AP Environmental Science Quiz: Lethal Dose 50 Ld50

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Lethal Dose 50 Ld50Question 1 of 20

A dose-response study reports: at $10\ \text{mg/kg}$ , 10% mortality; at $20\ \text{mg/kg}$ , 40% mortality; at $30\ \text{mg/kg}$ , 60% mortality. Based on this information, the $LD_{50}$ is closest to:

15\ \text{mg/kg}

25\ \text{mg/kg}

50\ \text{mg/kg}

5\ \text{mg/kg}

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AP Environmental Science Quiz

AP Environmental Science Quiz: Lethal Dose 50 Ld50

Practice Lethal Dose 50 Ld50 in AP Environmental Science with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Lethal Dose 50 Ld50, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Environmental Science.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

$15\ \text{mg/kg}$
$25\ \text{mg/kg}$ (correct answer)
$50\ \text{mg/kg}$
$5\ \text{mg/kg}$

Explanation: LD50 is determined from dose-response data by finding the dose that produces 50% mortality. Looking at the given data: 10 mg/kg causes 10% mortality, 20 mg/kg causes 40% mortality, and 30 mg/kg causes 60% mortality. The LD50 (50% mortality) falls between 20 and 30 mg/kg. Using interpolation, since 40% to 60% mortality spans from 20 to 30 mg/kg, the 50% point would be at 25 mg/kg, which is closest to option B.

Question 2

A chemical has $LD_{50}=0.25\ \text{g/kg}$ . Which of the following is the correct conversion to mg/kg?

$2.5\ \text{mg/kg}$
$25\ \text{mg/kg}$
$250\ \text{mg/kg}$ (correct answer)
$2500\ \text{mg/kg}$

Explanation: To convert from g/kg to mg/kg, multiply by 1000 since there are 1000 milligrams in one gram. The calculation is: 0.25 g/kg × 1000 mg/g = 250 mg/kg. This conversion maintains the same toxicity value but expresses it in different units. Both 0.25 g/kg and 250 mg/kg represent the same LD50 value for the chemical.

Question 3

A chemical's $LD_{50}$ is reported as $75\ \text{mg/kg}$ . Which of the following doses for a $60\ \text{kg}$ human corresponds to the $LD_{50}$ amount (hypothetical comparison only)?

$450\ \text{mg}$
$4.5\ \text{g}$ (correct answer)
$45\ \text{g}$
$0.45\ \text{g}$

Explanation: To calculate the LD50 dose for a human, multiply the LD50 value by the person's weight. The calculation is: 75 mg/kg × 60 kg = 4500 mg = 4.5 g. This hypothetical comparison shows that 4.5 grams would correspond to the LD50 amount for a 60 kg human. This calculation is purely theoretical since LD50 testing is not performed on humans, and animal LD50 values cannot be directly extrapolated to humans.

Question 4

A toxin's $LD_{50}$ in rats is $250\ \text{mg/kg}$ . A lab rat weighs $0.4\ \text{kg}$ . The $LD_{50}$ dose for this rat is:

$100\ \text{mg}$ (correct answer)
$625\ \text{mg}$
$10\ \text{mg}$
$0.1\ \text{mg}$

Explanation: To calculate the LD50 dose for a specific animal, multiply the LD50 value by the animal's weight. The calculation is: 250 mg/kg × 0.4 kg = 100 mg. This means that 100 milligrams of the toxin would correspond to the LD50 dose for a 0.4 kg rat. At this dose level, approximately 50% of rats of this weight would be expected to die from acute exposure.

Question 5

A chemical's $LD_{50}$ is $2\ \text{mg/kg}$ . Which dose is most likely to produce less than 50% mortality (all else equal)?

$0.5\ \text{mg/kg}$ (correct answer)
$2\ \text{mg/kg}$
$4\ \text{mg/kg}$
$10\ \text{mg/kg}$

Explanation: LD50 represents the dose that causes 50% mortality, so doses below this value would be expected to cause less than 50% mortality. The chemical has LD50 = 2 mg/kg, meaning this dose kills 50% of the population. Among the options, 0.5 mg/kg is the only dose lower than 2 mg/kg. Since it's below the LD50, this dose would most likely produce less than 50% mortality in a test population.

