17. Eukaryotes:

Protista

Protista

Protists are organisms in the kingdom Protista. These organisms are eukaryotes.

I. Unicellular AlgaeUnicellular algae refers to the green, red and brown algae. This algae is in the class of diatoms and chrysophytes.

SpirogyraSpirogyra are a free-floating filamentous form of green algae, commonly seen as bright green masses on the surfaces of freshwater ponds and ditches. The name of this algae is derived from the spiral arrangement of chloroplast in its filament-like body.

What is the shape of each cell?

Spirogyra cells are cylindrical in shape and are connected end to end, forming a long, unbranched filament-like structure.

What occupies most of the volume of the cell?

A large vacuole occupies most of the volume of the cell

ConjugationIn scalariform conjugation, the cells of adjacent filaments develop small tube-like structures called 'conjugation tubes', which fuse together to form a 'conjugation canal'. The cytoplasm of the male cell flows through this canal to the female cell and fuses with the latter's cytoplasm. The next step is the fusion of gametes (mature sexual reproductive cell with a single set of unpaired chromosomes) to form the zygospore. The zygospore, which is thick-walled, is brownish in color and is oval or circular in shape. The spores are released to form new filaments. This type of conjugation gives the algae a ladder-like appearance, due to the interlinking of filaments.

Isogamete

Isogamete - A gamete that has the same size and structure as the one with which it unites.

Zygospore

Chrysophyta – Golden brown algae

a division of mostly freshwater eukaryotic algae having the chlorophyll masked by brown or yellow pigment; yellow-green and golden-brown algae and diatoms

DiatomsDiatoms are delicate unicellular organisms that have a yellow-brown chloroplast that enables them to photosynthesize. Their cell walls are made of silica almost like a glass house. The construction of the cell wall, called the frustule, consists of two valves that fit into each other like a little pill box.

Diatoms•Diatoms have many shapes•Their accessory pigments fucoxanthin and β (beta) carotene give them a characteristic golden color. •Color is more obvious on the center portion.

II. EuglenoidsEuglenoids are single cellular organisms with euglena like features. They do not have cellwall but do possess pellicle. They have flagella and occur in fresh water. They have specific euglenoid movements which are creeping movements followed by contraction and expansion of the body. Reproduction is acoomplished by means of binary fission

Euglena Euglena is a single-celled microscopic algae. It is a unique organism that can accumulate nutrients by photosynthesis and move like an animal by twisting itself.Euglena is discoidal in shape. However, it can also be ovate, elongate or U-shaped.

•Euglena move by a flagellum (plural ‚ flagella), which is a long whip-like structure that acts like a little motor. The flagellum is located on the anterior (front) end, and twirls in such a way as to pull the cell through the water.•Toward the posterior of the cell is a star-like structure: the contractile vacuole. This organelle helps the cell remove excess water, and without it the euglena could take in some much water due to osmosis that the cell would explode.

III. ProtozoansProtozoans are the “animal-like” members of Protista, a paraphyletic grouping of mostly single-celled eukaryotic organism that feed heterotrophically and exhibit diverse mechanisms of mobility. They can contain more than one nucleus and developed organelles

Paramecium A single-celled freshwater animal that has a characteristic slipperlike shape and is covered with cilia

Conjugationsexual process in which two organisms of the same species exchange nuclear material during a temporary union completely transfer one organism’s contents to the other organism or fuse together to form one organism

Binary fission•Asexual means of reproduction of paramecium•Macronucleus is more visible

AMOEBAAmoeba is a genus of Protozoa consisting of unicellular organisms that do not have a definite shape