Correct answer: C) Concentration gradient
The process of movement of a particle in a solution from the region of higher concentration to the region of lower concentration across a membrane is called as concentration gradient.
For example: If we drop a few drop of dye in a glass of water, it will diffuse along a concentration gradient, i.e, the region where dye is found in highest concentration to the region where it is in lower concentration.
It will occur until the concentration of dye become uniform in all the direction in the glass of water.
Sexual reproduction is a process involving the fusion of two gametes to
Gametes are special reproductive cells produced by meiosis. It produces genetically dissimilar offspring. Offspring may inherit beneficial qualities from both parents and there is a greater genetic variation in the offspring, leading to species that are better adapted to changes in the environment.
The correct answer should be the Periderm.
It is not as simple as this, of course and you would be wise to know that periderm is just a part of the overall concept that is bark, because bark is not a biological term.