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A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and eukaryotic organisms.
Because the concentration of salt inside the cell and in the surrounding freshwater is different, Stentor must store water that enters it by osmosis and then discharge it from the vacuole. They can regenerate, and small fragments can grow into full organisms. Each cell has one (often elongated) macronucleus and several micronuclei.
The nucleus occupies an apical-to-central position in the cell, and food vacuoles are positioned in the basal region of the cytoplasm. [13] [14] Additionally, the cell body of many choanoflagellates is surrounded by a distinguishing extracellular matrix or periplast. These cell coverings vary greatly in structure and composition and are used by ...
A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word flagellate also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and their means of motion. The term presently does not imply any specific relationship or classification of the ...
Originally, the group included not only single-celled microorganisms but also some "lower" multicellular animals, such as rotifers, corals, sponges, jellyfish, bryozoans and polychaete worms. [12] The term Protozoa is formed from the Greek words πρῶτος (prôtos), meaning "first", and ζῷα (zôia), plural of ζῷον (zôion), meaning ...
It is a colourless species, with no pigmentation in the cell cortex. The body of the organism is covered with 40-80 longitudinal rows of cilia, and the oral region is encircled by a long spiraling row of specialized ciliary structures called membranelles which are mainly used for brushing prey into the cell mouth ( cytostome ).
They exist as single-celled organisms while food is plentiful. When food is in short supply, many of the single-celled amoebae congregate and start moving as a single body, called a 'slug'. The ability of the single celled organisms to aggregate into multicellular forms are why they are also called the social amoebae.
It is one of the largest single-celled organisms known, at up to 20 centimetres (8 in) across. [4] It was first described in 1882 by the oceanographer John Murray, after being discovered on an expedition in the ship Triton which dredged the deep ocean bed off the west coast of Scotland in an effort to find organisms new to science.