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Definition: The spiral model is similar to the incremental development for a system, with more emphasis placed on risk analysis. The spiral model has four phases: Planning, Design, Construct and Evaluation. A software project repeatedly passes through these phases in iterations (called Spirals in this model)....
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[tex]Spirogyra are free-floating green algae present in freshwater habitats such as ponds, lakes, etc. Spirogyra are commonly known as “water silk or pond silk”. They have a filamentous and unbranched vegetative structure. There are around 400 species of Spirogyra found. The genus Spirogyra is named after the unique spiral chloroplast present in the cells of algae.
Spirogyra are photosynthetic and contribute substantially to the total carbon dioxide fixation carried out. They increase the level of oxygen in their habitat. Many aquatic organisms feed on them.
Structure of Spirogyra
The vegetative structure of Spirogyra is an unbranched filamentous thallus
The thallus is multicellular with each cylindrical cell joined end to end
They are 10-100 µm in width and may grow several centimetres in length
They are present as a slimy mass due to the presence of mucilage sheath around the filament
The cell wall is made up of two layers, inner cellulose and outer pectose. The slimy mucilage sheath is due to the dissolution of pectose in water
In each cell, there is a nucleus, cytoplasm, a large central vacuole and spiral chloroplasts
Chloroplasts are ribbon-shaped and arranged spirally. There may be 1-16 chloroplasts present in a cell
Chloroplast contains many pyrenoids in a row. Pyrenoids store starch and protein