Chapter 5 · Life Processes

NCERT Class 10 Science Chapter 5 Intext Questions (Page 98)

All 3 questions of NCERT Class 10 Science Chapter 5 Intext Questions (Page 98) — Life Processes — in the book's order, each with its answer and a step-by-step solution.

1. Q1
   Describe the ​structure and ​functioning of ​nephrons.
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   A nephron filters blood at the glomerulus, re-absorbs the useful substances along the tubule, and passes the remaining urine to the collecting duct.

   Structure: A nephron is the basic filtration unit of the kidney, and each kidney contains a very large number of them packed close together. Each nephron consists of (1) a glomerulus — a cluster of very thin-walled blood capillaries supplied by a branch of the renal artery; (2) Bowman's capsule — the cup-shaped end of a long coiled tube, which encloses the glomerulus and collects the filtrate; (3) the tubular part of the nephron — the long coiled tube that leads on from the capsule, surrounded by a network of capillaries that carry blood on to a branch of the renal vein; and (4) a collecting duct, into which the tubule opens and which carries urine towards the ureter. Functioning: Blood enters the glomerulus under pressure, and water together with the small dissolved substances — glucose, amino acids, salts and the nitrogenous waste urea — is filtered through the thin capillary walls into Bowman's capsule (filtration). As this initial filtrate flows along the tubule, the useful substances — glucose, amino acids, salts and a major amount of water — are selectively re-absorbed into the surrounding capillaries; the amount of water taken back depends on how much excess water there is in the body and on how much dissolved waste has to be excreted (selective reabsorption). The fluid left — urea, excess water and excess salts — is urine; it passes into the collecting duct and then through the ureter to the urinary bladder, where it is stored until it is passed out through the urethra.

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2. Q2
   What ​are the ​methods ​used ​by ​plants ​to get rid ​of excretory products?
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   Plants lose gases through stomata and water by transpiration, store wastes in vacuoles, leaves, resins and gums, and release some into the soil.

   Plants have no excretory organs and use several methods to get rid of their excretory products: (1) Gaseous wastes — oxygen produced in photosynthesis and carbon dioxide produced in respiration — diffuse out through the stomata (and the surfaces of other parts). (2) Excess water is lost as vapour by transpiration. (3) Many waste products are stored in the vacuoles of cells. (4) Wastes may be stored in leaves, which then fall off, taking the wastes with them. (5) Other wastes are stored as resins and gums, especially in old xylem, whose cells are dead. (6) Some waste substances are excreted into the soil around the plant. Plants can use storage in this way because many of their tissues consist of dead cells and because they can lose parts such as leaves.

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3. Q3
   How ​is ​the ​amount ​of urine produced ​regulated?
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   The volume of urine is set by how much water the tubule re-absorbs, which depends on excess body water and dissolved waste.

   The amount of urine produced is regulated by how much water is re-absorbed from the filtrate as it flows along the tubular part of the nephron. About 180 L of initial filtrate is formed a day, but a major amount of its water is selectively re-absorbed and only a litre or two leaves as urine. The amount of water re-absorbed depends on two things: (1) how much excess water there is in the body — when the body has excess water, less is re-absorbed and a large volume of dilute urine is produced; when the body is short of water, more is re-absorbed and only a small volume of concentrated urine is produced; and (2) how much dissolved waste there is to be excreted — more waste needs more water to carry it out, so less water is re-absorbed and more urine is formed.

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