Invertebrate Immune Responses

Immunity has, for obvious reasons of practical application, been studied most intensely in vertebrates. The vast bulk of animals must rely on their own innate, inducible, broad-spectrum, nonspecific immunity, and a few model invertebrate systems have been studied in detail, with some information available from others as well. Generally, although many invertebrates have short lives and high repro-ductivity (r strategies) as a possible defense mechanism for the species, not the individual even...

The Basic Characteristics Of A Cell

A cell is a pool of controlled chemical composition bounded by an outer membrane. It is the main structure of undifferentiated single-celled organisms and the essential building block of highly complex multicellular animals composed of many different cell types. A cell (1) sequesters biological resources relative to the outside world, and also internally (2) maintains the necessary concentrations of chemical components, pH, and so forth (3) localizes, transports, exports, and imports select...

Vertebrate Immune Responses

All vertebrates have what is traditionally termed an innate immune response, a rather generic, nonspecific system. Gnathostomes (jawed vertebrates) also have an adaptive response, that learns via antigen-antibody reactions to combat specific pathogens. Innate immunity does not improve with subsequent exposures to a pathogen. Adaptive immunity is specific and has memory in that the adaptive response to a pathogen improves with each subsequent exposure during an individual's life, but this...

The Evolution Of Eyes

Photoceptor Types Eyes

Light can be detected in many ways, but light detection is not exactly what we mean when we think of vision. Vision is more complex because it implies the processing of intricate spatial patterns of incoming light along with its intensity and aspects of its spectral characteristics. In higher organisms, vision involves interpretation of complex signals by the central nervous system and translation of these into decision-making that usually includes a directed response, such as by muscular...

Other

There is a variety of other physical sensing in the animal and plant world, probably not even easily broken into specific categories. Some plants respond quickly to touch or other physical disturbance. Temperature is a very important variable to many species. Two types of vertebrate thermoreceptor neurons have been described. One is the cold receptor, which reacts when the skin is colder than resting body temperature. Warm receptors respond when the skin is warmer than resting temperature....

Chemosensation In Plants And Single Celled Organisms

Although we concentrate in this chapter on olfaction and gestation in multicellular animals, other organisms detect external chemical signals in other ways that we can briefly mention (again acknowledging that our singling out of animal taste and smell as separate senses is somewhat arbitrary and artificial relative to chemosensation in the world as a whole). Plants do not have sensory systems equivalent to taste or smell but they do respond to external chemical signals including by...

The Phenomena Of Replication

Multicellular organisms have various ways of producing a next generation. Some, like bacterial biofilms, are essentially aggregates of otherwise free-standing cells that Genetics and the Logic of Evolution, by Kenneth M. Weiss and Anne V. Buchanan. ISBN 0-471-23805-8 Copyright 2004 John Wiley & Sons, Inc. reproduce by individual cell division. The biofilm does not reproduce as a single entity. Slime molds are another class of cells that normally live as individual single-celled organisms,...

Some Concepts Of Evolution Are Useful But Should Not Be Overused

Biological theory, like all theory in science, is an attempt to order the diversity of facts of the world. But the history of science consistently shows that the same facts can be interpreted in various ways and that what is chosen or accepted as fact is often culturally rather than, or as well as, objectively determined. An excellent and in some senses founding treatment of this now commonplace idea was presented by the Polish physician Ludwik Fleck (Fleck 1979), in the context of the way that...

Drosophila Larval Stage

Mechanical Syncytium

Regarding arthropods, more is probably known about Drosophila than any other (Lawrence 1992). Cell walls form around the nuclei in the syncytium to form a hollow structure along which there quickly appears a series of segmental structures that differentiate along the AP axis as the embryo grows. Local organ primorida called imaginal disks develop at specific locations along the axis. The imaginal disks themselves serve as organizers for cellular subsets that are precursors of the various parts...

