3. Life Processes in Living Organisms — Part 2
Reproduction (Asexual & Sexual) • Modern Reproductive Technology • Reproductive Health • Population Explosion
Intro & Key Questions
Asexual Reproduction
Sexual Reproduction — Overview
Sexual Reproduction in Plants
Seed Germination
Sexual Reproduction in Humans
Menstrual Cycle
Reproduction & Modern Technology
Reproductive Health
Population Explosion
Can you recall?
- Important life processes in organisms?
- Which processes supply energy to the body?
- Main types of cell division (mitosis vs meiosis) and differences?
- Role of chromosomes in cell division?
Reproduction does not keep an individual alive, but maintains the continuity of the species.
Formation of a new organism from an existing one of the same species is called reproduction.
Reproduction: Asexual
Definition: Formation of a new organism without fusion of gametes. It is uniparental and usually involves mitosis; offspring are genetically identical to the parent (no recombination).
A. In unicellular organisms
- Binary fission — Parent cell divides into two similar daughter cells (bacteria, Amoeba, Paramecium, Euglena; also mitochondria & chloroplasts).
- Simple (Amoeba; random plane)
- Transverse (Paramecium)
- Longitudinal (Euglena)
- Multiple fission — Under adverse conditions the cell forms a cyst; repeated nuclear division followed by cytoplasmic division produces many daughter cells (amoebulae). Cyst breaks under favourable conditions.
- Budding in yeast — A small bulge forms, one daughter nucleus enters the bud; after growth the bud separates to form a new yeast cell.
B. In multicellular organisms
- Fragmentation — Parent body breaks into pieces; each fragment forms a new individual (Spirogyra, Sycon).
- Regeneration — Replacement of lost parts (limited: lizard tail). In Planaria, each half can regenerate the missing part → two new worms.
- Budding in Hydra — Repeated division of regenerative cells forms an outgrowth; bud shares cavity with parent, then detaches.
- Vegetative propagation (plants) — Using vegetative parts:
- Potato tuber “eyes”
- Bryophyllum leaf margin buds
- Sugarcane and grasses: nodes with buds
- Spore formation (fungi) — Mucor forms sporangia; spores disperse and germinate in warm, moist conditions.
Quick compare: Asexual is fast, needs only one parent, but no genetic variation (except mutations) — a drawback in changing environments.
Reproduction: Sexual — Overview
Two key steps
- Gamete formation: By meiosis → haploid (n) gametes.
- Fertilization: Fusion of male and female gametes → diploid zygote → embryo (mitosis) → new individual.
Why sexual? Genetic recombination & independent assortment create variation → better adaptation to changing environments → species survival.
Think: If gametes were diploid (2n), chromosome number would double every generation! Meiosis prevents that.
Sexual Reproduction in Plants
Flower: the reproductive unit
Four whorls from outside to inside: Calyx (sepals), Corolla (petals), Androecium (stamens ♂), Gynoecium (carpels ♀). Androecium & gynoecium are essential whorls.
- Bisexual flower — both ♂ and ♀ (e.g., Hibiscus)
- Unisexual flower — only ♂ or only ♀ (e.g., Papaya)
- Pedicellate vs Sessile flowers (with or without stalk)
Pollination & Double Fertilization
- Pollination: Transfer of pollen from anther to stigma — by wind, water (abiotic) or insects & animals (biotic). Self vs cross pollination.
- Pollen germination: On sticky stigma → pollen tube + two male gametes → tube grows through style to ovule.
- Double fertilization:
1) \( \text{Male gamete}_1 + \text{Egg} \rightarrow \text{Zygote (2n)} \)
2) \( \text{Male gamete}_2 + \text{Polar nuclei (n+n)} \rightarrow \text{Endosperm (3n)} \)
Seed Germination
After fertilization, ovule → seed and ovary → fruit. Under favourable conditions, the seed germinates. The zygote/embryo uses endosperm reserves to form a seedling, which grows into a new plant.
Sexual Reproduction in Humans
Male reproductive system
- Testes (in scrotum): Seminiferous tubules → spermatogenesis (meiosis); Sertoli & Leydig cells support.
- Ducts: Rete testis → vasa efferentia → epididymis (maturation) → vas deferens → ejaculatory duct → urinogenital duct.
- Glands: Seminal vesicles (fructose), prostate, Cowper’s — their secretions + sperms = semen.
- Penis (copulatory organ).
Fun facts: Each epididymis ≈ 6 m long; a sperm ≈ 60 µm; journey through male tract ≈ 6.5 m!
Female reproductive system
- Ovaries (oogenesis) → oocyte released at ovulation.
