6. Life Processes | Class 10 CBSE | Web Notes | Part 5 | Excretion



Excretion is the process of removal of harmful metabolic nitrogenous wastes from the body.

Unicellular organisms remove these wastes by simple diffusion from body surface into surrounding water.

Complex multicellular organisms use specialised organs for excretion.

Excretion in Human Beings

Human excretory system includes a pair of kidneys, a pair of ureters, a urinary bladder & a urethra.

Kidneys are located in the abdomen, one on either side of the backbone.

The purpose of making urine is to filter out waste products from the blood.

In the kidneys, nitrogenous wastes such as urea or uric acid are removed from blood.

Each kidney has large numbers of filtration units called nephrons packed close together.

At the end of each nephron, a cup-shaped structure called Bowman’s capsule is seen. It encloses a cluster of very thin-walled blood capillaries called glomerulus.

In glomerulus, blood is filtered and the Bowman’s capsule collects the filtrate.

Glucose, amino acids, salts & major amount of water in the initial filtrate are selectively reabsorbed as the urine flows along the tube.

In a healthy adult, the initial filtrate is about 180 L daily. However, only 1-2 litre/day is excreted out because the remaining filtrate is reabsorbed in the kidney tubules.

Water is reabsorbed based on amount of excess water in the body and amount of dissolved waste is to be excreted.

The urine from each kidney enters a long tube (ureter), which then passes to urinary bladder and stored in it.

As the bladder expands, pressure increases that leads to the urge to urinate through the urethra.

The bladder is muscular, so it is under nervous control. As a result, we can control the urge to urinate.

Artificial kidney (Hemodialysis)

- Kidney failure leads to accumulation of poisonous wastes in the body. In this case, an artificial kidney can be used. It is a device to remove nitrogenous wastes from the blood through dialysis.

- Artificial kidneys contain many semi-permeable tubes suspended in a tank filled with dialysing fluid (it has same osmotic pressure of blood, but no nitrogenous wastes).

- When patient’s blood is passed through these tubes, the waste products from blood diffuses into dialysing fluid.

- The purified blood is pumped back into the patient.

- This is similar to the function of the kidney, but there is no reabsorption involved.

Organ donation

Any people can donate their organ or tissue regardless of age or gender.

Transplantation is required when recipient’s organ has been damaged or failed by disease or injury.

In organ transplantation, the organ is surgically removed from one person (organ donor) and transplanted to another person (recipient).

Most organ and tissue donations occur just after the death or brain death of the donor. But some organs (kidney, part of a liver, lung, etc.) and tissues can be donated while the donor is alive.

Excretion in Plants

Oxygen is formed as a waste product of photosynthesis.

O2, CO2 & excess water are removed by transpiration.

Many other waste products are stored in vacuoles.

Waste products may be stored in leaves that fall off.

Some waste products are stored as resins and gums, especially in old xylem.

Plants also excrete some waste substances into the soil around them.

Select Your Next Topic 👇

👉 Part 1: What are Life Processes?
👉 Part 2: Nutrition
👉 Part 3: Respiration

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