--- title: Rivers, lakes and ponds — a lesson of Mova's school · trees and pragmatics description: «Rivers, lakes and ponds», a lesson of the biology course of Mova's primary school, sentence by sentence with dependency trees and pragmatics. It begins: Fresh water is a habitat of its own: rivers rush and carry mud and stones, while ponds and lakes stand still and fill with plants, insects, frogs --- [Mova](https://md.mova.elamur.ai/free/en/) · [this page in HTML](https://mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/) [home](https://md.mova.elamur.ai/free/en/) / [corpora](https://md.mova.elamur.ai/free/en/corpora/) / [school](https://md.mova.elamur.ai/free/en/corpora/school/) / [Biology](https://md.mova.elamur.ai/free/en/corpora/school/biology/) / Rivers, lakes and ponds # Rivers, lakes and ponds Lesson 10 of the biology course of Mova's primary school: 18 sentences, each with its syntax tree and pragmatics. The lessons are written for Mova, and their agreed trees are part of Mova corpus 0.4 (CC BY-SA 4.0). How Mova does on its tests: [the lesson at school](https://md.mova.elamur.ai/free/en/school-run/biology/10-rivers-lakes-and-ponds/). - [0](https://md.mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/0/) — Fresh water is a habitat of its own: rivers rush and carry mud and stones, while ponds and lakes stand still and fill with plants, insects, frogs and fish, and each kind of water has its own crowd. - [1](https://md.mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/1/) — A pond is a jungle in miniature: at a pond-dipping tray you can watch a dragonfly larva shoot out its hinged jaw and grab a tadpole, while a pond skater walks on the water's stretchy skin above. - [2](https://md.mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/2/) — Winter does not kill a lake, because water is heaviest at 4 degrees: the coldest water and the ice float on top like a lid, and fish swim on in the liquid water below. - [3](https://md.mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/3/) — Cartoon piranhas turn a cow into a skeleton in seconds; real red-bellied piranhas mostly eat insects, fish, worms and plants, feed in groups mainly for safety, and attacks on people are rare and usually just a bite. - [4](https://md.mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/4/) — Cartoons often show river otters floating on their backs and smashing shells on a stone on their tummy; that trick belongs to sea otters, which also hold paws while they sleep so they do not drift apart. - [5](https://md.mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/5/) — Pond skaters are insects with 6 legs; they stand on the water's surface, which acts like a thin stretchy skin, on long legs with water-repelling hairs, and they feel the ripples of insects falling in. - [6](https://md.mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/6/) — The kingfisher dives head-first from a perch and its dagger beak enters the water with little splash; Japanese engineers shaped a bullet train's nose like it to make the train quieter in tunnels. - [7](https://md.mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/7/) — Atlantic salmon grow big at sea, then swim up the river where they hatched to lay their eggs, finding it by smell; they stop eating on the way and live on the fat built up at sea, and they can leap over 3 metres to climb waterfalls. - [8](https://md.mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/8/) — Otters close their ears and nostrils underwater, keep warm with thick, air-trapping fur, and sea otters, not river otters, crack shells with stones while floating on their backs. - [9](https://md.mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/9/) — Dragonfly larvae live underwater for up to several years and catch insects, tadpoles and small fish with a hinged jaw that shoots out, and adult dragonflies catch over 90 per cent of the insects they chase. - [10](https://md.mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/10/) — Grey herons stand still in shallow water so fish do not notice them, then stab with a sudden strike, and they also raid garden ponds for goldfish. - [11](https://md.mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/11/) — Beavers fell trees with their teeth and build dams to make deep ponds that protect their lodge and do not freeze to the bottom; their orange front teeth contain iron, which makes them extra hard, and never stop growing. - [12](https://md.mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/12/) — Water is heaviest at about 4 degrees Celsius, so it sinks to the bottom of a lake while colder water and ice float on top, and fish survive under the ice. - [13](https://md.mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/13/) — Red-bellied piranhas have razor-sharp triangular teeth but mostly eat insects, fish, worms and plants, and attacks on people are rare, usually just bites when water is low and food is scarce. - [14](https://md.mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/14/) — After heavy rain, water rushing off the land makes rivers faster, higher and brown with soil, and the Amazon carries more water than the next several biggest rivers put together. - [15](https://md.mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/15/) — Great crested newts live on land for much of the year, wrap each egg in a folded leaf in a pond in spring, are protected by law in the UK and do best in ponds without fish, because fish eat their eggs and young. - [16](https://md.mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/16/) — Freshwater mussels filter and clean river water as they feed, pearl mussels can live over 100 years, and their babies spend their first months on the gills of salmon or trout. - [17](https://md.mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/17/) — A dragonfly has 6 legs and 4 wings, like many insects. - ← previous: [Coral reefs, rockpools and the seashore](https://md.mova.elamur.ai/free/en/corpora/school/biology/9-coral-reefs-rockpools-and-the-seashore/) - next →: [Swamps, marshes, mangroves and bogs](https://md.mova.elamur.ai/free/en/corpora/school/biology/11-swamps-marshes-mangroves-and-bogs/) - ↑ back to [Biology](https://md.mova.elamur.ai/free/en/corpora/school/biology/)