Grade 8 Science Exam Study Guide

Gear that increase the speed of rotation in a device are called multiplying gears. This means that when these gears are used, the output speed of rotation will be greater than the input speed. Multiplying gears are often used in machines or devices where a higher speed is required, such as in vehicles or industrial machinery. These gears are designed to increase the rotational speed by using a combination of gear sizes and ratios, allowing for a faster output.

Red blood cells have a crucial role in transporting oxygen to all the cells of the body. Oxygen is necessary for cellular respiration, which is the process by which cells generate energy. Red blood cells contain a protein called hemoglobin that binds to oxygen in the lungs and carries it to tissues throughout the body. This oxygen-rich blood is then delivered to cells, where it is used for various metabolic processes. Therefore, the correct answer is oxygen.

Gears are used to transmit power and change the speed or torque of a rotating device. When the number of teeth on the driven gear is smaller than the driving gear, it is called a reducing gear. This configuration decreases the turning speed of the device while increasing the torque. Therefore, reducing gears are used to decrease the turning speed in a device.

Approximately 74% of the Earth's surface is covered with water. This includes the oceans, seas, lakes, rivers, and other bodies of water. The large percentage of water on Earth is essential for supporting various ecosystems, regulating the climate, and providing habitats for numerous species.

In a cell, carbon dioxide (Co2) and waste are the substances that need to be removed. Carbon dioxide is a waste product of cellular respiration, and it needs to be eliminated from the cell to maintain proper pH levels. Waste, which includes metabolic byproducts and other harmful substances, also needs to be removed to ensure the cell's health and functionality. Therefore, Co2 and waste are the correct choices for substances that need to be removed from a cell.

A microscope is a device that is used to magnify tiny objects. It is specifically designed to view objects that are too small to be seen by the naked eye. Telescopes are used to observe objects that are far away in space, while binoculars are used to view objects at a distance.

The properties of light mentioned in the answer are consistent with scientific understanding. Light does indeed travel in straight lines, as demonstrated by experiments such as the double-slit experiment. Light can also be reflected, as seen when light bounces off a mirror or other reflective surface. Light can bend when it passes through different mediums, such as when it enters water or a prism. Finally, light is a form of energy, which is evident in its ability to do work and its involvement in various physical processes.

The correct answer is "Growth and Development". This is because when the number of cells in an organism increases, it undergoes growth, which refers to an increase in size or mass. Additionally, this increase in cell number also contributes to the development of the organism, which involves the process of maturation and differentiation of cells and tissues to form a functional organism. Adaptation and evolving are not directly related to the increase in cell number, but rather refer to changes in the genetic makeup and characteristics of a population over time in response to environmental pressures.

The term "transparent" refers to a material or substance that allows all light to pass through it. In other words, it is completely see-through, and no light is blocked or absorbed by the material. This means that objects or surfaces made of transparent materials are easily visible through them, as they do not obstruct the passage of light.

The correct answer is "Anything that has no fixed shape and can flow." This definition accurately describes a fluid as a substance that can change its shape and flow freely. Unlike solids, which have a fixed shape, fluids are capable of taking the shape of their container and can easily move or flow from one place to another.

The correct answer is the Respiratory System. When a patient is having trouble breathing, it indicates a problem with their ability to take in oxygen and remove carbon dioxide. The respiratory system is responsible for these functions, which include the lungs, airways, and diaphragm. The doctor would assess the patient's respiratory system to determine the cause of the breathing difficulty and provide appropriate treatment.

Cells are the smallest functioning units of life. They are responsible for carrying out all the necessary functions required for an organism to survive and reproduce. Cells contain various organelles that perform specific tasks, such as energy production, protein synthesis, and DNA replication. They also have the ability to communicate with each other and coordinate their activities. Without cells, life as we know it would not be possible.

As light passes through a convex lens, it is refracted or bent towards the center of the lens. This is because a convex lens is thicker at the center and thinner at the edges. The curvature of the lens causes the light rays to converge towards the center, creating a focal point. Therefore, the correct answer is "Center".

The force applied to a machine is called the input force. This is the force that is exerted on the machine to make it work or perform a task. The input force is the force that is applied to the machine's input point or input mechanism, and it is usually provided by an external source such as a person or a motor. The input force is responsible for initiating the machine's operation and is essential for the machine to function properly.

Heating a material increases the kinetic energy of its particles, causing them to move more rapidly. This increase in kinetic energy leads to an increase in particle motion.

The animal changing color from white in the winter to brown in the summer is an example of adaptation. This change in color allows the animal to blend in with its surroundings during different seasons, providing camouflage and increasing its chances of survival. Adaptation refers to the process by which organisms adjust to their environment in order to increase their fitness and chances of survival. In this case, the animal's ability to change color is a beneficial adaptation that helps it to better survive and avoid predators or capture prey.

Opaque is defined as a substance or material through which no light can pass. It is completely impenetrable by light, resulting in the absence of any transmission of light through it. This characteristic makes opaque objects or substances appear dark or solid, as they do not allow any light to pass through them.

