Class 7 Science NCERT Notes – Chapter 10: Life Processes in Plants (PDF, MindMap, Q&A, Quizzes)

Chapter 10 (Science): Life Processes in Plants – CBSE Class 7 NCERT Science Detailed Study Notes.

1. Plant Growth and Nutrition

All living beings, including plants, require food for growth. While animals consume food, plants produce their own. The growth in plants is observable through the emergence of new leaves and branches, an increase in height, and the thickening of the stem.

1.1 Essential Factors for Growth

Experiments demonstrate that two primary external factors are crucial for plant growth:

• Sunlight: Plants exposed to direct sunlight show significantly better growth compared to those kept in the dark.
• Water: Plants require an adequate and regular supply of water. A lack of water will cause the plant to die, even if it receives sufficient sunlight.

An experiment (Activity 10.1) using three potted plants under different conditions confirms this:

• Pot A (Sunlight + Water): Showed maximum growth.
• Pot B (Sunlight, No Water): The plant eventually died.
• Pot C (Dark + Water): Showed minimal growth.

This indicates that both sunlight and water are indispensable for a plant’s growth and health.

2. Photosynthesis: The Food Manufacturing Process

Plants produce their own food through a process called photosynthesis. Unlike animals, they do not eat food but synthesize it. The primary location for this process is the leaves, often referred to as the ‘food factories’ of the plant.

2.1 Ingredients for Photosynthesis

Four key components are necessary for photosynthesis to occur:

1. Sunlight: Provides the energy for the chemical reactions.
2. Water: Absorbed from the soil by the roots.
3. Carbon Dioxide (CO2): A gas taken from the air.
4. Chlorophyll: A green pigment found in the leaves that captures sunlight efficiently.

2.2 The Process and Products

During photosynthesis, plants use the energy from sunlight, captured by chlorophyll, to convert carbon dioxide and water into food and oxygen.

• Food Production: The food is initially produced as glucose, a simple carbohydrate that serves as an instant source of energy.
• Food Storage: Excess glucose is converted into starch, a more complex carbohydrate, which is stored in various parts of the plant (like leaves, seeds, and roots) for later use.
• Oxygen Release: Oxygen is a byproduct of photosynthesis and is released into the atmosphere.

The word equation for photosynthesis is:

Carbon dioxide + Water –(Sunlight / Chlorophyll)–> Glucose + Oxygen

2.3 The Role of Leaves

• Structure: Leaves are typically broad and flat, a design that maximizes the surface area for capturing sunlight.
• Chlorophyll: The green color of most leaves is due to chlorophyll. This pigment is essential for absorbing light energy. Experiments show that only the green (chlorophyll-containing) parts of a leaf produce starch.
• Stomata: These are tiny pores, primarily located on the lower surface of leaves, that facilitate gas exchange. Carbon dioxide enters the leaf, and oxygen exits through these pores.

2.4 Testing for Photosynthesis (Iodine Test for Starch)

The presence of starch, an indicator of photosynthesis, can be confirmed using an iodine test.

Procedure (Activity 10.2):

1. Soften the Leaf: Boil the leaf in water for five minutes.
2. Decolourise: Place the leaf in a test tube with alcohol and heat it in a beaker of boiling water. This removes the green chlorophyll, which would otherwise mask the color change.
3. Test: Place the decolourised leaf on a plate and add a few drops of diluted iodine solution.
4. Result: If the leaf turns blue-black, it indicates the presence of starch.

3. Respiration: Releasing Energy for Growth

While photosynthesis creates food, respiration is the process by which plants break down this food to release energy. This energy is then used for growth, development, and other life processes.

• Process: During respiration, glucose is broken down using oxygen.
• Location: Respiration occurs in all parts of a plant, both green and non-green.
• Products: The process releases carbon dioxide, water, and energy.

The word equation for respiration is:

Glucose + Oxygen –> Carbon dioxide + Water + Energy

An experiment with germinating seeds (Activity 10.8) demonstrates respiration. Seeds in a flask produce carbon dioxide, which turns lime water milky, confirming that respiration is taking place.

