RESPIRATION

Question 1

Breakdown of glucose

Answer 1

the first step is the break-down of glucose, a six-carbon molecule, into a three-carbon molecule called pyruvate. This process takes place in the cytoplasm. Further, the pyruvate may be converted into ethanol and carbon dioxide. This process takes place in yeast during fermentation. Since this process takes place in the absence of air (oxygen), it is called anaerobic respiration. Breakdown of pyruvate using oxygen takes place in the mitochondria. This process breaks up the three-carbon pyruvate molecule to give three
molecules of carbon dioxide. The other product is water. Since this
process takes place in the presence of air (oxygen), it is called aerobic
respiration. Sometimes, when there is a lack of oxygen
in our muscle cells, another pathway for the break-down of pyruvate is taken. Here the pyruvate is converted into lactic acid which is also a
three-carbon molecule. This build-up of lactic acid in our muscles during sudden activity causes cramps.

Question 2

How do fish breathe

Answer 2

Since the amount of dissolved oxygen is fairly low compared
to the amount of oxygen in the air, the rate of breathing in aquatic
organisms is much faster than that seen in terrestrial organisms.
Fishes take in water through their mouths and force it past the
gills where the dissolved oxygen is taken up by blood.

Question 3

Respiration in Human beings

Answer 3

In human beings, air is taken into the body through
the nostrils. The air passing through the nostrils is filtered by
fine hairs that line the passage. The passage is also lined with
mucus which helps in this process. From here, the air passes
through the throat and into the lungs. Rings of cartilage are
present in the throat. These ensure that the air-passage does
not collapse.
Within the lungs, the passage divides into smaller and smaller
tubes which finally terminate in balloon-like structures which
are called alveoli (singular–alveolus). The alveoli provide a surface
where the exchange of gases can take place. The walls of the alveoli
contain an extensive network of blood-vessels.
The blood brings carbon dioxide from the rest of the body
for release into the alveoli, and the oxygen in the alveolar air is
taken up by blood in the alveolar blood vessels to be transported
to all the cells in the body

Question 4

Why is some amount of air kept in the lungs

Answer 4

During the breathing cycle, when air is
taken in and let out, the lungs always contain a residual volume
of air so that there is sufficient time for oxygen to be absorbed
and for the carbon dioxide to be released