Indicator organisms are organisms that are utilized to detect the presence of another organisms that cannot be easily identified.
We do not test for pathogens like salmonella directly but use an indicator organism like coliform because these pathogens are not easily isolated and they are much harder to identify.
Pathogens like salmonella are not tested for directly because they are much lower in numbers when found in wastes or waterbodies and to identify them directly is expensive.
Also testing directly for these micro-organisms is very expensive and non-viable. So it is better to use indicator organisms to detect their presence.
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objects are brought into focus on the retina by changes in the curvature and thickness of the
Objects are brought into focus on the retina by changes in the curvature and thickness of the lens.
What is eye lens?The lens basically directs light rays onto the retina. The lens is clear and replaceable if necessary. As we age, our lenses deteriorate, necessitating the use of reading glasses.
The lens is normally clear and is located behind the iris. The pupil directs light to the lens.
Small muscles attached to the lens can cause the lens to change shape, allowing the eyes to focus on objects that are close or far away.
Light bends (refracts) and focuses on the retina at the back of the eye as it passes through the lens.
The lens's thickness and curvature can be adjusted to focus on objects at various distances and ensure that the image is as clear as possible (this process is known as accommodation).
Thus, eye lens helps to focus the object.
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