Morphology of Flowering Plants's Question 11 | Biology XI | NCERT Exemplar Questions

Botany

The Living World Biological Classification Plant Kingdom Morphology of Flowering Plants

Zoology

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Roots obtain oxygen from air in the soil for respiration. In the absence or deficiency of $\mathrm{O}_2$, root growth is restricted or completely stopped. How do the plants growing in marsh lands or swamps obtain their $\mathrm{O}_2$ required for root respiration?

Explanation

The roots of the plants (e.g., Rhizophora) growing in marshy/swamp areas become negatively geotropic. They grow vertically upwards in air, above the soil level and respire so called respiratory roots or pneumatophores.

Write floral formula for a flower which is bisexual, actinomorphic sepals five, twisted aestivation, petals five valvate aestivation; stamens six, ovary tricarpellary, syncarpous, superior, trilocular with axile placentation.

Explanation

Floral formula is a formula by which we can describe the flower by using some symbols. The various symbols describing the above given conditions are as follows

(i) Bisexual (ii) Actinomorphic $\oplus$ (iii) Sepals five $\mathrm{K}_5$ (iv) Twisted aestivation (v) Petals five $\mathrm{C}_5$ (vi) Valvate aestivation (vii) Stamens $\mathrm{A}_6$ (viii) Tricarpellary ovary $G_3$ (ix) Syncarpus $\mathrm{G}_{(3)}$

(x) Trilocular

(xi) Axile placentation

Floral formula would be

In Opuntia, the stem is modified into a flattened green structure to perform the function of leaves, (i.e., photosynthesis). Cite some other examples of modifications of plant parts for the purpose of photosynthesis.

Explanation

Opuntia is a xerophytic plant, in which leaves are modified into spine to reduce the rate of transpiration and they do not perform the photosynthesis at all.

So function of photosynthesis in Opuntia plant is performed by stem which is thick fleshy and flattened structure containing chlorophyll and stores food. It is known as phylloclade.

Sometimes, the stem, i.e., about one internode long modifies into a leaf like structure to carry out photosynthesis, as in Asparagus. They are present in axil of scale leaves while true leaves are reduced to scales or spines.

Similarly in some plants, roots become assimilatory as in the case of Trapa and Tinospora. These roots grow outside the soil, develop chlorophyll in them and perform photosynthesis.

In swampy areas like the sunderbans in West Bengal, plants bear special kind of roots called .........

Explanation

Pneumatophores Roots are the organs meant for the absorption of water and minerals from the soil. Cells of roots require $\mathrm{O}_2$ to respire. In swampy areas, soil does not have air, so no $\mathrm{O}_2$ is available to them.

In such cases, roots come out of the soil shows negative geotropism and breathe after coming in contact with air, e.g., Rhizophora. Such roots are called pneumatophores respiratory roots.

In aquatic plants like Pistia and Eichhornia, leaves and roots are found near ...........

Explanation

In Pistia and Eichhornia, in these floating plantes, the stem is like a runner where it branches to form leaves at the apex and roots below. The roots are found near the surface of water as both the plants are hydrophytes.

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