All living cells have similar types of complex molecules involved in these basic activities of life. These molecules interact in a soup, about 2/3 water, surrounded by a membrane that controls what can go in and out. In more complex cells, some of the most common types of molecules are organized into structures that perform the same basic functions more efficiently. In particular, a cell nucleus contains DNA and a protein skeleton helps organize operations. In addition to the basic cellular functions common to all cells, most cells in multicellular organisms perform certain special functions that others do not. For example, glandular cells secrete hormones, muscle cells contract, and nerve cells conduct electrical signals. Part of the genetic information is dedicated to protein synthesis. mRNA, a type of RNA, is produced as a transcript that carries the code for protein synthesis. Read this tutorial for more details. People have long been curious about living things, how many different species there are, how they are, where they live, how they relate to each other and how they behave. Scientists are trying to answer these and many other questions about the organisms that inhabit the Earth. In particular, they try to develop concepts, principles and theories that allow people to better understand the living environment. It is in the nature of things that natural selection results in organisms with traits well suited to survival in certain environments.
But chance alone, especially in small populations, can lead to the spread of hereditary traits that have no inherent advantage or disadvantage or disadvantage in reproduction. As an environment changes (in this sense, other organisms are also part of the environment), the pros or cons of traits may change. Thus, natural selection does not necessarily lead to long-term progress in a particular direction. Evolution builds on what already exists, so the more diversity already exists, the more there can be. But the interaction of living organisms does not take place at a passive environmental level. Ecosystems are shaped by the inanimate environment of terrestrial and aquatic solar radiation, precipitation, mineral concentrations, temperature and topography. The world contains a wide variety of physical conditions that create a variety of environments: freshwater and ocean, forest, desert, grasslands, tundra, mountain and many others. In all these environments, organisms use the Earth`s vital resources, each seeking its share in specific ways that are limited by other organisms. In any part of the habitable environment, different organisms compete for food, space, light, heat, water, air, and shelter. The interconnected and fluctuating interactions of life forms and the environment form a global ecosystem; To fully understand a part, you need to know how that part interacts with others. The elements that make up the molecules of living beings are continuously recycled.
The most important of these elements are carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus, calcium, sodium, potassium and iron. These and other elements, found primarily in energy-rich molecules, are transmitted along the food web and ultimately recycled by mineral nutrient breakdowns that can be used by plants. While there can often be local excesses and deficits, the situation around Earth is that organisms die and break down at about the same rate as new life is synthesized. That is, the total living biomass remains roughly constant, there is a cyclical flow of materials from old to new life, and there is an irreversible flow of energy from sunlight captured in the dissipated heat. The interdependence of organisms in an ecosystem often leads to approximate stability over hundreds or thousands of years. When a species breeds, it is controlled by one or more environmental factors: depletion of food or nesting sites, increased loss of predators, or invasion by parasites. When a natural disaster such as a flood or fire occurs, the damaged ecosystem is likely to recover in a series of stages, eventually resulting in a system similar to the original one. As complex as the functioning of living organisms may be, they share with all other natural systems the same physical principles of conservation and transformation of matter and energy. Over long periods of time, matter and energy are transformed between living things and between them and the physical environment.
In these large cycles, the total amount of matter and energy remains constant, although their shape and location are constantly changing. All cells in an organism are descendants of the single fertilized egg and have the same DNA information. When successive generations of cells form by division, small differences in their immediate environment cause them to grow slightly differently by activating or inactivating different parts of the DNA information. Later generations of cells differ even more and eventually mature into cells as diverse as glandular, muscle and nerve cells. Genes are expressed through the process of protein synthesis. This in-depth tutorial provides a detailed overview of the different stages of biological protein production, from the gene to the secretion process. Also included are topics on DNA replication during cell cycle interphase, DNA mutation and repair mechanisms, gene pool, modification and disease. The modern concept of evolution provides a unifying principle for understanding the history of life on Earth, the relationships between all living things, and the dependence of life on the physical environment. While it is far from clear how evolution works in every detail, the concept is so well established that it provides a framework for bringing together most biological knowledge into a coherent picture. Living organisms are made up of the same components as all other matter, involve the same type of energy conversions, and move with the same basic forces.
Therefore, all the physical principles discussed in Chapter 4, The Physical Environment, apply to life as well as to stars, raindrops and televisions.