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Q15:
Describe the post-fertilisation changes in a flower.
Solution :
Initial Theoretical Foundation: The Post-Fertilisation Transition
Following the process of syngamy and triple fusion (collectively known as double fertilisation), the flower undergoes profound morphological and physiological transformations. The ovule develops into a seed, and the ovary matures into a fruit. These events are driven by hormonal signaling, primarily involving auxins and gibberellins secreted by the developing embryo.
Step 1: Transformation of the Zygote and Primary Endosperm Nucleus
- Endosperm Development: The Primary Endosperm Nucleus (PEN) undergoes successive mitotic divisions to form a nutritive tissue known as the endosperm [Per the Law of Embryonic Nutrition]. In most angiosperms, this precedes embryo development to ensure a food supply.
- Embryogenesis: The zygote undergoes a series of ordered divisions (proembryo, globular, heart-shaped, and mature stages) to form the embryo [Per the Protoplasmic Continuity Principle].
Step 2: Transformation of Ovule Components into Seed Structures
| Pre-fertilisation Structure | Post-fertilisation Transformation |
|---|---|
| Ovule | Seed |
| Integuments (Outer/Inner) | Testa/Tegmen (Seed Coat) |
| Micropyle | Small pore in seed coat (for water/oxygen entry) |
| Funiculus | Stalk of the seed |
| Synergids and Antipodal cells | Degenerate (Apoptosis) |
Step 3: Transformation of Floral Whorls and Ovary
As the ovule matures into a seed, the surrounding floral structures undergo specific fates:
- Ovary: The ovary wall develops into the pericarp (fruit wall). The entire ovary becomes the fruit [Defined by the Botanical definition of fruit as a ripened ovary].
- Sepals, Petals, and Stamens: These usually wither and fall off (caducous) after fertilisation, though in some species (e.g., Solanaceae), the sepals remain attached (persistent).
- Stigma and Style: These structures degenerate as they are no longer required for pollination conduit.
Step 4: Visualizing the Structural Transition
Step 5: Analytical Summary of Physiological Changes
The transformation is regulated by the cessation of floral pigment production in petals and the redirection of metabolic resources (carbohydrates, amino acids) toward the developing seed. The maturation of the seed involves dehydration and dormancy, where the metabolic rate of the embryo reduces to ensure survival during unfavorable environmental conditions [Refer to Metabolic Stasis Theory].
Final Solution: Post-fertilisation changes involve the conversion of the ovary into a fruit, the ovule into a seed, the integuments into the seed coat, and the degeneration of accessory floral parts such as sepals, petals, and stamens, accompanied by the maturation of the zygote into an embryo nourished by the endosperm.
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.
- 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?
- 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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