Tardigrades: The Microscopic Survivors
ANNOUNCER: Part 4. You will hear a zoology student giving a presentation about an animal called tardigrade. First, you have some time to look at questions 31 to 40. Now listen carefully and answer questions 31 to 40.
SPEAKER: For my project on invertebrates, I chose to study tardigrades.
SPEAKER: These are microscopic, or more precisely near-microscopic, animals.
SPEAKER: There are more than 1,000 known species, belonging to the phylum Tardigrada.
SPEAKER: Most tardigrades measure between 0.05 millimetres and 1 millimetre in length.
SPEAKER: The largest species can grow up to about 1.2 millimetres.
SPEAKER: They are sometimes called water bears because they live in water and move in a bear-like way.
SPEAKER: Another nickname is moss piglet, based on their appearance when viewed from the front.
SPEAKER: Tardigrades were first discovered in Germany in 1773 by Johann Goeze.
SPEAKER: He gave them the scientific name Tardigrada.
SPEAKER: Although there are many species, they share similar physical features.
SPEAKER: Their bodies are short, rounded, and resemble a small barrel.
SPEAKER: The body is divided into four segments.
SPEAKER: Each segment has a pair of legs.
SPEAKER: At the end of each leg there are between four and eight claws.
SPEAKER: Some species don’t have claws but instead have suction discs.
SPEAKER: These help them cling to surfaces or capture prey.
SPEAKER: Tardigrades have no lungs or specialized breathing organs.
SPEAKER: Oxygen and nutrients move through a fluid filling the body cavity.
SPEAKER: Their head looks unusual and somewhat flattened.
SPEAKER: Their mouth contains a tube with sharp structures called stylets.
SPEAKER: These allow them to pierce cells of plants or animals.
SPEAKER: Tardigrades are found in every region of the world.
SPEAKER: They commonly live on the beds of lakes, on plants, and in wet environments.
SPEAKER: Research has shown that they can survive radiation and extremely high pressure.
SPEAKER: They can tolerate temperatures as low as −200°C.
SPEAKER: They can also withstand temperatures above 148°C.
SPEAKER: If conditions become extreme, tardigrades enter a state called cryptobiosis.
SPEAKER: They curl into a ball known as a tun.
SPEAKER: In this state their metabolism drops to less than 1% of normal.
SPEAKER: When water returns, they can revive within a few hours.
SPEAKER: During cryptobiosis they produce a protein that protects their DNA.
SPEAKER: In 2016, scientists revived tardigrades that had remained in this state for over 30 years.
SPEAKER: An earlier claim suggested a 120-year-old tun was revived, though that experiment has never been repeated.
SPEAKER: Scientists are currently studying how long tardigrades might survive in space.
SPEAKER: The longest survival recorded so far is about 10 days.
SPEAKER: Tardigrades feed by consuming liquids.
SPEAKER: They suck fluids from moss and seaweed.
SPEAKER: Some species even prey on other tardigrades.
SPEAKER: Tardigrades have existed for approximately 500 million years.
SPEAKER: During that time they have survived five mass extinctions.
SPEAKER: Because they are so widespread, they have not been evaluated by the International Union for Conservation of Nature.
SPEAKER: As a result, they are not listed as endangered.
SPEAKER: Many scientists describe tardigrades as a thriving species.
SPEAKER: Does anyone have any questions?
ANNOUNCER: That is the end of Part 4. You now have one minute to check your answers to Part 4.
ANNOUNCER: That is the end of the listening test. In the IELTS test, you would now have 10 minutes to transfer your answers to the listening answer sheet.
