There is a small flat spot present exactly in the centre of the posterior portion of the retina called as macula lutea.
The centre portion of the macula lutea is known as the fovea centralis.
The characteristic feature of the fovea is that it is composed <em>only of cones.</em>
Cones and rods are basically the photoreceptor cells present in the retina. The rods are responsible for black and white visions whereas the cones are responsible for coloured (<em>bright</em>) vision.
Since, the fovea is most concentrated with the cone cells and no rod cells are present in this area, it is the area of <em>highest visual acuity</em>. Visual acuity simply means the clarity of vision.
Another reason for the highest visual acuity in fovea is that the ganglion and bipolar cells which are responsible for some scattering of light, do not cover the cones present in the fovea and hence, the resolution is further enhanced.
So the statement that the <em>visual acuity is greatest at the fovea of the eye is true.</em>
The given compound is an alkane because all the bonds between carbon are single. Alkanes have all single bonds and are thus called saturated hydrocarbons.
I'm presuming you mean the three different subcatagories or taxa as there around 25/26 mammalian orders. The three taxa are - Prototheria or Monotreme = Mammals that lay eggs Metatheria Marsupial = Mammals with external development pouches.
The answer is the non-exercise activity thermogenesis. Energy expended from fidgeting is called the non exercise activity thermogenesis (neat). Basal metabolic rate is the energy expended to support metabolism. Thermic effect of food (tef) is the energy expended for the digestion, absorption, and metabolism of nutrients.