4. Transport Systems in Plants

Plants have specialized tissues to transport water, minerals, and food throughout their body. These systems are composed of thin, tube-like structures.

4.1 Transport of Water and Minerals (Xylem)

• Xylem: This is the tissue responsible for transporting water and dissolved minerals.
• Direction of Flow: The xylem carries these substances from the roots, where they are absorbed from the soil, upwards to the stem, branches, and leaves.
• Demonstration (Activity 10.7): Placing a plant twig in colored water shows that the color is drawn up through the stem and into the leaves and flowers, making the xylem pathways visible.

4.2 Transport of Food (Phloem)

• Phloem: This is the tissue responsible for transporting the food (glucose) produced during photosynthesis.
• Direction of Flow: The phloem carries food from the leaves to all other parts of the plant, including roots and seeds, for immediate energy use or for storage as starch.

5. Key Scientific Contributors

• Rustom Hormusji Dastur (1896–1961): An Indian plant scientist who studied the effects of water amount, temperature, and the color of light on the process of photosynthesis.
• Kamala Sohonie (1911–1998): A pioneering Indian woman scientist who earned her Ph.D. from Cambridge University for her work on plant respiration. Her research also contributed to improving the nutritive value of plant-based foods.

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Quiz and Q&A Section

Short-Answer Questions

(Answer in 2-3 sentences)

1. What are the two primary external factors necessary for plant growth as demonstrated in Activity 10.1?
2. Define photosynthesis and state where it primarily occurs in a plant.
3. What is chlorophyll and what is its main function in photosynthesis?
4. Name the four essential raw materials required for the process of photosynthesis.
5. What are the two main products of photosynthesis?
6. Explain why leaves are often referred to as the ‘food factories’ of plants.
7. What is starch, and how is it related to glucose in plants?
8. Describe the purpose of using an iodine solution in experiments on plant leaves.
9. Why is it necessary to decolourise a leaf before performing the starch test?
10. What are stomata, and what is their role in a plant’s life processes?
11. Write the word equation for photosynthesis.
12. Define respiration in plants.
13. Write the word equation for respiration in plants.
14. Compare the gas exchange in photosynthesis versus respiration.
15. What is the function of the xylem in a plant?
16. How did Activity 10.7 (with red ink) demonstrate the function of the xylem?
17. What is the function of the phloem in a plant?
18. An experiment shows that the part of a leaf inside a bottle with caustic soda does not produce starch. What does this prove?
19. How was the gas released by an aquatic plant in sunlight identified as oxygen in the described experiment?
20. In Activity 10.3, why did the non-green patches of a leaf fail to turn blue-black after the iodine test, even when exposed to sunlight?
21. Who was Rustom Hormusji Dastur and what did he study?
22. What happens to the lime water in a test tube connected to a flask of germinating seeds, and why?
23. Do leaves that appear red, violet, or brown carry out photosynthesis? Explain your answer.
24. What are the three things released when a plant breaks down glucose during respiration?
25. Who was Kamala Sohonie and what was her area of scientific contribution mentioned in the text?

Multiple-Choice Questions (MCQs)

