Wind wrote:A plant that intentionally kills living beings for survival, not sure if it earns any bad karma for it.
Yep. All the venus trap plants will become ugly weeds in their next round on the wheel of samsara.
The thread starter's question obviously hinges upon the definitions of sentience and consciousness, which is not a trivial matter at all. We know that we are conscious and we assume the same of other human beings. You guys clearly behave as if you were conscious, so it is rational for me to make that assumption, though I can't be sure. My dog appears to be conscious as well (again judging from its behaviour) and since similarities in behaviour can be observed in all mammals the assumption must be extended to the class of mammals. Other vertebrates have nervous systems, and display some of the behaviour that we observe in mammals, so the let's extend the assumption to the vertebrates subphylum and ultimately to the entire chordata phylum, because fish also appear to be conscious in similar (albeit more limited) ways. However, at this point it becomes a little fuzzy, namely at the taxonomic level of the phylum. Even biologists are a little confused about the phylum rank, because there is no universally accepted set of classes and cladistics appears to contradict Linnaean taxonomy in some points. Other phyla include molluscs, sponges, flatworms, or anthropods (the creepy crawly phylum). Some of them have nervous systems, others don't. A mollusc has one, a sponge doesn't. Should we elect the presence of a nervous system as the criterion for being conscious or sentient? Perhaps that would be the obvious thing to do, but what if we are wrong? It gets even more difficult, because nervous systems vary greatly. Jellyfishes, for example, have a very simple nervous system. Do jellyfishes experience suffering? That question is almost impossible to answer unless you are a jellyfish. Clearly, the boundaries are fuzzy.
Now, plants do not have nervous systems in the conventional sense, so can we say that plants aren't conscious if we agree on this criterion? Well, not really. There are some plants with structures that resemble nervous systems. The previously mentioned venus fly trap is a good example. Another well-known example would be the mimosa. These plants have mastered tactile response and movement... quite an achievement for a life form without a brain! It is scientifically accurate to speak of neurobiological capacities in these types of plant life. Quote from the always helpful Wikipedia (plant neurobiology): "Plants respond sensitively to environmental stimuli by movement and changes in morphology. They signal and communicate within and among themselves as they actively compete for limited resources, both above and below ground. In addition, plants accurately compute their circumstances, use sophisticated cost benefit analysis and take tightly controlled actions to mitigate and control diverse environmental stressors. Plants are also capable of discriminating positive and negative experiences and of 'learning' (registering memories) from their past experiences." WOW! I bet you wouldnn't have expected that from your common garden plants. Now that's what I would call "signs of sentience".
Bottom line: there are no simple criteria, nor is there even a consensus for what constitutes sentience.