Topic: Cells forming the body

Author: Elżbieta Szedzianis

Target group

Students of the 5th grade of an elementary school.

Core curriculum

I. Organization and chemism of life. The student:

4. makes microscopic observations of the cell (the basic unit of life), identifies (under the microscope, in a diagram, in a picture or based on a description) basic elements of cell structure (cell membrane, cytoplasm, cell nucleus, chloroplast, mitochondrion, vacuole, cell wall), and presents their functions,

5. compares the cell structure of bacteria, plants and animals, indicating features that allow distinguishing them.

The general aim of education

The students describe cell structure and divide organisms into eucaryotes and procaryotes.

Criteria of success

• You will explain the difference between eucaryotes and procaryotes, and give examples of them;

• prepare a microscopic preparation and observe the skin of an onion under the microscope;

• make a drawing of cells observed under the microscope.

Key competences

• communication in foreign languages;

• mathematical competence and basic competences in science and technology; 

• learning to learn.

Methods / techniques

Conversation, laboratory work, and work with text.

Individual work, work in pairs.

Teaching aids

• abstract;

• interactive or traditional board;

• tablets/computers;

• student microscopes, a microscope with a camera;

• onion;

• equipment for preparing a microscopic preparation.

Lesson plan overview (Process)

Before the lesson, the students watch the film entitled „How to make a microscope image drawing”. In particular, they have to pay attention to the shape of onion skin cells, cell structures shown in the film, and the principles of making a drawing based on a microscopic image.

Introduction

1. The teacher gives the topic, the goals of the lesson in a language understandable for the student, and the criteria of success.

2. The teacher reminds the homework and asks the students the following questions: How is the onion skin built? What about the rest of the onion?

Realization

1. The teacher asks the students to become familiar with the first paragraph in the abstract and formulate three sentences containing the most important information about cells and organisms that they build on the basis of this paragraph. The students give suggestions, the teacher writes them on the board, and the students in their notebooks, e.g.:

• Each organism is made of cells;

• The shape of a cell depends on the function performed.

• Organisms are divided into procaryotes (bacteria) and eucaryotes (other organisms).

2. The students make Observation 1 based on the instructions in the abstract. Note that the transparent skin will be clearly visible if you add a drop of the Lugola liquid to the water in the preparation. The teacher checks if the students have properly set the image in the microscope, helps if necessary. The students map the spatial shape of cells using modelling clay or Play‑Doh. They explain why onion skin cells are close to each other. The students identify cell structures such as the cell wall, cell nucleus, and cytoplasm.

3. The teacher chooses from the film entitled „How to make a microscopic image drawing” a frame with the criteria for drawing assessment and displays it on the screen. The teacher asks the students to draw three selected neighbouring cells in a notebook. The teacher checks if the students correctly reproduce the shape and proportions of the cells, and helps if necessary.

4. After drawing, the students exchange notebooks and give themselves points (0 or 1) for each criterion. They sign their names under the mark expressed by points.

Summary

1. The teacher displays the criteria of success and asks everyone to assess their achievements. The teacher asks the students to name the difficulties they have encountered during the microscoping and making a drawing, and provide ways to avoid or eliminate these difficulties.

2. The teacher collects five notebooks with evaluated drawings and explains that she will verify the marks and give grades to both by the author of the drawing and the person who checked it.

Homework for keen students.

Read the definition of a cell in the PWN Encyclopaedia: (Cell - *the smallest structure with a complex organization found in nature that is capable of living and self‑reproducing.) *and explain what a cell is in a way that will be understandable to a class 4 student. Write the explanation on the page in big letters and sign it. On the next lesson we will choose the best explanation.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Cellular structure of organisms

Cells are the basic elements that build every organism. Their size and shapes are very diverse, because they depend on the functions fulfilled. The smallest are bacterial cells that have on average one thousandth of a millimeter, or one micrometer (1 μm) in length. The largest cells are found in plants - hemp fiber can reach a length of 50 cm. All cells consist of smaller elements. One of them is the cell nucleus - due to its presence or its absence, cells are divided into prokaryotic (bacteria) and eukaryotic (protists, plants, animals,fungi).

The cells of plants, animals, fungi and bacteria differ in size, shape, internal structure but show a common construction plan. The components of the cells can be divided into living components of a cell, which include the cell membrane and the cytoplasm together with the structures suspended in it, and non‑living components of a cell, which are the cell wall and the vacuole.

