Biología, cells

CELL: the building blocks of the living organisms.
Structure cell: 
– Plasma membrane. (Lipids, proteins and carbohydrates). Is a very thin and stretchy cover that separates a cell from its environment.
– Cytoplasm. Is the substance contained inside the cells and in which the cell organelles are found. 
– Genetic material. Complex chemical substance that contains information (genetic information) to regulate cells function. 
There are two types of cells, depending on where DNA is located: prokaryotic cells and eukaryotic cells.
Prokaryotic cells: 
• Kingdom: Monera (bacteria).
• Unicellular. Size 1-10 mm (tiny).
• DNA in the cytoplasm called (nucleoid).
• Small DNA fragments (plasmids).
• Cytoplasm contains ribosomes.
• Plasma membrane folds in mesosomes: allow more metabolic activity.
• They have cell wall: outer rigid cover, gives shape to the bacteria.
• Have protrusions: used for locomotion.
• Have fimbriae: used to attach themselves to the substratum.
• Tail: flagellum.
• No chloroplast.
• No nucleus.
Eukaryotic cells: 
• Kingdoms: Protoctista, Fungi, Plantae, Animalia.
• Unicellular or multicellular. Size 10-100 mm.
• Chloroplast.
• Nucleus: DNA surrounded by membrane.
• They have cell wall.
• Cytoskeleton: give cell shape and enable it to move.

– Plant cell. Have a cell wall, nucleus and chloroplasts. Its function is photosynthesis.
– Animal cell. Don’t have cell wall, nucleus and chloroplasts.


A cell is not in a stage of division: interphase (nucleus in the middle).

– Nuclear membrane: 2 membranes covered in ribosomes (create proteins). Has perforations (nuclear pores).

– Nucleoplasm: is liquid in the nucleus.

– Nucleolus: where components of ribosomes are created.

– Chromatin: DNA filaments and proteins. In cell division, condenses and forms chromosomes.


It contains hereditary information, and it controls cell activity.


Nutrition provides matter and energy to grow, replace their structures, divide, interact.

Process of nutrition:

• Entry of substances (nutrients).

• Transformation of substances (metabolism).

• The excretion, or expulsion into the extracellular environment.

Entry of substances: plasma membrane is a selective barrier.

– Small molecules: pass freely through diffusion along the concentration gradient high to low.

– Medium-sized: ions pass with help of proteins.

Proteins form:

– Channels: proteins that open up to form a channel along the concentration gradient.

– Pumps: against the gradient, need energy to pump through the membrane.

– Large molecules: cannot pass through the membrane, in such cases:

– Endocytosis: the membrane engulfs the particle in a vesicle in the cytoplasm.

– Vesicle fuses with lysosomes that contains substances that digest c tents of the vesicle, the form small ones.

– Exocytosis: the residue of digestion is expelled.

There are two types of cellular metabolism: catabolism and anabolism.
• Enter to the cell and they are broken down and transformed (more simple ones).
• Release energy.
• Part of the energy formed in catabolism is lost in the form of heat.
• Cellular respiration for example.
• Create complex molecules.
• The formation of these requires a supply of energy.
• Some cells can use light energy (sun) via photosynthesis as well as the energy from catabolism.
Enzymes and metabolism:
• Control chemical reactions in cells.
• Increase the speed of these.


Heterotrophic nutrition:

• Incorporate organic matter made up by other organisms.

• Animals, fungi, protoctists.

Autotrophic nutrition:

• Create heir own food, organic matter from inorganic matter.

• The process takes place in chloroplasts.

• Plants, algee.


Cellular interaction:
Capture changes and respond to them correctly.
Stimuli is a response, it can be: 
– Chemical: changes of the composition of the environment, pH…
– Physical: changes in the temperature, pressure…
Cellular response is the reaction of the cell to stimuli. There are two types:
Static response: no movement produced.
Dynamic response: cell responds by moving.
Parent cells divide in two or more identical cells called daughter cells.
Unicellular organisms: 
The object of cell division is reproduction.
Multicellular organisms: 
Cell division enables the organism to increase size and to replace the cells in the body that die off.
Higher quality microscopes in 19th century, allows to describe cell structure and identify the cell as a basic unit.
Three German scientists (the biologist Matthias Schleiden, the zoologist Theodor Schwann and the doctor Rudolf Virchow) who summarised the ideas in “cell theory”. The three main principles of theory are:
– Cells are the structural units of living things (living things are made up of one or more cells).
– Cells are the functional units of living things (cell is the smallest part that carries out the vital functions)
– Cells are the origin of all living things (cells come from other cells)
Development of the optical and electron microscope (magnifies the image 500 000 to a million times.