Introduction to reproduction - class-X

Organisms reproduce for perpetuation of species because individuals have a limited life span. Organisms may reproduce sexually as well as asexually. The sexual reproduction involves formation of haploid gametes through the process of reduction division or meiosis. The haploid gametes fuse during fertilization to form diploid zygote. Thus, restoring the normal ploidy. The asexual reproduction does not involves gamete formation through meiosis or their fertilization. The vegetative propagation in plants is a type of asexual reproduction in which plant body is propagated directly from some vegetative part of adult plant.

Earthworms are monoecious or hermaphrodite (have both male and female sex organs) but are protandrous. The testes mature earlier than ovaries and hence, self-fertilisation is avoided.
Thus, the correct answer is option A.

The menstrual cycle refers to the series of events that periodically modifies the female reproductive tract of humans and advanced primates. In other mammals, a cycle of receptivity to sexual activity occurs that is probably less complex than the menstrual cycle and is known as the estrous cycle.

Those structures which are directly concerned with reproduction are considered primary sex characteristics. Secondary sexual characters can be used to differentiate between males and females and usually serve the purpose of attracting potential mates. Testosterone is responsible for male secondary sex characteristics such as a deep voice and facial hair. In the female, the hormones that most nearly parallel testosterone in their actions are the estrogens. Estrogens contribute to the development of the female secondary sex characteristics and stimulate the development of the mammary glands (breast in this question), the onset of menstruation, and the development and functioning of the reproductive organs. The other hormone produced by the female sex glands, called progesterone, assists in the normal development of pregnancy.

The process of formation of mature female gametes is called oogenesis. The reproductive cycle of female primates is called menstrual cycle. Menstrual cycle starts only after attaining sexual maturation (puberty). During ovulation only one ovum is released per menstrual cycle. The cyclical changes in the ovary and the uterus during menstrual cycle are induced by changes in the levels of pituitary and ovarian hormones.

Blastogenesis is the process of formation of offsprings asexually from reproductive bodies and does not include meiosis and fertilization. 

The recurring physiological changes induced and regulated by reproductive hormones in non-primates constitute oestrous cycle. It consists of short period of heat generation which is then followed by anoestrous phase. Oestrous cycle is initiated as a result of no fertilization and is characterized by sloughing off of uterine endometrium, which was proliferated for implantation of fertilized egg, and its reabsorption. Since, non primate females become receptive to male during oestrous phase, it is indicator of breeding period. Estrogens are secreted by developing follicles in ovary during follicular phase coincide with first oestrous (low estrogens) and then proliferative phase (high level of estrogens by developing follicles) in uterus.This makes option B incorrect since, estrogens level is low during oestrous cycle. 

Rhizomes (eg., Ginger), tubers (eg., Potato) and corms (eg., Colocasia) are underground storage stems which can be used for vegetative propagation.  Prefix "Allo" means different hence transfer of pollen from one flower to stigma of another flower is called allogamy. It is compulsory in unisexual flower but may also occur in bisexual flowers.

Apomixis is a process of asexual method of seed formation in which embryo develops from maternal tissues of the ovule without the processes of meiosis and gametogenesis. It is seen in higher plants. It conserves the genetic structure of plants. Heterosis can be maintained permanently in crop plants by this process. 

Intersex is referred to as the variation in sex characteristics that does not allow the individual to be distinctly called as male or female.
Hermaphrodite is an organism who has both male and female sex organs (not necessarily characteristics).
Bisexual means hermaphrodite.
If an individual exhibits both male and female secondary sexual characteristics is called as gynandromorph.
So, the correct answer is option D.

The different yolk's protein has distinct roles. Phosvitins are important in sequestering calcium, iron and other cations for the developing embryo. Phosvitins are one of the most phosphorylated (10%) proteins in nature, the high concentration of phosphate groups providing efficient metal-binding sites in clusters. Lipovitellins are involved in lipid and metal storage, and contain a heterogeneous mixture of about 16%  noncovalently bound lipid, most being phospholipid. Lipovitellin-1 contains two chains, LV1N and LV1C. Hence, option C is correct.

Earthworms are hermaphrodite animals, meaning that both testes and ovary are present in a single body but cross-fertilisation is the rule. At the time of reproduction two worms come to lie close to each other and exchange sperms. The sperms are stored in pouches called spermatheca. So, the correct answer is option C.

Metamorphosis is the process of development of organisms after hatching or birth. Insects that go through three stages of change in their life cycle have an incomplete metamorphosis. The first stage is the egg. During this time, the insect will hatch into a form, called a nymph. The nymph is basically a small version of the adult insect. Once a nymph outgrows its exoskeleton it will go through a process called moulting which is to leave the old skin or exoskeleton behind. The new skin will harden and become the new exoskeleton. This will happen many times until the insect finally becomes an adult. So, the correct answer is option B.

