The apparent and often spectacular movements of animals and insects, movements of the whole organism in relation to its surroundings arising from internally generated forces, have always been, by their very ubiquity, uppermost in our perception of motion in the living world. Movement in plants, generally of one organ in relation to the whole plant, whilst sometimes spectacular, have often in the past been seen as rather esoteric events, amusing perhaps, but of little importance in the general biological scheme of things. However, this is not so; plant movements are quite widespread in occurrence and all are most probably manifestations of a single physiological process, the change in volume of special motor cells. One particular movement, the opening and closing of stomata, which provides a basic control of photosynthesis, is of fundamental importance to the existence of the whole biosphere.

Like DNA and the various forms of RNA, a protein molecule is an information storage system. It contains in fact one or more polypeptide chains which may be regarded as linear sequences of twenty different types of monomer units. It is now clearly established that the chemical information corresponding to a given sequence of a polypeptide chain, containing n amino acid residues, is stored in a segment of one of the two strands of DNA containing 3n nucleotides. The transfer of such information from a gene to a polypeptide chain takes place according to the well-known process involving a transcription and a chemical translation step. This last step leads to a polymer which, in appropriate conditions, takes a three-dimensional conformation or tertiary structure which should correspond to a free-energy minimum of the molecule and its surrounding water solution.

The principle of the microprobe analysis of chemical elements is illustrated in Fig. i. Some kind of radiation is directed on to the specimen, generating signals characteristic of the elements present. Local analysis in situ is achieved in one of two ways. Most often the impinging beam is finely focused so that the signal at any moment comes only from a selected microregion. Alternatively, in some instruments, the impinging beam floods a larger region but the emergent signals characteristic of a particular element may be selected and focused to give an elemental ‘map’ or ‘image’.

Learning and memory are important elements of our daily lives, familiar to all through introspection. Yet the mechanisms underlying these processes are still for the most part unknown. Here are problems which combine a maximum of intrinsic and practical interest with a minimum of actual knowledge and understanding. Years of our lives are dedicated to the formation of certain long-term memories and behaviour patterns, yet we have only rudimentary notions of how such ‘schooling’ is best accomplished. There is no certainty in any aspect of the process. We are not sure whether relatively few cells or millions participate in a memory trace; whether these cells change as a whole, or whether the changes are limited to synaptic regions. In fact, we cannot be certain whether the changes are confined to the neurones or whether the glia also participate.

Protein chains are usually folded into one or several discrete globular units called domains (Schulz & Schirmer, 1979). Levitt & Chothia (1976) have shown that the structures of such domains frequently fall into one of the following three classes; α-proteins which are mainly α-helical, β-proteins which contain antiparallel β-strands and α/β proteins which have a central core consisting of a sheet of strands, most of which are parallel. The connexions between the parallel strands in αβ-proteins frequently contain helices which are packed on both sides of the sheet in a regular way (Chothia, Levitt & Richardson, 1977).

Mass spectrometric analysis of organic compounds was in the early 1950s done mostly for quantitative determination of petroleum products. The use of the mass spectrometer for qualitative analysis of solid organic material samples was shown by O'Neil & Wier (1951) and since then a continuous increase in mass spectrometric studies of different classes of organic compounds has been noted. After the gas chromatograph was developed by James & Martin (1952) the quantitative analysis of complex mixtures of organic compounds was possible and after a few years the gas chromatographic method was considered as routine. The first connection of a gas chromatograph (GC) to a mass spectrometer (MS) was made by Holmes & Morell (1957). They studied gases using a splitter system where only a small part or less than 1% of the effluent from a packed column was transferred to the ion source of the mass spectrometer. The next step in GC—MS development was made by Gohlke (1959), who studied compounds of low molecular weight using capillary column directly connected to a time-of-flight mass spectrometer. This was possible due to the fact that the carrier gas flow rate could be limited to about 1 ml/min. To avoid the sample loss resulting from using a packed column with the splitter system a jet molecular separator was constructed as an interphase between the packed column and a mass spectrometer with magnetic sector analyser (Ryhage, 1964). Mixtures of fatty acids and of hydrocarbons with a molecular weight of up to about 420 were studied. In this study spectra were taken at irregular intervals.

It is well known that excited states may be generated chemically in biological systems as evidencex and by the phenomenon of bioluminescence and it is natural to suspect that they may also be generated and used in dark processes (Szent-Györgyi, 1941; Steele, 1963; Cilento, 1965; White & Wei, 1970; White et al. 1971). Förster (1967) has pointed out that electronic excitation and subsequent transfer processes may occur in biological dark systems despite the fact that the energy available from enzymic processes is too low to excite aromatic amino acids and other biochemical structures. Hastings (1968) suggests that in some organisms light emission is just an alternative to the formation of an active species.

Serum lipoproteins are the macromolecular lipid–protein complexes, soluble in aqueous environment, which act as transport vehicles for polar and apolar lipids in the bloodstream. The growing multidisciplinary interest in these systems stems on the one hand from the fact that their physiological functions are intimately related to the pathways of lipid metabolism and catabolism, and on the other hand from their macromolecular nature which renders them accessible to a large variety of experimental approaches for the study of the physical and chemical principles of lipid-protein interaction.

Transport of ions through channels is fundamental to a number of physiological processes, especially the electrical properties of excitable cells (Hille, 1992). To understand this process at a molecular level requires atomic resolution structures of channel proteins.

The discovery of mode-locked laser operation now nearly two decades ago has started a development which enables researchers to probe the dynamics of ultrafast physical and chemical processes at the molecular level on shorter and shorter time scales. Naturally the first applications were in the fields of photophysics and photochemistry where it was then possible for the first time to probe electronic and vibrational relaxation processes on a sub-nanosecond timescale. The development went from lasers producing pulses of many picoseconds to the shortest pulses which are at present just a few femtoseconds long. Soon after their discovery ultrashort pulses were applied also to biological systems which has revealed a wealth of information contributing to our understanding of a broadrange of biological processes on the molecular level.It is the aim of this review to discuss the recent advances and point out some future trends in the study of ultrafast processes in biological systems using laser techniques. The emphasis will be mainly on new results obtained during the last 5 or 6 years. The term ultrafast means that I shall restrict myself to sub-nanosecond processes with a few exceptions.