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So, a plasma membrane helps in maintaining the integrity of the cell. Other molecules are only admitted at certain times and in limited amounts. However, it is semi-permeable and the movement of substance is highly regulated. Made up of proteins and lipids, the plasma membrane is porous in nature and allows the movement of substances, both inward and outward. It is responsible for the shape of the cell. It is a flexible boundary of a cell that separates a cell from its surroundings. Present only in animal cells, they play an important role in cell division. They are associated with protein synthesis. Made up of ribosomal RNA and ribosomal proteins, these are small round particles that are found either attached to the surface of the endoplasmic reticulum or scattered in the cytoplasm. They also help in transporting them to various organelles and plasma membrane. Question 19: Write a short note on: (a) Golgi Bodiesįound located near the nucleus, Golgi bodies modify the proteins made by the ribosomes. It helps in the transportation of proteins, nutrients and organelles within the cell.
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Question 18: What is Cytoplasmic streaming? Give its importance.Īnswer: The movement of the fluid part of the cytoplasm within a cell is known as cytoplasmic streaming. Most of the plant cells show presence of single large vacuole.Ī single large vacuole is absent in animal cells however, they often show presence of many small vacuoles. These cells show the presence of plastids like chloroplasts. They lack cell wall and only show presence of plasma membrane. They contain a rigid cell wall in addition to cell membrane. Therefore, they are classified as prokaryotic organisms. Question 7: Why are bacteria classified as prokaryotic organisms?Īnswer: Bacteria lack a membrane-bound nucleus and other internal organelles like mitochondria and Golgi bodies. (e) Spikes are present on the pollen grains.Īnswer: This is because, during pollination, the spikes help the pollen grains to stick to the body of the pollinating insect or animal. (d) The nerve cells are elongated and highly branched.Īnswer: The nerve cells are elongated and highly branched because the branches help in the passage of chemical and electrical messages throughout the body. (c) The red blood cells are round and concave.Īnswer: They are round and concave so that they can easily squeeze through the narrow blood capillaries. This can only occur because they are able to change their shape. So, for this to happen, they have to migrate through the walls of small blood vessels and find their way in tissues. WBCs keep circulating in the blood stream but are usually required at the site of infection inside tissues. They eliminate pathogens by ‘eating’ them (phagocytosis). (b) The white blood cells are irregular in shape.Īnswer: White blood cells protect us from foreign invaders or pathogens like bacteria, viruses, etc. For example – Amoeba keeps changing its shape to move and engulf food. (a) The cells found in an organism can come in a variety of different sizes and shapes.Īnswer: The cells in an organism can come in a variety of different sizes and shapes to perform a specific function in the body. Cell Structure and Functions Questions & Answers Question 6: Give reasons: