All Free Biology MCQs with Answers

1761. Horsetails are included in class of____________?

• A. Sphenopeida
• B. Lycopsida
• C. Psilopsida
• D. Pteropsida

Explanation: Horsetails such as Equisetum are placed in Sphenopsida, also spelled Sphenopsida in many older classifications. The likely alternative is b, Lycopsida, because both are seedless vascular plants, but Lycopsida includes lycophytes rather than horsetails.

1762. Of the following which one is not the characteristic of the plants included in psilopsida_____________?

• A. Gametophyte is colourless
• B. They have mycorrhizal association
• C. Rhizoids bear Rhizome
• D. Aerial branches have veinless outgrowths

Explanation: Psilopsida have a colourless, often mycorrhizal gametophyte, and their aerial branches carry small veinless outgrowths. Rhizoids arise from the subterranean rhizome, so saying that rhizoids bear the rhizome reverses the relationship; the likely alternative is d, but veinless aerial outgrowths are a genuine characteristic.

1763. Mammals became dominant in__________?

• A. Proterozoic era
• B. Mesozoic era
• C. Paleozoic era
• D. Cenozoic era

Explanation: Mammals became dominant during the Cenozoic Era after the mass extinction at the end of the Mesozoic removed the dominant non-avian dinosaurs. They originated earlier, but their major adaptive radiation and dominance occurred in the Cenozoic. Students may choose b because mammals existed in the Mesozoic, but they were not then the dominant large land animals.

1764. In some cases the blastomere can produce complete embryo the cleavage will be___________?

• A. Spiral and determinate
• B. Radial and indeterminate
• C. Spiral and indeterminate
• D. Radial and determinate

Explanation: When a blastomere can develop into a complete embryo, the cleavage is indeterminate because early cells retain the ability to form the whole organism. Radial cleavage is commonly associated with indeterminate development, whereas students may choose spiral and indeterminate by remembering only that some spiral-cleaving animals also show developmental flexibility.

1765. Competition between species will be greatest if they attempt to occupy the same___________?

• A. Ecosystem
• B. Community
• C. Habitat
• D. Niche

Explanation: Competition is greatest when species occupy the same ecological niche because they require the same resources and perform similar roles in the ecosystem. A habitat is merely the physical place where an organism lives and may contain many species with different resource requirements. Students may choose c by treating habitat and niche as synonyms, but niche includes the organism's resource use and ecological role.

1766. Which of the following relationship is NOT an example of symbiosis?

• A. Rhizobium and leguminous plants
• B. Marchantia sporophyte and gametophyte
• C. Algae and fungi in a lichen
• D. Mycorrhizal fungi and tree roots

Explanation: The relationship between a Marchantia sporophyte and gametophyte is an alternation-of-generations relationship within one plant life cycle, not symbiosis between separate organisms. Rhizobium with legumes, algae with fungi in lichens and mycorrhizal fungi with roots are classic close associations between different organisms. Students may choose a because Rhizobium is sometimes described as parasitic in other contexts, but its usual association with legumes is mutualistic symbiosis.

1767. The first eukarotes appeared about __________ years ago?

• A. 1.5 billion
• B. 2.5 billion
• C. 3.5 billion
• D. 4.5 billion

Explanation: The earliest widely accepted eukaryotic fossils are approximately 1.5 billion years old, although estimates vary with the fossil evidence used. Eukaryotic cells appeared after prokaryotes and are distinguished by a membrane-bound nucleus and organelles. Students may choose 2.5 billion years because it is also a commonly quoted approximate date for early complex cellular life, but 1.5 billion years is the intended textbook value.

1768. Following possess bilateral symmetry as larva and radial symmetry as adult:

• A. Chordata
• B. Hydra
• C. Echinodermata
• D. Hemichordata

Explanation: Echinoderms have bilaterally symmetrical larvae but develop radial, usually pentaradial, symmetry as adults. Students may choose Hydra because it is radially symmetrical, but Hydra remains radial and does not show the bilateral-larva to radial-adult transition.

1769. Pick the odd one out

• A. Psilophyton
• B. Rhynia
• C. Cooksonia
• D. Psilotum

Explanation: Psilophyton, Rhynia and Cooksonia are extinct early vascular plants known mainly from fossils, whereas Psilotum is a living whisk-fern genus. The likely mistake is choosing Cooksonia because it is less familiar, although it belongs to the same early fossil group as the other two.

1770. One celled green ptotists are included in___________?

• A. Monera
• B. Algae
• C. Slime molds
• D. Plants

Explanation: Unicellular green organisms traditionally grouped as green algae are placed in the algae category in this older classification scheme. A student may choose plants because green algae contain chlorophyll and perform photosynthesis, but their simple unicellular organization led to their separate placement in this question.