Unit 1: The basis of life                                              1   2   3   4   5   6

3. Cells

Cells are the smallest unit of life. They are the structural and functional units for all living beings.

That means that:

         - All living things are made up of one or more cells.

         - Cells carry out the functions of nutrition, interaction and reproduction.

         - All cells come from other cells.

a) Structure of a cell:

   Every cell has three main parts:

   - Cell membrane.

       It covers the whole cell. It is a thin layer of lipids that controls the substance

       exchange between the inside and the outside of the cell.

   - Cytoplasm.

       It is the inside of the cell. It is a jelly-like substance composed by water and

       dissolved substances.

       Many of the chemical reactions of the cell take place here.

       It contains the organelles. These small structures are responsible for different 

       functions:

   - Genetic material (DNA).

   It forms the chromosomes. Its function is to control and to regulate how cell works.

   DNA also contains the hereditary information.

b) Types of cellular organization:

There are two kinds of cellular organization: Prokaryote and Eukaryote.

  - Eukaryotic cells

  They are complex and bigger than prokaryotic cells.

  Their genetic material is separated from the cytoplasm inside the nucleus.

  They have many types of organelles that makedifferent metabolic functions.

  They form unicellular and multicellular organisms.

  They are the cells of all the other living beings (fungi, protoctists, animals

  and plants)

c) Types of eukaryotic cells

    There are two types of eukaryotic cells: animal cells and plant cells.

    Plant cells can be easily distinguished from animal cells because they have some

    exclusive organelles:

          - They have cell wall, surrounding the cell membrane.

             It gives the cell a polyhedral shape.

             Its function is protecting the cell and being a skeleton structure.

- They have chloroplasts, which function is to make photosynthesis.

- They have a big vacuole that takes up the biggest part of the cytoplasm.

   (Animal cells have vacuoles too, but they are smaller and numerous)

   Its function is accumulating water and useless substances.

     The plant cells are in algae and plants and the animal cells are in animals

     and protozoa.

3.1. Identify every one of the following cells and name the indicated

        structures:

3.2. Identify the following cell organelles. Indicate in each case, its function.

3.3. Answer these questions:

       a. Is there any multicellular organism made up of prokaryotic cells?

       b.What organelles are exclusive of plant cells?