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GED Science practice questions

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Question 1Scientific reasoning across life, physical and Earth science

Which organelle is responsible for producing energy in the form of ATP through cellular respiration?

  1. Nucleus
  2. Mitochondria Correct answer.
  3. Ribosome
  4. Golgi apparatus

Explanation

Mitochondria are often called the 'powerhouse of the cell' because they generate ATP through cellular respiration. They convert glucose and oxygen into ATP, carbon dioxide, and water. This energy powers all cellular activities.

Question 2Scientific reasoning across life, physical and Earth science

A student observes a slide under a microscope and notices cells with a cell wall, a large central vacuole, and chloroplasts. These cells are most likely from which type of organism?

  1. A bacterium
  2. An animal
  3. A plant Correct answer.
  4. A fungus

Explanation

Plant cells are uniquely identified by three structures not found in animal cells: a rigid cell wall (made of cellulose), a large central vacuole that stores water and maintains pressure, and chloroplasts for photosynthesis. Together these three features conclusively identify a plant cell.

Question 3Scientific reasoning across life, physical and Earth science

During photosynthesis, plants convert light energy into chemical energy stored in glucose. Which gas do plants release as a byproduct of this process?

  1. Carbon dioxide
  2. Nitrogen
  3. Oxygen Correct answer.
  4. Hydrogen

Explanation

The overall equation for photosynthesis is: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂. Oxygen is released as a byproduct when water molecules are split during the light-dependent reactions. This is why plants are vital to maintaining atmospheric oxygen levels.

Question 4Scientific reasoning across life, physical and Earth science

A Punnett square cross between two parents who are both heterozygous (Tt) for plant height, where T (tall) is dominant over t (short), shows which ratio of tall to short offspring?

  1. 4:0
  2. 3:1 Correct answer.
  3. 1:3
  4. 2:2

Explanation

When two Tt parents cross (Tt × Tt), the Punnett square gives TT, Tt, Tt, and tt - three possible tall plants (TT and two Tt) and one short plant (tt). This produces the classic 3:1 dominant-to-recessive ratio. This ratio is a hallmark of Mendelian genetics with one dominant and one recessive allele.

Question 5Scientific reasoning across life, physical and Earth science

Which of the following best describes the role of DNA in a cell?

  1. It provides energy for cellular activities
  2. It carries genetic instructions for making proteins Correct answer.
  3. It transports oxygen to body tissues
  4. It digests nutrients entering the cell

Explanation

DNA (deoxyribonucleic acid) stores genetic information as sequences of nucleotides. These sequences serve as instructions (genes) that direct the synthesis of proteins, which carry out virtually all cellular functions. The central dogma of molecular biology is: DNA → RNA → Protein.

Question 6Scientific reasoning across life, physical and Earth science

According to natural selection, which individuals in a population are most likely to survive and reproduce?

  1. The largest individuals
  2. Individuals with the most offspring
  3. Individuals best adapted to their environment Correct answer.
  4. The oldest individuals

Explanation

Natural selection, first described by Charles Darwin, states that individuals with traits better suited to their environment have a higher chance of surviving and reproducing. These adaptive traits are then passed to offspring, gradually changing the population over generations. Size and age are only advantageous if they contribute to environmental fitness.

Question 7Scientific reasoning across life, physical and Earth science

The graph below shows the population of rabbits and foxes over time in a meadow ecosystem. When fox populations increase, rabbit populations decrease. This is an example of which ecological relationship?

  1. Mutualism
  2. Commensalism
  3. Predator-prey interaction Correct answer.
  4. Parasitism

Explanation

A predator-prey relationship is characterized by one organism (the predator, fox) hunting and consuming another (the prey, rabbit). This creates cyclical population patterns: when foxes increase, rabbits decrease; fewer rabbits mean foxes decline due to food scarcity, allowing rabbits to recover. These oscillating cycles are a hallmark of predator-prey dynamics.

Question 8Scientific reasoning across life, physical and Earth science

A scientist studying genetics finds that a certain trait appears in every generation of a family, affects males and females equally, and is passed from affected parents to approximately half of their children. This pattern is most consistent with which type of inheritance?

