Sample Paper for CSIR NET Life Science

(1). A electron microscope has higher resolution as compared to the light microscope. This is because:

a. The wavelength of an electron is longer than the wavelength of light
b. The wavelength of an electron is shorter than the wavelength of light
c. The electrons can penetrate the sample better
d. They use different stains

(2). Nucleolus is involved in the synthesis of:

a. rRNA
b. tRNA
c. DNA
d. mRNA

(3). When changes in the phenotype or gene expression occur without changes in the underlying DNA sequence, the phenomenon is called:

a. Mutation
b. Eugenics
c. Epigenetics
d. Epistasis

(4). Which of the following is commonly known as the Complex II of electron transport system of mitochondria?

a. NADH dehydrogenase
b. Succinate dehydrogenase
c. Cytochrome c reductase
d. Cytochrome c oxidase

(5). From the perspective of developmental origin. Which of the following structures is homologous to a tortoise shell?

a. Exoskeleton of a lobster
b. Bones of a fish
c. Skull of humans
d. Feathers of birds

(6). Acoelomates are characterized by:

a. The absence of cavity surrounding the internal organs
b. The presence of huge body cavity, as in case of terrestrial animals
c. The presence of air sacs, as in case of birds
d. The absence of brain in a group of extinct species.

(7). Identify the phylum that is characterized by the animals that have segmented appendages.

a. Cnideria
b. Porifera
c. Arthropoda
d. Mollusca

(8). Which one of the following is the smallest biological unit capable of evolving over time?

a. A cell
b. An individual organism
c. A population
d. A species

(9). In case of parasites that require multiple hosts to complete their life cycle, what does definitive host mean?

a. It is the host that harbors the sexual stages of the parasite
b. It is the host in which the parasite reproduces sexually
c. It is the host in which the parasite feeds
d. It is the host in which the parasite remain in dormant stage

(10). Which one of the following is NOT a plant hormone?

a. Polyamines
b. Brassinosteroid
c. Nitric oxide
d. Karrikins
e. Jasmonates

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@. CSIR NET Life Sciences June 2015 Exam Model Question Part 2

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Answer Key and Explanations…

1. Ans. (b). The wavelength of an electron is shorter than the wavelength of light

Resolving power: The ability of an optical instrument (microscope) to visualize two closely placed objects as two separate entities. The limit of resolution, denoted as d is the minimum distance between two objects that reveals them as separate entities in the final image. As the value of d decreases, the resolution increases and finer details of the object can be visualized. The optical theory behind limit of resolution was formulated by the German physicist Ernst Abbe in 1873 and it is now known as the Abbe’s equation.

Abbe’s equation: limit of resolution (d) =0.61λ/n sin α
Where,
0.61 : a constant called Abbe constant
λ : the wavelength of light used (in nm)
n : refractive index of the medium (1 in the case of air, 1.5 in the case of oil)
Sin α : half of the cone of incident light

n Sin α is called as the Numerical Aperture (NA). NA is the light gathering capacity of the condenser
Thus Abbe’s equation can be re-written as d = 0.61λ/NA

Thus according to Abbe’s equation, lower values of ‘d’ can be obtained either by using shorter wavelength of light (λ) or by using larger values of numerical aperture. This is why electron microscopes have very high resolving power since there the value ‘d’ can be decreased by decreasing the wavelength of electron beans by applying the de Broglie wavelength principle.

The de Broglie wavelength is the wavelength, λ, associated with a massive particle and is related to its momentum, p, through the Planck constant, h. The relation states that the wavelength λ = h/p.

2. Ans. (a). rRNA
Nucleolus is a portion in the nucleus of eukaryotic cells and it is mainly composed of RNA and proteins. The main function of nucleolus is the synthesis of ribosomes. Nucleolus is present only in the interphase stage of cells and they disintegrate during the division phase of the cell cycle. They always associated with a specific chromosomal region in the nucleus called Nucleolar Organizing Region (NOR). The NOR in human is formed by the ribosomal DNA genes located in the chromosomes 13, 14, 15, 21 and 22. The ribosomal DNA region, which forms the NOR in human, contains genes for 5.8S, 18S and 28S rRNA molecules.

3. Ans. (c). Epigenetics
Epigenetics: is a branch of genetics which deals with the study of how external or environmental factors change the gene expression pattern in an organism. Epigenetic changes are usually not heritable (i.e., they are not genetically fixed).

Eugenics: studies and practices which are aimed to improve the genetic quality of human population and thereby social development.

Epistasis: one gene effect the expression of other gene(s). In other words, the expression of one gene is under the control of one or more genes (called modifier genes).

