NEET Biology | Q & A with explanation - Part 6

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This includes questions from Class 12 Biology chapters.

Q 1: Enlarged view of one microsporangium with wall layers are shown. Identify the layers.

(1) 1-Epidermis, 2- endothecium, 3- middle layers, 4- tapetum, 5- mmc
(2) 1-Epidermis, 2- endothecium, 3- middle layers, 4- mmc, 5- tapetum
(3) 1-Epidermis, 2- middle layers, 3- endothecium, 4- mmc, 5- tapetum
(4) 1-Epidermis, 2- tapetum, 3- middle layers, 4- mmc, 5- endothecium

✅ (2) 1-Epidermis, 2- endothecium, 3- middle layers, 4- mmc, 5- tapetum.

▶️ A microsporangium has 4 wall layers: epidermis, endothecium, middle layers & tapetum.
▶️ The outer 3 layers give protection and help in dehiscence of anther to release pollen.
▶️ The tapetum nourishes the developing pollen grains.
▶️ In young anther, each microsporangium has sporogenous tissue at centre. It consists of diploid cells called sporogenous cells or microspore mother cell (MMC) or pollen mother cell (PMC).
Q 2: Regarding pollen grains (male gametophyte), select true statements.
1. Generally, bilobed in shape.
2. Size may be 25-50 micrometer in diameter.
3. Its outer covering is made up of pectin.
4. Exine has germ pores where sporopollenin is absent.

(1) 2 & 4 are true
(2) 1 & 2 are true
(3) 3 & 4 are true
(4) 1 & 4 are true

✅ (1) 2 & 4 are true.

A pollen grain has a two-layered wall:
▶️ Exine: Hard outer layer. Made up of sporopollenin (highly resistant organic material).
▶️ Intine: Inner wall. It is a thin and continuous layer made up of cellulose and pectin.
Q 3: Testosterone is produced by

(1) Sertoli cells in seminiferous tubules
(2) Sertoli cells in interstitial spaces of testes
(3) Leydig cells in interstitial spaces of testes
(4) Leydig cells in seminiferous tubules

✅ (3) Leydig cells in interstitial spaces of testes.

▶️ In testis, Seminiferous tubule is lined internally with
1. Male germ cells (spermatogonia or sperm mother cells): They become sperms.
2. Sertoli cells: They give nutrition to the germ cells.
▶️ The regions outside the seminiferous tubules (interstitial spaces) contain blood vessels, interstitial cells (Leydig cells) and immunologically competent cells.
▶️ Leydig cells secrete testicular hormones (androgens).
Q 4: Select the correct order uterine wall layers from outer to inner.

(1) Perimetrium – Endometrium – Myometrium
(2) Endometrium – Myometrium – Perimetrium
(3) Endometrium – Perimetrium –Myometrium
(4) Perimetrium – Myometrium – Endometrium

✅ (4) Perimetrium – Myometrium – Endometrium.

▶️ Uterus (womb) is inverted pear-shaped. It is supported by ligaments attached to the pelvic wall.
▶️ Uterus has 3 parts: Upper fundus, middle body and terminal cervix. Cervix opens to vagina.
▶️ The uterine wall has 3 layers:
1. Perimetrium: External thin membrane.
2. Myometrium: Middle thick layer of smooth muscle.
3. Endometrium: Inner glandular & vascular layer.
Q 5: In periodic abstinence method, to prevent conception, coitus is avoided from

(1) 4th to 6th day
(2) 7th to 12th day
(3) 10th to 17th day
(4) 17th to 20th day

✅ (3) 10th to 17th day.

Types of Natural/ Traditional contraceptive methods:
▶️ Periodic abstinence: Avoid coitus from day 10 to 17 (fertile period) of menstrual cycle to prevent conception.
▶️ Coitus interruptus (withdrawal): Withdraw penis from the vagina just before ejaculation to avoid insemination.
▶️ Lactational amenorrhea: It is the absence of menstrual cycle and ovulation due to intense lactation after parturition. Fully breastfeeding increases lactation. This method helps to prevent conception. This is effective up to 6 months following parturition.
Q 6: Select the odd one out.