  1. Autosomal recessive
  2. X-linked recessive
  3. Autosomal dominant Correct answer.
  4. Mitochondrial inheritance

Explanation

Autosomal dominant traits appear in every generation (since having one copy of the dominant allele is sufficient), affect males and females equally (since the gene is on an autosome, not a sex chromosome), and are transmitted to approximately 50% of offspring when one parent is heterozygous (Aa × aa). These three characteristics together define autosomal dominant inheritance.

Question 9Scientific reasoning across life, physical and Earth science

In a food chain: Grass → Grasshopper → Frog → Snake → Hawk. Which organism is the primary producer?

  1. Grasshopper
  2. Frog
  3. Hawk
  4. Grass Correct answer.

Explanation

Producers (also called autotrophs) make their own food through photosynthesis using sunlight, water, and carbon dioxide. Grass is the producer at the base of this food chain. All other organisms listed are consumers (heterotrophs) that obtain energy by eating other organisms.

Question 10Scientific reasoning across life, physical and Earth science

Which human body system is primarily responsible for filtering waste products from the blood and excreting them as urine?

  1. Respiratory system
  2. Digestive system
  3. Excretory (urinary) system Correct answer.
  4. Circulatory system

Explanation

The excretory (urinary) system - which includes the kidneys, ureters, bladder, and urethra - filters blood to remove metabolic waste products such as urea (from protein breakdown), excess salts, and water. The filtered waste is excreted as urine. This system maintains the body's fluid balance and chemical homeostasis.

Question 11Scientific reasoning across life, physical and Earth science

A researcher reads the following passage: 'In 2019, scientists found that antibiotic-resistant bacteria evolved more quickly in hospitals than in the general community, likely because of the frequent use of antibiotics in those environments.' Based on this passage, what best explains why antibiotic resistance develops more quickly in hospitals?

  1. Bacteria in hospitals are larger and stronger
  2. Frequent antibiotic use creates strong selection pressure favoring resistant bacteria Correct answer.
  3. Hospital patients take more vitamins, making bacteria resistant
  4. Bacteria mutate faster near medical equipment

Explanation

Frequent antibiotic use kills susceptible bacteria but leaves resistant ones to survive and reproduce - a direct application of natural selection. This strong selection pressure in hospitals (where antibiotics are used repeatedly) rapidly increases the proportion of resistant bacteria in the population. This is why antibiotic stewardship is a major public health concern.

Question 12Scientific reasoning across life, physical and Earth science

What is the primary function of the human circulatory system?

  1. To break down food into nutrients
  2. To transport oxygen, nutrients, and waste products throughout the body Correct answer.
  3. To protect the body from pathogens
  4. To produce hormones that regulate growth

Explanation

The circulatory system (heart, blood vessels, and blood) serves as the body's transport network. It delivers oxygen from the lungs and nutrients from digestion to all body cells, while simultaneously carrying waste products (carbon dioxide, metabolic byproducts) away from cells to the appropriate excretory organs.

Question 13Scientific reasoning across life, physical and Earth science

The table below shows the percentage of each blood type in a population: Type A = 40%, Type B = 11%, Type AB = 4%, Type O = 45%. A person with Type O blood can donate to anyone. What percentage of the population can receive Type O blood?

  1. 45%
  2. 4%
  3. 11%
  4. 100% Correct answer.

Explanation

Type O blood is called the 'universal donor' because it lacks A and B antigens on red blood cells. Recipients with any blood type (A, B, AB, or O) can receive Type O blood without a rejection reaction. Therefore, 100% of the population (40 + 11 + 4 + 45 = 100%) can safely receive Type O blood.

Question 14Scientific reasoning across life, physical and Earth science

Which of the following correctly describes the process of mitosis?

  1. A single cell divides to produce four genetically diverse gametes
  2. A single cell divides to produce two genetically identical daughter cells Correct answer.
  3. Two cells fuse to form a single cell with combined DNA
  4. A cell replicates its DNA without dividing

Explanation

Mitosis is the type of cell division used for growth, repair, and asexual reproduction. It produces two daughter cells that are genetically identical to the parent cell (same chromosome number and DNA sequence). This contrasts with meiosis, which produces four genetically diverse gametes with half the chromosome number.

