Class 11 Biology
Question 1: What is meant by modification of root? What type of modification of root is found in the:
(a) Banyan tree (b) Turnip (c) Mangrove trees
Answer: Sometimes, roots are modified to serve some functions other than its main function of providing anchorage and absorption of water and minerals.
Banyan Tree: In banyan trees, hanging roots come out from branches. The hanging roots then go into the soil to provide additional support to the huge banyan tree. Such roots are called prop roots.
Turnip: The tap root in turnip is modified for food storage.
Mangrove trees: Mangrove trees are found in marshy area. In such plants, many roots come out vertically above the ground. These are hollow roots and are called pneumatophores. They facilitate exchange of gases in the roots.
Question 2: Justify the following statements on the basis of external features:
(i) Underground parts of a plant are not always roots.
Answer: In some plants, stems are also underground for some additional purpose; like food storage and vegetative propagation. Presence of scaly leaves on potato and ginger shows that they are not roots rather stems.
(ii) Flower is a modified shoot.
Answer: Flower comes out of stem hence it is a shoot. It serves the special purpose of sexual reproduction. Hence, flower is called a modified shoot.
Question 3: How is a pinnately compound leaf different from a palmately compound leaf?
Answer: Leaflets are present on a common axis (rachis); in case of pinnately compound leaves. In palmately compound leaves, the leaflets originate from the apex of the midrib.
Question 4: Explain with suitable examples the different types of phyllotaxy.
Answer: Phyllotaxy: The arrangement of leaves on the stem or branch is called phyllotaxy. There are three types of phyllotaxy, which are as follows:
Alternate: In this type of leaf arrangement, a single leaf arises at each node in alternate manner, e.g. China rose, mustard, sunflower, etc.
Opposite: In this type of leaf arrangement, a pair of leaves arise at each node. The leaves lie opposite to each other in this case, e.g. Calotropis, guava, etc.
Whorled: In this type of leaf arrangement, more than two leaves arise at a node, e.g. Alstonia.
Question 5: Define the following terms:
(a) aestivation (b) placentation (c) actinomorphic (d) zygomorphic (e) superior ovary (f) perigynous flower (g) epipetalous stamen
Answer: Aestivation: The mode of arrangement of sepals or petals; with respect to the other members of the same whorl is called aestivation.
Placentation: The arrangement of ovules in the ovary is called placentation.
Actinomorphic: When a flower shows radial symmetry, it is called an actinomorphic flower, e.g. mustard, datura, chilli, etc.
Zygomorphic: When a flower shows bilateral symmetry, it is called a zygomorphic flower, e.g. pea, gulmohar, bean, Cassia, etc.
Superior Ovary or Hypogynous Flower: When the ovary occupies the highest position and other floral parts are below it, the flower is called hypogynous. In this case, the ovary is said to be superior, e.g. mustard, China rose, brinjal, etc.
Perigynous Flower: When the ovary and other parts of the flower are situated at the same level, the flower is called perigynous. In this case, the ovary is said to be half-inferior, e.g. plum, rose, peach, etc.
Epipetalous Stamens: When stamens are attached to the petals, this arrangement is called epipetalous, e.g. brinjal.
Question 6: Differentiate between
(a) Racemose and cymose inflorescence
|Main axis continues to grow.||Main axis terminates.|
|Flowers are arranged in acropetal order.||Flowers are arranged in basipetal order.|
(b) Fibrous root and adventitious root
|Fibrous roots||Adventitious roots|
|Arise from embryonal axis||Do not come from embryonal axis|
|Main function is absorption of minerals and water||It can provide additional support and can carry out vegetative propagation.|
(c) Apocarpous and syncarpous ovary
Answer: Carpels are free in apocarpous ovary, while they are fused in syncarpous ovary.
Question 7: Describe modifications of stem with suitable examples.
Answer: Modifications of Stem
Modification for food storage: The underground stems of potato, ginger, turmeric, zamikand, Colocasia, etc. are modified for food storage. Such modifications are the tools of perenation to tide over unfavourable conditions.
Modifications for climbing: In some plants, stem tendrils develop form axillary buds. These are slender and spirally coiled structures. A tendril helps the plant to climb to a support, e.g. cucumber, pumpkin, grapevine, etc.
Modification for defence: In some plants, the axillary buds are modified into woody, straight and pointed thorns. Such thorns protect the plant from browsing animals, e.g. Citrus, Bougainvillea.
Modification for photosynthesis: In some plants of arid regions, the stems are modified into flattened or fleshy cylindrical structures. The flattened structure can be seen in Opuntia and the cylindrical structure can be seen in Euphorbia. Such structures contain chlorophyll and photosynthesis happens in them.
Modification for vegetative propagation: Stems are modified for vegetative propagation in many plants, e.g. grass, berry, dahlia, etc.
Question 8: What is a flower? Describe the parts of a typical angiosperm flower.
Answer: The flower is a reproductive part of an agiospermic plant. The flower serves the purpose of sexual reproduction. In a typical flower, there are four kinds of whorls. These whorls are successively arranged on the swollen end of the stalk or pedicel. The swollen end of the stalk is called thalamus or receptacle.
Whorls of Flower:
Calyx: The outermost whorl of a flower is called calyx. It is composed of sepals. Sepals are usually green and leaf-like structures. The sepals protect the flower during the bud stage. Calyx is called gamosepalous when sepals are united and is called polysepalous when sepals are free.
Corolla: The second whorl of a flower is called corolla. It is composed of petals. Petals are usually brightly coloured. The bright colours attract the insects and birds for pollination. Corolla is called gamopetalous when petals are united and is called polypetalous when petals are free. Corolla can be tubular, bell-shaped, funnel-shaped or wheel-shaped.
Androecium: The third whorl of a flower is called androecium. It is composed of stamens. A stamen is composed of a stalk and an anther. An anther is usually a bilobed structure. There are two chambers (pollen sacs) in each lobe of an anther. Pollen sacs produce pollen grains. A sterile stamen is called staminode.
Gynoecium: The central whorl of a flower is called gynoecium. It is composed of one or more carpels. A carpel is composed of three parts. The basal swollen portion is called ovary. The long tubular part over ovary is called style and the flat top at the style is called stigma. The style is the receptive surface for pollen grains. Each ovary bears one or more ovules which are attached to a flattened, cushion-like placenta.
Question 9: How do the various leaf modifications help plants?
Answer: Modification of Leaves
Tendrils: In some plants, leaves are modified into tendrils to assist in climbing, e.g. pea.
Spines: In some plants, leaves are modified into spines for defence, e.g. cactus. The leaf spine in cacti and in some other xerophytes also helps in reducing water loss by preventing transpiration.
Bulb: In some plants, the leaves are modified into bulb for food storage, e.g. garlic and onion.
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