NEET Biology Reproduction Genetics and Biotechnology MCQs Set 03

Answer: (c) 10th to 17th day

Explanation:
1. Ovulation occurs around the 14th day of a 28 day cycle.
2. The ovum survives for about a day and sperms for 2-3 days, so the fertile phase is roughly the 10th to 17th day.

Teacher's Note:
1. Ovulation is triggered by the LH surge in the middle of the cycle.
2. The "safe period" method of birth control avoids this window.

Answer: (c) Zygote, spermatogonia, primary spermatocyte

Explanation:
1. Zygote, spermatogonia, oogonia and primary spermatocytes are all diploid (2n).
2. Secondary spermatocytes, ovum, spermatids and sperms are haploid (n), because meiosis I has reduced the chromosome number.

Teacher's Note:
1. Meiosis I is the reduction division, so cells after it are haploid.
2. Primary spermatocytes are still 2n.

Answer: (c) Implants : subcutaneous

Explanation:
1. Hormonal implants are thin capsules inserted under the skin (subcutaneously), usually in the inner side of the upper arm.
2. LNG-20, Lippes loop and Multiload 375 are intrauterine devices placed in the uterus, not in the Fallopian tube, and they are not implanted in the wall of the uterus.

Teacher's Note:
1. Implants release a progestogen slowly and protect for several years.
2. IUDs are placed through the vagina into the uterus.

Answer: (c) garden pea

Explanation:
1. Mendel worked on the garden pea (Pisum sativum).
2. It has easily distinguishable contrasting characters, a short life cycle, and can be self or cross pollinated.

Teacher's Note:
1. Mendel studied 7 pairs of contrasting characters.
2. His experiments were carried out for about seven years.

Answer: (d) maternal (mitochondrial) disorder

Explanation:
1. In the third generation the mother is affected and every child, both sons and daughters, is affected.
2. In the other families an affected father has only unaffected children.
3. The trait is passed only through the mother, since mitochondria are inherited from the egg, so it is a maternal (mitochondrial) disorder.

Teacher's Note:
1. In mitochondrial inheritance affected mothers pass the disease to all offspring and affected fathers to none.
2. Autosomal and X-linked recessive traits would not make all the children of an affected mother and a normal father affected, with the daughters affected too.

Answer: (c) 80 cm

Explanation:
1. Each capital (contributing) allele adds the same amount. AaBb has 2 such alleles, adding \(50 - 20 = 30\) cm, so each allele adds 15 cm.
2. AABB has 4 contributing alleles, so the height is \(20 + 4\times15 = 80\) cm.

Teacher's Note:
1. In polygenic traits, the effect of each contributing allele is additive.
2. The phenotypes show a bell shaped distribution.

Answer: (b) Alec Jeffreys

Explanation:
1. Alec Jeffreys developed DNA fingerprinting in 1984, using VNTRs as probes.
2. Kary Mullis invented PCR, and Paul Berg made the first recombinant DNA.

Teacher's Note:
1. DNA fingerprinting uses variable number tandem repeats (VNTR).
2. It is used in forensics and paternity testing.

Answer: (a) Aspergillus niger

Explanation:
1. The fungus Aspergillus niger is used for the commercial production of citric acid.
2. Acetobacter aceti makes acetic acid, Clostridium butylicum makes butyric acid, and Lactobacillus makes lactic acid.

Teacher's Note:
1. Match the microbe with the acid: Aspergillus niger: citric acid.
2. Acetobacter aceti: acetic acid; Clostridium butylicum: butyric acid.

Answer: (c) corn borer

Explanation:
1. The genes cryIAc and cryIIAb control cotton bollworms, and cryIAb controls the corn borer.
2. Roundworms (nematodes) are controlled by a gene silencing method using RNAi.

Teacher's Note:
1. Cry proteins come from Bacillus thuringiensis.
2. They form pores in the gut of the susceptible insect larva.