Question 15Scientific reasoning across life, physical and Earth science

A scientist examines fossils of a marine organism found in rock layers at different depths. Fossils at greater depths (older layers) show simpler body structures, while fossils at shallower depths show more complex structures. This pattern is best explained by which scientific concept?

  1. The rock layers were formed by rapid flooding
  2. Organisms evolved greater complexity over time Correct answer.
  3. All organisms were created at the same time
  4. Simpler organisms always sink deeper in rock

Explanation

The fossil record shows a consistent pattern of increasing complexity over time as organisms evolved. Older (deeper) rock layers contain simpler ancestral forms, while younger (shallower) layers contain more complex descendants. This progression is direct evidence for biological evolution through natural selection acting across millions of years.

Question 16Scientific reasoning across life, physical and Earth science

In an experiment, a student grows plants in three conditions: full sunlight, partial shade, and complete darkness. After two weeks, the plants in darkness are yellow and stunted. What is the best scientific explanation for this result?

  1. Dark plants absorbed too much water
  2. Without light, plants cannot perform photosynthesis to make food Correct answer.
  3. Dark conditions cause plants to grow faster but without color
  4. Temperature differences explain the yellowing

Explanation

Without light, plants cannot carry out photosynthesis - the process by which they convert light energy into glucose for growth and energy. Additionally, chlorophyll (the green pigment required for photosynthesis) breaks down without light stimulation and is not replenished, causing the yellow color (a condition called etiolation). Plants in darkness are energy-starved and cannot sustain normal growth.

Question 17Scientific reasoning across life, physical and Earth science

Which of the following is an example of a mutualistic relationship?

  1. A tapeworm living in a human intestine
  2. Bees collecting nectar from flowers while pollinating them Correct answer.
  3. A remora fish eating scraps near a shark
  4. A cuckoo bird laying its eggs in another bird's nest

Explanation

Mutualism is a symbiotic relationship in which both organisms benefit. Bees benefit by obtaining nectar (food), while flowers benefit by being pollinated, which allows them to reproduce. This is a classic mutualistic relationship that has co-evolved over millions of years.

Question 18Scientific reasoning across life, physical and Earth science

The human nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS). Which components make up the CNS?

  1. Heart and lungs
  2. Brain and spinal cord Correct answer.
  3. All nerves throughout the body
  4. Sensory organs and motor nerves

Explanation

The central nervous system consists of the brain and spinal cord. The brain processes information and generates responses; the spinal cord transmits signals between the brain and the rest of the body. All other nerves in the body (those in the limbs, organs, and sensory structures) constitute the peripheral nervous system.

Question 19Scientific reasoning across life, physical and Earth science

Examine the following scenario: A farmer notices that some of his corn plants are dying while others are thriving. He suspects a new pesticide is killing the plants. To properly test this hypothesis, the farmer should:

  1. Spray all his corn with double the pesticide to see what happens
  2. Spray half the plants with the pesticide and leave the other half unsprayed as a control Correct answer.
  3. Ask a neighbor if the pesticide killed their plants too
  4. Read the pesticide label and assume the label is correct

Explanation

A proper scientific experiment requires a control group (untreated corn) and an experimental group (treated corn), with all other variables kept constant. By comparing the two groups, the farmer can determine whether the pesticide is the cause of the dying plants. Without a control, there is no basis for comparison and no way to isolate the pesticide as the variable.

Question 20Scientific reasoning across life, physical and Earth science

Which of the following correctly describes the relationship between genes, chromosomes, and DNA?

  1. Genes are made of chromosomes, which are made of DNA
  2. DNA is made of genes, which are organized into chromosomes
  3. Chromosomes contain DNA, which is organized into genes Correct answer.
  4. Genes contain chromosomes, which store DNA

Explanation

The correct hierarchy is: DNA (the molecule) is organized into genes (specific sequences that code for proteins), and genes are located on chromosomes (thread-like structures found in the nucleus). Humans have 23 pairs of chromosomes, each containing thousands of genes made up of billions of DNA base pairs.

Question 21Scientific reasoning across life, physical and Earth science

A biome chart shows the following data: Tropical rainforest has average annual rainfall of 200–400 cm and temperature of 25°C; Desert has 25 cm rainfall and 30°C temperature; Tundra has 25 cm rainfall and -10°C temperature. A scientist wants to study the biome with the greatest biodiversity. Based on the data, which biome should the scientist choose?