1. Which of the following is the form in which plants store their food? a) Glucose b) Chlorophyll c) Starch d) Oxygen
2. The tiny pores on the surface of leaves used for gas exchange are called: a) Xylem b) Phloem c) Stomata d) Veins
3. What color change indicates the presence of starch when iodine solution is used? a) Green to yellow b) Yellow-brown to blue-black c) Blue-black to colorless d) Green to red
4. The process of breaking down glucose to release energy in plants is called: a) Photosynthesis b) Transportation c) Respiration d) Absorption
5. Which tissue transports water and minerals from the roots to the leaves? a) Phloem b) Xylem c) Stomata d) Chlorophyll
6. According to the word equation, which two substances are the raw materials for photosynthesis? a) Glucose and Oxygen b) Carbon dioxide and Water c) Sunlight and Chlorophyll d) Starch and Water
7. In the experiment to test for the necessity of carbon dioxide, what chemical is used to absorb CO2? a) Iodine solution b) Red ink c) Alcohol d) Caustic soda
8. The green pigment in leaves responsible for capturing sunlight is: a) Starch b) Glucose c) Chlorophyll d) Xylem
9. Which of these is a product of respiration but a raw material for photosynthesis? a) Oxygen b) Glucose c) Energy d) Carbon dioxide
10. The experiment with a plant twig in red-colored water demonstrates: a) Food transport through phloem b) Water transport through xylem c) Gas exchange through stomata d) The process of respiration
11. What is the immediate form of carbohydrate produced during photosynthesis? a) Starch b) Cellulose c) Glucose d) Minerals
12. In Activity 10.1, the plant in Pot C (dark, with water) had the least growth because it lacked: a) Water b) Soil c) Sunlight d) Carbon dioxide
13. The process of boiling a leaf in alcohol serves to: a) Soften the leaf b) Test for starch c) Remove chlorophyll d) Add nutrients
14. Respiration in plants occurs in: a) Only the green parts b) Only the roots c) Only the leaves at night d) All parts of the plant
15. What gas is released as a byproduct of photosynthesis? a) Carbon dioxide b) Nitrogen c) Oxygen d) Water vapor
16. Which scientist mentioned in the text studied the effects of temperature and water on photosynthesis? a) Kamala Sohonie b) Rustom Hormusji Dastur c) Vrikshayurveda d) Bhaskar
17. Which tissue is responsible for transporting food from the leaves to other plant parts? a) Phloem b) Xylem c) Stomata d) Roots
18. An intense flame from a lit matchstick inserted into a test tube of gas collected from a plant in sunlight indicates the gas is rich in: a) Carbon dioxide b) Nitrogen c) Oxygen d) Hydrogen
19. Vrikshayurveda is an ancient Indian text that contains knowledge about: a) Plant respiration b) The discovery of chlorophyll c) Agricultural practices and plant growth d) The structure of xylem and phloem
20. What are the three products of respiration? a) Glucose, Oxygen, Energy b) Carbon dioxide, Water, Energy c) Carbon dioxide, Glucose, Water d) Oxygen, Water, Starch

Essay Questions

1. Describe in detail the complete process of photosynthesis. Your answer should include the necessary raw materials, the role of chlorophyll and sunlight, the products formed, and the word equation for the process.
2. Explain the experimental setup and results of Activity 10.1, which tested the effect of sunlight and water on plant growth. What can be inferred from the observations of Pots A, B, and C?
3. Compare and contrast the processes of photosynthesis and respiration in plants. Discuss their purposes, raw materials, products, where they occur, and their respective word equations.
4. Detail the procedure for conducting an iodine test to check for the presence of starch in a leaf. Explain the purpose of each step, including softening, decolourising, and adding the iodine solution.
5. Explain the transport system within a plant. Describe the functions of xylem and phloem, what substances they transport, and the direction of transport for each.
6. Describe the experiment that demonstrates that carbon dioxide is essential for photosynthesis. Explain how the setup works and what the expected results are for the different parts of the leaf.
7. Explain the experiment that shows oxygen is released during photosynthesis. How is the gas collected, and what test is used to confirm its identity?
8. A student observes a leaf with both green and white patches (variegated leaf). If this plant is kept in sunlight, what results would be expected after performing a starch test on the leaf? Explain the reasoning behind these expected results based on the information in the text.
9. Imagine all photosynthetic organisms on Earth disappeared. Based on the provided text, what would be the impact on other living organisms?
10. Describe the experiment that uses germinating seeds and lime water. What life process does this experiment demonstrate, and how do the results prove it?

