Essential Biology

By Justin Gerlach

This book covers the fundamentals of biology. It is primarily aimed at students completing school biology courses or about to start a biology degree course. It summarises the biology that ought to be seen as essential at those stages and corrects the most common misinterpretations that tend to occur. The fact that all aspects of biology are interlinked is highlighted. The book also emphasises that biology is not just about humans, or vertebrates, but that an appreciation of the vast diversity of life is important to a proper understanding of the subject.

• Language: English
• Publisher: Lulu.com
• Release date: Aug 15, 2021
• ISBN: 9781326442316

Book preview

Essential Biology

Justin Gerlach

Similar titles:

Essential Animals – 2020

Essential Vertebrates – in preparation

See: http://islandbiodiversity.com/essential.htm

© Justin Gerlach, 2021

Phelsuma Press, Cambridge U.K.

ISBN 97-1-326-44231-6

Imprint: Lulu.com

Essential Biology: key concepts in biology

Contents

Introduction5

Biodiversity: the diversity of living organisms7

Survival value: Darwinism and selection15

Causation: cell biology and physiology33

Ontogeny: growth, development and reproduction63

Evolution: ecology, time and the wider context73

Glossary and index80

References97

Introduction

Until the 19th century biology was a series of unconnected disciplines, ranging from broad natural history to embryology. With the discovery of evolution and genetics it became possible to link all these disciplines into a coherent study of Biology. This study was summarised as four fundamental ‘questions’ by Nikko Tinbergen in 1963:

Survival value

Causation

Ontogeny

Evolution

A full understanding of biology needs to consider all four aspects. Some of the important features of these are described here in the context of the diversity of life on earth.

The aim of this book is to provide a very brief outline of the great diversity of biological processes and developments and to illustrate how they are all linked. Most of this is covered in A-level biology courses; my intention here is to emphasise how the different components of such courses contribute to an understanding of the whole picture, and how that picture makes sense of the details. I have also aimed to clarify some common misconceptions in school biology and to fill some gaps that would be useful for students starting undergraduate biology courses. As well as some classic examples, I have used recent examples to emphasise current developments in biology.

Notable terms are marked in bold text and because biology has a great deal of terminology these terms are also covered by a glossary of brief definitions.

References: Tinbergen 1963

Species-scape: organisms scaled by number of species (concept by Wheeler 1990), based on the current number of described species (top) and the 1990 version by F. Fawcett (below). The great increase in the number of described insects makes most other groups smaller; note that in 1990 mammals are represented by a tiny elephant next to the fungi, the elephant is now almost invisible (named mammal species have grown from 4,600 to 6,500 whereas insects have gone from 790,000 to 1,024,000)

Biodiversity: the diversity of living organisms

Around a million and a half living species have been described, but the true diversity of life on earth is thought to be somewhere in the region of 12 million species (11 million eukaryotes, plus a million bacteria). Both these numbers are uncertain because our cataloguing of species is imperfect. Inevitably there are mistakes in the identification of species; sometimes species have mistakenly been given more than one name (synonyms) or sometimes what appears to be one species is actually several (cryptic species). At an extreme the necklace ground beetle Carabus monilis has a remarkable 91 synonyms. The number of species still to be described can only be estimated, and different approaches to estimation give wildly differing results.

The diversity of life is very unequally divided between groups; within the multicellular organisms there are far more animal species than plants, fungi or protists. Within the animals arthropods are particularly diverse. This is certainly true for the species that have been discovered so far, and is thought to be the case for those that remain to be identified. The species that are still to be described are probably not evenly distributed between the different groups. Most described species are arthropods, including around a million insect species, but it is thought that 80% of insects remain to be described. 20,000 species of nematode worms have been named, but probably far more than 80% have not been discovered. Other groups may have low diversity and also be relatively well studied. For example the horseshoe worms, Phoronida, have only 18 species, but experts on the group think it is unlikely that there are any more. Other low

Species richness of life’s divisions and kingdoms

diversity groups are definitely not well known. Two animal phyla stand out in particular: the Cycliophora discovered in 1995 with two known species (found only on the mouthparts of lobsters) and the Micrognathozoa, discovered in 1994 but not named until 2000. Currently only a single species of micrognathozoan has been named from just three sites in the world. Although we cannot guess how many species of cycliophoran or micrognathozoan there are, it is probable that many more species are yet to be discovered and described.

The process of species description comprises defining the species and giving it its scientific name (nomenclature). This is often referred to as its Latin name as the names were originally in Latin. Now they may also be a Latinised word from another language. Latin is used as it was the common academic language in the 18th century when nomenclature was formalised. Although for most purposes Latin was replaced by English in the 20th century, it is still retained in scientific names. The system of nomenclature we use today is attributed to the Swedish botanist Carl Linnaeus, or Carolus Linnaeus in the Latinised form that he adopted.

The two most recently discovered phyla: Micrognathozoa and Cycliophora, micrognathozoans are the smallest of the animals (0.1 mm) and cycliophorans are about 0.3 mm long

Linnaeus built on the systematic approach to species descriptions and classifications that had been developed by the British botanist John Ray in his Methodus Plantarum (1682). Ray’s names followed the common practice of being a short (3-4 word) diagnosis. Linnaeus developed this into the modern system by restricting all of his diagnoses to two words, one for the broad category and one for the individual species. In the 10th edition of his great work Systema Naturae (1758) the diagnoses were being used as names, and our system of genus and species is dated from that point. The first species to be named in the book, was, naturally, humans, using the Latin for human, Homo, with the simple diagnosis: nosce Te ipsum (know thyself). Homo was subdivided into sapiens (i.e. those who were able to know themselves) and troglodytes (‘cave-men’ - a mess of folkloric ‘wild-men’ and apes).

Over the past 100 years the use of scientific names has been further codified, with the creation of separate systems of rules (International Codes for Nomenclature) for viruses, bacteria, protists, fungi, plants and animals. These differ in detail but for all of them it is specified that genus and species (and subspecies) names should be in italics (or another type-face that different from the rest of the text). If hand-written, the convention is to underline the scientific name to make it distinct from ordinary text. This does not apply to higher level names (family, order, etc), except in bacteria and viruses where families are also italicised. Other important conventions are that the genus name starts with a capital letter but the species never does. The genus name may be abbreviated to its initial letter after the name has been written in full on first use. The word species may be abbreviated to sp., or spp. in plural (awkwardly similar to ssp. which is the standard abbreviation for subspecies). All these codes also specify that the genus must be based on one particular species, and that the species must be based on an individual specimen (type specimen). In the case of humans, this is Linnaeus himself!

Although the conventions of nomenclature seem trivial, and