CLASS 7 SCIENCE · CHAPTER 10 · STUDY NOTES
Life Processes in Plants
Use experiments and labelled plant structures to connect food-making, transport and respiration.
01 / EXPLORE & UNDERSTAND
Growth needs materials and energy
A growing plant makes new structures; it does not just fill with water.
Which condition changes?
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1. Notice several changes
New leaves, longer stems and thicker branches are signs of growth. Water supports growth, but watering alone does not provide all the substances and energy needed to build a plant.
2. Compare conditions fairly
The textbook compares similar plants with water and light, with light but no water, and with water but no light. Compare each altered condition with the first plant. Do not compare only the two deprived plants, because both light and water differ between them.
Your turn
Question
Which pair isolates the effect of light: A has water and light, B light only, C water only?
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02 / EXPLORE & UNDERSTAND
Leaves capture light to make food
Soil provides minerals; it is not a store of ready-made plant sugar.
1. Connect structure with job
Many leaves are broad and flat, exposing a large area to light. Chlorophyll captures some of that light energy. Other green parts, such as young stems, can also photosynthesise.
2. Do not judge only by visible colour
Red or purple leaves can contain chlorophyll hidden by other pigments. A non-green appearance does not automatically mean no photosynthesis. Roots usually absorb water and minerals rather than making sugar from sunlight.
Your turn
Question
Can a purple leaf still photosynthesise?
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03 / EXPLORE & UNDERSTAND
A starch test reveals stored food
Iodine gives evidence about starch, not a direct measurement of photosynthesis speed.
1. Read the colour change
In the teacher demonstration, a leaf is prepared and its green pigment removed before iodine is added. A blue-black result indicates starch. Removing pigment makes this change easier to see.
2. Respect the method’s limits
A leaf may already contain stored starch before a test. The presence of starch alone does not prove it was made during the last few minutes. The hot alcohol step is teacher-only: alcohol is flammable and must not be heated directly over a flame.
Your turn
Question
Why is the green pigment removed before the iodine test?
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04 / EXPLORE & UNDERSTAND
Compare light and chlorophyll together
Map the leaf’s patches before changing its colour in a test.
Match the green patches to the starch result
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1. Keep track of the green patches
The textbook compares patched leaves under light and dark conditions. In light, regions that had chlorophyll show starch after the iodine test. Match the result with the original patch map rather than guessing from the decolourised leaf.
2. Explain the dark comparison
A period in darkness lets the plant use stored starch. Under suitable conditions, a destarched leaf given light can make new food. A negative result in darkness does not mean that the leaf has stopped being alive: it still respires.
Your turn
Question
Why record where the green parts were before removing pigment?
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05 / EXPLORE & UNDERSTAND
Air supplies a food-making ingredient
Light is energy; carbon dioxide supplies material.
Remove carbon dioxide from one side
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1. Compare two parts of a leaf
In the teacher’s setup, half a leaf is inside a sealed bottle with a carbon-dioxide absorber; the other half is outside. Water, chlorophyll and light remain available. The outer half can form starch while the deprived inner half does not give the same result.
2. Identify the changed condition
The absorber removes carbon dioxide from the bottle air. It is not removing sunlight or chlorophyll. Sodium hydroxide is corrosive, so this setup is for teacher demonstration, not a home experiment.
Your turn
Question
Which missing ingredient explains the inner half’s result?
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06 / EXPLORE & UNDERSTAND
Build food from carbon dioxide and water
The process stores light energy in chemical form.
Inputs, energy and products
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1. Read inputs and outputs
Carbon dioxide + water → glucose + oxygen, in the presence of light and chlorophyll. Glucose is a simple sugar. Some is used, some transported, and some converted to starch for storage.
2. Interpret the water-plant experiment
A water plant in light releases bubbles that can be collected. Bubbles alone do not identify the gas. In the teacher demonstration, a gas test provides evidence of oxygen. Comparing light and dark helps connect the release with photosynthesis.
A little deeper: Science grows through controlled questions
NCERT describes Rustom Hormusji Dastur’s work on factors such as water, temperature and light affecting photosynthesis. One experiment rarely answers everything; changing one factor carefully helps identify its effect.
