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Plant physiology is the study of plant function and behaviour, encompassing all the dynamic processes of growth, metabolism, reproduction, defence, and communication that account for plants being alive. Considering that most of these processes take place at the level of cells, tissues, and organs, there is, because of the close association between structure and function in plants, also a close association between plant physiology and plant anatomy. Moreover, within the living cell, much of the metabolic activity is at the molecular level; therefore, a full understanding of a plant’s physiology requires an essential background in chemistry and physics. Many plant physiological insights into basic processes were gained from research based on a relatively small number of convenient experimental or model plants (e.g. beans, lettuce, maize, wheat, and in more recent times, Arabidopsis thaliana (L.) Heynh., the thale cress). Knowledge thus gained is then extrapolated to other plants as it is assumed that such processes operate similarly. For example, the vast majority of green plants have never been chemically analysed for the presence of chlorophyll, yet we assume that the green colour of their leaves is due to the presence of this pigment.