- Oviducts (fallopian tubes): Infundibulum with funnel opening & cilia → carry the oocyte to uterus.
- Uterus (implantation, development) & vagina (copulation, birth canal). Bartholin’s glands present.
Gametogenesis & Sex Determination
Humans: \(2n = 46 = 44 \text{ autosomes} + 2 \text{ sex chromosomes}\).
Male meiosis → two types of sperms: \((22+X)\) and \((22+Y)\).
Female meiosis → oocytes only \((22+X)\).
\((22+X)\_\text{sperm} + (22+X)\_\text{oocyte} \rightarrow (44+XX)\) girl
\((22+Y)\_\text{sperm} + (22+X)\_\text{oocyte} \rightarrow (44+XY)\) boy
Male meiosis → two types of sperms: \((22+X)\) and \((22+Y)\).
Female meiosis → oocytes only \((22+X)\).
\((22+X)\_\text{sperm} + (22+X)\_\text{oocyte} \rightarrow (44+XX)\) girl
\((22+Y)\_\text{sperm} + (22+X)\_\text{oocyte} \rightarrow (44+XY)\) boy
Always remember: The father’s sperm (X or Y) determines the baby’s sex. Blaming the mother is scientifically wrong.
Fertilization, Development & Birth
- Fertilization: Usually in the oviduct; a single sperm fuses with the ovum → zygote.
- Cleavage: Zygote divides (mitosis) → embryo → reaches the uterus → implantation.
- Placenta: Forms for nourishment, gas exchange & waste removal for the developing fetus.
- Gestation: ~9 months; childbirth (parturition) is triggered hormonally.
Menstrual Cycle (≈28–30 days)
Controlled by four hormones: FSH, LH, Estrogen, Progesterone.
- Follicular phase: FSH stimulates follicle; follicle secretes estrogen → endometrium builds.
- Ovulation: LH surge causes the follicle to rupture → oocyte released.
- Luteal phase: Corpus luteum forms → secretes progesterone (and estrogen) → endometrium becomes secretory (ready for implantation).
- Menstruation: If no fertilization/implantation, corpus luteum → corpus albicans; progesterone & estrogen drop → endometrium sheds (bleeding ~5 days).
Hygiene & care: During menstruation, rest and personal hygiene are important; heavy bleeding may cause weakness and infection risk increases.
Reproduction & Modern Technology
IVF — Test-tube Baby
In Vitro Fertilization: Fertilization outside the body; embryo implanted in the uterus. Helpful for low sperm count, blocked oviducts, etc.
Surrogacy
Embryo (from intended parents) implanted into a surrogate mother with a healthy uterus when implantation is a problem for the intended mother.
Sperm Bank
Screened & stored semen used (with consent and legal safeguards) for IVF/IA procedures. Donor identity is protected by law.
Twins
- Monozygotic (identical): One embryo splits early → two genetically identical babies (same sex). Late splitting can cause conjoined twins.
- Dizygotic (fraternal): Two oocytes ovulated & fertilized by separate sperms → two genetically different babies (same or different sex).
Reproductive Health
Health = Physical + Mental + Social well-being. Awareness can be low due to customs, illiteracy, shyness; special attention needed for women’s health.
- Hygiene: Cleanliness of genitals, especially during menstruation; appropriate sanitary products; safe disposal.
- STIs: Syphilis & Gonorrhoea (bacterial) — symptoms include sores/rashes, painful urination, pus discharge, inflammation. Early medical care is essential.
- Law & ethics: Minimum legal age of marriage in India: 18 (girls), 21 (boys) — protects health and rights.
Population Explosion
Definition: Very rapid population growth in a short period. Consequences: unemployment, reduced per-capita income, pressure on natural resources, debt burden.
Solution path: Family planning, education, women empowerment, public health access, and socio-economic reforms.
India — Census Snapshot
| Year | Population |
|---|---|
| 1901 | 238,396,327 |
| 1911 | 252,093,390 |
| 1921 | 251,321,213 |
| 1931 | 278,977,238 |
| 1941 | 318,660,580 |
| 1951 | 358,142,161 |
| 1961 | 439,234,771 |
| 1971 | 548,159,652 |
| 1981 | 683,329,097 |
| 1991 | 846,421,039 |
| 2001 | 1,028,610,328 |
| 2011 | 1,210,854,977 |
Explore: Visit a nearby public health center and interview a health officer about family planning methods (natural, barrier, hormonal, IUDs, surgical) and community programs.
Quick Recap — Must Remember
- Asexual reproduction is fast but does not create variation; sexual reproduction creates variation via recombination.
