. Explain the different types of stem modifications giving an example of each. 2. Explain the different types of leaf modifications giving an example of each. 3. What is pollination? What are the different types of cross-pollination? 4. Draw labelled diagrams of parts of a fruit and a seed and explain their structures. 5. What is seed dispersal? Describe the different methods by which seeds are dispersed.
Answers
1)Stems of various plants have undergone modifications to perform different functions.
* Underground stems or storage stems:
Examples: Rhizomes, Corms, tubers
In ginger and banana, the underground stem is called a rhizome. The underground stem in Colocasia (arvi) is known as a corm. Rhizomes and corms are underground stems, modified for the storage of food. Also, these stems help in the vegetative reproduction of these plants. The tips of the underground stem in potato plants become swollen due to the accumulation of food. The potato is a tuber that helps in the storage of food and bears eyes on it. Subtended by a leaf scar, these eyes bear buds that give rise to new plants.
* Supportive stems:
Example: tendril
The stem in some weak plants bears thin, slender, and spirally-coiled structures called tendrils that help the plant get attached to nearby structures for support. Tendrils are found in cucumbers, melons, and other members of the family Cucurbitaceae.
* Protective stems:
Example: Thorns
The stem in Bougainvillea and citrus plants (like lemon and orange) bear sharp, pointed structures called thorns, which protect the plant from herbivores.
* Photosynthetic stems:
Example: Opuntia
The stem in the Opuntia is green. It carries out the process of photosynthesis in the absence of leaves.
* Others stem modifications:
In some plants, underground stems such as grasses spread in the soil and help in the operation. These stems are called runners.
The short lateral stem called the offset in some aquatic plants (such as Eichhornia) bears leaves and tufts of roots at the node and gives rise to new plants.