Final answer:
Tardigrades, or Water Bears, are the smallest organisms known to tolerate extreme conditions such as high or low temperatures and the vacuum of space. They're roughly 0.5mm long and have been tested in outer space.
Step-by-step explanation:
The smallest living organism known to survive extreme heat, cold, and the absence of gravitational pull are called Tardigrades, also known as Water Bears or Moss Piglets. These tiny creatures measure approximately 0.5mm in length and have an extraordinary resistant to harsh environmental conditions. Tardigrades can withstand temperatures as low as -272 degrees Celsius (close to absolute zero) and as high as 150 degrees Celsius. Their ability to survive in the vastness of space has been tested and they can endure the vacuum and radiation exposure.
Learn more about Tardigrades