Why a Sperm Is Built for Speed and an Egg Is Built for Supplies
Learn the organs and accessory glands of the male reproductive system, the organs of the female reproductive system, how the structure of a sperm and an ovum suits each one's job, and the changes that appear in boys and girls at puberty.
How does the human body prepare to produce the next generation?
Every person begins as a single cell formed when a sperm from the father joins an ovum from the mother. Making these cells, bringing them together and protecting the baby that develops is the work of the reproductive system.
The testes and ovaries are the gonads, making sex cells called gametes as well as sex hormones. This part covers the male and female organs, the gametes and the changes of puberty.
The testes and ovaries are the gonads, making sex cells called gametes as well as sex hormones. This part covers the male and female organs, the gametes and the changes of puberty.
What are the organs of the male reproductive system, and what does each do?
The testes produce sperm and testosterone, a system of tubes stores and carries the sperm, and accessory glands add fluids that nourish and protect them, forming semen.
- Testes — a pair of oval organs that produce sperm and the hormone testosterone
- Scrotum — a pouch of skin outside the abdomen holding the testes, keeping them a little cooler than the body inside, which sperm production needs
- Epididymis — a long coiled tube on each testis where sperm are stored and mature
- Vas deferens — a tube that carries sperm from the epididymis towards the urethra
- Seminal vesicles — secrete a fluid containing fructose, a sugar that gives sperm energy
- Prostate gland — adds an alkaline fluid that helps sperm stay active
- Cowper's glands — secrete a clear lubricating fluid
- Urethra — a tube carrying urine or semen out through the penis
Semen is sperm together with the fluids of the three accessory glands.
An everyday example. An earthen matka keeps drinking water cooler than the room around it; in a similar way, the scrotum keeps the testes cooler than the rest of the body.
The substance. The urethra is a shared passage, but urine and semen never pass through it at the same time.
- Testes — a pair of oval organs that produce sperm and the hormone testosterone
- Scrotum — a pouch of skin outside the abdomen holding the testes, keeping them a little cooler than the body inside, which sperm production needs
- Epididymis — a long coiled tube on each testis where sperm are stored and mature
- Vas deferens — a tube that carries sperm from the epididymis towards the urethra
- Seminal vesicles — secrete a fluid containing fructose, a sugar that gives sperm energy
- Prostate gland — adds an alkaline fluid that helps sperm stay active
- Cowper's glands — secrete a clear lubricating fluid
- Urethra — a tube carrying urine or semen out through the penis
Semen is sperm together with the fluids of the three accessory glands.
An everyday example. An earthen matka keeps drinking water cooler than the room around it; in a similar way, the scrotum keeps the testes cooler than the rest of the body.
The substance. The urethra is a shared passage, but urine and semen never pass through it at the same time.
What are the organs of the female reproductive system, and what does each do?
The ovaries produce ova and female hormones, the fallopian tubes carry the ovum and are where fertilisation happens, the uterus holds and nourishes the developing baby, and the vagina connects the uterus to the outside.
- Ovaries — a pair of almond-shaped organs in the lower abdomen that produce ova and the hormones oestrogen and progesterone
- Fallopian tubes (oviducts) — each has a funnel with finger-like fringes near an ovary that catches the released ovum; fertilisation takes place here, and cilia and muscles move the ovum along
- Uterus — a hollow, muscular, pear-shaped organ with a thick inner lining; the embryo implants in this lining and develops here
- Cervix — the narrow neck of the uterus opening into the vagina
- Vagina — a muscular tube that receives sperm and serves as the birth canal
An everyday example. At a godh bharai ceremony, the rounded belly of the mother-to-be is her uterus, stretched many times its usual size by the growing baby; its muscular wall will later contract strongly during birth.
The misconception. Fertilisation does not happen in the uterus. It happens in the fallopian tube, and the embryo then travels to the uterus to implant.
- Ovaries — a pair of almond-shaped organs in the lower abdomen that produce ova and the hormones oestrogen and progesterone
- Fallopian tubes (oviducts) — each has a funnel with finger-like fringes near an ovary that catches the released ovum; fertilisation takes place here, and cilia and muscles move the ovum along
- Uterus — a hollow, muscular, pear-shaped organ with a thick inner lining; the embryo implants in this lining and develops here
- Cervix — the narrow neck of the uterus opening into the vagina
- Vagina — a muscular tube that receives sperm and serves as the birth canal
An everyday example. At a godh bharai ceremony, the rounded belly of the mother-to-be is her uterus, stretched many times its usual size by the growing baby; its muscular wall will later contract strongly during birth.
