Not quite, but you're more or less on the right track; I think you may have heard a slightly garbled or perhaps oversimplified version.
It is true that most animals and plants can synthesize vitamin C and that guinea pigs, humans, and most species of bat cannot. However, there are a few others that also cannot; capybaras (a large rodent), all primates in the suborder Haplorrhini (the "dry-nosed" primates, which includes humans, apes, and monkeys), and some kinds of birds and fish.
No, the skin is only capable of producing vitamin D in the presence of sunlight.
vitamin c
Often times milk or food will give you vitamin A. You can also get vitamin A from a variety of daily multi-vitamins.
Often times milk or food will give you vitamin A. You can also get vitamin A from a variety of daily multi-vitamins.
No. human body can not synthesize vitamin B 12. You have to consume the same through your food only. Only non-veg food contains the most of the vitamin B 12 you get. Strict vegans should be given injections of vitamin B 12.
Yes the skin is capable of producting vitamin D in the presence of sunlight. It is the only vitamin that can be produced by the body itself. All others must come via diet. Even vitamin D must be supplemented in diet as well.
Neither plants nor animals are independently capable of constructing vitamin B12 (Only bacteria have the enzymes required for its synthesis). B12 is replenished in the body from dietary sources.
No. Silica, or silicon dioxide, is not a vitamin and should not be consumed by humans or animals.
Producing vitamin K and some vitamins B in our body.
Sure, you eat oranges and then you leak sperm!
Carotene
The treatment for animals with scurvy is a vet visit to determine why the vitamin C deficiency is occurring. The treatment will also include vitamin C supplements.