germination of a broad bean Flashcards
define germination
the biochemical and physiological processes through which a seed becomes a photosynthesising plant
what are the main requirements for successful germination
1) temperature- optimum for enzymes between 5-30 degrees
2) water- to mobilise enzymes for transport in the xylem and phloem
3) oxygen- aerobic respiration releases energy which fuels metabolism and growth
very briefly outline stages of germination
1) seed imbibes water
2) testa splits
3) radicle emerges
4) plumule emerges
5) elongation pushes shoot above ground
outline the stage of germination where the seed imbibes water
1) water is imbibed rapidly through the seed micropyle
2) water causes tissues to swell and provide suitable conditions for enzymes
3) food reserves in the seed are insoluble in water and cant be transported
4) amylase hydrolyses starch to maltose and protease hydrolyses proteins to amino acids
5) transported in the phloem to apical meristems of the plumule and radicle for cell division and growth
outline what happens to the testa after water is imbibed
1) swollen tissues rupture the testa
2) the radicle emerges from the seed where it is positively geotropic and negatively phototropic so grows downwards
3) the plumule emerges as is positively phototropic and negatively geotropic so grows upwards
what is gibberellin
a plant growth regulator
what does gibberellin do
1) the embryo secretes gibberellic acid which diffuses through the endosperm to the aleurone layer
2) the gibberellic acid switches on genes cells in the aleurone layer resulting in the production of enzymes including amylase and protease
3) proteases hydrolyse proteins in the aleurone layer to amino acids which are used to make amylase
4) the amylase diffuses out the layer and hydrolyses starch stored in the endosperm cells
5) maltose and glucose diffuse through endosperm to the plumule and radicle