Lippes loop is a type of intrauterine contraceptive device made of inert plastic in a double S-shape, which can be inserted through the cervix into a cannula and takes a trapezoidal shape within the uterus. The Lippies Loop was made up of polyethylene and impregnated with radium phosphate for radiopacity. It was used worldwide but in many countries including India as well, it is being replaced with Copper T. It was manufactured in Kanpur. Hence, option D is the correct answer.

Parthenogenesis is a type of asexual reproduction in which the embryo grows and develops from egg without fertilization. Apogamy is a type of reproduction in which sporophyte develops from a gametophyte without fertilization. Parthenocarpy is the phenomenon of development of fruit without fertilization. In this, fruits are seedless. Pseudogamy is a form of reproduction in which the embryo develops from egg following the stimulus of pollination but without fertilization. It involves activation of egg by sperm but does not involve nuclear fusion. 

Binary fission is the asexual form of reproduction in which single-celled organism divides itself into two cells, in favourable condition.
Multiple fission is the asexual form of reproduction where the parent amoeba cell divides to give many daughter cells in unfavourable condition.
Thus, the correct answer is option B.

Sponges and Cnidarians are among the animals, that can reproduce by budding. A small part of the parent's body separates from the rest and develops into a new individual. Sometimes the buds remain attached and become more or less independent members of a colony. In some tunicate colonies, different individuals are connected by root-like structures called stolons. In others, they share body parts, such as their atrial (exhaling) siphon. These tunicates reproduce asexually through budding example Botryllus schlosseri. The scyphistoma reproduces asexually, producing similar polyps by budding, and then either transforming into a medusa or budding several medusae off from its upper surface. The medusae are initially microscopic and may take years to reach sexual maturity. So, the correct answer is option D.

Parthenogenesis (virgin development) is a form of asexual reproduction in which an unfertilized egg develops into an adult animal. The adult is typically haploid. Parthenogenesis is common among insects (especially honeybees and wasps, aphids etc.) and crustaceans; it also occurs among some other invertebrate and vertebrate groups, including some species of nematodes, gastropods, fishes, amphibians, and reptiles. Although a few species appear to reproduce solely by parthenogenesis, in most species episodes of parthenogenesis alternate with periods of sexual reproduction. Parthenogenesis may occur for several generations, followed at some point by sexual reproduction in which males develop, produce sperm and mate with the females to fertilize their eggs. In some species, parthenogenesis is a means of rapidly producing individuals when conditions are favorable.

Parthenogenesis refers to the development of an individual from unfertilized eggs. In honey bees, parthenogenesis is common and here, drones develop as a result of parthenogenesis only. The mode of parthenogenesis is arrhenotoky in which only females are produced. Frog and sea urchin reproduces by artificial parthenogenesis.

Maturation of the follicle is stimulated by follicle stimulating hormone (FSH) from the anterior pituitary, and oestrogen secreted by the follicle lining cells. Ovulation is triggered by a surge of luteinising hormone (LH) from the anterior pituitary, which occurs a few hours before ovulation. After ovulation, the follicle lining cells develop into the corpus luteum (yellow body), under the influence of LH from the anterior pituitary. The corpus luteum produces the hormone progesterone and some oestrogen. If the ovum is fertilised it embeds itself in the wall of the uterus where it grows and develops and produces the hormone human chorionic gonadotrophin (hCG), which stimulates the corpus luteum to continue secreting progesterone and oestrogen for the first 3 months of the pregnancy and, after which time this function is continued by the placenta.

Frogs reproduce by external fertilisation. The female frog ovulates in the water and releases its gametes. The sperm released from the male frog fertilizes to form zygote which turns into a well-developed egg. So, the correct answer is option B.

• Secondary sexual characters are those that appear at the time of puberty while the primary sexual characters are present from the time of birth. 
• These secondary sexual characters are caused by hormones released at the time of puberty.
• Beard growth starts in the male at the time of puberty in the male because of increased secretion of testosterone.

Fertilization can be internal or external. When the fertilization occurs inside the female body, then it is internal fertilization (e.g., most reptiles, some birds, some fishes.)
Fertilization in dogfish, shark is internal. While in catfish, toads and some frogs, it is external fertilization.
Hence, the correct answer is option (C).

Testes are the organs that produce the germ cells and scrotum is the pouch that contains the testes. The evolution of the scrotal sacs in mammals has been mysterious and there exist many hypotheses to explain the probable function of the scrotum. Primarily they provide a space, that isolate and serves to provide a temperature, lower than the body; essential for the production, maturation, and storage of sperm cells. Bats in this respect are unique and exhibit testicular migration between abdomen and scrotum, while the cauda epididymis is permanently in the scrotal sacs.