Life Processes in PlantsClass 7 Science NCERT Solutions
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Q1Let Us Enhance Our Learning
Complete the following table \begin{tabular}{|c|l|c|l|}\hline S.No. & Feature & Photosynthesis & Respiration \hline 1. & Raw materials & & \hline 2. & Products & & \hline 3. & Word equation & & \hline 4. & Importance & & \hline\end{tabular}
Solution
\begin{tabular}{|c|l|l|l|}
\hline S.No. & Feature & Photosynthesis & Respiration
\hline 1. & Raw materials & Carbon dioxide, Water & Glucose, Oxygen
\hline 2. & Products & Glucose, Oxygen & Carbon dioxide, Water, Energy
\hline 3. & Word equation & Carbon dioxide + Water Glucose + Oxygen & Glucose + Oxygen Carbon dioxide + Water + Energy
\hline 4. & Importance & Produces food and oxygen & Releases energy for growth and other activities
\hline \end{tabular}
\hline 1. & Raw materials & Carbon dioxide, Water & Glucose, Oxygen
\hline 2. & Products & Glucose, Oxygen & Carbon dioxide, Water, Energy
\hline 3. & Word equation & Carbon dioxide + Water Glucose + Oxygen & Glucose + Oxygen Carbon dioxide + Water + Energy
\hline 4. & Importance & Produces food and oxygen & Releases energy for growth and other activities
\hline \end{tabular}
Q2Let Us Enhance Our Learning
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?
Solution
If all organisms carrying out photosynthesis disappeared, it would have a devastating impact on all living organisms. Photosynthesis is the process by which plants and some bacteria convert light energy into chemical energy, producing glucose and oxygen. Without photosynthesis:
- Oxygen Depletion: The level of oxygen in the atmosphere would drastically decrease, as photosynthesis is the primary source of oxygen. Most living organisms, including animals and humans, depend on oxygen for respiration.
- Food Shortage: Plants are the primary producers in most food chains. If they disappeared, all organisms that depend on plants for food would eventually starve. This would also affect the organisms that eat those plant-eating organisms.
- Increase in Carbon Dioxide: Photosynthesis removes carbon dioxide from the atmosphere. Without it, the concentration of carbon dioxide would increase, potentially leading to climate change.
- Ecosystem Collapse: The entire ecosystem would collapse due to the disruption of the food web and the imbalance of gases in the atmosphere.
Q3Let Us Enhance Our Learning
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?
Solution
The starch in potatoes comes from the glucose produced during photosynthesis in the leaves of the potato plant. The food is synthesized in the leaves, which are the primary sites of photosynthesis. The glucose produced is then converted into starch for storage. This starch is transported from the leaves to other parts of the plant, including the potato tubers (which are modified stems), through a tissue called phloem. The phloem consists of tube-like structures that transport the food in the form of sucrose, which is then converted to starch in the potato.
Q4Let Us Enhance Our Learning
Does the broad and flat structure of leaves make plants more efficient for photosynthesis? Justify your answer.
Solution
Yes, the broad and flat structure of leaves does make plants more efficient for photosynthesis. This is because:
- Increased Surface Area: The flat shape provides a large surface area for capturing sunlight. More sunlight absorption means more energy is available for photosynthesis.
- Efficient Gas Exchange: The broad structure facilitates efficient gas exchange. Carbon dioxide, required for photosynthesis, can be absorbed more readily from the atmosphere, and oxygen, a byproduct, can be released more efficiently.
- Optimized Light Distribution: The flat shape allows for even distribution of light across the leaf surface, ensuring that all chlorophyll-containing cells receive adequate light for photosynthesis.
- Thinness for Diffusion: The thinness of the leaf ensures that carbon dioxide does not have to diffuse over long distances to reach the cells where photosynthesis occurs.
Q5Let Us Enhance Our Learning
X is broken down using Y to release carbon dioxide, Z , and energy. $$\mathrm{X}+\mathrm{Y} \longrightarrow \text { Carbon dioxide }+\mathrm{Z}+\text { Energy }$$$ , and Z are three different components of the process.
Solution
X, Y, and Z stand for the following:
X: Glucose ()
Y: Oxygen ()
Z: Water ()
This equation represents the process of respiration.
Q6Let Us Enhance Our Learning
Krishna set-up an experiment with two potted plants of same size and placed one of them in sunlight and the other in a dark room, as shown in Fig. 10.10. Answer the following questions-
(i)
What idea might she be testing through this experiment?
(ii)
What are the visible differences in plants in both the conditions?
(iii)
According to you, leaves of which plants confirm the iodine test for the presence of starch?
Solution
(i)
Krishna might be testing the idea that sunlight is essential for photosynthesis.
(ii)
The plant in sunlight is likely to be healthier and greener, with more upright leaves. The plant in the dark room may appear pale or yellowish, with droopy leaves, and may exhibit less growth.
(iii)
The leaves of the plant kept in sunlight will confirm the iodine test for the presence of starch. When iodine solution is added, the leaves will turn blue-black, indicating the presence of starch. The leaves of the plant kept in the dark will not show this color change because they have not been able to produce starch due to the lack of sunlight.
