Chapter 12: Patterns in Life: Diversity and Classification

Biodiversity means the variety of living organisms found on Earth. It includes different kinds of plants, animals, fungi, bacteria and microorganisms.

Biodiversity is seen in different habitats such as forests, deserts, oceans, rivers, mountains and grasslands. It is important because every organism plays a role in nature. For example, plants produce food and oxygen, bacteria and fungi decompose dead matter, and birds, bees and bats help in pollination.

Thus, biodiversity means the rich variety of life forms and their relationships with one another and their environment.

Grouping of organisms helps us understand diversity in an organised and systematic way.

It helps us to:

• Identify organisms easily.

• Understand similarities and differences among organisms.

• Know how organisms are related to one another.

• Study millions of organisms in smaller and simpler groups.

• Understand their structure, nutrition, reproduction and ecological role.

• Recognise newly discovered organisms.

• Support biodiversity conservation.

For example, when animals are grouped as vertebrates and invertebrates, we can easily understand which animals have a backbone and which do not.

Thus, grouping makes the study of biodiversity easier and more scientific.

Plants and animals are classified on the basis of their features, body structure and evolutionary relationships.

Plants are classified on the basis of:

• Presence or absence of true roots, stems and leaves

• Presence or absence of vascular tissues

• Presence or absence of seeds

• Whether seeds are naked or enclosed in fruits

• Presence or absence of flowers

• Dependence on water for reproduction

Examples of plant groups are Thallophyta, Bryophyta, Pteridophyta, Gymnosperms and Angiosperms.

Animals are classified on the basis of:

• Presence or absence of notochord

• Presence or absence of backbone

• Level of body organisation

• Body symmetry

• Presence or absence of body cavity

• Presence of segmentation

• Type of skeleton

• Habitat and mode of reproduction

Examples of animal groups are Porifera, Cnidaria, Platyhelminthes, Nematoda, Annelida, Arthropoda, Mollusca, Echinodermata and Vertebrates.

Classification helps in farming by helping farmers and scientists identify useful and harmful organisms.

It helps in:

• Identifying pest-resistant crop varieties.

• Selecting crops that can tolerate drought or poor soil.

• Recognising harmful pests, insects and disease-causing organisms.

• Identifying useful organisms such as Rhizobium, which helps in nitrogen fixation.

• Identifying decomposers that improve soil fertility.

• Conserving crop diversity to reduce the risk of crop failure.

• Improving food security.

For example, if scientists classify and identify a pest correctly, they can suggest suitable methods to control it. Similarly, classification of crop varieties helps farmers choose crops suitable for a particular climate or soil.

Yes, if many organisms share common features, they could also share a common ancestry.

Similar features in organisms may indicate that they evolved from a common ancestor. For example, different vertebrates such as fish, birds, reptiles and mammals have a backbone. This common feature suggests that they may have evolved from a common ancestral group.

However, scientists do not depend only on external features. They also study internal structure, cell structure, fossils and DNA to understand common ancestry more accurately.

Thus, common features can give important clues about evolutionary relationships.

A single-celled organism can carry out all life processes because its one cell performs all necessary functions.

In unicellular organisms, a single cell carries out functions such as:

• Nutrition

• Respiration

• Excretion

• Movement

• Response to stimuli

• Reproduction

For example, Amoeba takes in food, digests it, removes waste and reproduces using only one cell.

In multicellular organisms like humans, the body is made of billions of cells. These cells become specialised to perform different functions. For example, nerve cells carry messages, muscle cells help in movement and blood cells transport oxygen.

Thus, a unicellular organism performs all life processes within one cell, while multicellular organisms divide these functions among specialised cells, tissues and organs.

Features such as simple root-like structures, stem-like structures, leaf-like structures and spores reduce the dependence of plants on water to some extent.

In bryophytes, root-like structures called rhizoids help in attachment and absorption. Their body is more developed than algae, so they can live on moist land. However, they still require water for reproduction because their male reproductive cells need water to reach the female reproductive cells.

