Medicines for the Earth: The Eco-Physiology of Plants
Similarities Between Plant and Human Anatomy and Physiology
Plants and humans share numerous anatomical and physiological characteristics; we are actually more similar than different. Understanding these remarkable parallels gives us a greater appreciation for the kinship that exists between the plant and human realms, which in turn is the basis of reverence for nature and respectful coexistence with biodiversity.
The similarities between plants and humans can be simplified into three categories: basic life needs, anatomical and physiological characteristics, and subtle functions.
Basic life needs
The basic needs of plants and people are the same. Plants and people share the fundamental biological cycle of birth (germination), growing to maturity, reproduction, aging and decline, and death. Plants and people both need nutrients in order to grow and thrive, water to moisten the tissues and facilitate metabolic processes, air for respiration, and environmental and seasonal conditions conducive to life. Plants and people both need defense mechanisms to protect themselves from the elements and from other organisms; both suffer from diseases, viral and bacterial infections, and parasitic infestations.
Anatomical and physiological characteristics
There are numerous parallels between the anatomical structures and physiological functions of plants and people. Plants have outer cells that function similarly to skin. Just as human skin is lubricated and protected from the external elements by oily secretions of the sebaceous glands, the aerial surfaces of plants secrete wax produced from fatty acid precursors for waterproofing and immunity. Human bodies are shaped and supported by bony skeletons, while plants have their own connective tissues and skeletal structures; the growth and development of plant cells and organs rely on a skeleton comprised principally of microtubules and microfilaments. The blood vessels and capillaries of the human body can be compared to the xylem (wood) of plants, which is a complex vascular tissue containing water-conducting cells; the blood and lymph correlate with the various fluids that flow through the channels of the plants. The human alimentary canal is comparable to the roots, which draw nourishment into the outer tissues and cells of the plant. Humans and plants both have reproductive systems; human sperm and ova can be compared to the pollen-producing stamens and ovary-containing pistils.
Like humans, plants have complex immune systems. Plants produce purely mechanical defenses, such as spines and thorns. Chemically, they secrete essential oils and oleoresins, which function as immunological compounds to discourage herbivores, stimulate healing of wounds, and protect from insect and fungal pathogens. Plants react to pathogens and diseases by producing certain antibacterial compounds; phytoalexins are probably the most studied of these defensive compounds. These immune responses can be compared to various responses of the human immune system, such as the activation of lymphocytes.
Plant metabolic functions are governed by hormones, as are human functions. Gibberellins are one group of hormones that control growth and a wide variety of other plant developmental processes.
Plants have detoxification mechanisms that work to break down xenobiotics; many of these mechanisms are similar to how the human body deals with toxic compounds. Both plants and humans require certain nutrients and enzymes to efficiently remove toxins and to protect themselves from stress. For example, glutathione plays an important role in various physiological processes of both plants and humans, functioning primarily as an antioxidant.
Like humans, plants suffer oxidative stress and free radical damage when exposed to xenobiotic compounds, and produce antioxidants in response. Pollutant tolerance in plants is determined by many of the same physiological mechanisms as in humans. In general, there are more similarities between the metabolic pathways of plants and humans than there are differences.
The bodies of plants, like the bodies of humans, support complex microbial ecosystems. From the root tips to the tips of the highest leaves, plants provide a diverse habitat for a wide range of microorganisms. Just as the skin and mucous membranes of the human body are the biogeography for various colonies, each zone of a plant has its own cohort of microorganisms. Both the human and the plant body set the stage for its microbial inhabitants, and in turn, the microbes establish a range of varied relationships with their partners, ranging from relatively inconsequential transient visits, to symbiotic functions, to pathogenic attacks.
There are other fascinating parallels between plants and humans that are more in the realm of subtle energetic physiology than purely biochemical or anatomical functions. Plants, like humans, have circadian rhythms. There is accumulating evidence that plants have multiple circadian clocks both in different tissues and, quite probably, within individual cells. Plant growth, like the growth of the human body, is guided by gravity. Gravitropism, the ability of plant organs to use gravity, has been recognized for over two centuries. Like the human body, plants develop symmetry of form; like the human body, these processes arise in embryogenesis. Plants communicate, both with other plants and with other forms of life. The primary signaling mechanism for this is semiochemicals. These secreted compounds act as attractants and repellants of beneficial or destructive insects, and allow plants to inform other plants of events such as insect attacks and infestation. Studies have also demonstrated that plant growth is stimulated by certain kinds of music and inhibited by others, indicating some level of sensory awareness and sentience.