Grade XI. Biology. (Important Questions) #GrowWithGreen

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Samuel Casey
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1 Grade XI Biology (Important Questions) #GrowWithGreen

2 Questions 1. Give answers to the following. (a) What would happen to the genome of a sexually reproducing organism in the absence of meiosis? (b) What is the actual reason behind progenies being genetically different from parents as a result of sexual reproduction? (c) Mitosis results in the formation of two daughter cells. How does it differ during the formation of syncytium in the liquid endosperm of coconut? 2. Compare and contrast the features of dicot leaves from those of monocot leaves. Support your answer with neat and labelled diagrams. 3. Glucose is prepared in leaves by photosynthesis. How and in what form is it transported to the place where it is required? Explain with the help of a diagram. 4. How does the ATP molecule aid the process of muscle contraction? Describe briefly. 5. Give answers to the following. (a) Organisms of which phylum are spiny bodied? What is the most distinctive feature of this phylum? (b) List some salient features of the class to which Delphinus (common dolphin) belongs.

3 Solutions 1. (a) Meiosis results in the reduction of chromosome number by half in gametes, which again doubles during fertilization. In the absence of meiosis, the gametes would be diploid and the zygote would contain 4n as its chromosomal content. The chromosomal number would keep increasing with each successive generation and each progeny would have double the content of chromosome as compared to that in the parent. The stability of traits and the match in characters among species, over generations, is attributed to meiosis only. (b) Crossing over is mainly responsible for the genetic difference between the parent and the progeny as a result of sexual reproduction. Crossing over occurs during the pachytene stage of prophase I. During this stage, the exchange of genetic material takes place between the two non sister chromatids of homologous chromosomes. This phenomenon is regulated with the help of the enzyme recombinase. It results in the formation of recombinant homologous chromosomes. (c) At the end of mitosis, karyokinesis results in the segregation of duplicated chromosomes into daughter nuclei. It is followed by cytokinesis that results in complete separation of daughter cells. However, in the liquid endosperm of coconut, karyokinesis is not followed by cytokinesis as a result of which multinucleate condition arises, thereby leading to the formation of syncytium. 2. Tissue organization Epidermis Mesophyll Dicot leaf (Dorsiventral) Monocot leaf (Isobilateral ) Covers both upper (adaxial, bearing less/no stomata) and lower (abaxial, bearing more stomata) surface of leaf and bears a cuticle. Differentiated into palisade parenchyma (has parallel, arranged elongated cells) and spongy parenchyma (with loosely arranged oval/round cells); it possesses chlorophyll. Stomata present on both sides. Not differentiated into palisade and is spongy.

venation); surrounded by bundle Bulliform cells (modified sheath cells.

4 Vascular bundle Present in midrib and veins (reticulate Leaves have parallel venation. venation); surrounded by bundle Bulliform cells (modified sheath cells. epidermal cells), which are present along the vein, absorb water and make the cells turgid. Structure of Dicot leaf: Structure of monocot leaf:

5 3. Glucose is prepared in leaves by photosynthesis. It is first converted into sucrose (a disaccharide) and then translocated to the sink. The mechanism used for translocation of sugars from source to sink is called pressure flow or mass flow hypothesis. Sucrose is moved into companion cells and then into living phloem sieve tube cells by active transport. This creates a hypertonic solution in phloem resulting in movement of water into phloem from adjacent xylem by osmosis. This builds an osmotic pressure. At sink, active transport moves sucrose into the cells, which will use it. This decreases the osmotic pressure of phloem and water moves out of it. 4. Role of ATP in muscle contraction: Before contraction Prior to contraction, ATP binds to the head of myosin, where the ATPase activity of myosin head cleaves the ATP into ADP and phosphate. The energy of phosphate bonds gets transferred to the myosin head. The products of ATP cleavage remain attached to the head of myosin before contraction. During contraction As the binding of myosin head to actin takes place, ADP and phosphate molecules are released from the head of myosin. This allows a new ATP molecule to get attached to the myosin head. This binding of the new ATP detaches the head of myosin from actin. The new ATP molecule is cleaved to start the new cycle of muscle contraction.

6 5. (a) The animals of phylum Echinodermata are spiny bodied because of the presence of exoskeleton of calcareous ossicles in them. The most distinctive feature of this phylum is the presence of the water vascular system, which helps in locomotion, capturing food and respiration. (b) Delphinus (common dolphin) belongs to class Mammalia. The salient features of this class are as follows: (i) They have milk producing mammary glands to feed their young ones. (ii) They have two pairs of limbs for walking, running, climbing, burrowing, swimming and flying. (iii) They have hair on their body. (iv) They have different types of teeth in their jaws. (v) Their heart is four chambered and they respire through lungs. (vii) Their sexes are separate, and they undergo internal fertilisation. They are mostly viviparous, and the development is direct.

13.2 The Vascular Plant Body (textbook p )

13.2 The Vascular Plant Body (textbook p544 550) Learning Goal: Label and explain the anatomy of the Vascular Plant and it's Tissue Types Plants are classified into two main groups: and. Vascular plants