Slime Moulds: Structure, Life Cycle and Unique Features

Slime moulds are among the strangest organisms in biology: they begin life as tiny crawling cells, merge into a giant creeping blob that eats decaying leaves, and finally sprout miniature fruiting bodies that release spores into the air. They are saprophytic protists, meaning they feed on dead organic matter, and they live in cool, shady, moist forest floors.

Slime moulds matter because they blur the line between single cells and multicellular bodies: thousands of cells can flow together as one giant mass with millions of nuclei but no separating walls. Scientists study them to understand cell movement, and their simple problem-solving behaviour, such as finding the shortest path through a maze to reach food, fascinates researchers.

Key Concepts

• Saprophytic protists: feed on decaying twigs, leaves and other dead organic matter.
• Plasmodium: the feeding stage, a naked, multinucleate mass of protoplasm that creeps along engulfing food particles.
• Phagocytosis: the process of engulfing food particles practiced by the plasmodium.
• Fruiting bodies: stalked structures formed from the plasmodium under unfavourable conditions, bearing spores at their tips.
• Spores: have true walls, are extremely resistant, survive for many years, and are dispersed by air currents.
• Example: Physarum, the most studied slime mould.

How It Works

The life cycle starts when a resistant spore lands in a moist spot and germinates into small amoeba-like cells. These cells feed, grow and fuse with each other, forming the plasmodium, a slimy network that streams its cytoplasm in pulsing flows and may spread over several centimetres of rotting wood. When food runs out or conditions turn dry, the plasmodium stops feeding and reorganises itself into upright fruiting bodies. Each fruiting body produces thousands of walled spores at its tip; the spores blow away, survive harsh years, and restart the cycle wherever they land.

Worked Example

Question: One slime mould fruiting body releases about 10,000 spores. If a plasmodium forms 25 fruiting bodies and only 1 percent of all spores successfully germinate, how many new feeding cells begin the next generation?

Step 1: Total spores = 25 x 10,000 = 250,000.

Step 2: Germination rate = 1 percent = 0.01.

Step 3: New cells = 250,000 x 0.01 = 2,500.

Answer: About 2,500 new cells, showing how massive spore production compensates for heavy losses.

Real-World Applications

• Cell biology research: Physarum is a model for studying cytoplasmic streaming and cell movement.
• Nutrient cycling: by digesting dead wood and leaves, slime moulds return nutrients to forest soil.
• Behavioural studies: maze experiments with slime moulds explore how simple organisms solve problems without a brain.
• Education: their dramatic life cycle is a vivid classroom example of alternation between feeding and reproductive stages.

Slime moulds are saprophytic protists whose feeding stage is a creeping, multinucleate plasmodium. In hard times the plasmodium builds fruiting bodies that release tough, long-lived spores, and organisms like Physarum help scientists study movement, decomposition and simple problem-solving.