Grade 9 Science Quiz: Review Key Concepts

An ion is formed when an atom loses or gains an electron because the loss or gain of an electron creates an imbalance between the number of protons and electrons in the atom. If an atom loses an electron, it becomes positively charged and forms a cation. If an atom gains an electron, it becomes negatively charged and forms an anion. Therefore, the statement is true.

False. A molecule is not the same as an atom. An atom is the basic unit of an element, composed of a nucleus containing protons and neutrons, with electrons orbiting around. In contrast, a molecule consists of two or more atoms chemically bonded together. Molecules can be composed of the same or different types of atoms.

The correct order of the planets is: Mercury, Venus, Earth, Mars, Jupiter (not included in the question), Saturn, Uranus and Neptune

A star is made up of hydrogen and helium because in the core of a star, nuclear fusion reactions occur where hydrogen atoms combine to form helium, releasing a tremendous amount of energy in the process. This energy is what makes the star shine and produce heat and light.

False. While electric current is a common form of electricity involving the flow of charged particles, it's not the only form. Static electricity, for instance, involves the imbalance of charges at rest. Additionally, there is alternating current (AC) and direct current (DC). AC periodically changes direction, while DC flows in one direction. Various phenomena and technologies encompass different forms of electrical activity.

The Milky Way is a barred spiral galaxy. This means that it has a central bar-shaped structure composed of stars, around which the spiral arms of the galaxy extend. The Milky Way's classification as a barred spiral galaxy has been confirmed through various astronomical observations and research​ (ASEAN)​ .

Bioamplification, also known as biomagnification, is a process in which the concentration of toxins increases as they move up the food chain. This occurs because organisms at higher trophic levels consume a larger quantity of prey or plants that may contain toxins, resulting in the accumulation of these toxins in their bodies. As a result, the toxin levels become higher at each successive trophic level. Therefore, the statement "Bioamplification/biomagnification is when toxin levels get higher at each trophic level" is true.

The melting of ice into water is classified as a physical change because it involves a change in the state of matter without altering the chemical composition of the substance. When ice (solid water) is heated, the thermal energy increases the movement of water molecules, allowing them to overcome the forces that hold them in a rigid structure. As a result, the ice melts into liquid water, which is still H₂O. During this process, no new substances are formed, which is a hallmark of physical changes. The melting point of ice is 0°C (32°F) under standard atmospheric conditions. Understanding this process is fundamental in various scientific fields, including chemistry and environmental science.

In an electrical circuit, electrons flow from the negative end (cathode) to the positive end (anode). This flow is due to the attraction between negatively charged electrons and the positively charged end of the circuit. This movement of electrons constitutes the electric current.

Equilibrium is not an interaction among ecosystems. Equilibrium refers to a state of balance or stability within an ecosystem, where the population sizes and resources remain relatively constant over time. It does not involve any direct interaction between different ecosystems or organisms. In contrast, competition, mutualism, and predation are all types of interactions that occur between organisms in different ecosystems, influencing population dynamics and resource utilization.

The correct answer is Ca-1 N-2 O-6. There is one calcium atom (Ca), two nitrogen atoms (N), and six oxygen atoms (O) in the compound Ca(NO3)2. The subscript numbers indicate the number of each type of atom present in the molecule. The number of nitrogen atoms and oxygen atoms inside the parentheses is multiplied by 2 due to the 2 outside the parentheses.

Bioaccumulation is the process by which toxins gradually accumulate in the tissues of an individual organism over time. This occurs when the organism is exposed to these toxins through its environment or food sources, and is unable to eliminate them at the same rate they are being absorbed. As a result, the concentration of toxins in the organism's body increases, leading to potential harmful effects on its health.

The equation for photosynthesis is H2O+CO2 (light+chlorophyll) = oxygen+glucose. This equation represents the process by which plants and some other organisms convert carbon dioxide and water into oxygen and glucose, using sunlight and chlorophyll as catalysts.

