Pores present on the sides of insects are called spiracles while pores present on the surface of leaves are called stomata. These structures are responsible for the exchange of gases with the atmosphere. Differences between these two are as follows
(i) Spiracles are fewer in number as compared to stomata.
(ii) Spiracles lead to an extensive network of tracheal system which is absent in the leaves

(a) Snail, as it does not breathe by means of trachea.
(b) Earthworm, because it breathes through its skin and it (does not have lungs.
(c) Fish as most fish breathe through their gills and do not have lungs.
(d) Tadpole, as it breathes through hills and do not have lungs.

Test tube A will have higher concentration of CO₂, This experiment shows the relationship between plants and animals. During breathing, snail inhales dissolved oxygen from water and releases CO_2.
Water-plant along with respiration performs another important function called photosynthesis. During photosynthesis, water-plant absorbs CO₂, prepares food and releases oxygen.
Therefore, test tube Band C have less amount of CO₂ concentration as compared to test tube A.

When we inhale dust-laden air, dirt-particles are captured within the nostrils. Sometimes, they get past the nostril hair in the nasal cavity and irritate the lining of the cavity, as a result, we sneeze. Sneezing expels these foreign particles from the inhaled air and a dust free, clean air enters in our body

Differences between aerobic and anaerobic respiration are as follows

Similarities between aerobic and anaerobic respiration are as follows
(i) Both break down the glucose.
(ii) Release of energy takes place in both.
(iii) CO2 is the common product in both.

Our body needs energy for all activitie, while doing heavy exercises like running and there is a larger demand of energy to perform these activities. Hence, more oxygen is required to meet extra demand of energy. Therefore, an athlete breathes faster and deeper than usual after finishing the race

Move downwards During exhalation the ribs moves downwards causing a decrease in area of chest cavity forcing the air out.

15-18 Normal range of breathing rate is 15-18 breaths per minute, in an average adult person at rest.

Lactic acid It is produced during heavy exercise as sufficient oxygen is not available to muscles.

Spiracles In cockroaches, air for respiration enters through small tubes/holes present on then body called spiracles.

Our nostrils possess hairs and mucous lining. These help in preventing dirt, dust and germs from entering our respiratory system.

The respiratory organ of the following animals are as follows
(a) Fish - Gills (b) Human being - lungs

Earthworm is an animal where exchange of gases during breathing or respiration takes place through its thin and moist skin

The end product formed during anaerobic respiration in yeast are
(i) Ethyl alcohol
(ii) Carbon dioxide
(iii) Energy

Cellular respiration takes place in the mitochondria of the cell

During aerobic respiration, carbon dioxide and water are released along with a large amount of energy.
\(glucose\overset { { O }_{ 2 } }{ \longrightarrow } { O }_{ 2 }+water+Energy\)

(a) Paheli had cramps in her leg muscles after running. She felt pain in her legs because of accumulation of lactic acid in the leg muscles. Lactic acid is formed due to anaerobic respiration in the muscle cells after heavy exercise or running. After heavy exercise, we require large amount of energy.
To produce more energy to meet the oxygen requirement of muscles, muscle cells perform anaerobic respiration for a short duration. Lactic acid is formed due to partial breakup of glucose. It gets accumulated in the muscle cells and causes pain and muscle cramps.
(b) The massage or hot water bath gives the relief from muscle cramp or pain, because it improves the circulation of blood leading to increase supply of oxygen to the muscle cells . It helps in complete breakdown of lactic acid into carbon dioxide and water

(a) The plants do not possess any respiratory system still plants respire. The various parts of the plants like leaves, roots, etc., carry out respiration independently.
These parts take in oxygen from air in different manner and utilise it to obtain energy and give out CO₂, The leaves of plants possess tiny pores on their surface which is called as stomata. The gaseous exchange during respiration takes place through their stomata.
(b) Roots of the plants respire under the ground. Root cells get oxygen from the air present in the space between the soil particles.
There are several root hairs present on the roots of a plant.
The oxygen from the air (between soil particle) diffuses into root hair and reaches to the cells of the roots. This oxygen is utilised for respiration.

(a) The dough rises due to the release of carbon dioxide during anaerobic respiration by yeast cell.
(b) Yeast, during anaerobic respiration also produces alcohol which results in the sour smell of dough.
(c) Sugar is added into the dough, because it acts as a food for yeast. Yeast upon incomplete breakdown of sugar or food produces CO₂, alcohol and energy (in less amount).
(d) If the dough is kept in the refrigerators after it was prepared, then dough will neither raise nor become sour. Yeast requires high temperature to grow, multiply and to respire. At low temperature, the yeast will not respire to produce the byproducts of anaerobic respiration.