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What criteria do we use to decide whether something is alive?

Any visible movement such as walking, breathing, or growing is generally used to decide whether something is alive or not. However, a living organism can also have movements, which are not visible to the naked eye. Therefore, the presence of life processes is a fundamental criterion that can be used to decide whether something is alive or not.

Related Questions Life Processes

Root hairs have thin walls. Due to this, water enters the root hairs because of osmosis. Water from root hairs continuously moves into the root xylem. To maintain the osmotic gradients, the cells of root hairs take up ions from the soil.

The role of saliva in the digestion of food:
→ It moistens the food for easy swallowing.
→ It contains a digestive enzyme called salivary amylase, which breaks down starch into sugar.

HCl plays following role in our stomach:

(a) Make the medium acidic for action of enzyme pepsin.

(b) Kills the harmful bacteria present in food

(c) Prevents fermentation of food

The food of herbivores contains a huge amount of cellulose. The animals need the assistance of certain bacteria to digest cellulose and this process takes time. Due to this, herbivores have longer small intestine than carnivores. Meat is easier to digest and hence carnivores have small intestine which is much smaller than in herbivores.

The functional unit of kidney is called nephron.
A nephron is composed of a tuft of blood capillaries and highly coiled ducts. The tuft of blood capillaries is surrounded by a cup-shaped structure; called Bowman’s capsule.
• Waste material from blood are filtered out of the capillaries and they go through the wall of Bowman’s capsule.
• After that, the waste material and water pass through the ducts. When the mixture of water and other materials move through the duct, some materials and water are reabsorbed. This depends on excess amount of water present in the body.
• After reabsorption of water and other material, urine becomes concentrated. This then goes to the collecting duct.
• Urine from collecting ducts moves through ureter into the urinary bladder. From the urinary bladder, urine is expelled from the body as and when required.