Photosynthesis - Stomata - Xylem & Phloem - Transport - Respiration
Think about planting a seed in a pot. After a few days, a tiny green shoot appears. Over weeks and months, it grows into a tall plant with leaves, stems, flowers, and fruits. But what makes this happen?
When a seed gets water and warmth, it begins to germinate. The process goes like this:
A dry seed contains a tiny baby plant (embryo) and stored food. It is dormant (sleeping).
When it gets water and warmth, the seed coat breaks. A small root (radicle) grows downward. A shoot (plumule) grows upward.
The first leaves appear. The young plant is now called a seedling. It starts making its own food.
More leaves, stems, and branches grow. The plant produces flowers and fruits. It needs food, water, sunlight, and air continuously.
Absorbed from soil through roots. Essential for all life processes.
Provides energy for making food (photosynthesis).
Carbon dioxide from air is used in photosynthesis.
From soil, dissolved in water, absorbed by roots.
Animals find and eat food. But plants cannot move to search for food. So how do they get nutrition?
The answer is remarkable: plants make their own food! They use simple raw materials -- water, carbon dioxide, and sunlight -- to prepare food (glucose) in their leaves.
The mode of nutrition in which organisms make their own food from simple inorganic substances is called Autotrophic Nutrition.
The process by which green plants make food using sunlight, carbon dioxide, and water is called Photosynthesis.
Scientists have proved this through many experiments. The simplest proof is the iodine test: when we add iodine solution to a leaf that has been in sunlight, it turns blue-black, showing that starch (stored food) is present. A leaf kept in the dark does NOT turn blue-black -- no food was made! (See Activity 10.2)
Leaves are the main organs where photosynthesis takes place. They are called the food factories of the plant. But why leaves specifically?
Leaves are green because they contain a green pigment called Chlorophyll. This pigment is present inside small organelles called Chloroplasts.
A green pigment that absorbs sunlight energy. It captures light and uses that energy to drive photosynthesis. Without chlorophyll, photosynthesis cannot happen!
The tiny organelles (structures) inside leaf cells where chlorophyll is found. They are the actual "factories" where photosynthesis occurs. Each leaf cell has many chloroplasts.
Comes from the soil. Roots absorb water, which travels up through the stem (via xylem) and reaches the leaves.
Comes from the air. Leaves have tiny pores called stomata through which CO2 enters the leaf.
Comes from the Sun. Chlorophyll in the leaves captures sunlight energy, which powers the entire process.
Chloroplasts are oval/lens-shaped organelles. Inside, they contain a green fluid called stroma and stacks of membrane-bound discs called thylakoids. Chlorophyll molecules are embedded in the thylakoid membranes, ready to capture sunlight!
A leaf showing all inputs and outputs of photosynthesis
Cross-section showing layers of a leaf and location of stomata
We know that air contains about 0.04% Carbon dioxide (CO2). Even though this is a small amount, it is absolutely essential for photosynthesis.
Leaves have tiny microscopic pores called stomata (singular: stoma). Carbon dioxide from the air enters the leaf through these stomata. Each stoma is surrounded by two bean-shaped guard cells that control the opening and closing of the pore.
Without CO2, plants cannot make food. It is one of the two raw materials (along with water) needed for photosynthesis.
If part of a leaf is enclosed with NaOH (caustic soda, which absorbs CO2), that part does NOT make starch. This proves CO2 is needed. (See Activity 10.4)
Most abundant gas in air, but plants CANNOT use it directly from air. They get nitrogen from soil (as nitrates).
Used by plants for respiration. Also released by plants during photosynthesis!
Very small amount, but this is exactly what plants need for photosynthesis. Enters through stomata.
Now let us put it all together. Photosynthesis is the process where green plants use sunlight energy to convert carbon dioxide and water into glucose (food) and oxygen.
The Photosynthesis Factory
Provides the energy needed to combine CO2 and water. Without light, no photosynthesis!
Captures sunlight energy. Present in chloroplasts of green parts (mainly leaves).
Absorbed from soil by roots, transported to leaves through xylem.
Enters leaves through stomata from the atmosphere.
The main food product. It is a simple sugar. Some glucose is converted to starch for storage. Starch is what we detect using the iodine test (turns blue-black).
