Excretion in Humans - Chapter 5 (Class 7 - Concise Biology Selina) ICSE

  

Excretion in Humans - Chapter 5

(Class 7 - Concise Biology Selina) ICSE

Excretion in Humans is a vital biological process by which the body removes waste products and maintains internal balance, known as homeostasis. The primary organ involved in this process is the kidney, which plays a crucial role in filtering the blood and removing waste.

The functional unit of the kidney is the nephron, where the process of filtration occurs. Blood enters the nephron, where waste products, including urea—a nitrogenous waste formed from the breakdown of proteins in the liver—are filtered out. During this process, essential substances like glucose and certain salts are reabsorbed back into the bloodstream, while additional waste is added to the filtrate in a process known as secretion. The final product of this filtration process is urine, which is a liquid waste composed of urea, excess salts, and water.

Urine is then transported from the kidneys to the bladder via tubes called ureters. The bladder stores urine until it is ready to be expelled from the body through the urethra.

In addition to the kidneys, other organs also participate in excretion. The skin removes waste through sweat, which contains urea, salts, and water. The lungs expel carbon dioxide and water vapor as part of the respiratory process. The liver is responsible for detoxifying harmful substances and converting ammonia into urea.

Various disorders can affect the excretory system, such as kidney stones, which are hard deposits that can form in the kidneys, and urinary tract infections (UTIs), which can cause discomfort and health complications. In cases where the kidneys fail to function properly, leading to kidney failure, a medical procedure called dialysis may be required to artificially remove waste products and excess fluids from the blood.

Excretion in humans is essential for removing harmful substances, maintaining fluid and electrolyte balance, and ensuring the overall health and stability of the body's internal environment.

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Question 1

The kidneys are made up of tiny tubular units called:

1. Glomerulus
2. Nephrons
3. Capillaries
4. Neurons

Answer

Nephrons

Reason — Nephrons are the microscopic tubular structures, inside the kidney. they are also known as renal tubules.

Question 2

In human beings, urea is produced in:

1. Liver
2. Kidney
3. Spleen
4. Urinary bladder

Answer

Liver

Reason — Breakdown of excessive amino acids in liver results in formation of urea.

Question 3

Besides water, the urine mainly contains:

1. Urea
2. Nitric acid
3. Glucose
4. Bile pigments

Answer

Urea

Reason — Urea and water are the major constituents of urine.

Question 4

Filtration of excretory wastes from the blood occurs in:

1. Collecting tubule
2. Ureter
3. Urinary bladder
4. Nephrons

Answer

Nephrons

Reason — The Nephrons remove the waste substances by filtering it from the blood.

Short Answer Questions

Question 1

Fill in the blanks:

1. Nitrogenous wastes in urine are in the form of ............... and ............... .
2. The unit of human kidney is called ............... .
3. Evaporation of sweat from skin surface has ............... effect.

Answer

1. Nitrogenous wastes in urine are in the form of urea and uric acid .
2. The unit of human kidney is called nephrons .
3. Evaporation of sweat from skin surface has cooling effect.

Question 2

Define the following:

1. Excretion
2. Excretory organs
3. Dialysis
4. Nephron

Answer

1. Excretion — The process of removal of unwanted and toxic metabolic waste products from the body is called Excretion.
2. Excretory organs — The organs that remove the unwanted waste and toxic substance from the body are known as Excretory organs.
3. Dialysis — The process of filtration of blood with the help of machine, if both kidneys fail, is called Dialysis.
4. Nephron — Nephron is the structural and functional unit of kidney. It filters the blood, purifies it and produces urine.

Question 3

Write True or False for the following statements in the spaces provided. Rewrite the false statements in correct form.

1. Removal of solid undigested food is excretion.
2. Medulla of kidney passes urine into urinary bladder.
3. Excess sugar in blood is a symptom of diabetes.
4. Urine is devoid of blood cells.

Answer

1. False
   Corrected statement — Removal of all kind of unwanted and toxic metabolic wastes is called excretion.
2. False
   Corrected statement — The medulla drains the urine into a funnel-shaped structure called the renal pelvis which further passes it to the urinary bladder through ureters.
3. True
4. True

Question 4

Name the blood vessel that brings blood to the kidneys.

Answer

Renal Vein brings blood to the kidneys.

Question 5

Where in the urinary system do the following processes take place?

