Question

EVOLUTION CONNECTION Large brown algae called kelps can grow as tall as 25 m. Kelps consist of a holdfast anchored to the ocean floor, blades that float at the surface and collect light, and a long stalk connecting the blades to the holdfast (see Figure 28.12). Specialized cells in the stalk, although nonvascular, can transport sugar. Suggest a reason why these structures analogous to sieve-tube elements might have evolved in kelps.

Short answer

Despite being avascular, kelps have certain cells specialized for the transportation of sugar to various regions of the algal body. These cells are analogous to sieve tubes, and they might have evolved to facilitate the proper distribution of food to every part of the Kelp’s body.

Step-by-step solution

Algae

The eukaryotic domain comprises a total of four distinct kingdoms; algae belong to one of these four kingdoms (specifically, the Kingdom Plantae). Algae are avascular plants that also lack the ability to form seeds. These are classified into three groups based on their pigments; these are red, brown, and green.

Step 2:Brown algae

Brown algae are named so because of the presence of the pigment fucoxanthin(a xanthophyll pigment) that imparts the body if these algae a brown color. Structurally, they have a holdfast (provides substrate anchorage), blade (leaf-like structures that conduct photosynthesis), and a stalk (links the holdfast and blade).

Step 3:Specialized cells of Kelps

The kelps are one of the members of the brown algae group and are known for their astonishing height (may reach up to 25 m or more). The kelps are avascular like any other algae, but they possess special cells in their stalk that can transport sugars. These special cells are analogous to the vascular plant’s sieve tubes.

The specialized cells in Kelps might have evolved to ensure that the food (sugar molecules) synthesized by the blades are proportionally transported to every part of their long body, and the sugars can be used uniformly within the Kelp’s body for energy production.