(a) Microorganisms can be seen with the help of a microscope.
(b) Blue green algae fix nitrogen directly from air and enhance fertility of soil.
(c) Alcohol is produced with the help of yeast.
(d) Cholera is caused by bacteria (Vibrio cholerae).
(a) A microscope is a laboratory instrument which is used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. The image of an object is magnified through lens in the microscope.
(b) Blue-green algae are also known as Cyanobacteria. They normally look green and sometimes turn bluish when they are dying. They are a group of prokaryotic, autotrophic microorganisms that contain the photosynthetic pigments (chlorophyll and phycocyanin). They can convert inert atmospheric nitrogen into an organic form, such as nitrate or ammonia. These fixed forms of nitrogen are used by plants for their growth.
(c) The primary role of yeast is to convert glucose into ethanol and carbondioxide. Ethanol is released by the yeast cells as a waste product.
(d) Cholera is an acute diarrheal illness caused by infection of the intestine with Vibrio cholerae bacteria. People get sick when they swallow contaminated food or water. Severe watery diarrhea accompanied by vomiting can quickly lead to dehydration and even death if untreated.