in human somatic cell?

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48
56
46
42
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UPSC Geoscientist – 2023
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The correct answer is 46.
Human somatic (body) cells are diploid, meaning they contain two sets of chromosomes. Humans have 23 pairs of chromosomes, with one set of 23 chromosomes inherited from each parent. Thus, the total number of chromosomes in a human somatic cell is 23 * 2 = 46.
Of the 23 pairs, 22 are autosomes and one pair consists of sex chromosomes (XX in females, XY in males). Gametes (sperm and egg cells) are haploid and contain 23 chromosomes.

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73. Which one of the following has non-nucleated cells at maturity?

Which one of the following has non-nucleated cells at maturity?

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Xylem parenchyma
Xylem fibre
Palisade parenchyma
Companion cell
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UPSC Geoscientist – 2023
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Xylem fibre has non-nucleated cells at maturity.
Different types of plant cells have varying structures and functions, and their state at maturity (living or dead, presence or absence of organelles like nucleus) differs.
Xylem parenchyma cells are living cells and possess a nucleus at maturity. Palisade parenchyma cells are living, photosynthetic cells in leaves and have a nucleus. Companion cells are living cells associated with sieve tube elements in phloem and have a nucleus, which is metabolically active and supports the sieve tube element. Xylem fibres are sclerenchymatous cells that provide mechanical support. They develop thick lignified cell walls and are typically dead at maturity, meaning they lose their protoplast, including the nucleus, cytoplasm, and other organelles. Another prominent example of a non-nucleated cell at maturity in vascular plants is the sieve tube element of the phloem, which relies on the adjacent companion cell for metabolic support.

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74. The movement of a substance against a diffusion gradient with the use

The movement of a substance against a diffusion gradient with the use of energy is known as

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active transport
passive transport
water potential gradient
solute loss
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UPSC Geoscientist – 2023
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The movement of a substance against a diffusion gradient with the use of energy is known as active transport.
Transport across biological membranes can be passive or active. Passive transport mechanisms (like diffusion and facilitated diffusion) move substances down their concentration or electrochemical gradient and do not require metabolic energy. Active transport moves substances against their gradient, requiring the cell to expend energy, usually in the form of ATP.
Diffusion is the movement of substances from an area of high concentration to an area of low concentration. A diffusion gradient exists when there is a difference in concentration of a substance between two areas. Moving a substance from a low concentration area to a high concentration area, or against the natural flow of diffusion, requires work, which is powered by energy. This is the defining characteristic of active transport.

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75. Which one of the following processes describes the movement of particl

Which one of the following processes describes the movement of particles or molecules from a region of higher concentration to a region of lower concentration ?

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Diffusion
Osmosis
Plasmolysis
Deplasmolysis
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UPSC Geoscientist – 2024
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Diffusion is the net movement of molecules from a region of higher concentration to a region of lower concentration, driven by the concentration gradient. This process does not require a semi-permeable membrane or external energy input and continues until equilibrium is reached.
Diffusion is the movement of particles from high to low concentration.
Osmosis is a specific type of diffusion involving the movement of water across a selectively permeable membrane from a region of higher water potential (lower solute concentration) to a region of lower water potential (higher solute concentration). Plasmolysis and deplasmolysis relate to the effect of osmotic water movement on plant cells.

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76. Which organelle of Eukaryotic cells has DNA?

Which organelle of Eukaryotic cells has DNA?

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Lysosome
Golgi apparatus
Mitochondria
Endoplasmic reticulum
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UPSC Geoscientist – 2021
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Mitochondria, often called the powerhouse of the cell, are organelles in eukaryotic cells that contain their own genetic material in the form of circular DNA.
Eukaryotic cells have their primary DNA located in the nucleus. However, mitochondria (in animals, fungi, and plants) and chloroplasts (in plants and algae) also contain their own distinct DNA.
The presence of DNA in mitochondria and chloroplasts supports the endosymbiotic theory, which suggests that these organelles originated from free-living prokaryotic organisms that were engulfed by ancestral eukaryotic cells. Lysosomes, Golgi apparatus, and Endoplasmic reticulum are other eukaryotic organelles but do not possess their own DNA.

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77. In a mammalian cell, protein is synthesized on:

In a mammalian cell, protein is synthesized on:

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Golgi apparatus
Plasma membrane
Lysosomes
Rough endoplasmic reticulum
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UPSC Geoscientist – 2021
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Protein synthesis (translation) in mammalian cells occurs on ribosomes. Ribosomes can be found freely in the cytoplasm, or they can be attached to the membranes of the endoplasmic reticulum. When ribosomes are attached to the endoplasmic reticulum, it is called the Rough Endoplasmic Reticulum (RER), and it is the site where proteins destined for secretion, insertion into membranes, or delivery to other organelles (like lysosomes) are synthesized.
Ribosomes are the sites of protein synthesis, and they are associated with the RER for specific types of proteins.
The Golgi apparatus modifies, sorts, and packages proteins. The plasma membrane is the outer boundary of the cell. Lysosomes contain digestive enzymes. Free ribosomes synthesize proteins that function in the cytoplasm.

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78. Which of the following features are found in cells of meristematic tis

Which of the following features are found in cells of meristematic tissues in plants?

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Cells active with thick cellulose walls
Cells active with little cytoplasm and thin cellulose walls
Cells active with dense cytoplasm, thick cellulose walls, and no nuclei
Cell active with dense cytoplasm, thin cellulose walls and prominent nuclei
This question was previously asked in
UPSC Geoscientist – 2020
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Option D correctly describes the features of cells found in meristematic tissues.
Meristematic tissue consists of actively dividing cells responsible for growth in plants. These cells are characterized by dense cytoplasm, thin cellulose cell walls, and prominent nuclei, which are features necessary for high metabolic activity and rapid cell division.
Meristematic tissues are typically located at growing points, such as the tips of roots and shoots (apical meristems), or in layers responsible for increasing diameter (lateral meristems like cambium). The thin cell walls allow for easy expansion during growth, and the dense cytoplasm and prominent nucleus indicate a cell that is metabolically active and preparing for or undergoing division. Vacuoles are typically small or absent in meristematic cells.

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79. Plastids, in which materials such as starch, oils and protein granules

Plastids, in which materials such as starch, oils and protein granules are stored, are called:

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Leucoplasts
Chromoplasts
Chloroplasts
Chromatophores
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UPSC Geoscientist – 2020
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Plastids in which materials such as starch, oils, and protein granules are stored are called Leucoplasts.
Plastids are a type of organelle found in plant cells and some eukaryotic algae. They are broadly classified based on the pigments they contain. Leucoplasts are non-pigmented plastids primarily involved in the storage of food substances like starch (amyloplasts), lipids/oils (elaioplasts), and proteins (aleuroplasts).
Chromoplasts contain coloured pigments (like carotenoids) giving colour to flowers and fruits. Chloroplasts contain chlorophyll and are responsible for photosynthesis. Chromatophores are pigment-bearing cells (not necessarily organelles like plastids) found in animals and some plants for purposes like camouflage.

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80. Which one of the following correctly represents RER?

Which one of the following correctly represents RER?

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Endoplasmic reticulum having no ribosomes attached to its surface
Endoplasmic reticulum having ribosomes attached to its surface
Endoplasmic reticulum with rounded vesicles
Endoplasmic reticulum with Golgi appears on its surface
This question was previously asked in
UPSC Geoscientist – 2020
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RER stands for Rough Endoplasmic Reticulum, which is characterized by having ribosomes attached to its surface.
The endoplasmic reticulum (ER) is a network of membranes throughout the cytoplasm of eukaryotic cells. It exists in two forms: rough ER (RER) and smooth ER (SER). The presence of ribosomes on the outer surface of the membrane distinguishes RER from SER. These ribosomes are involved in the synthesis of proteins, particularly those destined for secretion or insertion into membranes.
Smooth Endoplasmic Reticulum (SER) lacks ribosomes and is involved in lipid synthesis, detoxification, and calcium storage. Vesicles are often formed from the ER, but are not the defining characteristic of RER. The Golgi apparatus is a separate organelle involved in further processing and packaging of proteins and lipids synthesized in the ER.

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