Revision: Reproduction in Lower and Higher Animals Biology HSC Science (General) 12th Standard Board Exam Maharashtra State Board

Reproduction is the process of formation of new individuals by sexual or asexual means, which can repeat the process in their own turn.

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Formation of new organism of same species by earlier existing organism is called as reproduction.

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Reproduction is a biological process that results in the formation of new individuals of the same kind, though usually with slight genetic, structural and physiological variations.

A mode of reproduction where a new organism is formed from a part of the parent body without involving gametes.

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The process of forming a new organism from an organism of the same species without the involvement of gametes is called asexual reproduction.

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When offspring is produced by a single parent by the formation of specialised asexual reproductive structures by the parent body, the reproduction is asexual.

All freshwater sponges like Spongilla and some marine sponges reproduce asexually by the formation of specialised endogenous buds, known as gemmules (internal buds).

In multicellular organisms like Hydra, when a bud grows on the parent body due to cell division and later becomes a new individual, it is called budding.

The process in which an organism develops a new individual from its body parts using specialised cells that multiply and differentiate into various tissues is called regeneration.

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When an organism regrows its lost or damaged body part, or forms a new organism from a body part, it is called regeneration.

The period of growth and development before an organism becomes sexually mature is called the juvenile phase.

A mode of reproduction involving the fusion of male and female gametes (sperm and egg) to form a zygote that develops into a new organism.

Puberty is the process of physical and hormonal changes by which a child’s body matures into an adult body capable of sexual reproduction to enable fertilization.

Reproduction is a process that results in the formation of new individuals of the same kind, though usually with slight genetic, structural and physiological variations.

The process of expulsion of semen from the urethra is called ejaculation.

The secretion of glands with spermatozoa is a whitish viscous fluid known as seminal fluid or semen.

Spermatogenesis is the process of formation and development of sperm cells (spermatozoa) in the testes from spermatogonial stem cells through mitosis and meiosis.

Hernia is an abnormal condition that is caused when the intestine, due to the pressure in the abdomen, bulges into the scrotum through the inguinal canal.

The opening of the vagina in young females is partially closed by a thin membrane called the hymen (or virgin knot).

The remnant of the follicle persists for sometime to convert . into a yellow mass called corpus luteum (corpus: body, luteum: yellow).

A maturing egg contained in a cellular sac is called the follicle.

When the follicle enlarges and fills with fluid as the egg grows, it is called a Graafian follicle.

The thin membrane partially covering the vaginal opening in young females is called the hymen.

The funnel-shaped opening of the oviduct that picks up the released egg with the help of cilia is called the oviducal funnel.

The lower part of the uterus is very narrow and is called cervix.

The external female genitalia is called the vulva.

A projection overlies the central part of the areola that is known as nipple.

The glandular tissue is divided into 15–20 mammary lobes that radiate outward from the nipple and contain clusters of milk-producing glands, called alveoli.

The skin over the centre of the elevation has a darkly pigmented circular area called areola.

Puberty is the period during which immature reproductive system of boys and girls matures and becomes capable of reproducing.

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The period during adolescence when the reproductive tissues mature and the body undergoes changes to attain sexual maturity is called puberty.

Adolescence is the time period between the beginning of puberty and adulthood. During this period, the body undergoes several changes alongside reproductive maturity. It begins around the age of 11 and lasts till 18 or 19 years of age. The period of adolescence may vary from person to person.

The release of the ovum from the ovary is called ovulation.

The rhythmic series of changes in the sex organs throughout the reproductive life of a female primate (e.g., monkeys, apes, and human beings) from puberty to menopause is called the menstrual cycle (L. mensis = month, lunar month).

It is the stage when a girl menstruates for the first time.

Gametogenesis is the process of formation of gametes i.e., sperms and ovary from the primary sex organs in all sexually reproducing organisms. Meiosis plays the most significant role in the process of gametogenesis.

Spermiation is the process of releasing mature spermatozoa. In this, spermatozoa are shed into the lumen of the seminiferous tubule for transport.

