Question

In an open circulatory system, (a) There is no heart (b) There is no need of blood vessels (c) There are open spaces or sinuses in the body (d) All the above

Short answer

The correct answer is (c). There are open spaces or sinuses in the body, which is a key characteristic of an open circulatory system.

Step-by-step solution

Evaluate Option (a)

The statement 'There is no heart' is incorrect. Even though the heart in an open circulatory system doesn't function exactly the same way as in a closed system, it still exists. Therefore, option (a) is incorrect.

Evaluate Option (b)

The statement 'There is no need of blood vessels' is partially correct. While in open system the blood is not entirely confined to blood vessels, it does still utilize vessels for part of the path.

Evaluate Option (c)

The statement 'There are open spaces or sinuses in the body' is correct. In an open circulatory system, major part of the body fluid resides in hemocoel and bathes the body's organs directly.

Evaluate Option (d)

The statement 'All the above' can only be correct if all other options are correct, which they aren't. Therefore, option (d) is incorrect.

Key concepts

heart

In the open circulatory system, the heart plays a crucial role, even though it functions a bit differently compared to the closed circulatory system. The heart in this system is responsible for pumping hemolymph, which is a fluid analogous to blood, into body cavities rather than through a series of closed vessel networks. This means that while the heart may not have the same complex structure or routine as in more advanced circulatory systems, it is still vital for maintaining circulation.

In some invertebrates, such as insects or some mollusks, the heart is tubular and functions with a series of chambers and ostia (valve-like openings). These help direct the flow of the hemolymph from the dorsal section of the creature to various parts of its body.

• Despite the simplicity, the heart is crucial for distributing nutrients and hormones throughout the body.
• The periodic contractions of the heart ensure that hemolymph reaches the otherwise open spaces within the organism’s body.
• The open nature of the system emphasizes the reliance on other mechanisms such as body movements to help with circulation.

blood vessels

Blood vessels in an open circulatory system do exist, but their role differs significantly from what we might expect in closed systems like those of mammals. In these systems, vessels are not used to maintain a closed loop of circulation but are instead used to channelize the flow of hemolymph towards certain regions before it disperses into the open body cavities.

These vessels can be thought of as pathways that assist in directing the initial movement of the hemolymph.

• Vessels aid in the distribution of hemolymph from the heart initially, guiding the fluid to essential areas before being released into open spaces.
• They provide a controlled way to push nutrients and oxygen to where they are most needed initially.

The vessels lack the rigidity and specialization seen in closed systems, offering a simpler, less regulated method for circulation. This means the blood vessels are adaptations that help manage the otherwise diffuse nature of the open system.

sinuses

An integral component of open circulatory systems are the sinuses, which can also be understood as the 'open spaces' within the body cavity where a majority of the circulation occurs. In these spaces, the hemolymph bathes the organs directly, allowing for nutrient and waste exchange with tissues.

These sinuses are part of a larger cavity known as the hemocoel, which serves as the primary site for internal fluid exchanges.

• The hemocoel and its sinuses provide room for organ growth and movement while ensuring efficient nutrient exchange.
• This arrangement allows for a direct method to supply cells with necessary components like nutrients and oxygen, albeit less efficiently than closed systems.

The openness of the system implies that hemolymph pressure is typically lower than in closed circulatory systems, leading to slower nutrient distribution. However, the simplicity supports the metabolic needs of many invertebrates quite adequately.