Cell Biology: The branch of biology which deals with the study of different aspects (Structure & function) of cell is called cell biology or cytology.
Why Do We Classify Living Organisms? OR
Why are living organisms classified?
Solution:
Living organisms are classified to bring order to the immense diversity of life on Earth. Local names for plants and animals can differ greatly from place to place, causing confusion and making scientific study difficult.
By classifying organisms, we assign them a universal scientific name and categorize them based on shared characteristics. This standardization allows scientists worldwide to communicate clearly, identify specific species accurately, and understand evolutionary relationships, ultimately making the study of life more efficient and precise.
2. Why are the classification systems changing every now and then?
Solution:
As we know, science is constantly growing, and we keep discovering new living things and better ways to study them.
At first, we just grouped organisms by where they lived or what they did. Then, we looked closer at their outer shapes, then inside structures and how they grew from embryos. Now, with amazing tools, we can even examine their DNA and other tiny chemicals!
Each new discovery gives us a clearer picture of how life is connected. So, classification systems change often because we're always learning more and improving our understanding of life's incredible diversity.
3. What different criteria would you choose to classify people that you meet often?
Solution:
The people we meet most often are categorized by characteristics such as gender, skin colour, education, career, hobbies, and nature.
4. What do we learn from the identification of individuals and populations?
Solution:
By identifying individuals and populations, we learn the following things:
(i) Sex
(ii) Skin colour
(iii) Native place
(iv) Mother tongue
(v) Food habit
(vi) Religion
(vii) Caste
5. Given below is the scientific name of Mango. Identify the correctly written name.
Mangifera Indica
Mangifera indica
Solution:
The answer is Mangifera indica. Here, Mangifera is its genus name, and indica is its species name which is always written in lowercase.
6. Define a taxon. Give some examples of taxa at different hierarchical levels.
Solution:
A taxon is a level of hierarchy in the system of classifying organisms.
Following are the hierarchical levels:
(i) Kingdom
(ii) Phylum
(iii) Class
(iv) Order
(v) Family
(vi) Genus
(vii) Species
7. Can you identify the correct sequence of taxonomical categories?
(a) Species Order Phylum Kingdom
(b) Genus Species Order Kingdom
(c) Species Genus Order Phylum
Solution:
From the given options, (a) and (c) is the correct sequence of taxonomical categories.
8. Try to collect all the currently accepted meanings for the word ‘species’. Discuss with your teacher the meaning of species in the case of higher plants and animals on the one hand and bacteria on the other hand.
Solution:
A group of individual organisms with basic similarities is called species. This is the basic unit of classification. Species are defined as individuals who share the same gene pool.
Higher plants and animals: Criteria of reproductive isolation can be used to classify the species.
Bacteria: Interbreeding and reproductive isolation cannot be used in the case of bacteria; here, a gene pool can be used to classify species.
9. Define and understand the following terms.
(i) Phylum (ii) Class (iii) Family (iv) Order (v) Genus
Solution:
i) Phylum is a taxonomical hierarchy below Kingdom and above Class. It is a taxon with one or more classes of organisms with similar characteristics.
ii) Class is a taxonomical hierarchy higher than Order and lower than Phylum. Class includes related to orders of the organisms. Example: Presence of notochord in mammals.
iii) Family has a group of related genera with still less number of similarities as compared to genus and species. Example: Fox and dog belongs to the same family. It is a group of entities below Order and above Genus.
iv) Order is a taxon below higher than Family and lower than class. Order being a higher category, is the assemblage of families which exhibit a few similar characters.
v) Genus comprises a group of related species which has more characteristics in common in comparison to species of other genera. Examples: Lion, tiger and leopard are classified under the genus Panthera. It is above species and below the family.
10. How is a key helpful in the identification and classification of an organism?
Solution:
The key is a taxonomic aid used to identify plants and animals based on similarities and dissimilarities. It represents the choice between two opposite characters. This is useful for identifying contrasting characters. They are two contrasting characters, where one character’s choice rejects another when the species, family, or genera is identified.
If the entity is not already recorded, efforts are made for the first verification and reconsider its discovery before naming it. Therefore, each entity can be classified as it is known or unknown.
11. Illustrate the taxonomical hierarchy with suitable examples of a plant and an animal.
Solution:
The table below depicts the taxonomic hierarchy with wheat as an example of a plant and humans as an example of an animal.
Chapter 2 – Biological Classification
1. Discuss how classification systems have undergone several changes over a period of time.
Solution:
Aristotle was the first to introduce scientific classification. He used simple morphological characters to classify plants into trees, shrubs, and herbs. He divided the animals into two groups, one with red blood and one without.
