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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?
Solution :
1. Identification of Cucurbitaceae Reproductive Structures
Cucurbitaceous plants (e.g., Cucumis sativus or Cucurbita pepo) are characteristically monoecious, meaning both staminate (male) and pistillate (female) flowers are borne on the same individual plant. The identification is based on the following morphological criteria:
| Feature | Staminate Flower (Male) | Pistillate Flower (Female) |
|---|---|---|
| Ovary | Absent (the floral axis attaches directly to the pedicel). | Present (a visible, swollen structure at the base of the flower resembling a miniature fruit). |
| Androecium | Functional stamens present, often fused into a central column. | Absent (or represented by non-functional staminodes). |
| Gynoecium | Absent. | Functional pistil with a stigma, style, and ovary. |
2. Visual Representation of Unisexual Flowers
3. Examples of Other Plants with Unisexual Flowers
Beyond the Cucurbitaceae family, many plant species exhibit unisexuality as a mechanism to promote outbreeding [Per the principle of Allogamy]. These can be categorized into:
- Monoecious Plants (Both male and female flowers on the same plant):
- Zea mays (Maize): Possesses male flowers in the terminal inflorescence (tassel) and female flowers in the axillary inflorescence (cob).
- Ricinus communis (Castor): Bears male and female flowers on the same inflorescence.
- Dioecious Plants (Male and female flowers on separate plants):
- Carica papaya (Papaya): Represents a system where distinct male and female individuals exist.
- Phoenix dactylifera (Date Palm): Exhibits complete separation of reproductive systems on different specimens.
4. Theoretical Basis for Unisexuality
The evolution of unisexual flowers serves as a significant evolutionary adaptation to ensure genetic diversity. By spatially separating the reproductive structures, these plants prevent autogamy (self-pollination) [Per Mendel’s Law of Segregation and the necessity of genetic variation]. This spatial isolation necessitates cross-pollination (geitonogamy in monoecious or xenogamy in dioecious species), which facilitates the recombination of alleles.
Final Solution: Cucurbit plants possess unisexual flowers distinguishable by the presence (pistillate) or absence (staminate) of the basal ovary. Other common examples of plants bearing unisexual flowers include Maize (monoecious) and Papaya (dioecious).
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?
- 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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