CBSE Class 10 Biology Life Processes Notes Set 04

Excretion in Animals and Plants

Excretion removes nitrogenous wastes made in metabolism, which are produced from proteins and nucleic acids. Egestion of undigested food is not excretion.

Human Excretory System and Nephron

The system has two kidneys, two ureters, the urinary bladder and the urethra. The kidney is bean shaped with an outer cortex and inner medulla. Each kidney has about a million nephrons. A nephron has the Bowman's capsule with the glomerulus (together the Malpighian body), the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule and the collecting duct.

1. Ultrafiltration: blood pressure forces water, glucose, amino acids, ions and urea through glomerular capillaries into the Bowman's capsule.
2. Selective reabsorption: useful substances return to blood, mostly in the PCT because of its microvilli.
3. Tubular secretion: extra wastes such as hydrogen ions, potassium and creatinine pass from blood into the tubule.
4. Urine flows through collecting ducts, ureter, bladder and urethra.
5. ADH from the pituitary raises water reabsorption in DCT and collecting duct. In hot weather ADH is high and urine is less and concentrated.
6. Kidneys also keep the pH and salt balance of blood.

Dialysis, Skin and Plants

1. Dialysis cleans the blood of a patient with kidney failure. Blood flows through semipermeable tubes in a solution with the same glucose and salts as blood but no urea, so urea diffuses out. Clean blood returns to a vein.
2. Skin removes water, salts and some urea in sweat. Lungs remove carbon dioxide and the liver makes urea.
3. Plants have no excretory organs. Oxygen and carbon dioxide leave through stomata, excess water by transpiration, and wastes are stored in vacuoles, in gums, resins and latex of old xylem, and removed with shed leaves and bark.