Chapter 2: Plants: Structure and Function - Notes

🌱 Chapter 2: Plants: Structure and Function

Subject: General Science
Class: 7th Standard (Maharashtra Board)

🔹 1. Introduction

• Plants are the foundation of life on Earth.
• They provide us with:
• Food – fruits, vegetables, grains, pulses
• Oxygen – essential for breathing
• Medicine – many plants are used in Ayurveda and modern medicine
• Wood and Shelter – for houses, furniture, tools
• Fuel – firewood, biofuels
• To truly understand their role in sustaining life, we must study the structure and function of different plant parts.

 

🔹 2. Main Parts of a Plant

Plants are mainly divided into two systems:

1. Root System 🌱
• The part of the plant that grows below the ground.
• Includes the roots, which anchor the plant and absorb water and minerals.
2. Shoot System 🌿
• The part of the plant that grows above the ground.
• Includes the stem, leaves, flowers, fruits, and seeds.
• This system helps in support, food preparation, reproduction, and transport.

🔹 3. Root

The root is the underground part of the plant. It usually grows downward into the soil and has no nodes, internodes, or buds. Roots are very important because they support the plant and supply it with water and minerals.

 

(A) Types of Roots

1. Tap Root System
• Found in dicot plants (plants with two cotyledons in their seed).
• Has one main primary root that grows vertically deep into the soil.
• Secondary roots (side branches) grow from the main root.
• Such roots help the plant to stand firmly and reach deep water.
• Examples: pea, mango, carrot, mustard.
2. Fibrous Root System
• Found in monocot plants (plants with one cotyledon in their seed).
• Has many thin roots of almost equal size.
• These roots grow from the base of the stem and spread out like a bunch.
• They are shallow but spread widely, holding the soil tightly.
• Examples: wheat, rice, onion, grass.

 

(B) Functions of Roots

1. Absorption
• Roots absorb water and minerals from the soil through their tiny root hairs.
• This is essential for photosynthesis and plant growth.
2. Anchorage
• Roots fix the plant firmly in the soil.
• Prevent the plant from being blown away by wind or washed away by water.
3. Storage of Food
• In some plants, roots are modified to store extra food.
• Examples: carrot, radish, beetroot, sweet potato, turnip.
4. Special Functions of Roots
• Some roots are modified to perform special tasks:
• Respiratory Roots (Pneumatophores): Found in mangroves, these roots grow above the soil to take in oxygen in swampy areas.
• Prop Roots: In banyan trees, thick roots grow from branches and provide extra support.
• Climbing Roots: In money plant and betel, roots help the plant climb surfaces.
• Epiphytic Roots: In orchids, roots absorb moisture from the air.

🔹 4. Stem 

(A) Structure of Stem

• Main Axis of Plant Body → The stem is the main axis of the shoot system.
• Bears Plant Parts → It bears branches, leaves, flowers, and fruits.
• Nodes and Internodes →
• Nodes – Points on the stem where leaves/branches arise.
• Internodes – Distance between two nodes.
• Vascular Tissues →
• Xylem – Conducts water and minerals from roots to leaves.
• Phloem – Conducts prepared food from leaves to other plant parts.
• Buds →
• Apical bud – Present at the tip, helps in length growth.
• Axillary bud – Present in the axil of a leaf, gives rise to branches/flowers.

 

(B) Functions of Stem

1. Support
• Provides support to leaves, flowers, and fruits.
• Keeps them in proper position for photosynthesis, pollination, and fruiting.
2. Conduction of Substances
• Xylem → Conducts water and minerals from roots to leaves.
• Phloem → Conducts prepared food (from leaves) to different parts of the plant.
3. Storage of Food
• Some stems store food materials → e.g., Potato (tuber), Onion (bulb), Ginger (rhizome).
4. Climbing / Support in Creepers
• Modified stems help plants to climb or spread → e.g., Money plant, Grapevine.
5. Vegetative Propagation
• Many plants can reproduce from stem parts → e.g., Potato, Sugarcane, Rose.

🔹 5. Leaf

(A) Structure of Leaf

1. Petiole
• The stalk that attaches the leaf to the stem.
• Supports the leaf and supplies water & food through vascular tissues.
2. Lamina (Leaf Blade)
• The flat, broad, green surface of the leaf.
• Performs photosynthesis and transpiration.
• Shows different shapes and sizes in different plants.
3. Midrib and Veins
• Midrib → The thick central vein running through the lamina.
• Veins → Smaller branches arising from the midrib.
• Functions:
• Provide support to lamina.
• Transport water and minerals (through xylem).
• Transport prepared food (through phloem).
4. Leaf Arrangement
• Arises at nodes of stem in different patterns → alternate, opposite, whorled.