Linnaeus introduced a two-kingdom classification, which includes Plantae and Animalia, respectively, of plants and animals. But this classification does not classify eukaryotes and prokaryotes, single-celled and multicellular organisms, photosynthetic (green algae) and non-photosynthetic (fungal) organisms. Therefore, the system was found to be less significant as it did not include more features.
Thus, the classification of living organisms has undergone several changes. R.H. Whittaker introduced a five-kingdom classification, including Monera, Protista, Fungi, Plantae and Animalia. Some of the characteristics included in this classification are the structure of cells, body organisation, mode of nutrition, mode of reproduction, and phylogenetic relationship to classify organisms. Subsequently, a three-domain system was proposed, which divided Kingdom Monera into two domains, leaving the remaining eukaryotic kingdoms in the third domain, thereby classifying the six kingdoms.
2. State two economically important uses of:
(a) heterotrophic bacteria
(b) archaebacteria
Solution:
a) Heterotrophic bacteria are used in the production of vitamins, antibiotics, cheese and curd.
They help fix nitrogen and are used in the formation of humus.
b) Archaebacteria are used in Biogas production.
They are used in the bioleaching of mines.
3. What is the nature of cell walls in diatoms?
Solution:
In diatoms, cell walls are embedded with silica imparting characteristic patterns onto the walls and are indestructible. These diatoms leave large amounts of cell wall deposits in their habitat to accumulate to form the diatomaceous earth.
4. Find out what the terms ‘algal bloom’ and ‘red tides’ signify.
Solution:
Algal blooms are found in contaminated water. They are an overgrowth of algae, especially blue-green algae (cyanobacteria). Their growth leads to water pollution. They inhale carbon dioxide and exhale oxygen.
Rapid multiplication of red-pigmented dinoflagellates, such as Gonaulax, gives the sea a red colour, a phenomenon known as red tides. These algae produce toxins that kill fish and other aquatic organisms.
5. How are viroids different from viruses?
Solution:
(i) Viroids are small infectious agents with single-stranded RNA without a protein coat, but viruses have single-stranded or double-stranded RNA bound with a protein coat.
(ii) Viroids are very small in size compared to viruses.
(iii) Viroids infect only plants, while viruses infect plants, animals, and microorganisms.
6. Describe the four major groups of Protozoa briefly.
Solution:
Four major groups of Protozoa are as follows:
Amoeboid protozoans: Found in the aquatic environment, they move and catch their prey using pseudopodia.
Flagellated protozoans: These protozoans are free-living or parasitic. Their locomotory structure is flagella.
Ciliated protozoans: They live in aquatic environments, and the presence of cilia makes them actively moving.
Sporozoans: They contain a wide variety of organisms, producing infectious spores throughout their life cycle. Their spore-like phase helps them move from one host to another.
7. Plants are autotrophic. Can you think of some plants that are partially heterotrophic?
Solution:
Insectivores and carnivorous plants are partially heterotrophic; these organisms are green and autotrophic, but they prey on and digest small components for their nitrogen supply.
Ex; Utricularia, Drosera, Nepenthes.
8. What do the terms phycobiont and mycobiont signify?
Solution:
Lichens are a symbiotic association of fungi and algae. Phycobiont is part of algae and part of mycobiont fungi. Mycobiont provides structural cover that protects the algae from unfavourable conditions. Similarly, phycobionts prepare food through the process of photosynthesis, which is used by both organisms.
9. Give a comparative account of the classes of Kingdom Fungi under the following:
(i) mode of nutrition (ii) mode of reproduction
Solution:
10. What are the characteristic features of Euglenoids?
Solution:
The typical features of Eugenoids are:
(i) Absence of cell wall.
(ii) Their body is flexible because there is a protein-rich layer called a pellicle.
(iii) Two flagella of different lengths are found.
(iv) They are autotrophic in the presence of sunlight and heterotrophic in the absence of sunlight.
11. Give a brief account of viruses with respect to their structure and nature of genetic material. Also, name four common viral diseases.
Solution:
Viruses are infectious agents that crystallise in structure when found outside the host cell. The genetic material is either DNA or RNA (never both), and they are located within the protein core. If the virus that infects plants has single-stranded RNA, then the viruses that infect animals are single or double-stranded DNA or RNA. The capsid is their protein coat, which in turn is made up of small subunits called capsomers, which protect nucleic acid.
Common viral diseases are Influenza, AIDS, Herpes and Rabies.
12. Organise a discussion in your class on the topic ‘Are viruses living or nonliving’?
Solution:
Non-living Characters
(i) No cellular structure
(ii) They can be stored in bottles like crystals
(iii) There will be no energy storage or energy liberation systems
(iv) They cannot grow or multiply outside the host
Living Characters
(i) They are host-specific
(ii) The presence of genetic material
(iii) The ability to multiply
(iv) They have antigenic properties
(v) They are obligate parasites
(vi) Mutations occur
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