A frame which is used for ecological sampling

A quadrat is a frame (usually a square or a circle) of known area used to isolate a subset of the population. This subset will comprise one sample. Quadrats come in various sizes (and shapes) with the size selected determined by features of the organisms in the population to be sampled.

Explanation:

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when the displaced particles are perpendicular to the direction the wave travels, is called a transverse wave, whereas in longitudinal wave the displace practices are parallel to the direction of the wave.

in the given image:

first image shows - longitudinal wave

second image shows - transverse wave

third image shows - longitudinal wave

fourth image shows - longitudinal wave