9.3 Reproduction in angiospermophytes

Assessment Statements 9.3.1 Draw and label a diagram showing the structure of a dicotyledonous animal-pollinated flower. 9.3.2 Distinguish between pollination, fertilization and seed dispersal. 9.3.3 Draw and label a diagram showing the external and internal structure of a named dicotyledonous seed. 9.3.4 Explain the conditions needed for the germination of a typical seed. 9.3.5 Outline the metabolic processes during germination of a starchy seed. 9.3.6 Explain how flowering is controlled in long-day and short-day plants, including the role of phytochrome.

Draw a labelled diagram showing the structure of a dicotyledonous animal-pollinated flower

Pollination, fertilization & seed dispersal pollination is the transfer of pollen grain from anther to the stigma usually of another flower pollen grains grow a pollen tube down the style to the ovule fertilization is the fusion of male & female gametes (nuclei) in the ovule to form a zygote ovary matures into a fruit while the ovule matures into seed dispersal of seeds is moving the seeds away from the parent plant to reduce competition mode of seeds dispersal depends on the type of fruit e.g. pods split open to scatter seeds, animal eats fruit and egests seed, wind blow the seeds from the parent plant

Draw a labelled diagram showing the external & internal structure of a named dicotyledonous seed

Conditions that are needed to allow a seed to germinate water is needed to rehydrate the seed presence of water in the embryo stimulates production of plant growth substance gibberellin gibberellin is needed for production of enzyme amylase water is needed to allow substances inside the seedling to be transported oxygen is needed for aerobic cell respiration to produce energy needed for growth warmth is needed to speed up metabolism i.e. optimum temperature for optimal enzyme activity warmth indicates to the seed that it is a favourable season for germination some seeds need a cold period to stimulate germination some seeds need fire to stimulate germination some seeds need to pass through an animal gut to stimulate germination

Metabolic events of germination in a typical starchy seed absorption of water by the seed stimulates gibberellic acid production in embryo gibberellic acid stimulates production of enzyme amylase & protease these enzymes catalyses the breakdown of starch to maltose & protein to amino acids respectively maltose diffuses to embryo where it is used for energy production and growth amino acids are used to produce new cellular components for growth

How flowering is controlled in long-day & short-day plants Pfr is active form of phytochrome in long-day plants, flowering is induced by dark periods shorter than a critical length i.e. flowering occurs when day is longer than a critical length enough Pfr remains in long-day plants at end of short nights to stimulate flowering Pfr acts as promoter of flowering in long-day plants in short-day plants, flowering is induced by dark periods longer than a critical length i.e. days shorter than a critical value at end of long nights enough Pfr has been converted to Pr to allow flowering to occur Pfr acts as inhibitor of flowering in short-day plants flowering is affected by light duration, photoperiod phytochrome, a receptor of photoperiod located within the leaf, exists in two interconvertible forms, Pfr & Pr Pr , red light absorbing phytochrome is converted to Pfr, far-red light absorbing phytochrome in red light or day light sunlight contains more red light than far red light so Pfr predominates during the day gradual reversion of Pfr to Pr occurs in darkness

Revision Questions Draw a labelled diagram showing the structure of a dicotyledonous animal-pollinated flower. [5] Draw a labelled diagram showing the internal structure of a named dicotyledonous seed. [5] Outline pollination, fertilization and seed dispersal. [4] Explain the conditions that are needed to allow a seed to germinate. [5] Describe the metabolic events of germination in a typical starchy seed. [5] Explain how flowering is controlled in long-day and short-day plants. [7]

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