Answer: (d) gel electrophoresis

Explanation:
1. Agarose is a natural polymer from seaweeds that is used to make the gel for separating DNA fragments by size in gel electrophoresis.

Teacher's Note:
1. DNA is negatively charged and moves towards the anode.
2. Smaller fragments move farther through the gel.

Answer: (b) rice

Explanation:
1. Jaya and Ratna were developed from IR-8 (the semi-dwarf rice from IRRI) and Taichung Native-1 for India.
2. They are varieties of rice. Sonalika and Kalyan Sona are semi-dwarf wheat.

Teacher's Note:
1. The Green Revolution used semi-dwarf wheat and rice.
2. Semi-dwarf varieties are resistant to lodging.

Answer: (a) high protein content

Explanation:
1. Atlas 66 is a wheat variety with high protein content, used as a donor for improving the protein content of other varieties.
2. High lysine is in maize (opaque-2) and high oil is in oil crops.

Teacher's Note:
1. Biofortification breeds crops for higher nutrient content.
2. Other examples: iron-rich fortified rice and vitamin A-rich carrots.

Answer: (b) Cockroach is a bisexual animal

Explanation:
1. Sweet potato bears bisexual flowers and the fruit fly has 2n = 8, so (a) and (c) are correct.
2. Embryophytes (bryophytes onwards) have internal fertilization, so (d) is correct.
3. Cockroach has separate male and female individuals, so it is unisexual and statement (b) is incorrect.

Teacher's Note:
1. Bisexual or hermaphrodite animals such as earthworm, sponge and tapeworm carry both sets of gonads in one body.
2. Cockroach is a unisexual (dioecious) insect.

Answer: (d) Ficus

Explanation:
1. Annual and biennial plants such as wheat (Triticum) and radish (Raphanus) show clearly distinct vegetative, reproductive and senescent phases.
2. Strobilanthus flowers once in 12 years and then dies, so its phases are also distinct.
3. In perennial trees such as Ficus the phases are very difficult to separate.

Teacher's Note:
1. Perennial plants can flower repeatedly over many seasons.
2. Bamboo and Strobilanthus are monocarpic perennials flowering once.

Answer: (b) Only a few gametes are released into the medium

Explanation:
1. In external fertilization a very large number of gametes is released into the water because many are lost.
2. So the statement that only a few gametes are released is incorrect; the other three statements are correct.

Teacher's Note:
1. Large numbers of gametes and offspring compensate for the high losses in external fertilization.
2. Bony fishes and amphibians are common examples.

Answer: (c) Agave

Explanation:
1. Wheat and pea are annual plants.
2. Mango is perennial but flowers every year (polycarpic).
3. Agave lives for many years but flowers only once and then dies, so it is perennial and monocarpic.

Teacher's Note:
1. Monocarpic plants flower and fruit only once in their lifetime.
2. Bamboo and Strobilanthus are other perennial monocarpic plants.

Answer: (b) Dianthus

Explanation:
1. Anthophore is the elongation of the thalamus between the calyx and the corolla, found in Dianthus and Silene.
2. Gynophore (between corolla and androecium) is seen in Cleome and Capparis, and Passiflora shows an androgynophore.

Teacher's Note:
1. The three internodal elongations of the thalamus are anthophore, androphore and gynophore.
2. Each lies between a different pair of whorls.

Answer: (a) Megasporangium - Micropyle - Basal region

Explanation:
1. The micropyle is a small opening at the tip end of the ovule, while the basal region of the ovule is the chalaza.
2. So set (a) is incorrect; the egg apparatus has synergids with filiform apparatus, maize tassels are the styles and stigmas, and Vallisneria pollen is carried on the water surface.

Teacher's Note:
1. Micropyle is the passage for the pollen tube to enter the ovule.
2. Chalaza is the basal part where the ovule body meets the funicle.

