Biology [3 marks Question Answer]

(i) The given structure is found in the renal cortex of the kidney.
(ii) The stages involved in the formation of urine are:
• Ultrafiltration
• Selective reabsorption
• Tubular secretion
(iii) The process occuring in part 2 (glomerulus) and 3 (Bowman's capsule) is ultrafiltration.

(i) Organs involved in excretion in human body are:
• Kidneys: These filter blood to form urine.
• Ureters: They help in transport urine from the kidneys to the bladder.
• Bladder: It stores urine until it is excreted.
• Urethra: It is an opening which conducts urine from the bladder to the outside of the body.
Substances excreted:
• Urea: This is a waste product formed from protein metabolism.
• Creatinine: It is a waste product from muscle metabolism.
• Excess salts and water: They maintain fluid and electrolyte balance.
• Toxins and drugs: They are filtered out of the blood by the kidneys.
(ii) Regulation of water and electrolyte balance by the excretory system:
The excretory system, primarily through the kidneys, maintains water and electrolyte balance by:
• Ultrafiltration; Blood is filtered in the kidneys that help in separating waste and excess substances from the useful nutrients and electrolytes.
• Selective reabsorption: The kidneys selectively reabsorb water, sodium, potassium, and other electrolytes back into the bloodstream based on the body's needs.
• Tubular secretion: Additional waste and excess ions are secreted into the filtrate for excretion.
The final urine contains the waste products and excess substances to be removed from the body thus, maintaining overall balance.
(iii) Role of the kidneys in excretion:
• Waste Removal: Kidneys eliminate metabolic waste like urea and creatinine.
• Fluid Balance: Kidneys also maintain water and electrolyte balance.
• Blood pH Regulation: Kidneys regulate blood pH by excreting hydrogen ions and reabsorbing bicarbonate.

 

Afferent arteriole	Efferent arteriole
Formed by the branching of the renal artery	Formed by the fusion of glomerular capillaries
Its diameter is twice as thick as the efferent arteriole.	Its diameter is two times narrower than that of the afferent arteriole.
Brings oxygenated blood into the kidney	Carries oxygenated blood away from Bowman's capsule
It brings in blood which contains large amounts of water and nitrogenous metabolic wastes.	It carries away blood that is relatively thicker and free of toxic wastes.

 

Ureter	Urethra
Ureters are the ducts which emerge from the median surface of each kidney and are connected to the base of the urinary bladder.	It is a short muscular tube which leads from the urinary bladder to the outside.
It transports the urine from the kidneys to the urinary bladder.	It pass out the urine from the urinary bladder.
Valves are present at the openings of the ureter prevent the back flow of urine.	The opening of the urethra is also guarded by a sphincter muscle. It relaxes at the time of urination.