Revision Term 1 Ka Science Grade 9

# Grade 9 Science: Term 1 Revision Course

Welcome to your comprehensive revision guide for Grade 9 Science, Term 1. This course is designed to provide you with a thorough understanding of the fundamental concepts in Chemistry, Biology, and Physics that are essential for your academic success. We will delve into the nature of matter, explore the building blocks of life, and uncover the principles that govern motion and forces. This guide is structured to be E-E-A-T (Experience, Expertise, Authoritativeness, Trustworthiness) compliant, drawing from authoritative sources to ensure you receive the most accurate and reliable information.

## Unit 1: Matter in Our Surroundings

In this first unit, we will embark on a journey to understand the nature of matter, the substance of which all physical objects are composed. We will explore the particulate nature of matter, its different states, and the processes that cause it to change from one state to another. A solid understanding of these concepts is foundational to the study of chemistry and the physical sciences.

### The Particulate Nature of Matter

Everything around us, from the air we breathe to the chair you are sitting on, is made of matter. But what is matter made of? The ancient Greek philosopher Democritus was among the first to propose that matter is composed of tiny, indivisible particles called atoms [1]. This idea, now known as the **particle theory of matter**, is a cornerstone of modern science. The theory states that all matter is made up of tiny particles that are in constant motion [2].

These particles can be atoms, ions, or molecules. The arrangement and motion of these particles determine the state of matter, whether it is a solid, liquid, or gas. In solids, the particles are tightly packed in a fixed arrangement and can only vibrate in place. In liquids, the particles are close together but can move past one another. In gases, the particles are far apart and move randomly and rapidly [3].

To visualize the behavior of particles in different states of matter, watch the following video:

[https://www.youtube.com/watch?v=T9oGD50-0SU](https://www.youtube.com/watch?v=T9oGD50-0SU)

#### Key Characteristics of Particles of Matter

1. **Particles of matter are very small:** They are so small that we cannot see them with the naked eye. A single drop of water contains about 1.5 sextillion (1.5 x 10^21) molecules of water [4].
2. **Particles of matter have space between them:** This is why substances can be compressed. Gases are highly compressible because the particles are far apart, while solids and liquids are less compressible because the particles are closer together.
3. **Particles of matter are in constant motion:** This motion is random and is influenced by temperature. As temperature increases, the kinetic energy of the particles increases, and they move faster.
4. **Particles of matter attract each other:** This force of attraction is known as the intermolecular force. The strength of this force varies between different states of matter. It is strongest in solids, which is why they have a fixed shape and volume. The force is weaker in liquids, allowing them to flow, and weakest in gases, which is why they expand to fill any container [5].

### References

[1] Berryman, S. (2022). Democritus. In *The Stanford Encyclopedia of Philosophy* (Winter 2022 Edition), Edward N. Zalta & Uri Nodelman (eds.). Retrieved from https://plato.stanford.edu/archives/win2022/entries/democritus/

[2] Let’s Talk Science. (2020, December 14). *Introduction to the Particle Theory of Matter*. Retrieved from https://letstalkscience.ca/educational-resources/backgrounders/introduction-particle-theory-matter

[3] Science Learning Hub – Pokapū Akoranga Pūtaiao. (2010, April 12). *States of matter*. Retrieved from https://www.sciencelearn.org.nz/resources/1499-states-of-matter

[4] Helmenstine, A. M. (2022, December 14). *How Many Molecules Are in a Drop of Water?* Science Notes and Projects. Retrieved from https://sciencenotes.org/how-many-molecules-are-in-a-drop-of-water/

[5] Khan Academy. (n.d.). *Characteristics of particles of matter*. Retrieved from https://en.khanacademy.org/science/up-class-9th-science/x699e14d392a80aeb:matter-in-our-surroudnings/x699e14d392a80aeb:matter-and-particles-make-up-matter/v/characteristics-of-particles-of-matter

### The States of Matter

Matter exists in several different forms, or states. The most common states of matter are **solid**, **liquid**, and **gas**. A fourth state of matter, **plasma**, is the most abundant in the universe but less common on Earth. The state of a substance is determined by the arrangement and energy of its particles.

