Patterns in Life : Diversity and Classification — NCERT Solutions

An insect has jointed legs, which is a defining feature of arthropods. A cylindrical body is typical of roundworms, and little segmentation fits earthworm-like forms more than insects. So the option that confirms it is an insect is body with jointed legs.

Animal cells have a cell membrane but do not have a cell wall. Since sponges are animals, the feature supporting their classification under the animal kingdom is the presence of a cell membrane.

For two animals, we can compare features such as body covering, body shape, segmentation, presence of legs or wings, mode of movement, habitat, and internal features if known.

For example, an earthworm has a soft, cylindrical, segmented body and no jointed legs, while a beetle has jointed legs and a hard external skeleton. These differences help us place the earthworm in Annelida and the beetle in Arthropoda.

So, the observed features help scientists group organisms into different categories based on common characteristics and classification criteria.

A scientist would choose cellular organisation as a more fundamental basis because it is a broader and more basic feature of life than xylem and phloem.

• Cell type tells whether an organism is prokaryotic or eukaryotic.
• Level of organisation tells whether it is unicellular or multicellular.

These characters are used to separate very different groups like Monera, Protista, Fungi, Plantae and Animalia. In contrast, xylem and phloem are found only in certain plants and are not useful for classifying all living organisms. Therefore, cellular organisation is a more universal and fundamental criterion.

The organism is single-celled and has a well-defined nucleus, so it is a eukaryote. The presence of multiple cilia suggests a protist like Paramecium. In the five kingdom classification, unicellular eukaryotes are placed in Kingdom Protista.

Diversity of organisms helps maintain the balance and stability of an ecosystem because different organisms perform different roles.

• Plants produce food and oxygen.
• Animals pollinate flowers and disperse seeds.
• Microorganisms recycle nutrients by decomposing dead matter.

These roles keep food chains working and maintain nutrient cycling. If one group becomes less common, others may be affected, so biodiversity helps ecosystems remain healthy and stable.

If all unicellular organisms were grouped into one kingdom, it would create confusion because unicellular organisms are very different from one another.

• Some are prokaryotic like bacteria.
• Some are eukaryotic like amoeba, paramecium and euglena.
• Some are autotrophic, some are heterotrophic, and some show both modes.

So, grouping all unicellular organisms together would ignore important differences in cell structure, nucleus, and mode of nutrition. It would not help us understand their relationships properly.

Viruses are not placed in any of the five kingdoms because they do not have cellular organisation. They are acellular and remain inactive outside a host cell. They contain genetic material, but they do not show the basic characteristics used for the five kingdoms, such as being cellular, having their own metabolism, and independent life processes.

Viruses should be kept outside the five-kingdom system because they are acellular and do not show independent life processes. They become active only inside a host cell.

This shows that scientific classification is evolving: as new knowledge and discoveries come, scientists revise systems to make them more accurate. So, classification is not fixed forever; it changes with new evidence and better understanding.

Viruses have genetic material, but they lack the following features needed for the five-kingdom system:

• Cellular organisation
• Independent metabolism
• Ability to carry out life processes on their own

Because they are acellular and inactive outside a host cell, they do not fit into Monera, Protista, Fungi, Plantae or Animalia. This shows that classification systems have limitations and may not include all forms of life neatly.

Both are non-seed plants, but they differ in important features:

• Bryophytes have a simple body, lack vascular tissues, and need water for reproduction. They are called the amphibians of the plant kingdom.
• Pteridophytes have true roots, stems and leaves and vascular tissues like xylem and phloem. They live better on land, but still need water for reproduction.

So, they are placed in different groups because pteridophytes are more advanced in body organisation and transport system than bryophytes.

Genus has fewer members but more features in common than class.

A classification hierarchy goes from kingdom → phylum → class → order → family → genus → species. As we move downward, groups become smaller and organisms share more characteristics. Therefore, genus is more specific than class and contains fewer organisms with more similarities.

To identify a Protista organism, the scientist should observe these characters:

• It is unicellular
• It is eukaryotic with a true nucleus
• It may be autotrophic or heterotrophic
• It may move using flagella, cilia, or pseudopodia
• It usually lives in water or moist places

So, unicellular eukaryotic organisation and mode of movement are key characters for placing it in Protista.

A unicellular organism should not be kept in Kingdom Fungi just because it is unicellular. The key identification feature for fungi is that they are heterotrophic eukaryotes, usually with a cell wall made of chitin, and they absorb nutrients.

If the organism is unicellular but has a chitinous cell wall and absorptive heterotrophic nutrition, it may be placed under fungi like yeast. So the identification key is unicellular, eukaryotic, heterotrophic, and cell wall made of chitin.

