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Transcript of Dahlia
Plantae Angiospermae Asteraecae Asterales Dahlia horetensis
The plant Dahlia, or scientifically known as Dahlia hortensis, is a monoecious and dicotyledonous flower. This means that it contains both female and male reproductive parts in one flower (being monoecious) and has two cotyledons in it’s seeds. This plant can visibly recognized as a dicotyledonous flower for several reasons. The Dahlia has veins in it’s leaves that are in a net shape. Additionally this plant has a primary root system. Another way you can recognize that the Dahlia is a dicot is my cutting it’s stem and seeing through a cross section that the vascular bundles form a ring. All three of these characteristics are characteristics of a dicotyledonous plant.
9.3.2 Pollination, Fertilization, and Seed Dispersal
9.3.3 Seed Structure
9.3.4 Seed Germination
Seed structure of a garden bean (Phaseolus vulgaris)
Pollination, fertilization, and seed dispersal are all steps that are necessary in order for plants to reproduce and grow new plants of a particular species. Pollination happens first.This is when pollen is transferred from the anther to the stigma.This can happen in through cross pollination or self pollination. Some cross pollinated plants are animal pollinated, some wind pollinated, and some (most) are pollinated both ways. Animal and wind pollination explains how the pollen gets to the stigma of a plant (via animals or wind). Plants can be pollinated from pollen of a different plant of the same species or the same plant/flower if that plant is monoecious. Dahlia can be both wind and animal pollinated. Although Dahlia does not have a strong scent to attract insects like bees and butterflies to pollinate them, the Dahlia has very bright colored petals which attract insects to it’s reproductive system where the insect can either pick up pollen from the anthers or drop some in the stigma in the process of collecting nectar. Plants that are mostly animal pollinated are bright, showy and give off a strong scent to attract insects; contrastingly, plants that are mostly wind pollinated are almost the opposite and usually green/ brown and they are small and “hidden” (or not showy). Fertilization happens after pollination. This is when the male gamete (pollen from the anthers) fuses with the female gamete (ovules) causing the zygote to form. Once the zygote develops into a seed, seed dispersal occurs. This is when seeds are moved away from the plant (in hopes that it will one day break dormancy and become a plant).
Dahlia being animal pollinated
External Dahlia seed structure
In order for seeds to germinate they NEED water, oxygen, favorable temperature. Water is necessary to activate activate enzymes which start respiration in the seed. Water also hydrates the seed and causes it to swell the seed so that it will burst open. Oxygen is needed so that the plant can respire until it's leaves have started growing. Most plants require a warm temperature to activate enzymes. The Dahlia requires a temperature between 60-70 degrees Fahrenheit for enzymes to activate and germination to occur. Dahlias seeds will germinate faster if they have bottom heat present as well.
1- Water enters the seed
2- Water activates the enzyme gibberellin acid (GA)
3- GA causes the production of the enzyme amylase
4- Amylase breaks starch down into maltose
5- Maltose is transported to the embryo and either hydrolyzed into glucose for use in cellular respiration or polymerised into cellulose and used in cell wall formation
9.3.5 Metabolic Processes in Germination of a Starchy Seed
Phytochrome pigment detects light in plants. It has two form, Pr (Inactive) and Pfr (Active). During daylight the Pr converts in Pfr can absorb far red light, and converts quickly back into Pr. However at night Pfr converts into Pr much slower. In long and short day plants the active Pfr amounts control flowering. In long day plants the Pfr is a promoter so more Pfr = flowering (more Pfr is available during the day). In short day plants (more appropriately called long night plants), such as the Dahlia, Pfr is an inhibitor. Therefore when the least amount of Pfr and most amount of Pr is present the plant flowers (so during the night because more Pr are accumulated during the night).
9.3.6 Flowering in long-day and short-day plants