I see lots of big fruit in the stores but typically they don’t taste as good. But that could be my bias.
Here’s the question which I believe has a straight answer. : “Consider 2 apples from the same tree. One has an average diameter of 2 inches and the other has 2.5 inches”. The ratio of the volume is 2.
Is the ratio of total vitamin C in each apple also 2 ?
I doubt there’s any completely straightforward and universal answer to this since not all fruits are the same, but for your apple, the bigger one is just more apple (not diluted or inflated with some non-apple filler), so the nutritional content scales pretty much as should be expected. Some of the nutrition is in the skin, so that scales with surface area, not volume.
Things like pumpkins though, maybe not so much - the bigger they are, the more void they tend to contain
Thank you - I suspected as much. May I have a cite please?
I don’t have one, sorry. Disregard my post if you feel it requires one.
Here you go, from the T. H. Chan School of Public Health at Harvard University no less,
To summarize, the bulk of the fiber is in the skin so as Mangetout surmised that scales with the surface area, while most of the Vitamin C content is found in the flesh which scales with the volume.
There is a side-link for bananas, I didn’t check it out because I don’t want to feel guilty about not eating the peels.
I see that mentioned in the cite
I don’t see any mention of this part in the cite. Can you please point me to which part of the page I should be looking at ? Thank you
It’s not in the cite, but from solid geometry. If we pretend that the apple is a solid sphere, then the skin is the surface of the sphere and the flesh is the interior, ignoring the inedible core. The surface area of a sphere is calculated from the square of the radius, the volume from the cube of the radius.
What other option could there possibly be? All it takes is to cut open two apples of different sizes and see that the larger one is not hollow or full of air. By what mechanism might a larger apple contain less of anything than the smaller apple of the same species? The larger apple will have a larger mass, larger weight, larger amount of every vitamin, more juice, more calories, more everything. Why does that statement need a cite?
Is the OP thinking that an apple has some finite amount of nutrients and as the volume increases those nutrients somehow become diluted?
That’s not necessarily so. Large fruit have had their DNA modified (usually through breeding) to be larger. The same process could change the amount of nutrition in the fruit. The thing is, when they breed larger fruit, they’re only concerned with size and looks. They didn’t care if the fruit was still as nutritious or even tasted as good.
The OP asked about two fruit from the same tree. They will have the same DNA.
Is this a good time to wax all pecksniffian and bring up multiply grafted trees? 
You need to factor in how much of any fruit is water.
Two apples on the same graft share genetics but could have grown in a different environment ie one could have been from the sunny side of the tree and the other shaded.
So the larger fruit may have the same number of cells in the pulp as the smaller, and therefore the same dry matter but each cell in the holds more water and it’s nutrition is effectively diluted.
Both effects would be in place and I’d have thought the larger apple would have more nutrients, but likely something less than 2 times and the effect on taste is well in the tastebuds of the taster
Consider potatoes. It’s often said that the bulk of nutrients in a potato (aside from the starch of the interior) is in the skin. But I’ve also read somewhere that this isn’t exactly right: Rather the bulk of nutrients is in the interior but most concentrated close to the surface, just under the skin. So you can peel a potato, just be sure to peel it very thinly and not deeply, without losing too much value.
The point to be made, that nutrients in the interior of a fruit or veggie might not necessarily be uniformly distributed.
Apples reach their final size quite early in the cycle, then they fill up with sugars; IANABiologist, but I don’t think it’s true that a larger apple (off the same branch) has the same number of cells as a smaller one.
There is though, as you say, considerable variability - not just between different varieties, or even different trees of the same variety, but even between individual apples of the same variety, on the same branch - any number of conditions (position on the tree, orientation of the stem, the position of the individual fruit within the cluster, attack by insects, the total amount of fruit set on a tree, sunlight, rainfall, day and night temperature, etc) can cause a tree to invest less or more energy in the development of individual fruits.
Whilst some of those factors can be dismissed by taking averages, I doubt anyone has researched averages that would be specifically useful to answering the OP definitively. Average yield or sugar content per variety, per set of conditions, per rootstock, etc will have been researched to death, but by final fruit diameter within a single variety on a single tree? It’s an interesting question, but not such a useful one.
Do fruit siblings really have the same DNA?
Barring spontaneous mutations, the fruit shares the same DNA with the leaves and branches (the rootstock may be different if the tree is grafted). The DNA inside the germ of the seeds in the apples will be unique in each seed
The fruit are not siblings. The trees produced from the seeds of those fruit are the siblings. The fruit themselves are just the fleshy ripe ovaries of the parent.
I didn’t know that but it makes sense. Thanks!
Way back in 7th grade general science class (circa 1965) we learned about “alternation of generations” in which plants, most visibly in lower species like ferns and mosses, alternate between sporophyte and gametophyte generations. It was mentioned that this pattern continues to exist in all plant life, even the more highly evolved forms – it’s just that one one the generations has become by far the most dominant and visible, and the other has become reduced to the point of being nearly vestigial.
Is this all correct?
Depending on what is actually correct about this, it may feed into the question of whether adjacent apples share DNA with each other or their parent tree. Can someone clarify?