Excretion in Organisms – Long Answer Questions
Medium Level (Application & Explanation)
Q1. Define excretion. Explain why it is necessary in living beings. Compare excretion in unicellular and multicellular organisms with examples.
Answer:
- Excretion is the removal of harmful metabolic wastes from the body.
- It helps maintain internal balance and keeps the organism healthy.
- In unicellular organisms, wastes pass out by simple diffusion through the cell membrane.
- For example, Paramecium releases waste into the surrounding water.
- In multicellular organisms like humans, excretion is done by special organs.
- Humans use kidneys, ureters, urinary bladder, and urethra to remove urine from the body.
Q2. Describe the human excretory system. State the role of each part in urine removal.
Answer:
- The human system has two kidneys, two ureters, a urinary bladder, and a urethra.
- Kidneys filter the blood and form urine.
- Ureters are tubes that carry urine from the kidneys to the bladder.
- The urinary bladder stores urine until the body is ready to pass it.
- The urethra is the final passage that releases urine outside.
- This system helps remove urea and maintain water and salt balance in the body.
Q3. Explain how urine is produced in the nephron. Include filtration and selective reabsorption.
Answer:
- The nephron is the basic unit of the kidney where urine is formed.
- First, filtration happens, and wastes like urea move from the blood into the nephron.
- Then, selective reabsorption returns useful things like glucose and amino acids to the blood.
- Water is also adjusted based on the body’s needs.
- In a healthy adult, about 180 liters of filtrate is made daily, but only 1–2 liters of urine is excreted.
- This shows that most useful substances and much water are reabsorbed back.
Q4. How do kidneys maintain water balance and control the concentration of urine in different conditions?
Answer:
- The kidneys keep the body’s water level in balance.
- When a person is well hydrated, the kidneys make dilute urine.
- When a person is dehydrated, the kidneys make concentrated urine.
- This control happens through selective reabsorption in the nephrons.
- The body thus keeps the blood clean and maintains the right fluid balance.
- This regulation protects cells from damage due to too much or too little water.
Q5. What is an artificial kidney (hemodialysis)? Explain how it works and how it differs from a natural kidney.
Answer:
- Hemodialysis is used when kidneys fail to clean the blood.
- The patient’s blood passes through tubes in a dialysing fluid.
- The fluid has no nitrogenous waste, so urea and other wastes move out by diffusion.
- This process helps keep the blood safe and balanced.
- A patient may need weekly sessions for several hours each.
- Unlike healthy kidneys, an artificial kidney does not reabsorb nutrients the same way, so it cannot fully copy all kidney functions.
High Complexity (Analysis & Scenario-Based)
Q6. Compare excretion in Paramecium and humans. Explain why their methods are suited to their living conditions.
Answer:
- Paramecium is unicellular and lives in water.
- It removes waste by simple diffusion through its cell membrane.
- This works well because it has a large surface area and lives in a fluid environment.
- Humans are multicellular and need special organs for excretion.
- The kidneys filter blood and make urine, which is carried by ureters and stored in the bladder.
- Human systems are complex, so a specialized excretory system ensures steady removal of urea and water balance.
Q7. A dialysis unit is setting up the dialysing fluid. Analyze what could go wrong if the fluid contains urea or lacks proper nutrient balance.
Answer:
- The dialysing fluid must have no nitrogenous waste like urea.
- If urea is present in the fluid, wastes will not move out of the blood.
- This will keep toxins inside the patient and can be dangerous.
- If the fluid is not balanced, useful nutrients like glucose may be lost from the blood.
- The result is weakness and imbalance in the patient’s body.
- So, the fluid must be carefully prepared to remove wastes but keep useful substances safe.
Q8. You plan to donate a kidney to a relative. Discuss the benefits, risks, and steps involved in such organ donation.
Answer:
- Organ donation can save lives, especially in kidney failure.
- A living donor can donate one kidney and live a healthy life with the other.
- You must go through medical tests to check fitness and compatibility.
- Proper consent and legal steps are required for ethical donation.
- After surgery, both donor and recipient need care and follow-up.
- Donation gives hope and improves the quality of life for the patient.
Q9. A tree faces injury and less water during summer. Analyze how it manages excretion and protects itself.
Answer:
- Plants release oxygen as a waste during photosynthesis.
- In drought, plants reduce transpiration to save water.
- They may store wastes in vacuoles or in old leaves.
- Trees can secrete resin to seal wounds and protect from infection.
- During leaf fall, plants remove excess salts and wastes with the leaves.
- These steps help plants survive stress and keep their internal balance.
Q10. A class uses a syringe and paper towels to model urine formation. Evaluate the model and suggest improvements to show nephron functions better.
Answer:
- The syringe acts like the nephron, and pushing water shows filtration.
- The paper towels show reabsorption by soaking extra water.
- The remaining water in the syringe stands for urine after reabsorption.
- To improve, add a filter paper to act like the glomerular filter.
- Use salt or sugar in water to show that useful solutes are reabsorbed.
- Note the limitation: the model cannot show active transport or precise control like real kidneys.