Trachealess Plant Example

Branching patterns are important and widespread in life. (A) Branching of the major nerves in humans (B) branching of the venous drainage system in humans. There are corresponding branching structures in the arteries and lymph ducts. From Andreas Vesal-ius' classical drawings of 1543, that helped introduced the modern era in anatomic studies (Vesalius 1543). That the result has a fractal dimension (a numerical way to characterize the richness of the branching pattern) would be an...

Invertebrate Nervous Systems

Nervous System Hydra

Action potentials probably existed in the first single-celled organisms, predating neuronal activity and the evolution of the nervous system, evolved for some other purpose, perhaps having to do with response to external chemical conditions. Some modern single-celled organisms can effect a kind of preneuronal electrical signaling and are capable of producing action potentials that regulate, for example, the direction of the beating of cilia and thus movement of the cell. Colonies of multicelled...

Eyes Exemplify Important Lessons About Reconstructing The Evolution Of Complex Structures

There has been enthusiastic acceptance of the Pax6 opsin solution to Darwin's problem about the repeated, apparently independent evolution of complex eyes. The intercalary evolution scenario has seemed quite convincing, and similar relationships are being identified for other traits indeed, in some ways that is becoming the rule rather than the exception, as we have seen. However, the picture is more complex and shows some of the dangers inherent in accepting evolutionary reconstructions that...

Relationship Of Cell Structure To The Concept Of A Tree Of Life

Exactly what counts as the oldest fossil evidence of life is somewhat controversial. However, many accept that the very earliest evidence includes structures known as stromatolites, which are made of layers of bacteria-like organisms of various types Schopf 2000 . Details are controversial with such old and often ambiguous material, but the evidence suggests that at least some stromatolites radiometrically date to about 3.85 billion years ago. Because the Earth is only around 5 billion years...

Azy

The Brain Lobes Broca

Cephalon into the cerebrum and the basal ganglia, which are involved in control of movement. As will be seen below, the thalamus is central to lower processing and relay of signals from sensory organs to higher centers of the cerebrum, where they are further processed and integrated. Figure 15-5A indicates some of the genes whose regional expression is correlated with these morphological areas. Overall dorsoventral differentiation is established or affected by mutually inhibitory interactions...

Somatic Sensation

Medial Lemniscus Pathway

We referred earlier to thigmonasty or vibration sense in plants. Plants also have thigmotropy or a sense of mechanical disturbance. The leaves of some plants, such as some mimosa or the venus fly trap, close when touched, in the same way that they close when sensing vibration. Roots often exhibit negative thigmotropy by turning away from objects in the soil that they touch as they grow. Perhaps the best example of thigmotropy in plants is the manner in which tendrils curl around objects. When...

Vertebrate Nervous Systems

Alligator Brain Stem

As chordate body plans evolved, neuronal connections tended to become centralized and cephalized with a knot of neurons organized into a ganglion at the head of the animal. Neuronal function became more specialized and hierarchically organized. This has been much more elaborated in vertebrates than in the somewhat similar path taken by some arthropod lineages. Vertebrate CNS development involves most of the signaling, transduction, transcription, receptor, patterning, and combinatorial...

Photoreception In Plants

Diagram Cholorplast Figure

Plants are always seeking the light desiring the sunshine, unconscious of either Joseph Conrad, Almayer's Folly, 1895 . Plants evolved from organisms like simple photosynthesizing cyanobacteria into large organisms with many leaves that allow the plant to maximize photosynthetic activity.They depend on light for many aspects of their life cycle, including photosynthesis, photoperiodism, photomovement, and development, flowering, and seed germination. Although they are sessile, they have become...

Vibration Sensing

Central Auditory Pathways

Vibration, the wavelike movement of air or other objects in which an organism comes into contact, can be created by traveling sound waves or by mechanical disturbance such as water currents or wind . By itself, vibration detection is a form of the sense of touch. However, like light, there is additional information carried by the frequency, amplitude, complexity, and location of vibratory motion. It is this that we refer to as hearing, but as usual there are subtleties and gradations. And it is...