Class 10 Science Excretion Exam Notes

Class 10 Science: Excretion (Exam Notes)

Excretion

Excretion is the elimination of metabolic waste products from the body.

Waste products

1. Nitrogenous waste products. They are the major waste products which are formed during the breakdown of extra amino acids, nucleic acids and alkaloids. The important nitrogenous waste products are urea, uric acid, creatine, creatinine and ammonia.
2. Non-nitrogenous waste products: oxalic acid, lactic acid.
3. Excess chemicals: excess minerals, drugs, pigments, vitamins, hormones, cholesterol, etc.
4. Bile pigments: bilirubin, biliverdin and urochrome.
5. CO\(_2\)
6. Excess water.

Excretion in human beings

A pair of kidneys is the main excretory organ in humans.

Structure and function of the kidney in humans

1. There are two bean-shaped, dark red coloured kidneys placed just below the stomach, one on each side of the mid-dorsal line.
2. The depression is called the hilus, from where the ureter originates and the renal artery and renal vein go in and out.

The ureter, entering through the hilus, expands. The medulla on the inner side has cone-like structures called renal pyramids. Each kidney contains about one million nephrons. The functional unit of the kidney is the nephron.

Structure of the nephron

Each nephron consists of a round Malpighian body formed by the Bowman's capsule, filled with a capillary network (afferent and efferent arterioles; afferent means incoming, efferent means outgoing) called the glomerulus. The Malpighian body is also called the Malpighian corpuscle. The Malpighian tubule is divided into 3 parts, forming a shaped convoluted tubule.

1. The proximal tubule: nearest to the Bowman's capsule.
2. Henle's loop: a 'U'-shaped thin tube-like structure.
3. Distal tubule: joins the collecting tubule.

The ascending limb of Henle's loop again gives a second convoluted tubule opening into the collecting tubule and finally into a larger tubule known as the duct of Bellini, which opens into the pelvis of the ureter at the apex of the renal pyramids. The entire kidney tubule is surrounded by blood capillaries called the vasa recta.

Mechanism of urine formation

It has four steps: ultrafiltration, selective reabsorption, secretion and concentration.

1. Ultrafiltration. Blood flows inside the glomerulus under pressure due to the narrowness of the efferent arteriole. As a result it undergoes pressure filtration or ultrafiltration. All small-volume solutes (e.g. urea, uric acid, amino acids, hormones, glucose, ions, vitamins) and water are filtered out and enter the Bowman's capsule. The product is called the nephric or glomerular filtrate. Its volume is 125 ml/min (180 litres/day).
2. Reabsorption. The nephric filtrate is also called primary urine. It passes into the proximal convoluted tubule, which is surrounded by peritubular capillaries. The latter reabsorb all the useful components of the nephric filtrate, e.g. glucose, amino acids, vitamin C, calcium, potassium, sodium, chloride, bicarbonate and water (75%). Selective absorption also occurs in the region of the distal convoluted tubule.
3. Secretion (augmentation). It occurs mostly in the distal convoluted tubule, which is also surrounded by peritubular capillaries. A smaller amount of tubular secretion also takes place in the area of the proximal convoluted tubule. Tubular secretion is the active secretion of waste products by the blood capillaries. It causes removal of all the waste products from the blood, viz. urea, uric acid, creatinine. Extra salts, K\(^+\) and H\(^+\) are also secreted into the urinary tubule to maintain a proper concentration and pH of the urine.
4. Concentration of the urine. 75% of the water content of the nephric filtrate is reabsorbed in the region of the proximal convoluted tubule. Some 10% of water passes out of the filtrate through osmosis in the area of the loop of Henle, because the loops of Henle are immersed in hyper-osmotic interstitial fluid. Further concentration takes place in the area of the collecting tubule in the presence of the hormone called antidiuretic hormone (ADH) or vasopressin. Absence of ADH produces a dilute urine. Hormone action, therefore, maintains the osmotic concentration of body fluids. Deficiency of ADH causes excessive, repeated dilute urination (diabetes insipidus). The process of passing urine is called micturition.

Excretion in plants

Plants do not produce nitrogenous wastes like urea and uric acid because extra amino acids and nucleotides are not formed. They produce other types of waste products, called secondary metabolites, e.g. alkaloids, tannins, aromatic oils.

1. Nitrogenous waste products. They are byproducts of general metabolism. The common ones are alkaloids, e.g. quinine, morphine, atropine.
2. Organic acids. They are metabolic intermediates. Some of them have no other use; on accumulation they may prove toxic, e.g. oxalic acid.
3. Tannins. They are complex aromatic compounds which are formed as secondary metabolites.
4. Latex. It is an emulsion of varied composition which is excreted by special tubular cells called laticifers.
5. Resins. They are oxidation products of aromatic oils.
6. Gums. They are degradation products of the cell wall.

Mechanism of excretion in plants

Plants do not have any mechanism to collect, transport and throw out their waste products. They have adopted varied strategies to protect their living cells from waste products.