A by-product released into the air through stomata. This oxygen is essential for the survival of almost all living organisms on Earth!
For photosynthesis, CO2 must enter the leaf. After photosynthesis, O2 must leave. How does this gas exchange happen? Through stomata!
Stomata are tiny pores found mostly on the lower surface (epidermis) of leaves. Each stoma is surrounded by two guard cells that are bean-shaped.
Animated Stomata: Guard cells open and close the pore
Carbon dioxide from the atmosphere enters the leaf through open stomata for photosynthesis.
Oxygen produced during photosynthesis exits the leaf through stomata into the air.
Water vapour escapes from inside the leaf through stomata. This process is called transpiration.
Guard cells control whether stomata are open or closed:
They swell up and bend apart, opening the stomatal pore. This allows gas exchange.
They become flaccid (limp) and come together, closing the stomatal pore. This reduces water loss.
Besides gas exchange, stomata are also responsible for transpiration -- the loss of water vapour from the aerial parts of the plant (mostly leaves). This may sound wasteful, but transpiration is actually very important!
As water evaporates from leaves, it creates a suction force that pulls water upward through the xylem from roots. This is how water reaches the top of tall trees!
Just like sweating cools our body, transpiration cools the plant on hot days through evaporative cooling.
As water moves upward due to transpiration, it carries dissolved minerals from the soil to all parts of the plant.
Roots absorb water from the soil. Leaves make food. But how do water and food reach all parts of the plant? Plants have a transport system made up of two types of tubes: Xylem and Phloem.
Xylem transports water and dissolved minerals from the roots upward to the stems, branches, and leaves. This transport is one-way (upward only).
Phloem transports prepared food (sugars/glucose) made in the leaves to all other parts of the plant -- stems, roots, flowers, fruits, and seeds. Phloem transport can go both upward and downward (bidirectional). This movement of food is called translocation.
Water + Minerals
Roots to Leaves (Upward only)
Prepared Food (Sugars)
Leaves to All Parts (Both ways)
| Feature | Xylem | Phloem |
|---|---|---|
| What it transports | Water and dissolved minerals | Prepared food (glucose/sugars) |
| Direction | Upward only (roots to leaves) | Both upward and downward |
| Movement called | Ascent of sap | Translocation |
| Driving force | Transpiration pull | Active transport using energy |
When water evaporates from leaves through stomata (transpiration), it creates a "pulling force" called transpiration pull. This pull draws water upward through the xylem from the roots -- like sipping water through a straw!
Yes! Plants respire just like animals. All living cells -- whether in plants or animals -- need energy to carry out life processes. This energy comes from respiration.
Respiration is the process of breaking down glucose (food) in the presence of oxygen to release energy, carbon dioxide, and water.
Every living cell in a plant respires -- root cells, stem cells, leaf cells, flower cells. Not just green parts!
Unlike photosynthesis (only during day), respiration happens 24 hours a day, 7 days a week -- continuously.
Respiration takes in oxygen and releases carbon dioxide -- exactly the opposite of photosynthesis!
| Feature | Photosynthesis | Respiration |
|---|---|---|
| Occurs in | Green parts (leaves) only | All living cells |
| When | Only in sunlight (daytime) | Day and night (always) |
| Uses | CO2 + Water + Light | Glucose + Oxygen |
| Produces | Glucose + Oxygen | CO2 + Water + Energy |
| Energy | Stores energy (in glucose) | Releases energy (for use) |
| Type of process | Anabolic (building up) | Catabolic (breaking down) |
Glucose + Oxygen → Carbon Dioxide + Water + Energy
These are the 8 activities from NCERT Chapter 10. Each is important for exams!
👆 Select conditions and watch what happens to the plant!
Aim: To show that both sunlight and water are essential for plant growth.
Setup: Plant seeds in three identical pots with soil:
👆 Follow the steps to test for starch!
Aim: To test whether a leaf contains starch (food made by photosynthesis).
Procedure:
👆 Click to apply iodine test on the variegated leaf!
Aim: To prove that chlorophyll is necessary for photosynthesis.
