Subject:

Biology

 

Class:

SS 1

 

Term:

First Term / 1st Term

 

Week:

Week 5

 

Topic:

THE CELL AND ITS ENVIRONMENT

 

 

 

Previous Knowledge: The pupils have previous knowledge of

 

The Cell

 

that was taught in their previous lesson.

 

 

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

• Demonstrate Diffusion and Osmosis
• Experimentally using living and non-living tissue.
• Recognize that osmosis is a form of diffusion.
• Recognize that plasmolysis can lead to wilting and hemolysis and lead to loss of blood.

 

 

Instructional Materials 

• Wall charts
• Online Resource
• Textbooks
• Laptop
• Flash cards
• www.edudelighttutors.com

 

Methods of Teaching 

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

 

Content: 

THE CELL AND ITS ENVIRONMENT

CONTENT

1. Introduction
2. Diffusion
3. Osmosis
4. Plant Nutrition
5. Micro and Macro Elements

Introduction

The topic ‘Cell and its Environment’ refers to the activities of the cell in a given environment or the functions of the cell given a particular condition. Some conditions can be harmful to the cell while others are helpful for proper functioning of the cell. This is why we discuss the cell and its environment.

Diffusion

Diffusion can take place in liquid and gases, but diffusion is faster in gases than in liquid, because air and gases as a medium has more spaces to be filled.

Diffusion can be defined as the process by which molecules of substances, such as liquid and gases move randomly from a region of higher concentration to a region of lower concentration until they are evenly distributed.

It is also a process by which fine particles (molecules) flow in and out of cells of living things, and it can occur in non-living things or membrane.

SUGGESTED PRACTICALS

Stand at the corner of the classroom, and spray perfume, after a while the scent of the perfume will circulate the whole class and every student will attest to the perception. This is diffusion in gas.

You can also demonstrate diffusion of solid material in liquid medium using potassium tetra oxo manganate (vii) crystals. i.e. KMnO₄

Materials: Distilled water, Beakers, Spatula, and KMnO₄.  

The Rate of Diffusion

The rate of diffusion is the time taken by molecules of a diffusing substance to be uniformly distributed in any given area of the diffusing medium.

Some factors may affect (inhibit or facilitate) the rate of diffusion:

1. State of matter of diffusing molecules
2. Size of diffusing molecules
3. Differences in concentration of diffusing molecules and the medium (conc. gradient).
4. Temperature of diffusing medium.

The Importance of Diffusion

In a biological system, diffusion is essential in the following ways:

1. Gaseous exchange in lungs during external respiration.
2. The movement of carbon iv oxide and Oxygen during photosynthesis and respiration in plants.
3. Movement of digestive food from the intestine into the blood circulatory system.
4. Movement of nutrients, and other metabolic products from the mother through the placenta to the foetus.
5. The upward movement of mineral salts and nutrients from the soil through the roots to other parts of the plant.

 

 

Diffusion

Diffusion is the natural tendency of molecules to flow from higher concentrations to lower concentrations. When the barrier between two substances is removed (as shown here), the molecules will diffuse throughout the entire container. While the number of molecules in the container is the same as it was before the barrier was removed, the substances are now at lower concentrations. The rate of diffusion depends on the weight of the molecules—heavy molecules diffuse more slowly than light molecules.

Osmosis

Osmosis is the movement of water molecules from a dilute solution into a more concentrated solution through a semi-permeable membrane. Living organisms have cells as semi-permeable membrane. Since the water molecules are small, the cell is somewhat limited in the amount of direct control it can impose on their passage across the membrane. In osmosis, the stronger solution is called hypertonic solution, while the weaker solution is called hypotonic solution. In osmosis, water molecules move from hypotonic to hypertonic solution, but when the concentrations are equal, the solution is said to be isotonic.

Application of Osmosis in Animals

The application of osmosis in animals includes the following:

1. Reabsorption of water in kidney tubules,
2. Entry of water into the cytoplasm of unicellular animals, e.g. Amoeba and Paramecium,
3. Movement of water in and out of living animal cells,
4. Absorption of water in the large intestine.

The Application of Osmosis in Plants

The application of osmosis in plants includes the following:

1. Absorption of water from the soil by the root hairs,
2. The movement of water in and out of living plant cells,
3. The movement of water from the root hairs to the cells of the cortex, and
4. Opening and closing of the stomata by the guard cells in the leaf.

Demonstration of Osmosis

1. Using a living membrane or tissue such as yam, pawpaw etc.
2. By Osmometer; Osmometer can be constructed using a thistle funnel covered with cellophane.
3. Cellophane is semi-permeable. The thistle funnel is filled with a strong sugar solution to a certain level.
4. It is then lowered into the beaker containing water. After about 30 minutes, it could be seen that the level of the solution in the thistle funnel has increased due to passage of water through the cellophane membrane.
5. This indicates that cellophane membrane is a semi-permeable membrane allowing only molecules of water to pass through, but preventing the passage of sugar molecules.
6. This is the demonstration of osmosis using a non-living membrane.

Osmotic Pressure

This is the minimum pressure that needs to be applied to a solution to prevent the inward flow of water across a semi-permeable membrane. It is the measure of the tendency of a solution to take in water by osmosis.  It is simply the pressure needed to stop osmosis. The osmotic pressure that a solution is capable of developing depends on the number or concentration of its solute molecules. The stronger the solution, the greater the osmotic pressure.

 

Osmosis

The experiment shown above demonstrates the process of osmosis. Water flows through a semipermeable membrane into a sugar solution, diluting the solution. The sugar molecules cannot pass through the membrane, so the water outside remains pure.

The Importance of Osmosis

1. Osmosis regulates the concentrations of salt and water of the blood and other body fluid in animals.
2. It maintains the cell shape through turgidity and plasmolysis if need be.
3. It enables the absorption of water molecules from the soil solution to the plants through the root hair.
4. Movement of water molecules within the plant from the root to the leaves.

 

 

 

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 cheap perfume and requests a student to spray it one end of the classroom
2. . Place a crystal of potassium permanganate in a beaker of water and leave it to stand and ask the students to observe what has happed
3.  Demonstrates experiments to show osmosis in a
   • . A non-living system
     and
   • . A living system
4. . Demonstrates experiment to show efforts of solutions of different concentrations on red blood cells, effects of water and sugar solution on onion cells.

 

 

Students Activities.

 

1. Sprays the perfume as directed by the teacher.
2. Describe what happened.
3. Repeat the experiments, observe, record and discuss their observation.
4. Describe what happened or the result of the experiment.
5. List the biological significance of these processes.

 

Evaluation

1. Define the terms (a) Science (b) Biology
2. State five branches of biology.
3. Define the term diffusion.
4. What is the rate of diffusion?
5. State three importance of diffusion.
6. Define the term osmosis.
7. Write two applications of osmosis each in plant and animals.
8. What is osmotic pressure?
9. Enumerate three importance of osmosis.
10. Of what use is (a) science (b) biology to man?
11.  Define Biology.
12.  Explain the meaning of biology
13. mention the two majors’ field of biology
14.  List steps involved in scientific methods or learning
15.  State five usefulness of biology

 

 

 

 

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