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Biodiversity

Biosphere – Set of Earth's ecosystems.
Ecosystems – System formed by the community and its physical-chemical environment, including all relationships between living beings and between these and the environment.
Community – Set of different populations, in interaction with each other, that occupy a given geographic area.
Population – Set of individuals of the same species that live in a given place and for a given period of time.
Individual – Living being of a given species, with characteristics similar to the other individuals in the population, capable of interbreeding with other individuals and producing fertile offspring.

In nature, a wolf is an individual and cannot live in isolation. It must establish relationships with other individuals of its species, for hunting and reproduction, for example, by forming part of a wolf population. This population interacts with populations of other species, for example when they fight over territory or feed on prey, such as rabbits or deer. All these populations interacting with each other form a community. The set of communities in a given geographical area, interacting with each other and with their physical and chemical environment, constitute an ecosystem. Finally, all of the planet's ecosystems form the biosphere.

In multicellular organisms , cells have developed specialized tasks and are grouped together in tissues. This is the case of cardiac muscle tissue, which is responsible for the contraction of the heart. Tissues, in turn, are organized into organs. The heart, formed by different tissues, is an organ. Different organs, which work in a coordinated manner towards the same objective, constitute an organ system. The heart is part of the circulatory system. Finally, different organ systems are organized into an organism. A mammal, such as a wolf, is an organism.

The cell is the basic unit of structure and functioning of a living being, that is, it corresponds to the simplest level of biological organization that we can call life. But the cell itself has other levels of organization – the organelles or cellular structures – such as mitochondria, which are formed by molecules, such as lipids and proteins, which are made up of atoms, such as carbon, oxygen and hydrogen.

Earth is a unique and extraordinary planet, being the common home of all species, where we still enjoy the best conditions of comfort, sustenance and protection for life. However, it was not always like this. The planet we know today is the result of a complex process of transformations that began about 4.6 billion years ago. With the advancement of science and technology, human intelligence has made our species the most dominant, capable of influencing natural processes, consuming large amounts of resources and, thus, shaping the future of the planet. Now, we have the responsibility to ensure the survival of all the species that share the Earth with us.

Earth is the only planet in the Solar System that has the ideal conditions for life as we know it. Some of the factors that make this possible include: the perfect distance from the Sun, the influence of the Moon and the giant planets, the presence of a magnetic field, the dynamism of the geosphere, the abundance of water, the diversity of natural environments and a protective atmosphere.
Distance from the Sun: Earth orbits within the habitable zone of the Solar System, at a distance that allows the presence of liquid water on its surface.

Some important events in Earth's history that created the conditions for the emergence of life over thousands of years include: the formation of the planet with impacts from other bodies in the Solar System; the creation of a solid crust, with continents and oceans; the development of an atmosphere with a greenhouse effect; the movement of tectonic plates and volcanic activity; atmospheric electrical phenomena; the formation of simple organic molecules and macromolecules; the emergence of the first primitive cells; the beginning of photosynthesis and the production of oxygen; the creation of the ozone layer and superglaciations that gave rise to new environments.

The Moon and the giant planets: The movement of the Moon around the Earth helps to stabilize the axis of rotation, maintaining a constant tilt, which is crucial for the cycle of the seasons . In addition, the gravitational force of the Moon is responsible for the occurrence of tides and ocean currents , which influence the Earth's climate . The gravity of the giant planets, especially Jupiter, attracts asteroids and comets that could collide with the Earth and cause extinctions .
Earth's magnetic field: This field acts as a protective shield, deflecting much of the harmful radiation emitted by the Sun.

Atmosphere: The atmosphere plays crucial roles in sustaining life, such as filtering harmful ultraviolet rays through the ozone layer , protecting against meteorite impacts , and regulating the environmental temperature compatible with life through the greenhouse effect . These characteristics help create suitable conditions for life.
The existence of the atmosphere is possible due to the size and mass of the Earth, which generate sufficient gravitational attraction to keep this layer of gases attached to its surface. Without this gravitational force, the atmosphere would disperse into space.