Newton's third law of motion states that for every action, there is an equal and opposite reaction. This principle is foundational in mechanics and can be observed in numerous everyday situations. For instance, when you push against a wall, the wall pushes back with equal force, even though it does not move. This law explains the interaction between forces and is essential for understanding how objects move in response to applied forces. It is also the basis for rocket propulsion; as a rocket expels gas downward, the equal and opposite reaction propels the rocket upward. Newton's laws of motion are fundamental to classical mechanics, providing a framework for analyzing the motion of objects.

Atoms are considered stable when their outermost electron shell, also known as the valence shell, is full. This configuration results in a lower energy state and makes the atom less likely to react with other atoms. The number of electrons needed to fill the valence shell varies depending on the element, but it is typically eight electrons (octet rule).

The Moon is indeed a natural satellite. A satellite is an object that orbits a planet. The Moon orbits the Earth, making it a natural satellite. It is Earth's only natural satellite and plays a crucial role in influencing tides and stabilizing Earth's rotation.

The ohm (Ω) is the SI unit of electrical resistance, named after the German physicist Georg Simon Ohm. Resistance quantifies how much a material opposes the flow of electric current. In an electrical circuit, components such as resistors create resistance, which affects how much current flows for a given voltage, according to Ohm's Law (V = IR, where V is voltage, I is current, and R is resistance). High resistance means that less current will flow, while low resistance allows more current to pass through. This concept is essential in designing electrical circuits, understanding circuit behavior, and ensuring the safety and efficiency of electrical devices.

Mitochondria are often referred to as the "powerhouses" of the cell due to their crucial role in energy production. They are membrane-bound organelles found in most eukaryotic cells. The primary function of mitochondria is to generate adenosine triphosphate (ATP) through a process called oxidative phosphorylation, which occurs during cellular respiration. During this process, glucose and oxygen are converted into ATP, carbon dioxide, and water. This energy is vital for various cellular functions, including muscle contraction, nerve impulse propagation, and biosynthesis of macromolecules. Mitochondria also have their own DNA, which is inherited maternally, and they play a significant role in apoptosis, the programmed cell death that is essential for development and homeostasis.

The law of conservation of mass, formulated by Antoine Lavoisier in the late 18th century, states that in a chemical reaction, matter is neither created nor destroyed. This principle implies that the total mass of the substances involved in a chemical reaction remains constant, provided that the system is closed and no mass enters or leaves the system. Therefore, the mass of the reactants (the starting materials) must equal the mass of the products (the substances formed) after the reaction has occurred.

False. Static electricity can occur with both conductors and insulators. While conductors allow the flow of electrons, insulators resist the flow. In static electricity, electrons can accumulate on the surface of insulators, creating a charge imbalance. This phenomenon is observed in various materials, not limited to conductors, as static charges can build up and discharge between objects with different electrical potentials.

Sulfuric acid is a highly corrosive strong mineral acid with the chemical formula H₂SO₄. It consists of two hydrogen atoms, one sulfur atom, and four oxygen atoms. Sulfuric acid is one of the most widely used chemicals in the world and has applications in various industries, including manufacturing fertilizers, refining oil, and treating metals. In laboratories, it serves as a dehydrating agent and is involved in many chemical reactions due to its strong acidic properties. Its production involves the Contact Process, where sulfur dioxide is oxidized to sulfur trioxide, which then reacts with water to produce sulfuric acid. It is important to handle sulfuric acid with care due to its exothermic reaction with water, which can lead to splattering.

Biodiversity is not a limiting factor because it refers to the variety of different species in an ecosystem, and does not directly limit the growth or survival of any particular species. Climate extremes, disease, predation, human disturbances, and competition can all limit the population size or distribution of certain species, but biodiversity itself is not a limiting factor in this context.

Sublimation is the process where a substance changes directly from a solid to a gaseous state without passing through the liquid state. This occurs when the molecules of the solid gain enough energy to break free from their fixed positions and enter the gaseous phase. An example of sublimation is dry ice, which is solid carbon dioxide that changes directly into carbon dioxide gas when it warms up.

