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.

Lifespan is the duration or period from birth to the natural death of an organism.

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 through cell division and later becomes a new individual, this 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.

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.

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

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.

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

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

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

The remnant of the follicle persists for some time 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.

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

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

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

The external female genitalia is called the vulva.

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.

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

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.

Puberty is the period during which the immature reproductive systems of boys and girls mature and become 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.

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).

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.

Gametogenesis is the process by which male and female primary sex organs produce gametes (sperms and ova).

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

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.

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

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

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The formation of a zygote by the union of a sperm and an ovum is called fertilization.

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

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

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

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

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

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

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

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.

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

Sexual reproduction involving fusion of gametes is also called amphimixis.

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

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

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

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

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

• 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.
• Lifespan = period from birth to natural death; ranges from 1 day (Mayfly) to 3,000–4,000 years (Sequoia).
• Two Types - All methods of reproduction fall into two categories: Asexual Reproduction and Sexual Reproduction.
• Single-celled organisms (Amoeba, Bacteria) do not undergo natural death — they divide by binary fission.
• Four life stages: Juvenile → Reproductive → Senescent → Death.
• In plants, the reproductive phase begins at flowering.
• Monocarpic plants flower once; Polycarpic plants flower every season.
• Asexual reproduction = one parent, clones produced, faster.
• Sexual reproduction = two parents, gametes, zygote formed, genetic variation.
• The three phases of sexual reproduction: Pre-fertilisation → Fertilisation → Post-fertilisation.

• 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.

• Freshwater sponges like Spongilla (and some marine sponges) reproduce asexually by forming specialised internal buds called gemmules, unlike Hydra, which reproduces by external budding.
• A gemmule has a central mass of archaeocytes - undifferentiated cells capable of forming a new sponge - surrounded by a resistant protective coat secreted by amoebocytes.
• Under unfavourable conditions such as drying or thermal stress, archaeocytes aggregate within the sponge body, and a protective layer forms around them, developing into a dormant, resistant gemmule.
• When favourable water and temperature conditions return, the gemmule germinates, and its archaeocytes become active, forming a new sponge.

• In multicellular organisms like Hydra, a bud grows on the parent body through cell division and later detaches to become a new individual.
• The bud arises from repeated multiplication of epidermal interstitial cells, contains both epidermis and gastrodermis, and its cavity stays continuous with the parent's gastrovascular cavity.
• As it grows, the bud develops a mouth and tentacles, then separates and attaches to a surface by its basal disc to live independently as a new Hydra.

• Regeneration is the process by which an organism regrows lost or damaged body parts - or forms a complete new individual from a body fragment - using specialised cells that multiply repeatedly and differentiate into various tissues.
• In Hydra and Planaria, a cut body fragment can regenerate the missing parts and grow into a complete organism (genetically similar clones), making it a form of asexual reproduction.
• Starfish also show strong regenerative ability, where a body fragment can, in some cases, grow into a complete new starfish, reflecting the high regenerative capacity of lower animals.

• Sexual reproduction involves the formation and fusion of male and female gametes (amphimixis) through meiotic division to create a diploid zygote.
• Life cycles progress from an initial juvenile phase focused purely on vegetative growth and development to a mature reproductive phase in which sex organs become functional.
• The reproductive process is strictly regulated by hormones and sequence-driven, consisting of three sequential stages: pre-fertilisation, fertilisation, and post-fertilisation.
• Pre-fertilisation focuses on gamete production and transfer, while post-fertilisation events track zygote development and the formation of embryonic structures.
• Meiotic cell division and cross-fertilisation blend parental genetic material, generating the vital variations needed to drive species adaptation and organic evolution.

• Humans are sexually reproducing and viviparous (giving birth to young ones, not eggs).
• 6 stages of reproduction in order: Gametogenesis → Insemination → Fertilisation → Implantation → Gestation → Parturition.
• Gametogenesis (gamete formation), Insemination (sperm transfer), Fertilisation (fusion → zygote), Implantation (blastocyst attaches to uterine wall), Gestation (embryo development), Parturition (delivery of baby).
• Sperm formation continues throughout a man's life; ovum formation ceases at around age fifty (menopause) in women.
• Testes (males) produce sperm; Ovaries (females) produce eggs; these are the primary reproductive organs (gonads).
• Features like beards (males) and breasts (females) are secondary sexual characteristics; 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.

