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.

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.

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.

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

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 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.

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

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

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

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

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.

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.

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

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).

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 primary sex organs produce gametes (sperms and ova).

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.

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.

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.

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.

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

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.

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

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.

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

Special cells present in multicellular organisms that have the ability to give rise to all other types of cells and help in growth and wound healing is called stem cells.

Stem cells are specialised cells that give rise to all other types of cells present in the body of multicellular organisms.

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.

Birth Control refers to the regulation of conception by preventive methods or devices to limit the number of offspring.

Amniocentesis is a technique used to diagnose fetal abnormalities by drawing a sample of amniotic fluid by a hypodermic needle inserted through the mother’s abdomen into the uterus

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.

• Meaning - Reproduction is the production of young ones similar to their parents. It is an essential biological process for the continuation of the species and continuity of life.
• Two Types - All methods of reproduction fall into two categories: Asexual Reproduction and Sexual Reproduction.
• Asexual Reproduction - New individuals are produced without the fusion of gametes. Offspring are genetically identical to the parent (clones).
• Sexual Reproduction - Involves the fusion of male and female gametes, resulting in offspring with genetic variation from both parents.

• Meaning - Asexual reproduction involves only one parent, produces no fusion of gametes, and results in offspring that are genetically identical to the parent, called clones.
• Modes of Asexual Reproduction - Common methods include Binary Fission (Amoeba, Paramoecium), Fragmentation (Spirogyra), Budding (Yeast, Protosiphon), Spore Formation/Zoospores (Chlamydomonas), Conidia (Penicillium), and Gemmules (Marchantia).
• In Plants - Asexual reproduction in plants is called Vegetative Propagation. It can be Natural or Artificial (e.g., cutting, grafting, tissue culture).
• In Animals — Common in lower animals only. Does not involve meiosis or gamete formation. Lower animals reproduce asexually by budding and gemmule formation.
• Key Feature — Since only one parent is involved and no fusion occurs, all offspring are morphologically and genetically identical (clones) to the parent.

• Lower organisms like Spongilla and Hydra reproduce asexually by gemmule formation and budding, respectively.
• A gemmule is an internal bud formed only in sponges — it is an asexually produced mass of dormant cells called archaeocytes, capable of developing into a new organism.
• Archaeocytes get coated by a thick, resistant layer secreted by amoebocytes. Gemmules are formed to survive unfavourable conditions.
• On return of favourable conditions (water and temperature), gemmules hatch and develop into a new individual. e.g., Spongilla.

• Sexual reproduction involves the formation and fusion of male and female gametes (amphimixis) to form a zygote, with gamete formation by meiosis.
• It occurs in two phases: juvenile phase (no reproduction) and reproductive phase (sex organs active), regulated by hormones.
• It includes three main events: pre-fertilisation (gamete formation and transfer), fertilisation (fusion of gametes), and post-fertilisation (zygote and embryogenesis).
• Sexual reproduction produces genetic variation due to meiosis, recombination, and fertilisation, which is important for evolution.
• Primary sex organs (testes, ovaries) produce gametes, and organisms may be seasonal or continuous breeders depending on the reproduction pattern.

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 includes testes, accessory ducts, accessory glands, and external genitalia (penis and scrotum).
• Testes are the primary sex organs present in the scrotum; they contain seminiferous tubules where sperm are produced, while Leydig cells secrete testosterone, and Sertoli cells provide nourishment.
• Accessory ducts—rete testis → vasa efferentia → epididymis → vas deferens → ejaculatory duct → urethra—help in storage, maturation, and transport of sperm.
• Accessory glands—seminal vesicles, prostate gland, and bulbourethral glands—add secretions like fructose, enzymes, and mucus, which nourish sperms and aid in their movement.
• The penis acts as the external genital organ, containing the urethra, and helps in the transfer of sperm during ejaculation.

• Includes — Ovaries, Fallopian tubes, Uterus, Cervix, Vagina, External genitalia, Bartholin's glands, Mammary glands — all in the pelvic region.
• Ovaries — outer cortex (follicles) + inner medulla; produce ova and ovarian hormones; release one ovum monthly after puberty.
• Fallopian tube — 3 parts: Infundibulum (fimbriae collect ovum) → Ampulla (site of fertilisation) → Isthmus (connects to uterus); cilia push egg towards uterus.
• Uterus — 3 layers: Perimetrium (outer), Myometrium (muscular), Endometrium (inner, menstrual changes); opens into vagina via cervix (birth canal).
• Zygote implants in the endometrium; the placenta connects the embryo to the mother for nutrient and waste exchange till birth.
• External genitalia — Mons pubis, Labia majora, Labia minora, Hymen, Clitoris. Bartholin's glands provide lubrication.
• Mammary glands — produce milk for newborn. Puberty begins at 10–14 years in females.