Waves and light have two similarities; they are both a form of energy, and travel out in all directions.

The brain is the control center for the whole body because it is responsible for coordinating and regulating all bodily functions. It receives and processes information from the senses, controls voluntary and involuntary movements, and is involved in cognitive processes such as thinking, memory, and emotions. Without the brain, the body would not be able to function properly and carry out essential tasks.

The skin is considered the largest organ in the human body because it covers the entire external surface. It serves as a protective barrier against pathogens, regulates body temperature, and helps in the excretion of waste products through sweat. The skin also contains various sensory receptors that allow us to perceive touch, pressure, and temperature. Overall, the skin plays a vital role in maintaining homeostasis and protecting the body from external threats.

Cells with similar functions are organized into tissues. Tissues are groups of cells that work together to perform a specific function in the body. They are specialized and have similar structures and functions. Tissues can be found in various parts of the body, such as the muscles, nerves, and organs. They allow for the efficient functioning of different systems in the body by coordinating and carrying out specific tasks.

The brain is the control center for the whole body as it receives and processes sensory information, initiates and controls movements, regulates bodily functions, and is responsible for higher cognitive functions such as thinking, memory, and emotions. It is the central organ of the nervous system and coordinates the activities of all other parts of the body, making it the correct answer.

The term "translucent" refers to a material or substance that allows some light to pass through it. It is neither completely opaque (where no light can pass through) nor completely transparent (where all light can pass through). Instead, it allows only a portion of light to pass through, resulting in a partial or diffused transmission of light.

A simple machine is a tool or device that consists of only one basic machine. It is called a simple machine because it has a straightforward design and performs a basic mechanical function. Examples of simple machines include levers, pulleys, inclined planes, screws, wedges, and wheels and axles. These machines are used to make work easier by multiplying or changing the direction of force.

As temperature increases, the viscosity of a substance decreases. This is because higher temperatures cause the molecules of the substance to move more quickly and have more kinetic energy. As a result, the molecules are able to overcome the attractive forces between them more easily, leading to a decrease in viscosity. Conversely, as temperature decreases, the molecules move more slowly and have less kinetic energy, making it more difficult for them to flow past each other, resulting in an increase in viscosity.

A chemical change involves a substance being transformed into a different substance with new properties. Iron rusting is a chemical change because it forms iron oxide, a new substance. Melting ice and boiling water are physical changes, as the substance remains water in different states. Cutting paper is also a physical change because it remains paper.

The term "solvent" refers to the substance that is responsible for dissolving another substance. In a solution, the solvent is the component that is present in greater quantity and has the ability to dissolve the solute. It is the medium through which the solute particles are dispersed and separated. The solvent interacts with the solute particles, breaking their bonds and surrounding them, resulting in the formation of a homogeneous mixture.

The oceanic zone refers to the deepest part of the ocean. It is characterized by its vast depth and lack of sunlight penetration. This zone is home to a wide variety of marine organisms that have adapted to the extreme conditions, such as high pressure and low temperatures. The oceanic zone is an important ecosystem that plays a crucial role in regulating Earth's climate and providing habitat for countless species.

Osmosis is defined as the tendency of particles to pass through a semipermeable membrane. This means that particles, such as water molecules, move from an area of lower concentration to an area of higher concentration, in order to equalize the concentration on both sides of the membrane. The semipermeable membrane allows only certain particles to pass through, while blocking others based on their size or charge. This process is important in various biological and physical systems, such as the movement of water in plant cells or the filtration of waste materials in the kidneys.

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Phloem and xylem are two types of transport tissues found in plants. Phloem is responsible for transporting nutrients, such as sugars, from the leaves to other parts of the plant, while xylem transports water and minerals from the roots to the rest of the plant. These tissues play a crucial role in the overall functioning and survival of the plant by ensuring the distribution of essential substances throughout its various parts.

Ultraviolet rays cause skin damage and can lead to cancer. Exposure to ultraviolet radiation from the sun or artificial sources like tanning beds can cause sunburn, premature aging of the skin, and increase the risk of skin cancer. It is important to protect the skin from excessive exposure to ultraviolet rays by using sunscreen, wearing protective clothing, and seeking shade.

The correct answer is "A measure of how the speed of the object is affected by a machine." The speed ratio is a measure of how the speed of an object is influenced or changed by the use of a machine. It indicates the relationship between the input speed and the output speed of the machine. A higher speed ratio indicates that the machine can increase the speed of the object, while a lower speed ratio indicates a decrease in speed. Therefore, the speed ratio helps determine the effectiveness and impact of a machine on the speed of an object.

Liquid and gas are forms of matter that will take the shape of their container. Unlike solids, which have a fixed shape and volume, liquids and gases are able to flow and conform to the shape of the container they are placed in. Liquids have a definite volume but no definite shape, while gases have neither a definite shape nor a definite volume. This property allows liquids and gases to be easily poured or transferred from one container to another, making them highly adaptable to different environments.