- Plants show double fertilization — unique to angiosperms.
- Human sex determination depends on the sperm (X or Y).
- Menstrual cycle: FSH & LH (pituitary), Estrogen & Progesterone (ovary) — tightly coordinated.
- IVF, surrogacy, and sperm banks assist childless couples; ethical & legal guidelines apply.
- Reproductive health = hygiene, STI awareness, nutrition, and respect for legal marriage age.
- Population control through informed family planning is crucial for sustainable growth.
Exercise — Perfect Solutions (Sexual Reproduction)
1) Complete the point-wise comparison.
Asexual Reproduction
- Reproduction that occurs with the help of somatic cells is called asexual reproduction.
- Uniparental reproduction (only one parent is involved).
- This reproduction occurs with the help of mitosis only.
- Offspring are genetically identical to the parent (no recombination/variation except mutation).
- Occurs by various methods: binary fission, multiple fission, budding, fragmentation, regeneration, vegetative propagation, spore formation, etc.
Sexual Reproduction
-
Involves the formation and fusion of gametes (male & female).
Includes meiosis (for gametogenesis) and mitosis (for growth of the zygote/embryo).
Usually biparental. - Male and female parent are necessary for sexual reproduction.
-
Fusion of gametes is called fertilization (internal or external).
A diploid zygote is formed which grows into an embryo and then a new individual. - New individual formed is genetically different from parents (genetic recombination → variation).
-
Ensures variation & adaptability;
Slower than asexual reproduction;
Common in higher plants and most animals;
In flowering plants: double fertilization is unique;
In humans: XX/XY sex-determination;
Promotes evolution and species survival.
2) Fill in the blanks.
a) In humans, sperm production occurs in the organ testes.
b) In humans, the Y chromosome is responsible for maleness.
c) In male and female reproductive system of human, the pituitary gland is same (common endocrine control via FSH & LH).
d) Implantation of embryo occurs in the uterus (endometrium).
e) Asexual type of reproduction occurs without fusion of gametes.
f) Body breaks into several fragments and each lives as a new individual. This is fragmentation type of reproduction.
g) Pollen grains are formed by meiosis in the locules of anthers.
b) In humans, the Y chromosome is responsible for maleness.
c) In male and female reproductive system of human, the pituitary gland is same (common endocrine control via FSH & LH).
d) Implantation of embryo occurs in the uterus (endometrium).
e) Asexual type of reproduction occurs without fusion of gametes.
f) Body breaks into several fragments and each lives as a new individual. This is fragmentation type of reproduction.
g) Pollen grains are formed by meiosis in the locules of anthers.
3) Complete the paragraph using the given words.
Words: (Luteinizing hormone, endometrium of uterus, follicle stimulating hormone, estrogen, progesterone, corpus luteum)
Growth of follicles present in the ovary occurs under the effect of follicle stimulating hormone. This follicle secretes estrogen. The endometrium of uterus grows/regenerates under the effect of estrogen. Under the effect of luteinizing hormone, the fully grown follicle bursts, ovulation occurs and the corpus luteum is formed from the remaining part of the follicle. It secretes progesterone and estrogen. Under the effect of these hormones, glands of the endometrium of uterus are activated and it becomes ready for implantation.
4) Answer the following in short.
a) Types of asexual reproduction in unicellular organisms (with examples)
- Binary fission — Parent divides into two equal cells (Amoeba—simple; Paramecium—transverse; Euglena—longitudinal; bacteria; also mitochondria & chloroplasts).
- Multiple fission — Under adverse conditions, encystment & repeated nuclear division produce many daughter cells (Amoeba).
- Budding — Unequal division forms a bud that detaches (Yeast).
b) Concept of IVF
In Vitro Fertilization is fertilization of ovum and sperm outside the body (in a lab). The resulting embryo is transferred to the uterus at the right stage. Helpful for blocked oviducts, low sperm count/motility, or unexplained infertility.
c) Precautions to maintain reproductive health
Personal hygiene (especially during menstruation), safe sexual practices (barrier methods), timely medical consultation for symptoms, vaccinations where applicable (e.g., HPV), balanced nutrition & exercise, awareness of legal age for marriage (Girls 18, Boys 21), avoidance of substance abuse, and respect for consent and privacy.
d) What is menstrual cycle? Describe in brief.
A ~28–30 day cycle controlled by FSH, LH, estrogen, progesterone involving: (i) Follicular phase (FSH → follicle growth; estrogen rebuilds endometrium), (ii) Ovulation (LH surge releases oocyte), (iii) Luteal phase (corpus luteum → progesterone; endometrium becomes secretory), (iv) Menstruation (if no implantation, hormones drop and endometrium sheds).
