All Free Biology MCQs with Answers

1681. The simplest of oxygen producting photosynthetic organisms are____________?

• A. Algae
• B. Bacteria
• C. Cyanobacteria
• D. Chlamydomonas

Explanation: Cyanobacteria are among the simplest organisms that perform oxygenic photosynthesis, using light energy to split water and releasing oxygen. They are prokaryotes, unlike algae and Chlamydomonas, which are eukaryotic photosynthetic organisms. Students may choose a because algae are often introduced as simple photosynthetic organisms, but cyanobacteria are structurally simpler.

1682. Locomotory structures are not found in which of the following group?

• A. Amoebas
• B. Zooflagellates
• C. Ciliates
• D. Apicomplexans

Explanation: Apicomplexans are generally non-motile in their mature stages and lack the usual locomotory structures such as cilia, flagella or pseudopodia. Amoebas move by pseudopodia, zooflagellates by flagella and ciliates by cilia. Students may choose c because some apicomplexans show gliding movements, but gliding is not produced by the standard locomotory organelles listed for the other groups.

1683. Total number of amino acids discovered so far in cells and tissues are______________?

• A. 20
• B. 25
• C. 150
• D. 170

Explanation: Although 20 amino acids are commonly used to build proteins, about 170 amino acids have been identified in cells and tissues, including non-protein amino acids. Students most often choose 20 because they confuse the standard protein-forming amino acids with the total number discovered.

1684. In Glycin an amino acid R group is replaced by____________?

• A. H
• B. CH3
• C. COOH
• D. C = O

Explanation: Glycine is the simplest amino acid because its side, or R, group is a hydrogen atom, giving it the structure NH2-CH2-COOH. Students may choose CH3 because alanine has a methyl R group, not glycine.

1685. The one which is incorrect pair?

• A. Sori - Indusium
• B. Arthrophytes - Jointed
• C. Dichotomous - Vernation
• D. Lycopods - Ground pries

Explanation: Sori are clusters of fern sporangia and may be covered by an indusium, arthrophytes have jointed or segmented stems, and lycopods are commonly called ground pines. Dichotomous refers to branching into two equal branches, not vernation, which describes the arrangement of young leaves in a bud, so that pair is incorrect.

1686. Maximum number of species of living things on earth are___________?

• A. Algae
• B. Fungi
• C. Insects
• D. Protozoa

Explanation: Insects constitute the largest number of known animal species because their body plan, small size and reproductive success allow them to occupy many habitats. Fungi are also highly diverse, but their known species count is lower than that of insects.

1687. Carbon atom is_____________?

• A. Monovalent
• B. Divalent
• C. Trivalent
• D. Tetravalent

Explanation: Carbon is tetravalent because it has four electrons in its outer shell and can form four covalent bonds. This allows carbon atoms to make chains, branches and rings in organic molecules. The likely mistake is choosing divalent because oxygen commonly forms two bonds, but carbon can form four.

1688. Which one is an organic compound_____________?

• A. CO2
• B. Water
• C. Lipids
• D. HCI

Explanation: Lipids are organic compounds because they contain carbon-based structures and are produced by living organisms. CO2 contains carbon but is classified as an inorganic compound because it lacks the complex carbon-hydrogen framework typical of organic molecules. Students most likely choose CO2 by assuming every carbon-containing compound is organic.

1689. Which chemical component has the greatest contribution in the total mammalian cell weight__________?

• A. Proteins
• B. Carbohydrate
• C. Lipids
• D. Water

Explanation: Water usually makes up the greatest proportion of a mammalian cell's mass, commonly about 70% or more, and acts as the main solvent for cellular reactions. Proteins, lipids and carbohydrates together generally contribute less total mass than water. Students often choose proteins because they are the most abundant organic macromolecules, but the question asks for the total cell weight, not only dry organic matter.

1690. The branch of biology which deals with the study of chemical compounds and the chemical processes in the fliving organisms is called_________________?

• A. Chemistry
• B. Biochemistry
• C. Molocular biology
• D. Both a and b

Explanation: Biochemistry studies the chemical substances and chemical processes occurring in living organisms, including metabolism and the structure of biomolecules. Molecular biology mainly focuses on molecules such as DNA, RNA and proteins and their interactions, so it is narrower than the definition given here. The likely distractor is molecular biology because both fields study biological molecules.