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Answer Keys

Answer Key: Short-Answer Questions

1. The two primary external factors for plant growth are sunlight and water. The experiment showed that a plant with both sunlight and water grew best, while a plant without water died and one without sunlight had very limited growth.
2. Photosynthesis is the process by which plants synthesize their own food. It primarily occurs in the leaves, which are adapted to capture sunlight and are often called the ‘food factories’ of the plant.
3. Chlorophyll is a green pigment found in plant leaves. Its main function is to capture energy from sunlight, which is then used to power the chemical reactions of photosynthesis.
4. The four essential raw materials for photosynthesis are carbon dioxide (from the air), water (from the soil), sunlight (as an energy source), and chlorophyll (to capture the sunlight).
5. The two main products of photosynthesis are glucose (a simple carbohydrate used for energy and stored as starch) and oxygen (a gas released into the atmosphere).
6. Leaves are called ‘food factories’ because they are the primary site where photosynthesis takes place. Their broad, flat structure is designed to capture sunlight, and they contain the chlorophyll necessary to convert raw materials into food for the entire plant.
7. Starch is a type of carbohydrate that plants use to store food. Glucose, a simple sugar, is the immediate product of photosynthesis, and any excess glucose is converted into starch for long-term storage in the leaves, roots, or seeds.
8. Iodine solution is used as an indicator to test for the presence of starch. When it comes into contact with starch, the solution changes color from yellow-brown to a distinct blue-black, confirming that photosynthesis has occurred.
9. A leaf must be decolourised by boiling it in alcohol to remove the green chlorophyll. This step is crucial because the green pigment would otherwise hide the blue-black color change from the iodine test, making it difficult to observe the result.
10. Stomata are tiny pores found on the surface of leaves, especially the lower side. They play a vital role in gas exchange, allowing carbon dioxide to enter the leaf for photosynthesis and oxygen to be released as a byproduct.
11. The word equation is: Carbon dioxide + Water –(Sunlight / Chlorophyll)–> Glucose + Oxygen.
12. Respiration in plants is the process of breaking down food (glucose) in the presence of oxygen to release energy. This energy is essential for the plant’s growth, development, and other life functions.
13. The word equation is: Glucose + Oxygen –> Carbon dioxide + Water + Energy.
14. In photosynthesis, plants take in carbon dioxide and release oxygen. In respiration, plants take in oxygen and release carbon dioxide.
15. The xylem is a plant tissue composed of thin tubes that transports water and dissolved minerals from the roots up to the rest of the plant, including the stem and leaves.
16. In Activity 10.7, a plant twig was placed in water containing red ink. The red color was transported up the stem and into the leaves and white flowers, making the pathways of the xylem visible and demonstrating its function of upward water transport.
17. The phloem is a plant tissue made of thin tubes that transports food, produced in the leaves during photosynthesis, to all other parts of the plant for energy or storage.
18. Caustic soda absorbs carbon dioxide from the air. The experiment proves that carbon dioxide is a necessary raw material for photosynthesis, as the part of the leaf deprived of it was unable to produce starch.
19. The gas was collected in an inverted test tube, and when a lit matchstick was inserted into it, the matchstick produced an intense flame. This test confirms the gas is rich in oxygen, as oxygen supports combustion.
20. The non-green patches of the leaf lack sufficient chlorophyll. Since chlorophyll is essential for capturing sunlight to produce starch, these patches could not perform photosynthesis and therefore did not turn blue-black.
21. Rustom Hormusji Dastur was an Indian plant scientist. He studied the process of photosynthesis, specifically examining the effects of the amount of water, temperature, and the color of light on the process.
22. The lime water turns milky. This happens because the germinating seeds are respiring, a process which releases carbon dioxide, and lime water turns milky in the presence of carbon dioxide.
23. Yes, these leaves can still carry out photosynthesis. They contain chlorophyll, but its green color is hidden by larger amounts of other colored pigments like red, violet, or brown. An iodine test can confirm the presence of starch in these leaves.
24. When a plant breaks down glucose during respiration, it releases carbon dioxide, water, and energy.
25. Kamala Sohonie was an Indian woman scientist who made remarkable contributions in the area of respiration in plants. She also worked on improving the nutritive values of plant foods.

Answer Key: MCQs

1. c) Starch
2. c) Stomata
3. b) Yellow-brown to blue-black
4. c) Respiration
5. b) Xylem
6. b) Carbon dioxide and Water
7. d) Caustic soda
8. c) Chlorophyll
9. d) Carbon dioxide
10. b) Water transport through xylem
11. c) Glucose
12. c) Sunlight
13. c) Remove chlorophyll
14. d) All parts of the plant
15. c) Oxygen
16. b) Rustom Hormusji Dastur
17. a) Phloem
18. c) Oxygen
19. c) Agricultural practices and plant growth
20. b) Carbon dioxide, Water, Energy

Answers: Essay Questions

1. Photosynthesis is the fundamental process plants use to create their own food. It primarily takes place in the leaves. The process requires four key ingredients: carbon dioxide from the air, which enters through pores called stomata; water, which is absorbed from the soil by the roots and transported to the leaves; sunlight, which provides the necessary energy; and chlorophyll, a green pigment in the leaves that captures this light energy. Using the captured solar energy, plants convert carbon dioxide and water into glucose, a simple sugar. This glucose is used for immediate energy or converted into starch for storage. A crucial byproduct of this process is oxygen, which is released into the atmosphere. The word equation summarizing this is: Carbon dioxide + Water –(Sunlight / Chlorophyll)–> Glucose + Oxygen.
2. Activity 10.1 was designed to test the necessity of sunlight and water for plant growth. Three similar potted saplings were used: Pot A was placed in direct sunlight and watered daily. Pot B was placed in direct sunlight but was not watered. Pot C was kept in a dark place but was watered daily. After two weeks, the plant in Pot A showed the maximum growth. The plant in Pot B died due to lack of water. The plant in Pot C showed very little growth, with yellowing leaves. From these results, it can be inferred that both sunlight and water are essential for healthy plant growth; the absence of either one severely hinders or prevents it.
3. Photosynthesis and respiration are two vital but opposite processes in plants. The purpose of photosynthesis is to produce food (glucose) and store energy, while the purpose of respiration is to break down that food to release energy for growth and development. For raw materials, photosynthesis uses carbon dioxide and water, whereas respiration uses glucose and oxygen. The products are also reversed: photosynthesis produces glucose and oxygen, while respiration produces carbon dioxide, water, and energy. Photosynthesis only occurs in the parts of the plant containing chlorophyll (mainly leaves) and requires sunlight. In contrast, respiration occurs in all living parts of the plant (green and non-green) continuously, day and night. The equations are:
   • Photosynthesis: Carbon dioxide + Water –> Glucose + Oxygen
   • Respiration: Glucose + Oxygen –> Carbon dioxide + Water + Energy
4. The iodine test checks for starch, proving photosynthesis has occurred. The procedure is as follows:
   1. Softening: First, the leaf is placed in boiling water for about five minutes. This step kills the leaf cells and softens the cell walls, making them permeable to alcohol and iodine.
   2. Decolourising: The softened leaf is then placed in a test tube of alcohol, which is heated in a beaker of boiling water (not over a direct flame, as alcohol is flammable). This step is essential to remove the green chlorophyll pigment, which would otherwise mask the final color change. The leaf becomes pale or colorless.
   3. Testing: The decolourised leaf is placed on a plate, and a few drops of diluted iodine solution are added. If starch is present, the leaf will turn a distinct blue-black color. If no starch is present, it will remain a yellowish-brown color.
5. Plants have a dual transport system composed of specialized tissues. The xylem is responsible for transporting water and dissolved minerals. It acts like a pipeline, moving these substances from the roots, where they are absorbed from the soil, upwards through the stem to all other parts of the plant, especially the leaves, where water is needed for photosynthesis. The phloem is responsible for transporting food. It carries the glucose produced in the leaves during photosynthesis to every part of the plant that needs energy, such as the growing tips, flowers, and roots. This food can also be transported to storage areas like seeds or roots to be converted into starch.
6. The experiment to prove carbon dioxide’s necessity involves a destarched potted plant. A wide-mouthed bottle containing a caustic soda solution (which absorbs carbon dioxide) is set up. Half of a single leaf is carefully inserted into the bottle through a split cork, while the other half remains outside in the open air. The entire setup is then placed in sunlight for several hours. Afterwards, the leaf is detached and tested for starch using the iodine test. The expected result is that the part of the leaf that was outside the bottle turns blue-black, indicating starch production. The part of the leaf that was inside the bottle with the caustic soda will not turn blue-black, showing that without carbon dioxide, photosynthesis and starch production cannot occur.
7. The experiment to show oxygen release during photosynthesis uses an aquatic plant (like hydrilla) placed under a funnel in a beaker of water. An inverted test tube filled with water is placed over the stem of the funnel. The setup is then placed in bright sunlight. Bubbles of gas will be seen rising from the plant and collecting at the top of the test tube, displacing the water. To confirm the gas is oxygen, the test tube is carefully removed, and a lit matchstick is quickly inserted into it. The matchstick will burn with an intense flame, which is the characteristic test for a high concentration of oxygen. A control setup placed in the dark would not produce any gas bubbles.
8. If a variegated leaf from a plant kept in sunlight is tested for starch, only the green parts of the leaf would turn blue-black. The white or non-green patches would show no color change and remain yellowish-brown. The reasoning is that the green patches contain chlorophyll, which is essential for capturing sunlight to perform photosynthesis and produce starch. The white patches lack chlorophyll; therefore, even with sunlight, water, and carbon dioxide, they cannot perform photosynthesis and produce starch.
9. If all photosynthetic organisms disappeared, the impact on other living organisms would be catastrophic. According to the text, plants are the producers of food that all animals rely on, either directly by eating plants or indirectly by eating other animals that eat plants. Without photosynthetic organisms, the primary source of food for nearly all life on Earth would be gone. Furthermore, photosynthesis releases oxygen into the atmosphere. The disappearance of these organisms would lead to a depletion of oxygen, which is essential for the respiration of most living creatures.
10. The experiment with germinating seeds in a sealed flask connected to a test tube of lime water demonstrates the process of respiration. The germinating seeds are living organisms that require energy to grow. To get this energy, they break down their stored food through respiration. A key product of respiration is carbon dioxide gas. The experiment proves this because the carbon dioxide produced by the seeds travels through the tube and bubbles into the lime water. The lime water turns from clear to milky, which is the definitive chemical test for the presence of carbon dioxide, thus confirming that the seeds are respiring.

