Difference between 生き物 and 生物

Question

I had assumed that 生物 was just a fancier word for 生き物 in the way that onyomi compounds often are. But when I looked in the dictionary I became less sure.

For 生物 I see:

動物・植物・微生物など生命をもつものの総称。
Animals, plants, microbes etc. A generic term for things which are living.

But for 生き物 I get:

生きているもの。特に、動物。生物(せいぶつ)。
Living things. Especially animals. (synonym for) 生物

From these definitions I see that 生物 clearly refers to both plants and animals, but 生き物 seems to refer primarily to animals. But then the definition of 生き物 says it is a synonym for 生物.

So the question is, are these words synonyms or do they have distinct meanings? Would it be weird to refer to plants as 生き物 for example?

Answer 1

They're synonyms, but 生き物 is more colloquial. You can still use it in formal situations, but it's not common to use 生物 in normal speech. It's not weird to refer to plants as 生き物, but I think animals would first come to mind.

Answer 2

As in @deeeeekun's answer, 生き物 is more colloquial and it is used to describe living things with clear vital sign. Students taking care of rabbits or golden fish in an elementary school is [生き物係]{いきものがかり}. (いきものがかり is a popular music group in Japan for this 20 years.)

The homophone word 活きもの is used to describe fresh fish (Probably alive, but necessary if it's fresh enough for being sold).

[生物]{せいぶつ} is used in a more academic context. In most cases, I think calling cats as "creatures"/"animals" is more common than calling them as "organism". I guess [生物]{せいぶつ} does not have any poetic sense like "creatures", so biology :[生物学]{せいぶつがく}, an academic discipline, is always read as [生物学]{せいぶつがく}.

Homonym:[生物]{なまもの} is used to describe fresh fish like tuna-sashimi. If you have food-poisoning and you might be worried about having eaten fish not being cooked.