In pteridophytes, the presence of true roots, stems, leaves and vascular tissues reduces dependence on water for transport. But they also need water for reproduction.

Thus, features like rhizoids, simple body differentiation and vascular tissues help plants live on land, but bryophytes and pteridophytes still require moist conditions for reproduction.

Taller plants need specialised transport tissues because water, minerals and food have to be carried over long distances within the plant body.

Specialised transport tissues are:

• Xylem — transports water and minerals from roots to leaves.

• Phloem — transports food prepared in leaves to other parts of the plant.

In small plants, materials can move from cell to cell over short distances. But in taller plants, this is not enough because roots, stems and leaves are far apart.

Therefore, taller plants need xylem and phloem for efficient transport and proper growth.

Seeds and fruits help plants survive and spread to new places.

Seeds help plants because:

• They protect the developing embryo.

• They contain stored food for the young plant.

• They allow plants to survive unfavourable conditions.

• They reduce dependence on water for reproduction.

Fruits help plants because:

• They protect seeds.

• They help in seed dispersal.

• They attract animals and birds, which carry seeds to new places.

Seeds may be dispersed by wind, water, animals, birds and insects. This helps plants grow in new habitats and reduces competition with the parent plant.

Thus, seeds and fruits help plants survive, reproduce and spread successfully in different environments.

The beetle’s hard external skeleton is called an exoskeleton. It helps the beetle survive in many ways.

The exoskeleton:

• Protects the soft internal body parts.

• Reduces water loss from the body.

• Supports powerful muscles.

• Helps in movement.

• Protects the beetle from injury and predators.

• Helps it survive in dry and exposed environments.

An earthworm has a soft segmented body and usually needs moist soil to survive. But a beetle’s exoskeleton gives it better protection and helps it live in different environments, including dry land.

The term biodiversity does not relate only to the variety of organisms. It also includes other elements.

Biodiversity includes:

• Variety of organisms

• Variety of genes within organisms

• Variety of habitats

• Variety of ecosystems

• Interactions among organisms

• Ecological roles of organisms

For example, biodiversity includes not only plants and animals, but also their roles in nature, such as pollination, decomposition, food chains, seed dispersal and nutrient cycling.

Thus, biodiversity includes the variety of life as well as the relationships among organisms and their environment.

If I find a new organism in a pond, I will observe the following features to classify it:

• Whether it is unicellular or multicellular

• Whether it has a true nucleus or not

• Whether it has a cell wall

• Its mode of nutrition, whether autotrophic or heterotrophic

• Its body structure

• Its method of movement

• Its method of reproduction

• Its ecological role, such as producer, consumer or decomposer

• Its similarity with already known organisms

These features are important because classification is based on cell type, cell structure, level of organisation, mode of nutrition and ecological role.

For example, if the organism is unicellular and has a true nucleus, it may belong to Protista. If it is unicellular and lacks a true nucleus, it may belong to Monera.

Genetic studies provide deep information about living beings because they study DNA, which carries hereditary information.

DNA contains instructions for:

• Growth

• Development

• Body structure

• Functioning of cells

• Inherited features

By comparing DNA, scientists can understand how closely organisms are related. Organisms with similar DNA are likely to have a common ancestry.

Genetic studies also help scientists:

• Identify organisms accurately.

• Understand evolutionary relationships.

• Improve classification systems.

• Study inherited features.

• Discover differences that may not be visible externally.

Thus, genetic studies provide deeper information than only external features because they reveal relationships at the molecular level.

Changes in climate can affect biodiversity by changing the conditions needed for organisms to survive.

Climate change may cause:

• Increase in temperature

• Change in rainfall patterns

• Droughts

• Floods

• Melting of ice

• Habitat loss

• Changes in flowering and breeding seasons

These changes can affect plants, animals and microorganisms. Some species may not be able to adapt quickly and may decline in number or become extinct.

For example, if temperature increases, organisms adapted to cold regions may lose their habitat. If rainfall decreases, plants that need moist conditions may not survive. This can also affect animals that depend on those plants.