  1. Desert
  2. Tundra
  3. Tropical rainforest Correct answer.
  4. All biomes have equal biodiversity

Explanation

The tropical rainforest has the highest biodiversity of any biome on Earth. Its combination of high rainfall (200–400 cm/year) and warm year-round temperatures (around 25°C) creates ideal conditions for plant growth, which in turn supports an enormous variety of animals, fungi, and microorganisms. Biodiversity generally increases with rainfall and moderate-to-warm temperature stability.

Question 22Scientific reasoning across life, physical and Earth science

What distinguishes a virus from a living cell?

  1. Viruses are larger than cells
  2. Viruses lack a nucleus but cells have one
  3. Viruses cannot reproduce on their own and lack cellular machinery Correct answer.
  4. Viruses are made of carbohydrates while cells contain proteins

Explanation

Viruses are acellular (not made of cells) and cannot reproduce independently. They must invade a host cell and hijack its cellular machinery (ribosomes, enzymes, ATP) to replicate. Unlike living cells, viruses have no metabolism, no ribosomes of their own, and no cell membrane in the biological sense. This is why viruses are considered non-living by most biologists.

Question 23Scientific reasoning across life, physical and Earth science

The diagram shows energy transfer in a food web. Producers capture 10,000 kcal of energy from sunlight. Primary consumers (herbivores) receive approximately 10% of the producer's energy. Secondary consumers (carnivores) receive 10% of the herbivore's energy. How much energy (in kcal) is available to secondary consumers?

  1. 1,000 kcal
  2. 100 kcal Correct answer.
  3. 10 kcal
  4. 10,000 kcal

Explanation

The 10% energy rule (ecological efficiency) states that only about 10% of energy is transferred from one trophic level to the next; the rest is lost as heat. Producers: 10,000 kcal → Primary consumers: 10% × 10,000 = 1,000 kcal → Secondary consumers: 10% × 1,000 = 100 kcal. So secondary consumers have only 100 kcal available.

Question 24Scientific reasoning across life, physical and Earth science

A patient's medical report states that their cells cannot properly regulate the cell cycle, leading to uncontrolled cell division. This condition is best described as:

  1. Cellular respiration
  2. Cancer Correct answer.
  3. Mitosis
  4. Homeostasis

Explanation

Cancer is defined as uncontrolled cell division resulting from mutations that disable normal cell-cycle checkpoints and regulatory genes (tumor suppressor genes and proto-oncogenes). When the cell cycle is not properly regulated, cells divide without limit, forming tumors. This is the fundamental cellular basis of all types of cancer.

Question 25Scientific reasoning across life, physical and Earth science

Which of the following statements best explains why plants are essential to most life on Earth?

  1. Plants produce carbon dioxide needed for animal respiration
  2. Plants serve as the primary producers that convert solar energy into chemical energy for food webs Correct answer.
  3. Plants are the only source of water for land animals
  4. Plants create soil from bare rock, which is necessary for all life

Explanation

Plants (and other photosynthetic organisms) are the primary producers of virtually all ecosystems. They capture solar energy and convert it into organic compounds (glucose), forming the base of food webs. Without producers, no energy would enter the food web, and all consumer organisms - from insects to mammals - would be unable to obtain the energy they need to survive.

Question 26Scientific reasoning across life, physical and Earth science

The table below shows four organisms and their characteristics. Which organism is most likely a decomposer? | Organism | Has chloroplasts | Eats other organisms | Breaks down dead matter | |---|---|---|---| | Oak tree | Yes | No | No | | Rabbit | No | Yes | No | | Mushroom | No | No | Yes | | Hawk | No | Yes | No |

  1. Oak tree
  2. Rabbit
  3. Mushroom Correct answer.
  4. Hawk

Explanation

Decomposers break down dead organic matter (leaves, dead animals, waste) into simpler chemical compounds, recycling nutrients back into the ecosystem. Mushrooms (fungi) are classic decomposers. The table shows the mushroom breaks down dead matter, while the oak tree produces its own food through photosynthesis, and the rabbit and hawk consume other organisms.

