Question

7.

During the development of a frog's fertilized egg, the following takes place:

	A.	Rapidly dividing cells lead to the formation of the "animal pole" in a region of the egg that is rich in amino acids and nucleic acids precursors.
	B.	Cells divide more slowly in the "vegetal pole" as they are located in a region of the egg richer in lipids with fewer amino acids and nucleic acid precursors.
	C.	In early stages of development, cells are dividing so fast that the embryo does not increase in volume.
	D.	All of the above

8.

1. Find the incorrect description.

   	A.	Light Microscopy — Usually has a resolution of 0.2 µm and a maximum magnification of 1000X. Light goes through the specimen. It usually requires staining of specimens (cells, tissue slices)
   	B.	Confocal Microscopy — Allows visualization of cells in three dimensions because it takes images in optical sections and integrates them using computer power.
   	C.	Atomic Force Microscopy — Similar in principle to light microscopy, but uses an electron beam instead of photons. Enlargement up to 106X and resolution of biological specimens about 1 nm.
   	D.	Fluorescence Microscopy — Excitation light is absorbed by fluorescent probes in the specimen and reemitted at a lower energy, i.e., a longer wavelength.

9.

1. During titration of glycine with HCl, what is the proportion of ⁺H₃N–CH₂–COO^– /⁺H₃N–CH₂–COOH at pKa₁?

   	A.	75%/25%
   	B.	0%/100%
   	C.	50%/50%
   	D.	25%/75%

11.

1. Consider the compound pairs below:

   1. HCHO, CH₃CHO (formaldehyde, acetaldehyde)
   2. CH₄, CH₃CH₃ (methane, ethane)
   3. HCOOH, CH₃COOH (formic acid, acetic acid)
   4. CH₃OH, CH₃CH₂OH (methanol, ethanol)
   5. CO₂, CO (carbon dioxide, carbon monoxide)

   What is their correct order, from the most oxidized to the most reduced?

   	A.	v > iii > i > iv > ii
   	B.	i > iv > ii > v > iii
   	C.	i > ii > iii > iv > v
   	D.	v > iv > iii > ii > i

Answer 1

7. D. All of the above statements are true. (In embryos, there is an animal pole and a vegetal pole, distinguished by higher rate of cell division in animal pole, and slower rate of division in vegetal pole. Initially the cell division is not accompanied by significant production of rest of the cellular material apart from nucleus. This keeps the volume of the embryo same while the number of cells inside keeps on increasing.)

8. Incorrect description: Atomic Force Microscopy (Here a cantilever/tip system or a probe is used to scan the surface of a substance, and a laser beam is used to detect deflections of the probe from the surface. This method gives an accurate picture of the surface of the analyte.)

9. 50%/50% (pKa is the point where titration is half complete, i.e. 50% of the deprotonation has been completed and 50% is remaining. For pKa1 of glycine, the COOH group will deprotonate first and become COO-. This process attains 50% status at pKa1. So the concentration will be 50%/50%. Similarly for pKa2, the NH3+/NH2 concentration would be 50%/50%.

11. A. v>iii>i>iv>ii

Oxides are the most oxidized (CO2, CO). Oxides get reduced first to carboxylic acids (formic acid, acetic acid). They get reduced to aldehydes (formaldehyde, acetaldehyde). Aldehydes get reduced to alcohol (methanol, ethanol), which finally get reduced to hydrogenated versions (methane, ethane).