Thus, climate change can disturb food chains, reduce habitats and threaten biodiversity.

The correct option is:

(ii) Body with jointed legs

Reason:

• Insects belong to the group Arthropoda.

• The main characteristic of arthropods is the presence of jointed appendages or jointed legs.

• Earthworms belong to Annelida and have a soft, segmented body but do not have jointed legs.

So, the presence of jointed legs confirms that the animal is an insect.

The correct option is:

(iii) Presence of a cell membrane

Reason:

• Sponges are placed in Kingdom Animalia because they are multicellular heterotrophic organisms.

• Animal cells have a cell membrane but do not have a cell wall.

• Sponges do not photosynthesise and do not have a cell wall.

• Therefore, the presence of cell membrane supports their classification under the animal kingdom.

Let us take two common animals: earthworm and butterfly.

Earthworm:

• It has a soft and cylindrical body.

• Its body is divided into many segments.

• It does not have jointed legs.

• It lives in moist soil.

• It belongs to Annelida.

Butterfly:

• It has a segmented body.

• It has jointed legs.

• It has wings.

• It has a hard external covering called exoskeleton.

• It belongs to Arthropoda.

Conclusion: These features help us distinguish between the two animals. Segmentation, jointed legs, wings, body covering and habitat help us place animals into different groups.

A scientist would choose cellular organisation as a more fundamental characteristic because it applies to all living organisms, while xylem and phloem are found only in some plants.

Reasons:

• Cellular organisation tells us whether an organism is unicellular or multicellular.

• It also tells us whether the cell is prokaryotic or eukaryotic.

• These features are basic and are found across all kingdoms.

• On the other hand, xylem and phloem are vascular tissues found only in higher plant groups like pteridophytes, gymnosperms and angiosperms.

• They cannot be used to classify bacteria, protists, fungi or animals.

Therefore, cellular organisation is a broader and more fundamental basis of classification than the presence of xylem and phloem.

The organism would most likely belong to Kingdom Protista.

Reasons:

• It is single-celled, so it is unicellular.

• It has a well-defined nucleus, so it is eukaryotic.

• It has cilia, which help in movement.

• These features are commonly found in protists such as Paramecium.

Therefore, the organism is most likely a protist, probably similar to Paramecium.

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

Importance of diversity in an ecosystem:

• Plants produce food and oxygen.

• Animals act as consumers and help in pollination and seed dispersal.

• Fungi and bacteria decompose dead organisms and recycle nutrients.

• Predators control the population of prey.

• Pollinators help plants reproduce.

• Different organisms form food chains and food webs.

If one species disappears, other organisms that depend on it may also be affected. Therefore, biodiversity makes ecosystems more stable and helps them recover from disturbances.

If all unicellular organisms were grouped into a single kingdom, many problems would arise because unicellular organisms are not all alike.

Problems:

• Some unicellular organisms are prokaryotic, like bacteria.

• Some are eukaryotic, like Amoeba and Paramecium.

• Some are autotrophic, like Chlamydomonas.

• Some are heterotrophic, like Amoeba.

• Some have a cell wall, while others do not.

• Some have very different cellular structures and genetic features.

For example, bacteria and Amoeba are both unicellular, but bacteria do not have a true nucleus, while Amoeba has a true nucleus.

Thus, grouping all unicellular organisms together would ignore important differences in cell structure, nutrition and evolutionary relationships.

Viruses are not placed in any of the five kingdoms because they do not show all characteristics of living organisms.

Reasons:

• Viruses are acellular, meaning they are not made of cells.

• They do not have cellular organisation.

• They do not perform life processes independently.

• They remain inactive outside a host cell.

• They can reproduce only inside a living host cell.

• The five kingdom classification is based mainly on cellular features, such as cell type, cell structure and level of organisation.

Since viruses lack cellular organisation, they do not fit into Monera, Protista, Fungi, Plantae or Animalia.

I would keep viruses outside the five kingdom system but mention them as a separate acellular biological entity.

Justification:

• Viruses contain genetic material, but they are not made of cells.

• They do not have cytoplasm, cell organelles or cellular organisation.

• They cannot reproduce independently.

• They become active only inside a host cell.

• The five kingdom classification is based on cellular organisation, so viruses do not fit properly in it.

What this shows:

This shows that scientific classification is not fixed forever. It changes when scientists discover new information. As knowledge about DNA, cell structure and microorganisms increases, classification systems are revised and improved.

Thus, viruses show the limitations of the five kingdom classification and the evolving nature of science.

Viruses do not fit into the five kingdom system because they lack some basic features used for classification.

Features that prevent viruses from fitting into five kingdoms:

• They are acellular.

• They do not have a true cell structure.

• They do not have cytoplasm or cell organelles.

• They cannot carry out metabolism independently.

• They cannot reproduce outside a host cell.

• They remain inactive outside living cells.

What this tells us:

This tells us that classification systems have limitations. A system based on cellular organisation cannot properly classify acellular entities like viruses. It also shows that classification systems must change as scientific knowledge increases.

Bryophytes and pteridophytes are placed in different groups because they have different levels of body organisation.

Bryophytes:

• They do not have true roots, stems and leaves.

• They have root-like structures called rhizoids.

• They do not have vascular tissues.

• They need water for reproduction.

• Examples: Moss, Marchantia

Pteridophytes:

• They have true roots, stems and leaves.

• They have vascular tissues: xylem and phloem.

• They do not produce seeds or flowers.

• They also need water for reproduction.

• Example: Fern

Conclusion:

Even though both groups lack flowers and seeds, pteridophytes are more advanced because they have true roots, stems, leaves and vascular tissues. Therefore, they are classified separately.

Genus has fewer members but more features in common.

Explanation:

• Classification moves from broad groups to specific groups.

• The hierarchy is:

Kingdom → Phylum → Class → Order → Family → Genus → Species

• Class is a broader category and includes many organisms.

• Genus is a smaller and more specific category.

• Organisms in the same genus are more closely related and share more common features.

For example, tiger and lion belong to the genus Panthera. They share many similarities, so genus has fewer members but more common features than class.

The scientist should observe the organism’s cell type and level of organisation.

Characters that identify it as Protista:

• It should be unicellular.

• It should have a true nucleus, meaning it is eukaryotic.

• It may show locomotion.

• It may show autotrophic nutrition.

• It may live in water or moist places.

Explanation:

Some protists, such as Euglena, show both locomotion and autotrophic nutrition. Euglena moves with the help of a flagellum and can perform photosynthesis in light.

Therefore, if the organism is unicellular, eukaryotic, motile and autotrophic, it can be placed in Kingdom Protista.

To identify a unicellular eukaryotic organism as fungi, I would suggest checking the following features:

Identification key:

• It should be unicellular and eukaryotic.

• It should have a cell wall made of chitin.

• It should be heterotrophic.

• It should absorb nutrients from organic matter.

• It should not perform photosynthesis.

• It may reproduce by budding or spores.

Example:

Yeast is unicellular and eukaryotic, but it is placed in Kingdom Fungi because it has a chitin cell wall and shows heterotrophic nutrition.

Therefore, the presence of a chitin cell wall and absorptive heterotrophic nutrition are important keys for placing a unicellular organism in Kingdom Fungi.

Organism Q clearly belongs to Kingdom Fungi.

Supporting observation:

• It is multicellular.

• It has a filamentous body.

• It has a cell wall.

• It has no chlorophyll.

• It grows on dead organic matter.

These features show that organism Q is a fungus because fungi are heterotrophic and absorb nutrients from dead and decaying matter.

Organism P would be placed in Kingdom Monera.

Justification:

• It is microscopic.

• It has no true nucleus.

• It has a rigid cell covering.

• It can survive in high salinity and temperature.

The absence of a true nucleus shows that it is a prokaryotic organism, which is the main feature of Kingdom Monera.

