IB MYP Integrated Sciences e-Assessment - All Chapters
Question (1 mark)
When chlorine is added to the pool water, hypochlorous acid $(\mathrm{HOCl})$ is formed. Hypochlorous acid is a weak acid. A sample of the hypochlorous acid was tested with a pH meter.
Select the pH you would expect this sample to have.
▶️Answer/Explanation
Ans:
Since hypochlorous acid is a weak acid, its pH would be below 7, but not extremely low.
A reasonable pH for a weak acid would be around 4 to 6.
Question (3 mark)
During exercise, cellular respiration increases to release more energy. Increased cellular respiration produces more $\mathrm{CO}_2$ which causes a drop in blood pH . In response the breathing rate increases as shown in the diagram below:
Explain how an increase in breathing rate will help to regulate the pH of the blood.
▶️Answer/Explanation
Ans:
Increased CO₂ Removal: When you breathe faster, you exhale more carbon dioxide (CO₂) from your lungs.
Reduced CO₂ in Blood: Since CO₂ is a byproduct of cellular respiration, increased respiration leads to more CO₂ in the blood. By exhaling more CO₂, you reduce the amount of CO₂ dissolved in your blood.
pH Regulation: CO₂ in the blood reacts with water to form carbonic acid (H₂CO₃). This acid lowers the pH of the blood (makes it more acidic). By removing CO₂, you reduce the amount of carbonic acid formed.
pH Increase (Back to Normal): With less carbonic acid, the pH of the blood rises back towards its normal range of 7.35-7.45.
Question (4 marks)
A student is investigating the growth of bean sprouts. The student collected data for 3 plants over 7 days. The data for the first 2 plants is given in the table below. Measure the height of the third plant for days 5, 6 and 7 and record your values in the table. You should measure the height, from the top of the soil to the highest point of the plant.
Calculate the missing mean values to complete the table. Show your working in the box below and add your final values to the table.A
▶️Answer/Explanation
Ans:
Day 5: 3.2 cm
Day 6: 6.1 cm
Day 7: 8.4 cm
Day 5
Values: \( 4.4, 2.8, 3.2 \)
$
\text{Average} = \frac{4.4 + 2.8 + 3.2}{3} = \frac{10.4}{3} \approx 3.47
$
Day 6
Values: \( 6.8, 5.1, 6.1 \)
$
\text{Average} = \frac{6.8 + 5.1 + 6.1}{3} = \frac{18.0}{3} = 6.0
$
Day 7
Values: \( 8.1, 8.3, 8.4 \)
$
\text{Average} = \frac{8.1 + 8.3 + 8.4}{3} = \frac{24.8}{3} \approx 8.27
$
Question (1 mark)
An MYP year 5 student is carrying out an investigation to see how the pH of the soil affects the growth of mung bean sprouts. The mung bean sprouts germinated one week before the investigation started. This experiment was performed once for each pH value and was done over 10 days. The bean sprouts were watered regularly.
Mung bean sprouts can grow in a range of conditions as shown in the animation below
Select the correct description for the pH of each soil type.
pH = 5
pH = 7
pH = 9
▶️Answer/Explanation
Ans:
pH = 5: This is acidic.
pH = 7: This is neutral.
pH = 9: This is basic (or alkaline).
Question (2 marks).
Formulate a research question for the investigation shown in the animation above.
▶️Answer/Explanation
Ans:
How does varying soil pH (5, 7, and 9) affect the growth rate (measured by height) of mung bean sprouts over a 10-day period?
Question (4 marks)
Farming is an important activity in the development of human societies. Food products, fibre for clothes, biofuel, medicinal plants and other products are used to sustain and enhance life. Farming can also help to reduce poverty by raising family incomes for people who live in rural areas.
Mung beans are one of the most consumed sprouts and are primarily grown in Asian countries. These plants grow from 45 cm to 1 m tall. Like many other types of seeds, mung beans require specific conditions to germinate and sprout.
Identify the independent variable, dependent variable and two control variables for this investigation.
