But bacteria recombine their genetic materials by three ways:-
1) Conjugation occurs when a bacterium passes DNA to a second bacterium through a tube (sex pilus) that temporarily joins two cells; this occurs only between bacteria in the same or closely related species.
2) Transformation involves bacteria taking up free pieces of DNA secreted by live bacteria or released by dead bacteria.
3) Transduction : - Bacteriophages transfer portions of bacterial DNA from one cell to another.
The bacteria are classified based on their source of energy, carbon and hydrogen/ electron source are of following type:-
Based on carbon source: - Autotrophs whose main carbon source is carbon dioxide and heterotrophs whose carbon source is reduced organic molecules.
Based on energy source: - Phototrophs: - the light is their energy source and chemotrophs who get their energy by oxidation of organic and inorganic compounds.
Based on hydrogen and electron source: - Lithotrophs: - the electron source is reduced inorganic molecule and organotrophs whose electron source is organic molecules.
The bacterial growth mainly involves increase in cell mass and cell division. Under favorable condition bacteria grow in geometric progression i.e. doubles at regular intervals. This growth is called exponential growth (Fig. 10). The bacterial growth can be divided into four phases as:-
Lag phase: - The population remains temporarily unchanged and no apparent cell division though cell may be growing in volume and mass.
Log phase: - Where the cells are dividing regularly by binary fission and growing by geometric progression. The cells divide at constant rate based on growth medium.
Stationary phase: - The population growth is limited due to nutrients exhaustion, accumulation of inhibitory metabolites or end products and limitation of biological spaces.
Death phase: - Due to limitation of nutrients bacteria die and no more cell divisions.
The generation time of bacteria and growth rate can be calculated from the growth curve by the equation: - G (generation time) = (time, in minutes or hours)/n (number of generations).
G = t/n where t = time interval in hours or minutes
B = number of bacteria at the beginning of a time interval.
b = number of bacteria at the end of the time interval. n = number of generations.
b = B x 2n (This equation is an expression of growth by binary fission).
Solving for n: logb = logB + nlog2.
where n= number of generations.
Algae
They are photosynthetic eukaryotes. They have different types of photosynthetic pigments i.e. chlorophyll such as blue, red, brown and green. They are mostly found in moist environment. They are microscopic and float in surface waters (phytoplankton) and live attached to rocky coasts (seaweeds). Size ranges from 0.5 um to over 50 m long Lack vascular tissues- no true roots, stems, or leaves. They mainly reproduced by both sexual and asexual modes of reproduction and have no multicellular reproductive organs. They are many different types of algae such as:
Red algae: Their size and complexity vary from thin films growing on rocks to complex filaments.Their accessory pigments called phycobilins mask the chlorophyll a and give them their red color. Due to these specialized pigments, red algae are often able to photosynthesize in deeper water than other algae. Red algae do not have flagella.They have many benefits such used as food and laboratory product i.e. agar used to grow bacteria and fungi is derived from red algae.
Green algae: They are found mostly in fresh waters and on land. Most species float in rivers, lakes, reservoirs, and creeks. They can also live on rocks, soil, and tree bark. Green algae are organisms with a variety of body forms including single cells, filaments, colonies, and thalli. They possess the same photosynthetic pigments (chlorophyll a and b) and some green algae have stiff cell walls composed of cellulose, as do plants.