A Biology Lesson Note - Cell and the environment

Hello teachers, students, and researchers, I am here again today, Monday, 31sth March, 2020, to share a this lesson note on Cell and the Environment.

Subject: Biology
Topic: Cell and the environment
Class: SS2
Age: 14-16 years
Period: Double period
Time: 90 minutes (45 minutes per period)
Sex: Co-educational
Date: March 31, 2020

Content: Diffusion, Osmosis, Haemolysis, Plasmolysis, Turbidity
Behavioral Objectives: during and at the end of the lesson, students should be able to;

  1. Diffusion.
  2. Osmosis.
  3. Differences between Diffusion and Osmosis

Instructional materials: Blackboard, chalk, lesson note, perfume, funnel, beaker, yam tuber, sugar solution, water, knife, petri-dish, microscope.
Reference material: Essential biology secondary school (M.C. Michael).
Entry behavior: The teacher asks the students questions to test their level of understanding about the lesson.
Presentation: The lesson is presented step by step as follows:

STEP I: DIFFUSION
Diffusion id defined as the process by which molecules or ions of a substance (i.e. gases and liquid) move from a region of high concentration to a region of low concentration until they are evenly distributed. The substance involved in diffusion may be liquid gases or solid.

Factors Affecting or Controlling Diffusion
The rate or speed of diffusion is controlled by a number of factors which include:
1. State of matter: Diffusion varies with three states of matter. The diffusion of gases is much faster than that of liquid because the gas molecules are freer and therefore faster than liquid molecules.
2. Molecular size: The natures of the size of the molecule affect diffusion. In general, the smaller the molecule, the slower the rate of diffusion.
3. Difference in concentration: For diffusion to take place in a medium there must be difference in the concentration of the substance in two areas. The greater the differences in the concentration of the molecules, the greater the rate of diffusion.
4. Temperature: High temperature increases the speed at which molecules move. Thus,, the higher the temperature, the faster the fast the rate of diffusion.

STEP II OSMOSIS
Definition: Osmosis is defined as the flow of water or solvent molecules from a region of dilute or a weaker solution to a region of concentrated or stronger solution through a selectively or differentially permeable membrane. It should be noted that osmosis is a special form of diffusion.

Conditions Necessary for Osmosis to take Place
There are three major conditions which are necessary for osmosis to place. These are:

  1. Presence of a weaker solution e.g. dilute water.
  2. Presence of a stronger solution e.g. sugar or salt solution.
  3. Presence of a selectively or differentially permeable membrane.

Living Cells as Osmo-Meter
In osmosis, there are usually two solutions which are separated by differentially permeable membrane. The weaker solution is said to be HYPOTONIC while the stronger solution is said to be HYPERTONIC. When both solutions have the same concentration, they are said to be ISOTONIC.

1. HYPOTONIC: When a cell of living plant or animal is surrounded by pure water or solution whose solute concentration is lower, water passes into the cell by osmosis. The solution is therefore said to be hypotonic.
2. ISOTONIC: When the solute concentration of cell and its surrounding medium are the same; the solution is said to be isotonic.
3. HYPERTONIC: When the cell is surrounded by a stronger solution, they will be lost by the cell. The shrinking of the cell is as a result of the surrounding solution be hypertonic.

In living cells, when water move across the membrane into a solution of a higher concentration, a pressure is created in the cell. This pressure is called osmotic pressure. The solution is said to be exert a higher osmotic pressure than the weaker solution. Osmotic pressure is a force that draws in water into the cell. The pressure which a solution can potentially exert is called its osmotic osmo-regulation is the control of substances in as the contractile vacuole in amoeba and paramecium.

Differences between Diffusion and Osmosis

S/N.DIFFUSIONOSMOSIS
1.Diffusion occurs in gases and liquid.Differentially permeable membrane is required
2.Differentially permeable membrane is not requiredDifferentially permeable membrane is required
3.It occurs in living and non-living things.It occurs in living organisms.

I am your Research Assistant @Uyobong. We hope to meet again tomorrow for some helpful educational research tips. Feel free to use the comment section of this post to ask questions so we can interact the more.

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