General Science Grade 8 Study Notes

General Overview

  • Textbook: General Science Student Textbook for Grade 8
  • Publisher: Addis Ababa Education Bureau, 2021, a joint effort by multiple authors including Yonas Nibret, Sefiw Melesse, and Abebe Habte.
  • Purpose: Designed for Grade 8 students in Ethiopia, featuring comprehensive information on various scientific topics.

Care Instructions for the Textbook

  • Protect the book:
    • Use plastic covers, newspapers, or cardboard.
  • Keep in clean, dry places.
  • Avoid writing in the book.
  • Use bookmarks instead of marking pages.
  • Repair torn pages with tape or paste.
  • Handle carefully when passing to others.
  • Properly pack when storing in bags.

Acknowledgments

  • Key Contributors:
    • Ato Zelalem Mulatu
    • Ato Admasu Dechasa
    • Ato Dagnew Gebru
  • Management Team: Continuous support from various division heads and technical advisors of the Addis Ababa Education Bureau.

Table of Contents

UNIT ONE: Basics of Scientific Investigation

  • 1.1 Scientific Measurements (Page 2)
  • 1.2 Doing Scientific Investigation (Page 16)
  • Review Exercise (Page 23)

UNIT TWO: Composition of Matter

  • 2.1 Early Thinking about the Composition of Matter (Page 26)
  • 2.2 Inside of an Atom (Page 27)
  • 2.3 Molecules (Page 31)
  • Review Exercise (Page 35)

UNIT THREE: Classification Of Compounds

  • 3.1 Introduction (Page 38)
  • 3.2 Organic Compounds (Page 40)
  • 3.3 Inorganic Compounds (Page 45)
  • 3.4 Neutralization Reaction and Salts (Page 64)
  • Review Exercise (Page 71)

UNIT FOUR: Human Body Systems and Health

  • 4.1 Integumentary Systems (Page 75)
  • 4.2 Muscular System (Page 85)
  • 4.3 Skeletal System (Page 89)
  • 4.4 Digestive System (Page 98)
  • 4.5 Respiratory System (Page 106)
  • 4.6 Circulatory System (Page 109)
  • 4.7 Reproductive System (Page 114)
  • Review Exercise (Page 125)

UNIT FIVE: Ecosystem and Conservation of Natural Resources

  • 5.1 Ecosystem and Interactions (Page 127)
  • 5.2 Soil (Page 130)
  • 5.3 Water (Page 143)
  • 5.4 Air (Page 157)
  • 5.5 Forests (Page 160)
  • 5.6 Biodiversity (Page 166)
  • Review Exercise (Page 169)

UNIT SIX: The Solar System

  • 6.1 Family of the Solar System (Page 171)
  • 6.2 Formation of the Solar System (Page 176)
  • 6.3 Earth in Comparison with Solar System (Page 180)
  • 6.4 Our planet’s Suitability for Life (Page 185)
  • Review Exercise (Page 191)

UNIT SEVEN: Physical Phenomena in the Surrounding

  • 7.1 Phenomena of Light (Page 194)
  • 7.2 Vision and Imaging (Page 200)
  • 7.3 Sound (Page 206)
  • 7.4 Heat (Page 213)
  • 7.5 Simple Circuit (Page 219)
  • 7.6 Magnetism (Page 222)
  • Review Exercise (Page 229)

UNIT ONE: Basics of Scientific Investigation

Learning Outcomes

At the end of this unit, students will be able to:

  • Identify basic and derived units of measurement.
  • Explain the concept of measuring physical quantities.
  • Describe the components of a scientific investigation.
  • Demonstrate ability to work effectively and respectfully with others in performing fair testing.

1.1 Scientific Measurements

Introduction

  • This section covers indigenous and modern methods of measurement, classification into fundamental and derived quantities, and the distinction between accuracy and precision.

Key Concepts

  • Measurement: The process of obtaining the magnitude of a quantity relative to an agreed standard.
  • Physical Quantities: Properties of an object that can be measured. Examples include length, mass, time, temperature, area, volume, density, force, etc.
  • Units of Measurement:
    • Fundamental units: Basic quantities that cannot be expressed in terms of other units.
    • Length: Meter (m)
    • Mass: Kilogram (kg)
    • Time: Second (s)
    • Derived units: Quantities derived from fundamental units (e.g., area: $m^2$, volume: $m^3$).

Significant Methods

  • Indigenous Methods: Locally practiced measurements passed down through generations.
  • Measurement units include hand-span, digit, cubit, pace, etc.
  • Modern Methods: Established scientific units and techniques utilized globally.

Activities and Exercises

  • Group measurements (Activity 1.1): Measure objects using indigenous units.
  • Discussion on reliability of indigenous methods (Exercise 1.2).

UNIT TWO: Composition of Matter

2.1 Early Thinking about the Composition of Matter

Historical Perspectives

  • Democritus (460-370 BC): Proposed that matter consists of indivisible particles called "atomos".
  • Aristotle (384-322 BC): Argued matter is infinitely divisible, consisting of four elements: fire, earth, air, and water.

Comparisons

  • Discrete Theory (Democritus): Matter has limits to division; consists of atoms.
  • Continuous Theory (Aristotle): Matter is infinitely divisible.

Activities

  • Group discussions to compare concepts of matter (Activity 2.2).

2.2 Inside of an Atom

Structure of Atoms

  • Atoms consist of a central nucleus with protons and neutrons, surrounded by electrons.
  • Atomic Properties:
    • Proton (positive charge, mass ≈ $1.673 imes 10^{-24}$ g)
    • Neutron (neutral, mass ≈ $1.675 imes 10^{-24}$ g)
    • Electron (negative charge, mass negligible)

UNIT THREE: Classification Of Compounds

3.1 Introduction

Organic vs. Inorganic Compounds

  • Organic Compounds: Contain carbon and hydrogen (e.g., hydrocarbons).
  • Inorganic Compounds: Comprising elements other than carbon; includes oxides of carbon, carbonates, etc.

Key Chemical Reactions

  • Neutralization reaction forming salts (e.g., acid + base = salt + water).

Important Concepts

  • Understanding common acids (HCl, H2SO4, etc.) and their corresponding salts.

Conclusion of Unit 3

  • The foundational concepts of organic and inorganic chemistry and their practical implications.