Cells: The Fundamental Units of Life
Living things are composed of minimal units called cells. All basic chemical and physiological functions—for example, repair, growth, movement, immunity, communication, and digestion—are carried out inside the cell. Depending on the number of cells that form them, living beings can be classified into unicellular and multicellular.
Unicellular Organisms
Unicellular organisms are those formed by a single cell. In this group, the most representative are protozoa, which can only be seen under a microscope.
Multicellular Organisms
Multicellular organisms have a particular organization:
- Cell: The smallest unit that is part of a living being.
- Tissue: A set of cells that have similar features and functions with the same origin.
- In plants, organs include the root, seed, leaves, and flowers.
- Systems: Result from the union of several organs, which function in a coordinated manner to play a certain role. For example: we speak of the digestive system, renal system, circulatory system, nervous system, reproductive system, and so on.
- Organism: A living being composed of a set of systems that works in harmony. Some living things have no structured organs or systems but have a simple organization that allows for good development. If an organ is damaged or altered, it causes a disruption of the living being.
Three Basic Parts of Every Cell
- The plasma membrane
- Cytoplasm
- The nucleus
The Cell Membrane
The cell membrane surrounds the entire cell and maintains its integrity. It is a semipermeable, or selectively permeable, membrane; this indicates that only some substances (molecules) pass through it. It has the ability to change, forming pores and channels in the process.
Functions:
- Regulates the passage of substances into and out of the cell.
- Allows the passage of certain substances and prevents the passage of others.
- Isolates and protects the cell from the external environment.
The Cytoplasm
A cellular structure located between the cell membrane and the nucleus. It consists of water, and other substances—such as proteins, enzymes, fluids, carbohydrates, and minerals—are dissolved in it.
- It incorporates a number of substances, which will be transformed or broken down to release energy.
- Substances are stored in reserve.
- It is the support that shapes the cell and is the basis of its movements.
Cell Organelles
They are small intracellular structures, separated by one or two membranes. Each performs a certain function, allowing for cell life. They have their own genetic material called mitochondrial DNA.
To that end, the energy is contained in certain molecules. For example, glucose.
This diffuses into the cytoplasm to be occupied in the various reactions in which energy is required. This reaction can store energy.
Chloroplasts
Organelles are found only in cells that are forming plants and green algae. They are larger than mitochondria and are surrounded by two membranes, one external and one internal.
For this to be done, it requires CO2, water, and solar energy, substances with which the plant produces glucose. In this way, oxygen also passes into the atmosphere.
Protein synthesis takes place on ribosomes, which aims to build the cell body, regulate certain metabolic activities, and so on.
They consist of very thin membranes and connect the cell nucleus with the external environment.