Diversity In The Living World

Step 1: At rest, a neuron has a resting potential due to unequal distribution of ions across the membrane.
Step 2: When a nerve impulse is initiated, voltage-gated sodium channels open.
Step 3: Sodium ions ( ) move rapidly from the extracellular fluid (ECF) into the intracellular fluid (ICF).
Step 4: This inward movement of sodium ions causes depolarization of the membrane, resulting in the action potential.

Step 1: Animals are eukaryotic organisms and possess DNA enclosed within a nucleus, which helps distinguish them from prokaryotes.
Step 2: Animals uniquely possess specialized tissues such as nervous tissue for impulse conduction and muscle tissue for movement.
Step 3: Cell walls providing structural support are characteristic of plants, fungi, and some protists, but animals lack cell walls. Hence, cell walls with structural support do not help distinguish animals from other forms of life.

Step 1: Eukaryotic cells possess a well-defined nucleus enclosed by a nuclear membrane, so statement (1) is correct.
Step 2: Humans are multicellular eukaryotic organisms, and eukaryotes are found in humans as well as other multicellular organisms; hence statement (2) is correct.
Step 3: Membrane-bound organelles such as the endoplasmic reticulum are characteristic features of eukaryotic cells, so statement (3) is correct.
Step 4: Not all eukaryotes have a cell wall. Animal cells lack a cell wall, making statement (4) incorrect. Therefore, statements (1), (2), and (3) are true.

Step 1: Epithelia are indeed classified based on the shape of cells present in the surface layer, so statement (a) is correct.
Step 2: Transitional epithelium shows variability in the shape of surface cells depending on stretching, so statement (b) is correct.
Step 3: In pseudostratified epithelium, all cells rest on the basement membrane, making statement (c) correct.
Step 4: Desmosomes function mainly in cell-to-cell adhesion and provide mechanical strength, but they do not act as barriers to diffusion. Tight junctions serve that function. Therefore, statement (d) is incorrect.

Step 1: Lynn Margulis and Karlene Schwartz proposed a five-kingdom classification system.
Step 2: The five kingdoms are Prokaryotes, Protoctista, Fungi, Plantae, and Animalia.
Step 3: Plantae includes all multicellular photosynthetic organisms. Therefore, the correct answer is Plantae.

Step 1: Prokaryotic organisms possess genetic material in the form of DNA.
Step 2: Unlike eukaryotes, prokaryotes do not have true histone proteins associated with their DNA.
Step 3: Their DNA is present in a nucleoid region and is not enclosed by a nuclear membrane. Hence, the prokaryotic genetic system has DNA but no histones.

Step 1: In pseudostratified columnar epithelium, all cells rest on the basement membrane, but their nuclei are located at different heights.
Step 2: Due to the varying positions of nuclei, the tissue gives the false appearance of being multilayered, even though it consists of only a single layer of cells.
Step 3: Stratified epithelia, such as stratified squamous or stratified columnar epithelium, are truly multilayered.
Step 4: Transitional epithelium is specialized for stretching and is also truly stratified. Hence, the epithelium described is pseudostratified columnar epithelium.

Different animal groups vary greatly in the number of species that have been described. Step 1: Insecta is the largest animal group, comprising more than half of all known animal species due to their high adaptability and reproductive rates.
Step 2: Mollusca is the second-largest group, including snails, clams, octopuses, and related organisms.
Step 3: Aves (birds) have fewer species compared to insects and molluscs but more than mammals.
Step 4: Mammalia has the least number of described species among the given groups. Hence, the correct descending order is:

Step 1: Cell theory states that all living organisms are composed of cells, and the cell is the basic structural and functional unit of life.
Step 2: Statement I is incorrect because animal cells do not have a cell wall.
Step 3: Statement II is incorrect because not all living cells directly require glucose; some organisms use other sources of energy or synthesize glucose themselves.
Step 4: Statement III correctly represents a fundamental principle of cell theory. Therefore, only statement III is correct.

Step 1: Animal cells possess a centrosome, which contains centrioles involved in spindle formation during cell division.
Step 2: Plant cells lack centrosomes and centrioles.
Step 3: Plastids and large central vacuoles are characteristic of plant cells.
Step 4: Golgi bodies are present in both plant and animal cells. Hence, the distinguishing feature is the presence of a centrosome in animal cells.

Step 1: Biological classification arranges organisms into hierarchical categories based on similarities.
Step 2: The correct descending order from highest to lowest is:
Step 3: From the given categories, the correct order is: Hence, option (d) is correct.

Step 1: Analyse each statement carefully.
Option (A): Eukaryotic cells possess membrane-bound organelles such as nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, etc. True
Option (B): Prokaryotic cells do \emph{not} have a true nucleus; their genetic material lies in a nucleoid region. False
Option (C): Although eukaryotic cells do contain genetic information, this statement is too general and not distinguishing, since all living cells (including prokaryotes) possess genetic material. Not the correct choice here.
Option (D): Prokaryotic cells are surrounded by a cell membrane, but this feature is also common to all cells and is not the key distinguishing statement in this question. Not the best answer.
Step 2: Identify the most accurate and distinguishing statement. The defining and universally accepted true statement among the options is:
Hence, the correct answer is

Step 1: Understand the context of biological nomenclature. In biological classification, the names of authors who describe or publish a new species are cited along with the scientific name, following specific conventions.
Step 2: Recall the meaning of common author-linking terms.
in — used when a name is published within another author’s work
ex — used when one author proposed the name but another validly published it
emend — used when an author later modifies (emends) the original description
et — a Latin word meaning \textit{“and”}, used to connect the names of two or more joint authors
Step 3: Identify the correct term. Since the question asks for the word used to link the names of two or more authors, the correct epithet is et.
Hence, the correct answer is

Step 1: Recall the function of squamous epithelium. Squamous epithelium is made up of thin, flat cells and is specially adapted for:
diffusion,
filtration,
exchange of gases.
Step 2: Examine each option.
Kidney: Tubules are lined by cuboidal epithelium.
Pancreatic duct: Lined mainly by cuboidal/columnar epithelium.
Lung alveoli: Lined by simple squamous epithelium to allow rapid diffusion of and .
Heart: Inner lining (endocardium) is specialized endothelium, not generally cited in this context.
Step 3: Identify the correct structure. Since gas exchange requires a very thin lining, squamous epithelium is characteristically found in lung alveoli.
Hence, the correct answer is

Step 1: Examine each kingdom with respect to cell wall and mode of nutrition.
Plantae: Have cell walls (cellulose) but are autotrophic (photosynthetic).
Fungi: Have cell walls (mainly chitin) and are entirely heterotrophic.
Animalia: Are heterotrophic but do not have cell walls.
Protista: May or may not have cell walls, and can be autotrophic or heterotrophic.
Step 2: Identify the kingdom satisfying both conditions. Only Fungi possess:
a definite cell wall, and
exclusively heterotrophic mode of nutrition.
Hence, the correct answer is