The Cell

Subject:

Biology

 

Class:

SS 1

 

Term:

First Term / 1st Term

 

Week:

Week 4

 

Topic:

The Cell

 

 

Previous Knowledge: The pupils have previous knowledge of

 

Classification of living things Kingdoms Monera, Protista

 

that was taught in their previous lesson.

 

 

Behavioural  Objectives : At the end of the lesson, learners will be able to

• recognize single celled organism: Amoeba, paramecium, euglena, chadamoydomones
• distinguish between free-living cells and idonies, filaments and tissues.
• describe the general structure of a cell.
• list the function performed by the organ cells.
• Differentiate between plant and animal.

 

 

Instructional Materials 

 

 

• Charts showing forms in which cells exist.
• A generalized diagram of a cell.
• Diagram/charts of plant and animal cells
• microscopic slides,
• cover slips and ditch water
• Culture of bacteria and blue-green algae
• Prepared slides of amoeba, Chlamydomonas etc.

 

Methods of Teaching 

• Role modelling
• Questions and Answers
• Explanation
• Discussion
• Recitation
• Imitation
• Story Telling
• Dramatization

 

Content: 

The Cell

 

Classification of Living Things Based on The Number of Cells

All living things are classified into two major groups depending on the number of cells they possess. These groups are:

1. Unicellular or Acellular organism: Organisms which consist of only one cell e.g. Amoeba, Paramecium, Chlamydomonas and Euglena.
2. Multicellular Organisms: Organisms which consist of two or more cells, e.g. Hydra, Flowering plants, Fish, Bird, Man etc.

Forms in Which Cells Exist

Living cells exist basically in four forms;

1. As single and free-living organisms

These are organisms which possess only one cell and are able to live freely on their own. The single cell carries out all life processes such as feeding. Euglena, etc. Parts of the cell may be specialized to carry out a particular process, for example Paramecium.

Paramecium is a fresh-water protozoan. It lives in ponds and puddles and feeds mainly on bacteria. It is often described as having a slipper shape and is about 0.25mm long. It has a stiff outer-covering called the pellicle which gives it a fixed shape. Its cytoplasm is divided into a clear outer layer called the ectoplasm and a granular inner layer called the endoplasm. The endoplasm contains several food vacuoles, two contractile vacuoles and two nuclei. The larger one called the mega nucleus and the smaller one the micronucleus. It moves (swims) in the water by means of cilia. The cilia are tiny projections of the ectoplasm through the pellicle.  The oral groove and gullet are specialized for feeding, while the contractile vacuole is specialized for water regulation.

2. As a colony

A colony consists of many similar cells which are joined together. E.g. Volvox, Pandorina, etc. Diagram of volvox

3. As a filament

This consists of many similar or identical cells joined end to end to form unbranched filaments. e.g. spirogyra, zygonema, Oscillatoria andOedogoniumm.

Each cell in a colony or filament behaves as an individual. Each carries out life processes independently of its neighbors.

4. As a part of a living multicellular organism

In multicellular organism cells which perform the same function are grouped together to form a tissue, e.g. tissues of the ileum wall, the retina, and the blood (a tissue which perform a specific function form an organ and a group of organisms working together to perform a specific task form a system.

The Structure and Functions of the Cell

From the general point of view, the cell is considered an idea. The dictionary explains the meaning as ‘a small room in a prison for one or more persons’ or as ‘a small number of people.’ When one commits a crime, such a person is put in a police cell while the investigation is going on.

However, in Biology the term cell is a vital subject matter and has a special definition. It is defined as the smallest, structural and functional unit of life having a nucleus at the center and bounded by a cell membrane.

There are two types of cells: Plant and Animal cells. See diagram below

 

Plant Cell

Plant cells contain a variety of membrane-bound structures called organelles. These include a nucleus that carries genetic material; mitochondria that generate energy; ribosomes and rough endoplasmic reticulum that manufacture proteins; smooth endoplasmic reticulum that manufactures lipids used for making membranes and storing energy; and a thin lipid membrane that surrounds the cell. Plant cells also contain chloroplasts that capture energy from sunlight and a single fluid-filled vacuole that stores compounds and helps in plant growth. Plant cells are surrounded by a rigid cell wall that protects the cell and maintains its shape.

