Animal KingdomClass 11 Biology NCERT Solutions
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Q1Exercises
What are the difficulties that you would face in classification of animals, if common fundamental features are not taken into account?
Solution
If common fundamental features such as level of organisation, symmetry, nature of coelom, segmentation, and presence of notochord were not taken into account, the classification of animals would face several significant difficulties:
- Lack of a Scientific Basis: The classification would become arbitrary and superficial, likely based on non-fundamental characters like habitat (aquatic, terrestrial), mode of nutrition, or colour. This would not reflect the true evolutionary relationships among animals.
- Complexity and Confusion: With over a million described species, creating a logical and manageable system without fundamental criteria would be nearly impossible. It would lead to a chaotic and confusing arrangement where unrelated animals might be grouped together, and closely related ones might be placed far apart.
- Inability to Place New Species: Assigning a systematic position to newly discovered species would be extremely difficult. Without a clear framework based on fundamental features, there would be no objective way to determine where a new species fits within the animal kingdom.
- No Reflection of Evolutionary Relationships: A classification based on fundamental features helps in understanding the evolutionary pathways and relationships (phylogeny) between different groups. Without it, the classification system would fail to provide any insight into how different animal groups have evolved.
Q2Exercises
If you are given a specimen, what are the steps that you would follow to classify it?
Solution
To classify a given animal specimen, I would follow a systematic approach by examining its fundamental features in a hierarchical order, as described in the chapter:
- Level of Organisation: First, I would determine the level of body organisation. Is it at the cellular level (like sponges), tissue level (like coelenterates), organ level (like platyhelminthes), or organ-system level (like annelids, arthropods, etc.)?
- Symmetry: Next, I would observe its body symmetry. Is the animal asymmetrical (sponges), radially symmetrical (coelenterates, ctenophores), or bilaterally symmetrical (platyhelminthes to chordates)?
- Germinal Layers: I would determine if the animal is diploblastic (having two germ layers, ectoderm and endoderm, like coelenterates) or triploblastic (having three germ layers, including mesoderm, like platyhelminthes to chordates).
- Nature of Coelom: For triploblastic animals, I would identify the nature of the body cavity (coelom). Is the animal an acoelomate (no body cavity, like platyhelminthes), a pseudocoelomate (false coelom, like aschelminthes), or a coelomate (true coelom, like annelids to chordates)?
- Segmentation: I would check for the presence of metameric segmentation, where the body is divided into repeating segments (like in annelids and arthropods).
- Presence of Notochord: I would look for the presence of a notochord at any stage of its life. If present, it is a chordate; if absent, it is a non-chordate.
- Specific Phylum/Class Features: Finally, based on the above characteristics, I would look for specific distinguishing features to place it into a particular phylum and class. For example, jointed appendages for Arthropoda, a water vascular system for Echinodermata, or feathers and a beak for Aves.
Q3Exercises
How useful is the study of the nature of body cavity and coelom in the classification of animals?
Solution
The study of the nature of the body cavity and coelom is very useful and serves as a fundamental basis for the classification of animals, particularly for triploblastic organisms. The presence or absence of a coelom and its type helps in distinguishing major animal phyla.
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Primary Level of Classification: It divides the triploblastic animals into three major groups:
- Acoelomates: These animals lack a body cavity between the body wall and the gut wall. This feature is characteristic of the Phylum Platyhelminthes (flatworms).
- Pseudocoelomates: In these animals, the body cavity is not lined by mesoderm. Instead, the mesoderm is present as scattered pouches. This type of body cavity is called a pseudocoelom and is characteristic of the Phylum Aschelminthes (roundworms).
- Coelomates: These animals possess a true coelom, which is a body cavity lined by mesoderm on all sides. This advanced feature is found in all phyla from Annelida to Chordata, including Arthropoda, Mollusca, Echinodermata, and Chordata.
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Indication of Complexity: The evolution of a true coelom allowed for greater complexity in organ systems, providing space for organs to develop, function, and be cushioned. Therefore, the nature of the coelom is a good indicator of an animal's position on the evolutionary scale. This makes it a crucial characteristic in understanding the phylogenetic relationships between different animal groups.
