''Pinnularia'' is a genus of fresh water

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

, more specifically a type of

diatom A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...

Habitat

''Pinnularia'' is a predominantly fresh-water algae usually found in ponds and moist soil. They can also be found in springs,

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environment ...

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...

s, and oceans. Members of this genus are most commonly found in of water, at .

External structure

''Pinnularia'' are elongated elliptical unicellular organisms. Their cell walls are composed chiefly of

pectic Pectin ( grc, πηκτικός ': "congealed" and "curdled") is a heteropolysaccharide, a structural acid contained in the primary lamella, in the middle lamella, and in the cell walls of terrestrial plants. The principal, chemical component o ...

substances on a rigid

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

framework, and composed of two halves called thecae (or less formally, valves). These halves overlap like a

Petri dish A Petri dish (alternatively known as a Petri plate or cell-culture dish) is a shallow transparent lidded dish that biologists use to hold growth medium in which cells can be cultured,R. C. Dubey (2014): ''A Textbook Of Biotechnology For Class- ...

and its cover, the outer larger valve called

Epitheca ''Epitheca'' is a genus of dragonflies in the family Corduliidae The Corduliidae, also knowns as the emeralds, emerald dragonflies or green-eyed skimmers, is a family of dragonflies. These dragonflies are usually black or dark brown with area ...

and the smaller called

hypotheca Hypothec (; german: Hypothek, french: hypothèque, pl, hipoteka, from Lat. ''hypotheca'', from Gk. : hypothēkē), sometimes tacit hypothec, is a term used in civil law systems (e.g. law of entire Continental Europe except Gibraltar) or mixed ...

. The margins of the two thecae are covered by a connecting band called a cingulum and all together are referred to as a frustule, and the whole cell is covered by a mucilaginous layer. The surface view is called valve view and band view is called girdle view.

Internal structure

The

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. The ...

is arranged approximately in layers conforming to the shape of the cell's walls. A large central

vacuole A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic mo ...

is present with the nucleus suspended in its centre by a transverse cytoplasmic bridge. Two

chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in ...

s are present along the sides of the cells, and contain chlorophyll a, c, beta-carotene and

fucoxanthin Fucoxanthin is a xanthophyll, with formula C42H58O6. It is found as an accessory pigment in the chloroplasts of brown algae and most other heterokonts, giving them a brown or olive-green color. Fucoxanthin absorbs light primarily in the blue-green ...

pigments. One or two pyrenoids are usually present in each chloroplast, although like many heterokont algae, ''Pinnularia'' tend to store their energy as

fat In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food. The term often refers spec ...

. The cytoplasm also contains

chrysolaminarin Chrysolaminarin is a linear polymer of β(1→3) and β(1→6) linked glucose units in a ratio of 11:1. It used to be known as leucosin. Function Chrysolaminarin is a storage polysaccharide typically found in photosynthetic heterokonts. It is ...

and some volutin.

Reproduction

''Pinnularia'', like most diatoms, can reproduce by simple cell division. Nuclear division occurs by

mitosis In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is mainta ...

and cell divides into two parts. Each daughter receives one of the parent cell's thecae, which becomes that cell's

epitheca ''Epitheca'' is a genus of dragonflies in the family Corduliidae The Corduliidae, also knowns as the emeralds, emerald dragonflies or green-eyed skimmers, is a family of dragonflies. These dragonflies are usually black or dark brown with area ...

. The cell then synthesizes a new

. Thus, one daughter is the same size as the parent, and one is slightly smaller. With subsequent generations, the average cell size of a ''Pinnularia'' population gradually becomes smaller. When a minimum average size is reached,

auxospore In certain species of diatoms, auxospores are specialised cells that are produced at key stages in their cell cycle or life history. Auxospores typically play a role in growth processes, sexual reproduction or dormancy.Hoek, C. van den, Mann, ...

formation occurs and

sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...

restores the population's average cell size.

References

External links

''Pinnularia major'' (Kützing)
{{Authority control Diatom genera Naviculales Taxa named by Christian Gottfried Ehrenberg