Which of the following is correct statement ?

Options

A. Starch is a polymer of `alpha`-glucose
B. Amylose is a component of cellulose
C. Proteins are composed of only one type of amino acid
D. In cyclic structure of fructose, there are four carbons and one oxygen atom

Explanation

To determine which statement is correct, let's analyze each option step by step.

### Step 1: Analyze Statement A
**Statement A:** "Starch is a polymer of alpha glucose."
- **Explanation:** Starch is indeed a polysaccharide made up of glucose units. Specifically, it is composed of alpha-D-glucose units linked together primarily by α(1→4) glycosidic bonds. Therefore, this statement is **correct**.

### Step 2: Analyze Statement B
**Statement B:** "Amylose is a component of cellulose."
- **Explanation:** Amylose is actually a component of starch, not cellulose. Cellulose is composed of beta-D-glucose units. Therefore, this statement is **incorrect**.

### Step 3: Analyze Statement C
**Statement C:** "Proteins are composed of only one type of amino acids."
- **Explanation:** Proteins are made up of 20 different amino acids. They can be combined in various sequences to form different proteins. Thus, this statement is **incorrect**.

### Step 4: Analyze Statement D
**Statement D:** "In cyclic structure of fructose, there are 4 carbons and 1 oxygen atom."
- **Explanation:** Fructose has the molecular formula C6H12O6, meaning it contains 6 carbon atoms. In its cyclic form, fructose does not have only 4 carbons; it has 5 carbons and 1 oxygen in the ring structure. Therefore, this statement is **incorrect**.

### Conclusion
After analyzing all the statements:
- **Correct Statement:** **A** - "Starch is a polymer of alpha glucose."