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๐ก Movers and hunters
Animals cannot make their own food, so they move, sense and respond — searching for food, escaping predators and interacting with their world.
What is Kingdom Animalia?
- Animals are multicellular heterotrophs that depend on other organisms for food.
- Most show locomotion , rapid response to stimuli and coordinated behaviour.
- A major criterion for classifying animals is the presence or absence of a notochord (a flexible rod-shaped structure).
NCERT Question 2 — Sponges represent one of the
Sponges represent one of the simplest animal body plans. Their bodies lack true tissues and organs. Which feature of sponge cells supports its classification under the animal kingdom? (i) Absence of mitochondria (ii) Ability to photosynthesise (iii) Presence of a cell membrane (iv) Presence of a cell wall
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NCERT Question 15 — During a long-term ecological study,
During a long-term ecological study, students examined organisms collected from three different environments — a freshwater pond, damp soil near decaying logs and the digestive tract of animals. Instead of naming organisms directly, scientists recorded only structural, cellular and nutritional features.
P:
Microscopic; no true nucleus; rigid cell covering; survives high salinity and temperature.
Q:
Multicellular; filamentous body; cell wall present; no chlorophyll; grows on dead organic matter.
R:
Unicellular; true nucleus; contractile vacuole present; moves using flagella; shows photosynthesis in light but heterotrophic in the absence of light.
S:
Multicellular; well-differentiated tissues; backbone present; aquatic respiration during early life stage.
T:
Acellular; contains genetic material; remains inactive outside a host cell. (i) Identify one organism that clearly belongs to the Kingdom Fungi. State one observation that supports your answer. (ii) Which organism would be placed in the Kingdom Monera? Mention one characteristic that justifies this placement. (iii) Organisms R and Q are both eukaryotic, yet they are placed in different kingdoms. Analyse the criteria that separate them. (iv) Explain why organism S cannot be classified using the mode of nutrition alone. (v) Organism T does not fit into any of the five kingdoms. Which fundamental characteristic used in classification does it lack and what does this reveal about the limitations of classification systems? (vi) If classification were based only on habitat, which organisms might be incorrectly grouped together? Explain the scientific consequences of such a classification. (vii) Imagine scientists discover a new organism that is multicellular, eukaryotic, lacks chlorophyll and absorbs nutrients from a host externally. Should it be placed under fungi or animalia? Justify your reasoning using classification criteria.
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How are animals classified by the notochord?
- Based on the notochord, animals are split into non-chordata (invertebrata) and chordata .
- Invertebrates lack a notochord; chordates have one, in which the notochord can act as a precursor to the vertebral column.
- Chordata is further classified into protochordata and vertebrata .
What are the main invertebrate phyla?
- Porifera (sponges) — multicellular but no tissues; Cnidaria (hydra, jellyfish) — tissue-level with tentacles; Platyhelminthes (flatworms) — bilateral symmetry, one opening.
- Nematoda (roundworms) — cylindrical body with two openings; Annelida (earthworms) — segmented bodies with a body cavity.
- Arthropoda (insects, crabs, spiders) — jointed legs and an exoskeleton; Mollusca (snails, octopuses) — soft bodies, often with a shell; Echinodermata (starfish) — spiny, with a calcium-carbonate internal skeleton.
NCERT Question 1 — Meena and Hari observed an
Meena and Hari observed an animal in their garden. Hari called it an insect while Meena said it was an earthworm. Choose the correct option which confirms that it is an insect. (i) Bilateral symmetrical body (ii) Body with jointed legs (iii) Cylindrical body (iv) Body with little segmentation
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| Phylum (example) | Habitat | Level of organisation | Skeleton |
|---|---|---|---|
| Porifera (sponge) | Water (marine) | Cellular | ✗ |
| Cnidaria (jellyfish) | Water (fresh and marine) | Tissue | ✗ |
| Platyhelminthes (flatworm) | Water / inside host | Organ | ✗ |
| Nematoda (roundworm) | Soil / water / inside host | Organ system (digestive system) | ✗ |
| Annelida (earthworm) | Moist soil / water | Organ system | ✗ |
| Arthropoda (spider) | Land / water | Organ system | Exoskeleton |
| Mollusca (snail) | Water / moist land | Organ system | Exoskeleton |
| Echinodermata (starfish) | Marine water | Organ system | Endoskeleton |
๐งต Threads of Curiosity
Research studies show that one kilogram of sponge can filter up to 24,000 litres of sea water per day — drawing in food and oxygen through the countless pores in its body.
๐ Bridging Science and Society
Some infectious diseases are caused by parasitic worms that enter through contaminated water and food and live in our alimentary canal, taking nutrients from our body (the organism they live on is the host ). To stay safe, wash hands properly, maintain personal hygiene, eat properly cooked food and drink boiled or filtered water.