The misconception. Fertilisation does not happen in the uterus. It happens in the fallopian tube, and the embryo then travels to the uterus to implant.
How are a sperm and an ovum built, and how does each structure suit its function?
A sperm is tiny and streamlined, with a head carrying genetic material, a middle piece full of mitochondria and a tail for swimming; an ovum is large, round and non-moving, packed with cytoplasm and stored food and protected by coverings.
Structure of a sperm:
- Head — contains a nucleus with 23 chromosomes; at its tip is the acrosome, holding enzymes that dissolve a path through the coverings of the ovum
- Middle piece — packed with mitochondria that release energy for swimming
- Tail — beats to move the sperm forward
Structure of an ovum:
- Large and round, one of the largest cells in the body
- Nucleus with 23 chromosomes
- Plenty of cytoplasm with some stored food, to supply the early embryo
- Protective membranes and a layer of follicle cells around it
- Cannot move by itself; it is moved along the oviduct
How structure suits function. Sperm are numerous, light and mobile because they must travel far; the ovum is usually released singly and well stocked because it must feed the early embryo.
An everyday example. A Mumbai dabbawala cycles fast carrying only the lunch box, while the kitchen at home holds all the supplies — the sperm is the courier, the ovum the stocked kitchen.
The substance. The sex of the baby is decided by the sperm, which carries either an X or a Y chromosome; the ovum always carries an X.
Structure of a sperm:
- Head — contains a nucleus with 23 chromosomes; at its tip is the acrosome, holding enzymes that dissolve a path through the coverings of the ovum
- Middle piece — packed with mitochondria that release energy for swimming
- Tail — beats to move the sperm forward
Structure of an ovum:
- Large and round, one of the largest cells in the body
- Nucleus with 23 chromosomes
- Plenty of cytoplasm with some stored food, to supply the early embryo
- Protective membranes and a layer of follicle cells around it
- Cannot move by itself; it is moved along the oviduct
How structure suits function. Sperm are numerous, light and mobile because they must travel far; the ovum is usually released singly and well stocked because it must feed the early embryo.
An everyday example. A Mumbai dabbawala cycles fast carrying only the lunch box, while the kitchen at home holds all the supplies — the sperm is the courier, the ovum the stocked kitchen.
The substance. The sex of the baby is decided by the sperm, which carries either an X or a Y chromosome; the ovum always carries an X.
What secondary sexual characters develop in boys and girls at puberty?
At puberty, testosterone brings a deeper voice, facial hair and a more muscular body in boys, while oestrogen brings breast development, wider hips and the start of menstruation in girls.
Secondary sexual characters develop at puberty under sex hormones, usually in the early teens and often a little earlier in girls.
In boys (testosterone):
- Voice deepens as the voice box enlarges
- Hair grows on the face, chest, armpits and pubic region
- Shoulders broaden and muscles develop
- Sperm production begins
In girls (oestrogen):
- Breasts develop
- Hips widen
- Hair grows in the armpits and pubic region
- Menstruation begins
In both: a growth spurt, more active oil and sweat glands that can cause pimples, and emotional changes.
An everyday example. Outgrowing a school uniform within a year in Class 7 or 8 is a sign of the growth spurt that comes with puberty.
The substance. The age at which these changes begin varies widely between healthy children, so starting earlier or later than classmates is usually normal.
Secondary sexual characters develop at puberty under sex hormones, usually in the early teens and often a little earlier in girls.
In boys (testosterone):
- Voice deepens as the voice box enlarges
- Hair grows on the face, chest, armpits and pubic region
- Shoulders broaden and muscles develop
- Sperm production begins
In girls (oestrogen):
- Breasts develop
- Hips widen
- Hair grows in the armpits and pubic region
- Menstruation begins
In both: a growth spurt, more active oil and sweat glands that can cause pimples, and emotional changes.
An everyday example. Outgrowing a school uniform within a year in Class 7 or 8 is a sign of the growth spurt that comes with puberty.
The substance. The age at which these changes begin varies widely between healthy children, so starting earlier or later than classmates is usually normal.
Exam tip
What earns full marks on reproductive organs and gametes?
Label diagrams completely, give one function per organ, and link each part of a gamete to its job.
