Topic: Herbivores, adaptation to a herbivorous diet, plants' defence mechanisms

Target group

8th‑grade students of elementary school

Core curriculum

General requirements

I. Knowledge of biological diversity and basic biological phenomena and processes. Pupil:

3. presents and explains the relationship between the organism and the environment.

Specific requirements

VII. Ecology and environmental protection. Pupil:

3. analyzes antagonistic interactions: intra‑species and interspecies competition, parasitism, predation and herbivorousness.

General aim of education

You will learn how the animals have adapted to the collection and digestion of plant food.

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• recognize and discuss the adaptation of animals to food acquisition;

• explain what determines the number of predators and their victims in the ecosystem;

• indicate features that are adaptations to defend against predators;

• explain the relationship between the type of food (plant, animal) and the structure of the digestive system;

• give examples and recognize the characteristics of plants that are adapted to defend against herbivores.

Methods/techniques

• activating

  • discussion;

  • brainstorming.

• expository

  • talk.

• programmed

  • with computer;

  • with e‑textbook.

• practical

  • exercices concerned;

  • experiment.

Forms of work

• individual activity;

• activity in pairs;

• activity in groups;

• collective activity.

Teaching aids

• e‑textbook;

• several specimens of live pot plants (eg pelargonium, cactus, aloe vera, ivy);

• notebook and crayons/felt‑tip pens;

• interactive whiteboard, tablets/computers.

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

• The teacher plays the abstract recording for all students. Participants listen carefully and give feedback on the difficulty of the text being heard using the traffic light method. Students are provided with green, yellow and red cards. While listening to the recording, they display the appropriate color for self‑assessment and to inform the teacher:
  green - I'm fine, I understand everything;
  yellow - I have some doubts;
  red - I do not understand anything, please help.
  The teacher responds depending on the needs of the students, deciding to repeat the recording, listen to the recording while following the text or translate the text.

Realization

• The teacher uses the text of the abstract for individual work or in pairs, according to the following steps: 1) a sketchy review of the text, 2) asking questions, 3) accurate reading, 4) a summary of individual parts of the text, 5) repeating the content or reading the entire text.

• By working with the brainstorming method, students are looking for an answer to the question why long food stay in the digestive tract of herbivores enables its more accurate digestion. The instructor monitors the classroom situation on an ongoing basis and guides students to the right answer..

• Working in pairs or small groups, the pupils analyze the role of skin covering the upper lip of herbivorous animals in feeding with the example of a cow. The volunteer or a person indicated by the teacher presents the result of the analysis in the class forum. The other students join the discussion by completing the statement about their own conclusions and observations..

• Students look at potted plants in the studio and discuss the protective adaptations of each species to protect them against eating by herbivores. The teacher also indicates to pupils such features as, for example, thickened skin on the leaves or woody stems, which may decide about the unattractiveness of a given plant as a food..

• Students carry out the interactive exercises checking the level of knowledge learned during the lesson. The teacher initiates a discussion during which the correct solutions for all the exercises performed by the students are discussed.

Summary

• The teacher chooses one student by random method and asks him or her to explain in own words the meaning of a given word or concept learned during the lesson.

• At the end of the lesson the teacher asks: If there was going to be a test on the material we have covered today, what questions do you think would you have to answer? If the students do not manage to name all the most important questions, the teacher may complement their suggestions.

Homework

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

• Imagine that you have the opportunity to interview an academic - a specialist in the field of today's lesson. What questions would you like to ask him? Write them down.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Herbivores, adaptation to a herbivorous diet, plants' defence mechanisms

Plants are the source of food for herbivores. Among herbivores we can find many insects, but also some fish, birds and mammals, mainly ungulates. Interestingly, there are almost no herbivorous species among amphibians; herbivorous reptiles are also very rare. Taking food of plant origin requires the development of certain features (adaptation).

Adaptations for digesting plant food can be traced on the example of herbivorous mammals. Plant‑based food is relatively easy to acquire, but difficult to digest. Its main ingredient is cellulose (a polysaccharide that builds walls of the plant’s cells), which mammals cannot decompose because they lack adequate digestive enzymes. A portion of plant‑based food provides significantly less energy as compared to the same portion of food of animal origin. For this reason, herbivores graze for many hours every day and have a long, extensive digestive tract, in which the food can stay and be digested for a long time.

A large African elephant eats about 200 kg of grass, leaves, small twigs and fruit daily. Of all this, almost half is removed with faeces. A giraffe consumes similar foods, but eats 10 times less than the elephant in relation to its body weight. This is because the giraffe is a ruminant, and the digestion is facilitated by the microorganisms that live in its stomach. Thanks to them, the giraffe digests its food more efficiently.

Hard plant food requires insects to be equipped with chewing mouthparts that are capable of cutting off leaves, drilling wood, and eating fruit. These organs have wide and flat edges, similar to scissors.

Herbivorous birds have a high energy demand, which is why they feed mainly on fruit or seeds. They usually have thick, strong beaks. The hawfinch, 18 centimetres long and weighing only 5 decagrams, can crush beech seeds, fruit seeds and hazelnuts with its beak. The crossbills have crossed mandibles, which are specialized in extracting seeds from cones. The hummingbird, which feeds on the liquid nectar of flowers, has a long, narrow, and relatively soft beak.

Among mammals, the adaptation to digesting plant‑based food is evident in the structure of their teeth. The front teeth of mammals that feed on the grass, the incisors, are arranged in a line, thanks to which they form a sharp cutting edge. The rear teeth, in turn, are wide and have a flat crown, covered with sharp folds resembling a grater. They are used to grind food. Teeth of herbivores wear out over time, even up to the gums. In rodents that feed on harder food, the incisors grow throughout their lives. Thanks to that, these mammals can bite bark and wood, hard seeds and fruits.

The giraffe has a special nutritional adaptation. It eats the leaves of spiny bushes, therefore it has prehensile, tough lips and tongue, which measures up 50 centimetres. These organs are resistant to thorny pricks.

Plants eaten by animals grow less and bear less seeds. That is why they have developed various strategies to defend themselves against herbivores, one of which is mechanical defence. Plants protect themselves against biting by producing hard leaves (e.g. spruce), which can be digested by few animals, leaves covered with thick hairs (e.g. mullein), which are an impenetrable barrier for small organisms, or create spikes and prickles and thorns that discourage the touching (e.g. blackberry, blackthorn).

The second strategy is the production of repellent substances. Some plants have an unpleasant, burning taste (e.g. pepper fruits), cause poisoning (e.g. aconite), or have an unpleasant odour (e.g. geranium). Yet another adaptation is observed in the unarmed white nettle, which resembles the nettle. This similarity probably reduces possible herbivore threat.

• The digestive system of herbivores is extensive, adapted to the digestion of plant food.

• Plants protect against herbivores through, among others, the production of thorns and prickles.

• Defence mechanisms increase the chance of survival.