4. Ans. (b). Succinate dehydrogenase
Succinate dehydrogenase is bound to the inner mitochondrial membrane. It is the only enzyme which participates in both citric acid cycle and electron transport system.

5. Ans. (b). Bones of a fish
This question is little bit confusing since except the option (a), all other three options (b, c and d) are partially correct. This question was asked once in the GATE Life Science examination (GATE XL 2010). Among the three correct options, the most appropriate answer is option (b). i.e., the turtle shells are homologous to the bone of fishes.

The turtle shell is the dorsal and ventral shield of turtles, tortoises and terrapins. It is a complex honey structure completely enclosing the vital organs including head and legs. Ontogenetically turtle shell is the modified bony elements such as ribs and pelvis. Histologically the turtle shell consists of both skeletal bones and dermal bones.

Dermal bone: membrane bones formed within the dermis and grow only by accretion. They are developed by intra-membranous ossification and in most cases; the dermal bones are also the part of vertebrate skeletal systems such as skull, jaws, gills and shells of tortoises. Thus taking the bony nature of turtle shells, it can be considered as homologous to the bones of fishes.

Bird feathers: They are one of the most complex integumentary appendages found in vertebrates. They are developed in the tiny epidermal follicles that produce keratin, a fibrous protein, especially β-keratin.

β-keratin is found in feathers, beaks and claws of birds and claws, scales and shells of reptiles including turtles.

α-keratin is found in the mammalian hairs, horns and hoofs.

Exoskeleton of all arthropods including lobsters are made up of chitin, a homo-polysaccharide of β-1-4 linked N-acetylglucosamine residues.

6. Ans. (a). The absence of cavity surrounding the internal organs
Acoelomates lack the fluid filled body cavity (coelom) between the body wall and digestive tract.

Taxa which lack the true coelom are:

(a). Platyhelminthes (flat-worms: Eg. Planaria, Cestoda)
(b). Gastrotricha
(b). Entoprocta
(c). Gnathostomulida
(d). Cyliophora

Gastrotricha, Entoprocta and Ganathostomulida are traditionally called as Blastocoelomates

7. Ans. (c). Arthropoda
Phylum Arthropoda is the largest phylum in animal kingdom and it includes about 80% all known animal species in the biosphere. Arthropods are characterized by:

(1). Chitinaceous exoskeleton
(2). Segmented body
(3). Jointed and paired appendages

8. Ans. (c). A population
A population is a group of individuals of a same species inhabiting in a particular area. The smallest unit of evolution is a population. For the process of evolution to continue, the allelic frequency of the population (not the individuals) should be changed. If a population is experiencing any change in allelic frequencies (we call it as genetic drift), this population is said to be NOT in Hardy–Weinberg equilibrium. In other words, A POPULATION IN HARDY-WEINBERG EQUILIBRIUM DO NOT SHOWS THE PROCESS OF EVOLUTION. The different causes which induce changes in allelic frequencies may be migration, emigration, mutation, selection etc. and all these factors are collectively called as the EVOLUTIONARY FORCES in a population.

9. Ans. (b). It is the host in which the parasite reproduces sexually
Some parasites requires more than one host organism to complete its life cycle. In such case, the host in which the parasite sexually reproduces is called definitive host or primary host. The other host, in which the parasite stay only for a short transition period during which some developmental stages may be completed, is called secondary host or intermediate host.

Example: Humans are the intermediate host (secondary host) of Trypanosome which causes sleeping sickness, while tsetse fly is the definitive host, in which the parasite undergoes sexual reproduction.

10. Ans. (d). Karrikins
Karrikins are not plat hormones and they are not synthesized in plants. However, karrikins are considered as a plant growth regulator since it can stimulate seed germination. Karrikins are found in the smoke of burning plant materials.

Auxins, Cytokinins, Abscisic acid, Ethylene and Gibberellins are the five major classes of plant hormones. Besides the five categories, there are many minor categories of plant hormones or plant growth regulators and some of them are:

(1). Brassinosteroids: they are considered as the sixth class of plant hormone. They are a class of polyhydroxysteroids which stimulate cell elongation, cell division, gravitropism and resistance to stress. Brassinosteroids inhibits root growth and abscission of leaves, flowers and fruits.

(2). Jasmonates: they promote the production of defense proteins against the invading pathogens. Jasmonates also have role in seed germination and root growth.

(3). Polyamines: As the name suggests, they are highly basic molecules essential for the plant growth and development. Polyamines are known to affect cell division, both mitosis and meiosis in plants.

(4). Nitric oxide (NO): NO is a signal molecule in hormonal and defense response in plants such as stomatal closing, root development, germination, nitrogen fixation, cell death and stress.