GSEB Class 11 Biology Solutions Chapter 2 Biological Classification

Question 1. Discuss how classification systems have undergone several changes over a period of time.
Answer: Two-kingdom systems were unable to describe photosynthetic, non-photosynthetic, unicellular, and multicellular organisms. Anatomical and environmental aspects became very important for further description. Progress in technology has given many new tools to scientists. Based on cell structure, way of nutrition, reproduction, and phylogenetic relationship, R.H. Whittaker proposed five-kingdom classifications: Monera, Protista, Fungi, Plantae, and Animalia. However, Whittaker's system did not cover viruses or lichens as cellular organisms. These entities cause numerous infectious diseases. Stanley characterized viroids, which T.O. Dienes later found to be smaller than viruses. Therefore, classification systems have seen several changes over time and continue to evolve.
In simple words: Early two-kingdom systems couldn't explain all life forms. With better technology, scientists saw a need for more detailed classifications. Whittaker introduced a five-kingdom system based on different features. However, even his system missed things like viruses. So, classification keeps changing as we learn more.

Exam Tip: When discussing changes in classification, mention the limitations of older systems, the advancements that led to new systems (like Whittaker's five-kingdom system), and the organisms that still pose classification challenges (e.g., viruses).

Question 2. State two economically important uses of:
(1) heterotrophic bacteria
(2) archaebacteria
Answer:
(1) Heterotrophic bacteria:
• They help with nitrogen fixation in the roots of leguminous plants.
• As decomposers, they are used in making antibiotics.
(2) Archaebacteria:
• They help produce biogas from cow-dung.
• They live in the guts of ruminant animals and assist them in digesting starch.
In simple words: Heterotrophic bacteria help plants get nitrogen and are used to make medicines. Archaebacteria produce cooking gas from animal waste and help cows digest their food.

Exam Tip: Remember specific examples for each type of bacteria and clearly state the economic benefit associated with each use.

Question 3. What is the nature of cell-wall in diatoms?
Answer: Diatoms have two thin shells that overlap and fit together. This wall is very strong because it is made of silica. The silica wall has been designed with five ridge lines, pores, and other features. The outer part of the wall is called the epithica, while the inner part is known as the hypotheca.
In simple words: Diatoms have a tough cell wall made of silica, like two overlapping parts. The outer part is called epithica, and the inner part is called hypotheca.

Exam Tip: Key terms like 'silica', 'overlapping shells', 'epithica', and 'hypotheca' are crucial when describing diatom cell walls.

Question 4. Find out what do the terms 'algae bloom' and 'red-tides' signify.
Answer: Red tides occur when certain dinoflagellates, which contain red pigment in their cells, multiply very quickly. These small marine organisms form a red layer over the ocean, making the water appear as red tides. An algal bloom is when colonies of cyanobacteria, such as Nostoc Anabaena, grow rapidly in polluted water bodies.
In simple words: Red tides happen when tiny red sea creatures grow a lot, making the ocean look red. An algal bloom is when many cyanobacteria grow fast in dirty water.

Exam Tip: Distinguish between the organisms causing red tides (dinoflagellates) and algal blooms (cyanobacteria) and mention their connection to rapid multiplication and water conditions.

Question 5. How are viroids different from viruses?
Answer:
Virus:
1. They are smaller than bacteria.
2. Their genetic material can be either RNA or DNA.
3. They have a protein coat, which consists of capsomeres.
4. They cause diseases such as Mumps and AIDS.
Viroids:
1. They are smaller than viruses.
2. Only RNA is present, and it is in a free form.
3. They do not have a protein coat.
4. They cause diseases like potato spindle tuber disease.
In simple words: Viruses are tiny, have a protein coat, and can have RNA or DNA. Viroids are even smaller, have only free RNA, and no protein coat. Both cause diseases.

Exam Tip: For comparative questions, use clear, distinct points for each entity being compared. Focus on structural differences (protein coat, type of genetic material) and relative size.

Question 6. Describe briefly the four major groups of Protozoa.
Answer:

Exam Tip: When describing groups of organisms, a table is an excellent way to present comparative information clearly. Focus on key distinguishing characteristics like locomotion, habitat, and nutrition for each group.

Question 7. Plants are autotrophic. Can you think of some plants that are partially heterotrophic?
Answer: Plants typically contain chlorophyll and produce their own food. However, some plants do show a heterotrophic way of obtaining nutrition.
(1) Insectivorous plants: These plants have special leaves that catch insects. The trapped insects are killed and digested by proteolytic enzymes released by the leaf's outer layer. An example is the Pitcher plant.
(2) Parasitic form: Cuscuta develops haustoria, which are structures that grow into the host plant's vascular bundles to take in water and nutrients.
In simple words: Most plants make their own food, but some eat other things. Insect-eating plants like the Pitcher plant catch and digest bugs. Parasitic plants like Cuscuta steal food and water from other plants using special roots.

