Grade XI. Biology. (Important Questions) #GrowWithGreen

Transcription

1 Grade XI Biology (Important Questions) #GrowWithGreen

2 Questions 1. Use the following information to answer the question (a) Identify the family shown in the floral diagram given. Also, give its floral formula. (b) Explain the type of aestivation observed in its corolla. (c) Write down the various vegetative characters of this family. 2. (a) What is the effect of substrate concentration on enzyme activity? Draw a graph representing its effects. (b) Why does high temperature destroy enzyme activity? 3. How is the concentration gradient maintained in the medullary interstitium to produce urine that is four times concentrated than the initial filtrate formed? 4. (a) Who proposed the fluid mosaic model of plasma membrane? (b) What do you mean by fluidity of cell membrane? State its importance. (c) Schematically represent the fluid mosaic model of plasma membrane. 5. Give answers to the following. (a) Explain why it is said that length of intestine depends on the component of food forming the major part of diet of organism. Explain it with the help of example. (b) Which digestive gland is a heterocrine gland? Justify your answer.

3 Solutions 1. (a) The given floral diagram represents family Fabaceae. Its floral diagram can be depicted as: (b) The corolla of the Fabaceae has five petals that consist of a posterior large petal (standard), which overlaps the two lateral petals (wings), which, in turn, overlap the smallest anterior petals (keel). This type of aestivation is vexillary or papilionaceous. (c) The vegetative characters of the given family are as follows: (i) Plants are mostly trees, shrubs and herbs with nodules in their roots. (ii) The stem is either erect or climber. (iii) Leaves are alternate, pinnately compound or simple, leaf base pulvinate, stipule and venation reticulate. 2. (a) The velocity of an enzymatic reaction increases initially with an increase in the substrate concentration. However, when the reaction reaches maximum velocity (V max ), there is no further increase in the reaction with the rise in concentration of the substrate. This is because all active sites of enzymes get occupied by the substrate due to low concentrations of enzyme molecules and there are no free enzyme molecules left to bind with the substrate.

4 (b) High temperature destroys enzyme activity because enzymes are proteins in nature and proteins get denatured by heat. 3. The counter current mechanism in the Henle s loop and vasa recta helps in maintaining the concentration gradient in the medullary interstitium. The flow of filtrate in two limbs of Henle s loop and the limbs of vasa recta is in opposite direction, thus forming a counter current. The osmolarity is maintained by the medullary interstitium through the proximity between Henle s loop, vasa recta and by the counter current mechanism. NaCl is returned to the interstitium by ascending portion of vasa recta. Small amount of urea entering the ascending limb of Henle s loop is transported back to the interstitium by the collecting tubule. This transport is facilitated by counter current mechanism. Thus, maintaining a concentration gradient. This gradient helps in the easy passage of water from the collecting tubule. As a result, the urine produced is four times concentrated than the initial filtrate formed. 4. (a) Fluid mosaic model of plasma membrane was proposed by Singer and Nicolson in (b) Fluidity is the measure of the ability of the membrane to allow movement within itself. Fluid nature of the membrane is important for cell division, cell growth, and formation of intercellular junctions, secretion and endocytosis. (c) 5. (a) Yes, it is true that the length of intestine depends on the component of food. It is the small intestine where the complete digestion and absorption takes place. For example, in herbivorous animals, the main food component is plants containing cellulose. Hence, their intestine is large as it takes time to digest complex molecules such as cellulose. On the other hand, in case of flesh eating animals, protein is the main food component.

5 Proteins can be digested easily. Hence, the length of intestine is small in carnivores. (b) Pancreas is both exocrine and endocrine in nature. Hence, it is also known as heterocrine gland. Its exocrine part secretes pancreatic juices that contain enzymes for digestion. The endocrine cells of pancreas are called the islets of Langerhans. These cells secrete hormones such as insulin, glucagon that help in regulating blood sugar level.