BIOLOGICAL MOLECULES: LIPIDS

Lipid consists elements of

• carbon, oxygen, hydrogen, sulphur

• carbon, hydrogen, oxygen, nitrogen

• carbon, oxygen, phosphorus

• carbon, oxygen, hydrogen

Although carbohydrates and lipids are made of the same elements, they dissolve in different types of solvents, as

• carbohydrates dissolve in nonpolar solvents while lipids dissolve in polar solvents

• monosaccharides dissolve in nonpolar solvents, like water, while oils dissolve in polar solvents, like benzene

• polysaccharides dissolve in polar solvents, like carbon tetrachloride, while waxes dissolve in nonpolar solvents

• monosaccharides dissolve in polar solvents, like water, while oils dissolve in nonpolar solvents, like benzene

Xerophytes are plants that have adapted to live in dry conditions. How do lipids contribute to reducing water loss during transpiration in xerophytes leaves?

• Xerophyte leaves have a high phospholipid content that reduces water loss.

• Xerophytes have waxy leaves that reduce water loss.

• Xerophyte leaves have a low oil content that reduces water loss.

• • Xerophyte leaves have a low phospholipid content that reduces water loss.

  
  

Write an equation of formation of trigycerides

Which of the following is used to dissolve lipids?

• Carbon tetrachloride only

• Benzene only

• Water

• • Both carbon tetrachloride and benzene

  
  

Oil is always in a liquid state at room temperature. What could prevent oil from solidifying in the fridge?

• Its low glucose content

• Its high melting point

• Its high phosphate content

• Its unsaturated fatty acids

The lipids forming the main component of cell membranes of animal cells are different from other lipids because they have ...

• phosphorus (P)

• calcium (Ca)

• oxygen (O)

• hydrogen (H)

Answer explanation

The lipids forming the main component of cell membranes are complex lipids called phospholipids. They are complex because, in addition to the alcohol (glycerol) and fatty acids that form simple lipids (e.g., fats, oils, and waxes), they contain a phosphate group and often an additional choline group, which contains a phosphorus (P) atom and a nitrogen (N) atom respectively. The phosphate group (that is present in every phospholipid) is the reason phospholipids are different from many other lipids, as simple lipids only consist of carbon, hydrogen, and oxygen atoms.

Unlike other fat molecules, how many fatty acids are in a phospholipid molecule?

• Two fatty acids

• Four fatty acids

• Only one fatty acid

• Three fatty acids

Answer explanation

Simple lipids like fat and oil molecules consist of three fatty acids and a glycerol molecule. Phospholipids (shown below) are complex lipids that differ from other fat molecules as they are only made of two fatty acids. Instead of the third fatty acid, phospholipids contain a phosphate group.

Lipids are insoluble in water but soluble in

Triglycerides are composed of three fatty acids and a glycerol molecule through