Q4Exercises
Distinguish between intracellular and extracellular digestion?
Solution
The key differences between intracellular and extracellular digestion are as follows:
| Feature | Intracellular Digestion | Extracellular Digestion |
|---|---|---|
| Location | Digestion of food occurs inside the food vacuoles within individual cells. | Digestion occurs in a cavity outside the cells, such as the gastro-vascular cavity or the alimentary canal. |
| Process | The cell engulfs food particles, and digestive enzymes are secreted into the food vacuole to break them down. | Digestive enzymes are secreted into the digestive cavity, where food is broken down into simpler molecules, which are then absorbed by the cells. |
| Size of Food | Only very small food particles can be ingested and digested. | Larger pieces of food can be ingested and broken down. |
| Organisms | It is the primary mode of digestion in primitive animals like sponges (Phylum Porifera). | It is found in more complex animals like coelenterates, platyhelminthes, and all higher phyla from Aschelminthes to Chordata. |
| Example Phyla | Phylum Porifera. | Phylum Coelenterata (both intra- and extracellular), Phylum Chordata. |
Q5Exercises
What is the difference between direct and indirect development?
Solution
The difference between direct and indirect development lies in whether a larval stage is present during the life cycle of an organism.
Direct Development:
In direct development, there is no intermediate larval stage. The young ones that hatch from an egg or are born are essentially miniature versions of the adult. They grow in size to become mature adults without undergoing any major transformation (metamorphosis).
- Example: Reptiles, birds, and mammals (e.g., humans, dogs).
Indirect Development:
In indirect development, the life cycle includes a larval stage that is morphologically distinct from the adult. The larva hatches from the egg and undergoes a drastic transformation, known as metamorphosis, to become an adult. The larva often has a different habitat and food source compared to the adult.
- Example: Sponges, coelenterates, echinoderms (e.g., starfish), and amphibians (e.g., the tadpole larva of a frog).
Q6Exercises
What are the peculiar features that you find in parasitic platyhelminthes?
Solution
Parasitic platyhelminthes (flatworms) show several peculiar features and adaptations for their parasitic mode of life. Based on the chapter, these features include:
- Hooks and Suckers: Many parasitic forms possess specialized structures like hooks and suckers. These are used for attaching firmly to the internal surfaces of the host, such as the intestinal wall, to avoid being dislodged.
- Direct Nutrient Absorption: Some parasitic flatworms, like the tapeworm (Taenia), lack a digestive system. They live in the host's intestine and absorb pre-digested nutrients directly from the host through their body surface.
- Complex Life Cycle: They often have complex life cycles involving one or more intermediate hosts to facilitate their transmission and completion of their life cycle. Development often proceeds through many larval stages.
- High Reproductive Capacity: To ensure the continuation of their species against high odds, they produce a vast number of eggs.
Q7Exercises
What are the reasons that you can think of for the arthropods to constitute the largest group of the animal kingdom?
Solution
Arthropods constitute the largest phylum of the animal kingdom, with over two-thirds of all named species on Earth. The reasons for their immense success and diversity can be attributed to several key features mentioned in the chapter:
- Chitinous Exoskeleton: They possess a hard, protective, and waterproof outer covering called a chitinous exoskeleton. This prevents water loss, provides protection from predators, and offers support, which was crucial for their successful colonization of terrestrial environments.
- Jointed Appendages: The name Arthropoda means "jointed feet." These jointed appendages are highly adaptable and have been modified for a variety of functions, including walking, swimming, feeding (jaws), sensing (antennae), and defense. This versatility has allowed them to occupy a wide range of ecological niches.
- Body Segmentation: Their segmented body (head, thorax, and abdomen) allows for specialization of different body regions for different functions, leading to efficient movement and functioning.
- Diverse Respiratory Systems: Arthropods have evolved various respiratory organs like gills, book gills, book lungs, and a tracheal system. This diversity allows them to thrive in aquatic as well as terrestrial habitats.
- Well-developed Sensory Organs: They possess advanced sensory organs such as antennae, compound and simple eyes, and statocysts (balancing organs), which make them highly aware of their environment and efficient at finding food, mates, and avoiding predators.
