Lesson Notes By Weeks and Term - Senior Secondary 1

Cell and its environment

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TERM – 1ST TERM

WEEK FIVE

Class: Senior Secondary School 1

Age: 15 years

Duration: 40 minutes of 5 periods each

Date:

Subject: Biology

Topic: Cell and its Environment

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

  1. Define diffusion and describe its processes.
  2. Define osmosis and state its significance

iii. Define plasmolysis

  1. Define Hemolysis
  2. Define active transport

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS:  Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

PRESENTATION

TEACHER’S ACTIVITY

STUDENT’S

ACTIVITY

STEP 1

INTRODUCTION

The teacher explains diffusion, it's processes and significance to the students

 

Students pay

attention

STEP 2

EXPLANATION

Teacher discusses osmosis, it's processes and significance

Students pay

attention and

participate

 

STEP 3

DEMONSTRATIO

N

Teacher explain other terms, plasmolysis, Hemolysis, flaccidity, active transport

 

Students pay

attention and

participate

STEP 4

NOTE TAKING

The teacher writes a summarized

note on the board

 

The students

copy the note in

their books

 

NOTE

Cell and its Environment

Diffusion

Diffusion is the spontaneous movement of particles (atoms, ions, or molecules) from an area of higher concentration to an area of lower concentration. This movement occurs down a concentration gradient, with the goal of achieving equilibrium, where the concentration becomes uniform throughout the available space.

Process of Diffusion

The process of diffusion involves the random motion of particles. It can occur in gases, liquids, or solids. The speed of diffusion depends on factors such as temperature, particle size, and the medium through which diffusion is taking place.

In gases and liquids, diffusion is facilitated by the constant motion of particles. In solids, diffusion can occur through the movement of atoms or molecules within the structure of the material.

Significance of Diffusion

  1. Nutrient and Gas Exchange: Diffusion is crucial for the exchange of gases (like oxygen and carbon dioxide) in biological systems. It also facilitates the movement of nutrients into cells and waste products out of cells.
  2. Biological Processes: Diffusion plays a fundamental role in biological processes such as respiration and photosynthesis. In these processes, gases move in and out of cells to support metabolic activities.
  3. Cellular Uptake of Substances: Cells utilize diffusion to take up essential molecules. For example, nutrients can diffuse across cell membranes to reach cells.
  4. Chemical Reactions: Diffusion helps in mixing substances, allowing for chemical reactions to occur. In a homogeneous mixture, reactants can come into contact more frequently, facilitating reactions.

Osmosis

Osmosis is the passive movement of solvent molecules, usually water, across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration. This occurs until equilibrium is reached. The process can be broken down into several steps:

  1. Selective Permeability:

   - The membrane through which osmosis occurs is selectively permeable, allowing only certain molecules (usually water) to pass through while restricting the movement of solutes.

  1. Gradient Setup:

   - There is a concentration gradient of solutes on either side of the membrane. One side has a higher solute concentration (hypertonic), and the other side has a lower solute concentration (hypotonic).

  1. Movement of Water:

   - Water molecules move through the membrane in both directions, but the net movement is from the region of lower solute concentration (hypotonic) to the region of higher solute concentration (hypertonic).

  1. Equilibrium:

   - Osmosis continues until equilibrium is reached. At equilibrium, the concentration of solutes is the same on both sides of the membrane, though there is a constant movement of water molecules.

  1. Osmotic Pressure:

   - Osmosis creates a pressure known as osmotic pressure. This pressure is the force required to prevent the movement of water across the membrane and is determined by the concentration difference of solutes.

 

Significance of osmosis

Osmosis is crucial in biological systems, as it allows for the passive movement of water molecules across cell membranes, ensuring proper cell hydration and maintaining internal balance. This process is vital for the functioning of cells and organisms, influencing processes like nutrient absorption, waste removal, and overall cell integrity. Osmosis plays a fundamental role in various biological functions, contributing to the stability and functionality of living systems.

Plasmolysis

Plasmolysis is the process in which a plant cell loses water and the cell membrane pulls away from the cell wall. Here's an overview of the steps involved in plasmolysis:

  1. Hypertonic Environment:

   - Plasmolysis typically occurs when a plant cell is placed in a hypertonic (higher solute concentration) external environment. In this situation, the concentration of solutes outside the cell is higher than inside.

  1. Loss of Water:

   - Water molecules move out of the plant cell through osmosis, following the concentration gradient from an area of higher water concentration (inside the cell) to an area of lower water concentration (outside the cell).

  1. Cell Membrane Detachment:

   - As water exits the cell, the protoplast (living part of the cell) shrinks away from the cell wall. The cell membrane detaches from the cell wall, leading to a gap between the membrane and the wall.

  1. Plasmolysed Cell:

   - The cell is now in a plasmolysed state. The cell becomes flaccid, losing its normal turgor pressure. The gap between the cell membrane and cell wall is visible under a microscope.

  1. Reversibility:

   - Plasmolysis is generally reversible if the plant cell is placed in a hypotonic (lower solute concentration) environment. In a hypotonic solution, water will move back into the cell, and the protoplast will expand, restoring turgor pressure and the cell's normal state.

Hemolysis

   - Hemolysis is the rupture or destruction of red blood cells. This can occur when red blood cells are exposed to a hypotonic solution, causing water to enter the cells and potentially burst them.

Turgidity

   - Turgidity refers to the state of a cell when it becomes swollen and rigid due to the absorption of water. This is often observed in plant cells when they are in a hypotonic environment.

Flaccidity

   - Flaccidity is the opposite of turgidity. It occurs when a cell loses water and becomes limp, causing it to lose its rigidity. This often happens in plant cells in a hypertonic environment.

Osmoregulation

   - Osmoregulation is the process by which organisms regulate the concentration of water and solutes within their cells to maintain internal balance. It involves various mechanisms, including osmosis and active transport.

Active Transport

   - Active transport is a process that requires energy (usually ATP) to move molecules against their concentration gradient, from an area of lower concentration to an area of higher concentration. This mechanism is essential for maintaining concentration gradients in cells.

EVALUATION: 1. What is diffusion, state two significance of diffusion

  1. What is osmosis, state two significance of osmosis
  2. Define plasmolysis

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively