Question 5. How are viroids different from viruses?

Answer: Viroids are free RNAs without the protein coat, while virus have a protein coat encapsulating the RNA.

Question 4. Find out what do the terms ‘algal bloom’ and ‘red-tides’ signify.

Answer: Dianoflagellates can be of different colours depending on the type of pigment present. The red dianoflagellate sometimes multiply at a very rapid rate. This is called as algal bloom. This gives a red appearance to the part of affected sea. This is also known as ‘red tide’. Toxins released by them can kill other marine species.

Question 3. What is the nature of cell-walls in diatoms?

Answer: The cell walls in diatoms are embedded with silica, which makes them indestructible. They form two thin overlapping shells which fit together as in a soap box. Thus diatoms have left behind large amounts of cell wall deposits in their habitat.

State two economically important uses of: (a) heterotrophic bacteria (b) archaebacteria

(a) Economically Important Use of Heterotrophic bacteria:

(i) Preparation of curd

(ii) Production of antibiotics

(b) Economically Important Use of Archaebacteria:

(i) Methanogens are type of archaebacteria and are present in the gut of ruminating animals. They are responsible for production of methane from ruminating animal’s dung.

(ii) Archaebacteria can live in the most harsh environments, like sulphur springs, volcano, etc. They are important as they give us clue how life may have started when the earth was too hot or too cold.

. Illustrate the taxonomical hierarchy with suitable examples of a plant and an animal.

Taxonomical Hierarchy

1. Man

Phylum: Chordata

Class: Mammalia

Order: Primata

Family: Hominidae

Genus: Homo

Species: Homo sapiens

2. Mango

Phylum: Angiosperm

Class: Dicotyledons

Order: Sapindales

Family: Anacardiaceae

Genus: Mangifera

Species: Mangifera indica