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Several equations have been proposed to describe ontogenetic growth trajectories for organisms justified primarily on the goodness of fit rather than on any biological mechanism. Here, we derive a general quantitative model based on fundamental principles for the allocation of metabolic energy between maintenance of existing tissue and the production of new biomass. We thus predict the parameters governing growth curves from basic cellular properties and derive a single parameterless universal curve that describes the growth of many diverse species. The model provides the basis for deriving allometric relationships for growth rates and the timing of life history events.

Penguins use twice as much metabolic energy as other terrestrial animals of a similar mass to walk a given distance1,2, which was thought to be because side-to-side waddling requires excessive work. Here we show that waddling actually conserves mechanical energy and suggest instead that walking is expensive for penguins because their short legs require them to generate muscular force rapidly.

Wallabies and kangaroos increase their speed of hopping with little increase in their use of metabolic energy, apparently by means of elastic energy savings in their hindlimb tendons1,3. Here we report that, because of this storage capacity, female tammar wallabies can carry large young in their pouch at very low cost, with no increase in metabolic energy expenditure.

Understanding the allocation of metabolic energy between the sustenance of an organism and its growth is an important issue in ecology. West et al.1 have built on their earlier attempts to explain the exponent for the allometric scaling of metabolism and have derived a single, parameterless universal curve that describes the growth of many species. Here we show that the universal curve arises from general considerations that are independent of the specific allometric model used by West et al. and that the data do not distinguish between a 3/4 or 2/3 exponent in the relationship between metabolic rate and mass scaling.

IF Ca2+ were distributed passively across the nerve membrane, the existence of a membrane potential of 50–60 mV negative with respect to the external medium would lead to an accumulation of Ca inside the cell. However, ionised Ca is normally 105-fold less concentrated inside the cell than it is outside1–3, a difference which is essential for the normal function of excitable preparations such as muscles and the synaptic regions of neurones. The observation that the extrusion of Ca depends in part on external Na led to the proposal that the energy for Ca extrusion may be derived from the transmembrane Na electrochemical gradient4,5. More recently, it has been found that cellular metabolic energy in the form of ATP interacts with the Ca transporting system6,7. Nevertheless, its role as an energy source for Ca transport is still something of a puzzle. At present, it is not clear whether ATP is consumed when Ca is transported across the axolemma or whether it only interacts with the Ca-transporting system without itself being hydrolysed. On the assumption that ATP might energise Ca transport, it should be possible to demonstrate an ATP-driven net Ca extrusion in the absence of other energy sources such as those derived from the normally existing ionic gradients across the membrane. We report here experimental evidence for a direct involvement of ATP as an energy source for Ca transport in squid axons.

IN appropriate conditions single cells obtained by dissociation of embryonic tissues form organised cell masses resembling tissues. We wish to present results indicating that the adhesive properties of chick embryonic cells depend on maternal age. These unexpected observations were made in studies on the mechanism of intercellular adhesion. The formation of initial aggregates between chick embryonic liver cells is a two-step process1; cells rapidly and reversibly bind to each other to form aggregates in a step that is not inhibited by metabolic poisons. The reversibly bound cells are then converted into stably bound cells in a process requiring metabolic energy.

Many oxygen-evolving nonheterocystous cyanobacteria can synthesise nitrogenase1,2, but only a few are able to protect the enzyme from inhibition and denaturation by oxygen3–5. It is difficult to reconcile concomitant oxygenic photosynthesis and the obligately anaerobic process of nitrogen fixation in the remaining strains. One possibility is a temporal separation of the processes: Plectonema boryanum (U. Tex strain 594) has been shown6 to fix nitrogen and then grow oxygenically to the limits of the fixed nitrogen when incubated without combined nitrogen under N2/CO2. Growth was not extensive. Here conditions are described in which the same strain of P. boryanum will simultaneously fix nitrogen and grow extensively, fully pigmented, apparently with sufficient metabolic energy to drive nitrogen fixation.

Black goats of small body size (15–22 kg) dominate the herds of the Bedouins inhabiting the extreme deserts of the Middle East1; only a few white goats appear in such herds. Annual rainfall in these deserts varies from 15 to less than 150 mm; resources of food are sparse and watering points widely spaced. Summer is extremely hot and winter may be bitterly cold. Cloudy days are rare and solar radiation is immense all the year round2. Presumably, special adaptations would have been required in order to thrive in these harsh deserts. Can the black colour of the Bedouin goat be considered such an adaptation? Here, we have attempted to answer this question, and have found that by absorbing more of the Sun's energy on cold days, the temperature of the coat dramatically increased and the goat's oxygen consumption decreased significantly.

IT has often been assumed, as in the theory of active transport of ions, that metabolic energy is required to transfer sodium ions from a low intracellular concentration to a higher concentration in blood serum or an external fluid1–3. On that assumption, the efficiency of any transport mechanism would be expressed as the ratio of output of work to input of energy. Theoretical calculations have been based on the following approximation, derived from the laws of ideal solutions

IT is generally believed that the semipermeability of cell membranes is closely associated with the living functions of the cell. According to Harvey1 “…Selective permeability … becomes the surest test to distinguish the living from the dead, holding where all others fail. It can truly be said of living cells that by their membrane ye shall know them.”