Morphology of Flowering Plants – The Leaf: NEET MCQs with Answers

Explanation: Alstonia has simple leaves with whorled phyllotaxy; palmately compound leaves are seen in silk cotton, so Palmately compound – Alstonia is the mismatched pair. China-rose has alternate phyllotaxy, the leaflets of pea are modified into tendrils, and Calotropis has opposite phyllotaxy.

Explanation: In a pinnately compound leaf, a number of leaflets are present on a common axis, the rachis, as in neem; being a dicot, neem also has reticulate venation. Mango and Alstonia have simple leaves, and silk cotton has palmately compound leaves.

Explanation: In the xerophyte Opuntia the leaves are reduced to spines, which check transpiration and protect the plant, while the flattened green stem (phylloclade) takes over photosynthesis. In pea it is the terminal leaflets that become tendrils.

Explanation: Bladderwort is Utricularia, in which the leaf segments form bladder-like traps; Sundew is Drosera, whose leaves bear sticky glandular hairs; and Venus flytrap is Dionaea, whose leaf lamina forms a hinged trap. All three are insectivorous plants that supplement their nitrogen requirement by trapping insects.

Explanation: Alstonia is a dicotyledonous plant, so its leaves have reticulate (net-like) venation, and about five simple leaves are borne in a whorl at each node. Neem has compound leaves, while Calotropis and China rose do not show whorled phyllotaxy.

Explanation: In Australian Acacia the leaf lamina falls off early and the petiole becomes flattened, green and leaf-like; such a modified petiole is called a phyllode. Phyllodes are held vertically and bear fewer stomata, which reduces transpiration in the dry habitat.

Explanation: Three plants — Ocimum, guava and Calotropis — show opposite phyllotaxy, in which a pair of leaves arises at each node and lies opposite to each other. China rose, mustard and sunflower have alternate phyllotaxy, whereas Alstonia and Nerium have whorled phyllotaxy.

Explanation: In xerophytes such as Opuntia, Asparagus and Solanum surattense, the leaves are reduced to sharp, pointed spines. This modification checks transpiration and also protects the plant from grazing animals, the photosynthetic function being taken over by the green stem.

Explanation: Phyllotaxy is the pattern of arrangement of leaves on the stem. In whorled phyllotaxy more than two leaves arise at a node and form a whorl, as in Alstonia (about five leaves per whorl). Mustard and China rose show alternate phyllotaxy while Calotropis shows opposite phyllotaxy.

Explanation: In Australian Acacia the leaf blade is shed early and the petiole flattens out, turns green and takes over photosynthesis; such a modified petiole is a phyllode, and it reduces transpiring surface in a dry climate. Asparagus has cladodes and Opuntia and Euphorbia have flattened or fleshy photosynthetic stems, all of which are stem modifications rather than leaf modifications.

Explanation: Australian Acacia has a phyllode (flattened photosynthetic petiole).

Explanation: Alstonia has whorled, simple leaves with reticulate venation.

Explanation: In Australian Acacia the petiole becomes flattened and leaf-like (a phyllode) and performs photosynthesis after the pinnate leaflets fall off.

Explanation: Alstonia (Devil tree) shows whorled phyllotaxy with simple leaves having reticulate venation.

Explanation: In Alstonia more than two leaves arise at each node (whorled phyllotaxy). Calotropis is opposite, and mustard and China rose are alternate (NEET 2019).