1. Urine formation
2. Transport of urine away from kidney
3. Temporary storage of urine

Answer

1. Urine formation — Nephrons
2. Transport of urine away from kidney — Ureter
3. Temporary storage of urine — Urinary bladder

Long Answer Questions

Question 1

Define excretion. Write the four organs of human urinary system in their correct sequence.

Answer

The process of removal of unwanted and toxic metabolic waste products from the body is called Excretion.

The four organs of human urinary system in their correct sequence are:

1. Kidneys
2. Ureters
3. Urinary bladder
4. Urethra

Question 2

Why is excretion necessary in living beings?

Answer

The body produces many substances of which some are useful while the others are useless. If retained in the body, unwanted and toxic metabolic waste substances may become poisonous and cause much harm and in severe cases, even death. That is why excretion is necessary in living beings.

Question 3

What is meant by osmoregulation?

Answer

The process of maintaining or regulating the water and salt concentration in the body is called osmoregulation. Kidneys help in osmoregulation in our body.

Question 4

Describe the structure of kidney with the help of a labelled diagram.

Answer

Internally, each kidney is composed of an outer darker region called cortex and an inner lighter region called medulla. The medulla drains the urine into a funnel-shaped structure called the renal pelvis. Inside the kidney, there are millions of microscopic tubular structures called renal tubules or nephrons. The nephron is also called unit of kidney. Each nephron starts as a cup-like Bowman's capsule which continues behind as a narrow tubule. The tubule is convoluted and opens into a collecting duct. All the collecting ducts then open into the renal pelvis which leads into the ureter.

Below diagram shows the structure of the kidney:

Question 5

What are the two ways by which a person can get relief in case of kidney failure?

Answer

The two ways by which a person can get relief in case of kidney failure are:

1. Dialysis
2. Kidney transplant

Question 6

Draw a diagram of human excretory system and label the following parts:
Kidney, ureter, urinary bladder and urethra.

Answer

Below diagram shows the human excretory system with kidney, ureter, urinary bladder and urethra labelled:

Question 7

How are kidney stones formed?

Answer

Kidney stones are formed when crystal forming substances such as calcium oxalate, calcium phosphate and uric acid are more than the fluid in the urine. When these chemicals start sticking together, they form crystals, called kidney stones. They may be formed in any area of the excretory system and cause severe pain.

Question 8

What are the symptoms of a urinary tract infection?

Answer

Following are the symptoms of urinary tract infection:

1. Strong and frequent urge to urinate.
2. Painful urination.
3. Burning sensation while urinating.

Here’s a FAQ on Excretion in Humans:

1. What is excretion in humans?

Answer: Excretion in humans is the process by which the body removes waste products generated by metabolic activities, helping to maintain homeostasis and prevent the buildup of toxic substances.

2. Which organs are involved in the human excretory system?

Answer: The primary organs involved in excretion are the kidneys, ureters, bladder, and urethra. Other organs like the skin, lungs, and liver also play a role in excretion.

3. What are the main functions of the kidneys?

Answer: The kidneys filter blood to remove waste products such as urea, excess salts, and water, forming urine. They also help regulate blood pressure, electrolyte balance, and red blood cell production.

4. What is a nephron?

Answer: A nephron is the functional unit of the kidney where filtration, reabsorption, and secretion take place. Each kidney contains millions of nephrons.

5. What substances are excreted in urine?

Answer: Urine typically contains urea, excess salts, water, and other waste products filtered from the blood.

6. How do the lungs and skin contribute to excretion?

Answer: The lungs expel carbon dioxide and water vapor as waste products during respiration. The skin excretes waste through sweat, which contains urea, salts, and water.

7. What is urea, and how is it formed?

Answer: Urea is a nitrogenous waste product formed in the liver from the breakdown of proteins. It is transported to the kidneys for excretion in urine.

8. What happens if the kidneys fail to function properly?

Answer: If the kidneys fail, waste products can accumulate in the body, leading to kidney failure. This may require dialysis, a medical procedure that artificially removes waste and excess fluid from the blood.

9. What are some common disorders of the excretory system?

Answer: Common disorders include kidney stones, which are hard deposits formed in the kidneys, and urinary tract infections (UTIs), which are infections in any part of the urinary system.

10. What is dialysis, and when is it used?

Answer: Dialysis is a medical treatment used when the kidneys cannot filter blood effectively. It helps remove waste, excess fluid, and maintain electrolyte balance in the body.

11. Why is excretion important for the human body?

Answer: Excretion is crucial for removing toxic waste products, regulating body fluids and electrolytes, and maintaining overall health and balance in the body’s internal environment.

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