- It is the process by which an individual multiplies in number by producing more individuals of its own type.
- Basic Features of Reproduction include :
- Synthesis of RNA and proteins
- Replication of DNA
- Cell division
- Formation of reproductive units or bodies
- Development of reproductive units into young ones.
- Types of Reproduction
- I. Asexual Reproduction
- II. Sexual Reproduction
I. Asexual Reproduction
- Asexual Reproduction is the process of multiplication of individuals without the formation or fusion of gametes.
- It involves a single parent and the young ones produced through it are genetically similar to the parent.
- Asexual reproduction occurs in several ways :
1. Binary Fission
- It involves the division of the nucleus followed by that of the cytoplasm, breaking the body into two young ones.
- It occurs in unicellular organisms, e.g., Amoeba, Euglena, Paramecium, etc.
2. Multiple Fission
- In this the nucleus divides into several daughter nuclei, followed by the simultaneous division of the cytoplasm.
- The nuclei move towards the periphery and each one is surrounded by small amount of cytoplasm which gives rise to new daughter cells.
- It occurs in protozoa e.g., Plasmodium.
- In many protozoa and bacteria the asexual reproduction occurs by the division of nucleus into several daughter nuclei, and then each daughter nucleus gets enclosed by small amount of cytoplasm to form a spore.
- Budding is an unequal division of the parent where the identity of the parent body is still maintained.
- It is in contrast to binary fission where parent body divides equally into two and no identity of the parent is left.
- Bud is an outgrowth formed on the surface of the body which finally gets detached and develops into a young one.
- It is common in Hydra.
- The body may break into two or more fragments, and each fragment develops into a complete individual e.g., Filamentous algae, Spirogyra.
II. Sexual Reproduction
- The process of sexual reproduction involves the formation and fusion of gametes (Syngamy) and results in the formation of a new organism genetically different from parent.
- Sexual reproduction is usually biparental, i.e., involves a male and a female individual producing a male and a female gamete respectively.
- Such animals are called unisexual or dioecious e.g., frog, cockroach, humans.
- In certain animals, the male and female sex organs are present in the same individual.
- Such species are called monoecious or bisexual. e.g., earthworm, leech.
- Parthenogenesis is a specialized reproduction in which eggs develop without fertilization e.g., bees, ants, wasps, etc.
Mammalian Reproductive System
- The reproductive system of sexually reproducing animals consists of :
- Primary Sex Organs (called gonads) which produce gametes and hormones.
- Secondary Sex Organs / Glands which participate in reproduction but do not form gametes.
- Accessory Sex Organs / Characters which distinguish the two sexes in appearance.
Primary Sex Organs
Secondary Sex Organs
Accessory or External Sex Character
Epididymis Vas deferens Ejaculatory duct Urethra Seminal vesicle Prostate Gland Cowper's gland Penis
Low pitch voice Beard Broad shoulder Narrow hips
Fallopian tubes (oviducts) Uterus Vagina External Genitalia / Vulva Bartholian's Gland Mammary glands
High pitch voice Smooth face Narrow shoulder Broad hips
Male Reproductive System
I. Testes – Primary Sex Organs
- Testes are paired structures which lie outside the abdominal cavity in a thin pouch skin called scrotum.
- Temperature of scrotum is 2°C below the body temperature.
- Testis contains 1 to 3 seminiferous tubules which are embedded in loose interstitial connective tissue containing blood capillaries, nerve fibres and numerous small groups of large glandular cells called interstitial cells or cells of Leydig which secrete male hormone, testosterone.
- Testosterone shows the onset of puberty and also maintains spermatogenesis and libido (sexual urge).
II. Secondary Sex Organs
- 1. Epididymis :
- It stores sperms prior to ejaculation and contributes to seminal fluid, for nourishing sperms and providing them motility.
- 2. Vas Deferens :-
- They conduct sperms.
3. Ejaculatory Duct :
- Aids in the emission of the seminal fluid.
4. Urethra :
- It leads from urinary bladder through the prostate gland and into the penis.
- It forms the outflow pathway for the urine and for the seminal fluid.
5. Seminal Vesicles :
- They secrete viscous fluid which constitute the main part of the ejaculate.
- Seminal fluid contains fructose (as a source of energy which provide nourishment for the activity of sperm), citric acid and prostaglandins (these two stimulate the movement of sperms in female tract).
6. Prostate Gland :
- It contributes an alkaline component to the seminal fluid for sperm motility.
- It helps the sperms to become active and counteracts any adverse effect urine may have on the sperms.
- It also provides a characteristic odour to the seminal fluid.
7. Cowper’s Gland :
- It secretes a clear, viscous mucous which is lubricating in function.
8. Penis :
- It is a cylindrical and highly vascularised copulatory organ.
- The tip of the penis is called glans penis.
- The penis contains three cylindrical strands of erectile tissue: two corpora cavernosa and the corpus spongiosum which contains the urethra.
- During sexual excitement, the elastic covernosa spaces become filled with blood which then compresses the penile vein through the centre of the body of the penis.
- Since no blood flows out of the penis, it becomes enlarged and erect.
- Female Reproductive System
I. Ovary – Primary Sex Organ
- The two ovaries are small bodies which remain attached to the abdominal wall.
- Produce ova or egg. Normally, only one egg matures in each ovary every alternate month.
1. Fallopian Tubes (or Oviducts) :
- Extend from Ovary to the Uterus. Their muscular contractions push the egg down into the uterus.
- Oviducts also Transport Spermatozoa from the Uterus towards the ovary and produce trophic substances that ensure the Development of Fertilized Conceptus.
2. Uterus :
- It is situated in the pelvic cavity between the urinary bladder and the rectum. Its walls are composed of smooth muscle fibres called myometrium.
- The uterus is the site for implementation of the pre – embryo and for the subsequent embryonic and foetal development.
3. Vagina :
- It is a muscular tube starting from the lower end of the uterus up to the outside.
- The vagina receives the male penis during copulation.
- The great elasticity of its wall also allows the passage of the baby during childbirth.
- The opening of the vagina in young females is partially closed by a thin membrane called hymen.
- The hymen is frequently ruptured in childhood due to exercise or disease.
4. Vulva :
- The external female genitalia is called the vulva.
- In the upper – most angle of the vulva, in front of the urethral opening is located a small erectile clitoris which is highly sensitive as it contains numerous sensory nerve endings for touch and pressure.
5. Bartholin’s Glands :
- A pair of small glands which occur one on each side of the vaginal opening.
- These glands correspond to Cowper’s gland of male.
- The secretion of this gland is thick, viscous and alkaline for lubrication during copulation.
6. Mammary Glands :
- They are modified sweat glands that lie over the pectoral muscles.
- They are also present in males but in a rudimentary form.
- Internally each gland has 15 – 20 lobulated milk glands each having a number of lobules containing number of alveoli.
- Its secretion is under the control of prolactin hormone (of pituitary) while milk ejection is under the control of oxytocin hormone.
- Process of formation of gametes in gonads.
- It includes spermatogenesis (formation of sperms by the testes) and oogenesis (formation of eggs by the ovaries).
- It is controlled by gonadotrophic hormones (FSH, LH, ICSH, etc.) secreted by pituitary gland.
- Meiosis forms the most significant part of the process of gametogenesis.