Question 27Scientific reasoning across life, physical and Earth science

A student reads: 'Scientists have observed that the finches on the Galápagos Islands have beaks of different shapes and sizes. Finches on islands with hard seeds have thick, powerful beaks, while those on islands with insects in tree bark have long, narrow beaks.' What conclusion is best supported by this observation?

  1. Finches traveled between islands and exchanged beaks
  2. Beak shape evolved in response to the available food source on each island Correct answer.
  3. All Galápagos finches have the same ancestors but look different due to diet
  4. Finches on different islands are completely unrelated species

Explanation

This is a direct application of adaptive evolution by natural selection. Finches with beak shapes suited to available food survived and reproduced better on their respective islands. Over many generations, populations diverged into forms specialized for their local food sources. Darwin's finches are the classic textbook example of adaptive radiation.

Question 28Scientific reasoning across life, physical and Earth science

Which body system is primarily responsible for producing hormones such as insulin, which regulates blood sugar levels?

  1. Nervous system
  2. Endocrine system Correct answer.
  3. Digestive system
  4. Immune system

Explanation

The endocrine system is composed of glands (pancreas, thyroid, adrenals, pituitary, etc.) that produce and secrete hormones directly into the bloodstream. The pancreas produces insulin, which signals cells to take up glucose from the blood, lowering blood sugar levels. Diabetes occurs when insulin production or function is impaired.

Question 29Scientific reasoning across life, physical and Earth science

A scientist compares the DNA sequences of four species to determine their evolutionary relationships. The results show: Species A and B share 98% DNA similarity; Species A and C share 75%; Species A and D share 40%. Which species is most closely related to Species A?

  1. Species B Correct answer.
  2. Species C
  3. Species D
  4. Cannot be determined from this data

Explanation

Greater DNA sequence similarity indicates more recent common ancestry and therefore closer evolutionary relationship. Species B shares 98% of its DNA with Species A - the highest similarity - meaning they diverged from a common ancestor most recently. This type of molecular evidence is a primary tool in modern phylogenetics (the study of evolutionary relationships).

Question 30Scientific reasoning across life, physical and Earth science

In which phase of the cell cycle does DNA replication occur?

  1. G1 phase (first gap)
  2. S phase (synthesis phase) Correct answer.
  3. G2 phase (second gap)
  4. M phase (mitosis)

Explanation

DNA replication occurs during the S (synthesis) phase of interphase. During this phase, each chromosome is duplicated to create two identical sister chromatids joined at the centromere, ensuring that both daughter cells will receive a complete set of genetic information when the cell divides during M phase (mitosis). The cell cycle order is: G1 → S → G2 → M.

Question 31Scientific reasoning across life, physical and Earth science

A researcher tracks a rabbit population on an island for 10 years. The population grows rapidly for the first 5 years, then levels off. The graph shows an S-shaped curve. What best explains why the population stopped growing rapidly?

  1. The rabbits ran out of room to live and were forced off the island
  2. The population reached carrying capacity due to limited food, space, and resources Correct answer.
  3. A new species of rabbit arrived and replaced the original population
  4. The rabbits evolved to reproduce more slowly over time

Explanation

An S-shaped (logistic) growth curve indicates that a population's growth slows as it approaches the carrying capacity (K) of its environment - the maximum population size that available resources (food, water, shelter) can sustainably support. As population density increases, competition for resources intensifies and birth rates fall while death rates rise, creating the plateau.

Question 32Scientific reasoning across life, physical and Earth science

Which of the following best describes the role of enzymes in the human body?

  1. Enzymes store genetic information for cell division
  2. Enzymes are biological catalysts that speed up chemical reactions without being consumed Correct answer.
  3. Enzymes provide energy to cells during respiration
  4. Enzymes carry oxygen in the blood to body tissues

Explanation

Enzymes are proteins that function as biological catalysts - they lower the activation energy required for chemical reactions, dramatically speeding them up. Crucially, enzymes are not consumed in the reactions they catalyze; they can be reused many times. Without enzymes, metabolic reactions in the body (digestion, cellular respiration, DNA replication) would occur far too slowly to sustain life.

