(a) The cellular respiration, photosynthesis, and other metabolic reactions produce a lot of excretory products in plants. Carbon dioxide, excess water produced during respiration and nitrogenous compounds produced during protein metabolism are the major excretory products in plants. Plants produce two gaseous waste products i.e., oxygen during photosynthesis and carbondioxideduring respiration. Excretion of gaseous waste in plants takes place through stomatal pores on leaves. Oxygen released during photosynthesis is used for respiration while carbon dioxide released during respiration is used for photosynthesis. Excess of water is also excreted from the plant body through the stomatal pores and from the surfaces of fruits and stems. The process of elimination of water is called transpiration. Besides these leaves helps in excretion through a process called abscission. Abscission is falling off old and yellow leaves. By the help of this process plants get rid off toxins etc. Many plants store waste materials in the vacuoles of mesophyll cells and epidermal cells. When old leaves fall, the waste materials are excreted along with the leaves. Other than gaseous wastes, metabolism in plants also generates organic by-products. These wastes are stored in different forms in different parts. The gums, oils, latex, resins, etc. are some waste products stored in plant parts like barks, stems, leaves, etc. Eventually, plants shed off these parts.
(b) A nephron is the basic structural and functional unit of the kidney. They are the microscopic structure composed of a renal corpuscle and a renal tubule. The mammalian nephron is a long tubelike structure, its length varying from 35−55‌mm long. At one end, the tube is closed, folded and expanded, into a double-walled, a cup like structure called the Bowman's capsule or renal corpuscular capsule, which encloses a cluster of microscopic blood vessels called the glomerulus. This capsule and glomerulus together constitute the renal corpuscle.
The structure of nephron comprises two major portions :
(i) Renal Tubule
(ii) Renal Corpuscle
The major function of tubules is reabsorption and the process can either be through active transport or passive transport. In addition, secretions by tubules help in the urine formation without affecting the electrolyte balance of the body.
Function of Nephron :
The primary function of nephron is removing all waste products including the solid wastes and other excess water from the blood, converting blood into the urine, reabsorption, secretion and excretion of numerous substances. As the blood passes through the glomerulus with high pressure, the small molecules are moved into the glomerular capsules and travel through a winding series of tubules. The cell present in each tube absorbs different molecules excluding the glucose, water and other beneficial molecules which are called as the ultra filtrate. As the ultra-filtrate molecules travel down the tubules they become more and more hypertonic, which results in more amount of water to be extracted from the ultra-filtrate before it exits the nephrons. The blood surrounding the nephron travels back into the body through the renal blood vessels, which are free of toxins and other excess substances. The obtained ultra-filtrate is urine, which travels down via the collecting duct to the bladder, where it will be stored and released through the urethra.