1st PUC Biology Question and Answer Chapter 2: Biological Classification

Biological Classification Question and Answer:

Question 1.
Discuss how classification systems have undergone several changes over a while.

Answer:
The classification of organisms has evolved significantly over time. Early attempts, like those of Aristotle, were based on simple characteristics, such as classifying plants into trees, herbs, and shrubs, and animals based on the presence of red blood. Later, Linnaeus introduced a two-kingdom system, dividing life into Plantae and Animalia. However, this system did not account for differences between eukaryotes and prokaryotes, or unicellular and multicellular organisms.

With advancements in science, it became clear that additional factors like cell structure, nutrition, and evolutionary relationships needed consideration. To address this, R.H. Whittaker proposed a five-kingdom system, which includes:

1. Monera
2. Protista
3. Fungi
4. Plantae
5. Animalia

Question 2.
State two economically Important uses of:

• Heterotrophic bacteria
• Archaebacteria

Answer:
(a) Heterotrophic Bacteria:

1. Used in the production of curd from milk.
2. Aid in nitrogen fixation in the roots of leguminous plants.

(b) Archaebacteria:

1. Methanogens, found in the guts of ruminants like cows and buffaloes, produce methane from animal waste.
2. Archaebacteria thrive in extreme environments, such as salty areas and hot springs, providing insights into the early evolution of life on Earth.

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

Answer:
The cell walls of diatoms are made up of two thin overlapping shells that fit together like a soap box. These walls are embedded with silica, making them indestructible. As a result, diatoms leave behind large deposits of their cell walls in their habitats.

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

Answer:
Algal Bloom refers to the rapid multiplication of algae, leading to the formation of large colonies in water. Dinoflagellates, a type of algae, come in various colours due to different pigments. When red-pigmented dinoflagellates multiply rapidly, they give the sea a reddish appearance, a phenomenon known as a Red Tide.

Question 5.
How are viroids different from viruses?

Answer:
Viroids consist of free RNA without a protein coat, while viruses have RNA or DNA enclosed in a protective protein coat.

Question 6.
Describe briefly the four major groups of Protozoa.
Answer:
(a) Amoeboid Protozoa:
These organisms inhabit fresh water, seawater, or moist soil. They move and capture prey using pseudopodia (false feet), as seen in Amoeba. Marine forms may have silica shells, and some, like Entamoeba, are parasitic.

(b) Flagellated Protozoa:
Members of this group can be free-living or parasitic, and they move using flagella. Parasitic forms, such as Trypanosoma, can cause diseases like sleeping sickness.

(c) Ciliated Protozoa:
These are aquatic and move actively using thousands of cilia. They have a gullet that opens to the cell surface, and the coordinated movement of cilia directs food-laden water into the gullet. Example: Paramecium.