(1) Violet flower
(2) Round seed
(3) Yellow pod
(4) Tall stem

✅ (3) Yellow pod

▶️ Yellow pod is a recessive trait. Violet flower, Round seed and Tall stem are dominant traits.
▶️ Mendel selected 7 pairs of true breeding pea varieties:
Q 7: The graphical representation to calculate probability of all genotypes of offspring in a genetic cross, is called

(1) Pedigree analysis
(2) Karyotype
(3) Punnett square
(4) Chromosome map

✅ (3) Punnett square

▶️ Pedigree analysis is an analysis of genetic traits in several generations of a family.
▶️ Karyotype is a graphical representation of an individual’s chromosomes, including their number, size, shape, and any abnormalities.
▶️ Chromosome map (genetic map) is a graphical representation that shows the relative positions of genes on a chromosome.
Q 8: Nucleotide arrangement in DNA can be seen by

(1) X-ray crystallography
(2) Electron microscope
(3) Ultracentrifuge
(4) Light microscope

✅ (1) X-ray crystallography

▶️ X-ray crystallography: This technique was used by Maurice Wilkins & Rosalind Franklin, whose work greatly contributed to the discovery of the double helix structure of DNA. It provides a three-dimensional picture of the molecule’s atomic structure.
▶️ Electron microscope: It can provide images of DNA.
▶️ Ultracentrifuge: This is used for separating different components of a sample, such as DNA, RNA, and proteins, based on their size and density.
Q 9: Which is true according to Chargaff’s rule?

(1) A + G = T + C
(2) A + T = C + G
(3) A + G/T + C = 2
(4) A + T/C + G = 1

✅ (1) A + G = T + C

▶️ In DNA, 4 types of nitrogen bases such as Adenine (A), Thymine (T), Guanine (G) and Cytosine (C) are present.
▶️ Erwin Chargaff’s rule: In DNA, the ratio of A to T and the ratio of G to C are equal.
A+G = T+C     or     A+G / T+C = 1
▶️ It means that, in DNA, total number of purines (A and G) equals to total number of pyrimidines (T and C).
Q 10: The 2 key concepts of Darwinian Theory are

(1) Branching descent and natural selection
(2) Branching descent and Use & disuse of organs
(3) Acquired characters and natural selection
(4) Mutation and natural selection

(1) Branching descent and natural selection

▶️ Branching Descent: This concept suggests that different species descend from a common ancestor.
▶️ Natural Selection: According to Darwin, variations occur naturally in all individuals of a species. In the struggle for existence, individuals with useful variations survive. This is called natural selection.
▶️ The concept of “Use & Disuse of organs” and “Acquired characters” are part of Lamarck’s theory.
▶️ A mutation is a change in the DNA sequence of an organism. Mutations lead to variations that may be acted upon by natural selection. But Darwin had not explained it as a key concept.
Q 11: Treatment of snake-bite by antivenin is an example of

(1) Artificially acquired active immunity
(2) Artificially acquired passive immunity
(3) Naturally acquired passive immunity
(4) Specific natural immunity

✅ (2) Artificially acquired passive immunity

▶️ Acquired immunity is 2 types:
▶️ Active immunity: In this, antibodies are produced in a host body when the host is exposed to antigens. 2 types:
1. Natural Active Immunity: Develops during natural infection by microbes.
2. Artificial Active Immunity: Develops by injecting the microbes deliberately during immunization.
▶️ Passive immunity: Here, readymade antibodies are given to the body. 2 types:
1. Natural Passive Immunity: E.g. Antibodies (IgG) from mother → Placenta → Foetus , Antibodies (IgA) in colostrum → infants
2. Artificial Passive Immunity: E.g. Anti-tetanus serum (ATS).
Q 12: “The soldiers of a country kill their own king”. This statement can be related to

(1) AIDS
(2) Autoimmunity
(3) Graft rejection
(4) Allergy

✅ (2) Autoimmunity

▶️ Due to genetic and other unknown reasons, the body may attack self-cells resulting in damage to the body. It is called autoimmunity and the diseases caused by it are called auto-immune diseases.
▶️ E.g. Rheumatoid arthritis, Myasthenia gravis etc.
Q 13: Select the mismatching set.

(1) Penicillin, Fleming, Staphylococci
(2) Baculovirus, IPM, Biocontrol
(3) Cyanobacteria, nitrogen fixation, biofertilisers
(4) LAB, ethanol, cheese

✅ (4) LAB, ethanol, cheese

▶️ Alexander Fleming discovered Penicillin. He observed that Staphylococci could not grow around Penicillium notatum. He extracted penicillin from it.
▶️ Baculoviruses are biocontrol agents used in IPM (Integrated Pest Management) program.
▶️ Cyanobacteria is used as biofertilizers as they fix atmospheric nitrogen.
▶️ Lactic acid bacteria (LAB) converts milk to curd.
▶️ Yeast is used to produce ethanol.
▶️ Swiss cheese has large holes due to production of CO2 by Propionibacterium sharmanii.
Q 14: First recombinant DNA (rDNA) was produced in 1972 by two scientists namely

