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How are the alveoli designed to maximise the exchange of gases?

The alveoli are designed to maximise the exchange of gases in the following way:
(i) The alveoli are thin walled and richly supplied with a network of blood vessels to facilitate exchange of gases between blood and the air filled in alveoli.
(ii) Alveoli have balloon like structure. Thus, provide maximum surface for exchange gases.



How are fats digested in our bodies? Where does this process take place?

Digestion of fat takes place in the small intestine.
Digestion of Fat: The fats are present in the form of large globules in the small intestine. Fats digesting enzymes are not able to act upon large globules efficiently.
Bile juice secreted by the liver poured in the intestine along with pancreatic juice. The bile salts present in the bile juice emulsify the large globules of fats. So, by emulsification large globules break down into fine globules to provide larger surface area to act upon by the enzymes
Lipase enzyme present in the pancreatic juice causes break down of emulsified fats. Glands present in the wall of small intestine secrete intestinal juice which contains lipase enzyme that converts fats into fatty acids and glycerol. Small Intestine: Region of digestion of fats:

Digestion of fat takes place in the small intestine.Digestion of Fat:


What is the role of saliva in the digestion of food?

Role of saliva in digestion of Food:
(i) The saliva contains salivary amylase enzyme that breaks down starch which is a complex molecule to simple sugars.

starch     +   salivary amylase                               sugars(complex)                                                     (simplarmolecule)                                                    molecules)

(ii) The saliva moisten the food that help in chewing and breaking down the big pieces of food into smaller ones. So, that salivary amylase can digest the starch efficiently.


What are the necessary conditions for autotrophic nutrition and what are its by products?

Necessary conditions for autotrophic nutrition:

(i) Presence of chlorophyll in the living cells.
(ii) Supply of water to green parts or cells of the plant either through roots or by surrounding environment.
(iii) Availability of sufficient of sunlight to provide light energy required to carry out photosynthesis.
(iv) Sufficient supply of carbon dioxide which is one of the important component for the formation of carbohydrates during photosynthesis.


What are the differences between aerobic and anaerobic respiration? Name some organisms that use the anaerobic mode of respiration.

Aerobic respiration

Anaerobic respiration

1. Aerobic respiration takes place in the presence of free oxygen.

1. It takes place in the absence of oxygen.

2. In aerobic respiration complete oxidation of glucose takes place.

2. In anaerobic respiration the glucose molecule is incompletely broken down.

3. End products of aerobic respiration are CO2, water and energy.

3. End product of anaerobic respiration are ethyl alcohol (or lactic acid) CO2 and a little energy.


4. Large amount of energy is released i.e., 38 molecules of ATP per glucose molecule.

4. Small amount of energy is released i.e., 2 ATP molecules per glucose molecule.

5. First step of aerobic respiration (glycolysis) takes place in cytoplasm while second (Kreb’s cycle) and third (Electron transport chain) steps take place in mitochondria.

5. Complete anaerobic respiration occurs in cytoplasm.

Organisms which use anaerobic respiration are yeasts, bacteria and parasites like tape worm (Taemia), Ascaris etc.