Question

Select the correct statement from the ones given below with respect to Periplaneta americana. (a) Nervous system located dorsally, consists of segmentally arranged ganglia joined by a pair of longitudinal connectives. (b) Males bear a pair of short thread like anal styles. (c) There are 16 very long Malpighian tubules present at the junctions of midgut and hindgut. (d) Grinding of food is carried out only by the mouth parts.

Short answer

(a) Nervous system located dorsally, consists of segmentally arranged ganglia joined by a pair of longitudinal connectives.

Step-by-step solution

- Analyzing Statement (a)

Examine whether Periplaneta americana's nervous system is dorsally positioned and has segmentally arranged ganglia joined by longitudinal connectives.

- Analyzing Statement (b)

Investigate the statement concerning the presence of anal styles in male Periplaneta americana and if they are short and thread-like.

- Analyzing Statement (c)

Verify the number of Malpighian tubules in Periplaneta americana and their length, as well as their location at the junction of midgut and hindgut.

- Analyzing Statement (d)

Assess the mechanism of food grinding in Periplaneta americana to determine if it is exclusively performed by the mouth parts.

Key concepts

Nervous System of Insects

The nervous system of insects like Periplaneta americana is a fascinating and highly efficient network. Similar to other arthropods, the nervous system in insects is characterized by a series of segmentally arranged ganglia. Each segment of the insect's body has one ganglion on each side, and these are connected by a pair of longitudinal connectives running parallel to the insect’s body. The ganglia essentially serve as mini-brains, controlling the functions of their respective body segments.

In contrast to humans, the nervous system in insects is primarily located ventrally, not dorsally. To understand this better, imagine the insect's nerve cord running along the belly side, rather than along the back. This configuration allows for rapid signal transmission across the segments, enabling quick and coordinated responses necessary for survival in various environments.

Anal Styles in Insects

Anal styles are unique structures found in some male insects, serving as an integral part of their reproductive anatomy. Specifically in Periplaneta americana, which is the scientific name for the American cockroach, males possess a pair of short, thread-like anal styles. These structures, located at the posterior end of the abdomen, play a role in copulation, helping to secure the male to the female.

It is interesting to note that not all insects have anal styles, and their presence or absence, as well as their specific form can be indicative of different species or orders within the class Insecta. For example, in some species, the anal styles are more pronounced and may even assist in dispersing pheromones, adding complexity to their reproductive and communicative behaviors.

Malpighian Tubules Function

Malpighian tubules are integral to the excretory and osmoregulatory systems of insects, including Periplaneta americana. These fine, hair-like tubules extend from the junction between the midgut and hindgut, floating freely in the hemolymph, which is the insect equivalent of blood. They are involved in the filtration of this hemolymph, removing waste products and excess salts from the insect's body.

In Periplaneta americana, there are typically a large number of these tubules, although the exact number can vary. The waste removed by the tubules is excreted along with the feces, helping to maintain the insect's internal chemical balance. This process is vital as it allows the insect to conserve water, which is particularly important in terrestrial habitats where moisture retention can be crucial for survival.

Insect Digestion Process

Mastering the understanding of the digestion process in insects, such as Periplaneta americana, reveals a complex journey that begins the moment food is ingested. Initially, solid food is broken down mechanically by the mouthparts, which include mandibles and maxillae. This is contrary to the simplified notion that grinding occurs solely at the initial stage.

Following this, the ingested matter moves through the esophagus to the crop, where temporary storage occurs, and then to the proventriculus, which triturates or further grinds down the food. Digestive enzymes then mix with the food as it enters the midgut, where the bulk of nutrient absorption occurs. Lastly, the hindgut is responsible for reabsorption of water and electrolytes, and compaction of indigestible material into fecal pellets. Thus, the process comprises mechanical and enzymatic actions across different parts of the insect's gut.