theSIGNAL SCIENCE
20 October 2026
"The important thing is to never stop questioning."
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Science

A Pond Alga Taught Scientists to Flip Neurons

This year's Nobel prize in physiology or medicine honors three researchers who turned a single-celled alga's light sensor into a switch for the brain.

Here is a strange thought. One of the great tools of modern neuroscience began with a pond alga that has no eyes, no brain and no nerves. Why would anyone study it? Peter Hegemann in Berlin and Georg Nagel in Würzburg simply wanted to know how Chlamydomonas senses light.

Light-sensing, after all, is not a privilege of animals with eyes. Single cells use light to swim towards or away from it, to make energy and to keep pace with the demands of a 24-hour day. The two scientists found that the alga relies on one protein, channelrhodopsin, set into its outer membrane. Inside sits a small light-absorbing molecule, retinaldehyde.

When light strikes it, the molecule changes shape, and the protein changes with it. A tiny passage opens through the membrane. Positively charged particles, including sodium, rush in from the surrounding water, and that signal helps the alga swim. Now comes the a-ha moment.

Photo: Keith Mapeki / Unsplash
Green algae like Chlamydomonas use a single light-sensitive protein to steer through water.
Discuss
  • Why might basic research on a tiny alga turn out to matter for medicine decades later?
  • How is switching neurons with light different from using drugs or electrodes to change brain activity?
  • The researchers began with curiosity, not a medical goal. Should science funding favor curiosity-driven or goal-driven projects?
Science

Japan Aims for Mars's Potato-Shaped Moon

Before dawn on Tanegashima island, thousands of people woke early to watch a rocket vanish into black sky. Its cargo, Japan's MMX probe, is heading for Phobos, a pitted, potato-shaped moon of Mars. Why risk it? Phobos's gravity is a thousandth of Earth's, so a French-German rover named Idefix, after a cartoon terrier, will bounce before it settles.…
  • If a tiny sample from Phobos arrives in 2031, what should scientists ask first?
∞
Optogenetics lets researchers control specific nerve cells with light and see what happens to behavior.
Karl Deisseroth, psychiatrist and bioengineer, Stanford University
Science

One Ocean Roars While Its Neighbour Sleeps

Twenty-two named storms, and two months of the season still to go. The eastern Pacific has already beaten an average year, fuelled by El Niño's warm water and weak high-altitude winds. Hurricane Polo exploded into 180 mph gusts. Yet the Atlantic is eerily quiet. Why? El Niño boosts wind shear there, tearing storms apart. Only Isaias has become a hurricane, and it formed later than any on satellite record.…
  • If El Niño silences one ocean and energises another, how reliable are seasonal storm forecasts?
GLOBAL · Science
Who's paying whom? The circular money machine behind the AI boom (or bubble)
ASIA · Science
World's oldest shipwreck discovered off coast of Turkey
AMERICAS · Science
Having a baby is too expensive, 4 in 5 parents say
EUROPE · Science
The uranium cubes that exposed Nazi Germany’s nuclear failure
theSIGNAL IN THE LAB
1VOCABULARY
light-gated ion channelswind shear
El Niñopittedblunt
humblecargo
2GRAMMAR FOCUS
Cleft sentences — It was X that / What I need is
Cleft sentences split one idea into two parts to stress a particular piece of information: 'It was/is X that...' emphasises a person, thing or time, while 'What/All + clause + is...' puts the focus on the final element. After 'It was' we can use 'that', 'who' (for people) or 'which'.
It · that · What · who · All · where · was · is
  1. was a simple curiosity about how algae sense light that led to optogenetics.
  2. It was Hegemann and Nagel discovered that the alga relies on channelrhodopsin.
  3. It is the protein's change of shape opens a tiny passage through the membrane.
  4. researchers now have is a way to control specific cells with light instead of blunt electrodes or drugs.
  5. It was Deisseroth, a Stanford psychiatrist and bioengineer, helped to place channelrhodopsin inside neurons.
  6. the MMX probe hopes to bring back from Phobos is about 10 grams of dust.
3DEPENDENT PREPOSITIONS
Complete each phrase with the correct preposition. All from today’s articles.
  1. The alga relies ___ one protein, channelrhodopsin, set into its outer membrane.
  2. Light-sensing is not a privilege ___ animals with eyes.
  3. The molecule changes shape, and the protein changes ___ it.
  4. Researchers can now control specific cells with light, instead ___ blunt electrodes or drugs.
  5. The eastern Pacific has already beaten an average year, fuelled ___ El Niño's warm water.
4CRITICAL THINKING
The alga story is told as a neat success, but we only hear about curiosity projects that happened to pay off. What evidence would you need to judge whether a nation's research spending is wise, and who should decide which unusual questions deserve public money? Consider also how the writer's choice of dramatic phrases, such as 'a-ha moment', shapes your impression of how science really progresses.
5CREATIVE · HEADLINES
Write a headline for the top story in each of the following styles. One line each, no explanation:
  • TABLOID NEWSPAPER
  • LUXURY MAGAZINE
  • ACTIVIST BLOG
6WRITING
Imagine you are a science teacher who has just read about the pond alga. Write a short paragraph (about 100 words) explaining to teenagers why an everyday organism in a pond or puddle might deserve their attention, using at least one example from the article.
7DEGREES OF EXTREMITY
Complete each ladder from mild to strong.
  • unusual→→
  • interesting→→
  • quiet→→
  • strong→→
  • grew quickly→→
  • tired→→
8SPEAKING
  1. Describe a discovery that surprised you. Why did it stay in your memory?
  2. Would you volunteer to travel to a distant moon? What would worry you?
  3. Which natural force do you find most frightening, and why?
  4. Why do some people get obsessed with tiny details that others ignore?