- High Reproductive Rate: Most arthropods are oviparous and lay a large number of eggs, ensuring a high rate of survival and proliferation of the species.
Q8Exercises
Water vascular system is the characteristic of which group of the following:
(a)
Porifera
(b)
Ctenophora
(c)
Echinodermata
(d)
Chordata
Solution
The correct answer is (c) Echinodermata.
As stated in the section on Phylum Echinodermata, "The most distinctive feature of echinoderms is the presence of water vascular system which helps in locomotion, capture and transport of food and respiration."
Q9Exercises
"All vertebrates are chordates but all chordates are not vertebrates". Justify the statement.
Solution
This statement is correct and can be justified by understanding the classification of Phylum Chordata.
The fundamental characteristics of all chordates, present at some stage of their life, are:
- Presence of a notochord.
- A dorsal, hollow nerve cord.
- Paired pharyngeal gill slits.
Phylum Chordata is divided into three subphyla: Urochordata, Cephalochordata, and Vertebrata.
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Urochordata and Cephalochordata (Protochordates): These animals possess a notochord but lack a vertebral column. In Urochordata, the notochord is present only in the larval tail. In Cephalochordata, the notochord extends from head to tail and persists throughout life. Since they have a notochord, they are classified as chordates. However, because they do not have a bony or cartilaginous vertebral column, they are not vertebrates.
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Vertebrata: In this subphylum, the notochord is present during the embryonic period but is replaced by a cartilaginous or bony vertebral column in the adult.
Therefore, all members of the subphylum Vertebrata possess the defining chordate features (at least embryonically) and are thus chordates. However, the chordate phylum also includes the protochordates (Urochordata and Cephalochordata), which are not vertebrates. This justifies the statement that "all vertebrates are chordates, but all chordates are not vertebrates."
Q10Exercises
How important is the presence of air bladder in Pisces?
Solution
The presence of an air bladder is very important, and it is a key distinguishing feature between the two main classes of fishes (Pisces): Chondrichthyes (cartilaginous fishes) and Osteichthyes (bony fishes).
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In Osteichthyes (Bony Fishes): The air bladder is present. Its primary function is to regulate buoyancy. By adjusting the amount of gas in the bladder, a bony fish can maintain its desired depth in the water column without having to expend energy on constant swimming. This allows it to remain stationary, saving a significant amount of energy.
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In Chondrichthyes (Cartilaginous Fishes): These fishes, such as sharks and rays, lack an air bladder. As a result, they are denser than water and will sink if they stop swimming. They must swim constantly to generate lift with their fins and stay afloat. The absence of an air bladder is a major reason for their continuous movement.
In summary, the air bladder is a crucial organ for bony fishes, providing them with neutral buoyancy and allowing for greater energy efficiency compared to cartilaginous fishes.
Q11Exercises
What are the modifications that are observed in birds that help them fly?
Solution
Birds (Class Aves) exhibit several significant modifications that are adaptations for flight:
- Presence of Feathers: Feathers provide insulation, but more importantly, they create the aerodynamic surfaces of the wings and tail necessary for lift and steering during flight.
- Modification of Forelimbs into Wings: The forelimbs are modified into wings, which are the primary structures for generating flight.
- Pneumatic Bones: The endoskeleton is fully ossified (bony), but the long bones are hollow and filled with air cavities (pneumatic). This makes the skeleton strong yet lightweight, reducing the overall body weight for easier flight.
- Streamlined Body: The body is streamlined to reduce air resistance during flight.
- Additional Chambers in Digestive Tract: The digestive tract has a crop and gizzard, allowing for quick and efficient processing of food to meet the high energy demands of flight.
- Efficient Respiratory System: Respiration is by lungs, which are supplemented by air sacs. This system ensures a continuous supply of oxygen to the muscles, which is essential for sustained flight.
- Four-Chambered Heart: A completely four-chambered heart ensures an efficient supply of oxygenated blood to the body by preventing the mixing of oxygenated and deoxygenated blood, supporting a high metabolic rate.
Q12Exercises
Could the number of eggs or young ones produced by an oviparous and viviparous mother be equal? Why?
