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Q18:
Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?
Solution :
Step 1: Biological Definitions and Embryonic Milieu
To evaluate the comparative survival risks of offspring, it is necessary to establish the developmental environments dictated by the two primary modes of animal reproduction: oviparity and viviparity.
- Oviparous Organisms: In oviparous animals (e.g., reptiles, birds, amphibians, and most fishes), females lay fertilized or unfertilized eggs into the external environment. The entire period of embryonic development occurs outside the maternal body. The embryo relies exclusively on a finite nutrient reserve contained within the yolk. Terrestrial eggs are often encased in a calcareous shell ($CaCO_3$) for rudimentary protection.
- Viviparous Organisms: In viviparous animals (e.g., most mammals), the zygote develops into a young one inside the reproductive tract (typically the uterus) of the female organism. Nourishment is provided continuously through a direct maternal connection, such as the placenta.
Step 2: Analytical Breakdown of Vulnerabilities in Oviparous Organisms
Offspring of oviparous animals face severe selective pressures and heightened mortality risks due to several physiological and ecological factors:
- Exposure to Environmental Extremes: Because eggs are incubated externally, they are highly susceptible to sudden abiotic fluctuations. Variations in temperature, humidity, and oxygen availability can cause developmental arrest or desiccation. [Per the principles of thermoregulation, poikilothermic eggs cannot independently maintain optimal metabolic temperatures.]
- High Predation Pressure: Eggs are immobile and contain high-density nutrients (yolk), making them an optimal, defenseless food source for a multitude of predators (e.g., snakes, birds, mammals).
- Mechanical Damage: Terrestrial and aquatic eggs are vulnerable to being crushed, displaced, or destroyed by natural disturbances, such as storms, floods, or trampling.
- Nutritional Limitations: The developing embryo has a strictly limited energy supply. If development is delayed due to environmental factors, the embryo may exhaust its nutrient reserves before hatching is possible.
Step 3: Evolutionary Protections Conveyed by Viviparity
Viviparity evolved as a highly successful reproductive strategy that minimizes early developmental mortality. The maternal body acts as a dynamic, highly regulated incubator.
Because the embryo is retained internally, it is shielded from the external abiotic environment and physically protected from predators. Furthermore, physiological homeostasis provides constant temperature regulation, and placentation ensures an uninterrupted supply of nutrients, oxygen, and immunological factors directly from the maternal bloodstream.
Step 4: Comparative Data Summary
| Parameter | Oviparous Animals | Viviparous Animals |
|---|---|---|
| Site of Development | External environment (outside the maternal body). | Internal environment (inside the maternal reproductive tract). |
| Environmental Exposure | High susceptibility to desiccation and temperature fluctuations. | Shielded; exact physiological homeostasis maintained. |
| Predation Risk | Extremely high (eggs are immobile and defenseless). | Negligible during gestation (embryo moves with the mother). |
| Overall Survival Probability | Lower pre-hatching survival rates. | Significantly higher pre-birth survival rates. |
Final Solution: The offspring of oviparous animals face a significantly greater risk than those of viviparous animals because their embryonic development occurs entirely in the external environment. They are constantly subjected to extreme environmental fluctuations, lethal desiccation, and high predation pressures, lacking the physiological homeostasis and physical protection afforded to viviparous embryos developing securely within the maternal body.
More Questions from Class 12 Biology Reproduction in Organisms EXERCISES
- Q1: Why is reproduction essential for organisms?
- Q1: Why is reproduction essential for organisms?
- Q2: Which is a better mode of reproduction: sexual or asexual? Why?
- Q2: Which is a better mode of reproduction: sexual or asexual? Why?
- Q3: Why is the offspring formed by asexual reproduction referred to as clone?
- Q3: Why is the offspring formed by asexual reproduction referred to as clone?
- Q4: Offspring formed due to sexual reproduction have better chances of survival. Why? Is this statement always true?
- Q4: Offspring formed due to sexual reproduction have better chances of survival. Why? Is this statement always true?
- Q5: How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?
- Q5: How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?
- Q6: Distinguish between asexual and sexual reproduction. Why is vegetative reproduction also considered as a type of asexual reproduction?