Yeast clearly belongs to Kingdom Fungi. One supporting observation is that it is a heterotrophic eukaryote with a cell wall made of chitin. The chapter also notes that yeast is unicellular but is still placed under fungi because of its chitinous cell wall.

Bacteria would be placed in Kingdom Monera because they are single-celled prokaryotes. A key characteristic justifying this is that they do not have a true nucleus.

Organisms R and Q are both eukaryotic, but they are separated by these criteria:

• R is unicellular, has a true nucleus, moves with flagella, and can show both autotrophic and heterotrophic nutrition. So it fits Protista.
• Q is multicellular, filamentous, has a cell wall, lacks chlorophyll, and grows on dead organic matter. So it fits Fungi.

Thus, they are placed in different kingdoms mainly because of level of organisation, mode of nutrition, and body structure.

Organism S cannot be classified using mode of nutrition alone because nutrition does not tell us enough about its overall identity.

From the table, S is multicellular, has well-differentiated tissues, backbone present, and shows aquatic respiration during early life stage. These features show that it is a vertebrate, and more than one criterion is needed to classify it properly.

So, a single feature like nutrition is not enough; classification needs a combination of cell structure, organisation, and body features.

Organism T lacks cellular organisation because it is acellular. It contains genetic material but remains inactive outside a host cell.

This shows the limitation of classification systems: some forms, like viruses, do not fit neatly into the five kingdoms because they do not show all the basic characteristics of living organisms.

If classification were based only on habitat, very different organisms would be grouped together incorrectly.

For example, organisms living in water could include fish, protists, algae, and even some invertebrates. Similarly, organisms living on land could include plants, insects, earthworms, mammals, and many others.

The scientific consequence would be that we would ignore important differences in cell structure, body organisation, and nutrition. Such classification would not show real relationships among organisms and would be scientifically misleading.

It should be placed under fungi, not animalia.

Reason:

• It is multicellular and eukaryotic.
• It lacks chlorophyll, so it cannot make its own food.
• It absorbs nutrients externally, which is the characteristic mode of nutrition of fungi.

Animals are heterotrophic, but they generally ingest food rather than absorb it externally. So classification criteria place it under Fungi.

(i) Q belongs to Kingdom Fungi. One supporting observation is that it has a filamentous body, cell wall present, no chlorophyll, and grows on dead organic matter.

(ii) P belongs to Kingdom Monera. One supporting characteristic is that it is microscopic and has no true nucleus.

(iii) R and Q are both eukaryotic, but they differ in level of organisation and mode of nutrition. R is unicellular protist with a true nucleus and flagella, while Q is multicellular fungus with filamentous body and absorptive nutrition.

(iv) S cannot be classified using mode of nutrition alone because nutrition does not determine whether it is an invertebrate or vertebrate. Its multicellular body, tissues, backbone, and aquatic respiration are also needed for proper classification.

(v) T lacks cellular organisation; it is acellular. This shows that classification systems have limitations because some entities like viruses do not fit into the five kingdoms.

(vi) If classification were based only on habitat, organisms from the same environment but different groups would be mixed together. For example, water organisms such as P, R, and S would be grouped together even though they belong to different kingdoms. This would hide real differences and make scientific classification inaccurate.

(vii) It should be placed under fungi. It is multicellular, eukaryotic, lacks chlorophyll, and absorbs nutrients from a host externally, which matches fungal nutrition rather than animal nutrition.

From the activity, organisms were to be grouped as active during the day, during the night, or both. The picture includes animals that are active in different time periods, so the correct choice is both during the day and the night.

Scientists can keep track of so many species by using biological classification. They group organisms systematically based on shared features such as external features, cell structure, mode of nutrition, internal structures, reproduction, ecological role, and genetic similarity. This makes the study of biodiversity more organised, helps in identifying and naming organisms, and allows scientists to compare and discuss species using a common system.

Scientists can distinguish the four hornbills by looking at features such as their size, body shape, external appearance, nesting requirements, feeding habits, and the parts of the forest they occupy. The chapter says these birds nest in large, old trees with suitable cavities and feed on specific fruits, so differences in tree size, fruit availability, and other visible characteristics can help separate one species from another.

If the large, old trees disappeared, the hornbills would lose their nesting sites because they nest only in trees with suitable cavities. As a result, their populations would decline, and the forest ecosystem would be affected because hornbills also help in maintaining biodiversity through their role in the food web and seed dispersal patterns.

Scientists would likely discover more knowledge about organisms at the DNA level, about cell structure, and about evolutionary relationships. The chapter says that with advances in microscopes and genetic studies, scientists compare organisms using genetic data and similar DNA indicates common ancestry. This would affect classification by making it more accurate and may lead to changes in classification systems, such as adding new groups or revising old ones, because classification is an ongoing process that changes as new evidence is found.