NEET Practice Questions (MCQs) with Answers & Solutions

The mechanism of aerobic respiration was discovered by Sir Hans Adolf Krebs. He elucidated the citric acid cycle, also known as the Krebs cycle, which is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetate derived from carbohydrates, fats, and proteins into carbon dioxide and water.

The first step of glycolysis is the phosphorylation of glucose. During this step, a phosphate group is added to glucose to form glucose-6-phosphate. This reaction is catalyzed by the enzyme hexokinase and is crucial for trapping glucose in the cell and making it more chemically reactive for subsequent steps in glycolysis.

During the complete oxidation of one molecule of glucose in liver cells, a total of 38 ATP molecules are produced. This includes 2 ATP from glycolysis, 2 ATP from the Krebs cycle, and 34 ATP from the electron transport chain (ETC) and oxidative phosphorylation.

The Respiratory Quotient (RQ) is the ratio of CO2 produced to O2 consumed. When fats and proteins are used as respiratory substrates, the RQ is less than one because they require more oxygen to be oxidized compared to carbohydrates, which have an RQ of 1.

Hexokinase is the enzyme that catalyzes the phosphorylation of glucose to form glucose-6-phosphate in the first step of glycolysis. This reaction is crucial for trapping glucose within the cell and beginning its breakdown for energy.

The compound that links glycolysis and the Krebs cycle is Acetyl CoA. During glycolysis, glucose is broken down into pyruvic acid. This pyruvic acid is then converted into Acetyl CoA, which enters the Krebs cycle for further oxidation.

The greatest number of ATP molecules are formed during the electron transport chain. This stage of cellular respiration generates a large amount of ATP through oxidative phosphorylation, driven by the electron gradient established by NADH and FADH2 produced in earlier stages.

The overall goal of glycolysis, the Krebs cycle, and the electron transport system is the formation of ATP in small steps. These processes collectively break down glucose and other molecules to produce ATP in a controlled manner, ensuring that energy is released and captured efficiently.

In plants, the embryo develops from the zygote. The zygote is formed after the fertilization of the egg cell by a sperm cell. The zygote then undergoes multiple cell divisions and differentiation to form the embryo.

The embryo of a flowering plant is always diploid (2n). This is because it develops from the zygote, which is formed by the fusion of a haploid (n) sperm cell with a haploid (n) egg cell, resulting in a diploid (2n) cell.