After spermiogenesis, sperm heads become embeded in sertoli cells from which they obtain their nutrition and finally get released into the lumen of seminiferous tubules. This process of release of mature sperms from sertoli cells is called spermiation.

Spermiogenesis is the process of transforming spermatids into mature, flagellated spermatozoa (sperms).

The process of transformation of a circular spermatid to a spermatozoon is called spermiogenesis.

Gametogenesis is the process by which male and female gametes are formed from germinal cells in the gonads through a series of developmental stages.

Formation of haploid sperms (male gametes) from diploid spermatogonia (sperm mother cells) is called spermatogenesis.

The formation of ova in the ovary from primordial germinal cells is said to be oogenesis.

Union of a male gamete with the egg cell to form a zygote is called fertilization.

The fusion of the male gamete (sperm) and female gamete (ovum) to form a zygote is called fertilisation.

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Formation of zygote by union of sperm and ovum is called as fertilization.

The formation of a zygote by the union of male and female gametes is known as fertilization.

A hollow embryonic stage formed after morula; in humans it is called blastocyst.

A series of rapid mitotic divisions of the zygote without increase in size is called cleavage.

Cleavage is the process of early mitotic division of the zygote to generate a multicellular morula stage.

The process of formation of blastula from morula is called blastulation.

An extra-embryonic sac involved in waste storage and placental development is called allantois.

A study of the development of an organism from fertilization to the formation of young one is known as embryogeny.

A solid, mulberry-like ball of cells formed after cleavage is called morula.

A disc-like structure attached to the uterine wall that supplies food and oxygen to the foetus and removes waste is called placenta.

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The intimate connection established between the foetal membrane and the uterine wall is known as placenta.

After nine months of pregnancy, the fully developed foetus is ready for delivery. The process of childbirth is called parturition.

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Parturition is the act of expelling the full term foetus from the mother's uterus at the end of gestation.

The term lactation refers to the secretion and ejection of milk by the mammary glands.

It is a technique in which amniotic fluid is withdrawn from the uterus of a pregnant lady and the amniotic cells are cultured and studied for cytological observations to determine any chromosomal abnormalities.

Azoospermia is defined as the absence of spermatozoa in the ejaculate semen on atleast two occasions and is observed approximately in 1% of the population.

The genetically identical offspring produced during asexual reproduction are called clones.

The formation of a resistant internal bud consisting of dormant cells in sponges to survive unfavourable conditions is called gemmule formation.

The mode of reproduction in which offspring are produced by a single parent without gamete formation and fertilisation is called asexual reproduction.

Sexual reproduction involving fusion of gametes is also called amphimixis.

The externally visible features that distinguish males and females are called secondary sexual characters.

Organs other than gonads that assist in reproduction are called secondary sex organs.

The organs that produce gametes, i.e., testis in males and ovary in females, are called primary sex organs.

The process in which a new individual develops from a small outgrowth (bud) on the parent body is called budding.

• Sexual reproduction involves the formation and fusion of male and female gametes to form a zygote, which develops into a new organism.
• It is a slow, complex, and energy-expensive process, but it results in offspring that are genetically different from parents and from each other.
• Genetic variation arises due to meiosis, DNA recombination, and fertilisation, which is essential for evolution and natural selection.
• To maintain chromosome number, haploid gametes are formed by meiosis and fuse during fertilisation.
• Organisms must pass through a juvenile (vegetative) phase before entering the reproductive phase, which is regulated by hormones.
• Sexual maturity is marked by puberty in animals and flowering in plants; plants may be monocarpic or polycarpic.
• Based on breeding time, animals are classified as seasonal breeders or continuous breeders.

1. Human reproductive organs are divided into primary (gonads) and accessory parts.
2. Primary gonads: Testes in males produce sperms; ovaries in females produce eggs.
3. Accessory organs include ducts and glands that aid in fertilisation and embryo development.
4. Secondary sexual characters (e.g., beard, breasts) are not reproductive parts, as they do not directly participate in reproduction.

