Pinnularia is a freshwater alga. It is found in the pond.
It is also present in moist soil.
Pinnularia is an unicellular organism.
It consists of elongated and elliptical cells.
The cell wall is mainly composed of pectic substances and silica is impregnated in the cell wall. Therefore, their wall becomes very hard.
The cell wall is composed of two halves called valves or theca.
These halves overlap like a Petri dish.
The margins of the two valves are covered by a connecting band or girdle band.
The two valves with their inner protoplasts are called a frustule.
The frustule has two views. The surface view is called the valve view and the band view is called the girdle view.
The outer larger valve is called epitheca.
The smaller inner valve is called the hypotheca.
Cytoplasm is arranged in the parietal layer.
A large central vacuole is present inside the cell.
A single nucleus is suspended in the center near the vacuole by the transverse cytoplasmic bridge.
Two chloroplasts are present along the two sides of the cells. These are the most prominent structures. They contain chlorophyll a, c, beta-carotene, and diatomic or fucoxanthin pigment. Fucoxanthin gives the alga characteristic color.
One or two pyrenoids are present in the chloroplast. But they do not synthesize starch.
Their storage compound is oil or chrysolaminarin.
Locomotory organs are absent in Pinnularia. It moves by characteristic gliding movements.
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