Unicellular Organisms Objective 1.2 Identify unicellular organisms, including bacteria and...

Unicellular Organisms

Objective 1.2 Identify unicellular organisms, including bacteria and protista, by their methods of locomotion, reproduction, ingestion, excretion, and effects on other organisms.

There are two types of microorganisms: Eukaryotic and prokaryotic. Let’s look at each one.

Eukaryotic

any organism that contains specialized organelles in the cytoplasm, a membrane-bound nucleus enclosing genetic material organized into chromosomes, and an elaborate system of division by mitosis or meiosis, characteristic of all life forms except bacteria, blue-green algae, and other primitive microorganisms.

Prokaryotic

any cellular organism that has no nuclear membrane, no organelles in the cytoplasm except ribosomes, and has its genetic material in the form of single continuous strands forming coils or loops, characteristic of all organisms in the kingdom Monera, as the bacteria and blue-green algae.

Right: Colorized micrograph of a prokaryotic cell of the bacterium. Left: Colorized micrograph of a eukaryotic cell of the green algae.

Eukaryotes

Protists

Protists are an extremely diverse assortment of eukaryotes.

Protists

Protists are more diverse than all other eukaryotes.No longer classified in a single kingdom.

ParaphyleticMost protists are unicellular, some are

colonial or multicellular.

Protista/protist

A unicellular, eukaroytic organism belonging to the former taxonomic kingdom Protista. They produce their own food.

Nutrition in Protists

Microorganisms such as prokaryotic bacteria and eukaryotic protists need food to survive. Some are producers that make their own food while others are consumers which must take in food (ingestion) from an external source.

Microorganism

any organism too small to be viewed by the unaided eye, as bacteria, protozoa, and some fungi and algae, that typically consists of only a single cell.

Ingestion

To take in and absorb as food

Many bacteria are decomposers that break down dead organisms and wastes. All organisms must get rid of wastes through the process of excretion.

Let’s look each type of way a organism consumes food and get rids of waste.

consumer

an organism, usually an animal, that feeds on plants or other animals

producer

an organism, as a plant, that is able to produce its own food from inorganic substances.

Decomposer

An organism, often a bacterium or fungus, that feeds on and breaks down dead plant or animal matter, thus making organic nutrients available to the ecosystem.

Excretion

The act or process of discharging waste matter from the cell.

Reproduction and Life Cycles

Reproduction is essential to the continuation of every species. Some organisms reproduce asexually by binary fission. Other organisms reproduce sexually by conjugation. Some prokaryotic organisms produce endospores when conditions are unfavorable for development.

Binary fission

A method of asexual reproduction that involves the splitting of a parent cell into two approximately equal parts.

Conjugation

A process of sexual reproduction in which ciliate protozoans of the same species temporarily couple and exchange genetic material.

Endospores

A small asexual spore, as that formed by some bacteria.

Locomotion

Unicellular organisms have various modes of locomotion, or movement.

Protists have three main methods of locomotion.

Let’s look at each type of locomotion.

Locomotion

The act of moving from place to place: self-propelled movement 

Locomotion in Protists

Some protists, like this Euglena, have one or two long flagella that they can whip around an propel themselves through the water.

Flagella

a long, lash like appendage serving as an organ of locomotion in protozoa, sperm cells, etc.

Locomotion in Protists

Some, like this Tetrahymena, are covered with numerous, but shorter, cilia that facilitate movement and/or feeding.

Cilia

A microscopic hairlike process extending from the surface of a cell or unicellular organism. Capable of rhythmical motion, it acts in unison with other such structures to bring about the movement of the cell or of the surrounding medium.

Locomotion in Protists

Others use ameboid movement to get around. A pseudopod is

extended forward, followed by the rest of the organism.

Pseudopod

A temporary footlike extension of a one-celled organism, such as an amoeba, used for moving about and for surrounding and taking in food.