Master Chapter 10 Class 7 - Life Processes in Plants (Curiosity) with comprehensive NCERT Solutions, Practice Questions, MCQs, Sample Papers, Case Based Questions, and Video lessons.
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Welcome to Chapter 10. In our last journey, we explored the fascinating and complex world of nutrition in animals. We learned how we, and other animals, eat food, how a long and complex alimentary canal digests that food, and how our bodies absorb the nutrients to get energy.
But this leads to a very big, and very obvious, question. We know that animals eat food to grow. But what about plants? Have you ever seen a plant eat?
Of course not. Plants don't have mouths. They don't hunt, they don't graze, and they don't move around to find a meal. And yet, just like us, they grow. A tiny seed becomes a sapling, which grows into a massive tree, developing new leaves, branches, flowers, and fruits 1. Just like us, they need essential nutrients like carbohydrates, proteins, and fats to fuel this growth2.
So, if they don't eat, where do they get their food?
This chapter is a scientific investigation to solve this profound mystery. We will start by brainstorming, just like the students in the book:
"Maybe plants take up food from the soil through their roots." 3
"When we water plants regularly, they grow better... I think water also contributes." 4
"I think sunlight plays some role in the growth of plants." 5
These are all excellent hypotheses. Now, we must test them.
Our first experiment (Activity 10.1) is a simple but powerful one. We will take three identical potted plants and treat them differently:
Pot A: We will give it both sunlight and water.
Pot B: We will give it sunlight but no water.
Pot C: We will give it water but no sunlight (by keeping it in the dark) 6.
The results, after two weeks, are crystal clear.
The plant in Pot A thrives, growing taller and producing new green leaves.
The plant in Pot B withers and dies7.
The plant in Pot C becomes weak, and its leaves turn yellow8.
This experiment gives us our first two crucial clues. It proves, without a doubt, that water and sunlight are both essential for a plant to grow and stay healthy9.
But this still doesn't answer our main question. Water and sunlight are just conditions. Where does the food come from? Where does the substance—the carbohydrates and proteins—come from?
The answer is the single most important concept in all of biology. Plants do not eat food from the soil. They make their own food.
They are the ultimate creators. Their leaves are like tiny, high-tech "food factories"10101010. And this amazing, world-changing process of making food is called photosynthesis11.
Like any factory, the leaf needs a list of raw ingredients to manufacture its product. This chapter is our journey to find every single ingredient on that list.
The Product: The "food" that plants make is a simple sugar called glucose, a type of carbohydrate. This glucose serves as instant energy for the plant and is also converted into starch for storage 12121212.
The "Starch Test": To find our ingredients, we need a way to see if food (starch) has been made. We will learn a new scientific technique: the Iodine Test. We will learn how to take a leaf, boil it in alcohol to remove its green colour, and then add a few drops of iodine solution. If the leaf turns blue-black, it means starch is present 13.
Now, we can use this test to find all the ingredients for photosynthesis.
The Energy Source: SUNLIGHT
We will test our hypothesis from Pot C. If we take a plant that has been kept in the dark for 36 hours and test its leaves, we find no starch14. The factory was shut down. Sunlight is the energy that powers the entire process.
The "Factory Machine": CHLOROPHYLL
We will test a special "variegated" leaf—one that has both green and non-green (white) patches. After leaving it in the sun, we will perform the starch test. We will find that only the green parts turn blue-black15. The white parts (which lack the green pigment chlorophyll) make no starch16. This proves that chlorophyll is the essential "machine" inside the leaf that captures the sun's light energy17.
The Raw Material from the Ground: WATER
We already proved this with Pot B. Without water, the plant dies. Water is a key raw material that is pulled up from the soil.
The Raw Material from the Air: CARBON DIOXIDE
This is the most amazing ingredient of all. We will learn about a clever experiment (Activity 10.4) where a part of a leaf is enclosed in a bottle containing caustic soda, a chemical that absorbs carbon dioxide 18.
The part of the leaf outside the bottle (with access to air) makes starch.
The part of the leaf inside the bottle (with no carbon dioxide) makes no starch 19.
This proves that plants "eat" a gas from the air. That gas is carbon dioxide—the very gas that we and other animals breathe out.
This is a complex, multi-step process. We are learning about invisible gases, chemical pigments, and microscopic pores, all working together in a perfect chemical reaction. It is easy to get lost in the details of which ingredient does what.
This is where Teachoo comes in. We are masters at breaking down these big, complex, and vital processes into simple, logical steps. We will guide you through each experiment, helping you clearly understand the role of each ingredient—sunlight, water, chlorophyll, and carbon dioxide. We help you connect all the dots so you can see the complete, beautiful picture of photosynthesis.
Now that we have all our ingredients, we can write out the full "recipe" for photosynthesis as a word equation:
Carbon dioxide + Water → Glucose (food) + Oxygen
Wait... Oxygen? Where did that come from?
This is the final, astonishing part of the process. When plants make their food, they release a "waste" gas. We will learn about an experiment (Activity 10.5) where a water plant, when placed in sunlight, produces tiny bubbles of gas 21. When this gas is collected and a glowing matchstick is inserted, the matchstick bursts back into an intense flame. This is the definitive test for oxygen 22.
The very oxygen that we and all other animals need to breathe is the "waste" product of photosynthesis.
We have now solved the puzzle of the "food factory" in the leaves. But this creates two new problems:
How does the water get from the roots up to the leaves?
How does the food (sugar) get from the leaves down to the roots and other parts?
This chapter will introduce us to the plant's internal "plumbing system," a network of microscopic tubes.
Xylem: This is a set of tubes that acts like a bundle of tiny straws, transporting water and minerals up from the roots, through the stem, and to every leaf 23. We will prove this by placing a white flower in red-coloured ink and watching its petals turn red.
Phloem: This is a second set of tubes that transports the food (sugars) made in the leaves down to all other parts of the plant—the stem, the roots, the fruits—providing energy for growth or for storage 24.
We have learned that plants take in carbon dioxide and release oxygen during photosynthesis. This can be confusing, because we know we do the opposite. We inhale oxygen and exhale carbon dioxide.
So, do plants breathe? Are they using the oxygen they make?
Yes, they absolutely do.
We must learn to separate two different processes:
Photosynthesis: This is the food-making process. It only happens in green parts (with chlorophyll) and only when there is sunlight.
Respiration: This is the energy-releasing process. Just like animals, plants must respire 24 hours a day to stay alive. They take in oxygen (which they get from the air) and use it to break down the glucose they made, releasing energy for their own growth and survival25252525.
This process of respiration is the exact opposite of photosynthesis:
Glucose + Oxygen → Carbon~dioxide + Water + Energy
We will prove this by taking germinating seeds (which are alive but have no sunlight for photosynthesis) and showing that they release carbon dioxide, which can turn lime water milky 27.
This chapter reveals the incredible, self-sustaining nature of plants. They are the only living things on our planet that can create their own food from sunlight, air, and water. And in the process, they create the very oxygen that we need to live.
To get started on this journey, click on any topic link to begin your exploration