1. What is meant by modification of root ? What type of modification of root is found in the
(a) banyan tree
(c) mangrove tress
Primarily, there are two types of root systems found in plants, namely the tap root system and fibrous root system. The main function of the roots is to absorb water and minerals from the soil. However, roots are also modified to perform various other functions. The roots of some plants act as storage sites for food, some provide support to massive plant structures, while others absorb oxygen from the atmosphere.
Roots and its modifications in various plants:
(a) Banyan tree
The banyan tree (Ficus benghalensis) has massive pillar-like adventitious roots arising from the aerial part of the stem. These roots grow towards the ground and provide support to the tree. Such, roots are called as prop roots.
The roots of turnip (Brassica rape) help in the storage of food. Similar food-storing roots are found in radishes, carrots and sweet potatoes.
(c) Mangrove tree
The roots of mangrove plants grow vertically upwards from the soil for the absorption of oxygen from the atmosphere as the soil is poorly aerated. These types of roots are called as pneumatophores.
2. Justify the following statement on the basis of external features :
(i) underground parts of a plant are not always roots.
(ii) flower is a modified shoot.
Various parts of plants are modified into underground structures to perform various functions such as stems, leaves and even fruits.
(i) The stems in ginger and banana are underground and swollen due to storage of food. They are called as rhizomes. Similarly, corm is an underground stem in Colocasia and Zamin-khand. The tips of the underground stem in potato become swollen due to the accumulation of food and forms tuber. Tubers bear eyes, which are subtended by a leaf scar. Basal leaves in onions become fleshy because of the accumulation of food. In peanuts, the flower after fertilization gets pushed into the soil by growing a flower stalk. The formation of fruits and seeds takes place inside the soil.
(ii) During the flowering season, the apical meristem gives rise to the floral meristem. The axis of the stem gets condensed, while the internodes lie near each other. Instead of leaves, various floral appendages arise from the node. Therefore, it can be said that the flower is a modified shoot.
3. How is a pinnately compound leaf different from a palmately compound leaf ?
Pinnately compound leaf: The leaflets are attached to the common axis, called as rachis.
Examples include neem and Cassia fistula (also called as golden shower plant).
Palmately compound leaf: The leaflets are attached at a common point on the leaf stalk.
Examples include silk cotton (Bombax) and Cannabis.
4. Explain with suitable examples the different types of phyllotaxy :
Phyllotaxy refers to the pattern or arrangement of leaves on the stem or branch of a plant. It is of three types: alternate, opposite and whorled phyllotaxy.
In alternate phyllotaxy, a single leaf arises from the node of a branch. This type of phyllotaxy is observed in the sunflower, mustard and peepal. Plants with opposite phyllotaxy have two leaves arising from the node in opposite directions. It is found in guava and jamun plants. Plants with whorled phyllotaxy have three or more leaves arising from the node. It is found in Alstonia.
5 . Define the following terms :
(a) Aestivation : The term ‘aestivation’ refers to the mode in which sepals or petals are arranged in a floral bud with respect to other floral members. There are four types of aestivation in plants, i.e., valvate, twisted, imbricate, and vexillary.
- It is indefinite inflorescence in which flowers are arranged acropetally that is a younger flower at the center while older flower at the base.
- Example – pea,wheat.
- It is definite inflorescene with an older flower at center and young flower at the base
- Example – petunia,chili
- It is the primary root that is short–lived and replaced by lateral roots and mainy found in monocots
- It is found in plants like wheat, rice etc..
- The root that aries from a part of a plant other than radicle
- It is found in banyan,dahlia etc.
- More than one carpel is present but fused.
- These are found in lotus and rose.
- More than one carpel is present but free
- These are found in mustard and tomato
8. Describe modifications of stem with suitable examples
Stems of various plants have undergone modifications to perform different functions.
1. Underground stems or storage stems: Examples: Rhizomes, Corms, tubers
In ginger and banana, the underground stem is called as a rhizome. The underground stem in Colocasia (arvi) is known as corm. Rhizomes and corms are underground stems, modified for the storage of food. Also, these stems help in 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.
2. Supportive stems:
The stem in some weak plants bears thin, slender and spirally-coiled structures called as 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.
3. Protective stems:
The stem in Bougainvillea and citrus plants (like lemon and orange) bear sharp, pointed structures called as thorns, which provide protection to the plant from herbivores.
