Exploration Class 9 Science Chapter 12: Patterns in Life: Diversity and Classification — NCERT Solutions

Explanation: The concept map branches step by step, and every branching point is one criterion. The first split is cell type: prokaryotes, whose nucleus is primitive and not bound by a membrane, form Monera (bacteria, archaea, cyanobacteria), while the rest are eukaryotes with a membrane-bound nucleus. The eukaryotes are then split by level of organisation into unicellular forms, which make up Protista (Amoeba, Paramecium, Chlamydomonas, Euglena), and multicellular forms. The multicellular branch splits on cell structure, separating those with a cell wall from those without a cell wall (Animalia). Finally, mode of nutrition and ecological role separates the walled group into heterotrophic decomposers with a chitin wall (Fungi) and autotrophic producers with a cellulose wall that carry out photosynthesis (Plantae).

Explanation: The map applies four criteria in a fixed order, and the two given here are the first and the third. Cell type is the broadest cut because the absence of a membrane-bound nucleus is a fundamental difference, so it removes the prokaryotes (Monera) in a single step. Cell structure, the presence or absence of a cell wall, is applied only within the multicellular eukaryotes, where it separates the walled Fungi and Plantae from the wall-less Animalia. These two criteria alone are not sufficient, however: Protista may or may not have a cell wall, so it is caught only by the level of organisation criterion (unicellular), and Fungi and Plantae both have a cell wall, so they are told apart only by the material of that wall (chitin versus cellulose) and by mode of nutrition (decomposer versus photosynthetic producer). So the two specific criteria agree with the map but are incomplete, since a workable classification needs all four criteria acting together.

Explanation: The Sangai is endemic to a single habitat, so conserving the deer means conserving the phumdis it lives on. Phumdis are floating mats of soil and vegetation that must sink low enough in the dry season to touch the lake bed and take up nutrients; when water levels are held artificially high the mats grow thin and can no longer bear the deer's weight, so restoring the natural cycle of water levels is the single most important measure. Because the whole population is confined to Keibul Lamjao National Park, one disease outbreak, fire or flood could wipe it out, which is why captive breeding and establishing a second population elsewhere act as insurance against extinction. Anti-poaching patrols and legal protection address direct killing, while controlling encroachment, fishing huts, pollution and invasive weeds protects the quality of the habitat itself. Local participation matters because conservation fails if the people who depend on the lake are given no alternative livelihood.

Explanation: Cnidarians such as hydra have a sac-like gastrovascular cavity with only one opening that works as both mouth and anus, which is an incomplete digestive tract. Since the same opening is used both ways, the animal must expel undigested remains before it can swallow its next meal, so feeding is interrupted rather than continuous and the rate of food intake is limited; incoming food also mixes with waste in the same cavity. A one-way tube can be divided into specialised regions such as stomach and intestine that work like an assembly line, each secreting its own enzymes and absorbing at its own stage, but a single-opening sac cannot, so digestion is slower and less efficient. Cnidarians are only at the tissue level of organisation and have no circulatory system, so digested food has to reach every cell by diffusion. That restricts them to a thin, small body and prevents the evolution of larger and more complex forms.

Explanation: At a glance the four birds look like one kind of hornbill, so without classification the biodiversity of the Pakke Tiger Reserve would be badly undercounted. By comparing characteristics such as size, plumage and the shape of the bill and casque, scientists establish that these are four distinct species, which is a real measure of the species richness of that forest. Placing all four in the same family at the same time communicates that they share a common ancestor and a common body plan, so classification shows diversity and relatedness together. Each species then receives a unique scientific name, which lets sightings and records from anywhere in the world be pooled without confusion. Finally, once the species are separated, the habits, food and threats of each can be studied on their own, so a species that is endangered can be identified and given targeted protection instead of staying hidden inside a vague group.