• The male reproductive system is located in the pelvic region and consists of testes, ducts, glands, and external genitalia.
• A pair of testes present in the scrotum produce sperms in seminiferous tubules and secrete the hormone testosterone.
• Accessory ducts—rete testis, vasa efferentia, epididymis, vas deferens, and ejaculatory duct—transport and mature sperms.
• Accessory glands (seminal vesicles, prostate gland, and bulbourethral glands) add secretions that nourish sperms and aid their movement.
• The penis, containing the urethra, acts as the external genital organ for the delivery of sperms during ejaculation.

1. The female reproductive system includes a pair of ovaries, oviducts (fallopian tubes), a uterus, a vagina, and Bartholin’s glands.
2. All reproductive organs are located inside the abdominal cavity.
3. Ovaries release one ovum (egg) monthly after puberty, alternating between each ovary.
4. The egg enters the oviduct through its funnel-shaped end and is pushed towards the uterus by cilia.
5. Fertilisation usually occurs in the oviduct; the zygote implants in the uterus lining if formed.
6. The placenta connects the embryo to the mother for nutrient and waste exchange until birth.

• Ovaries are the primary female sex organs that produce ova and secrete the hormones estrogen and progesterone.
• They are almond-shaped, solid structures located in the lower abdominal cavity and attached by the mesovarium.
• Each ovary is covered by germinal epithelium and internally divided into cortex and medulla.
• The cortex contains ovarian follicles with immature oocytes, supported by granulosa cells.

• Mammary glands are paired structures in female mammals that develop fully after puberty and consist of lobes, alveoli, ducts, nipple and areola.
• The glandular tissue contains alveoli that produce milk, which is transported through ducts and released via the nipple.
• Milk secretion is stimulated by prolactin, while milk ejection (let-down reflex) is controlled by oxytocin after childbirth.
• The first milk secreted, called colostrum, is rich in antibodies and nutrients; after lactation or menopause, the glands undergo atrophy.

1. Fertilisation is the union of sperm and ovum to form a zygote and is internal in humans.
2. During copulation, millions of sperms are ejaculated into the vagina, but only one sperm fertilises the ovum in the oviduct.
3. The acrosome of the sperm releases enzymes that help it penetrate the egg membrane; chemical changes then prevent entry of other sperms.
4. Fusion of sperm nucleus and egg nucleus restores the diploid chromosome number (46) in the zygote.
5. From puberty to menopause (45–50 years), only about 400 ova are released; ageing oocytes may lead to chromosomal abnormalities if fertilised.
6. Gametes are formed by meiosis: sperms are of two types (22+X or 22+Y), while ova are of one type (22+X); meiosis in ova completes during fertilisation.

• Reproductive health, as defined by WHO, refers to complete physical, emotional, behavioural, and social well-being in all aspects related to reproduction.
• India’s Reproductive and Child Health (RCH) programmes aim to promote reproductive health through family planning, maternal and child care, awareness creation, and access to medical facilities.
• Education and awareness, including sex education for adolescents, help prevent myths, sexually transmitted diseases (STDs), unsafe practices, and promote hygienic and responsible sexual behaviour.
• Preventive measures such as menstrual hygiene, genital cleanliness, planned parenthood, immunisation, and statutory bans on sex determination are essential for a healthy society.
• Sexually transmitted diseases like syphilis and gonorrhoea adversely affect reproductive health, highlighting the need for early diagnosis, treatment, and improved medical infrastructure.

• Infertility is the inability of a couple to conceive despite regular, unprotected intercourse, and it may arise due to defects in the male partner, female partner, or both.
• Male infertility commonly results from poor sperm production or quality, such as oligospermia (low sperm count), azoospermia (absence of sperms), asthenozoospermia (poor motility), or teratozoospermia (abnormal structure).
• Female infertility may be caused by poor egg production, hormonal imbalance, defects in the ovaries, fallopian tubes, uterus, cervix, or improper functioning of fimbriae.
• Mechanical or physiological barriers, such as blockage of reproductive passages or thick cervical mucus, may prevent the meeting of sperm and egg, leading to infertility.
• Diagnosis and treatment involve identifying the underlying cause through medical tests and treating it by hormonal therapy, surgery, immunosuppressive drugs, or lifestyle modifications under medical supervision.