Topic: Year in a lake

Target group

4th‑grade students of elementary school

Core curriculum

Grade IV

VI. The natural environment of the immediate area. Pupil:

12) determines living conditions in water (sunshine, oxygen content, water resistance) and indicates the adaptation of organisms (eg fish) to the living environment.

General aim of education

Students characterize the living conditions prevailing in the lake at different times of the year.

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• discuss the relationship between changes in water temperature in the lake and the formation of water layers;

• discuss the relationship between the density of water and ice and the survival of organisms in the bottom zone;

• describe the living conditions in the lake at different times of the year.

Methods/techniques

• activating

  • discussion.

• expository

  • talk.

• exposing

  • film.

• programmed

  • with computer;

  • with e‑textbook.

• practical

  • exercices concerned.

Forms of work

• individual activity;

• activity in pairs;

• activity in groups;

• collective activity.

Teaching aids

• e‑textbook;

• notebook and crayons/felt‑tip pens;

• interactive whiteboard, tablets/computers;

• sheets of gray paper;

• colored markers.

Lesson plan overview

Before classes

• Students get acquainted with the content of the abstract. They prepare to work on the lesson in such a way to be able to summarize the material read in their own words and solve the tasks themselves.

Introduction

• The teacher asks the chosen student to characterize the conditions in the water that affect the life of aquatic organisms.

• The teacher explains the aim of the lesson and together with students determines the success criteria to be achieved.

Realization

• Students read the fragment „Lake water temperature” and analyze the illustration „Clake water temperature changes depending on the season”. They explain how the distribution of water at specific temperature changes in the following seasons in the lake.

• The teacher announces a movie. He instructs his pupils to write a research question and a hypothesis in the form provided in the abstract. Then he plays the video and the students note their observations and conclusions. The teacher points the person who shares his insights and explains the reasonableness of the conclusions noted.

• The teacher asks students to carry out the recommended interactive exercise themselves.

• The teacher divides the class into groups. Each team receives a sheet of paper, pencils and felt‑tip pens. After reading the excerpt „Life under the ice”, they make a poster showing the title of the paragraph. After the appointed time, students compare posters, show similarities and differences between them.

• The instructor asks the chosen person to explain the relationship between the density of water and ice and the survival of the organisms in the bottom zone.

Summary

• The teacher asks students to carry out the recommended interactive exercise themselves.

Homework

• Develop a lap book containing issues learned during the lesson and bring your work to the next class.

• Listen to the abstract recording at home. Pay attention to pronunciation, accent and intonation. Learn to pronounce the words learned during the lesson.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Year in a lake

In the summer, due to the lake surface being heated, three water zones are formed. The upper zone is characterised by high and constant temperature. The wind keeps constantly mixing water and air, which facilitates the dissolution of oxygen in water. Therefore, this water zone is the best oxygenated. The intermediate zone is colder and its waters are not mixed. In the bottom layer, where the temperature reaches 4°C, there is also no water movement.

In autumn, the upper and intermediate zones gradually become colder. They reach a temperature nearing 4°C. The division into zones disappears and lake water is mixed.

In winter, water continues to get colder. Zones re‑emerge. Ice floats on the surface. Under the ice, the upper zone with a constant temperature slightly above 0°C is formed. In the intermediate zone, water temperature rises from 0 to 4°C. The bottom zone has the densest water with a constant temperature of 4°C.

In spring, when the Sun starts heating the lake waters, ice melts. At a certain point the water reaches 4°C and waters are once again mixed. Further mixing results in warmer, lighter water rising to the surface and stop mixing with denser, heavier water with a temperature of 4°C that dwell near the lake bed. Water mixing in the spring and autumn delivers oxygen to the benthic zone of the lake.

When the frosts come, heat stored during the summer in lake waters allows them to remain in a liquid state. Chilled lake water freezes only after a longer period of frost. A thin layer is formed and as frost continues the ice layer keeps growing thicker. Animals move to the lake bed where water is the warmest at 4°C. Ice floating on the surface of the lake allows them to survive winter. It prevents water from being mixed by the wind, thus protecting deeper layers from becoming colder and freezing.

The lake freezing over also causes problems. The amount of light that reaches the depths is reduced and ice cuts off access to air. Therefore, oxygen cannot dissolve in water. Organisms have to limit their activity. Aquatic plants and phytoplankton in partial darkness reduce carbon dioxide assimilation and oxygen production. Fish reduce predation and some stop eating altogether, burrow in mud and spend entire months motionless. The ones that don’t hibernate occupy the warmest places of the lake and use oxygen delivered near the lake bed as a result of water mixing in autumn. The parts of plants that protrude above the water surface die when the surface is covered in ice. However, their parts that are submerged and buried in mud at the bottom of the lake are able to survive until spring.

Certain amphibians also spend winter at the bottom of lakes. Several weeks spent underwater won’t do them harm. Amphibians breathe through their lungs, but they can also absorb oxygen from water through the skin. In spring, amphibians awake and start absorbing oxygen through their lungs.

• Ice floats on the water surface.

• Changes in air temperature in subsequent seasons of the year affect lake water temperature.

• The ice layer saves lake organisms from freezing during winter.