 

Animal Cell

An animal cell typically contains several types of membrane-bound organs, or organelles. The nucleus directs the activities of the cell and carries genetic information from generation to generation. The mitochondria generate energy for the cell. Proteins are manufactured by ribosomes, which are bound to the rough endoplasmic reticulum or float free in the cytoplasm. The Golgi apparatus modifies, packages, and distributes proteins while lysosomes store enzymes for digesting food. The entire cell is wrapped in a lipid membrane that selectively permits materials to pass in and out of the cytoplasm.

The Cell as a Living Unit of an Organism

The cell is defined as the simplest, the smallest and most basic unit of life. It is the structural and functional unit of a living organism. The cell can carry out all life activities such as feeding, respiration, movement etc.

 

The Cell Theory

The man who first discovered and described cell in living things is called Robert Hooke in 1665, he also invented the microscope, but the cell theory was proposed by another man called Mathias Schleiden, a German Botanist 1838, and Theodor Schwann, a German Zoologist, these two men postulated the theory known as cell theory in 1839. In 1855, another German Biologist, Rudolf Virchow stated that all cells come originated from cells.

The cell theory states that:

1. All living things are composed of one or more cells
2. Cell is the structural and functional unit of all living things;
3. Cell originates from a pre-existing cell; and
4. Cell contains hereditary materials.

Another name for cell components are cell organelles e.g of an organelle is the nucleus of a cell as shown below.

 

CONTENT

CELLS

The cell is defined as the smallest unit of a living organism. It is the first level of organization life. All plants and animals are made up of cells. Some of these plants and animals are made of only one cell hence they are called unicellular organisms while others are made up of many cells and are therefore called multicellular organisms. Examples of unicellular organisms are Amoeba, Euglena, Paramecium, Plasmodium, Trypanosome, Chlamydomonas. Examples of multicellular are flowering plant, man, etc.

TISSUES

A tissue is a group of similar cells forminga layer in an organism which performs a particular function. In other words, a tissue consists of two or more different types of cells aggregating together to perform a specific function. Examples of tissues in higher plants are mesophyll layer in leaves. epidermal tissue. Sclerenchyma tissue, xylem tissue, parenchyma tissues in stem. Examples of tissues in higher animals include muscle, bone, cartilages and blood (a liquid tissue). Examples of organisms which exist at the tissue level of organisationof life are Hydra, Algae, sponges and fungi.

ORGANS

An organ is a group of similar tissues forming a layer in an organism which performs aspecific function. Examples of organs in plantsare leaves, flowers, roots, stems, seeds etc. Examples of organs in animals are the lung, liver, brain, kidney, heart, ear, and eye which perform specific functions.  Examples organism of plants are roots, stems, leaves, flowers, fruits and seeds, bulbs e.g. (onion) 

SYSTEMS

A system is a group of similar organs whichwork together to perform specific functions. Examples of systems in plant are the shoot systemand root system. Examples of systems in animals are digestive, reproductive, respiratory,skeletal, nervous, excretory and circulatory systems. Thesesystems work together to make up an organism. For an organism to perform well, all the cells, tissues, organs and systems must also function normally.

FUNCTION OF SOME HUMAN ORGANS AND SYSTM

NAME	TYPES OF STRUCTURE	MAIN FUNCTIONS
Lung	organ	Exchange of gases containing O, CO2, etc. between the body and the atmosphere
Skin	Organ	Protection, support, irritability body temperature regulation.
Spinal Cord	Organ	Reception and interpretation of response to stimuli.
Digestion system	Organ	Injection, digestion, absorption and egestion
Reproduction system	Organ	Production of offspring

 

THE COMPLEXITY OF MULTICELLULAR ORGANISMS HAS ADVANTAGES AND DISADVANTAGES 

Advantages of Complex Organization

1. There is division of labour because of the presence of specialised organs and systems.
2. Increase in size and complexity to a very great extent.

iii. Specialised organs and system enable them to live and survive in different habitants

1. Efficiency is increases and maintained in the functioning of the organism, because various processes are performed by different organs or system.

