Chapter 19, Problem 40A

Summary Introduction

To analyze :

The classification of acellular slime molds during the plasmodial stage as multicellular organisms.

Introduction :

The acellular slime molds commonly grow on dead and decaying organic matter. The somatic phase of their life cycle is a free-living diploid multinucleate plasmodium. Plasmodium is a mass of multinucleate protoplasm that is devoid of the cell wall.

Explanation of Solution

Plasmodium is brightly colored and possesses branches known as veins. These veins appear and reappear due to the streaming of the multinucleated protoplasm. The plasmodium is also known as a giant cell that behaves like an amoeba.

Plasmodium bears sporangia once it reaches a certain stage of maturity. The sporangium contains several diploid nuclei that undergo meiosis to form uninucleate spores that are surrounded by cell walls. The spores germinate after falling on a suitable substratum and in the presence of water. The germinating spores release myxamoeba that fuse in pairs to form a diploid zygote. The diploid nucleus of the zygote divides without the formation of cell walls and hence form a multinucleate amoeboid structure known as plasmodium.

Conclusion

The plasmodium is a diploid multinucleated structure but it couldn't be considered as a multicellular organism. It is because the plasmodium is a single cell that contains multiple nuclei in its protoplasm formed after the division of the diploid zygote. The nuclear division of the zygote doesn't follow cell wall formation that results in the formation of plasmodium.