The largest type of galaxy in the universe is the elliptical galaxy. These galaxies are characterized by their smooth, oval or elliptical shape and typically contain older stars with less interstellar gas and dust, resulting in less active star formation. Elliptical galaxies can vary in size, with some being small and others being massive. They are often found in regions of high galaxy density, such as galaxy clusters, and are one of the main classifications of galaxies based on their shape and structure.

Nitrogen makes up about 78% of the Earth's atmosphere, while oxygen accounts for approximately 21%. The remaining 1% consists of other gases, including argon, carbon dioxide, neon, and trace amounts of other gases. Nitrogen is a key component of the atmosphere, and while it is relatively inert and does not easily react with other substances, it plays a crucial role in various biological and chemical processes, such as the nitrogen cycle, which is essential for life on Earth. Oxygen is vital for respiration in many living organisms, but it is not the most abundant gas. Carbon dioxide is present in much smaller quantities, primarily as a result of natural processes and human activities, and hydrogen is also found in trace amounts in the atmosphere.

A lunar eclipse occurs when the Earth passes between the Sun and the Moon, casting a shadow on the Moon, which can only happen during a full moon. There are three types of lunar eclipses: total, partial, and penumbral. In a total lunar eclipse, the entire Moon moves through the Earth's darkest shadow (umbra), often taking on a reddish hue known as a "Blood Moon." A partial lunar eclipse occurs when only a portion of the Moon enters the umbra, while a penumbral lunar eclipse is when the Moon passes through the Earth's lighter outer shadow (penumbra), resulting in a subtle shading. Unlike solar eclipses, which are viewable from specific locations, lunar eclipses can be seen from anywhere on the night side of the Earth, making them widely accessible for observation.

Biodiversity is a measure of how many different species are present in a particular ecosystem. It quantifies the diversity of species within that ecosystem, indicating the number of different organisms that coexist in a given area. This measure does not take into account the abundance or population size of each species, but rather focuses on the total number of distinct species present.

When an atom gains an electron, it becomes an anion. An anion is a negatively charged ion because it now has more electrons than protons. This results in an overall negative charge for the atom. A cation, on the other hand, is a positively charged ion formed when an atom loses an electron. "Onion" is not a term used in chemistry to describe the result of an atom gaining an electron.

The acceleration due to gravity on Earth is approximately 9.8 meters per second squared (m/s²). This value represents the rate at which an object accelerates downward when in free fall, neglecting air resistance. It results from the gravitational force exerted by the Earth on an object, which depends on the object's mass and the distance from the Earth's center. This acceleration is crucial for understanding various phenomena in physics, including projectile motion, the behavior of falling objects, and the dynamics of satellites orbiting the Earth. The concept of gravitational acceleration is also foundational in Einstein's theory of general relativity, which describes gravity as the curvature of spacetime caused by mass.

Chloroplasts are specialized organelles found in plant cells and some algae, essential for photosynthesis—the process by which light energy is converted into chemical energy stored in glucose. Chloroplasts contain chlorophyll, the green pigment that captures sunlight, and other pigments that absorb different wavelengths of light. During photosynthesis, carbon dioxide from the atmosphere and water from the soil are used in the presence of sunlight to produce glucose and oxygen. This process is vital for plant growth and energy production and plays a crucial role in the global carbon cycle, as plants are primary producers that form the base of the food chain. Chloroplasts also contain their own DNA, resembling bacterial DNA, which supports the endosymbiotic theory of their origin.

The production of smell does not necessarily indicate a chemical change because it can also occur in physical changes. Smells can be produced when substances evaporate or when they are physically broken down, without any chemical reactions taking place. Therefore, the production of smell alone is not sufficient evidence to indicate a chemical change.

