Tonoplast is a membrane around ?->(Show Answer!)

1. Tonoplast is a membrane around

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MCQ-> The membrane-bound nucleus is the most prominent feature of the eukaryotic cell. Schleiden and Schwann, when setting forth the cell doctrine in the 1830s, considered that it had a central role in growth and development. Their belief has been fully supported even though they had only vague notions as to what that role might be, and how the role was to be expressed in some cellular action. The membraneless nuclear area of the prokaryotic cell, with its tangle of fine threads, is now known to play a similar role.Some cells, like the sieve tubes of vascular plants and the red blood cells of mammals, do not possess nuclei during the greater part of their existence, although they had nuclei when in a less differentiated state. Such cells can no longer divide and their life span is limited Other cells are regularly multinucleate. Some, like the cells of striated muscles or the latex vessels of higher plants, become so through cell fusion. Some, like the unicellular protozoan paramecium, are normally binucleate, one of the nuclei serving as a source of hereditary information for the next generation, the other governing the day-to-day metabolic activities of the cell. Still other organisms, such as some fungi, are multinucleate because cross walls, dividing the mycelium into specific cells, are absent or irregularly present. The uninucleate situation, however, is typical for the vast majority of cells, and it would appear that this is the most efficient and most economical manner of partitioning living substance into manageable units. This point of view is given credence not only by the prevalence of uninucleate cells, but because for each kind of cell there is a ratio maintained between the volume of the nucleus and that of the cytoplasm. If we think of the nucleus as the control centre of the cell, this would suggest that for a given kind of cell performing a given kind of work, one nucleus can ‘take care of’ a specific volume of cytoplasm and keep it in functioning order. In terms of material and energy, this must mean providing the kind of information needed to keep flow of materials and energy moving at the correct rate and in the proper channels. With the multitude of enzymes in the cell, materials and energy can of course be channelled in a multitude of ways; it is the function of some information molecules to make channels of use more preferred than others at any given time. How this regulatory control is exercised is not entirely clear.The nucleus is generally a rounded body. In plant cells, however, where the centre of the cell is often occupied by a large vacuole, the nucleus may be pushed against the cell wall, causing it to assume a lens shape. In some white blood cells, such as polymorphonucleated leukocytes, and in cells of the spinning gland of some insects and spiders, the nucleus is very much lobed The reason for this is not clear, but it may relate to the fact that for a given volume of nucleus, a lobate form provides a much greater surface area for nuclear-cytoplasmic exchanges, possibly affecting both the rate and the amount of metabolic reactions. The nucleus, whatever its shape, is segregated from the cytoplasm by a double membrane, the nuclear envelope, with the two membranes separated from each other by a perinuclear space of varying width. The envelope is absent only during the time of cell division, and then just for a brief period The outer membrane is often continuous with the membranes of the endoplasmic reticulum, a possible retention of an earlier relationship, since the envelope, at least in part, is formed at the end cell division by coalescing fragments of the endoplasmic reticulum. The cytoplasmic side of the nucleus is frequently coated with ribosomes, another fact that stresses the similarity and relation of the nuclear envelope to the endoplasmic reticulum. The inner membrane seems to posses a crystalline layer where it abuts the nucleoplasm, but its function remains to be determined.Everything that passes between the cytoplasm and the nucleus in the eukaryotic cell must transverse the nuclear envelope. This includes some fairly large molecules as well as bodies such as ribosomes, which measure about 25 mm in diameter. Some passageway is, therefore, obviously necessary since there is no indication of dissolution of the nuclear envelope in order to make such movement possible. The nuclear pores appear to be reasonable candidates for such passageways. In plant cells these are irregularly, rather sparsely distributed over the surface of the nucleus, but in the amphibian oocyte, for example, the pores are numerous, regularly arranged, and octagonal and are formed by the fusion of the outer and inner membrane.Which of the following kinds of cells never have a nuclei?
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MCQ-> Read the passage carefully and answer the questions given below it. Certain words/ phrases have been given in bold to help you locate them while answering some of the questions. Once upon a time, there lived a washerman in a village. He had a donkey by the name of Udhata. He used to carry loads of clothes to the river bank and back home everyday. The donkey was not satisfied with the food, that was given to him by his master to eat. So he wandered into the nearby fields stealthily and ate the crops growing there. Once, the donkey, while wandering around, happened to meet a fox. Soon, both of them became friends and began to wander together in search of delicious food. One night, the donkey and the fox were eating water-melons in a field. The water- melons were so tasty, that the donkey ate in a large quantity. Having eaten to his appetite, the donkey became so happy that he was compelled by an intense desire to sing. He told the fox that he was in such a good mood that he had to express his happiness in a melodious tone. ‘Don’t be a fool. If you sing, the people sleeping in and around this field will wake up and beat us black and blue with sticks,’ said the fox worriedly. `You are a dull fellow’, the donkey said hearing the words of fox. ‘Singing makes one happy and healthy. No matter what comes. I’ll definitely sing a song.” The fox became worried to see the donkey adamant to sing a song in the midst of the field, while the owner was still sleeping only a little distance away. Seeing his adamance, he said to the donkey, ‘Friend, wait a minute before you start first, let me jump over to the other side of the fence for my safety.’ Saying so the fox jumped over to the other side of the fence without losing a moment. The donkey began in his so-called melodious tone. Hearing, suddenly, a donkey braying in the field, the owner woke up from his sleep. He picked up his stick lying by his side and ran towards the donkey who was still braying happily. The owner of the field looked around and saw the loss caused by the donkey. He became very angry and beat him so ruthlessly that the donkey was physically incapacitated temporarily. He, somehow, managed to drag himself out of the field with great difficulty. The fox looked at the donkey and said in a sympathetic tone, T m sorry to see you in this pitiable condition. I had already warned you, but you didn’t listen to my advice.’ The donkey too realised his folly and hung his head in shame.Why did donkey want to sing ?
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