Exam Tip: Clearly define autotrophic and heterotrophic nutrition. For partially heterotrophic plants, provide specific examples (e.g., Pitcher plant, Cuscuta) and briefly explain their unique nutritional mechanism.

Question 8. What do the terms phycobilins and mycobiont signify?
Answer: Lichens represent a symbiotic association between algae and fungi. The fungal part of this partnership is called the mycobiont, and the algal part is known as phycobilins.
In simple words: Lichens are a team-up between algae and fungi. The fungus part is the mycobiont, and the algae part is called phycobilins.

Exam Tip: When defining terms related to symbiotic relationships like lichens, always clearly identify both components and their respective names. Emphasize the cooperative nature of the association.

Question 9. Give a comparative account of the classes of Kingdom Fungi under the following:
• Mode of nutrition
• Mode of reproduction
Answer:

Exam Tip: For comparative questions, especially for the Kingdom Fungi, organizing your answer in a table based on the specified criteria (nutrition and reproduction) ensures clarity and covers all necessary points. Remember to include key terms like saprophytic, parasitic, zoospores, conidia, and basidiospores.

Question 10. What are the characteristic features of Euglenoids?
Answer: Euglenoids display the following distinct characteristics:
1. They live in freshwater, being free-living in ponds and ditches.
2. They lack a cell wall but possess a flexible pellicle, which is made of protein.
3. All euglenoids have one or two flagella, which help them in swimming.
4. They feature a red-pigmented eyespot and a gullet located near the base of the flagellum.
5. Some are green and holophytic, like other plants, while a few are non-green and saprobic, resembling holographic animals.
6. They store carbohydrates in the form of paramylum.
In simple words: Euglenoids are freshwater organisms that swim with flagella. They have a protein-rich skin instead of a cell wall. They also have a red eye-spot and store food as paramylum. Some are green like plants, while others get food like animals or from dead things.

Exam Tip: When listing characteristics, ensure you cover structural details (pellicle, flagella, eyespot), habitat, and nutritional modes (autotrophic/heterotrophic aspects) for a complete answer.

Question 11. Give a brief account of viruses with respect to their structure and the nature of genetic material. Also, name four common viral diseases.
Answer: (1) The term "virus" means venom or "poisonous fluid." These organisms are smaller than bacteria because they can pass through bacteria-proof filters. They are living organisms, but they are not free-living in nature; they only exist as obligate intracellular parasites.
(2) Protein viruses also contain genetic material, either RNA or DNA. A virion is a nucleoprotein, and its genetic material is infectious. These are obligate parasites, capable of self-replicating, non-cellular organisms.
(3) All plant viruses have single-stranded RNA, and all animal viruses have either single or double-stranded RNA or double-stranded DNA.
(4) Bacterial viruses (Bacteriophage viruses that consume bacteria) mostly contain double-stranded DNA. The protein coat protects the nucleic acid; this coat is called a capsid and is made up of small units called capsomeres.
(5) These capsomeres are organized in helical or polyhedral geometric shapes. Viruses cause diseases like mumps, smallpox, herpes, influenza, and AIDS in humans.
(6) In plants, symptoms can include mosaic patterns, leaf rolling and curling, yellowing, vein clearing, dwarfing, and stunted growth.
Common viral diseases:
1. Cough and cold
2. Mumps
3. Smallpox
4. Influenza
In simple words: Viruses are tiny, infectious particles that need a host cell to live. They have genetic material (RNA or DNA) protected by a protein coat called a capsid. They cause various illnesses in humans and plants, such as colds, mumps, smallpox, and influenza.

Exam Tip: When describing viruses, include their key characteristics (size, obligate parasites, structure with genetic material and capsid), differentiate between plant and animal virus genetic material, and provide specific examples of diseases they cause.

Question 12. Organize a discussion in your class on the topic – 'Are viruses living or non-living?'
Answer: Viruses are considered a link between living and non-living things. They possess certain characteristics of living organisms and some non-living features. Crystallization is a non-living trait, but viruses can reproduce inside a living body. In reality, they are metabolically inactive when outside a host cell. They reproduce by using the host cell's metabolic machinery and then infect chemically.
In simple words: Viruses are a puzzle because they show traits of both living and non-living things. They can be crystallized like non-living matter, but they can reproduce and cause infection inside a living host. Outside a host, they are inactive.

Exam Tip: To answer whether viruses are living or non-living, highlight both living characteristics (reproduction, genetic material, evolution) and non-living characteristics (crystallization, metabolic inactivity outside a host) to present a balanced argument.