Explanation: (i) Millions of species cannot be remembered one by one, so scientists group them by shared characteristics into a nested hierarchy of kingdom, phylum, class, order, family, genus and species, and give each species a unique binomial scientific name, so records stay unambiguous and any newly found species can be slotted into the system. (ii) The four hornbills share the general hornbill body plan, so scientists rely on finer characters: the Great hornbill is very large with a bright yellow bill and a broad casque, the Rufous-necked hornbill has a rufous head and neck, the Oriental Pied hornbill is the smallest and is black and white with a black-and-white casque, and the Wreathed hornbill has ridges or wreaths at the base of its bill and a coloured throat pouch. (iii) Hornbills nest only in natural cavities that form in large, old trees, so if those trees vanish there are no nest sites, breeding stops and the population crashes. Hornbills are also major seed dispersers and are called the farmers of the forest, so their decline means fewer seeds are carried away from parent trees and forest regeneration slows down. Old trees are food sources and homes for many other birds, mammals, insects and epiphytes as well, so losing them removes habitat for a large part of the community and disturbs the balance of the whole forest.

Explanation: A forest is not uniform, since light, moisture, canopy height and above all food differ from place to place, so each species settles where the conditions and resources suit it, that is, in its own niche. The case study shows this directly: the four hornbill species occur in different parts of the reserve according to where fruit is available, which also reduces competition between them and lets all four coexist in the same forest. The tightest link is between the hornbills and the large old trees, which supply the fruit they eat and the natural cavities in which they nest. In return the hornbills swallow the fruit and drop the seeds far from the parent tree, so new trees come up across the forest. Neither partner would do well without the other, and this mutual dependence explains why the distribution of the birds tracks the distribution of the trees.

Explanation: Figure 12.2 is one forest scene split down the middle, the left half lit as day and the right half dark as night, so where an animal is drawn tells you when it is active. On the bright day side the spotted deer, leopard and lion-tailed macaque are at the left among the trees and near the water, the sloth bear walks on the grassy bank, the grey langur sits high on a branch, a crow flies in the open sky, a dragonfly and butterflies are in the air, and a myna and a small orange-yellow bird perch on rocks at the water's edge, so all of these are diurnal. On the dark night side bats fly in the air, an owl perches on a branch with a snake coiled along the same branch, fireflies glow, a slow loris clings to a branch at the right, a porcupine and a civet move on the forest floor, a frog sits near the bank and a gharial lies in the stream, so all of these are nocturnal. The tiger and the rabbit are drawn near the middle, at the boundary of the two halves, which matches their real habit of being active by day as well as by night, mainly around dawn and dusk. Set out as a table with the columns Animal, Location in the scene and Time of activity, one row per animal, the pattern becomes clear: the same forest supports two different sets of animals in turn, so its space and food are shared across the 24-hour cycle instead of being competed for by everyone at once.

Explanation: Characteristics are passed from parents to offspring, so when many organisms share the same fundamental features, the simplest explanation is that they all inherited those features from one ancestral population from which they later diverged. This is exactly the reasoning behind biological classification: organisms grouped together because of shared characteristics generally turn out to share ancestry, so the groups reflect evolutionary relationships rather than mere convenience. The more fundamental the shared feature, such as being made of cells or using DNA as the genetic material, the older the common ancestor it points to. Similarity by itself is not conclusive, though, because organisms that are not closely related can evolve similar features when they live in similar environments, as with the streamlined shape of a fish and a dolphin. That is why scientists compare many characteristics together, and today also compare DNA, before concluding that organisms share an ancestral origin.

Explanation: Poriferans are sessile filter feeders in which water is drawn in through many tiny pores called ostia, passes through canals lined by collar cells whose flagella drive the current and trap food particles, and leaves through a large opening called the osculum. All their essential functions ride on that water current, namely food capture, gas exchange by diffusion across the cells, and removal of waste, and not one of them can work in air. Sponges have no organs, no lungs or tracheae, no circulatory or excretory system and no waterproof covering, so on land their cells would lose water at once and die. Their soft body is also held up by the surrounding water and by a skeleton of spicules, so out of water it would collapse under its own weight, and being fixed in one place they could not move to find water either. Land animals need a moist respiratory surface protected inside the body, a way to conserve water and a skeleton that works against gravity, and the sponge body plan has none of these, which is why sponges are confined to aquatic, mostly marine, habitats.

