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Q15:
Describe the post-fertilisation changes in a flower.
Solution :
Step 1: Initial Post-Fertilisation Setup and Resource Reallocation
Following the distinct angiosperm process of double fertilisation—comprising syngamy (fusion of a male gamete with the egg cell) and triple fusion (fusion of a male gamete with two polar nuclei)—the flower undergoes profound morphological and physiological transformations. The primary objective shifts from attracting pollinators to providing a highly protected, resource-rich environment for embryonic development and subsequent seed dispersal. [Per the principles of evolutionary resource allocation, energy is diverted from accessory floral organs to the reproductive outcomes].
Step 2: Senescence and Abscission of Floral Whorls
The accessory and non-essential reproductive parts of the flower undergo programmed cell death (apoptosis) and abscission:
- Sepals (Calyx) and Petals (Corolla): Wither and fall off. (Exception: In certain plants like tomato, brinjal, and strawberry, the sepals remain persistent and enlarge).
- Stamens (Androecium), Style, and Stigma: Shrivel and detach from the receptacle, as their functional roles in pollen production and reception are complete.
Step 3: Embryogeny (Development of the Zygote)
The diploid zygote ($2n$), formed by syngamy, undergoes a period of rest before commencing mitotic divisions. It develops into an embryo. The developmental pathway progresses through specific defined stages: the proembryo, globular stage, heart-shaped stage, and finally, the mature embryo consisting of an embryonal axis (plumule and radicle) and cotyledons (one in monocots, two in dicots).
Step 4: Endosperm Development
The triploid Primary Endosperm Nucleus (PEN) ($3n$), formed via triple fusion, rapidly divides mitotically to generate the endosperm tissue. [Developmental justification: The endosperm develops prior to the embryo to ensure a guaranteed, ready supply of nutrition—such as starch, proteins, and oils—for the growing embryonic cells].
Step 5: Transformation of the Ovule into the Seed
The entire ovule matures into a seed, driven by the following structural modifications:
- Integuments: The outer and inner integuments of the ovule lose water, desiccate, and harden to form the protective seed coats: the thick outer testa and the thin inner tegmen.
- Micropyle: Remains as a minute pore in the seed coat. [Physiological necessity: This pore is critical for the entry of $O_2$ and $H_2O$ during seed germination].
- Nucellus: Typically consumed by the developing embryo and endosperm. If it persists, it forms a thin layer known as the perisperm (e.g., in black pepper and beet).
- Funicle: Transforms into the seed stalk.
Step 6: Transformation of the Ovary into the Fruit
Simultaneous with seed development, the ovary enlarges and ripens into a fruit, stimulated by phytohormones (such as auxins and gibberellins) synthesized by the developing seeds. The ovary wall differentiates and thickens to form the pericarp (fruit wall), which may further divide into the epicarp, mesocarp, and endocarp in fleshy fruits.
Analytical Mapping of Post-Fertilisation Changes
| Pre-Fertilisation Floral Structure | Post-Fertilisation Transformation |
|---|---|
| Ovary | Fruit |
| Ovary Wall | Pericarp (Fruit Wall) |
| Ovule | Seed |
| Outer Integument | Testa (Outer Seed Coat) |
| Inner Integument | Tegmen (Inner Seed Coat) |
| Zygote ($2n$) | Embryo |
| Primary Endosperm Nucleus ($3n$) | Endosperm |
| Synergids and Antipodal Cells | Degenerate / Disintegrate |
Visual Conceptualization: Flow of Transformation
Final Solution: The primary post-fertilisation changes in a flower include the abscission of accessory organs (sepals, petals, stamens), the maturation of the diploid zygote into an embryo, the development of the triploid primary endosperm nucleus into nutrient-rich endosperm, the hardening of the ovule into a seed, and the expansion and differentiation of the ovary wall into the pericarp of a fruit.
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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