Question 6

A cleaning product contains Chemical Q. In rats, the reported acute oral $LD_{50}$ is $500\ \text{mg/kg}$ . Approximately how much of Chemical Q corresponds to the $LD_{50}$ dose for a $0.250\ \text{kg}$ rat?

$125\ \text{mg}$ (correct answer)
$2{,}000\ \text{mg}$
$500\ \text{mg}$
$0.5\ \text{mg}$

Explanation: To calculate the actual LD50 dose for a specific animal, multiply the LD50 value (in mg/kg) by the animal's body weight (in kg). For Chemical Q with an LD50 of 500 mg/kg and a rat weighing 0.250 kg, the calculation is: 500 mg/kg × 0.250 kg = 125 mg. This means 125 mg of Chemical Q would be the dose expected to kill 50% of rats weighing 0.250 kg each. The LD50 is always expressed per unit body weight to allow for scaling across different sized organisms. Answer A correctly shows this calculated dose of 125 mg.

Question 7

A pesticide has an $LD_{50}$ of $50\ \text{mg/kg}$ (oral, mouse). Approximately what dose would be expected to kill 50% of a test population of $0.020\ \text{kg}$ mice (20 g), assuming similar sensitivity?

$1.0\ \text{mg}$ (correct answer)
$1000\ \text{mg}$
$2.5\ \text{mg}$
$0.10\ \text{mg}$

Explanation: To find the lethal dose for 50% of the mice, we multiply the LD50 value by the body weight. The pesticide has an LD50 of 50 mg/kg, and each mouse weighs 0.020 kg (20 g). The calculation is: 50 mg/kg × 0.020 kg = 1.0 mg. This means 1.0 mg of the pesticide would be expected to kill 50% of the 20-gram mice. The LD50 concept assumes similar sensitivity across the test population when body weight is accounted for. Answer A (1.0 mg) is correct because it represents the proper application of the LD50 value to the specific body weight.

Question 8

A dose-response experiment yields these results for Chemical T: $5\ \text{mg/kg}$ causes 0% mortality, $10\ \text{mg/kg}$ causes 30% mortality, $15\ \text{mg/kg}$ causes 50% mortality, $20\ \text{mg/kg}$ causes 90% mortality. What is the $LD_{50}$ ?

$10\ \text{mg/kg}$
$15\ \text{mg/kg}$ (correct answer)
$20\ \text{mg/kg}$
$5\ \text{mg/kg}$

Explanation: LD50 is determined by finding the dose that produces exactly 50% mortality in the dose-response data. Looking at the experimental results: 5 mg/kg causes 0% mortality, 10 mg/kg causes 30% mortality, 15 mg/kg causes 50% mortality, and 20 mg/kg causes 90% mortality. Since 15 mg/kg produces exactly 50% mortality, this is the LD50 value for Chemical T.

Question 9

Which chemical is least toxic (highest $LD_{50}$ ) given the following values: A = $2\ \text{mg/kg}$ , B = $20\ \text{mg/kg}$ , C = $200\ \text{mg/kg}$ , D = $0.2\ \text{mg/kg}$ ?

A
B
C (correct answer)
D

Explanation: The least toxic chemical has the highest LD50 value because it requires more substance to kill 50% of the population. Comparing the LD50 values: A = 2 mg/kg, B = 20 mg/kg, C = 200 mg/kg, D = 0.2 mg/kg. Chemical C has the highest LD50 at 200 mg/kg, meaning it requires the most substance per kg of body weight to cause 50% mortality, making it the least toxic among the options.

Question 10

A dose–response curve for two substances (tested in the same organism and conditions) shows that Substance R reaches 50% mortality at a lower dose than Substance S. What can be concluded about their $LD_{50}$ values and relative toxicity?

Substance R has a lower $LD_{50}$ and is more toxic than Substance S. (correct answer)
Substance R has a higher $LD_{50}$ and is more toxic than Substance S.
Substance R has a lower $LD_{50}$ and is less toxic than Substance S.
They must have identical $LD_{50}$ values because both reach 100% mortality at high doses.

Explanation: A dose-response curve plots the relationship between dose and the percentage of organisms affected (in this case, mortality). The LD50 is the dose at which the curve crosses the 50% mortality line. If Substance R reaches 50% mortality at a lower dose than Substance S on the same graph, this means Substance R has a lower LD50 value. Since a lower LD50 indicates higher toxicity, Substance R is more toxic than Substance S. The fact that both substances eventually reach 100% mortality at high doses is irrelevant to their LD50 values, which specifically measure the dose for 50% mortality. Answer A correctly states that Substance R has a lower LD50 and is more toxic.

