Sexual dimorphism/external differentiation of sex occurs in

Options

A. Ascaris
B. Amoeba
C. Pheretima
D. All the above

Answer

To solve the question regarding sexual dimorphism or external differentiation of sex, we can follow these steps:

### Step 1: Understand the concept of sexual dimorphism
Sexual dimorphism refers to the differences in physical characteristics between males and females of the same species, beyond just the differences in their reproductive organs.

**Hint:** Look for examples of organisms where males and females have distinct physical traits.

### Step 2: Analyze the options provided
The options given are Ascaris, Amoeba, Ferentima, Ferritima, or all of the above. We need to evaluate each option for the presence of sexual dimorphism.

**Hint:** Consider the biological classification and reproductive strategies of each organism.

### Step 3: Evaluate Ascaris
Ascaris is a genus of parasitic worms (roundworms) known for having separate sexes (dioecious). In Ascaris, males and females exhibit distinct physical differences. Males are typically smaller and have a curved posterior end, while females are larger and have a straight body. The reproductive organs are also different, with males having a complex reproductive system confined to the posterior part of the body.

**Hint:** Focus on the anatomical differences between male and female Ascaris.

### Step 4: Evaluate Amoeba
Amoeba is a unicellular organism that reproduces asexually through binary fission. There are no distinct male or female forms in Amoeba, so it does not exhibit sexual dimorphism.

**Hint:** Consider the reproductive method of Amoeba and its implications on sexual differentiation.

### Step 5: Evaluate Ferentima and Ferritima
Ferentima (often referred to as earthworms) are hermaphroditic, meaning they possess both male and female reproductive organs in the same individual. While there may be some external differences, they do not exhibit clear sexual dimorphism as seen in Ascaris.

**Hint:** Think about how hermaphroditism affects the presence of sexual dimorphism.

### Step 6: Conclusion
Based on the evaluations, the only organism that clearly exhibits sexual dimorphism is Ascaris. Therefore, the correct answer to the question is Ascaris.

**Final Answer:** Sexual dimorphism/external differentiation of sex occurs in Ascaris.