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Plant Structure

The seed plants (gymnosperms and angiosperms) are the dominant and most studied group of plants, so their anatomy and development are considered here. The leaves and other aerial portions are all covered with a cuticle, a waxy layer that inhibits water loss. The leaves have stomata, microscopic pores which open in response to certain environmental cues for uptake of carbon dioxide and release of oxygen during photosynthesis. Leaves have veins, which connect them to the stem through a vascular system which is used for transport of water and nutrients throughout the plant.

There are two special types of cells in the vascular system, xylem and phloem. Xylem is mainly responsible for the movement of water and minerals from the roots to the aerial portions, the stems and leaves. Phloem is mainly responsible for the transport of food, principally carbohydrates produced by photosynthesis, from the leaves throughout the plant. The vascular system of plants differs from the circulatory system of animals in that water moves out of a plant's leaves by transpiration, whereas an animal's blood is recirculated throughout the body.

The roots of a plant take up water and minerals from the soil, and also anchor the plant. Most plants have a dense, fibrous network of roots, and this provides a large surface area for uptake of water and minerals. Mycorrhizae are symbioses between fungi and most plant roots and are important for water and mineral uptake in most plants. The fungal partner benefits by receiving carbohydrates from the plant, which benefits by being better able to absorb minerals and water from the soil. Mycorrhizae form on the roots of nearly all land plants, and many biologists believe they played a vital role in the evolution of the terrestrial habit.

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Science EncyclopediaScience & Philosophy: Planck mass to PositPlant - Plant Evolution And Classification, Evolution Of Plants, Classification Of Plants, Plant Structure, Plant Development