Geosphere dynamics: The movement of tectonic plates and the rock cycle are processes that shape landscapes, form soils and create new environments, driving the evolution and diversity of species.
Water: The abundance of liquid water is essential for life, as it makes up between 70% and 90% of the body weight of living beings and participates in all their vital processes.
Natural environments: The variety of habitats on Earth favors the capacity for adaptation and the growth of biodiversity, increasing the chances of survival and continuity of species.

The Earth was an uninhabitable place with no breathable air for hundreds of millions of years after its formation. Over time, however, it developed an atmosphere that was quite different from the one we know today. The primitive atmosphere was composed of methane, ammonia, hydrogen, nitrogen, carbon dioxide and water vapour, but there was no oxygen.
Oxygen only appeared in the atmosphere due to its release by living beings, namely through photosynthesis. The first photosynthetic beings were not plants or algae, as they did not yet exist. The first living beings to carry out photosynthesis and release oxygen into the atmosphere were microorganisms similar to today's bacteria that began to appear in the primitive oceans, more than 3,000 million years ago.

The oxygen generated by these living beings slowly accumulated in the atmosphere, which changed its composition and created, around 400 million years ago, the conditions necessary for the formation of an ozone layer. This layer is capable of filtering ultraviolet radiation, thus allowing living beings to colonize terrestrial environments outside of water.
The enrichment of the atmosphere with oxygen, produced in photosynthesis, allowed this gas to become available and be used by living beings in cellular respiration, which in turn releases the carbon dioxide consumed in photosynthesis into the atmosphere.
The Earth's atmosphere has undergone continuous changes in its composition over geological time, responsible for drastic climate changes and mass extinctions. Currently, it is human activities that produce a growing and global impact on the atmosphere with consequences that are still difficult to predict.

One of the most worrying effects of human activities is the carbon emissions into the atmosphere, with the consequent increase in the greenhouse effect. The solar radiation that reaches the Earth is mostly absorbed by its surface, heating it. This heated surface radiates heat into the atmosphere, which retains part of this heat, with the rest being lost to space. Without an atmosphere, this heat would be completely lost, and the planet would be very cold, with an average temperature of -18°C. Such low temperatures are not suitable for life as we know it.
Gases present in the atmosphere, such as carbon dioxide, methane and water vapor, help to retain part of the heat emitted by the Earth's surface, preventing it from being lost to space. This natural process keeps the atmosphere warm, making the planet's surface a suitable place for life, with an average temperature of 15°C. This phenomenon is known as the greenhouse effect.

Heat exchanges between Earth and space show how the planet functions as a large system. These exchanges mainly involve energy, since exchanges of matter are minimal, making the Earth a closed system.
However, the Earth system is composed of several smaller subsystems that constantly interact, exchanging matter and energy, characterizing themselves as open systems. Thus, any disturbance in one subsystem can impact the functioning of the others. The main subsystems are the atmosphere, the hydrosphere, the geosphere and the biosphere.

Atmosphere subsystem: refers to the mixture of gases that surrounds the Earth. The atmosphere ensures a comfortable temperature for life, protects living beings from harmful solar radiation, mitigates the impacts of meteorites and contains gases vital for living beings such as carbon dioxide, used in photosynthesis, and the oxygen necessary for cellular respiration.
Hydrosphere subsystem: It is formed by the planet's water reservoirs, which are found on or near its surface. Including seas and oceans, rivers, lakes, glaciers, groundwater and clouds (formed by water or ice particles suspended in the atmosphere). In addition to being the main constituent of living beings, water is the habitat of many forms of life.

Geosphere subsystem: This includes the Earth's crust, including the seabed and continental masses, as well as all the materials found in the interior of the planet. It is the support on which living beings can settle or develop their activity. It provides mineral salts necessary for the production of organic matter and for the proper functioning of organisms.
Biosphere subsystem: This corresponds to all living beings on the planet. This enormous biodiversity establishes various relationships between itself and exploits the opportunities for food, shelter or reproduction offered by physical means as diverse as water, land and air.