5) “In sexual reproduction, the newborn shows similarities in characters.” Explain.
In sexual reproduction, the offspring inherits one set of genes from each parent. Due to this, certain traits (e.g., blood group, facial features, hair texture) resemble parents. Yet, because of recombination/assortment, the child is not identical and also shows unique variations.
6) Sketch the labelled diagrams.
a) Human male reproductive system (schematic)
b) Human female reproductive system (schematic)
c) Flower with sexual organs (schematic)
d) Menstrual cycle (overview)
| Phase | Days (approx.) | Key Hormones | Major Events |
|---|---|---|---|
| Menstrual | 1–5 | ↓ Estrogen & Progesterone | Shedding of endometrium (bleeding) |
| Follicular | 1–13 | FSH, Estrogen | Follicle growth; endometrium rebuilds |
| Ovulation | ~14 | LH surge | Rupture of follicle; oocyte released |
| Luteal | 15–28 | Progesterone (± Estrogen) | Endometrium becomes secretory; ready for implantation |
7) Give the names.
a) Hormones related with male reproductive system: FSH, LH, Testosterone, Inhibin.
b) Hormones secreted by ovary: Estrogen, Progesterone (also Inhibin; Relaxin later in pregnancy).
c) Types of twins: Monozygotic (identical), Dizygotic (fraternal) (Conjoined twins are a rare late-split variant of monozygotic).
d) Any two sexual diseases: Syphilis, Gonorrhoea (also HIV/AIDS, HPV, Genital herpes).
e) Methods of family planning: Condoms (barrier), Oral contraceptive pills, IUCD (Copper-T), Vasectomy/Tubectomy, Safe-period/Rhythm.
b) Hormones secreted by ovary: Estrogen, Progesterone (also Inhibin; Relaxin later in pregnancy).
c) Types of twins: Monozygotic (identical), Dizygotic (fraternal) (Conjoined twins are a rare late-split variant of monozygotic).
d) Any two sexual diseases: Syphilis, Gonorrhoea (also HIV/AIDS, HPV, Genital herpes).
e) Methods of family planning: Condoms (barrier), Oral contraceptive pills, IUCD (Copper-T), Vasectomy/Tubectomy, Safe-period/Rhythm.
8) “Gender of the child is determined by the male partner.” True or False? Explain.
True. Female gamete is always \(22+X\). Male produces two kinds of sperms: \(22+X\) and \(22+Y\). Fertilization outcomes:
\( (22+X)\_{\text{sperm}} + (22+X)\_{\text{oocyte}} \rightarrow (44+XX) \) — Girl
\( (22+Y)\_{\text{sperm}} + (22+X)\_{\text{oocyte}} \rightarrow (44+XY) \) — Boy
Thus the sperm (from the father) contributes either X or Y, deciding the sex of the child.
\( (22+Y)\_{\text{sperm}} + (22+X)\_{\text{oocyte}} \rightarrow (44+XY) \) — Boy
9) Explain asexual reproduction in plants.
Plants reproduce asexually mainly by vegetative propagation using normal body parts:
- Stem/tuber: Potato tuber “eyes” give new plants.
- Leaf buds: Bryophyllum buds on leaf margins form plantlets.
- Nodes: Sugarcane and grasses propagate via buds on nodes/runners.
- Bulbs/rhizomes (e.g., onion, ginger — syllabus extension).
10) “Modern techniques like surrogate mother, sperm bank and IVF help human beings.” Justify.
These methods address specific infertility causes:
- IVF: Overcomes blocked oviducts, low sperm count/motility; fertilization outside the body, embryo transfer to uterus.
- Surrogacy: Provides a healthy uterine environment when implantation/carrying to term is a challenge.
- Sperm bank: Screened donor semen enables conception when the male partner lacks viable sperm; used with IVF/IA under legal-ethical safeguards.
11) Explain sexual reproduction in plants.
- Flower has calyx, corolla (accessory), androecium (stamens ♂), gynoecium (carpels ♀). Ovule contains embryo sac (egg cell + 2 polar nuclei).
- Pollination (self/cross) by wind, water, insects transfers pollen to stigma → pollen tube grows via style carrying two male gametes.
- Double fertilization (unique to angiosperms):
Egg (n) \(+\) Male gamete (n) \( \rightarrow \) Zygote (2n)
Polar nuclei (n+n) \(+\) Male gamete (n) \( \rightarrow \) Endosperm (3n) - Post-fertilization: Ovule → seed; ovary → fruit; seed germinates under favourable conditions to form a new plant.