Setup: Use a variegated leaf -- a leaf with both green and white/pale parts (like a Croton leaf). The green parts have chlorophyll, the white parts do not.
👆 Follow the steps to test if CO₂ is needed!
Aim: To prove that carbon dioxide is necessary for photosynthesis.
👆 Toggle sunlight and watch for oxygen bubbles!
Aim: To show that plants release oxygen during photosynthesis.
👆 Click to open and close the stomata!
Aim: To observe stomata on the lower surface of a leaf.
👆 Place the stem in colored water and watch it rise!
Aim: To show that water travels upward through the stem via xylem.
👆 Follow the steps to test for CO₂ from respiration!
Aim: To show that germinating seeds (plants) release CO2 during respiration.
Correction: Plants DO respire -- day and night, in all cells. Photosynthesis and respiration are two different processes!
Correction: O2 is a PRODUCT (output), not a requirement. The requirements are CO2, water, sunlight, and chlorophyll.
Correction: Xylem carries water and minerals. PHLOEM carries food. Remember: Xylem = water UP, Phloem = food everywhere.
Correction: Stomata are mostly on the LOWER surface of leaves. This reduces water loss from direct sunlight.
| Concept | Key Points |
|---|---|
| Autotrophic Nutrition | Plants make their own food. "Auto" = self, "trophic" = nutrition. |
| Photosynthesis | CO2 + H2O + Sunlight + Chlorophyll = Glucose + O2 |
| Chlorophyll | Green pigment in chloroplasts. Captures sunlight energy for photosynthesis. |
| Stomata | Tiny pores on lower leaf surface. Allow gas exchange (CO2 in, O2 out) and transpiration. |
| Guard Cells | Bean-shaped cells around each stoma. Control opening and closing. |
| Xylem | Transports water and minerals upward from roots to leaves. |
| Phloem | Transports prepared food from leaves to all parts (both directions). |
| Transpiration | Loss of water vapour from leaves through stomata. Creates transpiration pull. |
| Translocation | Transport of food by phloem from leaves to other plant parts. |
| Respiration | Glucose + O2 = CO2 + H2O + Energy. Happens in all cells, day and night. |
| Day vs Night | Day: both photosynthesis + respiration (net O2 release). Night: only respiration (net CO2 release). |
| Activity | What It Proves | Key Observation |
|---|---|---|
| 10.1 Sunlight & Water | Both are essential for plant growth | Only pot with sun + water grows healthy; dark pot = etiolated; dry pot = wilts |
| 10.2 Iodine Test | Leaves contain starch (food) | Leaf turns blue-black with iodine = starch present |
| 10.3 Variegated Leaf | Chlorophyll is needed for photosynthesis | Only green parts turn blue-black; white parts = no starch |
| 10.4 NaOH / CO2 | CO2 is needed for photosynthesis | Leaf half with NaOH (no CO2) = no starch; exposed half = starch present |
| 10.5 Hydrilla Bubbles | Plants release O2 during photosynthesis | Bubbles from plant in sunlight; glowing matchstick relights |
| 10.6 Stomata Observation | Stomata exist on leaf surface | Bean-shaped guard cells with pore visible under microscope |
| 10.7 Coloured Water | Water travels upward through xylem | Coloured water rises through stem; cross-section shows coloured xylem dots |
| 10.8 Lime Water Test | Plants release CO2 during respiration | Lime water turns milky = CO2 is produced by germinating seeds |
6CO2 + 6H2O → C6H12O6 + 6O2
(Sunlight + Chlorophyll needed)
C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy
(Happens day and night)
Iodine + Starch = Blue-black colour. This is the standard test for photosynthesis.
CO2 + Lime water = Milky white. This confirms respiration releases CO2.
Photo (light) + Synthesis (combining). Making food using light.
Auto (self) + Troph (feeding). Organism that feeds itself.
Loss of water vapour from leaves through stomata.
Transport of prepared food from leaves to other parts via phloem.
Tiny pores on leaves for gas exchange. Singular: stoma.
Organelle in plant cells containing chlorophyll. Site of photosynthesis.
A plant that is pale, weak, and yellow because it was grown without sunlight.
Bean-shaped cells that surround and control the opening/closing of stomata.
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