Question

1. The nucleus is a membrane-bound organelle that contains the cells genetic information. What other intracellular organelle is the nucleus continuous with (connected to)?

a. Lysosome

b. Mitochondria

c. Plasma membrane

d. Endoplasmic reticulum

2.

A new element has been created by scientists. Element X exists in several forms, as an ion (X+), a small molecule (X2), a large molecule (X-X-X-X-X-X-X-X), and as part of a protein (X-Protein). Which form of element X is most likely to be able to cross a lipid bilayer without help?

a. X⁺

b. X₂

c.
X-X-X-X-X-X-X-X (X₈)

d. X-Protein

3.

Membranes in cells are composed mainly of phospholipid molecules. These molecules self-assemble in water to form bilayers. What property of these molecules drives this formation?

a. They are hydrophobic

b. They are hydrophilic

c. They are amphipathic

d. None of the above

Answer 1

1.

Answer – d. Endoplasmic reticulum

Explanation –

The outer nuclear membrane encloses the endoplasmic reticulum lumen and so, the outer nuclear membrane is continuous with the endoplasmic reticulum. Thus, the intracellular organelle which is connected to (continuous with) nucleus is endoplasmic reticulum.

Therefore, the correct option is d. Endoplasmic reticulum.

2.

Answer – b. X2

Explanation –

The ability of a molecule to cross a lipid bilayer without help depends upon two factors – concentration gradient, so a molecule moves from a region of high concentration to a region of low concentration and the other factor is, permeability coefficient which depend upon partition coefficient or in simple terms, the hydrophobicity of the molecule.

Ions and large proteins cannot move even concentration gradient exist. Thus, option (a) and (d) are incorrect.

Between X2 and X-X-X-X-X-X-X-X, the one which have small size have higher chances of crossing lipid bilayer. Thus, among the following options X2 is most likely to be able to cross a lipid bilayer without help.

Therefore, the correct option is b. X2.

3.

Answer – c. They are amphipathic

Explanation –

Phospholipid molecules consist both a hydrophilic(water-loving) polar side groups and hydrophobic(water-repellent) hydrophobic side chains. These type of molecules are known as amphipathic and this, amphipathic, property of phospholipids help in self-assembling in water to form bilayers.

Therefore, the correct option is c. They are amphipathic.