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Glossary of Key Terms

• Carbohydrate: A nutrient, such as glucose or starch, that provides energy. Plants produce carbohydrates during photosynthesis.
• Carbon Dioxide: A gas present in the air that is a raw material for photosynthesis.
• Caustic Soda: A strong chemical used in experiments to absorb carbon dioxide from the air.
• Chlorophyll: The green pigment found in plants, primarily in the leaves, that captures energy from sunlight for photosynthesis.
• Decolourisation: The process of removing color, specifically removing chlorophyll from a leaf by boiling it in alcohol before an iodine test.
• Glucose: A simple carbohydrate (sugar) that is the initial food product of photosynthesis. It serves as an instant source of energy for the plant.
• Iodine Test: A chemical test used to detect the presence of starch. A blue-black color indicates a positive result.
• Leaves: The primary sites of photosynthesis in a plant, often called ‘food factories’. They are typically broad and flat to maximize sunlight absorption.
• Phloem: A set of thin, tube-like structures in plants that transports food (glucose) from the leaves to all other parts of the plant.
• Photosynthesis: The process by which plants use sunlight, water, and carbon dioxide to create their own food (glucose) and release oxygen.
• Respiration: The process in which plants break down glucose using oxygen to release energy, carbon dioxide, and water. This occurs in all living parts of the plant.
• Starch: A type of carbohydrate into which plants convert excess glucose for storage.
• Stomata: Tiny pores, usually on the lower surface of leaves, through which gases like carbon dioxide and oxygen are exchanged with the atmosphere.
• Xylem: A set of thin, tube-like structures in plants that transports water and dissolved minerals from the roots up to the stem, leaves, and other parts of the plant.