• 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.

• The menstrual cycle is a series of monthly changes in females of reproductive age.
• The beginning of the cycle is called menarche, and its permanent stop is called menopause (around 45–50 years).
• It occurs mainly in primates, including humans, and involves changes in the ovaries and uterus.
• The cycle is controlled by hormones (gonadotropins and ovarian hormones) and repeats every ~28 days.
• In the middle of the cycle, ovulation occurs, where an egg is released from one of the ovaries.

• Fertilisation in humans is the fusion of male and female gametes (sperm and ovum) and is an internal process occurring in the oviduct, leading to the formation of a diploid zygote.
• During copulation, millions of sperms are released into the vagina, but only one sperm reaches the ovum due to selection and protective barriers around the egg.
• Before fertilisation, sperm undergo capacitation and move towards the ovum; interaction between sperm and egg involves recognition molecules like fertilizin (ovum) and antifertilizin (sperm).
• The sperm’s acrosome releases enzymes that help digest the egg coverings (corona radiata and zona pellucida), allowing sperm entry through the membrane.
• After entry, the sperm nucleus and the ovum nucleus fuse (syngamy), forming a zygote (2n); this process restores the diploid chromosome number (46 in humans).
• Fertilisation triggers completion of meiosis II in the oocyte, formation of the second polar body, and formation of the female pronucleus and male pronucleus.
• In humans, sperm carry 22+X or 22+Y chromosomes, while ova carry 22+X only, determining the genetic sex of the offspring.

• Meaning - Placenta is a temporary structural and functional connection between foetal and maternal circulation, formed by chorionic villi (finger-like projections of trophoblast) interdigitating with uterine tissue and maternal blood.
• Attachment - The placenta is attached to the wall of the uterus on one side and connected to the baby via the umbilical cord on the other side.
• Umbilical cord - Contains two small arteries (carry blood towards the placenta) and one large vein (returns blood to the foetus).
• Functions - Supplies oxygen and nutrients to the foetus; removes CO₂ and excretory wastes from foetal blood to maternal blood.
• Hormones produced - Placenta produces hCG (human Chorionic Gonadotropin), hPL (human Placental Lactogen), Oestrogen, and Progesterone. By the end of the 1st trimester, progesterone production shifts to the placenta.

• Parturition is the process of childbirth, i.e., the delivery of the foetus at the end of the gestation period.
• It is controlled by a neuro-endocrine mechanism involving signals from the fully developed foetus and placenta.
• Foetal signals trigger uterine contractions known as the foetal-ejection reflex (labour pain).
• Hormones like ACTH and corticosteroids from the foetus stimulate the release of oxytocin from the mother’s pituitary gland.
• Parturition occurs in three stages: dilation, expulsion of the baby, and after birth (placenta removal).

• Lactation is the process by which mammary glands produce milk at the end of pregnancy, under the influence of the hormone Prolactin.
• The first milk secreted soon after childbirth is called Colostrum — it is sticky, yellowish and rich in proteins, lactose and antibodies (IgA); fat content is low.
• Antibodies (especially IgA) in colostrum provide passive immunity to the newborn when its own immune system is not yet fully developed.
• Lactation helps the mother in feeding and nourishing the newborn baby, providing all essential nutrients required in early life.

• 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 to conceive after 12 months or more of regular unprotected intercourse and may be due to male, female, or both partners.
• Male infertility includes low sperm count, no sperm production, poor sperm motility, or abnormal sperm structure.
• Female infertility may result from hormonal imbalance, poor egg production, or defects in reproductive organs like the ovaries, fallopian tubes, uterus, or cervix.
• Mechanical or physiological problems, such as blocked reproductive tracts or thick cervical mucus, can prevent fertilisation.
• Infertility is diagnosed and treated by identifying the cause and using methods like hormonal therapy, surgery, or lifestyle changes.
• Assisted Reproductive Technologies (ART) help infertile couples and include IVF, ICSI, GIFT, ZIFT, AI, and IUI, which assist in fertilisation and conception.