Solution
No, the number of eggs produced by an oviparous mother and the number of young ones produced by a viviparous mother are generally not equal. Oviparous mothers typically produce a much larger number of offspring.
Here is why:
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Oviparous Animals (Egg-laying): These animals, like fishes, amphibians, and reptiles, lay their eggs in the external environment. The eggs and developing embryos face numerous threats, including predation, harsh environmental conditions (temperature, humidity), and lack of food. To compensate for the very low survival rate of each individual egg, these animals produce a large number of eggs to ensure that at least a few offspring survive to adulthood.
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Viviparous Animals (Live-bearing): These animals, like most mammals, give birth to live young. The embryo develops inside the mother's body, where it receives complete protection from predators and environmental dangers, as well as a constant supply of nourishment. After birth, the young are often cared for by the parents. This internal development and parental care lead to a very high survival rate for the offspring. Because the chances of survival are high, viviparous animals invest more energy in fewer offspring, producing a much smaller number of young ones.
Q13Exercises
Segmentation in the body is first observed in which of the following:
(a)
Platyhelminthes
(b)
Aschelminthes
(c)
Annelida
(d)
Arthropoda
Solution
The correct answer is (c) Annelida.
According to the chapter, animals in the Phylum Annelida are the first to exhibit true metameric segmentation. The text states, "They are triploblastic, metamerically segmented and coelomate animals. Their body surface is distinctly marked out into segments or metameres..." The phyla preceding Annelida, such as Platyhelminthes and Aschelminthes, are described as unsegmented.
Q14Exercises
Match the following:
(a)
Operculum (i) Ctenophora
(b)
Parapodia (ii) Mollusca
(c)
Scales (iii) Porifera
(d)
Comb plates (iv) Reptilia
(e) Radula (v) Annelida
(f) Hairs (vi) Cyclostomata and Chondrichthyes
(g) Choanocytes (vii) Mammalia
(h) Gill slits (viii) Osteichthyes
Solution
Here is the correct matching based on the characteristics described in the chapter:
- (a) Operculum matches with (viii) Osteichthyes. (The operculum is the gill cover in bony fishes.)
- (b) Parapodia matches with (v) Annelida. (Parapodia are lateral appendages for swimming in aquatic annelids like Nereis.)
- (c) Scales matches with (iv) Reptilia. (Reptiles have a body covered by dry, cornified skin and epidermal scales.)
- (d) Comb plates matches with (i) Ctenophora. (Ctenophores have eight external rows of ciliated comb plates for locomotion.)
- (e) Radula matches with (ii) Mollusca. (The radula is a file-like rasping organ for feeding found in molluscs.)
- (f) Hairs matches with (vii) Mammalia. (The presence of hair is a unique characteristic of mammals.)
- (g) Choanocytes matches with (iii) Porifera. (Choanocytes or collar cells line the spongocoel in sponges.)
- (h) Gill slits matches with (vi) Cyclostomata and Chondrichthyes. (Cyclostomes have 6-15 pairs of gill slits, and Chondrichthyes have gill slits without an operculum.)
Correct Matches:
(a) - (viii)
(b) - (v)
(c) - (iv)
(d) - (i)
(e) - (ii)
(f) - (vii)
(g) - (iii)
(h) - (vi)
Q15Exercises
Prepare a list of some animals that are found parasitic on human beings.
Solution
Based on the examples given in the chapter, here is a list of animals that are parasitic on human beings:
-
Phylum Platyhelminthes (Flatworms):
- Taenia (Tapeworm) - An endoparasite in the intestines.
- Fasciola (Liver fluke) - An endoparasite in the liver.
-
Phylum Aschelminthes (Roundworms):
- Ascaris (Roundworm) - An endoparasite in the intestines.
- Wuchereria (Filaria worm) - An endoparasite that causes filariasis (elephantiasis).
- Ancylostoma (Hookworm) - An endoparasite in the intestines.
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Phylum Annelida:
- Hirudinaria (Blood sucking leech) - An ectoparasite that feeds on blood.
-
Phylum Arthropoda:
- Anopheles, Culex, and Aedes (Mosquitoes) - They act as vectors for various diseases (like malaria, dengue) and are ectoparasites that feed on blood.