The answer is D. The natural selection is a theory which illustrates the gradual process of evolution in the population due to the change of environment. The key point is the mutation (variation) exists in the population before the environment changing. For C, if the environment does not change, though the adaptation is useful to environment, it will not be selected. Because the organisms without the adaptation will not die.
Can you be more specific with the question. Are you talking about DNA coding with complementary bases?
Answer:
Pupillary light reflex refers to the contraction that the pupils present when they light up. In cases of injury to the optic nerve, when the eye where the injured optic nerve is illuminated, since it cannot conduct the stimulus to the brain, neither pupil closes.
Explanation:
Pupillary light reflex refers to the reaction that causes the pupil to close with light thanks to the contraction of the sphincter of the pupil and to open in the dark thanks to the relaxation of that muscle by not receiving any stimulus. A light stimulus reaches the eye and in the retina it is transformed, through a chemical reaction, into an electrical stimulus that will be transmitted through the optic nerve and the visual pathways to the brain. The visual cells of the retina, rods and cones, also act as light receptors that control the pupil's motor activity. Thus, pupil-motor thresholds to light follow the same spectral sensitivity deviations as visual thresholds, which are a function of the state of light adaptation of the retina.
Urinary obstruction, Neurogenic bladder, Catheterization, Pregnancy and diabetes
Scientists
can also glimpse the awful effects of Alzheimer's disease when they look at
brain tissue beneath the microscope:
Alzheimer's tissue has numerous fewer nerve
cells and synapses than a well brain.
<span>
<span>Plaques, unusual
clusters of protein particle, which are construct up between nerve cells.</span>
</span>
<span>
<span><span>Dead and dying nerve cells contain tangles,</span> which
are produce of twisted strands of a further protein.</span>
</span>
<span>Scientists
are not absolutely sure what causes cell death and tissue deficiency in the
Alzheimer's brain, but plaques and tangles are key suspects.</span>