Organisms R and Q are both eukaryotic, but they are placed in different kingdoms because of differences in their organisation, nutrition and structure.

Organism R:

• It is unicellular.

• It has a true nucleus.

• It moves using flagella.

• It has a contractile vacuole.

• It shows photosynthesis in light and heterotrophic nutrition in the absence of light.

• It belongs to Kingdom Protista.

Organism Q:

• It is multicellular.

• It has a filamentous body.

• It has a cell wall.

• It has no chlorophyll.

• It grows on dead organic matter.

• It belongs to Kingdom Fungi.

Conclusion:

R is placed in Protista because it is a unicellular eukaryote, while Q is placed in Fungi because it is a multicellular, absorptive heterotroph with a cell wall.

Organism S cannot be classified using the mode of nutrition alone because many organisms share the same mode of nutrition.

Given features of S:

• It is multicellular.

• It has well-differentiated tissues.

• It has a backbone.

• It shows aquatic respiration during its early life stage.

Most animals are heterotrophic, so mode of nutrition alone would only tell us that S is an animal. It would not tell us whether it is a fish, amphibian, reptile, bird or mammal.

The presence of a backbone is a more useful feature. Aquatic respiration during early life suggests that it may be an amphibian, such as a frog.

Therefore, classification requires multiple features such as body structure, backbone, respiration, reproduction and habitat, not just mode of nutrition.

Organism T lacks cellular organisation.

Explanation:

• T is acellular.

• It contains genetic material.

• It remains inactive outside a host cell.

• These features are similar to viruses.

The five kingdom classification is based on features such as cell type, cell structure, level of organisation and mode of nutrition. Since organism T is not made of cells, it cannot be placed in any of the five kingdoms.

Conclusion:

This reveals that classification systems have limitations. They may not include all biological entities, especially those that do not fit the basic criteria of the system.

If classification were based only on habitat, many unrelated organisms would be incorrectly grouped together.

Examples:

• Organisms living in water, such as fish, algae, Amoeba and aquatic bacteria, would be grouped together even though they are very different.

• Organisms living in the digestive tract of animals, such as bacteria, parasitic worms and viruses, might be placed in one group.

• Organisms living in damp soil, such as fungi, earthworms and bacteria, might be grouped together.

Scientific consequences:

• Important differences in cell structure would be ignored.

• Prokaryotes and eukaryotes could be wrongly placed together.

• Autotrophs and heterotrophs could be mixed incorrectly.

• Evolutionary relationships would not be clear.

• Identification and study of organisms would become confusing.

Therefore, classification based only on habitat is not scientific enough. It should be based on cell type, body organisation, nutrition, reproduction and evolutionary relationships.

The organism should be placed under Kingdom Fungi.

Reasons:

• It is multicellular.

• It is eukaryotic.

• It lacks chlorophyll, so it cannot prepare its own food.

• It absorbs nutrients from a host externally.

• Absorptive nutrition is a key feature of fungi.

Animals are also multicellular and eukaryotic, but they usually ingest food and digest it internally. Fungi absorb nutrients from dead matter, hosts or other organic sources.

Therefore, based on lack of chlorophyll and external absorption of nutrients, the organism should be placed under Kingdom Fungi.

In the future, scientists may discover new information about organisms through advanced studies of DNA, genes, proteins, fossils, cell structure and microorganisms.

Scientists may come up with new knowledge about:

• Genetic relationships among organisms

• Evolutionary history of species

• Newly discovered microorganisms

• Unknown species in oceans, forests and extreme environments

• Better fossil evidence

• Differences between organisms at the molecular level

• New links between extinct and living organisms

Effect on classification system:

• Classification systems may become more accurate.

• Some organisms may be moved from one group to another.

• New groups or categories may be created.

• Relationships among organisms may be understood more clearly.

• Classification may become more based on DNA and evolutionary relationships than only visible features.

Conclusion: Scientific classification keeps changing as new knowledge is discovered. This shows that science is a continuous process of observation, reasoning, evidence and improvement.