生物？非生物？

Ingram, MIT Biology hypertextbook:

How can one define life? The simplest definition is that any living thing must have three general properties:

* metabolism
* growth
* reproduction

Farabee, The Online Biology Book

Living things have a variety of common characteristics.
# Organization
# Homeostasis - maintenance of internal conditions
# Adaptation
# Reproduction and heredity
# Growth and development
# Detection and response to stimuli
# Interactions with environment

Modern biology is based on several great ideas, or theories:
1. The Cell Theory
2. The Theory of Evolution by Natural Selection
3. Gene Theory
4. Homeostasis

甚麼是生物, 甚麼是非生物? 這個如其說是生物學的問題, 不如說是哲學問題. 所謂生物的特徵, 其實是說生物學家從甚麼角度去研究生物, 了解生物的「運作」.

BTW, metabolism譯做新陳代謝, 其實是個誤解. 一般來說, 新陳代謝這個詞, 指事物除舊更新的過程. 可是metabolism, 即是生物學上講的「新陳代謝」, 是指細胞裡的一切化學反應, 無論把物質分解還是合成, 以維持生命所需. (用來定義生物, 大有循環論證的味道)

所以metabolism, 平實一點講就是biochemical reactions (in cells)