dagaz

Life is incredibly complex so you are never going to a get a nice all-encompassing definition which you can put into one sentence. Although there are some grey areas still under debate, nearly all biologists would agree with the following characteristics of a living organism: 1) able to metabolise - that is they can use energy to accumulate, modify, produce and eliminate materials which are necessary for growth and reproduction. 2) have the capacity for growth, development and reproduction. 3) contain DNA which provides inheritable genetic traits. 4) use homeostatic responses to minimise the effects of changes in the environment. 5) show adaptive potential which will allow them to respond to long term changes in their environment through evolution. 6) cell theory also tells us that all living things are made from cells.

The word 'biotic' literally means 'living thing' so the biotic features of an aquarium are just those things in it which are actually living - plants, animals, etc.

Quote:"Do all plant species have a male and a female form?" No. In fact many, if not most, naturally occuring flowering plants are bisexual - that is they have male and female parts in the same flower on the same tree. Some of these plant species have special receptors in their stigma (the female receptive part) which won't allow pollen from the same flower or even the same individual to prevent it from self-pollinating. Other plant species time it so that even though they have male parts (filament and anther, collectively called stamen) in the same flower as the female parts (ovary, style and stigma, collectively called carpel) they produce and are receptive to pollen at different times. Other plants find self-pollination acceptable and don't have any barriers towards it. And yes there are plants out there which are dioecious (male and female flowers on different plants) or even monoecious (separate male and female flowers on the same tree). Quote:"for the varieties of plants that do produce male and female forms, what determines this?" This is largely genetic. Quote:"but not all plants produce flowers do they?" No, only flowering plants (Angiosperms) produce flowers. Conifers (Gymnosperms) reproduce by cones and ferns (Pteridiophytes) and other primitive plants reproduce by spores. For the ferns and other primitive plants reproduction is asexual.