At the molecular level, the heat comes from the agitation of the molecules and therefore their atoms. This increase in agitation causes the molecules to be less condensed between them and will separate after breaks in the intermlecular bonds. This distends the material, as we see when we heat a metal, or a transformation of the phase of the material, such as melting ice or boiling water.
Survivorship curve = so, first of all, it's a curve, as in a graph.
It describes "survivorship" - the rate of survival, in other words: out of 100 organisms that are born, how many survive. This rate is different among species, for example, most humans live out to most of their life span, and almost all can survive well beyond a reproductive age.
However, in frogs for example, many many individuals are born, but only few can survive to adulthood: most die very young, before reproductive age.
So if you hear about a new species: let's say dogs, and you want to know how long they would live, you would look at their sirvivorship curve (and in some breeds of dogs, those that are likely not to be in shelters, but in homes, the survivorship curve would be similar as in humans: almost all individuals born can live long.
The tissue you are referring to here is the xylem, a <u>vascular tissue</u>, whose basic function is to transport water and nutrients from the roots to the rest of the plant.
