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Sexual Reproduction In Flowering Plants — BIOLOGY STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 ScienceBIOLOGYSexual Reproduction In Flowering Plants4 Marks
Question
Write a short note on endosperm development.
✓

Answer

→ Endosperm development precedes embryo development.
→ The primary endosperm cell divides repeatedly and forms a triploid endosperm tissue.
→ The cells of this tissue are filled with reserve food materials and are used for the nutrition of the developing embryo.
→ In the most common type of endosperm development, the PEN undergoes successive nuclear divisions to give rise to free nuclei. This stage of endosperm development is called free-nuclear endosperm.
→ Subsequently cell wall formation occurs and the endosperm becomes cellular.
→ The number of free nuclei formed before cellularisation varies greatly.
→ The coconut water from tender coconut that you are familiar with, is nothing but free- nuclear endosperm (made up of thousands of nuclei) and the surrounding white kernel is the cellular endosperm.
→ Endosperm may either be completely consumed by the developing embryo (e.g., pea, groundnut, beans) before seed maturation or it may persist in the mature seed (e.g. castor and coconut) and be used up during seed germination.

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The process of translation requires transfer of genetic information from a polymer of nucleotides to synthesise a polymer of amino acids. The relationship between the sequence of amino acids in a polypeptide and nucleotide sequence of DNA or mRNA is called genetic code. George Gamow suggested that in order to code for all the 20 amino acids, code should be made up of three nucleotides.

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Amino acid
mRNA triplet
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UUU
Lysine
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Polypeptide produced
UUUAAAUUUAAA
Phenylalanine-Iysine-phenylalanine-Iysine

What are the DNA codes for the amino acids phenylalanine and lysine?

S.no
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Lysine
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CCC
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TTT
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