- Male diagram: testis, scrotum, epididymis, vas deferens, seminal vesicle, prostate, Cowper's gland, urethra, penis
- Female diagram: ovary, fallopian tube with funnel, uterus, cervix, vagina
- State the site of fertilisation as the fallopian tube
- Sperm: acrosome, nucleus, mitochondria, tail — each with its function
- Ovum: large size, stored food, coverings
- Separate the hormone responsible for secondary characters in each sex
The trap. Writing that the vas deferens produces sperm. Sperm are produced in the testes; the vas deferens only carries them.
- Male diagram: testis, scrotum, epididymis, vas deferens, seminal vesicle, prostate, Cowper's gland, urethra, penis
- Female diagram: ovary, fallopian tube with funnel, uterus, cervix, vagina
- State the site of fertilisation as the fallopian tube
- Sperm: acrosome, nucleus, mitochondria, tail — each with its function
- Ovum: large size, stored food, coverings
- Separate the hormone responsible for secondary characters in each sex
The trap. Writing that the vas deferens produces sperm. Sperm are produced in the testes; the vas deferens only carries them.
Did you know
Why does a boy's voice crack during puberty?
Some teenage boys find their voice suddenly jumping from deep to squeaky in the middle of a sentence.
Testosterone makes the voice box and vocal cords grow longer and thicker over a fairly short time. Longer, thicker cords vibrate more slowly, giving a deeper sound.
While the cords are changing, the brain is still learning to control them, so the pitch sometimes slips. Once growth settles, the voice steadies at its new, lower pitch.
Testosterone makes the voice box and vocal cords grow longer and thicker over a fairly short time. Longer, thicker cords vibrate more slowly, giving a deeper sound.
While the cords are changing, the brain is still learning to control them, so the pitch sometimes slips. Once growth settles, the voice steadies at its new, lower pitch.
Exam relevance
How do reproductive organs and gametes lead into NEET Biology?
This is foundation work for Class 12 Human Reproduction in NEET Biology.
What gets built on. The chapter describes the seminiferous tubules of the testis, with Sertoli cells that nourish developing sperm and Leydig cells that make testosterone, the Graafian follicle in the ovary, and the processes of spermatogenesis and oogenesis that form haploid gametes. The detailed structure of a sperm and the coverings of the ovum reappear there, followed by fertilisation and implantation.
Question types. Labelled diagrams of the reproductive systems and of a sperm, and match-the-column items pairing structures with functions.
The trap that costs marks. Swapping the roles of Sertoli cells, which nourish sperm, and Leydig cells, which secrete testosterone.
What gets built on. The chapter describes the seminiferous tubules of the testis, with Sertoli cells that nourish developing sperm and Leydig cells that make testosterone, the Graafian follicle in the ovary, and the processes of spermatogenesis and oogenesis that form haploid gametes. The detailed structure of a sperm and the coverings of the ovum reappear there, followed by fertilisation and implantation.
Question types. Labelled diagrams of the reproductive systems and of a sperm, and match-the-column items pairing structures with functions.
The trap that costs marks. Swapping the roles of Sertoli cells, which nourish sperm, and Leydig cells, which secrete testosterone.
Key takeaways
What must you be able to do from this part?
- Testes make sperm and testosterone; scrotum keeps them cooler
- Epididymis stores sperm; vas deferens carries them
- Seminal vesicles, prostate and Cowper's glands add fluids to form semen
- Ovaries make ova, oestrogen and progesterone
- Fallopian tube is the site of fertilisation; uterus holds the embryo; vagina is the birth canal
- Sperm: acrosome, nucleus, mitochondria-rich middle piece, tail
- Ovum: large, non-moving, stored food, protective coverings
- Puberty: testosterone in boys, oestrogen in girls bring secondary sexual characters
Sketch a sperm and an ovum side by side from memory, and see whether you can write one reason for every feature you draw.
- Epididymis stores sperm; vas deferens carries them
- Seminal vesicles, prostate and Cowper's glands add fluids to form semen
- Ovaries make ova, oestrogen and progesterone
- Fallopian tube is the site of fertilisation; uterus holds the embryo; vagina is the birth canal
- Sperm: acrosome, nucleus, mitochondria-rich middle piece, tail
- Ovum: large, non-moving, stored food, protective coverings
- Puberty: testosterone in boys, oestrogen in girls bring secondary sexual characters
Sketch a sperm and an ovum side by side from memory, and see whether you can write one reason for every feature you draw.