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REET L2 (Maths-Science) · Science

Excretion — REET Notes

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The excretory system is an important life-processes topic in REET Level 2 Science, and the kidney, nephron, and the process of urine formation get asked about the most. This page walks through the human excretory system, the excretory products of different organisms, and excretion in plants, in order, following the syllabus.

  • 0 questions in REET 2024
  • Class 9-10 level content
  • 7 min read
Verified 17 September 2026 · Source: NCERT Science Textbook (Class 9-10)

How this topic is asked in REET

To be upfront: no direct question on the excretory system came up in the REET 2024 paper — it saw zero (0) questions in 2024. This page is built entirely on the language of the official REET Level 2 (Maths-Science) syllabus. Since 'Life Processes' is a syllabus section, there's a real chance of direct factual MCQs on nephron structure, kidney function, and excretory products (urea/uric acid/ammonia).

What is excretion, and why it matters

Metabolic activities in the body produce a number of harmful, unwanted nitrogenous waste products, such as urea, uric acid, and ammonia. The process of removing these waste products from the body is called excretion. If these substances keep accumulating in the body, they can cause toxicity, which is why a healthy excretory system is essential for life.

Organs of the human excretory system

The human excretory system mainly has four parts — the kidneys (a pair, i.e. 2), the ureters (one from each kidney), the urinary bladder (where urine is stored temporarily), and the urethra (through which urine leaves the body). The structural and functional unit of the kidney is the nephron, and each kidney has millions of nephrons. Each nephron has parts such as Bowman's capsule, the glomerulus (a tuft of capillaries), the proximal convoluted tubule (PCT), the loop of Henle, and the distal convoluted tubule (DCT).

The process of urine formation

Urine formation happens in three steps. First, filtration — blood passes through the glomerulus in the kidney and is filtered into Bowman's capsule, where water, glucose, salts, and nitrogenous waste are filtered out. Second, reabsorption — in the tubules (PCT and the loop of Henle), substances useful to the body, such as glucose, the necessary amount of water, and salts, are reabsorbed back into the blood. Third, secretion — some additional waste substances are added into the tubule. Finally, the remaining fluid, now urine, passes through the collecting duct, then the ureter, into the bladder, and leaves the body through the urethra.

Types of organisms based on their excretory product

ClassMain excretory productExamples
AmmonotelicAmmonia (needs a lot of water)Most aquatic animals, fish
UreotelicUreaHumans and most mammals
UricotelicUric acid (needs less water, semi-solid)Birds, reptiles, insects

The type of excretory product an organism has is linked to how much water it needs to conserve.

Other excretory organs and important facts

Skin
Removes extra water, salts, and some urea in the form of sweat
Lungs
Remove the carbon dioxide produced during respiration
Dialysis
A medical procedure that artificially purifies the blood when the kidneys fail
Excretion in plants
Gases (O₂/CO₂) via stomata, excess water via transpiration, and solid waste disposed of as gum/resin or by shedding leaves

Kidney location, structure, and the composition of urine

Both human kidneys sit in the abdominal cavity, on either side of the spine, and are shaped like a bean. Each kidney receives impure blood via the renal artery, which is filtered clean inside the kidney and returns to the body's circulatory system via the renal vein. This arrangement shows how deeply connected the excretory and circulatory systems are.

The final urine that's formed is mostly about 95% water, with the rest carrying dissolved urea and other nitrogenous waste, extra salts, and some other metabolic products. A healthy person's urine normally has no glucose or protein in it, because these useful substances get reabsorbed back into the blood during reabsorption — if a urine test finds glucose or protein, it can be a sign of a health problem.

Kidneys also work to maintain the body's water balance and keep the right amount of salts in the blood, which is why they're seen not just as a 'waste-removal organ' but as an important regulatory organ that keeps the body's internal environment stable. Drinking enough water and eating a balanced diet helps keep the kidneys healthy.

How to teach this to students

Classroom activity

Have students observe their own sweat after exercise or running, and discuss how this is also a form of excretion; get them to build a simple kidney-and-nephron model out of clay or cardboard.

Teaching aids

Showing a labelled chart of the excretory system and an enlarged diagram of a nephron in class is useful at Class 9-10 level.

Common misconception

Students often think urine 'collects' in the kidney, when actually urine is formed in the kidney and collects in the bladder — this distinction needs to be made clear.

Assessment idea

Give students an unlabeled diagram of the excretory system and have them label the organs in order (kidney → ureter → bladder → urethra), and write out the path urine flows.

Memory trick / exam tip

To remember the order urine flows, build a sentence — 'Kidney makes it, ureter carries it, bladder stores it, urethra lets it out.' And remember that the structural and functional unit of the kidney is always the 'nephron' — this is a one-word answer that gets asked repeatedly in REET, so lock it in.

Practice questions

Question 1

What is the structural and functional unit of the kidney called?

  1. Aन्यूरॉन
  2. Bनेफ्रॉन
  3. Cएल्वियोलस
  4. Dहेपेटोसाइट

Explanation

The nephron is the structural and functional unit of the kidney, forming urine through filtration, reabsorption, and secretion.

Question 2

What is the main nitrogenous excretory product in humans?

