Chapter 19, Problem 25A

Summary Introduction

Introduction :

Algae are used as a food source for the animals as well as for humans. In different regions of the world, algae are used as a food supplement for the farm animals. They are also used in different types of dishes and processed food items. They are autotrophs because they produce their own food through the process of photosynthesis. They are the most important producers of food and oxygen for the aquatic ecosystems.

Answer to Problem 25A

Correct answer :

The correct answer is option (D) red algae.

Explanation of Solution

Explanation/justification for the correct answer :

Option (D) red algae. Red algae are found multicellular form. They are placed in phylum Rhodophyta. They contain a three different photosynthetic pigment known as phycoerythrin, phycocyanin, and chlorophyll A that provide them their red color. They provide natural food to the fish and other aquatic animals. They are also consumed by the humans in different ways. Porphyra is a species of red algae is used in sauces, soups, and condiments. Some species provide agar and carrageenan. Agar is a jelly like substance that used in the dairy toppings, puddings, and in other instant food items. Agar is also used to preserve the canned fish and meat. Carrageenan is used to stabilize and thicken the syrups, puddings, and some other products. Red algae are used as a food source from hundreds of years because they are rich in minerals, calcium, vitamins, antioxidants, and magnesium. Red algae are used as an important source in the human food supply. So, the correct answer is option (D).

Explanation for incorrect answer :

Option (A) dinoflagellates. Dinoflagellates are unicellular algae. Most of the dinoflagellates are marine plankton but they are also found in freshwater habitats. They contain some toxins that attack the neurological system and can cause ciguatera fish poisoning, amnesic shellfish poisoning, and some other syndromes. Therefore, they can be harmful for the humans and that’s why not used in the human food supply. So, this is an incorrect option.

Option (B) euglenoids. Euglenoids are also unicellular algae. Usually they are found in shallow freshwater but some are also found in saltwater. They are used in cosmetic products and they also contain some substances that are edible. They are not generally used in the human food supply. So, this is an incorrect answer.

Option (C) protozoans. Protozoans are single celled eukaryotes. They are either parasitic or free living and feed on the organic matter like organic tissues and debris or other microorganisms. Most of the protozoans are infectious to the humans and cause diseases. They are not used in human food supply. So, this option is also incorrect.