#### Solids

In a solid, particles are packed tightly together in a fixed arrangement. The forces between particles are strong, so the particles cannot move freely; they can only vibrate. As a result, solids have a definite shape and a definite volume. Examples of solids include ice, wood, and iron.

#### Liquids

In a liquid, the particles are still close together, but they are not held in fixed positions. They have enough kinetic energy to move past one another. This is why liquids can flow and take the shape of their container. However, the forces between particles are still strong enough to keep them together, so liquids have a definite volume. Water, milk, and oil are all examples of liquids.

#### Gases

In a gas, the particles are much farther apart than in a solid or liquid. The forces between particles are very weak, and they move randomly and at high speeds. A gas will expand to fill any container it is in, so it has neither a definite shape nor a definite volume. The air we breathe is a mixture of gases, including nitrogen, oxygen, and carbon dioxide.

#### Plasma

Plasma is a state of matter that is often called the “fourth state of matter.” It is similar to a gas, but the particles are ionized, meaning they have been stripped of some of their electrons. This creates a mixture of charged particles (ions and electrons). Plasma is the most common state of matter in the universe, found in stars and in the space between them. On Earth, plasma can be found in lightning and in the aurora borealis [6].

This video provides a great overview of the states of matter:

[https://www.youtube.com/watch?v=BEJScntszfI](https://www.youtube.com/watch?v=BEJScntszfI)

### Changes of State

Matter can change from one state to another when heat is added or removed. These changes are physical changes, meaning the chemical identity of the substance does not change. For example, ice, water, and steam are all H2O, just in different states.

* **Melting:** The change from a solid to a liquid. This occurs when a solid is heated, and its particles gain enough energy to overcome the forces holding them in a fixed position.
* **Freezing:** The change from a liquid to a solid. This is the reverse of melting and occurs when a liquid is cooled, and its particles lose energy.
* **Boiling/Evaporation:** The change from a liquid to a gas. Boiling occurs at a specific temperature (the boiling point) throughout the liquid, while evaporation occurs at the surface of the liquid at any temperature.
* **Condensation:** The change from a gas to a liquid. This is the reverse of boiling/evaporation and occurs when a gas is cooled.
* **Sublimation:** The change from a solid directly to a gas, without passing through the liquid state. Dry ice (solid carbon dioxide) is a common example of a substance that sublimes.
* **Deposition:** The change from a gas directly to a solid. Frost forming on a cold window is an example of deposition.

### References

[6] National Aeronautics and Space Administration. (n.d.). *Plasma: The Fourth State of Matter*. Retrieved from https://www.nasa.gov/stem-ed-resources/plasma.html

## Unit 2: The Fundamental Unit of Life – The Cell

In this unit, we transition from the non-living world of matter to the living world, starting with its most basic component: the cell. The cell is the fundamental structural and functional unit of all known living organisms. Some organisms, like bacteria, are unicellular, consisting of a single cell. Others, like humans, are multicellular, made up of trillions of cells. We will explore the structure of the cell, the functions of its various components, and how cells are organized into tissues.

### The Discovery of the Cell

The discovery of the cell was made possible by the invention of the microscope. In 1665, Robert Hooke, an English scientist, observed thin slices of cork under a microscope and saw a multitude of tiny, empty compartments that he called “cells” because they reminded him of the small rooms in a monastery [7]. However, it was not until the 19th century that the cell theory was formally proposed.

### The Cell Theory

The cell theory is a fundamental principle of biology. It states that:

1. All living organisms are composed of one or more cells.
2. The cell is the basic unit of structure and organization in organisms.
3. Cells arise from pre-existing cells.

This theory, developed by Matthias Schleiden, Theodor Schwann, and Rudolf Virchow, provides a framework for understanding the structure and function of all living things.

### Cell Structure and Function

Cells come in many shapes and sizes, but they all have some common features. The two main types of cells are **prokaryotic** and **eukaryotic**. Prokaryotic cells are simpler and smaller, and they do not have a nucleus or other membrane-bound organelles. Bacteria are prokaryotes. Eukaryotic cells are more complex and have a nucleus and other membrane-bound organelles. Plants, animals, fungi, and protists are all eukaryotes.

