CBSE Class 7 Science Excretory System Worksheet Set 01

Answer: (d) All of these. Several bacteria can infect the urinary tract.

Teacher's Note:
1. UTI is most often caused by bacteria.
2. It is usually treated with antibiotics.

Answer: (d) All of these. All three contain nitrogen and are formed from protein breakdown.

Teacher's Note:
1. Ammonia is the most toxic.
2. Urea and uric acid are less toxic.

Answer: (c) Uterus. The uterus is part of the reproductive system.

Teacher's Note:
1. Kidneys, skin and lungs all remove wastes.
2. The uterus holds the developing baby.

Answer: (d) Kidney. The kidneys filter blood and form urine.

Teacher's Note:
1. The other three are passages and storage.
2. They do not make urine.

Answer: (a) Urinary. Kidney stones form from salts in urine.

Teacher's Note:
1. They can block the flow of urine.
2. Drinking water helps to prevent them.

Answer: Urea (ammonia and uric acid are also correct).

Teacher's Note:
1. Nitrogenous wastes come from the breakdown of proteins.
2. Urea is the main one in humans.

Answer: liver

Teacher's Note:
1. This makes the waste safe to carry in blood.
2. The urea is then filtered out by the kidneys.

Answer: medulla

Teacher's Note:
1. The outer darker zone is the cortex.
2. The medulla leads to the pelvis.

Answer: Carbon dioxide

Teacher's Note:
1. It is a waste of cell respiration.
2. Water vapour is also given out.

Answer: nephron

Teacher's Note:
1. Each kidney has about a million nephrons.
2. Nephrons filter the blood.

Answer: urochrome

Teacher's Note:
1. It is formed from the breakdown of haemoglobin.
2. More water makes urine paler.

Answer: False. The lungs expel carbon dioxide.

Teacher's Note:
1. Oxygen is taken in, not removed as waste.
2. Carbon dioxide is the waste gas.

Answer: True. They are filtration, reabsorption and secretion.

Teacher's Note:
1. Filtration happens in the glomerulus.
2. Useful substances are taken back during reabsorption.

Answer: True.

Teacher's Note:
1. UTI is caused by bacteria.
2. A doctor should always be consulted.

Answer: False. In the kidney they are called kidney stones (renal calculi).

Teacher's Note:
1. Stones are named by where they form.
2. Bladder stones form only in the bladder.

Answer: True.

Teacher's Note:
1. It cleans the blood of patients whose kidneys have failed.
2. The process is called dialysis.

Answer: Excretion

Teacher's Note:
1. Wastes are produced by the cells all the time.
2. If they build up, they harm the body.

Answer: Nephrons

Teacher's Note:
1. Each nephron has a filtering unit and a tube.
2. Blood is cleaned as it passes through.

Answer: Sweat glands

Teacher's Note:
1. Sweat also helps to cool the body.
2. It is an accessory route of excretion.

Answer: Excretory organs are the organs that remove waste products from the body. Examples: kidneys, skin, lungs and liver.

Teacher's Note:
1. Kidneys are the main excretory organs.
2. The others help in removing particular wastes.

Answer: Bile pigments (bilirubin and biliverdin) are waste products formed in the liver from the breakdown of old red blood cells. They leave the body with bile in the faeces.

Teacher's Note:
1. They give faeces their brown colour.
2. Too many in blood causes jaundice.

Answer: Ureter: a tube that carries urine from a kidney to the bladder. Urinary bladder: a muscular bag that stores urine. Urethra: the tube through which urine leaves the body.

Teacher's Note:
1. There are two ureters and one urethra.
2. The bladder can stretch as it fills.

Answer: A UTI is an infection of any part of the urinary system, usually caused by bacteria, that can cause pain and a burning feeling while passing urine.

Teacher's Note:
1. It can be treated with antibiotics.
2. Drinking plenty of water helps to prevent it.

Answer: Excretion is the removal of metabolic wastes from the body. It is important because wastes such as urea are harmful if they build up and it helps keep the body's water and salt balance right.

Teacher's Note:
1. Cells make wastes all the time.
2. Removing them keeps the body healthy.

Answer: A Malpighian body is a filtering unit made of the Bowman's capsule and the glomerulus. It lies in the cortex of the kidney, at the start of each nephron.

Teacher's Note:
1. Blood is filtered through the glomerulus.
2. The filtrate collects in the capsule.

Answer: A dialyser is an artificial kidney machine. Blood from the patient flows through it, wastes pass into a special fluid, and the cleaned blood is returned to the body. It is used when the kidneys have failed.

Teacher's Note:
1. The treatment is called dialysis.
2. It is a temporary measure until a transplant if needed.

Answer: Kidney failure is when the kidneys cannot remove waste properly. ARF (acute renal failure) is a sudden loss of function, often reversible. ESRD (end stage renal disease) is a permanent loss, needing dialysis or a transplant.

Teacher's Note:
1. ARF may be caused by infection, injury or dehydration.
2. ESRD is the last stage of kidney disease.

Answer: Urine is formed in three stages: filtration of blood in the glomerulus, reabsorption of useful substances such as glucose and water, and secretion of extra wastes. It is about 95% water with urea, salts and other wastes.

Teacher's Note:
1. Nephrons carry out all three stages.
2. The urine then goes to the bladder.

Answer: Nitrogenous wastes (ammonia, urea, uric acid), carbon dioxide, excess water and salts, and bile pigments.

Teacher's Note:
1. Different organs remove different wastes.
2. Kidneys remove most of the nitrogenous wastes.

Answer: The kidneys and urinary tract may be affected, leading to stones or infections. He should drink plenty of water daily.

Teacher's Note:
1. Water helps to flush out wastes.
2. Little water makes urine concentrated.