Video Transcript
The figure shows two different unicellular organisms. Which statement applies to both organisms? (A) Both organisms can remove excess water. (B) Both organisms move toward light. (C) Both organisms can make their own food. Or (D) both organisms have a single nucleus.
Euglena and Paramecium are both unicellular, or single-celled, organisms. They must carry out all essential life processes within just one cell. For example, to obtain nutrition, Euglena cells are able to carry out photosynthesis as they have chloroplasts. Photosynthesis uses light energy and simple inorganic molecules to make food in the form of sugars. Paramecium cells cannot carry out photosynthesis as they do not have chloroplasts. This means that option (C), both organisms can make their own food, is incorrect.
To maximize the light they can absorb for photosynthesis, Euglena cells have an eyespot to detect light and a taillike flagellum to move quickly toward it. Paramecium cells do not have either of these features. They are able to move fairly slowly using hairlike cilia that coat their surface. As they do not have an eyespot or a flagellum, Paramecium cells cannot detect light or move toward it quickly. This doesn’t matter however, as we know that these cells do not carry out photosynthesis. So, they do not need light. Therefore, option (B), both organisms move toward light, can also be eliminated.
The instructions for controlling various life processes, such as growth and reproduction, are encoded by genetic material. In both Paramecium and Euglena cells, genetic material is found in an organelle called the nucleus. However, while Euglena only has one nucleus, we can see that the Paramecium cell actually contains two nuclei: a large macronucleus and a smaller micronucleus. With this information, we can eliminate answer option (D): both organisms have a single nucleus.
The contractile vacuole is an organelle present in both the Paramecium cell and the Euglena cell that plays an important role in excretion, another vital life process. The contractile vacuole is responsible for collecting and then removing excess water from the cell. Therefore, as they both have contractile vacuoles, the statement that applies to both organisms is given in answer option (A): both organisms can remove excess water.