Question 33Scientific reasoning across life, physical and Earth science

Read the following passage: 'The human immune system has two main responses: the innate immune response, which is non-specific and responds quickly to any pathogen, and the adaptive immune response, which is specific and develops memory cells that recognize particular pathogens after first exposure.' According to the passage, what is the advantage of the adaptive immune response?

  1. It responds faster than the innate immune response
  2. It can recognize and remember specific pathogens for faster future responses Correct answer.
  3. It produces antibiotics to kill bacterial pathogens
  4. It works only outside the body to prevent infection

Explanation

The passage explicitly states that the adaptive immune response 'develops memory cells that recognize particular pathogens after first exposure.' This immunological memory allows faster and stronger responses upon re-exposure to the same pathogen, forming the biological basis for vaccination. The innate response is faster initially but lacks this specificity and memory.

Question 34Scientific reasoning across life, physical and Earth science

A geneticist crosses a true-breeding red flower plant (RR) with a true-breeding white flower plant (rr). According to Mendelian genetics, all of the F1 offspring will be:

  1. All white (rr)
  2. All red (RR)
  3. Half red and half white (50% Rr)
  4. All pink (Rr) if red is dominant Correct answer.

Explanation

When a homozygous dominant (RR) is crossed with a homozygous recessive (rr), all F1 offspring inherit one R allele from one parent and one r allele from the other, producing all Rr offspring. If R (red) is dominant over r (white), all F1 plants will show the dominant red phenotype. Note: if the question says 'all pink,' that would describe incomplete dominance - but with standard dominance, all Rr plants appear red.

Question 35Scientific reasoning across life, physical and Earth science

What is the primary function of the skeletal system?

  1. To produce blood cells and provide structural support Correct answer.
  2. To break down nutrients from food
  3. To regulate the body's temperature
  4. To produce hormones for growth regulation

Explanation

The skeletal system serves multiple functions, including providing structural support (holding the body upright and protecting organs), enabling movement (bones serve as levers for muscles), and producing blood cells in the red bone marrow (hematopoiesis). Both structural support and blood cell production are primary functions of the skeletal system.

Question 36Scientific reasoning across life, physical and Earth science

An ecologist studies nitrogen cycling in a forest. She finds that certain bacteria convert nitrogen gas (N₂) from the atmosphere into ammonia (NH₃) that plants can use. This process is called:

  1. Denitrification
  2. Nitrification
  3. Nitrogen fixation Correct answer.
  4. Decomposition

Explanation

Nitrogen fixation is the conversion of atmospheric nitrogen gas (N₂) into a biologically usable form such as ammonia (NH₃). This process is performed by nitrogen-fixing bacteria, including Rhizobium species living in root nodules of legumes. Nitrogen fixation is an essential step in the nitrogen cycle because most organisms cannot use N₂ directly from the atmosphere.

Question 37Scientific reasoning across life, physical and Earth science

Which of the following best describes the function of the large intestine in the human digestive system?

  1. Breaking down proteins into amino acids
  2. Absorbing water and forming solid waste Correct answer.
  3. Producing bile to digest fats
  4. Absorbing glucose and amino acids into the bloodstream

Explanation

The large intestine (colon) is primarily responsible for absorbing water and electrolytes from indigestible food matter, and for compressing the remaining material into solid waste (feces) for elimination. The small intestine (not the large intestine) is where most nutrient absorption (glucose, amino acids, fatty acids) occurs after chemical digestion.

Question 38Scientific reasoning across life, physical and Earth science

A bar graph shows the average height of plants grown with different amounts of fertilizer: 0 mg = 5 cm, 50 mg = 15 cm, 100 mg = 22 cm, 150 mg = 22 cm, 200 mg = 18 cm. What does this data suggest about fertilizer use?

  1. More fertilizer always produces taller plants
  2. Plant height increases linearly with fertilizer amount
  3. There is an optimal fertilizer amount beyond which more fertilizer does not help or may be harmful Correct answer.
  4. Fertilizer has no effect on plant height

Explanation

The data shows plant height increases from 0 to 100 mg of fertilizer, plateaus at 100–150 mg (both yield 22 cm), then decreases at 200 mg (18 cm). This pattern indicates an optimal range - too little fertilizer limits growth, but beyond the optimal amount, excess fertilizer may be toxic to the plant (causing osmotic stress or nutrient toxicity). This is the law of limiting factors in biology.

