Grade 7 WS Case Based Study (Ch-2&10)

 

Case study passages and answer the questions:

Chapter 2

Case Study 1: The Magic Science Fair Writing

Passage: At a Science Fair held on National Science Day, siblings Ashwin and Keerthi were greeted with a blank white sheet of paper. As they walked further, a volunteer sprayed a liquid over their paper. To their surprise, the invisible words "Welcome to the Wonderful World of Science" instantly appeared in a bright color. Their teacher explained that this was due to a chemical reaction between an invisible, acidic or basic "ink" and the liquid in the spray bottle, acting as an indicator.

Questions:

1. What are the common characteristics of acidic substances like the one used as invisible ink?
2. If the letters on the paper turned bright red, what can we deduce about the ink's pH range?
3. How does blue litmus paper behave when it comes into contact with an acidic liquid?
4. Name two natural indicators that the siblings could have prepared using plants in their garden.

Case Study 2: Treating an Ant Bite

Passage: During a school picnic, Rahul accidentally sat on an ant hill and was bitten multiple times by red ants. His skin started burning and swelling. His teacher rushed over and applied a paste of baking soda on the affected area to soothe the stinging sensation. The teacher explained that the ant had injected a specific type of acid into his skin, which required a basic substance to neutralize its effect. [1, 5]

Questions:

1. What type of acid is injected into the skin by an ant bite?
2. Why is baking soda effective in providing relief from the ant bite?
3. What is the scientific term used for the reaction between an acid and a base?
4. State the end products of a neutralization reaction.

Case Study 3: Testing Unknown Substances

Passage: Ayesha's grandmother used to write secret letters using orange juice, which were invisible until exposed to a specific testing paper. Curious to know how it worked, Ayesha prepared various test solutions in her kitchen. She tested lemon juice, soap solution, salt water, and curd. She recorded the color changes by dipping strips of China rose extract, turmeric paper, and blue litmus paper into these solutions.

Questions:

1. Classify the four kitchen solutions Ayesha tested into acidic, basic, and neutral categories.
2. What color change will Ayesha observe when she dips turmeric paper into the basic soap solution?
3. Why does China rose extract turn a dark pink or magenta color in acidic mediums?
4. If Ayesha mixed the acidic lemon juice directly with the basic soap solution in equal quantities, what would be the nature of the resulting mixture?

Case Study 4: Oxygen which is essential for the survival of all organisms is produced during photosynthesis. In the absence of photosynthesis, life would be impossible on the earth. During photosynthesis, chlorophyll containing cells of leaves, in the presence of sunlight, use carbon dioxide and water to synthesise carbohydrates. During the process oxygen is released. The presence of starch in leaves indicates the occurrence of photosynthesis. Starch is also a carbohydrate.

Q.1.  Which component is essential for the survival of all the living organisms?

(a) Oxygen       (b) Carbon dioxide          (c) Carbon Monoxide          (d) Hydrogen

Q.2.  Name the green pigment present in leaves.

Q.3.  How we come to know the occurrence of photosynthesis in a plant?

Chapter 10: Life Processes in Plants

Case Study 1: The Leaf as a Food Factory

Case Study:Rohan placed a potted plant in a dark room for 48 hours to destarch its leaves. Then, he covered one of its leaves partially with black paper using a paper clip. He placed the plant in bright sunlight for a few hours. He plucked the covered leaf, removed the black paper, and tested the leaf for starch using an iodine solution. He observed that the part of the leaf that was covered in black paper did not turn blue-black, while the rest of the leaf did.

Questions:

1. Application: Why was the plant kept in the dark for 48 hours before the experiment began?
2. Analysis: Why didn't the covered part of the leaf turn blue-black with iodine?
3. Synthesis: What two primary life processes did this experiment test in the plant?

Case Study 2: Transportation in Plants

Case Study: Priya set up an experiment to understand how plants transport water. She took two identical stems with white flowers. She placed Stem A in a beaker of pure water and Stem B in a beaker of water mixed with red food coloring. She left both plants in a warm, sunny room for 12 hours. After 12 hours, she observed that the white petals of Stem B turned red, while the petals of Stem A remained white.

Questions:

1. Observation: Which specialized plant tissue is responsible for transporting the colored water from the roots to the petals?
2. Analysis: Why did placing the plant in a warm, sunny room cause the flower petals to turn red faster?
3. Concept Check: What is the primary function of the phloem in a plant?

Case Study 3: The Gas Balance in Nature

Case Study: During the day, plants take in carbon dioxide from the atmosphere and release oxygen. At the same time, they break down glucose through respiration, which consumes oxygen and releases carbon dioxide. A student argued that because plants release CO₂ during respiration, they are just as harmful as factories.

Questions:

1. Analysis: How do the processes of photosynthesis and respiration work together to maintain the balance of gases in the atmosphere?
2. Evaluation: Why is the student's argument incorrect?
3. Critical Thinking: If all the plants in a forest suddenly died, what impact would it have on animals and humans?