Question

3) In which organisms will we observe anatomical evidence of their ability to reproduce sexually? 4) Of the protists we image for the digital image collection, which ones are photosynthetic? 5) How do we know that the photosynthetic ability of Euglena is secondarily derived?

Answer 1

3) A fossil named Bangiomorpha pubescens, a multicellular organism is the oldest record in fossils for sexually reproduction. B. pubescens was a form of red algae or seaweed. The evidence that these fossils sexually reproduced is in the finding that the spores or reproductive cells they generated came in two forms – male and female.

4) Protists that are capable of photosynthesis include various types of algae, diatoms, dinoflagellates, and euglena. These organisms are often unicellular but can form colonies. They also contain chlorophyll, a pigment which absorbs light energy for photosynthesis. Photosynthetic protists are considered plant-like protists. They absorb sunlight and use this energy to make glucose.

5) Endosymbiosis refers to the phenomenon of an organism living within another organism. It is proposed that the chloroplasts of Euglena have arisen from secondary endosymbiosis of green algae. The theory is supported by the presence of a third membrane around the chloroplasts of Euglena which is not endoplasmic reticulum (ER) in origin and may be derived from the plasmalemma of the original symbiont. These extra membranes likely formed due to secondary endosymbiosis, when an existing Plantae cell containing a primary plastid was engulfed and reduced to a plastid.