NEET Practice Questions (MCQs) with Answers & Solutions

Though not explicitly stated as 'why' trace amounts are effective in a single sentence, the text explains that hormones 'act as intercellular messengers and are produced in trace amounts' and 'produce their effects on target tissues by binding to specific proteins called hormone receptors... Hormone-Receptor complex formation leads to certain biochemical changes in the target tissue.' This binding and subsequent biochemical cascade allows even trace amounts to have a significant effect.

Under the classification based on chemical nature, NCERT lists '(ii) steroids (e.g., cortisol, testosterone, estradiol and progesterone).'

The NCERT states: 'Hormones which interact with intracellular receptors (e.g., steroid hormones, iodothyronines, etc.) mostly regulate gene expression or chromosome function by the interaction of hormone-receptor complex with the genome.'

The context states: 'This is not possible according to the Heisenberg uncertainty principle. Bohr model of the hydrogen atom, therefore, not only ignores the dual behaviour of electron but also contradicts Heisenberg uncertainty principle.'

The context mentions: 'It was also unable to explain the splitting of spectral lines in the presence of magnetic field (Zeeman effect) or an electric field (Stark effect).'

The context states: 'However it fails when applied to microscopic objects like electrons, atoms, molecules etc. This is mainly because of the fact that classical mechanics ignores the concept of dual behaviour of matter especially for sub-atomic particles and the uncertainty principle.'

The context states: 'In fact an insight into the structure of the atom was needed which could account for wave-particle duality of matter and be consistent with Heisenberg uncertainty principle. This came with the advent of quantum mechanics.'

The context notes: 'An orbit is a clearly defined path and this path can completely be defined only if both the exact position and the exact velocity of the electron at the same time are known. This is not possible according to the Heisenberg uncertainty principle.'

The context defines it: '*Hydrogenic atoms are the atoms consisting of a nucleus with positive charge +Ze and a single electron, where Z is the proton number. Examples are hydrogen atom, singly ionised helium, doubly ionised lithium, and so forth. In these atoms more complex electron-electron interactions are nonexistent.'

The text states: 'Classic al mechanics, based on Newton’s laws of motion, successfully describes the motion of all macroscopic objects... However it fails when applied to microscopic objects... This is mainly because of the fact that classical mechanics ignores the concept of dual behaviour of matter especially for sub-atomic particles and the uncertainty principle.' Option 3 is incorrect because classical mechanics does describe macroscopic objects successfully.