Topic: Life originated in water

Author: Leokadia Stalewicz

Target group

8th‑grade students of elementary school

Core curriculum

General requirements

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

2. explains biological phenomena and processes occurring in selected organisms and in the environment.

Specific requirements

VI. The evolution of life. Student:

1. explains the concept of organism evolution.

General aim of education

You'll find out how the earliest stages of life on Earth were going

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• to describe the conditions prevailing in selected geological eras;

• to present the main stages of plant and animal evolution;

• to organize chronologically the most important events in the history of life on Earth.

Methods/techniques

• expository

  • talk;

  • explanation.

• activating

  • discussion.

• exposing

  • exposition.

• 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.

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.

• Then he writes the subject of the lesson on the blackboard or interactive whiteboard. Students write it in notebooks.

• The teacher asks students about when the Earth was created, whether they met with theories about the origin of life on Earth. He asks them to share the pros and cons of life in the water.

Realization

• The teacher asks students to read the abstract themselves, paying particular attention to the illustrations.

• The teacher presents and discusses the interactive illustration „The beginnings of life on Earth.” Students jointly analyze the various stages of the evolution of living beings with particular attention to the duration of each of these stages and the time which elapsed from the beginnings of life to the formation of the first multicellular organisms.

• The instructor divides the class into several groups, after which each of them recommends a study based on the abstract entitled „Life originated in water”, „The first unicellular organisms” and „The formation of multicellular organisms” of one of the following topics: composition of the Earth's atmosphere in the period of life on Earth; the first unicellular organisms; first eukaryotic cells; influence of self‑nutritious organisms on the composition of the Earth's atmosphere; the first multicellular organisms.

• A representative of each group reports the result of joint work. After the end of each paper, students from other groups can ask questions and discuss with the group discussing the topic. If necessary, the teacher complements students' statements and provides additional explanations.

• 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

• At the end of the class, the teacher asks the students questions:

  • What did you find important and interesting in class?

  • What was easy and what was difficult?

  • How can you use the knowledge and skills you have gained today?

  Willing/selected students summarize the lesson.

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

Life originated in water

Life appeared on Earth about 3.9 billion years ago, but up to this day we are not able to describe all the processes that led to the production of living matter. Our understanding of the earliest stages of the evolution of life is based mainly on hypotheses. Another source of information is the genetic material of the first unicellular organisms. The principle is: the more differences (mutations) are present in the DNA of the studied species, the earlier their common ancestor lived.

What is certain is that life originated in water. According to one of the hypotheses, organic particles were created spontaneously from inanimate matter in the warm and shallow ocean bays near volcanoes, where waters were rich in numerous minerals. This process took place under anaerobic conditions. The atmosphere at that time was oxygen‑free, saturated with hydrogen, methane, carbon and nitrogen oxides, which were the source of elements necessary for the production of organic compounds.

First simple organic compounds were formed as a result of chemical reactions caused by cosmic rays, UV radiation and electrical discharges released during storms. Such compounds transformed over time into amino acids, proteins and nucleic acids. The macromolecular compounds have acquired the ability to self‑replicate. This process lasted long enough to form the simplest cells made of the increasingly more complex organic particles.

The first fossil evidence of the existence of unicellular organisms comes from around 3.6 billion years ago. These organisms resembled the modern bacteria. They were surrounded by a cell membrane and contained a DNA molecule. The first cells did not have a separate cell nucleus, chloroplasts or mitochondria. As heterotrophs, they obtained nutrients by absorbing simple organic compounds from the environment and produced energy during anaerobic respiration. Soon after that, organisms capable of carrying out chemosynthesis, and later photosynthesis, which resembled the modern cyanobacteria, appeared. Autotrophic organisms had an advantage over heterotrophic ones, which is why their number was constantly growing.

According to one of modern theories, cells containing chloroplasts and mitochondria were created as a result of symbiosis.

It is likely that the cells which were the ancestors of today's nucleated cells absorbed specialized aerobic bacteria (which began to function as mitochondria) as well as cyanobacteria capable of photosynthesis (equivalents of present chloroplasts). The evidence for this is the presence of DNA in chloroplasts and mitochondria of modern nucleated cells. Unicellular organisms with nucleus have given rise to a huge variety of unicellular algae and protozoans, which have been developing to this day. Nucleated cells were probably created about 2.1 billion years ago.

As a result of photosynthesis, oxygen began to accumulate in the atmosphere. This led to the formation of oxygen‑breathing organisms, which became the dominant life forms on Earth. Their presence influenced the stabilization of the composition of the atmosphere. The appearance of oxygen‑breathing organisms that excreted carbon dioxide promoted the development of autotrophic organisms.

Changes in the composition of the atmosphere also included a decline in the concentration of greenhouse gases – methane and carbon dioxide – which could have caused global glaciation. The result of that was – as we assume – the great extinction of organisms, and then their expansion after the re‑warming, already in the form of other multicellular species.

The first multicellular organisms appeared around 1.5 billion years ago. It is assumed that they originated from unicellular organisms that did not separate after the division, or concentrated in organized multicellular groups – colonies. After that, multicellular forms with clusters of specialized cells that acted as tissues appeared. The first multicellular plants were small algae – probably the green algae. Fossils as old as 1.2 billion years confirm that.

In the animal world, the first multicellular forms probably appeared around 900 million years ago. They resembled modern sponges and cnidarians, and lived in shallow, coastal zones of seas.

The oldest evidence of the existence of multicellular animals are fossils preserved in the Ediacara hills in Australia. Traces of amazing animals known as the Ediacaran fauna have been found there. These primitive, soft‑bodied organisms appeared on Earth at the end of the first global glaciation and inhabited the seas about 560‑540 million years ago. They were built differently than the animals we know nowadays and rested immobile at the bottom of the sea or attached to it with an organ that resembled the pulvillus. They did not have a digestive tract and we assume that they derived the energy from the symbiotic bacteria living in their tissues, which carried out chemo- or photosynthesis.

• Life originated in water.

• The key event in the evolution of life was the emergence of nucleated cells and multicellular organisms.

• The first multicellular plants were the green algae.

• The rapid development of aquatic invertebrates took place 540 million years ago.

• In the history of life on Earth, mass extinctions of species have occurred repeatedly.