Question 1

Discuss how classification systems have undergone several changes over a period of time?

Accepted Answer

Classification systems have evolved significantly over time as our understanding of organisms has improved. Initially, organisms were classified based on simple morphological features. Linnaeus introduced the binomial nomenclature and a hierarchical system based on physical characteristics. Later, with the advent of microscopy, microorganisms were discovered, leading to the inclusion of new groups. The five-kingdom system proposed by Whittaker classified organisms into Monera, Protista, Fungi, Plantae, and Animalia based on cell structure, mode of nutrition, and reproduction. With molecular biology and genetic studies, the three-domain system was introduced, dividing life into Bacteria, Archaea, and Eukarya, reflecting evolutionary relationships more accurately. Thus, classification has shifted from morphology-based to phylogeny-based systems. — Step-by-step, classification started with morphology, then included microscopic organisms, followed by five kingdoms based on cell type and nutrition, and finally molecular phylogeny leading to three domains.

Question 2

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

Accepted Answer

(a) Economically important uses of heterotrophic bacteria:
1. Decomposition: They decompose organic matter, recycling nutrients in ecosystems.
2. Industrial production: Used in the production of antibiotics, enzymes, and fermented foods like yogurt and cheese.

(b) Economically important uses of archaebacteria:
1. Methanogens: Used in biogas production by converting organic waste into methane.
2. Extremophiles: Enzymes from archaebacteria are used in industrial processes requiring high temperature or extreme conditions, such as PCR (Taq polymerase from Thermus aquaticus, a related extremophile). — Heterotrophic bacteria play roles in decomposition and fermentation industries, while archaebacteria contribute to biogas production and provide enzymes for biotechnology.

Question 3

What is the nature of cell-walls in diatoms?

Accepted Answer

The cell walls of diatoms are made of silica (silicon dioxide). They have a unique glass-like, rigid, and intricate cell wall called a frustule, which is composed of two halves that fit together like a box and its lid. This silica cell wall provides protection and structural support. — Diatoms have silica-based cell walls called frustules, which are hard and intricately patterned, unlike cellulose walls in plants.

Question 4

Find out what do the terms 'algal bloom' and 'red-tides' signify.

Accepted Answer

'Algal bloom' refers to a rapid increase or accumulation of algae in water bodies, often resulting in a dense green or colored layer on the surface. 'Red-tides' are a type of algal bloom caused by certain dinoflagellates that produce reddish pigments, turning the water red or brown. These phenomena can be harmful as they may produce toxins affecting aquatic life and humans. — Algal blooms are rapid algae growths; red-tides are harmful blooms with red pigmentation caused by dinoflagellates.

Question 5

How are viroids different from viruses?

Accepted Answer

Viroids are small, circular, single-stranded RNA molecules without a protein coat, and they infect plants causing diseases. Viruses consist of nucleic acid (DNA or RNA) enclosed within a protein coat called a capsid and sometimes a lipid envelope. Viruses infect animals, plants, and bacteria. Thus, viroids lack a protein coat and are smaller and simpler than viruses. — Viroids are naked RNA molecules infecting plants; viruses have nucleic acid plus protein coat and infect various organisms.

Question 6

Describe briefly the four major groups of Protozoa.

Accepted Answer

The four major groups of Protozoa are:
1. Flagellates (Phylum Zoomastigophora): Move by flagella, e.g., Trypanosoma.
2. Amoeboids (Phylum Sarcodina): Move by pseudopodia, e.g., Amoeba.
3. Ciliates (Phylum Ciliophora): Move by cilia, e.g., Paramecium.
4. Sporozoans (Phylum Sporozoa): Non-motile, parasitic, e.g., Plasmodium.
Each group differs in locomotion and mode of life. — Protozoa are classified based on locomotion: flagella, pseudopodia, cilia, or non-motile parasitic forms.

Question 7

Plants are autotrophic. Can you think of some plants that are partially heterotrophic?

Accepted Answer

Some plants are partially heterotrophic, meaning they can photosynthesize but also obtain nutrients from other sources. Examples include:
- Insectivorous plants like Nepenthes and Dionaea (Venus flytrap) that trap insects to supplement nitrogen.
- Parasitic plants like Cuscuta (dodder) that derive nutrients from host plants.
- Saprophytic plants like Monotropa (Indian pipe) that obtain nutrients from decaying organic matter. — Certain plants supplement autotrophy with heterotrophic nutrition by trapping insects or parasitizing other plants.

Question 8

What do the terms phycobiont and mycobiont signify?

