Topic: Algae

Author: Elżbieta Szedzianis

Target group

Students of the 5th grade of an elementary school.

Core curriculum

4. Protists - organisms with a diverse cellular structure. The student:

1) shows the diversity of protist structure (single‑cellular, multi‑cellular) on selected examples,

2) presents selected life activities of the protists (breathing, nutrition, reproduction).

The general aim of education

The students characterize algae.

Criteria of success

• provide three common features for algae,

• you can distinguish algae from other organisms,

• on the basis of observations, you will show three features that adapt algae to life in water.

Key competences

• communication in foreign languages;

• communication in the mother tongue;

• learning to learn.

Methods / techniques

Conversation, laboratory method, work with text.

Individual work and work in groups.

Teaching aids

• abstract;

• interactive or traditional board;

• tablets/computers;

• rockweed specimens soaked in water;

• cuvettes.

Lesson plan overview (Process)

Introduction

1. The teacher explains the aim of the lesson and the success criteria to be achieved by the students.

Realization

1. The teacher displays photos or illustrations of various algae representatives on the screen, i.e. kelp, spirogyra, chlorella, euglena, rockweed, gulfweed, red algae. The teacher explains that algae, in addition to chlorophyll, have other dyes needed for photosynthesis. The teacher asks the students to show the common characteristics of these organisms.

2. Based on their own statements (possibly corrected by the teacher), the students write in the notebooks three common features of algae.

3. The teacher asks the students to perform interactive task No. 1.

4. The teacher asks the students to determine the importance of algae in nature, taking into account their way of eating.

5. The teacher asks the students to analyse the illustration entitled „Algae distribution in the sea” (abstract), and explain how the living environment influences the colour of algae.

6. The teacher divides the class into four‑person groups, giving each group the rockweed soaked in water. The teacher explains that they will observe algae and indicate adaptation to life in water. The teacher asks the students to describe the shape of the rockweed and explain how it relates to the aquatic environment. The students write their observations in the table.

Summary

1. The teacher displays selected images of algae and other organisms on the screen and asks the students to determine if they are algae, and justify their answers.

2. The teacher displays the student criteria of success and asks everyone to assess their achievements.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Algae

Algae are a group of unrelated organisms whose common feature is the inhabitation of waters. Algae belong to three kingdoms. Cyanobacteria belongs to bacteria, diatoms and brown algae – to protists, green algae and red algae – to the plant kingdom.

Multicellular algae do not have specialized tissues or organs. Their body is called a thallus. It can reach even several dozen meters in length. Algae usually float in the water or live attached to the bottom in places where the light reaches in the amount which is sufficient for the algae present there.

Algae are autotrophic. In their cells there are chloroplasts containing chlorophyll and other dyes that facilitate the conduct of photosynthesis, as well as give them a characteristic color. The names of algae groups come from the dominant color of the cells: the green algae are green, the red algae are red, and the brown algae are yellow and brown. Products of photosynthesis run by algae are stored in cells as spare substances. The cell wall is made of cellulose.

Brown algae inhabit cool sea waters of the northern hemisphere. They have multi‑cellular thallus bodies, usually in the shape of elastic bands. In addition to chlorophyll, their cells also contain brown dyes.

The representative of this group is Fucus vesiculosus, which occurs, among others, in the Baltic Sea. A strong leathery pleated thallus resembles a terrestrial plant. It attaches to the ground with a disc‑shaped holdfast. Leaves‑like elements grow from stem‑like parts. They contain air‑filled bubbles that carry algae in the water. This facilitates the harvest of light, and in the event of breaking off – the movement of parts of the thallus and the settling in subsequent places.

Already in early spring, roadside ditches get covered with a green, dense, floating coat. These are clusters of filamentous algae – green algae. Most of them live in freshwater, but many species inhabit the sea. Only a few can be found on land. Aquatic green algae float on the surface as plankton or live attached to the bottom of the reservoir. Land species occur in humid places.

Green algae take different shapes. They may be in the form of long threads or spheres. The thallus of multicellular green algae is long and tapered or flat and branched, resembling organs of terrestrial plants.

Green algae reproduce sexually and asexually. Single‑celled algae,  Pleurococcus and chlorella reproduce by cell division. The thallus of multicellular algae, such as sea lettuce, is torn apart by movements of water or animals into fragments that give rise to new plants. Most green algae produce spores. During reproduction, algae produce gametes and release into water, where they are combined. After fertilization, a zygote is created, from which a new organism develops.

Red algae live mainly in the seas. Attached to underwater boulders in quiet places, safe from violent waves, they create a wonderful underwater landscape. Their delicate, lace‑like thalli wave and surrender to water movements. Red algae as autotrophic organisms contain chlorophyll, which is masked by red or blue dyes supporting the photosynthesis process. It gives them a characteristic red or purple color. Most species of red algae live at considerable depths, so additional dyes allow them to absorb the part of the light that has not been stopped by the water layer.

Green algae, red algae and brown algae inhabit seas in a specific order forced by the amount of light reaching the given depth. For light, water is a type of filter that stops part of it depending on the depth. The deeper, the less light reaches the plants. Green algae which grow shallowly use (like terrestrial plants) blue and red light. Algae living deeper support photosynthesis with additional dyes. Brown algae equipped with a yellow‑brown dye capture light of green and blue color. The green and blue light reaching the deepest is used by red algae. The depth to which the light penetrates depends on the transparency of the water, which is why algae grow in different depths in different reservoirs.

Algae are the largest oxygen producer on Earth. They are small, freely floating on the surface of water and they produce plant plankton (phytoplankton), the basic food of fish and other aquatic animals. Algae seated at the bottom of the reservoirs form vast, underwater meadows that are a refuge, a place of feeding and breeding of animals. Some species of red algae participate in building coral reefs. Dead algae falling down to the bottom are decomposed, and the mineral compounds contained in them fertilize water, enabling the development of subsequent generations of autotrophic organisms.

Man uses algae in various areas of life. In medicine, they are components of drugs recommended in diseases of the digestive system. Those that contain a lot of iodine are used in the treatment of thyroid diseases. In cosmetics industry, algae are used to make creams and face masks that moisturize the skin and improve its elasticity. Certain species of algae are used to obtain agar‑agar, a gelling substance used for the production of sweets, medicines, and as a base for the media on which bacteria are grown. In Japan and China, some species of algae are treated as a component of meals, and others used for fertilizing the soil.

It happens, however, that algae become cumbersome. Plankton green algae, growing excessively on the surface of water reservoirs, can create water efflorescence limiting the access of light to plants living in their deeper layers. This prevents the efficient course of photosynthesis in the water reservoir, causes a significant reduction in the amount of oxygen and contributes, among others, to mortality of fish.

• Multi‑cell algae do not produce tissues and do not have roots, stems and leaves.

• The bodies of brown, green and red algae take different shapes: from filamentous to ribbony, looking like leaves of terrestrial plants.

• Single‑cell, colonial and multi‑cell organisms are found among green algae.

• Red algae are mainly sea algae living at great depths.

• Different colours of algae are caused by the presence of additional dyes that support the process of photosynthesis, which takes place in water at various depths.

• Algae are the largest oxygen producer on the Earth.