Excretion

Living organisms are one giant chemical lab. Hundreds of chemical reactions happen in our bodies between various biomolecules. In plants, photosynthesis is basically a chemical reaction. All these metabolic reactions have byproducts that are eliminated through the process of excretion. Let us learn about how this elimination of waste products occurs in plants and animals.

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Excretion in Plants

There is an immense difference in the structure and composition of plants and animals. Did you know that when chemical reactions occur in plants, oxygen is released? This oxygen is supposedly a waste product that the photosynthesis process generates.

Photosynthesis occurs in plants, in the presence of sunlight. This chemical reaction gives rise to oxygen, which is a gas. It diffuses through the stomata or the openings in the leaves. Any excess water that is present in plants gets evaporated through the transpiration process.

Another interesting feature here in plants is that some of the plant wastes are stored in cellular vacuoles, in leaves that fall off. Some other waste products are stored in the xylem, like resins and gums.

Excretion in Animals

Animals are generally more complex in nature when compared to plants, especially the animals belonging to the higher order phyla. Even among some lower organisms, excretion occurs through specialized organs, such as the nephridia seen in earthworms. In others, excretion happens through diffusion.

In the higher phyla and classes of the animal kingdom, animals such as fish, birds, reptiles, etc. have a specific excretory system in place to get rid of the metabolic wastes.

Browse more Topics under Life Processes

• Nutrition in Plants
• Nutrition in Animals
• Respiration
• Transportation in Plants
• Transportation in Human Beings

You can download Life Processes – Excretion Cheat Sheet by clicking on the download button below

Excretory system in Human Beings

This is a well-developed and complex system that takes care of eliminating the wastes from the human body. This is a vital function that helps in the smooth functioning of the human body. Kidneys are the main organs of the excretory system in human beings. Ureters, urinary bladder, and urethra along with blood vessels are the other components present. The urine that is formed in the kidneys is transported through the ureters to the urinary bladder. It is expelled out through the urethra.

But, a point to be noted is that skin and lungs, also have a role to play in excreting or eliminating waste substances from the body. The sweat glands in the skin help in the excretion of small amounts of water, salts, and urea. Lungs help in getting rid of carbon dioxide through the respiration process. Let us learn more in detail about the human excretory system.

Kidneys

They are a pair of bean-shaped organs that lie in the abdominal cavity. Not only excretion, kidneys also control the balance of water and other mineral ions in the body. The kidney in humans has two distinct regions, which are the cortex and medulla. Both the cortex and medulla are enclosed externally by three layers. These layers consist of a tough connective tissue, fat tissue, and renal capsule.

Internally, the cortex forms the outer layer and the medulla is the inner layer. There is also a region called the hilum of the kidney. This is the part where blood vessels enter the kidney. The ureters, some blood vessels, and nerves also exit from this point. The complex network of blood vessels i.e. arteries, veins, and capillaries, in this area play a significant role in the filtration and elimination process.

The cortex has tiny tubules called the nephrons. These nephrons are the basic units of filtration in the kidneys. Hence they are called the functional units of the kidney. Each nephron has three parts, namely renal corpuscle, a renal tubule, and the capillary network. The renal corpuscle has clusters of tiny blood capillary network. This is called the glomerulus and Bowman’s capsule.

The blood vessels bring in blood that has to be filtered. The blood supply to the kidneys starts with the aorta, which branches out into renal arteries and ends with renal veins that exit out of the kidneys, to join the vein called inferior vena cava.

Process of Filtration and Urine Formation

Through the process of filtration, urine is formed in the nephrons. Ultrafiltration occurs in the glomerulus part of the nephrons. Inside the glomerulus, there is high pressure, due to which waste products get filtered and urine is formed. The nephrons filter out wastes, minerals, and water while retaining red cells proteins and large molecules.

The urine travels down the collecting duct system. In the tubular part of the nephron, water is reabsorbed. From here, the concentrated urine eventually enters into the ureter. The ureter is a long tube that connects the kidneys to the urinary bladder. Here, the urine is stored until it is passed out through the urethra. Human urine is mainly composed of water, urea, uric acid and salts.

Now you know how important kidneys are in the human body. But what happens when kidneys fail to function? Read along to find out.

What Happens when Kidneys Fail?

Our kidneys do many tasks that are essential for the proper running of the human body. They are responsible for maintaining the balance in the body. They eliminate wastes and also help control blood pressure.

But, kidneys also can get damaged. When they are damaged, they cannot perform their functions well. This then turns out to be a question of life and death. If kidneys fail completely, it can lead to death. The waste products and excess water get accumulated in the body, with no proper channel for elimination. When both the kidneys fail, kidney transplantation and dialysis can be of help.

Dialysis

It is a treatment, where a device performs some of the tasks that kidneys perform. This device separates the wastes from the blood. Dialysis helps in the following.

• It removes wastes, salt and excess water from the body, preventing their build-up.
• It keeps the levels of certain chemicals in safe limits.
• Dialysis also helps to control blood pressure.

Solved Question For You

Q: Why are kidneys important? Justify your answer.

Ans: Kidneys play a crucial role in eliminating wastes from the body. They also help in maintaining the body balance. Blood pressure in the body is also regulated by the kidneys. When kidney failure occurs, it could lead to death. Kidney transplantation and Dialysis are the two options that are present in case of kidney failure.