The Fundamental Unit of Life Answers

5 The Fundamental Unit of Life In the Chapter The cell is the fundamental organisational unit of life. Cells are enclosed by a plasma membrane composed of proteins and lipids. The cell membrane is an active part of the cell. It controls the movement of materials between the ordered interior of the cell and the outer environment. In plant cells, a cell wall composed mainly of cellulose is located outside the cell membrane. The presence of the cell wall enables the cells of plants, fungi and bacteria to exist in hypotonic media without bursting. The nucleus in eukaryotes is separated from the cytoplasm by double-layered membrane and it directs the life processes of the cell. The ER functions both as a passageway for intracellular transport and as a manufacturing surface. The Golgi apparatus consists of stacks of membrane-bound vesicles that function in the storage, modification and packaging of substances manufactured in the cell. Most plant cells have large membranous organelles called plastids, which are of two types-chromoplasts and leucoplasts. Chromoplasts that contain chlorophyll are called chloroplasts and they perform photosynthesis. The primary function of leucoplasts is storage. Most mature plant cells have a large central vacuole that helps to maintain the turgidity of the cell and stores important substances including wastes. Prokaryotic cells have no membrane-bound organelles, their chromosomes are composed of only nucleic acid, and they have only very small ribosomes as organelles. Intext Exercises Page No. 59 1. Who discovered cells, and how? Ans. (i) The cell was discovered by Robert Hook, in 1665. (ii) He discovered cell in a cork slice with the help of a primitive microscope. 2. Why is the cell called the structural and functional unit of life? Ans. (i) In all living organisms whether as large as elephant or as small as bacteria, it is the cell which constitute the body. Hence, it is called structural unit of life. (ii) In all living organisms, it is the cell which performs different functions. The cells are the smallest units involved in the division of labour. Hence, it is called the functional unit of life. Page No. 61 1. How do substances like CO, and water move in and out the cell? Discuss. Ans. The substances move from place of higher concentration to the place of lower concentration in a cell. When the concentration of CO, in the external environment of the cell is higher than that inside the cell CO, moves inside the cell. When the concentration outside the cell becomes low and it is high inside the cell due to metabolic activities, the CO, moves out. In the same way, water also moves outside and inside the cell. 2. Why is plasma membrane called a selectively permeable membrane? Ans. Plasma membrane allows some substances to go in and out of the cell, but does not allow some other substances to either enter or leave the cell. That is why, it is called as selectively permeable membrane. Page No. 63 1. Fill in the gaps in the following table illustrating difference between prokaryotic and eukaryotic cells. Ans. Prokaryotic Cell 1. Size: generally small (1um) 1 um = 10m 2. Nuclear region: not surrounded by a nuclear membrane and known as-nuceoid. 3. Chromosome: single 4. Membrane-bound cell organelles absent Eukaryotic Cells. 1. Size: generally large (5 um) 2. Nuclear region: well defined and surrounded by a nuclear membrane 3. More than one chromosome 4. Membrane-bound cell organelles present Page No. 65 1. Can you name the two organelles we have studied that contain their own genetic material? Ans. (i) Mitochondria, (ii) Plastids 2. If the organization of a cell is destroyed due to some physical or chemical influence, what will happen? Ans. If the structure of a cell is destroyed, the cell will not be able to perform its basic functions, such as respiration and nutrition, and will not be able to synthesise protein. This may stop all the life activities of the organism and may result in its death. 3. Why are lysosomes known as suicide bags? Ans. When the cell is destroyed, the lysosomes explode and their enzymes eat (digest) their own cell. That is why, they are called suicide bags. 4. Where are proteins synthesized inside the cell? Ans. The proteins are synthesized in the Ribosome inside the cell.