One day the science teacher of class 7 collected some modified adventitious roots and some underground modified stems and showed these to his students.
a. What is nodulose root?
b. What do you mean by prop root?
c. Draw the level diagrams of the adventitious roots modified for performing physiological functions.
d. Analyze the reasons of modification of the roots and stems mentioned above.
Answers
Angiospermic or flowering plants show a great variety of shape, size and form. The size ranges from the minute Wolffia and Lamna (0.1cm) to the tall Eucalyptus (up to 100 metre) and large sized Banyan (Ficus bengalensis). In habit, they range from herbs and shrubs to trees.
Morphology (Gr. Morphos = Form; logos = Study) is the branch of science which deals with the study of form and structure. In botany, it generally means the study of external features, forms and relative positions of different organs on plants.
It is virtually impossible to recognise and know all the flowering plants even for a professional taxonomist. However, a student of botany takes the help of morphology for recognition, identification and classification of plants. Some distinct morphological features are most significant in the study of phytogeography, phylogeny and evolution.
Parts of a flowering plant: Flowering plants consist of a long cylindrical axis which is differentiated into underground root system and an aerial shoot system. The root system consists of root and its lateral branches. The shoot system has a stem, a system of branches and leaves. The different parts of a plant are called organs. Organs are differentiated into two types, vegetative and reproductive. Vegetative organs take part in nourishing and fixing the plant, viz., root, stem, leaves. Reproductive organs are required in multiplication. They comprise flowers, fruits and seeds (formed inside fruits). Organs similar in basic internal structure and origin which may appear different and perform different functions are called homologous organs. The relationship amongst these organs is called homology. Organs performing a similar function or having a similar external form but different internal structure and origin are termed as analogous organs. The relationship in analogous organs is called anology.
The Root
The root is usually an underground part of the plant which helps in fixation and absorption of water. The root with its branches is known as the root system.
(1) Characteristics of the root
(i) The root is the descending portion of the plant axis and is positively geotropic.
(ii) It is non-green or brown in colour.
(iii) The root is not differentiated into nodes and internodes.
(iv) As a rule the root does not bear leaves and true buds.
(v) Usually the root tip is protected by a root cap.
(vi) The root bears unicellular root hairs.
(vii) Lateral roots arise from the root which are endogenous in origin (arises from pericycle).
(2) Parts of the root : From the tip of the root upwards, the following parts can be traced in root.
(i) Region of root cap : The tip of the root is called calyptra or root cap. It is for protection of root tip against any injury. It is formed from meristem called calyptrogen. Pandanus is the only plant with multiple root caps. In the aquatic plants like Pistia, Lemma and Eicchornia instead of root caps, they have root pockets for buoyancy. The root caps are absent in parasites and mycorrhizal roots.
Explanation:
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