(20 points) you may use both sides of this page to answer this question.
In a temperate rainforest in Washington State, a moss is found growing on an oak tree (Angiosperm). Discuss the characteristics that make the oak evolutionarily advanced relative to the moss. Be sure to discuss any selective advantages associated with the advanced traits.
Mosses, the first terrestrial plants, are primitive compared to an oak tree. Important evolutionary advances that have occurred between bryophytes and angiosperms include the move from haploid to diploid dominance, the development of vascular tissues, heterospory, the production of seeds, and the production of flowers.
The diploid dominant stage of the oak is advantageous relative to the haploid dominant stage of the moss because deleterious mutations can be masked in the heterozygote in the diploid stage.
The production of vascular tissues, xylem and phloem, allow plants to move water, nutrients, and sugar around the plant. Coupled with the development of true leaves, stems, and roots, the production of a vascular system allows plants to no longer be limited to inhabiting moist environments and allows them to increase in size. Thus, the plants possessing vascular tissues can exploit more ecological niches and achieve greater reproductive success.
The production of heterospores allows plants to produce microgametophyte and megagametophyte generations. In angiosperms, the microgametophyte develops into the pollen grain and the female gametophyte is an 8 celled structure located in the ovule. Because the sperm are able to move to the ovule in the pollen tube via cellular processes, heterosporous plants no longer require swimming sperm so they are not limited to living in environments that are wet during the reproductive season. Thus, heterosporous plants can exploit more ecological niches.
Reproducing by seeds is a large advantage compared to reproducing by spores. Inside an angiosperm seed, the embryonic plant is protected from desiccation by the seed coat and following germination, the developing embryo is provided resources held by the endosperm cells. Thus, an individual seed has a much higher chance of survival than an individual spore.
Reproducing via flowers is advantageous over the reproductive style of the moss. First, flowers can aid in the dispersal of pollen from one plant to another. Second, in mosses, the zygote is formed in the archegonia. In flowering plants, the zygote is produced inside of the ovule which is held inside of the ovary of the flower. The ovary provides protection to the developing zygote. Ultimately, the ovary develops into the fruit which can help to disperse the seeds either by animals or the wind.
(20 points)
Plants convert electromagnetic energy in light to potential energy stored in glucose by the process of phtotosyntheis. Discuss, in detail, the energy conversions that occur during this process.
The process of photosynthesis converts electromagnetic energy in light into potential energy stored in glucose. Important energy conversions occur in the following processes, (1) in a photosystem, (2) in the light dependent reactions, and (3) in the light independent reactions.
In a photosystem light energy is converted into potential energy held in an excited electron. Photosystems are clusters of antennae pigments, a reaction center, and a primary electron acceptor that are located in thylakoid membranes. When antennae pigments absorb a photon of light energy and electron is excited to a higher energy level. When the electron returns to resting stage, the energy released is used to excite an electron in an adjacent pigment, a process known as resonance. Resonance funnels energy to the reaction center chlorophyll a where an electron is excited to a higher energy level and then that electron, and its potential energy, is passed to the primary electron acceptor.
In the light dependent reactions, potential energy in an electron excited in a photosystem is converted to chemical energy in ATP and NADPH by the process of electron flow. Cyclic electron flow converts potential energy in an excited electron to chemical energy in ATP. The excited electron from PS II moves down an electron transport chain. Energy released each time the electron moves from one molecule to the next is used to actively transport hydrogen ions from the stroma inside the thylakoid space. The resulting hydrogen ion concentration gradient powers the process of chemiosmosis that results in the production of ATP. In non-cyclic electron flow, ATP is produced by a similar mechanism as the excited electron moves from PSII to PSI. When the electron is re-excited in PSI it undergoes a different pattern of electron flow that results in the production of NADPH.
The light independent reactions convert the potential energy stored in the short term energy storage molecules ATP and NADPH into potential energy in glucose that can be stored for a longer period of time. The Calvin Cycle, which takes place in the stroma, uses the ATP and NADPH produced in the light dependent reactions to covert carbon dioxide into glucose. ATP and NADPH are required to convert PGA into glyceraldehyde phosphate which can either be used to created glucose or can be converted into RuBP, a reaction that requires the addition of energy from ATP.
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