Your turn
Question
Is sunlight a substance that turns into a leaf’s starch?
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07 / EXPLORE & UNDERSTAND
Tiny pores connect the leaf and air
A microscope reveals structures that eyes alone cannot resolve.
Find a pore between two guard cells
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1. Locate the opening
In the textbook’s magnified view, look for an opening between paired cells. That pore is a stoma; the plural is stomata. The whole purple surface is not one stoma.
2. Connect gases and water loss
Carbon dioxide can enter and oxygen can leave during photosynthesis. Water vapour also escapes through stomata in transpiration. Opening pores helps exchange but also affects water loss.
Your turn
Question
Does “stomata” mean the entire leaf surface?
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08 / EXPLORE & UNDERSTAND
Water travels through xylem
Roots take up water and dissolved mineral nutrients.
Compare the twigs before and after
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1. Follow the coloured-water evidence
In a teacher-prepared twig experiment, coloured water makes transport pathways visible. Colour can appear in the stem, leaf veins and white petals. A twig in plain water provides a comparison.
2. Identify what the colour means
The dye travels with water through xylem. It does not prove that the plant normally drinks ink or that every cell is a hollow pipe. Xylem is a specialised transport tissue running through connected plant parts.
Your turn
Question
Which tissue carries water and dissolved minerals up a plant?
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09 / EXPLORE & UNDERSTAND
Food travels to where it is needed
A root can receive food even when it does not photosynthesise.
Two transport tissues
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1. Trace sugar beyond the leaf
Leaves produce sugars in photosynthesis. Phloem carries food to growing regions and storage organs, including roots, fruits and seeds. A non-green part can therefore receive food made elsewhere.
2. Avoid the “always down” rule
Food may need to move upwards to a developing bud or downwards to a root. Its route depends on source and destination. Xylem and phloem have different main jobs; they are not interchangeable pipes.
Your turn
Question
Why can a developing fruit receive sugar even if its own photosynthesis is limited?
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10 / EXPLORE & UNDERSTAND
Plants use food for energy, too
Making food does not remove the need to release usable energy from it.
1. Look at germinating seeds
In the book demonstration, germinating seeds produce extra carbon dioxide, detected using lime water. The seeds can respire in darkness using stored food. Outside air already contains a little CO2, so a comparison is important.
2. Include every living part
Leaves, roots and other living plant cells respire during both day and night. Aerobic respiration uses glucose and oxygen and releases carbon dioxide, water and energy. A non-green root still needs energy.
Your turn
Question
Can a germinating seed release carbon dioxide in darkness?
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11 / EXPLORE & UNDERSTAND
Photosynthesis and respiration work together
Do not use the shortcut “plants breathe only at night”.
1. Compare two jobs
Photosynthesis uses light energy to make food and releases oxygen. Respiration releases usable energy from food. In a lit leaf, both can happen at once. Net oxygen release means photosynthesis is exceeding oxygen use by respiration, not that respiration stopped.
2. Think about a bottle garden
A suitable planted bottle can recycle water and gases for some time, but still receives light energy from outside. It is not a system that creates energy. Its survival depends on conditions; a sealed bottle is not automatically balanced.
A little deeper: A scientist connected plant processes and nutrition
NCERT introduces Kamala Sohonie’s research on plant respiration and her later work on the nutritive value of plant foods. Understanding how plants make and use food also helps us understand agriculture and human nutrition.
Your turn
Question
Why does a bottle garden still need light from outside?
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Take these ideas with you
- Light provides energy; carbon dioxide and water provide photosynthesis materials.
- Glucose can be used, transported or stored as starch.
- Stomata are pores for gas exchange and water-vapour loss.
- Xylem transports water and minerals; phloem transports food.
- All living plant parts respire, day and night.
- A fair experiment changes one factor and includes a comparison.
Use your understanding in a new situation
Question
Explain why “fertiliser is the plant’s ready-made sugar” is wrong.
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A root receives sugar made in a leaf and uses it for growth. Name the transport tissue and energy-releasing process.
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Sign inNew here? Sign up freeNCERT · Chapter source PDF, pages 13, 14, 16 · Original Learnijoy explanations and practice.