Humans as multicellular organism

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The three functions of the organism: interaction, nutrition and reproduction.

Nutrition: is the process by which cell and organism get energy from food.

Interaction: is the ability of an organism to detect and react to external or internal stimuli.

Reproduction: is the biological process to produced a new individual organism from their parents.


-The cell is a functional unit of all organisms, the smallest living part of the body and the building bloq of life.

Some organisms such as bacteria are unicellular. The consist of a single cell.
Some other organisms such as humans are multicellular.

The largest cells are ostrich eggs.

There are two types of cells:

-Eucaryotic cells
-Procaryotic cells

Prokaryotic cells lack a nucleus and other organelles of eukaryotic cells
Eukaryotic cells have nucleus, are larger and the main difference: contain membrane.

Bound compartments of the cell (Dibujo):

-Endoplasmic reticulum: has two form: rough endoplasmic reticulum (it has ribosomes on its surface and produces proteins) and the smooth endoplasmic reticulum (lacks ribosomes)

-Cell nucleus (the most important): to control the cell. It contains the DNA (chromosomes, chromatine). The nucleolus is the place of the nucleus where the ribosomes subunits are assembled.

-Plasma membrane: the cell membrane envelopes the cell and separates its interior of the enviroment.

-Ribosomes: are complexes made of RNA and proteins. They syntesise proteins.

-Mitochondrion: to make respiration. Generates energy

-Vacuoles: separate the wrong things
-Cytoplasm: is inside the cell and contain all organelles.

-Golgi body: processes and packages the molecules that are produced by the cell

-Centriole: produces the microtubules of a cell and participates in cell division

-Lysosomes: contain digestive enzymes.

All cells carry out three kinds of function: nutrition, interaction and reproduction.

Cell nutrition

Is the function by which cells interchange substances and energy with their environment.
Cell have to carry out a lot of chemical reactions to maintain their proper function. All these reactions need energy.

Since the beginning of evolution cells have developed highly efficient metabolic systems. The aim of metabolic systems is to produce energy in the form of ATP molecules.
Cell metabolism is the set of chemical reactions by which cells transform molecules.
Metabolism has two categories: anabolism and catabolism
Through catabolism the cell breaks down molecules to produce energy.
Through anabolism the cell uses energy to build complex molecules and to carry out biological functions.
Cellular respiration is a catabolic process. Its the process by which energy of nutrients is released in the form of ATP.
Carbohydrates, fats and proteins can be used as fuel in cellular respiration.
Cell respiration takes place in the mitochondria.

Cell interaction

Cells receive stimuli from their environment and react to them.
The interaction function refers to the capacity of the cell to receive stimuli and respond to them. This cell is called cell sensitivity.
Cells can respond in two different ways: static response and dynamic response.

Cell reproduction

Through reproduction a type of cell can increase its number of cells (population)
In addition, sexual reproduction can help to introduce genetic variation into a specie which can be beneficial in the future.
Cell reproduction or cell division consist of a single cell dividing into two daughter cells.

Cells can reproduce in two ways: Mitosis and meiosis.

In mitosis the daughters cells are identical clones of the original cell

In meiosis cells have two sets of chromosomes (diploid cells) form haploid cells that have half the chromosomes. Is a special type of cell division necessary for sexual reproduction

46 chromosomes (diploid cells)
(23 pairs) [2n]
23 (haploid cells)

through cellular differentation                                                                                                     nervous cells

                                                                                                                                                      blood cells

One embryo


Two embryo




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