Question 11

In an acute toxicity study, Substance A has an $LD_{50}$ of $12\ \text{mg/kg}$ (oral, rat) and Substance B has an $LD_{50}$ of $180\ \text{mg/kg}$ (oral, rat). Which statement correctly compares their toxicity?

Substance B is more toxic because its $LD_{50}$ is higher.
Substance A is more toxic because it has the lower $LD_{50}$ . (correct answer)
Substance A and B have the same toxicity because both are measured in mg/kg.
Substance B is more toxic because it requires a smaller dose to kill 50% of the population.

Explanation: LD50 (Lethal Dose 50%) is the dose of a substance that kills 50% of a test population, expressed as mg of substance per kg of body weight. A lower LD50 value means less substance is needed to cause death, indicating higher toxicity. Substance A has an LD50 of 12 mg/kg while Substance B has an LD50 of 180 mg/kg. Since Substance A requires only 12 mg/kg to kill 50% of the population compared to 180 mg/kg for Substance B, Substance A is more toxic. The correct answer is B because it accurately states that Substance A is more toxic due to its lower LD50 value.

Question 12

A researcher reports that a solvent has an $LD_{50}$ of $2\ \text{g/kg}$ in rabbits. Which statement correctly interprets this value?

A dose of $2\ \text{g}$ kills 50% of all rabbits regardless of mass.
A dose of $2\ \text{g/kg}$ is expected to kill 50% of exposed rabbits. (correct answer)
A dose of $2\ \text{g/kg}$ kills 50% of rabbits only if exposure is chronic.
A dose of $2\ \text{kg/g}$ is expected to kill 50% of exposed rabbits.

Explanation: LD50 represents the dose that causes 50% mortality in a test population when expressed per kilogram of body weight. The value 2 g/kg means that 2 grams of solvent per kilogram of rabbit body weight is expected to kill 50% of exposed rabbits. This is a standardized measure that accounts for body weight differences, making it applicable across different sized animals within the species. The LD50 specifically measures acute toxicity from single or short-term exposure.

Question 13

A toxin has an $LD_{50}$ of $120\ \text{mg/kg}$ for a certain mammal. A wildlife biologist estimates an animal weighs $5\ \text{kg}$ . The $LD_{50}$ amount of toxin for this animal is closest to:

$24\ \text{mg}$
$600\ \text{mg}$ (correct answer)
$120\ \text{mg}$
$0.6\ \text{mg}$

Explanation: To calculate the LD50 amount for a specific animal, multiply the LD50 value by the animal's weight. The calculation is: 120 mg/kg × 5 kg = 600 mg. This means that 600 milligrams of the toxin would correspond to the LD50 dose for a 5 kg animal. At this dose level, approximately 50% of animals of this weight would be expected to die from acute exposure to the toxin.

Question 14

A chemical has $LD_{50}=900\ \text{mg/kg}$ . Which statement is correct about a chemical with $LD_{50}=90\ \text{mg/kg}$ (same species/route)?

It is less toxic.
It is more toxic. (correct answer)
It has the same toxicity.
It is non-toxic because the value is below 100.

Explanation: When comparing LD50 values, a lower value indicates higher toxicity. The first chemical has LD50 = 900 mg/kg, while the second has LD50 = 90 mg/kg. Since 90 mg/kg is 10 times lower than 900 mg/kg, the second chemical requires much less substance to kill 50% of the population. Therefore, a chemical with LD50 = 90 mg/kg is more toxic than one with LD50 = 900 mg/kg.

Question 15

A lab compares three substances in the same species: A: $LD_{50}=5\ \text{mg/kg}$ , B: $LD_{50}=50\ \text{mg/kg}$ , C: $LD_{50}=500\ \text{mg/kg}$ . Which ranking from least toxic to most toxic is correct?

