The scientific methods

1. Observation – most biological investigations start with an observation. It could be a structure, process or a behavioral pattern.

2. Comparison – this method help pick up traits in separate organs.

3. Defining a problem a scientist’s natural reaction is to ask questions about it. What will happen? Why is it so? How does it take place?

4. Hypothesis.

5. Controlled experiment - which is necessary to use for investigation the reaction of an organism.

6. Theory. When a hypothesis is supported by evidence, it becomes a theory.

7. Historical method - this method give us data about structure of modern animals with compare as animals of past.

8. Method of statistical processing.

III. Levels of organization

Each level of organizations more complex and fewer units than the previous one molecular->cellular->tissue->organs->organ system->individual organisms -> population -> community ->ecosystem ->biomes ->biosphere.

The cell is a basic unit of structure and function in living organisms. Prerequisite of discovery the cell was invention the microscope and using them in study of biological object. In 1665 England physics Robert Hooke examined slice of cork under microscope and concluded that cork consist of many cells, reminding bee’s honeycomb.

In 1665 Robert Hooke examined slice of cork under microscope and used the term cell.

In 1831 England botanist Robert Brawn describe nucleus as a spherical body in plant cells.

In 1838 German botanist M.Schleiden (1804-1881) examined plant tissues and found all of them composed of cells.

In1838 German zoologist Teodor Schwann (1810-1882) examined animal tissues and found the cells covered by plasma membranes.

Schleiden and Schwann unified the idea and proposed Cell Theory.

In 1855 Virchow discovered that all cells arise from pre-existing cells by cell division.

Cell is basic structural unit of all organisms (plants and animals).

Cell theory of R.Virchov (1821-1902) - His work “Cellular pathology”. The main position of his

theory “omnis cellular cellula” means “every cell from cell”.

The basic features of modern cell theory are:

1. The elementary parts of all tissue are formed of cell.

2. All cells arise from pre-existing cells

3. All cells are basically alike in chemical composition and metabolic activities.

4. The function of an organism as a whole is the outcome of activities and interactions of the constituent cells.

5. Plant and animal cells are similar.

Prokaryotic cell – a cell in which the genetic material is not enclosed by a membrane to form a nucleus but lies free in the cytoplasm. The cell lacks all membrane bound organelles.

Eukaryotic cell – a cell which has a membrane bound nucleus. It also has number of membrane bound organelles.

Differences between Prokaryotic and Eukaryotic cells

Feature	Prokaryotic	Eukaryotic
1. Nuclear membrane	Absent	Present
2. DNA	Naked	Combined with proteins
3. Chromosomes	Single, circular DNA	Multiple
4. Nucleolus	Absent	Present
5. Division	Amitosis	Mitosis or meiosis
6. Cell wall	Non-cellulosic	Cellulosic (only plants)
7. Organelles	Non surrounded	Envelope bound organelles present
8. Cytoplasmic inclusions (Colgi apparatus, ER, vacuoles, lysosomes)	Absent	Present

Eukaryotic cells can be divided into two basic types – plant cells and animal cells.

Differences between Animal and Plant cells

	Animal cell	Plant cell
1	The cell is enclosed by a plasma membrane. The cell wall is absent.	The cell is enclosed by a cell wall present outside the plasma membrane.
2	Centriole is present	Centriole is absent
3	Absence of plastids	Plastids are present
4	Vacuoles are either small or absent altogether	A mature cell has a large central vacuole