Explanation: Every species survives only within a certain range of temperature, moisture and other conditions, so when the climate changes faster than species can adapt they must shift their range, usually towards the poles or up mountains, or perish. Species that cannot move or have nowhere left to go, such as endemic species on mountain tops and islands or those tied to one habitat like the Sangai on its phumdis, are lost first, so specialists disappear while a few tolerant generalists spread. Climate change also disturbs timing: if flowering, insect emergence, breeding and migration shift by different amounts, pollinators and flowers or birds and their prey no longer match, and these broken interactions damage the whole food web. Warmer and altered conditions let pests, disease-carrying organisms and invasive species enter regions that once excluded them, adding further pressure on native species. On top of this, more frequent droughts, floods, cyclones and forest fires, together with melting ice, rising sea level and warmer, more acidic oceans that bleach coral reefs, destroy habitats outright, so ecosystems lose species, food chains shorten and the ecosystem becomes less stable and slower to recover.

Explanation: Visible features are outcomes, whereas the genetic material is the cause, since DNA carries the instructions that decide how an organism is built, how it works, how it develops from a single cell and what it passes to the next generation, so studying genes explains an organism at its most fundamental level instead of merely describing its surface. DNA is also universal, because essentially every living thing from bacteria to humans uses the same genetic material and the same code, which is itself strong evidence that all life shares a common origin and which gives one common yardstick that can be applied to every organism. Since DNA is a long sequence, it provides a huge number of characters to compare, far more than the handful of visible features, so it is detailed enough to separate two species that look almost identical, such as closely related hornbills, and to detect relationships between organisms whose appearance is completely different. It also cuts through misleading resemblance, because unrelated organisms that evolved similar forms in similar habitats can be told apart by their genes, which makes classification reflect true ancestry. Finally, genetics explains heredity and variation, that is, why offspring resemble their parents and yet differ from them, which is the basis of evolution, of plant and animal breeding and of understanding inherited disease.

Explanation: Biodiversity is far too vast to grasp organism by organism, so without a system the sheer number of species remains a vague impression rather than real knowledge. Classification solves this by grouping organisms with shared characteristics into a nested hierarchy from kingdom down to species, so an enormous variety is reduced to a manageable number of groups that can be studied and compared, which makes the study systematic. It also measures the scope of diversity honestly, because careful comparison shows that organisms which look alike are often several distinct species, so the true richness is revealed instead of undercounted, and each species is fixed by a unique scientific name so that records everywhere refer to the same organism. Since the groups rest on characteristics inherited from common ancestors, the hierarchy also shows how organisms are related to one another and how life evolved, turning a bare list into a pattern that carries meaning. Finally, once species are distinguished and named, any organism can be identified and rare or threatened species can be recognised and protected, so classification is the tool that turns the overwhelming variety of life into something we can comprehend and conserve.

Explanation: In a unicellular organism such as Amoeba or Paramecium the entire body is one cell, and every function is performed by organelles inside it: the cell membrane and contractile vacuole for exchange and water balance, food vacuoles for digestion, pseudopodia or cilia for movement and mitochondria for respiration. This works only because the cell is microscopic, so its surface area is very large in relation to its volume and no point inside lies far from the surface, which lets oxygen, food and wastes be exchanged with the surroundings and distributed by simple diffusion fast enough to keep it alive. As a body grows, volume increases as the cube of its size (length³) while surface increases only as the square (length²), so the surface-area-to-volume ratio falls sharply and diffusion becomes far too slow to supply cells deep inside; a human could never survive as one giant cell. Multicellular organisms therefore keep their cells small and increase their number instead, and those cells divide the work between them, so that similar cells form tissues, tissues form organs and organs form organ systems, each dedicated to one function, such as lungs for gas exchange and blood for transport. A specialised cell performs its own task far more efficiently than a general-purpose cell could, and this division of labour is what allows multicellular organisms to become large, complex and long-lived, so it is not that they need billions of cells to do the same job, but that size and complexity force a different and more efficient solution.

Explanation: The presence of jointed legs is the most defining characteristic of the phylum Arthropoda, to which insects belong. While both insects and earthworms can have bilateral symmetry, only insects have jointed appendages.

Explanation: The absence of a rigid cell wall is a fundamental characteristic of animal cells, distinguishing them from plants, fungi, and bacteria. All other options are incorrect for classifying a sponge as an animal.