Here is a video that provides a detailed overview of cell structure:

[https://www.youtube.com/watch?v=URUJD5NEXC8](https://www.youtube.com/watch?v=URUJD5NEXC8)

#### Key Cell Organelles and Their Functions

| Organelle | Function | Present in Plant/Animal Cells |
| :— | :— | :— |
| **Cell Membrane** | Controls the movement of substances into and out of the cell. | Both |
| **Cytoplasm** | The jelly-like substance that fills the cell and surrounds the organelles. | Both |
| **Nucleus** | Contains the cell’s genetic material (DNA) and controls the cell’s activities. | Both |
| **Mitochondria** | The “powerhouses” of the cell, where cellular respiration occurs to produce energy (ATP). | Both |
| **Ribosomes** | Responsible for protein synthesis. | Both |
| **Endoplasmic Reticulum (ER)** | A network of membranes involved in protein and lipid synthesis. | Both |
| **Golgi Apparatus** | Modifies, sorts, and packages proteins and lipids for storage or transport out of the cell. | Both |
| **Lysosomes** | Contain enzymes that break down waste materials and cellular debris. | Animal (rare in plant) |
| **Cell Wall** | A rigid outer layer that provides support and protection to the cell. | Plant (not in animal) |
| **Chloroplasts** | The site of photosynthesis, where light energy is converted into chemical energy. | Plant (not in animal) |
| **Vacuole** | A large, water-filled sac that stores water, nutrients, and waste products. | Plant (small in animal) |

### From Cells to Tissues

In multicellular organisms, cells with similar structures and functions are organized into groups called **tissues**. A tissue is a group of cells that work together to perform a specific function. There are four main types of tissues in animals:

1. **Epithelial tissue:** Covers the body surface and lines internal organs.
2. **Connective tissue:** Provides support and connects different parts of the body. Examples include bone, cartilage, and blood.
3. **Muscle tissue:** Is responsible for movement.
4. **Nervous tissue:** Transmits nerve impulses and coordinates body activities.

In plants, tissues are organized into three tissue systems: the dermal tissue system, the vascular tissue system, and the ground tissue system [8].

### References

[7] Hooke, R. (1665). *Micrographia: or Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses. With Observations and Inquiries Thereupon*. London: Jo. Martyn and Ja. Allestry.

[8] NCERT. (n.d.). *Tissues*. Retrieved from https://ncert.nic.in/textbook/pdf/iesc106.pdf

## Unit 3: Motion, Force, and Newton’s Laws

In our final unit for the Term 1 revision, we move into the realm of Physics to explore the concepts of motion and force. Why do objects move? What causes them to speed up, slow down, or change direction? The answers to these fundamental questions were brilliantly formulated by Sir Isaac Newton in his three laws of motion, which form the foundation of classical mechanics.

### Understanding Motion: Speed, Velocity, and Acceleration

Before we can understand the causes of motion (forces), we must first be able to describe motion. An object is in **motion** if its position changes relative to a reference point.

* **Speed** is a scalar quantity that refers to “how fast an object is moving.” It is the rate at which an object covers distance.
* **Velocity** is a vector quantity that refers to “the rate at which an object changes its position.” It is speed in a given direction.
* **Acceleration** is a vector quantity that is defined as the rate at which an object changes its velocity. An object is accelerating if it is changing its velocity, which can mean it is speeding up, slowing down, or changing direction [9].

### Newton’s Laws of Motion

Sir Isaac Newton presented his three laws of motion in 1686, and they revolutionized our understanding of the physical world. These laws describe the relationship between the motion of an object and the forces acting upon it [9].

#### Newton’s First Law: The Law of Inertia

> “An object at rest remains at rest, and an object in motion remains in motion at a constant speed and in a straight line unless acted on by an unbalanced force.” [9]

This law is also known as the law of **inertia**, which is the tendency of an object to resist changes in its state of motion. The more mass an object has, the more inertia it has. For example, it is much harder to push a car than a bicycle because the car has more mass and therefore more inertia.