Question 39Scientific reasoning across life, physical and Earth science

Which of the following describes a key difference between aerobic and anaerobic respiration?

  1. Aerobic respiration occurs only in plants; anaerobic only in animals
  2. Aerobic respiration requires oxygen and produces more ATP; anaerobic does not require oxygen and produces less ATP Correct answer.
  3. Anaerobic respiration produces carbon dioxide while aerobic does not
  4. Aerobic respiration occurs only in mitochondria; anaerobic only in the nucleus

Explanation

Aerobic respiration uses oxygen to fully break down glucose, producing a large amount of ATP (about 36–38 ATP per glucose) plus carbon dioxide and water. Anaerobic respiration occurs without oxygen, producing only 2 ATP per glucose plus lactic acid (in animals) or ethanol and CO₂ (in yeast). Aerobic respiration is far more efficient in ATP production.

Question 40Scientific reasoning across life, physical and Earth science

A scientist hypothesizes that increased CO₂ in the atmosphere will accelerate plant growth. She grows identical plants in chambers with normal air (0.04% CO₂) and elevated CO₂ (0.08% CO₂) for 30 days. What is the independent variable in this experiment?

  1. The growth rate of the plants
  2. The type of plant used
  3. The concentration of CO₂ in the air Correct answer.
  4. The number of days the experiment runs

Explanation

The independent variable is the factor the scientist deliberately changes - in this case, the concentration of CO₂ (0.04% vs. 0.08%). The dependent variable is what is measured in response (plant growth rate). All other factors (plant type, light, water, temperature, duration) are controlled variables, kept the same across both groups.

Question 41Scientific reasoning across life, physical and Earth science

Which of the following correctly describes the relationship between mass, velocity, and kinetic energy?

  1. Kinetic energy is directly proportional to mass only
  2. Kinetic energy depends on mass and the square of velocity Correct answer.
  3. Kinetic energy is equal to mass divided by velocity
  4. Kinetic energy depends only on velocity, not mass

Explanation

The formula for kinetic energy is KE = ½mv², where m is mass and v is velocity. Because velocity is squared, doubling an object's speed quadruples its kinetic energy, while doubling its mass only doubles its kinetic energy. This means velocity has a greater effect on kinetic energy than mass does, which has important implications for safety (e.g., car crash physics).

Question 42Scientific reasoning across life, physical and Earth science

A 10 kg box is at rest on a flat surface. A force of 50 N is applied horizontally. Friction exerts a force of 20 N in the opposite direction. What is the net force acting on the box?

  1. 70 N
  2. 50 N
  3. 30 N Correct answer.
  4. 20 N

Explanation

Net force is the vector sum of all forces acting on an object. The applied force (50 N) and friction (20 N) act in opposite directions, so they subtract: Net force = 50 N - 20 N = 30 N in the direction of the applied force. This net force will cause the box to accelerate, as described by Newton's second law (F = ma).

Question 43Scientific reasoning across life, physical and Earth science

According to Newton's third law of motion, when a swimmer pushes against the pool wall, what happens?

  1. The wall absorbs the force and nothing else occurs
  2. The wall pushes back on the swimmer with an equal and opposite force Correct answer.
  3. The swimmer exerts more force than the wall can return
  4. Gravity acts on the swimmer to push them away from the wall

Explanation

Newton's third law states: 'For every action, there is an equal and opposite reaction.' When the swimmer pushes against the wall (action force), the wall pushes back on the swimmer with an equal force in the opposite direction (reaction force). This reaction force propels the swimmer away from the wall. The two forces are equal in magnitude but opposite in direction.

Question 44Scientific reasoning across life, physical and Earth science

What happens to the atoms in a chemical reaction?

  1. Atoms are created or destroyed to form new substances
  2. Atoms are rearranged to form new substances, but the total number of atoms remains the same Correct answer.
  3. Atoms gain or lose protons to become different elements
  4. Atoms double in mass when they bond with other atoms

Explanation

The law of conservation of mass states that in a chemical reaction, atoms are neither created nor destroyed - they are simply rearranged into new combinations (new molecules or compounds). This is why chemical equations must be balanced: the same number of each type of atom must appear on both sides of the equation. The total mass of reactants equals the total mass of products.

