''Pinnularia'' is a genus of fresh water

algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...

, more specifically a type of

diatom A diatom (Neo-Latin ''diatoma'') is any member of a large group comprising several Genus, genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of Earth's B ...

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 environm ...

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

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 ( ': "congealed" and "curdled") is a heteropolysaccharide, a structural polymer contained in the primary lamella, in the middle lamella, and in the cell walls of terrestrial plants. The principal chemical component of pectin is galacturo ...

substances on a rigid

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

framework, and composed of two halves called

theca In biology, a theca (: thecae) is a sheath or a covering. Botany In botany, the theca is related to plant's flower anatomy. The theca of an angiosperm consists of a pair of microsporangia that are adjacent to each other and share a common ar ...

e (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 Odonata, dragonflies in the family (biology), family Corduliidae. They are commonly known as baskettails. Baskettails' distinction is the specially adapted, upturned abdomen tip of the females which allows them to carr ...

and the smaller called

hypotheca Hypotheca may refer to: * The inner Frustule#Thecae, theca of the frustule (exoskeleton) of a diatom * Hypothec, in civil law, a sort of mortgage {{disambiguation ...

. The margins of the two thecae are covered by a connecting band called a cingulum and all together are referred to as a

frustule A frustule is the hard and porous cell wall or external layer of diatoms. The frustule is composed almost purely of silica, made from silicic acid, and is coated with a layer of organic substance, which was referred to in the early literature on ...

, and the whole cell is covered by a

mucilaginous Mucilage is a thick gluey substance produced by nearly all plants and some microorganisms. These microorganisms include protists which use it for their locomotion, with the direction of their movement always opposite to that of the secretion of ...

layer. The surface view is called

valve view A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings, ...

and band view is called

girdle view A Belt (clothing), belt without a buckle, especially if a cord or rope, is called a girdle in various contexts, especially historical ones, where girdles were a very common part of everyday clothing from antiquity until perhaps the 15th century, ...

Internal structure

The

cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

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 cell, plant and Fungus, fungal Cell (biology), cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water ...

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, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...

s are present along the sides of the cells, and contain

chlorophyll a } Chlorophyll ''a'' is a specific form of chlorophyll used in oxygenic photosynthesis. It absorbs most energy from wavelengths of violet-blue and orange-red light, and it is a poor absorber of green and near-green portions of the spectrum. Chlorop ...

, 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-gree ...

pigments. One or two

pyrenoid Pyrenoids are sub-cellular phase-separated micro-compartments found in chloroplasts of many algae,Giordano, M., Beardall, J., & Raven, J. A. (2005). CO2 concentrating mechanisms in algae: mechanisms, environmental modulation, and evolution. ''An ...

s are usually present in each chloroplast, although like many

heterokont The stramenopiles, also called heterokonts, are protists distinguished by the presence of stiff tripartite external hairs. In most species, the hairs are attached to flagella, in some they are attached to other areas of the cellular surface, an ...

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 specif ...

. 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 u ...

and some

volutin Volutin granules are an intracytoplasmic storage form of complexed inorganic polyphosphate, the production of which is used as one of the identifying criteria when attempting to isolate ''Corynebacterium diphtheriae'' on Löffler's medium. Polyphos ...

Reproduction

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

mitosis Mitosis () is a part of the cell cycle in eukaryote, eukaryotic cells in which replicated chromosomes are separated into two new Cell nucleus, nuclei. Cell division by mitosis is an equational division which gives rise to genetically identic ...

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 Odonata, dragonflies in the family (biology), family Corduliidae. They are commonly known as baskettails. Baskettails' distinction is the specially adapted, upturned abdomen tip of the females which allows them to carr ...

. The cell then synthesizes a new

hypotheca Hypotheca may refer to: * The inner Frustule#Thecae, theca of the frustule (exoskeleton) of a diatom * Hypothec, in civil law, a sort of mortgage {{disambiguation ...

. 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 Auxospores are specialised cells in diatoms 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, D. G. and Jahns, H. M. ...

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