Answer: Option A. ->
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Breathing rate: 1 Mark
Normal breathing rate: 1 Mark
Variation: 1 Mark
Breathing rate is the number of times a person breathes in a minute. One full inhalation and one full exhalation is counted as a single breath. The number of breaths per minute is calculated for a person to obtain the breathing rate.
The normal breathing rate for human beings during rest is 15 to 18 breaths per minute. 
Breathing rate increases during exercising or running. It slows down when sleeping.

Answer: Option A. ->
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Respiration: 1 Mark each
1. In unicellular animals, such as amoeba, exchange of gases takes place through cell surface.
2. They absorb oxygen from the surrounding air or water and give out carbon dioxide through plasma membrane by diffusion. 
3. The cells use the oxygen absorbed for cellular respiration and derive energy. 

Answer: Option A. ->
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Differences: 1 Mark each
Human beings have well-defined organs to breathe. We breathe through our lungs. 
Cockroaches have small openings called spiracles on the sides of its body. The air rushes through the spiracles and reaches tracheal tubes, then diffuses into the body tissues and reaches every cell.
Frog breathes through its skin under water. On land frog uses lungs to breathe. Earthworm also breathes through its skin. 
 

Answer: Option A. ->
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1 Mark each
Respiratory systems in animals have the following features:
1. They have a large surface area for efficient exchange of gases.
2. They have thin membranes for faster gaseous exchange.
3. They have a rich vascular (blood) supply.

Answer: Option A. ->
:

Observations: 1 Mark each
1. Test tube A will have the highest concentration of $C{O}_2$.
2. The experiment shows respiration in animals and plants.
3. Test tube A: During breathing, the snail inhales dissolved oxygen from water and releases $C{O}_2$.
4. Test tube B: The water plants along with respiration performs photosynthesis (food preparation); therefore it absorbs $C{O}_2$ and releases $O_2$.
5. Test tube C: The $C{O}_2$ released by the snail will be used by the plant for photosynthesis, thus there will be a balance of gases.

Answer: Option A. ->
:

Each point: 1 Mark
The process of breathing happens as follows:
1. We take in air through our nostrils. When we inhale, air passes through nostrils into the nasal cavity which reaches the lungs through windpipes.
2. The chest cavity where the lungs are present is surrounded by ribs on the sides and diaphragm forms the base.
3. Breathing involves the movement of the diaphragm and the rib cage.
4.During inhalation, ribs move up and the diaphragm moves down to increase the chest cavity space. When the volume in the lungs increases, pressure decreases, which fill the lungs with air.
5. During exhalation, ribs move down and the diaphragm moves up to its former position. The lungs contract and lower volume increase the pressure in the lungs, pushing the air out.