1. Old leaves. Waste products are stored in older leaves, which soon fall off.
2. Old xylem. Resins, gums, tannins and other waste products are deposited in the old xylem, which soon becomes non-functional, e.g. hard wood.
3. Bark. Bark consists of dead cells which are peeled off periodically. Tannins and other wastes are deposited in the bark. Incidentally, tannins are the raw material for dyes and inks.
4. Central vacuole. Most plant waste products are stored in the central vacuole of their cells. They are unable to influence the working of the cytoplasm due to the presence of a selectively permeable membrane called the tonoplast.
5. Root excretion. Some waste substances are actually excreted by the plants in the region of their roots.
6. Detoxification. The toxic oxalic acid is detoxified by formation of calcium oxalate, which gets crystallized into needles (raphides), prisms (prismatic crystals), stars (sphaeraphides) and crystal sand. Excess calcium is also precipitated as calcium carbonate crystals, e.g. cystolith.
7. Salt glands. They excrete excess salts obtained from the habitat.

(B) Henle loop - It is a 'U' shape thin tube like structure.

(C) Distal tubule - Join collecting tuble.

Ø MECHANISM OF URINE FORMATION

The process of passes urine in called Micturition.

Ø EXCRETION IN PLANTS

Question. Which of the following parts of a kidney contains the lowest concentration of urea ?
(A) Loop of Henle
(B) Branches of renal vein
(C) Bowman’s capsule
(D) Glomerulus
Answer : B

Question. The process of tubular secretion in nephron takes place in
(A) Glomerulus
(B) Ascending loop of henle
(C) Loop of Henle
(D) Distal convoluted tubule
Answer : D

Question. Urea is transported through
(A) RBCs
(B) WBCs
(C) Plasma
(D) lymph
Answer : C

Question. Major function of contractile vacuole is
(A) excretion
(B) circulation
(C) osmoregulation
(D) phagocytosis
Answer : C

Question. Which one is an accessory excretory organ ?
(A) Liver
(B) Stomach
(C) Intestine
(D) Heart
Answer : A

Question. Ammonia is converted into urea in
(A) kidney
(B) spleen
(C) liver
(D) nephron
Answer : C

Question. Uriniferous tubules of a kidney are concerned with formation of
(A) glucose
(B) amino acids
(C) hormones
(D) urine
Answer : D

Question. Plants excrete their excretion in form of -
(A) Solid
(B) Liquid
(C) Gaseous
(D) All of these
Answer : D

Question. Nitrogenous wastes are formed from the breakdown of :
(A) NH
(B) Fat
(C) Amino acids
(D) Water
Answer : C

Question. Functional unit of kidney is
(A) Nephron
(B) Nephritis
(C) Neuron
(D) Loop of Henle
Answer : A

Question. Technique which is used for purification of blood is known as :-
(A) Chromatography
(B) Dialysis
(C) ELISA
(D) None of these
Answer : B

Question. Excretion is removal of
(A) CO₂
(B) metabolic wastes
(C) nitrogenous waste
(D) all of these
Answer : D

Question. Urine is always fluid except in :
(A) Birds
(B) Humans
(C) Amphibians
(D) Mammals
Answer : A

Question. Osmoregulation is control over :
(A) Removal of nitrogen from the body
(B) Concentrations of salt and water in the body
(C) Osmotic properties of cell membrane
(D) pH of the blood
Answer : B

Question. In Amoeba, osmoregulation is carried out by :
(A) Food Vacuole
(B) Plasma membrane
(C) Contractile vacuole
(D) None of these
Answer : C

Question. The filterate from the glomerulus contains :
(A) Urea and uric acid
(B) Urea, uric acid and ammonia
(C) Urea, uric acid, ammonia and water
(D) Urea, uric acid, glucose and water.
Answer : D

Question. Frog’s tadpole are
(A) ureotelic
(B) ammonotelic
(C) uricotelic
(D) none of these
Answer : B

Question. Function of loop of Henle is
(A) conservation of water
(B) formation of urine
(C) filtration of blood
(D) passage of urine
Answer : A

Question. Solid waste of plant is -
(A) Raphides
(B) Sandal oil
(C) CO₂
(D) None of these
Answer : A

Question. Nitrogenous waste products are eliminated mainly as :
(A) Urea in tadpole and ammonia in adult frog
(B) Ammonia in tadpole and urea in adult frog
(C) Urea in both tadpole and in adult frog
(D) Urea in tadpole and uric acid in adult frog
Answer : B

Question. Which one of the following glands does not help in excretion ?
(A) liver
(B) sweat glands
(C) pancreas
(D) both (A) and (C)
Answer : C

Question. Excretion is a continous process but urine is not passed out continuously because of :
(A) Urinary bladder
(B) Cloaca
(C) Rectum
(D) Ureter
Answer : A

Question. If Henle’s loop is absent from mammalian nephron, which one of the following is to be expected ?
(A) Hardly any change in quality and quantity of urine formed
(B) Urine will be more concentrated
(C) Urine will be more dilute
(D) No urine formation
Answer : C

Question. Among which one of the following are part of nephron ?
(A) Cortex
(B) Medulla
(C) Bowman’s capsule
(D) Collecting duct
Answer : C

Question. Which blood vessel contains the least amount of urea?
(A) Hepatic vein
(B) Renal vein
(C) Hepatic portal vein
(D) Renal artery
Answer : B

Question. Diameter of the renal afferent vassel is
(A) Same as that of efferent
(B) Smaller than that of efferent
(C) Larger than that of efferent
(D) There is no efferent vessel
Answer : C