Q7Let Us Enhance Our Learning
Vani believes that 'carbon dioxide is essential for photosynthesis'. She puts an experimental set-up, as shown in Fig. 10.11, to collect evidence to support or reject her idea. Answer the following questions-
(i)
In which plant(s) in the above set-up(s) will starch be formed?
(ii)
In which plant(s) in the above set-up(s) will starch not be formed?
(iii)
In which plant(s) in the above set-up(s) will oxygen be generated?
(iv)
In which plant(s) in the above set-up(s) will oxygen not be generated?
Solution
(i)
Starch will be formed in plant (a), which is in sunlight with carbon dioxide.
(ii)
Starch will not be formed in plants (b), (c), and (d). Plant (b) lacks carbon dioxide, while plants (c) and (d) lack sunlight.
(iii)
Oxygen will be generated in plant (a), which is in sunlight with carbon dioxide.
(iv)
Oxygen will not be generated in plants (b), (c), and (d). Plant (b) lacks carbon dioxide, while plants (c) and (d) lack sunlight.
Q8Let Us Enhance Our Learning
Ananya took four test tubes and filled three-fourth of each test tube with water. She labelled them A, B, C, and D (Fig. 10.12). In test tube A, she kept a snail; in test tube B, she kept a water plant; in test tube C , she kept both a snail and a plant. In test tube D, she kept only water. Ananya added a carbon dioxide indicator to all the test tubes. She recorded the initial colour of water and observed if there are any colour changes in the test tubes after hours. What do you think she wants to find out? How will she know if she is correct?
Solution
Ananya wants to find out how plants and animals influence the carbon dioxide levels in water.
She will know if she is correct by observing the color changes in the test tubes with the carbon dioxide indicator. The indicator changes color based on the amount of carbon dioxide present:
- If the carbon dioxide level increases, the water will become more acidic, and the indicator will change to a color indicating higher acidity.
- If the carbon dioxide level decreases, the water will become less acidic, and the indicator will change to a color indicating lower acidity.
In test tube A (snail), the carbon dioxide level will increase due to the snail's respiration.
In test tube B (plant), the carbon dioxide level will decrease due to the plant's photosynthesis if exposed to light.
In test tube C (snail and plant), the carbon dioxide level will depend on the balance between the snail's respiration and the plant's photosynthesis.
In test tube D (water only), the carbon dioxide level will remain relatively stable.
Q9Let Us Enhance Our Learning
Design an experiment to observe if water transportation in plants is quicker in warm or cold conditions.
Solution
To observe if water transportation in plants is quicker in warm or cold conditions, an experiment can be designed as follows:
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Materials: Two similar young plants (e.g., balsam or celery), two beakers, water, red food coloring, a warm environment (e.g., a sunny windowsill or a heat lamp), and a cold environment (e.g., a refrigerator).
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Procedure:
- Take two beakers and fill them with the same amount of water.
- Add the same amount of red food coloring to each beaker.
- Cut the stems of the two plants to the same length and place one plant in each beaker.
- Place one beaker with the plant in the warm environment and the other in the cold environment.
- Observe the plants over several hours, noting how quickly the red color travels up the stem and into the leaves in each plant.
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Observation:
- Periodically check the plants and note the time it takes for the red color to appear in the leaves of each plant. Measure the height the red water has traveled up the stem at specific time intervals.
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Result:
- Compare the rate of water transportation in both conditions. If the red color appears faster and travels higher in the plant in the warm environment, it indicates that water transportation is quicker in warm conditions. If it is faster in the cold environment, then water transportation is quicker in cold conditions.
This experiment will help determine the effect of temperature on water transportation in plants.
Q10Let Us Enhance Our Learning
Photosynthesis and respiration are essential to maintain balance in nature. Discuss.
Solution
Photosynthesis and respiration are essential processes that maintain balance in nature through the following ways:
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Oxygen and Carbon Dioxide Balance: Photosynthesis uses carbon dioxide from the atmosphere and releases oxygen as a byproduct. Respiration, carried out by plants and animals, uses oxygen and releases carbon dioxide. These two processes counteract each other, maintaining a balance of these gases in the atmosphere. Without this balance, the atmosphere would become either oxygen-depleted or carbon dioxide-rich, making it uninhabitable for many organisms.
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Energy Flow and Food Production: Photosynthesis converts light energy into chemical energy in the form of glucose, providing the primary source of food for most ecosystems. This energy is then passed on to other organisms through the food chain. Respiration releases the energy stored in glucose, allowing organisms to carry out their life processes. This flow of energy sustains life and maintains the structure of ecosystems.
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Nutrient Cycling: Photosynthesis and respiration are involved in the cycling of essential nutrients. Carbon, for example, is taken up by plants during photosynthesis and returned to the environment during respiration and decomposition. This cycling ensures that nutrients are available for continuous use by living organisms.
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Climate Regulation: Photosynthesis helps regulate the Earth's climate by removing carbon dioxide, a greenhouse gas, from the atmosphere. This helps to mitigate the effects of climate change. Respiration, on the other hand, releases carbon dioxide, but the overall effect is balanced by photosynthesis.
In summary, photosynthesis and respiration are complementary processes that play a crucial role in maintaining the balance of gases, energy flow, nutrient cycling, and climate regulation in nature. They sustain life and ensure the stability of ecosystems.