A review of the basic structure of microbial biofilm reveals that at least three conceptual models exist: (i) heterogeneous mosaic biofilm, (ii) penetrated water‐channel biofilm and (iii) dense confluent biofilm. When consideration is given to the effects of growth resource, it may be that all three variants are correct but form at widely different substrate concentrations. Experimental research with bacterial colonies and models of the latter using cellular automata have confirmed this view. Use of cellular automata to model biofilm growth give results which strongly suggest that biofilm structure is largely determined by substrate concentration.

During resting tidal breathing the shape of the expiratory airflow waveform differs with age and respiratory disease. While most studies quantifying these changes report time or volume specific metrics, few have concentrated on waveform shape or area parameters. The aim of this study was to derive and compare the centroid co-ordinates (the geometric centre) of inspiratory and expiratory flow-time and flow-volume waveforms collected from participants with or without COPD. The study does not aim to test the diagnostic potential of these metrics as an age matched control group would be required. Twenty-four participants with COPD and thirteen healthy participants who underwent spirometry had their resting tidal breathing recorded. The flow-time data was analysed using a Monte Carlo simulation to derive the inspiratory and expiratory flow-time and flow-volume centroid for each breath. A comparison of airflow waveforms show that in COPD, the breathing rate is faster (17 ± 4 vs 14 ± 3 min(-1)) and the time to reach peak expiratory flow shorter (0.6 ± 0.2 and 1.0 ± 0.4 s). The expiratory flow-time and flow-volume centroid is left-shifted with the increasing asymmetry of the expired airflow pattern induced by airway obstruction. This study shows that the degree of skew in expiratory airflow waveforms can be quantified using centroids.

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1. We describe a new model of plant growth that is general, deterministic, non‐stationary and mechanistic in nature. Its purpose is to investigate the extent to which the morphology and function of the whole plant can be determined by resource acquisition and utilization on the part of its components. 2. The model is a two‐dimensional section, showing the plant in its above‐ and below‐ground environments. The whole plant is represented by a branching structure made up from standard ‘modules’. The behaviour of the complete plant is determined exclusively by a rule set that acts only at the level of the individual module. 3. At the level of the whole plant, the model displays a classic S‐shaped growth curve, plasticity in root–shoot allocation, and foraging in heterogeneous environments. 4. At the level of the plant population, the model exhibits self‐thinning along a –2/1 self‐thinning line. This accords with the behaviour expected of a two‐dimensional system and also adds weight to the ‘geometric’ interpretation of the –3/2 self‐thinning line commonly seen in crowded populations of real plants. 5. An imposed ‘mutation’ in one of the modular rules allows us to produce a modified plant type that displays active foraging. In a set of simulations involving a model community containing both the modified and standard plant types, the modified type predominates in resource‐rich environments, and vice versa. 6. The simulations demonstrate the effectiveness of modular rule‐based methods from which whole‐plant behaviour can arise as an emergent property. The model suggests that active foraging carries a cost that cannot satisfactorily be borne at low levels of resource availability. It also implies that competition for resources, both above and below ground is in the form of a ‘contest’ (rather than a ‘scramble’). The success of the modular model highlights the primacy of resource acquisition and utilization in determining the ecological status of the plant.