Topic: Amphibians – the semi‑aquatic animals

Author: Zyta Sendecka

Target group

6th‑grade student of the elementary school.

Core curriculum

10) Amphibians - student:
a) observes amphibians (photos, films, schemes, natural specimens in the field, etc.) and presents their common features and describes the adaptation of amphibians to life in water and on land,
b) defines amphibians as cold‑blooded animals,
c) presents the method of reproduction and development of amphibians,
d) explains the importance of amphibians in nature and for human beings;

Lesson objectives

Students describe the frogs’ adaptations for their habitats.

The criteria for success

• you will discuss the frogs’ adaptations for life in water and on land;

• you will describe the body structure of a frog;

• you will present the reproduction process of amphibians;

• you will explain how the amphibians’ respiratory mechanism works.

Key competences

• communication in the mother tongue;

• communication in foreign languages;

• mathematical competence and basic competences in science and technology; 

• digital competence;

• learning to learn;

• social and civic competences.

Methods/forms of work

Talk, alternative observation, the “Tell your neighbour” method, working with text.

Individual activity and frontal activity.

Teaching aids

• abstract;

• interactive whiteboard or traditional blackboard;

• tablets/computers.

Lesson plan overview

Introduction

The teacher specifies the subject and the objective of the lesson as well as the criteria for success.

Realization

1. The teacher displays an illustration found on the website: https://commons.wikimedia.org/wiki/Epidalea_calamita#/media/File:Kreuzkroete_fg01.jpg The teacher asks students to identify the creature on the picture and explain why the frog has masking colouring.

2. Students look at the illustration showing the structure of the frog and read an abstract entitled: “Body structure of amphibians”. Students analyse the adaptations of the frog to the habitat resulting from the structure of its body.

3. Students watch a video entitled „Frog respiratory motions” available in the e‑textbook Then, using the „Tell your neighbour” method, students describe what ways the air enters and leaves the frogs' organism and explain where and how gas exchange takes place.

4. Students read an abstract entitled „Reproduction of amphibians” and draw up a map of concepts that organises the most important issues regarding this process in their notebooks.

5. On the example of the amphibian development cycle, students indicate the adaptations of these animals to the habitat.

6. The teacher displays a map showing the number of amphibian species in the world. Students analyse the map. The teacher reminds that amphibians are cold‑blooded organisms. The teacher asks why they hardly ever occur in deserts and in the far north.

7. Students list the adaptations of amphibians for life on land and in water they have learnt during the lesson. The teacher comments on their statements, corrects any mistakes.

8. Students make notes in their notebooks.

Summary

Students do interactive exercises. The teacher discusses the solutions for the exercises with the students.

Homework for the interested students

Read the article posted on the website http://www.radiowroclaw.pl/articles/view/67205/10‑tys‑zab‑uratowanych‑przed‑rozjechaniem‑pod‑kolami‑samochodow and answer the following questions:

• Why do amphibians go on roads?

• How are they saved by volunteers?

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Amphibians – the semi‑aquatic animals

Amphibians are semi‑aquatic vertebrates that show adaptations for life in both of these environments. They occur on all continents except Antarctica. They live on land, e.g. in the soil, on trees or in fresh water. They never occur in seas and oceans.

Amphibians are cold‑blooded animals, which means that their body temperature depends on the temperature of the environment. In our climate, when it's getting colder, amphibians go into a state of numbness. They winter in clusters in different burrows, crevices and in the sludge at the bottom of water reservoirs. They become active again in early spring.

Due to the presence or absence of a tail, amphibians are divided into the Anura – frogs and toads, and Caudata – newts. In the body structure of Anura we can distinguish the head and trunk. The tail occurs in Caudata as well as larvae of Anura and Caudata. The national representatives of this division have got two pairs of limbs equipped with fingers facilitating moving on land. If they are connected by means of interdigital webbing, they facilitate swimming. Limbs are widely spaced to the sides, which makes the trunk stay in contact with the ground and gives the movements of most amphibians characteristic slowness and clumsiness. Nevertheless, they are capable of quickly escaping in an emergency.

All amphibians have naked, scaleless, thin skin. It is highly vascularised and moist, which significantly facilitates gas exchange. The mucus layer protects the amphibians from drying on land and makes it easier to move in water, reducing friction. The toad's skin is also equipped with venom glands. Their secretion protects these animals against attacks by predators, causing, for example, irritation of the mouth and hypersalivation. The pigment cells present in the skin allow the amphibians to adopt masking or warning colouring.

Larvae of amphibians take oxygen from water using gills. In adult individuals, the skin and lungs are involved in the gas exchange process. The air is pressed into the lungs by rhythmical depressing and elevating of the floor of the oral cavity.

Due to the fact that the amphibian skin is thin and porous, gas molecules and water can freely penetrate it. Strong blood flow in the skin makes the gas exchange occur on its entire surface. Oxygen taken through the skin into the blood is transferred to all tissues, and the resulting carbon dioxide is transported to the vessels underneath the skin and removed from the body. The mucus covering the body facilitates efficient gas exchange. This ensures constant skin moisture and facilitates the penetration of gas molecules that dissolve in water.

Amphibians are dioecious animals the reproduction and development of which takes place in water. During mating season (occurring in Poland from March to June) most amphibians embark on a journey to the nearest reservoir.

The female amphibian lays eggs, the so‑called spawn, in the water, which are surrounded by jelly‑like substance. The male, joined with the female in a mating position, covers them with sperm. The fertilisation takes place in water. After some time, the larvae, called tadpole, hatch from the fertilised eggs. They differ from adult forms: they are herbivorous, they use gills to breathe, they resemble fish in shape – they have a barrel‑shaped trunk with a head barely separated from the body. In the early stages of development, they have got no limbs, however, they have got a long tail with a skin fold acting as a fin. Tadpoles, similarly to fish, are equipped with a lateral line organ. During approximately 16 weeks of life in the water, they undergo a metamorphosis, during which the limbs develop and the tail disappears. Internal organs are also restructured, e.g. the gills disappear and the lungs develop. After transforming into an adult form, most of the anurous amphibians leave the aquatic environment.

• The skin of amphibians is naked, thin, delicate and covered with mucus, that is why, similarly to lungs, it is used to take oxygen and remove carbon dioxide.

• Amphibians are cold‑blooded vertebrates whose adult forms usually live in humid terrestrial habitats and who spend their breeding time in freshwater reservoirs.

• The development of amphibians involves metamorphosis. A larval form known as a tadpole occurs which breaths using gills.