Question 1

What is a coelom?

Accepted Answer

A coelom is a body cavity completely lined by mesoderm on both sides — the parietal layer lines the body wall and the visceral layer covers the gut. This 'mesoderm on both sides' condition is the exact definition NEET tests.

Question 2

What is the difference between a coelom and a pseudocoelom?

Accepted Answer

In a true coelom, mesoderm lines the cavity on both the body-wall side (parietal) and the gut side (visceral). In a pseudocoelom, mesoderm appears only as scattered patches on the body-wall side; the gut wall has no mesodermal lining. Aschelminthes (Nematoda) are pseudocoelomates.

Question 3

Which animals are diploblastic?

Accepted Answer

Only Coelenterata (Cnidaria) and Ctenophora are diploblastic — they have an outer ectoderm and an inner endoderm with non-cellular mesoglea in between. Porifera are NOT diploblastic; they are at the cellular level of organisation and fall outside the germ-layer classification.

Question 4

Are sponges symmetrical or asymmetrical?

Accepted Answer

Sponges (Porifera) are mostly asymmetrical — no plane through the body divides it into mirror halves. They are also at the cellular level of organisation, the simplest of all animal phyla.

Question 5

Are echinoderms radially or bilaterally symmetrical?

Accepted Answer

Both, at different life stages: echinoderm larvae are bilaterally symmetrical, while adults are radially symmetrical. NEET frequently tests this larva-versus-adult distinction.

Question 6

Which phylum is acoelomate?

Accepted Answer

Platyhelminthes (flatworms) are acoelomate — they are triploblastic, but the space between the gut and the body wall is packed with mesenchyme (parenchyma), leaving no body cavity at all.

Body Plan Lab — Symmetry, Germ Layers & the True Coelom

Practice

Learned it? Now prove it under the clock.