Biological molecules：練習題

Which colour change indicates a positive result when testing for starch using iodine solution?

Which statement correctly identifies a biological molecule and a unique chemical element that is always present in it, but typically absent from the other two major organic molecule groups (carbohydrates and fats)?

A segment of double-stranded DNA contains a total of 120 base pairs. If 20% of the total bases in this segment are guanine, how many thymine bases are present in this segment?

Which three chemical elements are present in carbohydrates, fats, and proteins?

Both starch and cellulose are large biological molecules found in plants. Which row correctly identifies their subunits and their primary function in the plant?

A: Starch (Amino acids, Energy store); Cellulose (Glucose, Structural support)
B: Starch (Glucose, Energy store); Cellulose (Glucose, Structural support)
C: Starch (Glucose, Structural support); Cellulose (Fatty acids, Energy store)
D: Starch (Fatty acids, Energy store); Cellulose (Glucose, Structural support)

State the three main chemical elements that make up carbohydrates.

A food sample is tested for reducing sugars and fats. Describe the specific sequence of steps and observations required to confirm the presence of both in a single solid sample.

Calculate the total number of hydrogen bonds in a double-stranded DNA segment where \( 30 \% \) of the \( 400 \) total bases are cytosine.

(a) List the chemical elements that make up the following biological molecules: carbohydrates, fats (lipids), and proteins.
(b) For each of the following food tests, state the biological molecule it is used to detect and describe the positive result:
(i) Iodine solution test
(ii) Benedict's solution test
(iii) Biuret test

(a) Identify the smaller molecules (monomers) that make up the large biological molecules: starch, protein, and fats.

(b) A student tests an unknown food sample. Explain how they would use Benedict's solution and Biuret reagent to test for the presence of reducing sugars and proteins, respectively. Include the expected positive colour changes for each test.

(c) Describe the double helix structure of a DNA molecule, referring to its two strands, bases, and how complementary base pairing occurs.