Unit 5: Living beings                                                         1   2   3   4   5

3. The cell

   Cells are the smallest units of life.

   They are the structural and functional units for all living beings.

         - 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.

   Most cells are very small. It is necessary a microscope to see them.

a) Structure of a cell:

   Every cell has three main parts:

         - The cell membrane covers the whole cell.

            It is a thin layer of lipids that controls the pass of substances

            in and out of the cell.

         - The cytoplasm is the inside of the cell.

                   - It is a jelly-like substance. Many of the chemical reactions

                     of the cell take place here.

                   - It contains the organelles. They are small structures

                     responsible for respiration, making and storing nutrients, etc.

         - The nucleus contains the DNA, the genetic material that forms

           the chromosomes. Its function is to control and to regulate

           how cell works. DNA contains the hereditary information

           that is passed from one cell to the daughter cell.

b) Types of cellular organisation:

c) Types of eukaryotic cells

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

Plant cells can be easily distinguished from the 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. Their 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 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.

Now, listen and relate each definition with the correspondant cell's part.

3.2. Indicate if the following sentences are referent to animal cells,  

        plant cells or both:

  a. They have mitochondria, the organelles which produce energy

  b. They have ribosomes, little organelles that make proteins

  c. They have a big vacuole that occupies the most part of the cytoplasm

  d. They have plasmatic membrane, that controls the pass of substances

  e. They have chloroplasts, which allow the photosynthesis

  f. They have cellular wall, a rigid structure located outside

  g. They have nucleus that contains the inheritance information

3.3. Answer these questions:

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

b. What organelles are exclusive of plant cells?