ï»¿ What do you understand by photoperiodism and vernalisation ? Describe their significance. from Biology Plant Growth and Development Class 11 Assam Board

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What do you understand by photoperiodism and vernalisation ? Describe their significance.

(A) Photoperiodism . It is the responseÂ of plants toÂ periods of day/night.Â The floweringÂ in some plants depends not only on a combination of light and darkÂ exposures but also their relative durations. The plants that need a longer durationÂ for a period exceeding a well defined criticalÂ duration, while the short day plants must be exposed to light for a period less than thisÂ critical duration before the flowering is initiated in them.

Significance : Photoperiodism helps in studying the response of flowering in various crop plants with respect to the duration of exposure to light.Â It is the phenomenon which helps in flowering out of season.

(B) Vernalization :Â Vernalisation refers specially to the promotion of flowering by a
period of low temperature. It is the treatment of cold (3-15Â°C) to arrest vegetative growth and initiate flowering.

Significance of vernalization :

1. It shortens the vegetative phase.

2. It makes the plant resistant to cold and fungal pathogens.

3.Â It prevents precocious reproductive development late inÂ the growing season, and enables the plant to have sufficient time to reachÂ maturity.

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Who isolated auxin and from where ?

Auxin was isolated byÂ F.W. Went from tips of coleoptiles of oat seedling.

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What is C/N ratio ?

C/N ratio is the ratio of carbohydrates and nitrogenous compounds which regulate the growth in plants.Â
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Who coined the term gibberellin ?

Yabuta.
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Â Term kinetinwas coined by whom ?

Skoog and Miller.
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Â Give the types of auxins.

Auxins are of two types :

(1)Â Natural auxins : These are naturally occuring auxins, isolated from plants and are regarded as phytohormones e.g. IAA. NAA etc.

(2)Â Synthetic auxins : These are synthesized by artificially e.g. IBA 2,4-D etc.

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