- Q6: Distinguish between asexual and sexual reproduction. Why is vegetative reproduction also considered as a type of asexual reproduction?
- Q7: What is vegetative propagation? Give two suitable examples.
- Q7: What is vegetative propagation? Give two suitable examples.
- Q8(a): Define (a) Juvenile phase,
- Q8(a): Define (a) Juvenile phase,
- Q8(b): Define (b) Reproductive phase,
- Q8(b): Define (b) Reproductive phase,
- Q8(c): Define (c) Senescent phase.
- Q8(c): Define (c) Senescent phase.
- Q9: Higher organisms have resorted to sexual reproduction in spite of its complexity. Why?
- Q9: Higher organisms have resorted to sexual reproduction in spite of its complexity. Why?
- Q10: Explain why meiosis and gametogenesis are always interlinked?
- Q10: Explain why meiosis and gametogenesis are always interlinked?
- Q11(a): Identify each part in a flowering plant and write whether it is haploid (\(n\)) or diploid (\(2n\)). (a) Ovary ———————————
- Q11(a): Identify each part in a flowering plant and write whether it is haploid ((n)) or diploid ((2n)). (a) Ovary ———————————
- Q11(b): Identify each part in a flowering plant and write whether it is haploid (\(n\)) or diploid (\(2n\)). (b) Anther ———————————
- Q11(b): Identify each part in a flowering plant and write whether it is haploid ((n)) or diploid ((2n)). (b) Anther ———————————
- Q11(c): Identify each part in a flowering plant and write whether it is haploid (\(n\)) or diploid (\(2n\)). (c) Egg ———————————
- Q11(c): Identify each part in a flowering plant and write whether it is haploid ((n)) or diploid ((2n)). (c) Egg ———————————
- Q11(d): Identify each part in a flowering plant and write whether it is haploid (\(n\)) or diploid (\(2n\)). (d) Pollen ———————————
- Q11(d): Identify each part in a flowering plant and write whether it is haploid ((n)) or diploid ((2n)). (d) Pollen ———————————
- Q11(e): Identify each part in a flowering plant and write whether it is haploid (\(n\)) or diploid (\(2n\)). (e) Male gamete ———————————
- Q11(e): Identify each part in a flowering plant and write whether it is haploid ((n)) or diploid ((2n)). (e) Male gamete ———————————
- Q11(f): Identify each part in a flowering plant and write whether it is haploid (\(n\)) or diploid (\(2n\)). (f) Zygote ———————————
- Q11(f): Identify each part in a flowering plant and write whether it is haploid ((n)) or diploid ((2n)). (f ) Zygote ———————————
- Q12: Define external fertilisation. Mention its disadvantages.
- Q12: Define external fertilisation. Mention its disadvantages.
- Q13: Differentiate between a zoospore and a zygote.
- Q13: Differentiate between a zoospore and a zygote.
- Q14: Differentiate between gametogenesis from embryogenesis.
- Q14: Differentiate between gametogenesis from embryogenesis.
- Q15: Describe the post-fertilisation changes in a flower.
- Q15: Describe the post-fertilisation changes in a flower.
- Q16: What is a bisexual flower? Collect five bisexual flowers from your neighbourhood and with the help of your teacher find out their common and scientific names.
- Q16: What is a bisexual flower? Collect five bisexual flowers from your neighbourhood and with the help of your teacher find out their common and scientific names.
- Q17: Examine a few flowers of any cucurbit plant and try to identify the staminate and pistillate flowers. Do you know any other plant that bears unisexual flowers?
- Q17: Examine a few flowers of any cucurbit plant and try to identify the staminate and pistillate flowers. Do you know any other plant that bears unisexual flowers?
- Q18: Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?
CBSE Solutions for Class 12 Biology Reproduction in Organisms
Chapters in CBSE - Class 12 Biology
- Human Reproduction
- Reproductive Health
- Principles of Inheritance and Variation
- Molecular Basis of Inheritance
- Evolution
- Human Health and Disease
- Strategies for Enhancement in Food Production
- Microbes in Human Welfare
- Biotechnology: Principles and Processes
- Biotechnology and Its Applications
- Organisms and Populations
- Ecosystem
- Biodiversity and Conservation
- Environmental Issues
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