Kidneys are vital organs for survival. Several factors like infections, injury or restricted blood flow to kidneys reduce the activity of kidneys. This leads to accumulation of poisonous wastes in the body, which can even lead to death. In case of kidney failure, an artificial kidney can be used. An artificial kidney is a device to remove waste products from the blood through dialysis. (a) (i) Name the artery that brings oxygenated blood to the kidney. (ii) Name the cluster the thin-walled blood capillaries present in the Bowman's capsule. (b) In human excretory system name the organ which stores urine. Is this organ under hormonal control or nervous control? (c) (i) List two major steps involved in the formation of urine and state in brief their functions. OR (c) (ii) In which part of the nephron does selective reabsorption take place? List the factors which the amount of water reabsorbed depends on.

(a) (i) The renal artery brings oxygenated blood (containing nitrogenous wastes) to the kidney.

(ii) The cluster of thin-walled blood capillaries present in the Bowman's capsule is called the glomerulus.

(b) The organ that stores urine is the urinary bladder. This organ is under nervous control (as it is muscular, allowing us to consciously control the urge to urinate).

(c) (i) The two major steps involved in the formation of urine are:

1. Ultrafiltration (Filtration): High-pressure filtration occurs in the glomerulus where nitrogenous wastes, glucose, amino acids, salts, and water are filtered out of the blood into the Bowman's capsule to form the initial filtrate.
2. Selective Reabsorption: As the filtrate flows through the tubular part of the nephron, useful substances such as glucose, amino acids, salts, and a major amount of water are selectively reabsorbed back into the surrounding blood capillaries.

OR

(c) (ii) Selective reabsorption takes place in the tubular part of the nephron (renal tubule).

The amount of water reabsorbed depends on:

1. How much excess water there is in the body: If the body is well-hydrated, less water is reabsorbed; if dehydrated, more water is reabsorbed.
2. How much dissolved waste there is to be excreted: More dissolved waste requires more water to remain in the tubule for excretion, affecting the reabsorption rate.