The pressure-flow model, first proposed by Ernst Münch, Phloem loading at the source and phloem unloading at the sink establish the pressure gradient.

a.) In source tissues, an accumulation of sugars in the sieve elements generates a lower or negative solute potential (ψs).

 b.) source tissue, causes a steep drop in the water potential (ψ), due to water potential gradient, water enters the sieve elements and causes turgor pressure (ψp ) decrease.

c.) In sink tissues, phloem unloading leads to a lower sugar concentration in the sieve elements, generating a higher or less negative solute potential.

d.) As the water potential of the phloem rises above that of the xylem, water tends to leave the phloem in response to the water potential gradient, causing a decrease in turgor pressure in the sieve elements of the sink.

Which of the following statements of sink and source tissue is FALSE?

#Question id: 2884

#Unit 2. Cellular Organization

When the temperature of a solution of DNA is raised to near the boiling point of water, the optical density, (called absorbance) at 260 nm markedly increases, a phenomenon known as hyperchromicity. Which of the following statement is INCORRECT from the given set of statements?

#Question id: 2885

#Unit 2. Cellular Organization

Which of the following function of DNA methylation in mammalian cell is incorrect?

#Question id: 2886

#Unit 2. Cellular Organization

Match the following sites of modifications on histones given in Column I with their effect on transcription given in Column II.

COLUMN I                                               COLUMN II

1) Methylation of H3K36 in transcribed region               a) Activation

2) Ubiquitinylation of H2BK120 in mammals                b) Repression

3) Phosphorylation of H2AT120                                    c) Elongation

4) Hypoacetylated Lysine

5) Acetylation of H4K8

#Question id: 2887

#Unit 2. Cellular Organization

Which of the following reasons has led to the evolutionary selection of an extra methyl group in DNA?

#Question id: 2888

#Unit 2. Cellular Organization

Repressive complexes have been discovered that are composed of multiple repressing proteins bound to RNAs many kilobases in length that do not contain long open reading frames and are consequently called long noncoding RNAs or lncRNAs. Which of the following statements is correct regarding the regulation of these lncRNAs?

#Question id: 2889

#Unit 2. Cellular Organization

The edges of each base pair are exposed in the major and minor grooves, creating a pattern of hydrogen-bond donors and acceptors and of hydrophobic groups (allowing for Vander Waals interactions) that identifies the base pair. The edge of an C : G base pair displays the following chemical groups in the following order in the major groove: