EXCRETION IN ANIMALS

Meaning

Excretion → The process of removing waste products from the body.
Waste materials are harmful if not removed.
Main wastes: Carbon dioxide (CO₂) and Nitrogenous wastes (like urea, ammonia).

Excretion in Different Animals

Amoeba (Single-Celled Animals)
- CO₂ → Removed by diffusion through the cell membrane.
- Nitrogenous wastes (ammonia) + Excess water → Removed by contractile vacuole.
Earthworm
- Nephridia → Tubular excretory organs that remove nitrogenous wastes.
- Moist skin → Also helps in excretion.
Humans
- Nephron → Functional unit of the kidney (about 1 million nephrons per kidney).
- Kidneys → Main excretory organs, remove urea and other wastes.

Removal of Waste in Humans

1. Lungs → Remove CO₂

CO₂ is produced during respiration (oxidation of food).
From tissues → into blood → carried to lungs → exhaled through nostrils.
Lungs = Excretory organs for respiratory waste.

2. Kidneys → Remove Urea

Urea is produced in the liver by breakdown of extra proteins.
Kidneys filter blood through nephrons, removing urea + extra salts + water → forms urine.

Key Points to Remember

Amoeba: Diffusion + Contractile vacuole.
Earthworm: Nephridia + Moist skin.
Humans: Kidneys (urea) + Lungs (CO₂).
Waste removal is necessary to prevent poisonous accumulation.

Quick Diagram Tips (for exams)

Draw Amoeba showing contractile vacuole.
Draw Earthworm with nephridia marked.
Draw Human excretory system with kidneys, ureters, urinary bladder, urethra.

Excretion in Humans, simplified but still detailed for student learning.

EXCRETION IN HUMANS

Definition

Excretion is the process by which the human body removes liquid and gaseous wastes to maintain internal balance and prevent toxicity.

Main Organs of Human Excretory System

Kidneys – Bean-shaped organs (2), located above the waist, at the back.
Ureters – Tubes carrying urine from each kidney to the bladder.
Urinary Bladder – Bag-like organ that stores urine.
Urethra – Tube that passes urine from bladder to outside the body.

Structure & Function of Kidneys

Function:
- Remove urea, unwanted salts, and excess water from blood.
- Clean blood by filtration.
Blood Supply:
- Renal artery → brings dirty blood to kidneys.
- Renal vein → carries clean blood away from kidneys.
Excretory Unit: Nephron (about 1 million per kidney).

Structure of a Nephron

Bowman’s Capsule – Cup-shaped structure at the start of nephron.
Glomerulus – Bundle of capillaries inside Bowman’s capsule, filters blood.
Tubule – Long coiled tube connected to Bowman’s capsule.
Collecting Duct – Receives urine from many nephrons.

Process of Urine Formation

Filtration (in Glomerulus):
- Dirty blood enters via renal artery → glomerulus filters it.
- Small molecules (glucose, amino acids, salts, urea, water) pass into Bowman’s capsule.
- Large molecules (proteins, blood cells) remain in the blood.
Selective Reabsorption (in Tubule):
- Useful substances (all glucose, amino acids, most salts, most water) reabsorbed into surrounding capillaries.
Formation of Urine:
- Waste substances (urea, some salts, excess water) left in tubule → urine.
Urine Pathway:
- Nephron → Collecting duct → Ureter → Urinary bladder (storage) → Urethra (excretion).

Composition of Human Urine

Water – ~95%
Urea – Main nitrogenous waste
Salts – Na⁺, K⁺, Cl⁻, etc.
Small amounts of uric acid and creatinine.

Key Facts

Each kidney filters blood many times a day.
Average adult produces 1–1.5 liters of urine daily.
Kidneys also maintain water balance and salt balance.

✅ Exam Tip: Draw and label:

Human Excretory System (kidneys, ureters, bladder, urethra)
Nephron structure (Bowman’s capsule, glomerulus, tubule, collecting duct)

Renal Failure (Kidney Failure) & Technology for Survival.

Renal Failure (Kidney Failure)

Meaning

Renal failure = Complete or severe loss of kidney function.
Kidneys can no longer remove waste (like urea) or maintain water–salt balance.

Causes of Kidney Failure

Infection in kidneys.
Injury to kidneys.
Very high blood pressure (hypertension).
Very high blood sugar (uncontrolled diabetes).
Restricted blood flow to kidneys.

Effects of Kidney Failure

Urea & wastes build up in blood → poisonous to body.
Water balance not regulated → swelling and fluid retention.
If untreated, can cause death.

Treatment Options

1. Kidney Transplant – Best long-term solution

Damaged kidney removed.
Matching kidney from a healthy donor is surgically transplanted.
Restores normal kidney function.
Donor can live with one kidney.

2. Dialysis (Artificial Kidney) – If transplant is not possible

A kidney machine removes nitrogenous wastes from the blood.
Process is called dialysis.
Works like a natural kidney: filters blood, removes urea, excess salts, and water.
Periodic treatment needed (several hours, multiple times a week).

Key Points to Remember

Kidney failure = life-threatening if untreated.
Transplant gives long-term relief.
Dialysis is a temporary/regular support method, not a cure.

✅ Exam Tip: Draw diagrams of:

Kidney Transplant process (damaged vs. transplanted kidney).
Artificial kidney setup for dialysis.

Dialysis

Meaning

Dialysis → A medical procedure to clean the blood of a person with kidney failure by removing waste products like urea, excess salts, and extra water.
Done using a kidney machine (also called dialysis machine or artificial kidney).

