All Free Biology MCQs with Answers

• A. Endoplasmic Reticulum
• B. Golgi Complex
• C. Centriole
• D. Mitochondria

Explanation: The smooth endoplasmic reticulum is responsible for many metabolic processes including: synthesis of lipids, phospholipids as in plasma membranes, and steroids.The cell structure involved in the synthesis of lipids is the endoplasmic reticulum (ER). On the other hand, the Golgi body is responsible for modification and packing. The centriole is involved in the division process and helps in the formation of spindle fibres Mitochondrion is involved in the formation of ATP for energy expenditure processes.

• A. Ribosome
• B. Mitochondria
• C. Lysosome
• D. Nucleolus

Explanation: The mitochondria are known for their double-membrane structure which is essential for their role in energy production. The outer membrane is smooth, while the inner membrane is highly folded to form structures called cristae which increase surface area for ATP production. This distinguishes them from other organelles like lysosomes, which have a single membrane, and ribosomes and the nucleolus, which are non-membranous.

• A. Cristae
• B. Cisternae
• C. Lamella
• D. Bifida

Explanation: The inner membrane of mitochondria is highly specialized and forms numerous infoldings known as cristae. These structures are vital as they increase the surface area of the membrane, allowing for more space for the electron transport chain and ATP synthase, which are key components in the production of ATP. The other options are incorrect: cisternae are associated with the endoplasmic reticulum and Golgi apparatus, lamella refers to a general thin layer or membrane, and bifida pertains to a medical condition unrelated to cell structure.

• A. Proteins
• B. Cholesterols
• C. Cytoskeleton
• D. Phospholipids

Explanation: The correct answer is Phospholipids because they form the bilayer that is the defining structure of the plasma membrane. This bilayer is composed of two layers of phospholipids, with hydrophilic (water-attracting) heads facing outward and hydrophobic (water-repelling) tails facing inward, creating a semi-permeable barrier.

• A. Prokaryotes
• B. Protists
• C. Fungi
• D. Plants

Explanation: The correct answer is Plants because mature plant cells contain a large central vacuole, which is vital for various functions, including the storage of nutrients and waste products, as well as maintaining turgor pressure to support the plant structure. In contrast, Prokaryotes (Option A) are simpler cells without membrane-bound organelles, so they do not have vacuoles. Protists (Option B) may possess vacuoles, but these are not typically large central vacuoles as seen in plants. Fungi (Option C) have smaller vacuoles and do not exhibit the same large central vacuole characteristic.

• A. Smooth Endoplasmic Reticulum
• B. Rough Endoplasmic Reticulum
• C. Golgi apparatus
• D. Lysosomes

Explanation: The detoxification of drugs is the function of SER while protein synthesis is the function of RER. Mechanical support, however, is the function of both RER AND SER.

• A. Centriole
• B. Endoplasmic Reticulum
• C. Nucleus
• D. Ribosome

Explanation: Ribosomes are the correct answer because they are non-membranous organelles that synthesize proteins and are found in both prokaryotic and eukaryotic cells. In contrast, centrioles, the endoplasmic reticulum, and the nucleus are membrane-bound organelles that are characteristic of eukaryotic cells and are absent in prokaryotic cells.

• A. Centrioles
• B. Rough Endoplasmic Reticulum (RER)
• C. Microtubules
• D. Ribosomes

Explanation: Centrioles are the correct answer as they are organelles specific to animal cells and are crucial for organizing microtubules during cell division. Higher plant cells do not have centrioles and rely on different structures for cell division. In contrast, the Rough Endoplasmic Reticulum (RER), microtubules, and ribosomes are present in both plant and animal cells, serving functions that are necessary in both types of eukaryotic cells.

• A. 80S
• B. 60S
• C. 50S
• D. 70S

Explanation: Prokaryotic ribosomes are characterized by a size of 70S, which is formed by the combination of a 50S large subunit and a 30S small subunit. In contrast, eukaryotic ribosomes are 80S, comprising a 60S large subunit and a 40S small subunit. Therefore, the correct answer is 70S. The options 80S and 60S are incorrect as they pertain to eukaryotic cells, while 50S is only a subunit of the prokaryotic ribosome rather than its total size.

• A. Centrioles
• B. Microtubules
• C. Plastids
• D. Sieve tubes

Explanation: Microtubules are cytoskeletal elements that are found in all eukaryotic cells, including both plant and animal cells, but are absent in prokaryotic cells. They play essential roles in maintaining cell shape, enabling intracellular transport, and facilitating cell division. In contrast, centrioles are not present in higher plant cells, plastids are exclusive to plant cells, and sieve tubes are specialized structures found only in the phloem of plant cells. Therefore, the correct answer is microtubules.