SCIENCE CLASS- 7
CHAPTER-10 (Life Processes in Plants)
Let Us Enhance Our Learning
1. Complete the following table.
| S.No. | Feature | Photosynthesis | Respiration |
|---|---|---|---|
| 1 | Raw Materials | Carbon dioxide and water | Glucose and oxygen |
| 2 | Products | Glucose and oxygen | Carbon dioxide, water and energy |
| 3 | Word Equation | Carbon dioxide + Water → Glucose + Oxygen | Glucose + Oxygen → Carbon dioxide + Water + Energy |
| 4 | Importance | Preparation of food in plants | Release of energy for life processes |
2. Imagine a situation where all the organisms that carry out photosynthesis on the Earth have disappeared. What would be the impact of this on living organisms?
Answer:
If all photosynthetic organisms disappeared, food production on Earth would stop because plants are the primary producers. Herbivores would die due to lack of food, followed by carnivores and omnivores. Oxygen levels in the atmosphere would gradually decrease, while carbon dioxide levels would increase. Since animals and humans depend on oxygen for respiration, most living organisms would not survive. Therefore, life on Earth would be severely affected and many species could become extinct.
3. A potato slice shows the presence of starch with iodine solution. Where does the starch in potatoes come from? Where is the food synthesised in the plant, and how does it reach the potato?
Answer:
The starch present in potatoes is produced by the plant through photosynthesis. Food is synthesised mainly in the green leaves, which are called the food factories of plants. During photosynthesis, glucose is formed and later converted into starch for storage. This food is transported from the leaves to the potato through the phloem. The potato stores this food in the form of starch.
4. Does the broad and flat structure of leaves make plants more efficient for photosynthesis? Justify your answer.
Answer:
Yes, the broad and flat structure of leaves makes plants more efficient for photosynthesis. A broad surface provides a larger area to absorb sunlight. Leaves also contain chlorophyll, which captures light energy. Their flat shape helps in efficient exchange of gases such as carbon dioxide and oxygen through stomata. Thus, the structure of leaves helps plants prepare food more effectively.
5. X is broken down using Y to release carbon dioxide, Z, and energy.
X + Y → Carbon dioxide + Z + Energy
What do X, Y, and Z stand for?
Answer:
X = Glucose
Y = Oxygen
Z = Water
The complete respiration equation is:
Glucose + Oxygen → Carbon dioxide + Water + Energy
6. Krishna set up an experiment with two potted plants of the same size and placed one in sunlight and the other in a dark room.
(i) What idea might she be testing through this experiment?
Answer:
She is testing whether sunlight is necessary for photosynthesis and plant growth.
(ii) What are the visible differences in plants in both the conditions?
Answer:
The plant kept in sunlight remains green, healthy, and grows normally. The plant kept in darkness becomes weak, pale yellow, and shows poor growth because it cannot prepare food properly.
(iii) According to you, leaves of which plant confirm the iodine test for the presence of starch?
Answer:
The leaves of the plant kept in sunlight will turn blue-black with iodine solution, confirming the presence of starch.
7. Vani believes that carbon dioxide is essential for photosynthesis.
(i) In which plant(s) will starch be formed?
Answer:
Starch will be formed only in Plant (a), which receives both sunlight and carbon dioxide.
(ii) In which plant(s) will starch not be formed?
Answer:
Starch will not be formed in Plants (b), (c), and (d) because one or more essential conditions for photosynthesis are absent.
(iii) In which plant(s) will oxygen be generated?
Answer:
Oxygen will be generated only in Plant (a), where photosynthesis takes place.
(iv) In which plant(s) will oxygen not be generated?
Answer:
Oxygen will not be generated in Plants (b), (c), and (d) because photosynthesis does not occur in these conditions.
8. Ananya took four test tubes containing a snail, a water plant, both together, and only water. What do you think she wants to find out? How will she know if she is correct?
Answer:
Ananya wants to investigate the relationship between photosynthesis and respiration and how these processes affect the amount of carbon dioxide in water.
The snail releases carbon dioxide during respiration. The water plant uses carbon dioxide during photosynthesis and releases oxygen. If the indicator shows increased carbon dioxide in the test tube containing only the snail and decreased carbon dioxide in the test tube containing only the plant, it supports her idea. In the test tube containing both the snail and plant, little or no change may occur because the carbon dioxide released by the snail can be used by the plant.
9. Design an experiment to observe if water transportation in plants is quicker in warm or cold conditions.
Answer:
Take two similar leafy plant twigs and place them in separate beakers containing equal amounts of water mixed with red ink. Keep one beaker in a warm place and the other in a cool place. Observe the movement of the coloured water through the stem and leaves after a few hours. Compare the extent of red colour in both plants. If the colour spreads faster in the plant kept in warm conditions, it shows that water transportation is quicker in warm conditions due to increased transpiration.
10. Photosynthesis and respiration are essential to maintain balance in nature. Discuss.
Answer:
Photosynthesis and respiration are complementary processes that help maintain balance in nature. During photosynthesis, plants use carbon dioxide and water to prepare food and release oxygen. During respiration, living organisms use oxygen to break down food and release carbon dioxide and energy. The oxygen released during photosynthesis is used in respiration, while the carbon dioxide released during respiration is used in photosynthesis. This continuous exchange of gases maintains the balance of oxygen and carbon dioxide in the atmosphere and supports life on Earth.