Accepted Answer

In lichens, the term 'phycobiont' refers to the algal component that performs photosynthesis, providing food. The 'mycobiont' is the fungal component that provides protection and absorbs water and minerals. Together, they form a symbiotic association. — Phycobiont = photosynthetic algal partner; mycobiont = fungal partner in lichens.

Question 9

Give a comparative account of the classes of Kingdom Fungi under the following:
(i) mode of nutrition
(ii) mode of reproduction

Accepted Answer

Comparative account of classes of Kingdom Fungi:
(i) Mode of nutrition:
- All fungi are heterotrophic and absorb nutrients from organic matter.
- Some are saprophytic (decompose dead matter), others are parasitic (feed on living hosts).

(ii) Mode of reproduction:
- Fungi reproduce both sexually and asexually.
- Asexual reproduction occurs by spores like conidia, sporangiospores.
- Sexual reproduction involves fusion of compatible nuclei forming zygospores, ascospores, or basidiospores depending on the class.
- For example, Zygomycetes reproduce sexually by zygospores; Ascomycetes by ascospores; Basidiomycetes by basidiospores. — Fungi are heterotrophic; reproduce asexually by spores and sexually by different spore types depending on class.

Question 10

What are the characteristic features of Euglenoids?

Accepted Answer

Characteristic features of Euglenoids:
- Unicellular, mostly freshwater organisms.
- Possess flagella for movement.
- Have chloroplasts and can photosynthesize (autotrophic), but can also feed heterotrophically.
- Cell covering is a flexible pellicle instead of a rigid cell wall.
- Presence of an eyespot (stigma) for detecting light.
- Reproduce asexually by binary fission. — Euglenoids are unicellular, flagellated, mixotrophic organisms with pellicle and eyespot.

Question 11

Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.

Accepted Answer

Viruses are acellular infectious agents consisting of a nucleic acid core (either DNA or RNA) surrounded by a protein coat called a capsid. Some viruses also have a lipid envelope. They lack cellular structures and can reproduce only inside host cells. The genetic material can be single or double-stranded.

Four common viral diseases are:
1. Influenza
2. HIV/AIDS
3. Common cold
4. Chickenpox — Viruses have nucleic acid plus protein coat, are obligate parasites; common diseases include influenza, HIV, cold, chickenpox.

Question 12

Organise a discussion in your class on the topic – Are viruses living or non-living?

Accepted Answer

Viruses exhibit characteristics of both living and non-living entities. They have genetic material and can evolve, which are features of living organisms. However, they lack cellular structure, cannot carry out metabolism, and reproduce only inside host cells, which are non-living characteristics. Therefore, viruses are considered at the edge of life, often described as 'organisms at the edge of life'. This topic is open for discussion considering various viewpoints. — Viruses have genetic material but lack metabolism and independent reproduction; hence debated as living or non-living.

Question 13

Who was the earliest known scientist to attempt a scientific classification of living organisms based on morphological characters, and how did he classify plants and animals?

Accepted Answer

Aristotle was the earliest known scientist to attempt a scientific classification. He classified plants into trees, shrubs, and herbs based on morphology, and animals into those with red blood and those without. — Aristotle used simple morphological characters to classify plants into trees, shrubs, and herbs. He also divided animals into two groups based on the presence or absence of red blood. This was one of the earliest attempts to classify organisms scientifically.

Question 14

Which two kingdoms were included in the Two Kingdom system of classification developed by Linnaeus, and what major limitations did this system have?

Accepted Answer

The Two Kingdom system included Plantae and Animalia. Its major limitations were the inability to distinguish between prokaryotes and eukaryotes, unicellular and multicellular organisms, and photosynthetic and non-photosynthetic organisms, leading to many organisms not fitting into either kingdom. — Linnaeus' system classified all organisms into either Plantae or Animalia. However, it did not consider cell structure differences like prokaryotic vs eukaryotic, or modes of nutrition such as photosynthesis vs heterotrophy. This made the system inadequate for many organisms.

Question 15

According to R.H. Whittaker's Five Kingdom classification, which kingdom includes organisms with prokaryotic cell type and non-cellulosic cell walls composed of polysaccharides and amino acids?

Accepted Answer

Kingdom Monera — Whittaker's Five Kingdom classification places prokaryotic organisms with non-cellulosic cell walls in Kingdom Monera. Protista, Fungi, and Plantae are eukaryotic kingdoms with different cell wall compositions.

Biology

Biology — Study Notes

Biological Classification

Characteristics of the Five Kingdoms

Kingdom Monera

Practice Questions — Biology

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