............... Molecules, cells tissues organs, systems and organ systems

Activities to do. Read the explanation of the human species, the levels of organization of matter and biomolecules, and perform the first exercise "Multiple Choice Test". Then read the explanations on the cell, tissues, organs, systems and organ systems and do the exercises the second "Multiple Choice Test" and the "Crossword".

1. The human species. The human being belongs to the group of mammals, that means it is a multicellular organism, with tissues heterotrophic nutrition (that is: feeding on organic material), with internal digestion, vertebrate and that suckle its young. It differs from other spaces by their high intelligence, which is proven by their ability to make objects and plan their future.

2. The human body. To facilitate the study five levels of organization of matter are differenced, which are:

  • Subatomic level. Includes subatomic particles. For example protons and electrons.
  • Atomic level. Includes atoms For example carbon atoms, hydrogen atoms, etc.
  • Molecular level. Includes molecules that are the union of two or more atoms. For example water molecules, glucose molecules, etc.
  • Cellular level. Includes cells. For example nerve cells, muscle cells, etc.
  • Multicellular level. Includes tissues, organs, systemsand systems of organs. For example connective tissue, kidney, nervous system, respiratory system, etc.


1 km = 1 000 m
1 m = 1 000 mm
1 mm = 1 000 micras
1 micra = 1 000 nm (nanometros)
1 nm = 10 angstroms
3. Types of molecules in the human body. These are called human biomolecules. They are classifies into:
  Water (H2O)
Inorganic Gases. The main ones are: CO2, O2 y N2
  Mineral salts. For example NaCl, CaCO3, Ca3(PO4)2, etc.
  Carbohydrates. Examples: glucose, starch, cellulose, etc.
  Organic Lipids. Examples: fats, cholesterol, etc.
    Proteins. Examples: albumin, collagen, etc.
  Nucleic acids. Are DNA and RNA

4. Inorganic biomolecules
Are those that are not mainly made of atoms C and H. For example:

  • water (H2O), which constitutes 63% of body weight
  • the gases involved in respiration, which are oxygen (O2) and carbon dioxide (CO2)
  • sodium chloride (NaCl) which is dissolved in the blood and within cells
  • calcium carbonate (CaCO3)
  • calcium phosphate - Ca3(PO4)2 - which constitute the bones,
  • etc.

5 . Organic biomolecules. Are those that are mainly made of C and H atoms. We distinguish the following types:

  • Carbohydrates. They are composed of carbon, hydrogen and oxygen in the proportion of CnH2nOn, which is why they are called carbohydrates. Examples are: the glucose which is dissolved in the blood and within cells and there is glycogen deposited in muscle cells which may degrade, leading to hundreds of glucoses.
  • Lipids. They are composed primarily of carbon and hydrogen and, typically, a very small amount of oxygen. They are insoluble in water and soluble in organic solvents, such as benzene C6H6. For example: fats and cholesterol.
  • Protein. They consist of tens or hundreds of amino acids (molecules having an acid group and amino group). For example, the albumin in the blood and the collagen present in bone.
  • Nucleic acids. Are constituted by C, H, O, N and P. For example the DNA is the carrier of genetic message.
Multiple Choice Test

6. Cells.
Human cells are eukaryotic cells, that is - cells with nuclei. Can be defined as living matter structures constituted by a membrane, cytoplasm and a nucleus that contains the genetic material or DNA. In the cytoplasm there are distinguished liquid or cytosol and some cell structures called organelles, such as mitochondria, endoplasmic reticulum, ribosomes, the Golgi apparatus, lysosomes etc.

The cells present nutritional function. Human cells present heterotrophic nutrition that means, it feeds organic material. The set of chemical reactions designed to obtain energy from food (called cellular metabolism) ends usually in cell breathing which is performed in mitochondria.

The cells also have connection function, since they can capture certain stimulants and issue dynamic responses, such as phagocytosis perform some types of white cells, and static responses, such as secretion of substances that make cells of the salivary glands.

The cells also have function of reproduction. Cell reproduction generates cells identical to the parent cell, implies a nucleus doubling called mitosis and cytoplasmic division in two, called cytodieresis.



7 . Tissues. Are sets of cells specialized to perform a particular activity, very similar to one another and which have the same embryological origin. The main tissues are:

  • Epithelial tissue (its function is to coat surfaces and segregate substances due to constituting glands),
  • Connective tissue (its function is to bind internal organs),
  • Cartilaginous tissue (its function is to form structures),
  • Adipose tissue (its function is to provide energy reserves),
  • Bone tissue (its function is to form skeletal structures),
  • Muscle tissues (its function is to make contractions and extensions),
  • Nervous tissue (its function is to capture and deliver stimulant responses) and
  • Blood (its function is to transport food, O2 and CO2).

Not all of living multicellular presents tissue. Some, such as algae and fungi, have no cells specialized in different functions, but all cells can perform all activities. It is said that these organisms have no tissue, that is, have no tissue structure, but have thallus structure.


8 . Organs. Structures that are composed of various tissues that together perform an act. For example the heart, which is the organ that pushes blood and which is constituted by muscle tissue, nervous tissue, connective tissue and blood.

9 . Systems. Sets of organs are formed by the same type of tissues, that can perform independent acts. We distinguish six different systems:

  • Nervous system
  • Muscular system
  • Skeletal system
  • Endocrine or hormonal system
  • Integumentary system (skin) and
  • Lymphatic system

10 . Systems of organs. Are sets of organs which may contain very different tissues, which act in coordination to realize of a function. For example, the digestive system presents such a different organs as teeth and intestine, which nevertheless, cooperate for digestive function. There are 5 different organ systems:

  • Circulatory System
  • Respiratory system
  • Digestive system
  • Urinal system and
  • Reproductive system
Muliple Choice Test
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