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Living things differ from raw matter in that they are made up of cells. Viruses are beings that do not have cells, but are capable of reproducing and undergoing changes in their genetic material. This is one of the reasons why they are still debating whether or not they are living beings.
The cell is the smallest part of living beings with definite form and function.. For this reason, we affirm that the cell is the structural unit of living beings. The cell - alone or together with other cells - forms the entire living being or part of it. In addition, it has all the "material" needed to perform the functions of a living being, such as nutrition, energy production and reproduction.
Each cell in our body has a specific function.. But all perform a "community" activity, working in an integrated manner with the other cells of the body. It is as if our organism were a huge society of cells, which cooperate with each other, dividing work among themselves. Together they guarantee the execution of the numerous tasks responsible for maintaining life.
The cells that make up the body of most living things have a membrane surrounding their nucleus, so they are called eukaryotic cells. The eukaryotic cell consists of cell membrane, cytoplasm and nucleus.
In these figures you can compare a human (animal) cell with a plant cell. The plant cell has a cell wall and may contain chloroplasts, two structures that the animal cell does not have. On the other hand, the plant cell has no centrioles and generally no lysosomes, two structures in an animal cell.
The plasma membrane
The plasma membrane is a very thin, delicate and elastic film that surrounds the contents of the cell. More than just a wrap, this membrane plays a major role in cell life, regulating the passage and exchange of substances between the cell and its environment.
Many substances passively enter and leave cells. This means that such substances move freely without the cell having to expend energy. This is the case of oxygen gas and carbon dioxide, for example.
Other substances enter and leave cells actively. In this case, the cell uses energy to promote their transport across the plasma membrane. In this transport there is participation of special substances, called carrier enzymes. Our nerve cells, for example, absorb potassium ions and eliminate sodium ions by active transport.
Observe the plasma membrane. It is made up of two lipid layers and proteins of different shapes between the two lipid layers.
Thus we say that the plasma membrane has selective permeability, that is, the ability to select substances that enter or leave according to the needs of the cell.Continues after advertising
Cytoplasm is usually the largest option of the cell. It comprises the material present in the region between the plasma membrane and the nucleus.
It is made up of a semi-fluid, gelatinous material called hyaloplasma. In hyaloplasma, cell organelles are immersed, structures that perform various vital functions, such as digestion, respiration, excretion and circulation. The most abundant substance in hyaloplasma is water.
Let us then study some of the most important organelles found in our cells: mitochondria, ribosomes, endoplasmic reticulum, Golgi complex, lysosomes, and centrioles.
Mitochondria and energy production. Mitochondria are membrane-bound organelles (membrane-wrapped) that are rod-shaped. They are responsible for cellular respiration, a phenomenon that allows the cell to obtain the chemical energy contained in the absorbed foods. The energy thus obtained can then be used to perform various cellular activities.
One of the most common "fuels" that cells use in cell respiration is glucose sugar. After the "burning" of glucose, with the participation of oxygen gas, the cell gets energy and produces waste, represented by carbon dioxide and water. Carbon dioxide passes into the blood and is excreted outside.
The equation below summarizes the process of cellular respiration:
glucose + oxygen gas ---> carbon dioxide + water + energy
Ribosomes and protein production
Cells produce various substances needed by the body. These include proteins. Ribosomes are non-membranous organelles responsible for the production (synthesis) of proteins in cells. They appear both isolated in the cytoplasm and adhered to the endoplasmic reticulum.
Endoplasmic reticulum and substance distribution
This organelle consists of a system of channels and flat pockets. It has several functions, including facilitating the transport and distribution of substances within the cell.
The membranes of the endoplasmic reticulum may or may not contain ribosomes attached to their outer surface. The presence of ribosomes gives the endoplasmic reticulum membrane a granular appearance; In the absence of ribosomes, the membrane exhibits a smooth or non-granular appearance.