The plasma membrane separates the cell from the environment. It is often called a „cell guardian”, because it is responsible for protecting its interior and for its contact with the environment. In plants, fungi and bacteria, there is a stiff, thick, cell wall outside of the membrane. It can be compared with a box that gives the shape of a cell.

A cytoplasm - a jelly substance composed of water and dissolved in it organic and inorganic compounds, surrounded by a plasma membrane. Cytoplasm is an environment in which chemical reactions necessary for life take place - it is semi‑fluid, and cellular structures are suspended in it. The cytoplasm allows them to move and exchange substances between them. In the cytoplasm, membranes are built like a plasma membrane and form a membranous structures like endoplasmic reticulum or Golgi apparatus.

The cell membrane is so thin that it cannot be seen in the light microscope. It consists of proteins and fats (lipids). The membrane is semi‑permeable: it permits the penetration of water and other small molecules that through pores (holes), and the larger particles are retained. Their uptake can be done according to the needs of the cell, but it usually requires energy consumption. The membrane receives and conducts stimuli (information) from the environment. It's flexible, therefore it allows cells to change shape.

The cell nucleus can be seen in a light microscope. It is most often a spherical structure surrounded by cytoplasm. The nucleus stores genetic material that contains information about cell structure and functioning. Thanks to this, it controls all its life activities, including division into daughter cells. The nucleus is surrounded by a double nuclear membrane with numerous orifices (pores) allowing the contact of the nucleoplasm with the cytoplasm of the cell. Nucleic acid molecules which including „instructions on the functioning of the cell and whole organism” penetrate from the cell nucleus into the cytoplasm. In the same way, the substances needed there get through from the cytoplasm to the cell nucleus.

Mitochondria are invisible in a light microscope. They are surrounded by a double protein‑lipid membrane: the outer one is smooth, the inner one - pleated and forms numerous, lamellate protrusions called cristae. There is a process of cellular respiration on the surface of the inner membrane. It consists in the release of energy accumulated in organic compounds. The more cristae in the mitochondria, the more intense respiration process is.

Mitochondrial matrix (matrix) an amorphous liquid substance that fills the interior of the mitochondrion.

Chloroplasts are well visible in plant cells viewed under a microscope. They contain a green dye - chlorophyll, which has the ability to absorb light energy. The process of photosynthesis takes place in chloroplasts. It consists in the production of organic compounds (sugars) from inorganic compounds (water and carbon dioxide).

The cytoplasm has an irregular plasma membrane system. These are membranes of the endoplasmatic reticulum that divide the cell's interior into smaller spaces and allow simultaneous overlap of various processes and transport of substances between individual cell elements. On the surface of some of the reticular membranes there are lumpy corpuscles - ribosomes. They participate in the synthesis of proteins.

Another membranous structure suspended in the cytoplasm is the Golgi apparatus. It is made up of several types of vesicles: large, flattened, arranged parallel to one another and small, spherical vesicles tearing away from them. The Golgi apparatus is involved in the synthesis and modification of some organic compounds, it also collects proteins and other substances.

Lysosomes are small irregularly shaped vesicles surrounded by a single protein‑lipid membrane produced by the Golgi apparatus. They occur in eukaryotic cells. Thanks to the presence of digestive enzymes, they participate, among others in the digestion of nutrients and damaged organelles.

Plant cells as well as fungal and bacterial cells are covered not only by the cell membrane. They have an additionally stiff cell wall. The basic building material of the wall is water‑insoluble sugar - cellulose (or chitin in most fungi). In young cells, the wall is thin and elastic (so as not to limit the growth of cells), but with age it becomes thicker. The cell wall strengthens the protection against the penetration of microorganisms, protects the cell against damage and gives it a shape.

Vacuoles are mainly found in plant and fungal cells that provide cells with firmness. They are vesicles surrounded by a single, membrane filled with cellular juice. Additionally, they contain superfluous substances and secretions collected periodically and used as needed. In animals, vacuoles occur exceptionally only in adipose tissue cells and are used to store its reserves.

There are many vacuoles in young plant cells. As the cells mature, the vacuoles combine to form one central vacuole.

• Cells – due to the presence or absence of the cell nucleus – we divide into procaryotic and eucaryotic.

• Each cell is surrounded by a cell membrane.

• In animal cells there are cell structures such as: cell membrane, cytoplasm, cell nucleus, mitochondrium, endoplasmic reticulum, Golgi apparatus.

• Plant cell – in contrast to animal – has chloroplasts, cell wall and vacuoles.

• The bacterial cell has no cell nucleus or any membranous structures in cytoplasm.

• The cell membrane is semipermeable – it allows the osmotic penetration of water, but retains large particles.