A, then B, then C
C, then B, then A (correct answer)
B, then A, then C
C, then A, then B

Explanation: To rank chemicals by toxicity, arrange them from highest to lowest LD50 values for least toxic to most toxic, since higher LD50 means lower toxicity. The LD50 values are: A = 5 mg/kg (most toxic), B = 50 mg/kg (intermediate), C = 500 mg/kg (least toxic). For ranking from least toxic to most toxic, start with the highest LD50 and end with the lowest: C (500 mg/kg), then B (50 mg/kg), then A (5 mg/kg).

Question 16

A dose-response study indicates the $LD_{50}$ for Chemical K is $40\ \text{mg/kg}$ . Which statement best describes what happens at $40\ \text{mg/kg}$ ?

40% of the population dies.
50% of the population dies. (correct answer)
50% of the population survives.
The population experiences no effect.

Explanation: LD50 represents the specific dose at which 50% mortality occurs in a test population. When Chemical K has an LD50 of 40 mg/kg, this means that at exactly this dose level, approximately 50% of the population dies from acute exposure. This is the fundamental definition of LD50 - the lethal dose for 50% of the population. It's important to note that saying 50% survives is equivalent to saying 50% die.

Question 17

A chemical with $LD_{50}=10\ \text{mg/kg}$ is compared to one with $LD_{50}=100\ \text{mg/kg}$ in the same species. Which is the correct ranking from most toxic to least toxic?

100 mg/kg, then 10 mg/kg
10 mg/kg, then 100 mg/kg (correct answer)
They are equally toxic.
Cannot be determined without knowing the sample size.

Explanation: To rank chemicals by toxicity, arrange them from lowest to highest LD50 values, since lower LD50 indicates higher toxicity. The LD50 values are: Chemical with 10 mg/kg (most toxic), Chemical with 100 mg/kg (least toxic). For ranking from most toxic to least toxic: 10 mg/kg, then 100 mg/kg. Therefore, the correct ranking from most toxic to least toxic is: 10 mg/kg, then 100 mg/kg.

Question 18

An insecticide has an $LD_{50}$ of $3\ \text{mg/kg}$ (oral, bird). Which dose is MOST likely to result in more than 50% mortality in a similar test population?

$0.3\ \text{mg/kg}$
$1\ \text{mg/kg}$
$3\ \text{mg/kg}$
$10\ \text{mg/kg}$ (correct answer)

Explanation: The insecticide has an LD50 of 3 mg/kg, meaning this dose causes 50% mortality in birds. To achieve more than 50% mortality, a dose higher than the LD50 is needed. Looking at the options: 0.3 mg/kg and 1 mg/kg are below the LD50, so they would cause less than 50% mortality. The dose of 3 mg/kg equals the LD50, causing exactly 50% mortality. Only 10 mg/kg is significantly higher than the LD50, making it most likely to cause more than 50% mortality. Answer D (10 mg/kg) is correct because it's the only dose substantially above the LD50 value.

Question 19

A chemical has an $LD_{50}$ of $50\ \text{mg/kg}$ in a certain bird species. About how many milligrams correspond to the $LD_{50}$ dose for a $2.0\ \text{kg}$ bird?

$25\ \text{mg}$
$100\ \text{mg}$ (correct answer)
$2.5\ \text{mg}$
$1000\ \text{mg}$

Explanation: To find the LD50 dose for a specific animal, multiply the LD50 value by the animal's body weight. The calculation is: 50 mg/kg × 2.0 kg = 100 mg. This means that 100 milligrams of the chemical would correspond to the LD50 dose for a 2.0 kg bird. At this dose level, approximately 50% of birds of this weight would be expected to die from acute exposure to the chemical.

Question 20

A researcher compares acute toxicity of two compounds in the same organism: Compound U has $LD_{50}=12\ \text{mg/kg}$ and Compound V has $LD_{50}=48\ \text{mg/kg}$ . Which statement is correct?

Compound V is 4 times more toxic.
Compound U is 4 times more toxic. (correct answer)
Compound U is less toxic because it has a lower $LD_{50}$ .
They are equally toxic because both are measured in mg/kg.

Explanation: To compare the relative toxicity of compounds, divide the higher LD50 by the lower LD50. Compound U has LD50 = 12 mg/kg and Compound V has LD50 = 48 mg/kg. The calculation is: 48 ÷ 12 = 4. This means Compound U is 4 times more toxic than Compound V because it requires 4 times less substance per kg of body weight to kill 50% of the population. Lower LD50 values always indicate higher toxicity.