Any cell without Ulothrix’s hold fast in unfavorable environment develops into gametangium. The protoplast of the gametangium divides by mitosis to produce 8, 16, 32 or 64 daughter protoplasts. Each fertilized protoplast develops into a biflagellate (two-flagellated) gamete. They are denoted as + and – strains for being heterogeneous in nature.

Ulothrix is a heterothallic algae. Its sexual reproduction is isogamous in nature. Its sex is described.
1. Gamete formation: Any cell without Ulothrix’s hold fast in unfavorable environment develops into gametangium. The protoplast of the gametangium divides by mitosis to produce 8, 16, 32 or 64 daughter protoplasts. Each fertilized protoplast develops into a biflagellate (two-flagellated) gamete. They are denoted as + and – strains for being heterogeneous in nature.
2. Gamete emerson : Gametes are enclosed by vesicles. They emerge from the gametangium enclosed in vesicles. The vesicle then breaks down and the gametes swim freely.
3. Fertilization: Fertilization of + strain and – strain from different filaments takes place. Fertilization results in the formation of a zygote.
4. Resting spore: The zygote of Ulothrix has four flagella. It is active for some time. Later the flagella is lost and the wall becomes a resting spore.
5. Germination: After resting, the nucleus of the zygote divides by meiosis to form immature protoplasts with 4-16 haploid nuclei. They have half +strain and half -strain properties. Each aborted protoplast develops into a flagellated spore. They are called meiospores as they are produced by the process of meiosis. Zoospores and aplanospores germinate under favorable conditions to form new filaments of Ulothrix.

In extremely dry conditions, the protoplast of the body cell of Ulothrix divides to form numerous daughter cells. Aberrant cells are covered by a gelatinous membrane. This condition is called Pamela Dasha. Under favorable conditions the gelatinous coating dissolves in water flow and each cell transforms into a zoospore. Each zoospore develops into a new alga.

In unfavorable environment one or more cells of Ulothrix swell up with abundant food storage and develop into resting spore covered by thick wall. These cells are called akinites. Each actinomycete germinates into a new alga in a favorable environment.

Protoplast of one or more cells is covered by a hard wall due to prolonged dormancy to form spherical hypnospore. Under favorable conditions, hypnospores germinate directly into new algae.

Protoplast of sporangium divides in unfavorable environment to produce stationary molecule. It becomes aplanospore or resting spore covered by a wall. Under favorable conditions it breaks through the wall and germinates to form new Ulothrix filaments.

One or more cells of Ulothrix develop into zoosporangium under favorable conditions. The protoplast of the zoosporangium divides into 32 protoplasts. Each immature protoplast transforms into a four-flagellated zoospore or cell. Zoospores are of two types. Microzoospores (8-32 per zoosporangium) and megazoospores (1-4 per zoosporangium). Zoospores are pear-shaped and have an eye spot. They emerge from the zoosporangium encased in vesicles. The vesicles then rupture and the zoospores float freely. After 2-6 days of swimming, the zoospores lose their flagella and are enveloped by walls. Later divides to form new Ulothrix filaments.

1. Zoospore: One or more cells of Ulothrix develop into zoosporangium under favorable conditions. The protoplast of the zoosporangium divides into 32 protoplasts. Each immature protoplast transforms into a four-flagellated zoospore or cell. Zoospores are of two types. Microzoospores (8-32 per zoosporangium) and megazoospores (1-4 per zoosporangium). Zoospores are pear-shaped and have an eye spot. They emerge from the zoosporangium encased in vesicles. The vesicles then rupture and the zoospores float freely. After 2-6 days of swimming, the zoospores lose their flagella and are enveloped by walls. Later divides to form new Ulothrix filaments.
2. Aplanospore: Protoplast of sporangium divides in unfavorable environment to produce stationary molecule. It becomes aplanospore or resting spore covered by a wall. Under favorable conditions it breaks through the wall and germinates to form new Ulothrix filaments.
3. Hypnospore: Protoplast of one or more cells is covered by a hard wall due to prolonged dormancy to form spherical hypnospore. Under favorable conditions, hypnospores germinate directly into new algae.
4. Akinity: In unfavorable environment one or more cells of Ulothrix swell up with abundant food storage and develop into resting spore covered by thick wall. These cells are called akinites. Each actinomycete germinates into a new alga in a favorable environment.
5. Pameloid: In extremely dry conditions, the protoplast of the body cell of Ulothrix divides to form numerous daughter cells. Aberrant cells are covered by a gelatinous membrane. This condition is called Pamela Dasha. Under favorable conditions the gelatinous coating dissolves in water flow and each cell transforms into a zoospore. Each zoospore develops into a new alga.

Each chloroplast contains one or more pyrinoids. It is made up of proteins. It stores carbohydrates.

1. Cellwall: Cells of Ulothrix are covered by a two-layer wall. The outer layer is composed of pectose and the inner layer is composed of cellulose. It gives specific shape to cells and protects them from external injury.
2. Plasma membrane: The thin membrane inside the cell wall is called plasma membrane. It is composed of lipids and proteins. It has tiny pores. A variety of chemicals pass through these pores in and out of the cell.
3. Protoplasm: All the living parts of the cell inside the cell wall are collectively called protoplasm. It consists of two parts. Cytoplasm and nucleus.
(i) Cytoplasm: The parts of cytoplasm are-
Chloroplast: Each cell contains one chloroplast. It is ribbon or girdle or cup or ring shaped. It produces food in the process of photosynthesis.
Pyrinoid: Each chloroplast contains one or more pyrinoids. It is made up of proteins. It stores carbohydrates.
Cell vacuole: Each cell has a small cell cavity. It is filled with tissue. Covering the central cavity is the primordium utricle.
Stored food: Starch is stored as stored food in their cells.
(ii) Nucleus : Ulothrix is a unicellular alga. Each of its cells has a well-formed nucleus. It controls all biological functions of cells.