▶️Answer/Explanation
Ans:
Independent Variable:
Soil pH
Dependent Variable:
Growth of mung bean sprouts
Control Variables:
Time
Light
Type of mung bean sprouts
Question (2 marks)
Farming is an important activity in the development of human societies. Food products, fibre for clothes, biofuel, medicinal plants and other products are used to sustain and enhance life. Farming can also help to reduce poverty by raising family incomes for people who live in rural areas.
Mung beans are one of the most consumed sprouts and are primarily grown in Asian countries. These plants grow from 45 cm to 1 m tall. Like many other types of seeds, mung beans require specific conditions to germinate and sprout.
Suggest why it is important to have control variables in a scientific investigation.
▶️Answer/Explanation
Ans:
Experiment Validity: Control variables are necessary for the sake of experiment validity. They control the effect of the independent variable on the dependent variable.
Controlling variables enables researchers to reduce the impact of extraneous variables so that they can be in a position to attribute the variation in the dependent variable to the manipulation of the independent variable.
Control variables enhance the capacity to find a cause-and-effect relation between the independent and dependent variables. Without control variables, it is difficult to tell whether the result was a result of the independent variable or not.
Increasing Reliability: Holding other variables constant improves the reliability and replicability of the experiment.
Question (1 mark)
The table below shows the data collected by the student. According to the information provided, state which pH allowed the best growth of mung bean sprouts.
▶️Answer/Explanation
Ans:
On Day 10, the plant height at pH 7 reached 10.4 cm, which is the highest compared to the other pH levels:
pH 5: 8.6 cm
pH 9: 8.1 cm
Question (1 mark)
The data from the table is presented in four graphs below.
Select the correct graph to present the data.
▶️Answer/Explanation
Ans:
Graph C clearly shows the plant height on the y-axis and time in days on the x-axis.
It effectively compares the growth of plants under different pH conditions over time using separate color-coded lines for each pH level.
The gradual progression of height for each pH level is easy to interpret.
Question (14 marks)
The pH scale is used to measure acidity. Solutions with pH values less than seven are acidic, solutions with pH values greater than seven are alkaline.
Question a (2 marks)
The freshwater organisms in a pond are part of a complex food web. Daphnia feed on single-celled plants called algae. A student wanted to investigate whether the algae and Daphnia living in a pond changed the pond’s environment during a 12-hour period. Use the simulation to collect values of pH. Select appropriate times of day and record the data in the table below.
▶️Answer/Explanation
Answer: | Time of day | pH | |————-|—-| | 6:00 | 7.56 | | 7:30 | 7.64 | | 9:00 | 7.81 | | 10:30 | 8.02 | | 12:00 | 8.25 | | 13:30 | 8.47 | | 15:00 | 8.64 | | 16:30 | 8.74 | | 18:00 | 8.74 |
Detailed Solution: The pH of the pond increases during the day due to photosynthesis by algae, which consumes carbon dioxide and reduces acidity. At night, respiration by organisms increases carbon dioxide levels, lowering the pH.
Question b (6 marks)
By interpreting your data from part (a), explain your results using scientific knowledge from your MYP studies.
▶️Answer/Explanation
Answer: Yes, the algae and organisms living in the pond clearly changed its pH within the 12-hour time period. The pH as of sunrise continued to increase until it started getting darker again.
Detailed Solution: The increase in pH during the day is due to photosynthesis by algae, which consumes carbon dioxide and reduces acidity. At night, respiration by organisms increases carbon dioxide levels, lowering the pH.
Question c (6 marks)
The graph below shows how the pH of the pond changes over a 24-hour period in the summer. Describe how the shape of the graph would change in winter and explain two reasons for any differences.
▶️Answer/Explanation
Answer: During the winter, the shape of the graph would be extended more horizontally in the decreasing sections but shorten horizontally in the increasing sections. During the winter, nights are longer, this being said with less hours of sun, the decrease of pH on the scale would go on for a longer period of time as it is night for longer. Another reason is because it is colder, causing a lower production of algae.
Detailed Solution: In winter, the shorter days and longer nights reduce the time available for photosynthesis, leading to a slower increase in pH during the day. Additionally, colder temperatures reduce the metabolic activity of algae, further decreasing pH changes.
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