• Semen is a viscous, milky, and alkaline fluid (pH 7.2 to 7.7) consisting of sperm suspended in accessory gland secretions.
• These secretions nourish the sperm (via fructose), neutralise vaginal acidity (via calcium and bicarbonates), and stimulate motility (via prostaglandins).
• An average ejaculation yields 2.5 to 5 ml of fluid, with sperm cells making up only about 10% of the total semen volume.
• Upon ejaculation, semen temporarily coagulates due to the protein fibrinogen, then liquefies after approximately 20 minutes due to the enzyme plasmin.
• Male sterility can be indicated by a sperm count below 20 × 10⁶ per ml, high numbers of non-motile or abnormal sperm, oligospermia (abnormally low sperm count), or azoospermia (complete absence of sperm).

• 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 the vagina via the 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 newborns. 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 containing 15 to 20 lobes with milk-producing alveoli, ducts, a pigmented areola, and a nipple.
• The hormone prolactin stimulates the alveoli to produce milk, while oxytocin triggers its ejection following childbirth.
• The initial milk secreted, known as colostrum, is highly concentrated with essential nutrients and antibodies for the newborn.
• Following the period of lactation or the onset of menopause, the glandular tissue naturally shrinks and undergoes atrophy.
• Weaning is the gradual developmental process of replacing a mother's milk with solid foods in an infant's diet.
• Clinically, breast cancer often presents as a painless lump, is diagnosed through mammograms or biopsies, and is treated with surgery, radiation, or chemotherapy.

• Puberty marks the transition to reproductive maturity, starting around age 10 for girls (thelarche) and age 11 for boys (gonadarche).
• Girls experience breast development, hip widening, and the onset of menstruation (menarche) driven by rising estrogen, FSH, and LH.
• Boys develop increased muscle mass, broader shoulders, facial hair, and a deepening voice due to elevated testosterone.
• Both sexes undergo a rapid growth spurt and develop pubic and axillary hair influenced by sex and growth hormones.
• Hormonal shifts increase skin and sweat gland activity, commonly leading to acne and heightened emotional and psychological changes.

• 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.

• Maintain proper hygiene during menstruation to prevent infections.
• Keep the pubic area clean by washing regularly.
• Change sanitary napkins every 4–5 hours or as needed.
• Use clean and dry sanitary products; avoid damp or dirty cloths.
• Dispose of used sanitary napkins properly in a hygienic manner.
• Poor hygiene or prolonged use of napkins can lead to the growth of harmful bacteria and infections.

• Gametogenesis is the process of formation of male and female gametes in the reproductive organs.
• It occurs in the testes of males and ovaries of females.
• Spermatogenesis produces sperms, while oogenesis produces ova (eggs).
• In this process, diploid germ cells form haploid gametes for sexual reproduction.

• Fertilization 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 fertilization, 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).
• Fertilization 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.

• Following fertilization, the single-celled zygote undergoes rapid mitotic divisions known as cleavage to form a solid, multicellular ball of cells termed the morula.
• The morula continues to divide and transforms into a hollow structure called the blastocyst, which consists of an outer trophoblast layer and an inner cell mass.
• By approximately the seventh day post-fertilization, the blastocyst embeds itself into the endometrial lining of the mother's uterus in a critical process called implantation.
• The inner cell mass subsequently undergoes gastrulation, a phase where it differentiates into three primary embryonic germ layers: the ectoderm, mesoderm, and endoderm.
• During organogenesis, these three germ layers systematically give rise to all specific tissues, internal organs, and organ systems, typically beginning with the formation of the heart.
• A temporary structural and functional organ known as the placenta develops from trophoblastic and maternal tissues to facilitate the essential exchange of nutrients, gases, and wastes.
• The complete sequence of embryonic and foetal development is sustained throughout a gestation period of approximately nine months, ultimately culminating in childbirth.

• Meaning – The 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 – The 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 neuroendocrine 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 afterbirth (placenta removal).

• Lactation involves the mammary glands secreting and ejecting milk to nourish and protect the newborn, initiated after childbirth.
• Prolactin, released by the anterior pituitary, stimulates alveolar cells to produce milk, a process called lactogenesis.
• Oxytocin, from the posterior pituitary, triggers the let-down reflex by causing myoepithelial cells to contract and eject milk when the baby suckles.
• Colostrum, the initial yellowish milk produced for a few days post-birth, is low in fat but highly concentrated in proteins, lactose, and essential antibodies.
• The abundant IgA antibodies present in colostrum transfer crucial natural passive immunity to the infant, protecting them while their own immune system develops.

• 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.