  1. Aअमोनिया
  2. Bयूरिया
  3. Cयूरिक एसिड
  4. Dकार्बन डाइऑक्साइड

Explanation

Humans and most mammals are ureotelic, meaning they excrete their main nitrogenous waste as urea.

Question 3

In birds and reptiles, the excretory product is mainly in which form?

  1. Aअमोनिया
  2. Bयूरिया
  3. Cयूरिक एसिड
  4. Dजल

Explanation

Birds and reptiles are uricotelic — they excrete uric acid in a semi-solid form, which conserves the body's water.

Question 4

Filtration of blood in the nephron takes place in which part?

  1. Aदूरस्थ कुंडलित नलिका (DCT)
  2. Bहेनले लूप
  3. Cबोमन संपुट व केशिका-गुच्छ (glomerulus)
  4. Dमूत्रवाहिनी

Explanation

Blood is first filtered as it passes through the glomerulus into Bowman's capsule, where water, salts, glucose, and nitrogenous waste get filtered out.

Question 5

Which structure carries urine from the kidney to the urinary bladder?

  1. Aमूत्रमार्ग (Urethra)
  2. Bमूत्रवाहिनी (Ureter)
  3. Cवृक्क धमनी
  4. Dहेनले लूप

Explanation

The ureter carries urine from each kidney to the bladder, while the urethra carries urine out of the body from the bladder.

Question 6

In what way does the skin act as an accessory excretory organ?

  1. Aयह यूरिक एसिड को ठोस रूप में निकालती है
  2. Bयह पसीने के रूप में जल, लवण व कुछ यूरिया निकालती है
  3. Cयह कार्बन डाइऑक्साइड का मुख्य उत्सर्जन अंग है
  4. Dयह मूत्र का भंडारण करती है

Explanation

The skin helps in excretion through sweat glands, releasing extra water, salts, and a small amount of urea.

Question 7

What is the artificial medical procedure to purify blood in case of kidney failure called?

  1. Aएंजियोप्लास्टी
  2. Bडायलिसिस
  3. Cबायोप्सी
  4. Dकिमोथेरेपी

Explanation

In dialysis, a machine draws blood out of the body, filters out waste products, and then returns the purified blood to the body.

Question 8

A teacher has students observe sweating after exercise and links it to excretion. Which teaching objective does this activity serve?

  1. Aकेवल शारीरिक व्यायाम करवाना
  2. Bदैनिक जीवन के अनुभव को वैज्ञानिक संप्रत्यय से जोड़ना
  3. Cसमय बर्बाद करना
  4. Dकेवल परीक्षा तैयारी

Explanation

Connecting an everyday experience, like sweating, to a scientific concept makes learning meaningful and lasting — this is a core feature of constructivist teaching.

Question 9

Plants mainly remove excess water through which process?

  1. Aप्रकाश संश्लेषण
  2. Bवाष्पोत्सर्जन (Transpiration)
  3. Cश्वसन
  4. Dपरागण

Explanation

Plants release excess water as vapour through their stomata, a process called transpiration, which is also a form of excretion in plants.

Question 10

What is the role of 'reabsorption' in human urine formation?

  1. Aअपशिष्ट पदार्थों को रक्त में वापस मिलाना
  2. Bउपयोगी पदार्थों जैसे ग्लूकोज़ व जल को वापस रक्त में अवशोषित करना
  3. Cमूत्र को मूत्राशय में जमा करना
  4. Dरक्त को केशिका-गुच्छ तक पहुँचाना

Explanation

In reabsorption, useful substances such as glucose and necessary water are absorbed back into the blood from the tubules (PCT and loop of Henle), which keeps the body nourished.

Frequently asked questions

What is the structural and functional unit of the kidney?+

The structural and functional unit of the kidney is the nephron, which carries out the entire process of urine formation.

How many kidneys does a human have?+

A healthy human normally has two kidneys, located in the abdominal cavity on either side of the spine.

How do plants excrete?+

Plants release gaseous waste through the stomata, extra water through transpiration, and some solid waste as gum/resin or by shedding old leaves.

What is dialysis?+

Dialysis is a medical procedure that uses a machine to artificially filter waste products out of the blood when the kidneys fail.

How many REET questions have come from the excretory system?+

No direct question on this topic came up in REET 2024, but being part of the 'Life Processes' section, it stays important for upcoming exams.

How much water does urine normally contain?+

A healthy person's urine is about 95% water, with the rest carrying dissolved urea, salts, and other metabolic waste.

Where does the kidney receive impure blood from, and where does the purified blood go?+

The kidney receives impure blood from the renal artery, and the blood filtered clean there returns to the circulatory system via the renal vein.

Read next

Respiration

REET notes: Respiration — read this before this topic.

Human Digestive System

REET notes: Human Digestive System — read this after this topic.

REET Syllabus

See the full official REET Level 1 and Level 2 syllabus, subject by subject.

REET 2024 Solved Paper

All REET 2024 questions with solutions and explanations in Hindi.

Official Sources

  1. NCERT Science Textbook (Class 9-10)
  2. NCERT Science Textbook (Class 6-8)

Change Log

  • 17 September 2026 — English page published — mirrors the fact-checked Hindi page, independently bilingual-accuracy checked