Chapter 8: How do Organisms Reproduce?

Answer: (b) yeast

Explanation: Yeast reproduces asexually by budding, where a small bud forms on the parent cell, grows, and eventually detaches. Amoeba reproduces by binary fission, Plasmodium by multiple fission, and Leishmania (causes kala-azar) by binary fission in a definite orientation.

Answer: (c) Vas deferens

Explanation: Vas deferens is part of the male reproductive system - it carries sperms from testes to urethra. Female reproductive system includes ovaries (produce eggs), fallopian tubes (site of fertilization), uterus (womb for embryo development), cervix, and vagina.

Answer: (d) pollen grains

Explanation: Anther is the male reproductive part of a flower (part of stamen) that produces pollen grains containing male gametes. Sepals are protective leaf-like structures, ovules are inside ovary (female part), and carpel is the entire female reproductive structure (stigma, style, ovary).

Answer:

Sexual Reproduction Advantages	Why It's Beneficial
Genetic variation	Combination of genes from two parents creates new gene combinations, increasing diversity
Evolutionary advantage	Variations help species adapt to changing environments and survive challenges
Disease resistance	Genetic diversity makes populations less vulnerable to diseases/pathogens
Long-term species survival	Variations provide raw material for natural selection
Elimination of harmful mutations	Recombination can separate harmful mutations from beneficial traits
Adaptation to new niches	New combinations may be better suited to different environments

Asexual reproduction produces identical clones (good for stable environments), while sexual reproduction creates diversity (better for changing environments).

Answer:

Testes (singular: testis) have dual functions:

1. Spermatogenesis (Production of male gametes):
• Produce millions of sperm cells daily in seminiferous tubules
• Sperm contain genetic material (23 chromosomes) and a tail for motility

2. Endocrine function (Hormone secretion):
• Leydig cells secrete testosterone, the primary male sex hormone
• Testosterone functions:
  - Develops male secondary sexual characteristics at puberty
  - Deepens voice
  - Promotes facial and body hair growth
  - Stimulates muscle and bone growth
  - Maintains libido (sex drive)
  - Regulates sperm production

Additional: Testes are located in scrotum outside abdominal cavity to maintain optimal temperature (2-3°C lower than body temperature) for sperm production.

Answer:

Menstruation (period) occurs due to the menstrual cycle - a monthly reproductive cycle in females of reproductive age.

Process:
1. Uterine preparation: Each month, uterus lining (endometrium) thickens with blood vessels to prepare for potential pregnancy.
2. Ovulation: An egg is released from ovary around day 14 of cycle.
3. If no fertilization: When egg is not fertilized by sperm:
  - Corpus luteum (empty follicle) degenerates
  - Progesterone levels drop sharply
4. Menstrual flow: Without progesterone, thickened uterine lining breaks down and is shed along with blood through vagina.
5. Cycle restarts: Menstruation lasts 3-7 days, then cycle begins again.

Biological purpose: To discard unneeded uterine tissue when pregnancy doesn't occur, making way for new cycle.

Age range: Typically starts at puberty (menarche, age 10-15) and stops at menopause (age 45-55).

Answer:


Flower structure (longitudinal section):

Male reproductive parts (Androecium):
1. Stamen: Male reproductive unit
  • Anther: Bilobed structure containing pollen sacs with pollen grains
  • Filament: Stalk supporting anther

Female reproductive parts (Gynoecium):
2. Carpel/Pistil: Female reproductive unit
  • Stigma: Sticky top surface for pollen reception
  • Style: Long tube connecting stigma to ovary
  • Ovary: Swollen base containing ovules (egg cells)
  • Ovules: Contain female gametes, develop into seeds after fertilization

Accessory parts:
3. Petals: Colorful, attract pollinators
4. Sepals: Green, protective outermost whorl
5. Receptacle: Base where all parts attach
6. Pedicel: Flower stalk

Note: In bisexual flowers (e.g., hibiscus), both stamen and carpel are present. In unisexual flowers (e.g., papaya), they are on separate flowers.