(1) Stanley Miller & Harold Urey
(2) Stanley Cohen & Robert Brown
(3) Stanley Cohen & Herbert Boyer
(4) Stanley Miller & Herbert Boyer

✅ (3) Stanley Cohen & Herbert Boyer

▶️ Stanley Cohen & Herbert Boyer (197(2) isolated an antibiotic resistance gene (piece of DNA) from a plasmid of Salmonella typhimurium. It was linked with a plasmid vector and transferred into E. coli. As a result, the gene was expressed & multiplied in E. coli.
▶️ Stanley Miller & Harold Urey are known for Miller-Urey experiment to prove theory of Chemical evolution.
▶️ Robert Brown discovered cell nucleus.
Q 15: Restriction enzymes cut the DNA strand leaving single stranded overhanging stretches at the ends. They are called

(1) Marker gene
(2) Blunt ends
(3) Sticky ends
(4) Recognition site

✅ (3) Sticky ends

▶️ Selectable marker (marker gene) is a gene that helps to select the transformants and eliminate the non-transformants. If a piece of DNA is introduced in a host bacterium, it is called transformation. Such bacterium is transformant.
▶️ Selectable markers of E. coli include the genes encoding resistance to antibiotics like ampicillin, tetracycline, etc.
▶️ Cloning sites are the recognition sites for restriction enzymes. To link alien DNA, the vector needs a single or very few recognition sites.
Q 16: An improved variety of transgenic Basmati rice

(1) Does not require chemical fertilizers and growth hormones.
(2) Gives high yield and is rich in vitamin A.
(3) Is completely resistant to all insect pests and diseases of paddy.
(4) Gives high yield but has no characteristic aroma.

✅ (2) Gives high yield and is rich in vitamin A.

▶️ Basmati rice has unique aroma & flavour.
▶️ India has 27 varieties of Basmati.
▶️ In 1997, an American company got patent rights on Basmati rice through the US Patent and Trademark Office. This allowed the company to sell a ‘new’ variety of Basmati.
▶️ This was actually derived from Indian farmer’s varieties.
▶️ Indian Basmati was crossed with semi-dwarf varieties and claimed as a novelty. Other people selling Basmati rice could be restricted by patent.
Q 17: A biologist studied the population of rats in a barn. He found that the average natality was 250, average mortality 240, immigration 20 and emigration 30. The net increase in population is

(1) 05
(2) Zero
(3) 10
(4) 15

✅ (2) Zero

▶️ The net increase in population can be calculated as follows:
Net Increase= (Natality + Immigration) − (Mortality + Emigration)
▶️ Substituting the given values:
Net Increase= (250 + 20) − (240 + 30) = 0
Q 18: The amount of living material in a trophic level at a given time is called

(1) Biomass
(2) Standing crop
(3) Dead biomass
(4) Dry weight

✅ (2) Standing crop

▶️ The amount of living material in a trophic level at a given time is called standing crop. It is measured as the biomass (mass of living organisms) or the number in a unit area.
▶️ Biomass of a species is measured in terms of fresh or dry weight. Dry weight is more accurate because it is the exact mass of the body which remains constant.
Q 19: Latitudinal range of tropics is

(1) 20.5° N to 20.5° S
(2) 23.5° N to 23.5° S
(3) 33.5° N to 33.5° S
(4) 43.5° N to 43.5° S

✅ (2) 23.5° N to 23.5° S

▶️ Species diversity decreases from equator to poles.
▶️ Tropics (latitudinal range of 23.5° N to 23.5° S) have more species than temperate or polar areas.
▶️ Biodiversity (species richness) is highest in tropics because
1. Tropics had more evolutionary time.
2. Relatively constant environment (less seasonal).
3. They receive more solar energy which contributes to greater productivity.
Q 20: Based on Rivet Popper Hypothesis, honeybees can be compared to

(1) Rivets on the seats of airplane
(2) Rivets on the windows of airplane
(3) Rivets on the wings of airplane
(4) Passenger in airplane

✅ (3) Rivets on the wings of airplane

▶️ ‘Rivet popper' hypothesis is an analogy used to understand the importance of biodiversity.
▶️ It is proposed by Paul Ehrlich.
▶️ In an airplane (ecosystem), all parts are joined with many rivets (species). If passengers pop a rivet (extinction of a species), it may not affect flight safety (functioning of the ecosystem). But as more and more rivets are removed, the plane becomes dangerously weak. Loss of rivets on the wings (key species (e.g., honeybee) that drive major ecosystem functions) is more dangerous than loss of a few rivets on the seats or windows.

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