All Free Biology MCQs with Answers

3511. Energy is ------- by the breakdown of complex molecules into simpler ones; such reactions are called catabolic reactions:

• A. Released
• B. Consumed
• C. Produced
• D. Destroyed

Explanation: Energy is released by the breakdown of complex molecules into simpler ones, and such reactions are called catabolic reactions. Catabolic reactions involve the breakdown of larger molecules into smaller ones, and this process releases energy that can be used by the cell or organism for various metabolic activities.

3512. The process of photophosphorylation takes place in:

• A. Nucelolus
• B. Chloroplast
• C. Nucleus
• D. Golgi bodies

Explanation: Option B is correct.The process of photophosphorylation takes place in the chloroplast. Photophosphorylation is the process by which light energy is used to produce ATP, the energy currency of the cell. It is the light-dependent reaction of photosynthesis. Photophosphorylation takes place in the thylakoid membranes of the chloroplast. The thylakoid membranes are stacked sacs that contain chlorophyll, the light-absorbing pigment. When sunlight hits the chlorophyll, it excites the electrons in the chlorophyll molecules. These excited electrons are then passed through a series of electron carriers, which eventually leads to the production of ATP. The ATP that is produced by photophosphorylation is used to drive the Calvin cycle, the light-independent reaction of photosynthesis. The Calvin cycle uses ATP to convert carbon dioxide into sugar.The other options are not organelles where photophosphorylation takes place:The nucleolus is a small structure within the nucleus that is involved in the production of ribosomes.The nucleus is the control center of the cell and contains the cell's DNA.The Golgi apparatus is involved in the packaging and processing of proteins and lipid

3513. Light reaction occurs in the _ of chloroplast:

• A. Outer membrane
• B. Inner membrane
• C. Granum
• D. Stroma

Explanation: Option C is correct.The light reaction occurs in the grana of the chloroplast. The chloroplast is a specialized organelle in plant cells that is responsible for photosynthesis. Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to produce oxygen and sugar. The chloroplast is divided into two parts: the stroma and the thylakoids. The stroma is a gel-like fluid that contains the enzymes needed for the Calvin cycle, the second stage of photosynthesis. The thylakoids are a series of flattened sacs that are stacked together to form grana. The light reaction occurs in the thylakoids of the chloroplast. The thylakoids contain chlorophyll, a green pigment that absorbs sunlight. The sunlight energy is used to split water molecules into hydrogen and oxygen. The hydrogen atoms are used to produce NADPH, a molecule that stores energy. The oxygen atoms are released into the atmosphere. The products of the light reaction, NADPH and ATP, are used in the Calvin cycle to produce sugar. The other options are not parts of the chloroplast where the light reaction occurs: The outer membrane is a thin membrane that surrounds the chloroplast. It protects the chloroplast from the outside environment. The inner membrane is a thicker membrane that surrounds the stroma. It controls the movement of molecules into and out of the chloroplast. The stroma is the gel-like fluid that contains the enzymes needed for the Calvin cycle.

3514. In alcoholic fermentation _ ATP Molecules are produced from one glucose molecule:

• A. 2
• B. 18
• C. 32
• D. 36

Explanation: Option A is correct. In alcoholic fermentation, two ATP molecules are produced from one glucose molecule. This process occurs in the absence of oxygen and is utilized by yeast and certain microorganisms to convert glucose into ethanol and carbon dioxide. The steps of alcoholic fermentation include:Glycolysis: Glucose is metabolized into two molecules of pyruvate, generating two ATP and two NADH in the process.Pyruvate decarboxylation: Each pyruvate is converted into acetaldehyde, releasing one molecule of carbon dioxide.Alcohol dehydrogenase: Acetaldehyde is then transformed into ethanol, which regenerates NAD+ from NADH.Overall, the net production from one glucose molecule in alcoholic fermentation is two ATP molecules.Options B, C, and D are incorrect as they suggest ATP yields associated with aerobic respiration, which are not applicable in the anaerobic process of alcoholic fermentation.

3515. The ATP formed in the preparatory phase of glycolysis is (are):

• A. 1
• B. 2
• C. 4
• D. 0

Explanation: The correct answer is Option D: 0 ATP. In the preparatory phase of glycolysis, two ATP molecules are utilized to phosphorylate glucose and its derivatives, resulting in no ATP being produced during this phase. This phase is essential for priming the glucose molecule for subsequent breakdown in the energy-producing phase, where four ATP molecules are generated. Thus, the net gain of ATP from glycolysis is two ATP per glucose molecule, derived from the four produced in the energy-generating phase minus the two consumed in the preparatory phase.Options A, B, and C are incorrect because they incorrectly imply that ATP is produced in the preparatory phase. Instead, this phase is characterized by an energy investment, where ATP is consumed rather than created.

3516. _ consists of units called dictyosomes

• A. Ribosomes
• B. Lysosomes
• C. Glyoxisomes
• D. Golgi complex

Explanation: Option D is correct.he Golgi complex consists of units called dictyosomes. A dictyosome is a stack of flattened sacs called cisternae. The Golgi complex is responsible for processing, modifying, and packaging proteins and lipids for secretion or transport to other parts of the cell. The other options are all cell organelles, but they are not made up of dictyosomes: Ribosomes are the site of protein synthesis. Lysosomes are organelles that contain enzymes that break down complex molecules. Glyoxisomes are organelles that are found in plant cells and are involved in the metabolism of fatty acids.

3517. Which process can take place in the presence and absence of oxygen?

• A. Glycolysis
• B. Cellular respiration
• C. Fermentation
• D. None of the above

Explanation: This is the correct answer. Glycolysis is the metabolic pathway that breaks down glucose into pyruvate, producing ATP (energy) in the process.It is the first stage of cellular respiration and can occur both in the presence (aerobic conditions) and absence (anaerobic conditions) of oxygen.

3518. Which is the factory for synthesis of sugars in autotrophic eukaryotes?

• A. Mitochondria
• B. Ribosome
• C. Chloroplast
• D. Amyloplast

Explanation: Chloroplasts are organelles found in autotrophic eukaryotes, such as plants and algae, where photosynthesis takes place. They are responsible for converting light energy into chemical energy, producing glucose and oxygen from carbon dioxide and water. Chloroplasts are often referred to as the "factory" for sugar synthesis in autotrophic eukaryotes.

3519. The carotenoids absorb light in the visible spectrum between _ and _ wavelengths.

• A. 400-600 nm
• B. 530-700 m
• C. 620-700 nm
• D. 500-600 nm

Explanation: Carotenoids are a group of pigments that absorb light in the visible spectrum, specifically in the range of 430-470 nanometers (nm). This range corresponds to the orange to red region of the visible spectrum.

3520. In the 'non-cyclic electron transport of light reaction', the deficit of _ electrons occur in the chlorophyll, as it absorbs energy

• A. 1
• B. 2
• C. 3
• D. 4

Explanation: In the non-cyclic electron transport of the light reaction, also known as the Z-scheme, the deficit of electrons occurs in the chlorophyll molecule (specifically, chlorophyll a) as it absorbs energy from light. This energy excites an electron, which is then transferred to a special molecule called an electron acceptor, leaving a deficit of two electrons in the chlorophyll molecule.