#83 - Dec 2024 - Garden Stuff - © Sandy Lang - slang@xtra.co.nz PLANTS & ANIMALSJanuary/February: Mid/late summer. Coolest since 2014 = maritime climate + climate change. Plants and animals are very different. But are they...? Genes and levels: We share ~40% of our genes with plants, so it’s the ~60% we don’t share that makes us different. We are least different at the biochemical level. Our DNA and cell metabolisms are similar. Even our cell organelles are similar. But differences increase as we look from the level of the cell, to the tissue, to the organ, to the whole organism. Evolution: First came plants (autotrophs – energy from light), then came the animals that eat plants (heterotrophs – energy from other organisms). Plants are at the bottom of every food chain. Plants don’t much need to move about, but they do need to grow tall to compete for light. Animals don’t much need to be big, but they do need to move about to find food. Different requirements but some similar mechanisms. Plant stiffness: For plants to evolve from unicells, to multicellular organisms, eventually to trees, requires they develop stiff support structures. An engineer will tell you stiffness requires some elements to be under compression and others under tension. So, plants developed tissues that can sustain tension (fibres - think ropes) and other tissues that can sustain compression (turgid cells – think bouncy castles inflated with water). So, the stems of young plants gain stiffness from tensioned fibres, embedded in a matrix of compressed cells. Lower cell pressure and they sag (wilt). Combine a lot of fibres together and the resulting tissue (wood) can also sustain compression - tree trunks don’t wilt. Animal mobility: Animals gain structure and mobility in a similar fashion. Here the tension tissues are muscles, and the compression tissues are rigid skeletons (think bone [us], cartilage [sharks] and chitin exoskeletons [flies]). Balanced tension between opposing muscles gives stiffness - imbalanced tension causes bending - controlled changes in imbalance cause motion. Plant mobility: While plants can’t locomote, they are mobile in that they bend their limbs about. They orientate flowers and leaves to the sun, they bend stems seeking support, they wrap tendrils tightly around things they find. Until recently we were unaware of these motions because we couldn’t see them (too slow). But time-lapse photography (now on your phone camera) reveals these motions by speeding them up. They look much like animal motions. They are caused by controlled pressure changes in the cell matrix. ___________________________________