Levels of organization 
All living things have a structural and functional organization. Going from the list complex to the most complex: 
Atom: The smallest component of the chemical elements that make up living thing(bioelements) primarily carbon(C), oxygen(O), hydrogen(H), nitrogen(N), phosphorus(P), sulfur(S), calcium(Ca), magnesium(Mg)and sodium(Na). 
Molecule: A group of two or more atoms joined together chemically. The molecules that make up living things are called biomolecules. 
Organelle: A group of biomolecular that work together to form cell structures. 
Cell: A group of organelles and structures. A cell is the simplest level of life. 
Tissue: A group of specialized cells that work together to perform a specific function. 
Organ: Group of different tissues that work together to carry out a specific function. 
Organ system: A group of similar or different organs that work together to carry out life functions. 
Organism: An independent living thing made up of organs systems that can carry all live functions. 
The chemical composition of living things 
Bioelements join together to form biomolecules. This can be classified into two types: Organic(there are found in living and non-living things:water- the most abundant substance found in living things. Mineral salts-substances that can be found in living things in the form of dissolved ions). Inorganic(they are only for the living things and contain significant amount of the chemical element carbon).

Prokaryote - Simple English Wikipedia, the free encyclopedia

All living things from the simple to the most complex are made up of cells. The cell is the simple living unit that can carry out the life functions of nutrition, interaction and reproduction. It is the basic unit of all living things: 
It is the structural JUnit because it forms all the structures. 
It is the functional unit because it carries out life functions internally. 
It is the biological ionic because it contains the genetic material of the individual. 
It is the basic unit because all cells come from a pre-existing through the process of cell division. 
Living things can be made of one cell or many cells: 
Unicelular organisms: Microscopic living things are made up of one cell. 
Multicellular organisms: Generally macroscopic living things are made up of many cells. Organization is complex. 
Cells perform three life functions: Cellular nutrition consist of the processes in which cells obtain the matter and energy necessary to perform live functions. To do this cells take substances colled nutrients, from the outside. Nutrients are used for energy and to obtain the substance necesario foreground and building or repair structures. Once inside the cell nutrients undergoes a series of chemical processes. These chemical processes are called celular catabolism and anabolism. Cell interaction enables to get information from their environment and communicate with other cells. Celular reproduction is the process by whitch parent shell device in tumors new cells called daughter cells. In unicellular organisms, cell división reproduces an entire organism. The new individual is identical to the parent. As a result, there is an increase in population. In multicellular organisms, cell division results in an increase in the number of cells that make up an organism. This increase is reflected in the growth of the organism or the repair of damaged or lost parts. 

Prokaryotic Cell 
Procaryotic cells have a simple structure and are generally much smaller than eukaryotic cells. They haven’t got nucleus(genetic material is dispersed in the cytoplasm). Ribosome are the only organelles. The cell membrane is usually covered by a cell wall. 
Eukaryotic Cell 
Eukaryotic cells are more complex and generally larger than prokaryotic cells. Eukaryotic cells are found in human beings animals and plants. Hola eukaryotic cells have three structures: 
Cell membrane(this membrane surrounds the cell and enables the change of substance is with outside environment. The membrane consists of two layers of phospholipids, with cholesterol and diverse protein molecules distributed throughout. This type of membrane is called a fluid Mosaic structure because the elements move and change position), Citoplasm (this substance fills the space between the cell membrane and the nucleus. The citoplasm contains hyaloplasm,organelles and cytoeskeleton)and Nucleus (this spherical structure contains the genetic material that control celular function). 
Cell organelles and structures 
Mitocondria: Oval shaped organs with two membrane. Through cellular respiration, mitocondria produce most of the energy of a cell. Vesicles: Small, rounded organelles that store, transport or digest celular substances. Lysosomes: Rounded vesicles produced by the Golgi body. Endoplasmatic reticulum: Network of interconnected membranous sacs and channels. There are two types(Rough ER, this type is connected with the nuclear envelope. Smooth ER, this type has not attached ribosomes. Lipids are synthesized hear). Golgi body: This organelle stores processes and packages  substances received from the endoplasmatic reticulum. Then secretory vesicles transport the substances out of the cell. Ribosomes: Non-membranous organelles made up of RNA and proteins. Centrosome: This organelle consist of your centrioles. Centrosomes participated in mitotic spindle formation when a Cell devides. Cilia and flagella: Cilia are short and abundant. Flagella usually only one or two are present. This cytoplasmatic projections are involved in cell movement. Cytoskeleton: Of different types of protein filaments. It mantains the shape of the cell and facilitate the movement of the cell, organelles and internal vecicles. 

Human tissue 
A tissue is a group of specialised cells that work together to perform a specific function. Tissue can be grouped into four types: Epithelial, connective, muscle and nervous. 
Epithelial: There are two main groups: Covering epithelia(this tissue covers internal and external body surfaces and regulates the exchange of substances.)and glanduar epithelia(this tissue makes up the glands:exocrine,endocrine,mixed). 
Connective tissue: This tissue connect other tissues. It have three components: cells,fibres and intercellular substance or matrix. There are several types: Bone tissue(the cells responsible for the bone formation), adipose tissue(They store lipids and protect some organs)cartilage tissue(its cells,chondrocytes, contain elastic fibres and produce a solid, flexible matrix) dense connective tissue(it is found between tissues and organs holding them together) and bloood tissue(this special tissue is made up of red and white blood cells. This this tissue transport sustances). 
Muscle tissue: This contractile tissue has elongated cells called myocytess or muscle fibres. It contains protein filaments of actin and myosin. There are three types of muscle tissue: Smooth muscle tissue, skeletal muscle tissue, cardiac muscle tissue. 
Nervous tissue. Nervous tissue cells transmitan recibe information throughout the body. There are two types of cells. Neurons(they transmit never impulses) and glial cells(nourish and support the neurons).

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