1. Cnidarians

2. Fungi

3. Protozoa

Select the correct answer using the codes given below.

(a) 1 and 2 Only

(b) 2 and 3 Only

(c) 1 and 3 Only

(d) 1, 2 and 3 

17. Ans: d

Explanation:

The term symbiosis was coined in 1879 by Heinrich Anton de Bary, a German mycologist, who defined it as: “the living together of unequally named organisms”. In this broad sense symbiosis includes all kinds of close biological relationships between species, hence spanning a continuum between pathogenic and mutualistic phenomena.  

The term symbiosis is derived from the Greek word for living together, symbiosis refers to a close and prolonged association between 2 or more organisms of different species that may last for the lifetime of 1 or all partners. 

Symbiosis is  prolonged associations between organisms often widely separated phylogenetically.

Symbioses can be mutualistic (all partners benefiting), commensalistic (one benefiting and the others unharmed), or parasitic.

Symbiosis in Cnidarians:

Symbiosis between invertebrates and photosynthetic partners are abundant in the marine environment, with the best known being the mutualism between members of the phylum Cnidaria (e.g., hard and soft corals, sea anemones, jellyfish, and hydrocorals) and dinoflagellate algae of the genus zooxanthellae. These dinoflagellates typically reside within the cells of the host cnidarian’s gastrodermis.

Symbiotic relationship of fungi:

Fungi have several mutualistic relationships with other organisms. 

• Symbiosis of fungi and plants: A mycorrhiza is a mutualistic relationship between a fungus and a plant. The fungus grows in or on the plant roots. The fungus benefits from the easy access to food made by the plant. The plant benefits because the fungus puts out mycelia that helps absorb water and nutrients like phosphorus and nitrogen. 
• Symbiosis of Fungi and Algae: A lichen is an organism that results from a mutualistic relationship between a fungus and a green alga or a fungus and a cynabacterium. The photosynthesizer benefits from the water and nutrients absorbed by the fungus. Lichens are often pioneer species in primary ecological succession. 
• Symbiosis of Fungi and insects: Some fungi have mutualistic relationships with insects. For example: Leafcutter ants grow fungi on beds of leaves in their nests. The fungi get a protected place to live. The ants feed the fungi to their larvae. Ambrosia beetles bore holes in tree bark and “plant” fungal spores in the holes. The holes in the bark give the fungi an ideal place to grow. The beetles harvest fungi from their “garden.”

Symbiosis in Protozoa :

Protozoa are a diverse group of unicellular eukaryotic organisms. Termites have a mutualistic relationship with protists that live in the insects’ gut. The termite benefits from the ability of the protists to digest cellulose. The termite itself cannot do this without the protozoa, it would not be able to obtain energy from its food (cellulose from the wood it chews and eats). The protozoa benefit by having a protective environment and a constant supply of food from the wood-chewing actions of the termite. 

The protists benefit from the enzymes provided by their bacterial endosymbionts, while the bacteria benefit from a doubly protective environment and a constant source of nutrients from two hosts.

Hence, option d is correct.

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