Disadvantages of Complex Organisation

1. An efficient system is necessary
2. If an organ/system is damaged/does not function properly, the other organs and systems might not function properly/might be damaged as well.

iii. Some organisms cannot function well if the coordination is poor or impaired.

1. If there is any defect in a system the organism may be endangered.

 

1. Cell as a living unit of organism.
2.  Forms in which living things exist:
   i. independent: amoeba, paramecium, euglena
   etc.
   ii. as colony, e.g. volvox
   iii. as filament e.g. spirogyra.
3. Cell structure:
   i. The Cell Theory
   ii. cell structure and
   function of cell
   components.
4. iii. differences and
   similarities between
   plant and animal cells.

 

 

Mitochondria

Mitochondria, minute sausage-shaped structures found in the hyaloplasm (clear cytoplasm) of the cell, are responsible for energy production. Mitochondria contain enzymes that help convert food material into adenosine triphosphate (ATP), which can be used directly by the cell as an energy source. Mitochondria tend to be concentrated near cellular structures that require large inputs of energy, such as the flagellum, which is responsible for movement in sperm cells and single-celled plants and animals.

Description and Functions of Cell Components

1. Cell wall          

Description: Non-living, made of cellulose, permeable to water and substance

Functions: Provides rigidity to the cell and gives it a definite shape.

2. Cell membrane

Description: Living and differentially permeable to water and substance.

Function: Allows selective movement of materials in and out of the cell.

3. Cytoplasm

Description: Semi-fluid mass enclosed within the cell membrane and contain many organelles.

Functions: The largest and liquid part of the cell in which metabolic reactions occur.

4. Nucleus

Description: Enclosed by a nuclear membrane, and contains chromatin and nucleolus.

Functions: It stores and carries hereditary information from generation to generation. It also translates genetic information into the kind of protein characteristic of the cell. It controls the cell’s life processes

5. Vacuoles

Description: This is the fluid filled spaces in the cytoplasm.

Functions: Help in maintaining turgidity in the plant cell.

6. Mitochondria

Description: It is a double membrane system, found in all cells. It contains the enzymes for cellular respiration.

Functions: it carries out metabolism for all life processes. Kreb’s cycle and electron transfer system take place in the mitochondria.

 

The topic is presented step by step

Step 1: The class teacher revises the old topic

Step 2: The class teacher introduces the new topic

Step 3: The class teacher allows the pupils to give their own contributions and gives room for pupils” participation

 

Class Teacher and Students Activities. Interaction or Participation 

This involves class teacher and pupils’ interaction, conversation, imitation or modeling through discussion, play method or just by recitation or asking and answering questions that are related to the topic that has just been taught.

 

Teacher Activities

1. Provides prepared slides of paramecium or euglena, volvox and spirogyra.

2. Guides students to collect spirogyra, from ponder ditch, feel and observe and record their observations.

3. Draws and labels how organisms are on the board. ii. Mounts slides of plants and animal cells for students’ observation.

iii. Present charts showing similarities and differences in plants and animals’ cells.

 

 

Students Activities.

1. Observe the slides under the microscope and record their observations
2. Observe spirogyra and note its nature
3. Draws and labels those organisms
4. Observes slides and charts of plants and animal cells draw and not their differences and similarities.

 

 

Evaluation

 

1. What is a cell?
2. State why the cell is a living unit.
3.  Identify the various forms in which cells exist.
4. Define the term cell.
5. Mention the two groups in which organisms can be placed based on the number of cells.
6. State the forms in which living cells exist
7. Sketch a well labelled diagram of plant and animal cells
8. State the cell theory.
9. Who is the first founder of the cell?
10. List four men who contributed to the discovery of the cell
11. Describe the nucleus and its functions.
12. What was the contribution of Felix Dujardin to cell theory?
13. State Five (5) differences between plant and animal cell.
14. Outline four similarities between plant and animal cell.
15. Describe and state the functions of the following cell components or organelles: (a) Endoplasmic reticulum (b) Ribosome (c) Centrioles, and (d) Chloroplasts
16. Describe the structure of the cell.
17. Differentiate and distinguish a plant cell from an animal cell

 

 

 

 

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