BIOLOGY [3 marks Question Answer]

Section through the kidney to show different regions The kidneys are composed of:

1. an outer darker area called Cortex
2. an inner lighter area called Medulla.

The microscopic structure of the kidney is formed of millions of tubules called renal tubules or nephrons.

Artificial kidneys: Kidneys play an important role not only by filtering the blood and getting rid of waste products but also by balancing salt levels in the body.

controlling blood pressure, and stimulating the production of red blood cells.
A person can lead a normal life with one kidney but when both of them stop functioning it could prove fatal if no treatment is provided. An artificial kidney or a dialyzer is a machine used to filter the blood of a patient whose kidneys are damaged. This process is called dialysis.

Large quantities of water are absorbed by plants for photosynthesis and other processes. Excess of water is lost in the form of water vapour through the stomata and lenticels from the aerial parts of the plant by transpiration. It helps plants to maintain the concentration of sap inside the plant body. If plants do not remove excess water through transpiration, the dilute sap will prevent further absorption of water and minerals from the soil.
Factors affecting the rate of transpiration are :

1. Sunlight: Rate of transpiration is more during the day as stomata are open. Stomata remain closed at night and thus no transpiration takes at night.
2. Temperature: Transpiration is more on hot days than on cold days.
3. Wind: Blowing wind removes water vapour faster from the leaves and hence transpiration rate increases.
4. Humidity: If the air is humid, the rate of transpiration is low.
   In the rainy season, transpiration is less since humidity is more.

The process of urine formation takes place in the following steps :

1. Glomerular Alteration – Blood containing waste material enters the kidneys through the renal artery. It then enters the glomerulus under high pressure. Water and small solutes are filtered in the Bowman’s capsule.
2. Tubular reabsorption – Filterate passes through the thin walls of the Bowman’s capsule into the urinary or renal tubule. As it passes through the tubule, water, and many useful substances are reabsorbed by the renal blood capillaries.
3. Tubular secretion – The remaining liquid, along with wastes such as urea, uric acid, etc is called urine and is collected in the urinary bladder.
4. Excretion – Urine leaves the kidneys and passes into the urinary bladder through the ureters. When the urinary bladder is full, urine is passed out through the urethra.

The microscopic filtering unit of the kidney is called nephron or uriniferous tubule. Each nephron consists of a cup-shaped structure at one end called Bowman’s capsule. Inside the cup is a network of blood capillaries called a glomerulus. The Bowman’s capsule and the glomerulus together form the Malpighian body. The Bowman’s capsule extends into a long tubule. These tubules are surrounded by a network of renal capillaries. The urinary tubules of the nephrons in each kidney join to form a common tube called a ureter.

1. Blood containing waste material enters the kidneys through the renal artery.
2. Blood enters the glomerulus under high pressure.
3. Water and small solutes are filtered in the Bowman’s capsule.
4. The filtrate passes through the thin walls of the Bowman’s capsule into the renal tubule
5. As the filtrate, passes through the tubule, water, and many useful substances are reabsorbed by the walls of the blood capillaries.
6. The remaining liquid, along with waste is called urine and is collected in the urinary bladder.