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Kingdom Animalia: General Characteristics, Mode of Nutrition, Reproduction and Classification

Animals, a very common name, that all of you have heard and seen. Have you ever thought if animals occupy a distinct place in the classification systems proposed by biologists? The answer is yes! Animals are grouped under a separate category called Kingdom Animalia. This forms the fifth kingdom in Whittaker’s Five Kingdom Classification. 

Let’s go through some of the general facets of animals.

Table of contents:

General Characteristics of Animals

Kingdom Animalia includes eukaryotic, multicellular heterotrophic organisms which lack a cell wall called Animals.

The bodies of animals show different levels of organisation, i.e., cellular, tissue, organ and organ system level of organisation, to perform diverse functions of the body.

  • Cellular level of organisation: Cells are present as loose aggregates. Example: Lower invertebrates such as sponges.
  • Tissue level of organisation: Specialised cells are organised to form tissues. Example: Sea anemones, Hydra, jellyfish
  • Organ level of organisation: Similar tissues are organised to form an organ which is specialised in a physiological function. Example: Flatworms show organs like eyes, brain etc. to perform specialised functions.
  • Organ system level of organisation: Organs performing a specific function are grouped together to form an organ system. Example: Vertebrates have different organ systems such as digestive system, circulatory system, reproductive system etc. for efficient body functioning.

Levels of organisation in animals

Definite growth patterns have been shown by animals. Embryos or larvae grow into adults having definite size and shape.

Complex and higher invertebrates and vertebrates possess sensory mechanisms to sense changes in their external environment. They also possess neuromotor mechanisms which ensure prompt response to any stimuli.

Most of the animals possess locomotory organs such as limbs, parapodia, etc. for locomotion.

Locomotion in animals

Mode of Nutrition in Animals

Animals cannot synthesise food on their own. They depend on plants directly or indirectly for satisfying their nutritional requirements. Thus, they show a heterotrophic mode of nutrition. 

Most of the animals have a holozoic mode of nutrition. This implies that animals engulf food as a whole and digest within their body, usually extracellularly in a specialised organ system called the digestive system. Few animals also exhibit intracellular digestion (digestion inside cells). Storage of reserve food material occurs in the form of glycogen or fat.

Heterotrophic nutrition in animals

Reproduction in animals

Most of the animals reproduce sexually (involves fusion of gametes from opposite sexes) while a few of them reproduce asexually (single parent produces genetically identical daughter cells). For example, Hydra reproduces asexually by means of budding.

Male and female animals copulate for sexual reproduction. Gametes are formed inside organisms. Gametes of opposite sexes fertilise to form zygotes followed by embryological development.

Fertilisation can be external (outside the female body) or internal (inside the female body) which varies among different animals.

Development can be direct (the embryo develops directly into smaller versions of adult forms) or indirect (the embryo develops into adults through intervening larval stages which are morphologically different from the adults). Some animals develop indirectly by forming larvae.

Classification of animals

Based on their characteristic features, animals can be classified into different phyla.

  • Non-chordates (notochord absent): This group has the following phyla:
    • Phylum Porifera
    • Phylum Coelenterata
    • Phylum Ctenophora
    • Phylum Platyhelminthes
    • Phylum Aschelminthes
    • Phylum Annelida
    • Phylum Arthropoda
    • Phylum Mollusca
    • Phylum Echinodermata
    • Phylum Hemichordata
  • Chordates (notochord present): This is further categorised as follows:
    • Subphylum Urochordata
    • Subphylum Cephalochordata
    • Subphylum Vertebrata
      • Agnatha
        • Class Cyclostomata
      • Gnathostomata
        • Superclass Pisces
          • Class Chondrichthyes
          • Class Osteichthyes
        • Superclass Tetrapoda
          • Class Amphibia
          • Class Reptilia
          • Class Aves
          • Class Mammalia

Practice Problems of Kingdom Animalia

    1. While observing under the microscope, you found that the specimen lacked cell wall, had reduced vacuoles. Predict the type of cell.
      1. Plant cell
  • Animal cell
    1. Bacteria
    2. Either a or b

Solution: Cells of animals lack a cell wall while the plant and bacterial cells have it. Animal cells also have fewer vacuoles compared to plant cells. Hence, the given specimen is an animal cell.

Hence, the correct option is b.

    1. Based on the presence of notochord, two major groups of animals are:
  • Chordates and Non-chordates
    1. Vertebrates and Chordates
    2. Vertebrates and Invertebrates
    3. Mammals and Insects

Solution: Based on the presence of notochord, animals are classified into two major groups. These are chordates and non-chordates.

Hence, the correct option is a.

    1. Which of the following characteristics distinguishes protists and animals?
      1. Protists have cell walls while animals lack cell walls
      2. Plasma membrane is absent in protists while animals have it
  • Protists are unicellular eukaryotes while animals are multicellular eukaryotes
    1. Protists are prokaryotes while animals are eukaryotes

Solution: Protists are unicellular eukaryotic organisms. Animals are usually multicellular organisms having eukaryotic cells. Hence, cellularity is the distinguishing feature between prokaryotes and eukaryotes.

Hence, the correct option is c.

    1. Which of the following features are different between plant cells and animal cells?
      1. Cell wall 
      2. Locomotory abilities
      3. Reserve food material
  • All of the above

Solution: 

Features 

Plant cell

Animal cell

Cell wall

Present 

Absent

Locomotory abilities

Absent

Present 

Reserve food material

Starch

Glycogen

Hence, all the features mentioned in the options are differentiating criterias between plant cells and animal cells.

Hence, the correct option is d.

FAQs of Kingdom Animalia

Question1.- Mention three prominent facets of animals.
Answer. Three prominent facets of animals are as follows:

  • Are composed of eukaryotic cells 
  • Are usually multicellular 
  • Are always heterotrophic
    1. Select the correct statement from the following.
      1. Both plants and animals show locomotion
      2. Both plants and animals don’t show locomotion
  • Plants exhibit movement while animals exhibit both locomotion and movement

Question2.- Plants exhibit locomotion while animals exhibit movement 
Answer. Plants cannot change their position by undergoing displacement, hence, they don’t exhibit locomotion. However, they show a change in position of body parts, thus showing movements. On the other hand, animals exhibit both locomotion (displacement) and movement (change in position of body parts).

Question3.- Mention the types of development undergone by an embryo.
Answer. Development can be of the following types:

  • Direct development: The embryo develops directly into smaller versions of adult forms.
  • Indirect development: The embryo develops into adults through intervening larval stages which are morphologically different from the adults. 

Question4.- Define holozoic mode of nutrition.
Answer. The mode of nutrition in which an animal engulfs food as a whole (ingestion), digests which is followed by absorption and assimilation of nutrients and egestion of undigested waste is called the holozoic mode of nutrition.

Other Related Topics

The Living World Biological Classification Plant Kingdom
Animal Kingdom Morphology of Flowering Plants Anatomy of Flowering Plants
Structural Organization in Animals Cells: The Unit of Life Biomolecules
Cell Cycle and Division Transport in Plants Mineral Nutrition
Photosynthesis in Higher Plants Respiration in Plants Plant Growth and Development
Digestion and Absorption Breathing and Exchange of Gases Body Fluids and Circulation
Excretory Products and their Elimination Locomotion and Movement Neural Control and Coordination
Chemical Coordination and Integration

Other Related Topic Of Biology

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