Question 45Scientific reasoning across life, physical and Earth science

Which of the following is an example of a physical change rather than a chemical change?

  1. Wood burning in a fireplace
  2. Iron rusting when exposed to water and oxygen
  3. Sugar dissolving in water Correct answer.
  4. Baking soda and vinegar reacting to produce bubbles

Explanation

A physical change alters the form or appearance of a substance without changing its chemical composition. When sugar dissolves in water, the sugar molecules remain intact - they simply disperse among water molecules and can be recovered by evaporating the water. In contrast, burning, rusting, and acid-base reactions produce new chemical substances with different properties.

Question 46Scientific reasoning across life, physical and Earth science

The periodic table organizes elements by atomic number. An element has atomic number 8, meaning it has 8 protons in its nucleus. Which element is this?

  1. Carbon (atomic number 6)
  2. Nitrogen (atomic number 7)
  3. Oxygen (atomic number 8) Correct answer.
  4. Fluorine (atomic number 9)

Explanation

The atomic number of an element equals the number of protons in its nucleus and uniquely identifies the element. Oxygen has atomic number 8, meaning every oxygen atom has exactly 8 protons. The periodic table is organized in ascending order of atomic number, from hydrogen (1) to oganesson (118). The atomic number (not atomic mass) defines the element.

Question 47Scientific reasoning across life, physical and Earth science

The diagram shows a circuit with a battery connected to three light bulbs in series. If one bulb burns out, what happens to the other bulbs?

  1. They continue to glow normally
  2. They get brighter because they receive more voltage
  3. They go out because the circuit is broken Correct answer.
  4. Two stay on and only one goes out

Explanation

In a series circuit, all components are connected in a single path. If any component (such as a burned-out bulb) breaks the circuit, current cannot flow through any part of the circuit, and all lights go out. This is a key disadvantage of series circuits compared to parallel circuits, where each component has its own independent path.

Question 48Scientific reasoning across life, physical and Earth science

Which of the following describes the difference between a conductor and an insulator?

  1. Conductors store electrical charge; insulators release it slowly
  2. Conductors allow electrons to flow freely; insulators resist electron flow Correct answer.
  3. Conductors block heat; insulators allow heat transfer
  4. Conductors are always metals; insulators are always gases

Explanation

Conductors are materials with loosely held outer electrons that can move freely, allowing electric current to flow easily (e.g., copper, aluminum, silver). Insulators have tightly bound electrons that resist movement, preventing current from flowing (e.g., rubber, glass, wood, plastic). This property determines their use in electrical wiring - conductors carry current; insulators protect against shock.

Question 49Scientific reasoning across life, physical and Earth science

A student reads: 'When a tuning fork vibrates, it creates compressions (areas of high pressure) and rarefactions (areas of low pressure) that travel through the air as sound waves.' Based on this passage, sound waves are classified as which type of wave?

  1. Transverse waves, because they travel through air
  2. Longitudinal waves, because particles move parallel to the direction of wave travel Correct answer.
  3. Electromagnetic waves, because they do not need a medium
  4. Standing waves, because compressions and rarefactions remain stationary

Explanation

Sound waves are longitudinal (also called compressional) waves because air particles oscillate back and forth parallel to the direction the wave travels. The compressions and rarefactions described in the passage are the alternating regions of high and low pressure characteristic of longitudinal waves. This is in contrast to transverse waves (like light or water surface waves), where particles move perpendicular to the direction of travel.

Question 50Scientific reasoning across life, physical and Earth science

Which of the following best describes what happens during an endothermic chemical reaction?

  1. Energy is released to the surroundings, making the surroundings warmer
  2. Energy is absorbed from the surroundings, making the surroundings cooler Correct answer.
  3. The reaction produces a gas as a byproduct
  4. The number of atoms in the reactants decreases

Explanation

Endothermic reactions absorb energy (usually as heat) from the surroundings. Because energy is taken in from the environment, the surroundings feel cooler - a classic example is an ice pack used for injuries (the chemical reaction inside absorbs heat from your skin). The prefix 'endo-' means 'within' or 'into,' indicating energy flows into the reaction.