Excretion, Control and Coordination
Excretion, Control and Coordination
This topic closes the first biology chapter and gives 1 to 2 questions in the Part-III paper. Excretory organs, the nervous system and the endocrine glands are the three areas examined, and the hormone-and-gland matching table is the format the paper asks most often.
Excretion in Humans
Excretion is the removal of metabolic waste. The kidneys are the main excretory organs, filtering nitrogenous waste from the blood as urine.
| Organ | Waste removed |
|---|---|
| Kidneys | Urea and excess water, as urine |
| Lungs | Carbon dioxide and water vapour |
| Skin | Excess water and salt, as sweat |
| Liver | Bile pigments |
The excretory system has two kidneys, two ureters, a urinary bladder and a urethra. The functional unit of the kidney is the nephron, and each kidney has a very large number of them. When both kidneys fail, blood is filtered artificially by dialysis.
Plants have no excretory organs. They store waste in leaves that fall, in bark, or release it into the soil — which is why the question about plant excretion has no organ as its answer.
✗ The lungs are not excretory organs | ✓ They are — they remove carbon dioxide and water vapour
The Nervous System
Control in the body works through two systems that operate at different speeds: the nervous system, which is fast and electrical, and the endocrine system, which is slower and chemical.
| Part | Function |
|---|---|
| Brain | Thinking, memory, control of the body |
| Cerebrum | Largest part; intelligence and voluntary action |
| Cerebellum | Balance and coordination of movement |
| Medulla | Involuntary actions such as heartbeat and breathing |
| Spinal cord | Carries messages; controls reflex actions |
| Neuron | Structural and functional unit of the nervous system |
A reflex action is an immediate involuntary response, such as pulling the hand away from a hot object. It is controlled by the spinal cord, not the brain, which is why it is so fast. That single fact is the most repeated question in the nervous system section.
The Endocrine System
| Gland | Hormone | Main effect |
|---|---|---|
| Thyroid | Thyroxine | Controls metabolism; deficiency causes goitre |
| Pancreas | Insulin | Controls blood sugar; deficiency causes diabetes |
| Adrenal | Adrenaline | Emergency hormone for fight or flight |
| Pituitary | Growth hormone | Controls growth; called the master gland |
| Testes | Testosterone | Male secondary characteristics |
| Ovaries | Oestrogen | Female secondary characteristics |
The pituitary is the master gland because it controls several others. The pancreas is a dual gland — it secretes digestive juice into the intestine and insulin into the blood, so it is both exocrine and endocrine. That dual role is a good discriminator question.
Iodine is needed to make thyroxine, which is why iodised salt prevents goitre. This links the topic back to the deficiency-disease table in the nutrition section.
परावर्ती क्रिया मेरुरज्जु से नियंत्रित होती है, मस्तिष्क से नहीं।
TRE pointer: The reflex action is controlled by the spinal cord fact is the most asked item in this topic, and brain is always among the options. The gland-and-hormone table is the second, with the pituitary as master gland and the pancreas's dual role as the two discriminators. Note the iodine-thyroxine-goitre chain, because it lets one fact answer questions in two different chapters. With −1/3 negative marking, this table repays memorising in full.
60-Second Recap
- Kidneys remove urea; lungs remove carbon dioxide; skin removes sweat.
- The nephron is the functional unit of the kidney; dialysis replaces failed kidneys.
- Plants have no excretory organs and shed waste through leaves, bark and soil.
- Reflex action is controlled by the spinal cord, not the brain.
- Cerebrum for intelligence, cerebellum for balance, medulla for involuntary actions.
- Pituitary is the master gland; pancreas secretes both digestive juice and insulin.
Frequently Asked Questions
Which part of the body controls reflex actions?
The spinal cord, not the brain. A reflex arc allows the message to travel to the spinal cord and back to the muscle without waiting for the brain, which is why the response is almost instantaneous. Brain is always offered as the wrong option.
Why is the pituitary called the master gland?
Because its hormones control the working of several other endocrine glands, including the thyroid and the adrenals, besides regulating growth directly. Despite its very small size it has the widest influence, which is why the name is used and asked about.
How is the pancreas both an exocrine and an endocrine gland?
It secretes digestive juices through a duct into the small intestine, which makes it exocrine, and it also secretes insulin directly into the blood, which makes it endocrine. This dual role is unusual and is used as a discriminating question.
How do plants get rid of their waste?
They have no excretory organs. Some waste is stored in leaves that later fall off, some in bark that is shed, and some is released into the surrounding soil. Gaseous waste leaves through the stomata, so no specialised organ is needed.
Next step: Biology is the biggest block in the Part-III science paper and the most table-heavy. Test this chapter in the BPSC TRE 4.0 mock test on ExamAtlas — five options, −1/3 negative marking, Part-III depth.