Answer:

Contraceptive methods prevent pregnancy by different mechanisms:

Method Type	Examples	How It Works
Barrier Methods	• Condoms (male/female) • Diaphragm • Cervical cap	Physically block sperm from reaching egg; also prevent STDs
Hormonal Methods	• Oral pills • Injectables • Implants • Patches	Alter hormone levels to prevent ovulation/thicken cervical mucus
Intrauterine Devices (IUDs)	• Copper-T • Hormonal IUDs	Prevent implantation or sperm movement in uterus
Surgical Methods	• Vasectomy (male) • Tubectomy (female)	Permanent; block sperm/egg transport
Natural Methods	• Rhythm method • Withdrawal • Lactational amenorrhea	Avoid intercourse during fertile period; least reliable
Emergency Contraception	Morning-after pills	Prevent pregnancy after unprotected sex

Only condoms provide protection against sexually transmitted diseases (STDs). Choice depends on effectiveness, convenience, and health considerations.

Answer:

Aspect	Unicellular Organisms	Multicellular Organisms
Common modes	Asexual: Binary fission, budding, multiple fission	Both asexual & sexual: Vegetative propagation, fragmentation, sexual reproduction
Complexity	Simple; entire organism divides	Complex; specialized reproductive tissues/organs
Cell involvement	Whole organism reproduces	Specific germ cells (gametes) for sexual reproduction
Genetic variation	Minimal (only mutations)	High in sexual reproduction (meiosis & fertilization)
Examples	Amoeba (binary fission), Yeast (budding), Plasmodium (multiple fission)	Humans (sexual), Hydra (budding), Planaria (regeneration), Plants (vegetative propagation)
Energy requirement	Low	High (especially for sexual reproduction)
Time for reproduction	Fast (minutes to hours)	Slow (days to years)

Unicellular organisms mainly use simple asexual methods for rapid multiplication; multicellular organisms use more complex methods, often involving specialized cells and organs.

Answer:

Reproduction maintains population stability through:

1. Replacement of dying individuals:
• Offspring replace parents who die, maintaining population numbers
• Compensates for mortality from predation, disease, old age

2. Genetic continuity:
• DNA copying ensures transmission of species-specific traits
• Preserves body design adapted to particular ecological niche

3. Population growth when needed:
• Can increase numbers when conditions are favorable
• Colonize new areas or recover from population crashes

4. Sexual reproduction adds evolutionary stability:
• Variations help populations adapt to environmental changes
• Genetic diversity prevents wipeout from diseases/changing conditions
• Some variants survive even if most perish

Example: If all bacteria were identical and temperature rose, all might die. But with variations, heat-resistant mutants survive and repopulate.

Balance: Reproduction rate balances with death rate to prevent extinction (too little reproduction) or overpopulation (too much reproduction).

Answer:

Contraceptive methods are adopted for various personal, social, and health reasons:

Reason Category	Specific Reasons
Family Planning	• Space children appropriately (2-3 year gap) • Limit family size to available resources • Complete education/career before having children
Health Reasons	• Prevent high-risk pregnancies (teenage/advanced age) • Protect maternal health (allow recovery between pregnancies) • Prevent transmission of sexually transmitted diseases (STDs)
Socio-economic Factors	• Economic stability before expanding family • Better education and opportunities for existing children • Reduce population pressure on resources
Personal Choice	• Choice to remain childfree • Control over reproductive rights • Timing pregnancies for personal readiness
Medical Conditions	• Prevent pregnancy when it risks mother's health • Avoid genetic disorders transmission • During treatment with teratogenic drugs
Social Reasons	• Delay marriage/childbearing for education • Prevent unintended pregnancies outside marriage • Support women's empowerment and choices

Contraception enables informed reproductive choices, improves maternal and child health, and contributes to sustainable development.