Oxygen constitutes approximately 46.6% of the Earth's crust by weight, making it the most abundant element in the crust. It primarily exists in the form of oxides, with silica (SiO₂) being the most prevalent mineral, found in rocks like quartz and granite. Oxygen is essential for the formation of many minerals and compounds and plays a critical role in geological processes. It is also vital for life, as it is a key component of cellular respiration in animals and the process of photosynthesis in plants. The availability of oxygen in the atmosphere, which is produced by photosynthetic organisms, is crucial for sustaining life on Earth.

A covalent bond is formed when two nonmetal atoms share pairs of electrons to achieve stability. This type of bonding occurs because nonmetals have similar electronegativities, meaning they attract electrons with comparable strength. Sharing electrons allows each atom to attain a full outer electron shell, satisfying the octet rule and leading to a more stable electronic configuration. Covalent bonds can vary in strength and length, depending on the number of shared electron pairs; single, double, and triple bonds represent one, two, and three shared pairs, respectively. Understanding covalent bonding is fundamental in chemistry, as it explains the structure and properties of many organic and inorganic compounds.

Friction, contact, and induction are all methods of creating static electricity. When two objects rub against each other, like rubbing a balloon on your head, friction occurs and creates static electricity. Contact occurs when a charged object comes into direct contact with a neutral object, causing the neutral object to become charged. Induction involves bringing a charged object close to a neutral object, causing a separation of charges and creating static electricity. Lightning, on the other hand, is not a method of creating static electricity. It is a natural phenomenon that occurs due to the buildup and discharge of electrical energy in the atmosphere.

A circumpolar constellation can be seen all year round.  Circumpolar constellations are located near the celestial pole, either the North or South Pole, and appear to circle around it. As a result, they never dip below the horizon and are visible throughout the year. This is in contrast to other constellations that rise and set with the rotation of the Earth and may not be visible at certain times of the year.

Carbon dioxide (CO₂) is a greenhouse gas that plays a significant role in Earth's climate system. It is produced through natural processes such as respiration, decomposition, and volcanic eruptions, but human activities, particularly the burning of fossil fuels and deforestation, have significantly increased its concentration in the atmosphere. CO₂ traps heat by absorbing infrared radiation, preventing it from escaping back into space, which contributes to the greenhouse effect. This process is crucial for maintaining Earth's temperature but has led to global warming and climate change due to the enhanced greenhouse effect caused by elevated CO₂ levels. Understanding the role of carbon dioxide in climate change is essential for addressing environmental issues and implementing sustainable practices.

Photosynthesis provides us with oxygen and glucose.

Oxygen: During photosynthesis, plants take in carbon dioxide (CO2) and water (H2O) and convert them into glucose and oxygen. The oxygen is released into the atmosphere, which is essential for the survival of most organisms on Earth, including humans.

Glucose: The glucose produced by plants during photosynthesis is a source of energy for many organisms. Herbivores eat plants to get this energy, and carnivores eat herbivores, thus the energy from photosynthesis flows through the food chain.

While photosynthesis does require light and water as inputs, it does not provide these as outputs. Therefore, “light” and “water” are not correct answers. As for “energy”, while it’s true that the glucose produced in photosynthesis stores energy that can be used by other organisms, the process itself does   provide energy in a form that can be used by humans or animals. 

Friction is not a method of electrical discharge. Discharging refers to the process of releasing or removing an electrical charge. The options "at a point," "a spark," and "moisture" are all methods that can cause discharging. However, friction does not directly involve the release or removal of electrical charge. Instead, friction refers to the force that occurs when two surfaces rub against each other, which can generate static electricity but is not a method of discharging it.

The circumpolar constellations are those that never set below the horizon and can be seen year-round in the northern hemisphere. Draco, Ursa Major, and the Ursa Minor (Little Dipper ) are all examples of circumpolar constellations. These constellations are visible throughout the night and are easily recognizable due to their prominent stars and distinctive shapes. Aquarius and Leo, on the other hand, are not circumpolar constellations, as they are set below the horizon at certain times of the year.