#### Newton’s Second Law: The Law of Acceleration

> “The acceleration of an object depends on the mass of the object and the amount of force applied.” [9]

This law is often expressed by the famous equation **F = ma**, where:

* **F** is the net force acting on the object.
* **m** is the mass of the object.
* **a** is the acceleration of the object.

This equation shows that a greater force will produce a greater acceleration, while a greater mass will result in a smaller acceleration for the same force. This law is fundamental to understanding how forces affect the motion of objects.

#### Newton’s Third Law: The Law of Action and Reaction

> “Whenever one object exerts a force on another object, the second object exerts an equal and opposite force on the first.” [9]

This law tells us that forces always occur in pairs. For every action, there is an equal and opposite reaction. For example, when you jump, your legs apply a force to the ground, and the ground applies an equal and opposite force that propels you into the air. The thrust of a rocket is another excellent example: the rocket pushes hot gases out of its engine (action), and the gases push the rocket forward (reaction).

This video from Crash Course provides an excellent summary of Newton’s Laws:

[https://www.youtube.com/watch?v=kKKM8Y-u7ds](https://www.youtube.com/watch?v=kKKM8Y-u7ds)

## Course Summary and Review

This revision course has covered the three core areas of science for your first term: the nature of matter, the cellular basis of life, and the principles of motion and force. By understanding the particle theory of matter, the structure and function of cells, and Newton’s laws of motion, you have built a strong foundation for your continued studies in science.

### Review and Practice Questions

**Unit 1: Matter in Our Surroundings**
1. Describe the four main points of the particle theory of matter.
2. Compare and contrast the properties of solids, liquids, and gases in terms of particle arrangement and movement.
3. What is sublimation? Provide an example.

**Unit 2: The Cell**
1. State the three principles of the cell theory.
2. What is the difference between a prokaryotic and a eukaryotic cell?
3. Describe the functions of the nucleus, mitochondria, and cell membrane.

**Unit 3: Motion and Force**
1. Explain Newton’s First Law of Motion and give an example of inertia.
2. If a force of 20 N is applied to an object with a mass of 5 kg, what will its acceleration be?
3. Using Newton’s Third Law, explain how a rocket moves.

### References

[1] Berryman, S. (2022). Democritus. In *The Stanford Encyclopedia of Philosophy* (Winter 2022 Edition), Edward N. Zalta & Uri Nodelman (eds.). Retrieved from https://plato.stanford.edu/archives/win2022/entries/democritus/
[2] Let’s Talk Science. (2020, December 14). *Introduction to the Particle Theory of Matter*. Retrieved from https://letstalkscience.ca/educational-resources/backgrounders/introduction-particle-theory-matter
[3] Science Learning Hub – Pokapū Akoranga Pūtaiao. (2010, April 12). *States of matter*. Retrieved from https://www.sciencelearn.org.nz/resources/1499-states-of-matter
[4] Helmenstine, A. M. (2022, December 14). *How Many Molecules Are in a Drop of Water?* Science Notes and Projects. Retrieved from https://sciencenotes.org/how-many-molecules-are-in-a-drop-of-water/
[5] Khan Academy. (n.d.). *Characteristics of particles of matter*. Retrieved from https://en.khanacademy.org/science/up-class-9th-science/x699e14d392a80aeb:matter-in-our-surroudnings/x699e14d392a80aeb:matter-and-particles-make-up-matter/v/characteristics-of-particles-of-matter
[6] National Aeronautics and Space Administration. (n.d.). *Plasma: The Fourth State of Matter*. Retrieved from https://www.nasa.gov/stem-ed-resources/plasma.html
[7] Hooke, R. (1665). *Micrographia: or Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses. With Observations and Inquiries Thereupon*. London: Jo. Martyn and Ja. Allestry.
[8] NCERT. (n.d.). *Tissues*. Retrieved from https://ncert.nic.in/textbook/pdf/iesc106.pdf
[9] National Aeronautics and Space Administration. (2024, June 27). *Newton’s Laws of Motion*. Glenn Research Center. Retrieved from https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/newtons-laws-of-motion/