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Plant Growth and Development - Photoperiodism

Grade 11CBSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Photoperiodism is the physiological response of plants to the relative lengths of light (day) and dark (night) periods.

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The site of perception of light/dark duration is the leaves. A hypothetical hormone called 'Florigen' is believed to migrate from leaves to shoot apices to induce flowering.

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Short Day Plants (SDP): These plants flower when the day length is less than a certain critical duration. They require a continuous long dark period (e.g., ChrysanthemumChrysanthemum, Glycine maxGlycine\ max).

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Long Day Plants (LDP): These plants flower when the day length exceeds a certain critical duration (e.g., RaphanusRaphanus - Radish, TriticumTriticum - Wheat).

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Day Neutral Plants (DNP): Flowering in these plants is independent of the photoperiod (e.g., Solanum lycopersicumSolanum\ lycopersicum - Tomato, Cucumis sativusCucumis\ sativus - Cucumber).

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Phytochrome is the pigment involved in sensing light. It exists in two interconvertible forms: PrP_r (inactive, absorbs red light at 660 nm660\ nm) and PfrP_{fr} (active, absorbs far-red light at 730 nm730\ nm).

📐Formulae

Pr→Darkness/Far−red light (730 nm)Red light (660 nm)PfrP_r \xrightarrow[Darkness / Far-red\ light\ (730\ nm)]{Red\ light\ (660\ nm)} P_{fr}

Critical Duration>Light period  ⟹  Flowering in SDP\text{Critical Duration} > \text{Light period} \implies \text{Flowering in SDP}

Critical Duration<Light period  ⟹  Flowering in LDP\text{Critical Duration} < \text{Light period} \implies \text{Flowering in LDP}

💡Examples

Problem 1:

A plant is exposed to a light period of 1010 hours and a dark period of 1414 hours. If a brief flash of red light is given during the middle of the dark period, what happens to a Short Day Plant (SDP)?

Solution:

The SDP will fail to flower.

Explanation:

Short Day Plants require a continuous, uninterrupted dark period. The flash of red light during the dark period converts PrP_r to PfrP_{fr} and breaks the 'dark continuity', inhibiting the flowering process in SDPs.

Problem 2:

Identify the type of plant if it flowers only when the night length is shorter than 1010 hours in a 2424-hour cycle.

Solution:

Long Day Plant (LDP)

Explanation:

If the plant requires the night (dark period) to be shorter than a specific threshold, it implies it requires the light period to be longer than the critical duration. This is the characteristic of an LDPLDP.

Photoperiodism - Revision Notes & Key Diagrams | CBSE Class 11 Biology