Answer: (c) stigma, style, ovary, thalamus

Explanation:
1. The stigma is the topmost receptive surface that receives pollen.
2. The style is the slender stalk below it, the ovary is the swollen basal part with ovules, and the pistil sits on the thalamus.

Teacher's Note:
1. The three parts of the carpel are stigma, style and ovary.
2. The thalamus or receptacle holds all the floral whorls.

Answer: (a) Anemophily

Explanation:
1. In versatile anthers the filament is attached at the middle of the anther, so the anther swings freely in the air.
2. This helps the dispersal of pollen by wind (anemophily), as in grasses.

Teacher's Note:
1. Wind pollinated flowers have light, dry, non-sticky pollen.
2. Feathery stigmas and versatile anthers are typical features of wind pollination.

Answer: (c) Wind

Explanation:
1. Light, dry and non-sticky pollen in large numbers is carried easily by air currents.
2. Long feathery stigmas are suited to catch the airborne pollen, which are features of wind pollination.

Teacher's Note:
1. Wind pollinated flowers are usually small, colourless and without nectar.
2. Corn and grasses are typical wind pollinated plants.

Answer: (b) 12, 36, 24

Explanation:
1. The nucellus is diploid, so 2n = 24 and n = 12.
2. Pollen grain is haploid (12), endosperm is triploid (36) and the embryo is diploid (24).

Teacher's Note:
1. Nucellus, integuments and embryo are sporophytic (2n).
2. Pollen grain and embryo sac cells are gametophytic (n), and endosperm is 3n.

Answer: (d) Degenerating synergid

Explanation:
1. The pollen tube enters the ovule through the micropyle.
2. It then enters the embryo sac by passing into one of the two synergids, which degenerates and releases the two male gametes.

Teacher's Note:
1. In porogamy the pollen tube enters through the micropyle, and in chalazogamy through the chalaza.
2. The synergid entry is common to both.

Answer: (c) Guides the entry of pollen tube into the embryo sac

Explanation:
1. The filiform apparatus consists of finger-like cell wall thickenings at the micropylar tip of the synergids.
2. It guides the pollen tube into the synergid and thereby into the embryo sac.

Teacher's Note:
1. Synergids have special cellular thickenings called the filiform apparatus.
2. These thickenings give chemical signals which attract the pollen tube.

Answer: (d) One male gamete and the secondary nucleus

Explanation:
1. The secondary nucleus is formed by the fusion of two polar nuclei.
2. One male gamete fuses with it, so three haploid nuclei fuse in total to give the triploid primary endosperm nucleus.

Teacher's Note:
1. Triple fusion is the fusion of one male gamete with two polar nuclei.
2. It occurs in the central cell of the embryo sac.

Answer: (d) One fertilizes an egg cell and the other fertilizes the cell that forms the food reserve tissue

Explanation:
1. One male gamete fuses with the egg cell (syngamy) to form the zygote.
2. The other fuses with the polar nuclei of the central cell (triple fusion) to form the endosperm, which is the food reserve tissue.

Teacher's Note:
1. There is only one egg cell in an embryo sac.
2. The endosperm nourishes the developing embryo.

Answer: (c) Bean

Explanation:
1. In bean, the endosperm is completely used up during seed development and food is stored in the cotyledons, so it is non-endospermic.
2. Castor, maize and onion seeds retain the endosperm at maturity.

Teacher's Note:
1. Pea, groundnut, bean and gram are common non-endospermic seeds.
2. Wheat, rice, maize, castor and coconut are endospermic.

Answer: (d) Both (a) and (b)

Explanation:
1. Parthenocarpy gives seedless fruits without fertilization.
2. It is useful only where the pericarp is eaten (banana, grapes, orange).
3. It is useless when the edible part is the seed or the endosperm, as in pomegranate seeds and coconut.

Teacher's Note:
1. Seedless fruits are of value for the edible fleshy pericarp.
2. Growth regulators such as auxin can induce parthenocarpy.