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Life Processes - Excretion

Grade 10CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Excretion is the biological process involved in the removal of harmful metabolic wastes (like nitrogenous materials) from the body.

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In unicellular organisms (e.g., Amoeba), waste is removed by simple diffusion from the body surface into the surrounding water.

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The human excretory system consists of a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra.

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Kidneys contain structural and functional units called nephrons. Each nephron consists of a Bowman's capsule (containing the glomerulus) and a renal tubule.

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Urine formation involves three main steps: 1. Ultrafiltration (filtering blood in the glomerulus), 2. Selective Reabsorption (reabsorbing useful substances like glucose, amino acids, and H2OH_2O), and 3. Tubular Secretion (secreting ions like K+K^+ and H+H^+ into the filtrate).

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Hemodialysis is an artificial process used to filter the blood of patients whose kidneys have failed, removing nitrogenous wastes like urea.

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Plants excrete oxygen (O2O_2) as a byproduct of photosynthesis and carbon dioxide (CO2CO_2) as a byproduct of respiration. Excess water is removed via transpiration.

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Plants also store waste products in cellular vacuoles, in old leaves that fall off, or as resins and gums in old xylem.

📐Formulae

Filtration Rate≈Volume of filtrate formed per unit timeFiltration\ Rate \approx \text{Volume of filtrate formed per unit time}

Excreted Urine=(Filtered Load−Reabsorbed Amount)+Secreted Amount\text{Excreted Urine} = (\text{Filtered Load} - \text{Reabsorbed Amount}) + \text{Secreted Amount}

Urea Formula:NH2CONH2\text{Urea Formula}: NH_2CONH_2

💡Examples

Problem 1:

What are the main components of the initial filtrate in the nephron, and how does it differ from final urine?

Solution:

The initial filtrate contains H2OH_2O, glucose, amino acids, salts, and nitrogenous wastes like urea. As it flows through the tubule, most H2OH_2O and all glucose/amino acids are reabsorbed.

Explanation:

Ultrafiltration is non-selective for small molecules. The body needs to reclaim essential nutrients and maintain water balance, leaving behind concentrated urea and excess salts in the urine.

Problem 2:

How is the amount of water reabsorbed regulated in the human body?

Solution:

The amount of H2OH_2O reabsorbed depends on how much excess water there is in the body and how much dissolved waste there is to be excreted.

Explanation:

If the body is dehydrated, more H2OH_2O is reabsorbed into the blood under the influence of hormones like ADH (Antidiuretic Hormone), resulting in concentrated urine.

Problem 3:

Describe how plants get rid of waste products other than gaseous wastes.

Solution:

Plants use strategies like storing waste in vacuolesvacuoles, shedding old leaves, and secreting wastes as resinsresins and gumsgums.

Explanation:

Since plants cannot move, they utilize dead tissues (like old xylem) and deciduous parts (leaves) to sequester and eventually discard metabolic byproducts.