Principle of Dialysis

Works on the principle of diffusion through a selectively permeable membrane.
Waste products pass out of the blood into a special fluid (dialysing solution), but useful substances stay in the blood.

Process of Dialysis

Blood collection:
- Blood is taken from an artery in the patient’s arm.
Passing through Dialyser:
- The blood flows into a dialyser made of long tubes of selectively permeable membrane (like cellulose).
- These tubes are coiled in a tank containing dialysing solution.
Dialysing Solution:
- Contains water, glucose, and salts in the same concentration as in normal blood (no urea).
- Prevents loss of useful substances from the patient’s blood.
Waste Removal:
- Urea and wastes in the blood pass through the membrane into the dialysing solution.
- Useful substances (glucose, salts, most water) remain in the blood.
Returning Clean Blood:
- Cleaned blood is pumped back into a vein in the patient’s arm.

Key Points

Dialysis must be done regularly if kidneys cannot function.
It is not a cure, but a life-support method until a kidney transplant is possible.
Each dialysis session can last 4–5 hours and may be needed 2–3 times a week.

Sample Question:
The kidneys in human beings are a part of the system for:
(a) Nutrition (b) Respiration (c) Excretion (d) Transportation
✅ Answer: (c) Excretion

complete CBSE Class 10 Science Q&A set based on the topics you gave:

Excretion in Animals
Excretion in Humans
Renal Failure (Kidney Failure)
Dialysis

CBSE Class 10 Science – Excretion (Q&A)

A. Multiple Choice Questions (MCQs)

In Amoeba, nitrogenous wastes are removed by:
(a) Diffusion (b) Nephridia (c) Contractile vacuole (d) Kidney
Answer: (c) Contractile vacuole
Which is the main excretory organ in humans?
(a) Lungs (b) Kidneys (c) Skin (d) Liver
Answer: (b) Kidneys
The functional unit of the kidney is:
(a) Glomerulus (b) Nephron (c) Bowman’s capsule (d) Tubule
Answer: (b) Nephron
The process of cleaning blood using a machine when kidneys fail is called:
(a) Transplant (b) Filtration (c) Dialysis (d) Respiration
Answer: (c) Dialysis
In dialysis, the selectively permeable membrane is made of:
(a) Glucose (b) Cellulose (c) Protein (d) Starch
Answer: (b) Cellulose

B. Very Short Answer (VSA) – 1 mark each

Name two excretory products in humans.
Answer: Carbon dioxide and urea.
Where is urea produced in the human body?
Answer: In the liver.
What is the main nitrogenous waste in human urine?
Answer: Urea.
Which organ removes carbon dioxide from the body?
Answer: Lungs.
Name the cup-shaped structure in nephron.
Answer: Bowman’s capsule.

C. Short Answer Questions – Type I (2 marks each)

Name the excretory organs in earthworm and Amoeba.
Answer:
- Earthworm → Nephridia and moist skin.
- Amoeba → Contractile vacuole (for ammonia & water) and cell membrane (for CO₂).
Write any two differences between dialysis and kidney transplant.
Answer:
- Dialysis → Periodic cleaning of blood using a machine; temporary measure.
- Kidney transplant → Surgical replacement of damaged kidney with a donor kidney; permanent solution.
What is the role of the glomerulus in nephron?
Answer: The glomerulus filters blood, allowing small molecules like glucose, amino acids, salts, urea, and water to pass into Bowman’s capsule while retaining large molecules like proteins and blood cells.

D. Short Answer Questions – Type II (3 marks each)

Explain the process of selective reabsorption in the nephron.
Answer: After filtration in Bowman’s capsule, the filtrate passes through the tubule. Useful substances like glucose, amino acids, most salts, and most water are reabsorbed into the surrounding blood capillaries. Waste products like urea remain in the tubule and form urine.
Write the composition of human urine.
Answer: Human urine contains about 95% water, urea as the main nitrogenous waste, salts (Na⁺, K⁺, Cl⁻), and small amounts of uric acid and creatinine.
Give two causes of kidney failure and its immediate effect on the body.
Answer:
- Causes: High blood pressure, uncontrolled diabetes.
- Effect: Accumulation of urea and wastes in blood; imbalance of water and salts; can be life-threatening.

E. Long Answer Questions (5 marks each)

Draw a neat, labeled diagram of the human excretory system and explain the function of each part.
Answer:
Functions:
- Kidneys: Filter blood, remove urea, salts, and excess water.
- Ureters: Carry urine from kidneys to bladder.
- Urinary bladder: Stores urine.
- Urethra: Passes urine out of body.
  (Diagram must be drawn with labels.)
Describe the process of urine formation in humans.
Answer:
Urine formation takes place in three steps:
- Filtration: In glomerulus, small molecules (glucose, amino acids, salts, urea, water) pass into Bowman’s capsule; large molecules remain in blood.
- Selective Reabsorption: In the tubule, useful substances are reabsorbed into surrounding capillaries.
- Urine Collection: Remaining waste substances (urea, some salts, extra water) form urine, which flows into collecting duct → ureter → bladder → urethra.
Explain the principle, process, and importance of dialysis.
Answer:
Principle: Diffusion through a selectively permeable membrane.
Process:
- Blood from an artery is passed into a dialyser containing cellulose tubes immersed in dialysing solution (same salt, glucose concentration as blood, no urea).
- Wastes like urea diffuse into solution; useful substances remain in blood.
- Clean blood is returned to the patient’s vein.
  Importance: Keeps patient alive by removing toxic wastes when kidneys fail.

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