Yeast Shows Physics can Give Rise to Multicellular Life Sans Mutations 

Syllabus: GS3/Science and Technology

Context

• A new study on Snowflake yeast by National Centre for Biological Sciences (NCBS) scientists offers an ‘unconventional view’ of how major changes first arise in the course of evolution.

What is Yeast?

• Yeast is a unicellular fungus.
• Commonly used in:
  • Baking (makes bread rise).
  • Alcohol production (fermentation).
  • Scientific research (model organism).
• Reproduction by budding:
  • A small bud forms on the parent cell.
  • The nucleus divides, one part goes into the bud.
  • The bud grows and detaches, becoming a new yeast cell.

What is Snowflake Yeast?

• Regular yeast grows as single cells; new cells (buds) separate after formation.
  • Snowflake yeast has a genetic mutation that prevents buds from separating.
• As a result, yeast cells stick together, forming a cluster like a snowflake.
  • These clusters grow rapidly and become visible to the naked eye within 12 hours.
• Significance in Science: Snowflake yeast is used to study how unicellular life evolved into multicellular organisms.
  • Normally, multicellular life needs special transport systems (like blood vessels) to move nutrients.
  • But snowflake yeast lacks such biological systems, yet still grows exponentially.

The Scientific Puzzle

• According to current understanding, growth should stop once inner cells can’t get nutrients.
• However, snowflake yeast in the lab continued to grow beyond expected limits.
• Scientists wanted to understand how nutrients were still reaching all cells.

New Discovery – Physical Process Behind Growth

• The study found that a simple physical process helps the yeast grow: fluid flow.
• Growth was seen only in liquid (solution), not in jelly-like mediums.
• There are two types of movement in fluids:
  • Diffusion: nutrients spread from high to low concentration.
  • Advection: whole fluid moves, carrying nutrients with it.
• Diffusion alone couldn’t explain large growth (only up to 50 micrometers).
• Scientists observed advection — fluid moved into the cluster from sides and exited from the top.
• Snowflake yeast consumes sugar (glucose) and produces alcohol and carbon dioxide.
• This makes surrounding fluid less dense.
  • Less dense fluids rise, creating natural upward flow (like hot air rising).
  • This flow brings fresh nutrients into the cluster, keeping all cells alive.

Evolutionary Significance

• Traditionally, multicellularity is thought to arise from gradual genetic mutations.
• This study shows that physics and chemistry alone could allow early multicellularity — before genetic changes.
• Later, genetic evolution could make multicellularity a permanent feature in life.

Source: TH