The "Bends" occurs when a diver ascends too quickly in the ocean. This is a condition known as decompression sickness, where nitrogen bubbles form in the body tissues due to the rapid decrease in pressure. These bubbles can cause various symptoms, including joint and muscle pain, dizziness, and even organ damage. It is important for divers to ascend slowly and follow proper decompression procedures to prevent the occurrence of the bends.

Efficiency is a measure of how well a machine utilizes energy. It indicates the ratio of useful output energy or work to the input energy or work. A machine with high efficiency is able to convert a larger proportion of the input energy into useful output energy, while a machine with low efficiency wastes more energy as heat or other forms of energy. Therefore, efficiency is a crucial factor in evaluating the effectiveness and performance of machines, as it determines how effectively they can convert energy into useful work.

Particles move the slowest in a solid because they are tightly packed and have less freedom of movement. In a solid, particles vibrate in fixed positions and cannot move around easily. On the other hand, particles move the quickest in a gas because they have the most freedom of movement. In a gas, particles are far apart and can move freely in all directions, colliding with each other and the walls of their container.

Mechanical Advantage refers to the amount by which a machine can multiply the force applied to it. It is a measure of the effectiveness of a machine in amplifying the input force to produce a greater output force. In simple terms, it quantifies the ratio between the output force produced by a machine and the input force applied to it. A higher mechanical advantage indicates that the machine can multiply the force to a greater extent, making it more efficient in performing work.

The solute refers to the substance that is being dissolved in a solution. In a solution, the solute is the component that is present in a smaller quantity and is dissolved by the solvent. It is the substance that undergoes a physical or chemical change to form a homogeneous mixture with the solvent. The solute particles are dispersed throughout the solvent and can be solid, liquid, or gas. Examples of solutes include sugar, salt, and carbon dioxide.

A mechanical mixture is defined as a mixture that is made up of more than one type of substance. Unlike a pure substance, which is made up of only one type of substance, a mechanical mixture consists of different substances that are physically mixed together. Although it may appear to be one type of substance, it actually contains multiple substances that can be separated through physical means, such as filtration or distillation.

Bioluminescence refers to the ability of living organisms to produce their own light. This phenomenon is commonly observed in various marine organisms such as jellyfish, fish, and bacteria. Bioluminescence is a result of a chemical reaction that occurs within the organism's cells, involving the interaction of a light-emitting molecule called luciferin and an enzyme called luciferase. This process is used by organisms for various purposes, including communication, attracting prey, and camouflage. Therefore, the correct answer is Bioluminescence.

The red octagon hazard symbol is commonly associated with danger. It is used to warn people about potentially hazardous situations or substances that could cause harm or injury. The word "Danger" further emphasizes the seriousness of the situation and alerts individuals to take immediate precautions to avoid any potential risks.

Tissues work together to form organs and organ systems. This is because tissues are groups of cells that work together to perform a specific function, and organs are made up of different types of tissues that work together to perform a more complex function. Organ systems, on the other hand, are groups of organs that work together to perform a specific function for the organism as a whole. Therefore, the correct answer is organs and organ systems.

As the river reaches its mouth, the flow of water slows down, causing it to deposit or drop the sediments it carries. Sediments refer to the particles of dirt, sand, silt, and other materials that are transported by the river. These sediments settle at the mouth, forming deposits and contributing to the formation of deltas or other landforms. Gravel and sand are types of sediment, but sediment is a more general term that encompasses a wider range of particle sizes and materials.

A drumlin is a type of landform that is characterized by its tear drop shape. These small hills are typically elongated in the direction of the glacier's movement during the ice age. They are formed as glaciers move and reshape the land, depositing sediment and rocks in the process. The meltwater from the glacier also contributes to the formation of drumlins. These landforms can be found in areas that were once covered by glaciers and are important in understanding the geological history of an area.

When gravity is greater than the buoyant force, an object will sink. Gravity is the force that pulls objects towards the center of the Earth, while the buoyant force is the upward force exerted by a fluid on an object submerged in it. If gravity is stronger than the buoyant force, the object will be pulled downwards more strongly than the fluid can push it upwards, causing it to sink.

No machine can be 100% efficient because some amount of power is always lost in the form of heat, friction, or other forms of energy. This lost power is typically referred to as waste energy or energy dissipation. Therefore, the remaining power is displayed as energy output, making the machine less than 100% efficient.

When a loud noise makes you jump, it triggers a reflex action known as the stimulus response. In this case, the loud noise acts as the stimulus, which causes a quick and involuntary response from the nervous system, resulting in the jumping reaction. This reflex action is a protective mechanism that helps us react quickly to potential threats or danger.

The normal line is a line that is perpendicular to a given line or surface at a specific point. It is always perpendicular, which means it forms a right angle with the line or surface. In this case, the correct answer is 90° because a normal line is always measured at a right angle, which is exactly 90 degrees.

When light passes through a concave lens, the lens causes the light rays to diverge or spread out. This is because a concave lens is thinner at the center and thicker at the edges, causing the light rays to bend away from the center. As a result, the light rays spread out in different directions after passing through the lens.