How do Organisms Reproduce?
1. Why do organisms reproduce?
- Reproduction is not essential for survival of an individual but is necessary for the continuation of species.
- It helps maintain the population and transfers genetic material (DNA) to the next generation.
- DNA copying (DNA replication) is not 100% accurate → leads to variations → important for evolution and adaptation.
2. Importance of Variation
- Variations allow some organisms to survive better in changing environments (natural selection).
- Sexual reproduction produces more variations than asexual reproduction.
3. Asexual Reproduction vs Sexual Reproduction
| Feature | Asexual Reproduction | Sexual Reproduction |
|---|---|---|
| Number of parents | Single parent | Two parents (male & female) |
| Gametes/Fusion | No gametes, no fusion | Gametes formed & fuse (fertilization) |
| Variations | Very few | Many |
| Speed | Fast | Slow |
| Examples | Amoeba, Hydra, Potato | Humans, Flowering plants, Dogs |
4. Modes of Asexual Reproduction
| Mode | Description | Examples |
|---|---|---|
| Binary Fission | Parent cell divides into two identical daughter cells | Amoeba, Paramecium |
| Multiple Fission | Nucleus divides many times → many daughter cells | Plasmodium |
| Budding | Small outgrowth (bud) forms on parent → separates | Hydra, Yeast |
| Fragmentation | Body breaks into fragments → each grows into new individual | Spirogyra |
| Regeneration | Lost body parts regrow → new organism forms | Planaria, Hydra |
| Spore Formation | Spores formed in sporangium → germinate | Rhizopus (Bread mould) |
| Vegetative Propagation | New plants from root, stem, or leaf | Potato, Bryophyllum |
Artificial Vegetative Propagation:
- Cutting: Rose, Money plant
- Grafting: Mango, Citrus
- Layering: Jasmine
- Tissue culture: Orchids, Banana (Fast & disease-free)
5. Sexual Reproduction in Flowering Plants
- Male parts (Stamen): Anther + Filament → produces pollen grains.
- Female parts (Pistil/Carpel): Stigma + Style + Ovary → contains ovules.
The Process:
1. Pollination: Transfer of pollen from anther to stigma (Self or Cross).
2. Fertilization: Pollen tube grows to the ovary → male gamete fuses with egg → forms Zygote.
3. Post-Fertilization: Zygote becomes embryo → Ovule becomes seed → Ovary becomes fruit.
6. Sexual Reproduction in Humans
Puberty: Changes like deepening voice and facial hair (boys), or breast development and menstruation (girls).
Male Reproductive System
[Image of human male reproductive system]- Testes: Produce sperms + testosterone.
- Vas deferens: Carries sperms to urethra.
- Glands: Add fluid to make semen (nutrition + transport).
Female Reproductive System
[Image of human female reproductive system]- Ovaries: Produce eggs + estrogen/progesterone.
- Fallopian tube: Site of fertilization.
- Uterus: Site of implantation and development.
Menstrual Cycle:
- If egg is fertilized: Zygote implants in uterus (Pregnancy).
- If egg is NOT fertilized: Uterus lining breaks down → Menstruation.
7. Reproductive Health & Contraception
| Method Type | Examples | How it works |
|---|---|---|
| Barrier | Condom, Diaphragm | Prevents sperm meeting egg (Protects from STDs) |
| Hormonal | Oral pills | Prevents ovulation |
| IUD | Copper-T | Prevents implantation in uterus |
| Surgical | Vasectomy / Tubectomy | Permanent sterilization (Blocks gamete transfer) |
STDs: Bacterial (Gonorrhoea, Syphilis) or Viral (HIV-AIDS, Warts).
MCQs: How do Organisms Reproduce?
1. Which of the following is NOT a method of asexual reproduction?
- A) Binary fission
- B) Budding
- C) Pollination
- D) Fragmentation
Ans: C
2. The process of fusion of male and female gametes is called:
- A) Pollination
- B) Fertilization
- C) Germination
- D) Fragmentation
Ans: B
3. In which organism does multiple fission commonly occur?
- A) Amoeba
- B) Hydra
- C) Plasmodium
- D) Spirogyra
Ans: C
4. The vegetative part through which Bryophyllum reproduces is:
- A) Stem
- B) Root
- C) Leaf
- D) Flower
Ans: C
5. Which contraceptive method provides protection against sexually transmitted diseases?
- A) Copper-T
- B) Oral pills
- C) Condom
- D) Vasectomy
Ans: C
6. The site of fertilization in the human female reproductive system is:
- A) Uterus
- B) Oviduct (Fallopian tube)
- C) Vagina
- D) Ovary
Ans: B
7. Which of the following is a post-fertilization event in plants?
- A) Pollination
- B) Formation of pollen tube
- C) Development of seed
- D) Transfer of pollen grains
Ans: C
8. The hormone mainly responsible for the development of secondary sexual characters in males is:
- A) Estrogen
- B) Progesterone
- C) Testosterone
- D) Insulin
Ans: C
9. Which method of reproduction maintains the genetic similarity most?
- A) Sexual reproduction
- B) Vegetative propagation
- C) Cross-pollination
- D) Self-pollination with variation
Ans: B
10. The process by which the uterus lining breaks and comes out as bleeding is called:
- A) Ovulation
- B) Menstruation
- C) Fertilization
- D) Implantation
Ans: B
11. Which of these is a surgical method of contraception in males?
- A) Tubectomy
- B) Vasectomy
- C) IUCD insertion
- D) Barrier method
Ans: B
12. In Rhizopus, asexual spores are produced inside:
- A) Zygospore
- B) Sporangium
- C) Gametangium
- D) Bud
Ans: B
13. The most important event that occurs during puberty in girls is:
- A) Growth of facial hair
- B) Deepening of voice
- C) Start of menstruation
- D) Broadening of shoulders
Ans: C
14. Which of the following produces seeds without fertilization?
- A) Mango
- B) Apple
- C) Banana (some varieties)
- D) Pea
Ans: C
15. The part of the flower that becomes fruit after fertilization is:
- A) Ovary
- B) Ovule
- C) Stigma
- D) Anther
Ans: A
16. Which method of asexual reproduction is observed in Planaria?
- A) Budding
- B) Binary fission
- C) Regeneration
- D) Spore formation
Ans: C
17. The copper-T is a/an:
- A) Hormonal method
- B) Barrier method
- C) Intra-uterine device (IUD)
- D) Surgical method
Ans: C
18. Which of the following is NOT a reason for variations being important?
- A) Helps in survival during environmental changes
- B) Forms basis of evolution
- C) Makes every individual exactly identical
- D) Allows adaptation to new conditions
Ans: C
19. The male gamete in flowering plants is present in:
- A) Ovule
- B) Pollen grain
- C) Embryo sac
- D) Style
Ans: B
20. Which of these organisms reproduces by fragmentation?
- A) Yeast
- B) Hydra
- C) Spirogyra
- D) Rhizopus
Ans: C
0 Comments