4. Photosynthetic stems:
The stem in the Opuntia is green. It carries out the process of photosynthesis in the absence of leaves.
5. Others stem modifications:
In some plants, underground stems such as grasses spread in the soil and help in perenation. These stems are called as runners.
The short lateral stem called as the offset in some aquatic plants (such as Eichhornia) bears leaves and tufts of roots at the node and gives rise to new plants.
9. Take one flower each of the families fabaclae and solanaceae and write its semi–technical description ?
The ovary in which the placenta forms a ridge along the ventral suture of the ovary and the ovules develop on two separate rows is known to have marginal placentation. This type of placentation is found in peas.
When the ovules develop on the inner walls of the ovary, the ovary is said to have parietal placentation.
In axile placentation, the placenta is axial and ovules are attached to it. Examples include China rose, lemon and tomato.
The ovary in which the placenta develops from its base and a single ovule is found attached to the base is said to have basal placentation. It is found in marigold and sunflower.
In free central placentation, the ovules develop on the central axis while the septa are absent. This type of placentation is found in Dianthus and primrose.
A flower can be defined as the reproductive unit of any flowering plant (angiosperms). Flowers carry out sexual reproduction in angiosperms. A typical flower is a modified stem with a condensed axis. A flower has four different parts i.e., the calyx, corolla, androecium, and gynoecium. Androecium and gynoecium represent the male and female reproductive organs of a flower (respectively).
Parts of flowers
(A) The calyx forms the outermost whorl of a flower, which contains sepals. They are green, leaf–like structures that cover and protect the flowers during the bud stage. When the sepals of a flower are free, they are called polysepalous, while fused sepals of a flower are called gamosepalous.
(B) The corolla of a flower is a layer that lies inside the calyx. It contains beautifully coloured petals, which help in attracting insects for pollination. When the petals are free, they are called polypetalous, while fused petals are called gamopetalous.
(C) The androecium or the stamen is the male reproductive part of a flower. It consists of two parts, the filament and the bilobed anther. The bilobed anther is the site for meiosis and the generation of pollen grains.
(D) Gynoecium represents the female reproductive part of a flower. It consists of an ovary. The ovary is connected by a long tube (called style) to the stigma. The ovary bears numerous ovules attached to the placenta.
12. How do various leaf modifications help plants
The main function of the leaves is to carry out the process of photosynthesis. However, in a few plants, leaves are modified to perform different functions.
(a) Tendrils: The leaves of a pea plant are modified into tendrils that help the plant in climbing.
(b) Spines: The leaves in cactus are modified into sharp spines that act as an organ of defence.
(c) Phyllode: The leaves of some Australian acacia are short-lived and soon replaced by flattened, green structures called as phyllodes that arise from the petiole of the leaves. The petioles in these plants synthesize food.
(d) Pitcher: The leaves of the pitcher plant are modified into pitcher-like structures, which contain digestive juices and help in trapping and digesting insects.
13. Define the term inflorescence. Explain the basis for the different types of inflorescence in flowering plants
An inflorescence is arrangement and distribution of flowers over an axis of the plant called peduncle.
(i) Growth: Growth of the peduncle is indefinite in racemose inflorescence and definite in cymose inflorescence.
(ii) Branching of Peduncle: Peduncle is unbranched in simple racemose inflorescence. It is branched in compound racemose inflorescence.
(iii) Number of Branches: Cymose inflorescence is differentiated into uniparous (monochasial), biparous (dichasial) and multiparous (polychasial) depending upon the number of branches.
(iv) Pedicel: Presence or absence of pedicel in racemose inflorescence.
(v) Length of pedicel.
(vi) Condensation: Condensation of groups of flowers results in special inflorescence types.
(vii) Sex of Flowers: Certain types have unisexual flowers. For example, Catkin.
14. Describe the arrangement of floral members in relation to their insertion on thalamus ?
Based on the position of the calyx, corolla and androecium in relation to the ovary on the thalamus, the flowers are divided into 3 types, namely hypognous, perigynous and epigynous. In hypogynous flowers, the ovary is superior as it is present on thalamus. The other floral parts are present below thalamus. Example includes china rose. In perigynous flowers, the ovary is half inferior. It is situated in the centre. The floral parts are present on the rim of the thalamus. Example includes rose. In epigynous flowers, the ovary is inferior. The thalamus is present around the ovary. Examples include cucumber.