Rocks and soil , in interaction with all subsystems, play an essential role in the existence of life on Earth. Rock fragments removed by erosion can be transported and enriched with organic matter, giving rise to soil. The constituents of soil are:
• mineral matter: made up of small rock fragments and mineral salts (46%);
• organic matter: in the form of humus, remains of leaves, branches, trunks and remains of decomposing animals (4%);
• water (25%) and air (25%): which occupy the spaces between soil particles.
Soil is a substrate for the fixation and growth of plants, which extract water and mineral salts from it. It is also responsible for the recycling of organic waste and the storage of nutrients. Soil filters and controls the flow of water that feeds underground reservoirs. Finally, soil is the habitat of numerous living beings.

In nature, it is possible to distinguish two basic types of cells:
Prokaryotic cells: This is the simplest cell, as its genetic material is not organized inside a nucleus and it does not have most of the organelles or cellular structures of more complex cells. Bacteria are prokaryotic cells.
Eukaryotic cells: This is the most complex cell, with an organized nucleus that contains the genetic material inside. It also has a variety of organelles in the cytoplasm, such as mitochondria, which do not exist in prokaryotic cells. All living beings, with the exception of bacteria, have this type of cell. This is the case of plants, which are made up of eukaryotic plant cells, and animals, which are made up of eukaryotic animal cells.

In a cell , a set of structures common to all cells can be identified: a cell membrane , which delimits its contents and functions as a surface for exchanges with the external environment; a cytoplasm , with organelles that perform specific functions in cellular work; and genetic material , which coordinates and controls its activity.

Living beings share and cohabit the Earth, the planet that is the birthplace of all biodiversity according to current knowledge. However, sharing the same planet is not the only common feature among living beings, since they are all made up of cells, the simplest unit capable of giving shape and making a living being function, that is, the cell is the basic, morphological and functional unit of life.
Since the beginning of life on Earth, the cell has evolved towards increasing complexity.
With rare exceptions, cells are not visible to the naked eye, so it is necessary to use magnifying instruments, such as microscopes, to be able to observe them.

• Cellular constituent: Chloroplasts – Organelles that ensure the production of organic matter through photosynthesis;
Prokaryotic cell: Absent
Plant eukaryotic cells: Present
Animal eukaryotic cells: Absent
• Cellular constituent: Plasma membrane – Maintains cell integrity and regulates the exchange of substances between the intra and extracellular environments.
Prokaryotic cell: Present
Plant/animal eukaryotic cells: Present
• Cellular constituent: Cell wall – Rigid structure that surrounds the cells, giving them shape and protection.
Prokaryotic cell: Present
Plant eukaryotic cells: Present
Animal eukaryotic cells: Absent

Living beings have emerged and evolved on Earth over geological time. Initially in the form of prokaryotic cells, they evolved into eukaryotic cells, both types remaining unicellular for a long time. Later, some eukaryotic cells grouped together into colonies, some of which evolved into multicellular beings.

• Cellular constituent: Genetic material – Controls cellular activities;
Prokaryotic cell: Condensed in the cytoplasm;
Eukaryotic plant/animal cells: Organized in the nucleus.
• Cellular constituent: Cytoplasm – Semi-fluid space, with dispersed organelles, where chemical reactions occur;
Prokaryotic cell: With some structures;
Eukaryotic plant/animal cells: With numerous organelles.
• Cellular constituent: Mitochondria – Organelles that ensure the obtaining of energy through cellular respiration;
Prokaryotic cell: Absent
Eukaryotic plant/animal cells: Present

Unicellular being – A living being consists of a single cell, which can be prokaryotic or eukaryotic. Bacteria are examples of prokaryotic unicellular beings, that is, they are prokaryotic cells. Paramecia, amoebae and yeast are examples of eukaryotic unicellular beings, that is, they are eukaryotic cells.
Multicellular being – A living being is made up of more than one cell, generally presenting a diversity of cells with specific functions. All multicellular living beings are eukaryotes, that is, all their cells are eukaryotic. Green, brown or red algae, mushrooms, plants and animals are examples of multicellular beings.