7. Give one function of the following
a) Plumule
b) Radicle
c) Cotyledons
d) Seed ceat
e) Micropyle
Answers
a) Plumule (shoot tip): The plumule is the part of the embryo that develops into the shoot bearing the leaves of the plant. The plumule gives rise to aerial shoots. The function of cotyledon: They store reserve food material or serve as photosynthetic organs in young seedlings.
b) Radicle : The radicle is the embryonic root of the plant,and grows downward in the soil. It is the first thing to emerge from a seed and down into the ground to allow the seed to suck up water and send out its leaves so that it starts photosynthesizing.
c) Cotyledons : The cotyledon in monocots is represented by a structure called the "scutellum" and is an outgrowth of the embryo. The scutellum is connected to the embryo by vascular tissue. The scutellum is right up against the endosperm. When germination is initiated, the embryo starts to secrete gibberellic acid (GA). After 24 hours the scutellum also starts to synthesise GA. The GA triggers synthesis of various enzymes by the aleurone layer (just under the pericarp/testa). These enzymes (including alpha-amylase) enable mobilisation of the endosperm and the products are absorbed by the scutellum and passed to the developing embryo.
d) Seed coat : The seed coat certainly represents a first line of defense against adverse external factors, but it also acts as channel for transmitting environmental cues to the interior of the seed. The latter function primes the seed to adjust its metabolism in response to changes in its external environment.
e) Micropyle : The micropyle helps to absorb water at the time of germination of the seed. It is through this micropyle that the root emerges at the time of germination of the seed. The opening of the micropyle allows the pollen to enter the ovule for fertilization.