Ferns-web - Lecture 6 Ferns and Vascular Tissue Last...

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Lecture 6: Ferns and Vascular Tissue Last lecture we discussed the four major innovations in the evolution of plants. The four major innovations correspond to four major groups. 1) The mosses and all other land plants have an embryophyte, which nourished the developing embryo. This, in addition to a cuticular layer and stomata, made the colonization of land successful. Remember, however, that mosses still require water for fertilization (swimming sperm), are dominated by the gametophyte and grow close to the ground. 2) The seedless vascular plants, as well as the gymnosperms and angiosperms, have vascular tissue. Vascular tissue transports water, nutrients and organic compounds like sugars throughout the plant. We’re going to focus on vascular tissue today before talking about seedless vascular plants. 3) The evolution of the seed in gymnosperms and angiosperms. 4) The evolution of the flower in angiosperms. Vascular Tissue As I mentioned last lecture, land plants have a heterogeneous environment – some parts of the plant are underground, while some are in the air. Roots - are subterranean. They anchor the plant and absorb water and minerals. Leaves - are aerial portions of the plant, and the sight of most photosynthesis. Shoots - function to support the plant and are also important in transport Remember that photosynthesis requires water, so the plant needs water to make its way from the ground (where it is absorbed by roots) to the leaves. Water is also important for the daily life of a cell, so all the shoot system of the plant needs water. In addition to water, other essential nutrients and minerals (like nitrogen) need to be transported from the soil to other parts of the plant. This transport is done by vascular tissue called Xylem . In addition to its role in transport, xylem has another important function: support. Without support, land plants couldn’t grow more than a few centimeters in height. In contrast, the roots have water. What they don’t have is organic compounds in the form of sugars like glucose (the product of photosynthesis) and sucrose.
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