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- Herausgeber: novum pro Verlag
- Kategorie: Gesellschafts- und Liebesromane
- Sprache: Englisch
Have you ever wondered how animals and humans on planet Earth evolved from primitive single-celled organisms into the complex animals and humans of today? Elena Grigorieva has used simple pictures and brief descriptions to demonstrate how animals and humans have evolved from single-celled creatures, called protozoans, to multicellular metazoans over aeons of time. This is a key question that scientists and laymen have long puzzled over. This book is particularly useful for young people, schoolgoers and undergraduate students as it describes how the eight predominant bodily systems collaborate. There is rising curiosity about the future of human beings, and the simple answer is that the future of humankind is in the hands of humans. The possibilities are infinite.
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Seitenzahl: 18
Veröffentlichungsjahr: 2023
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Contents
Imprint 2
From Unicellular Protozoans to Multicellular Metazoans 3
How Cells Specialise 6
How Animals Evolve 12
The Major Categories of Metazoan Cells 14
How Animals Develop 26
The Body Systems 29
Animal Anatomy 33
Imprint
All rights of distribution, also through movies, radio and television, photomechanical reproduction, sound carrier, electronic medium and reprinting in excerpts are reserved.
© 2023 novum publishing
ISBN print edition: 978-3-99131-569-8
ISBN e-book: 978-3-99131-570-4
Editor: Hugo Chandler, BA
Cover images: Wavebreakmedia Ltd, Ivan Kruk | Dreamstime.com, Elena Grigorieva
Cover design, layout & typesetting:novum publishing
Images: Elena Grigorieva
www.novum-publishing.co.uk
From Unicellular Protozoans to Multicellular Metazoans
Around 600 million years ago our planet Earth was very different from what it is now. There were no animals. Instead, there were various tiny, unicellular creatures which lived in the warm waters of the ancient oceans and lakes. Some of them had a long, tail-like structure – a flagellum, which they used for swimming. Biologists call these creatures protozoans.
In order to get nutrients essential for living, the protozoans ate other cells and organic structures. While feeding on bigger cells or food particles, the protozoans gathered into groups, or colonies. Eventually, some cells within such groups divided but remained connected to each other. This led to the formation of stable aggregates, where cells multiplied and grew as a single organism. Such multicellular organisms are called metazoans, and it is believed that the very first metazoans were the ancestors of all animals on Earth. They gave rise to the kingdom Animalia and marked the beginning of animal evolution.
How Cells Specialise
In the course of evolution, cells in some metazoans began to vary from each other in structure and function. This process is called cell specialisation and can be briefly described as follows.
Cells located on the outer side of metazoan organisms became more tightly connected to each other and were more resistant to the harmful effects of the environment, thereby protecting the inner-located cells. Over time, the outer cells gave rise to the epidermal cells, which form the outermost protective layer of the skin in complex animals.
