
Plants which bear naked seeds.
Answer
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Hint: Seeds plants are divided into two groups: Gymnosperms and Angiosperms. Gymnosperm seeds have no seed coat because of not forming a proper structure as a flower. They are more ancient than the angiosperms. Today, they all are dominating in the cold regions, where snow is the source of water. In warmer weather very few gymnosperms can be observed.
Complete answer:
Gymnosperms are plants in which the ovules are not enclosed by any ovary wall and remain exposed, both before and after fertilization. The seeds that develop post-fertilization are not covered, i.e., they are naked. Gymnosperms include medium-sized trees or tall trees and shrubs. One of the gymnosperms, giant redwood tree sequoia is one of the tallest tree species. The roots are generally tap roots. Roots in some genera have fungal association in the form of mycorrhiza (Pinus), while in some others like Cycas small specialized roots are present called coralloid roots and they are associated with $N_2$- fixing cyanobacteria. The stems are branched in Pinus and unbranched in Cycas. The leaves may be simple or compound. The leaves in gymnosperms are well adapted to withstand extremes of temperature, humidity and wind. In conifers, needle-like leaves reduce the surface area. Their thick cuticle and sunken stomata also help to reduce water loss. In gymnosperms male and female gametophytes do not have independent existence. They remain within the sporangia retained on the sporophytes.
Economic importance of gymnosperms:
1. Seeds are edible
2. Gymnosperm wood (timber) used in preparation of light furniture, plywood, etc.
3. Wood of gymnosperms (Picea, Larix) is used in the manufacturing of paper.
Note:
The gymnosperms are heterosporous, i.e., they produce haploid microspores and megaspores. All gymnosperms are vascular plants. Therefore, vascular tissues i.e., xylem and phloem are present. But here, xylem lack xylem vessels and phloem lack companion cells. Secondary growth takes place in the gymnosperm stem, so the stem is woody. Due to the absence of vessels gymnosperm wood is called soft wood.
Complete answer:
Gymnosperms are plants in which the ovules are not enclosed by any ovary wall and remain exposed, both before and after fertilization. The seeds that develop post-fertilization are not covered, i.e., they are naked. Gymnosperms include medium-sized trees or tall trees and shrubs. One of the gymnosperms, giant redwood tree sequoia is one of the tallest tree species. The roots are generally tap roots. Roots in some genera have fungal association in the form of mycorrhiza (Pinus), while in some others like Cycas small specialized roots are present called coralloid roots and they are associated with $N_2$- fixing cyanobacteria. The stems are branched in Pinus and unbranched in Cycas. The leaves may be simple or compound. The leaves in gymnosperms are well adapted to withstand extremes of temperature, humidity and wind. In conifers, needle-like leaves reduce the surface area. Their thick cuticle and sunken stomata also help to reduce water loss. In gymnosperms male and female gametophytes do not have independent existence. They remain within the sporangia retained on the sporophytes.
Economic importance of gymnosperms:
1. Seeds are edible
2. Gymnosperm wood (timber) used in preparation of light furniture, plywood, etc.
3. Wood of gymnosperms (Picea, Larix) is used in the manufacturing of paper.
Note:
The gymnosperms are heterosporous, i.e., they produce haploid microspores and megaspores. All gymnosperms are vascular plants. Therefore, vascular tissues i.e., xylem and phloem are present. But here, xylem lack xylem vessels and phloem lack companion cells. Secondary growth takes place in the gymnosperm stem, so the stem is woody. Due to the absence of vessels gymnosperm wood is called soft wood.
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