 

(B) Functions of Leaf

1. Photosynthesis (Food Preparation)
• Green leaves prepare food with the help of:
• Sunlight
• Carbon dioxide (from air)
• Water (from soil)
• Chlorophyll (green pigment)
• Produces Glucose (food) and releases Oxygen.
• Hence, leaf is called the “food factory of the plant”.
2. Respiration
• Exchange of gases (O₂ & CO₂) takes place through stomata.
• Oxygen is used for breakdown of food, and carbon dioxide is released.
3. Transpiration
• Excess water is lost in the form of water vapour through stomata.
• Helps in cooling the plant and absorption of minerals.
4. Storage / Modification (in some plants)
• In plants like Onion, Aloe vera, Bryophyllum, leaves also store food or help in vegetative propagation.

 

🔹 6. Flower

(A) Parts of a Flower

1. Sepals (Calyx)
• Small green leaf-like structures.
• Protect the flower when it is in bud stage.
2. Petals (Corolla)
• Brightly coloured and scented.
• Attract insects, birds, and other agents for pollination.
3. Stamens (Androecium – Male Part)
• Each stamen has:
• Anther → Produces pollen grains (male gametes).
• Filament → Thin stalk that supports the anther.
4. Carpel / Pistil (Gynoecium – Female Part)
• Central part of the flower.
• Consists of:
• Stigma → Sticky surface; receives pollen grains.
• Style → Tube-like structure; connects stigma to ovary.
• Ovary → Contains ovules (female gametes).

 

(B) Functions of Flower

1. Pollination (Transfer of Pollen Grains)
• Self-Pollination → Pollen grains from anther reach stigma of the same flower or same plant.
• Cross-Pollination → Pollen grains transferred to stigma of a different plant of the same species (by insects, wind, water, birds).
2. Fertilization
• Pollen grain reaches ovule through pollen tube.
• Male gamete unites with female gamete (ovum).
• This forms a zygote → seed → fruit.
3. Reproduction
• Flowers are the reproductive organs of plants.
• Ensure continuation of species by forming seeds and fruits.

🔹 7. Fruit and Seed

(A) Fruit

• Formation → Fruit is formed from the ovary of the flower after fertilization.
• Role → Protects the seeds and helps in their dispersal.
• Examples → Mango, Tomato, Pea, Apple, Orange, etc.
• Types (basic idea for students):
• Fleshy fruits → Mango, Tomato.
• Dry fruits → Pea, Groundnut.

 

(B) Seed

• Formed → After fertilization, the ovule develops into a seed.
• Parts of a Seed:

1. Seed Coat
• Hard outer protective covering.
• Protects seed from injury, dryness, and infection.
2. Cotyledons
• Also called “seed leaves.”
• Store food for the developing embryo.
• Number of cotyledons:
• Dicot seeds (two cotyledons) → e.g., Pea, Groundnut.
• Monocot seeds (one cotyledon) → e.g., Maize, Wheat.
3. Embryo
• The small baby plant present inside the seed.
• Has two parts:
• Radicle → Develops into the root.
• Plumule → Develops into the shoot.
• Under suitable conditions (water, air, warmth), the embryo grows into a new plant (germination).

 

🔹 8. Transportation in Plants

Plants need to transport water, minerals, and food to all their parts for survival and growth. This work is done by special tissues.

 

(A) Xylem 🚰

• Function: Carries water and minerals absorbed by roots to the stem, leaves, flowers, and fruits.
• Direction: Transport is only upward (from roots to aerial parts).
• Structure: Made of vessels and tracheids (hollow tube-like cells).
• Importance: Provides support along with conduction.

 

(B) Phloem 🍃

• Function: Transports prepared food (glucose and other nutrients) from leaves to other parts of the plant.
• Direction: Transport is both upward and downward as per requirement.
• Structure: Made of sieve tubes and companion cells.
• Importance: Supplies energy for growth, storage, and reproduction.

 

(C) Key Point

• Xylem = Upward transport of water & minerals.
• Phloem = Two-way transport of food.

 

 
🔹 9. Activities / Demonstrations

Practical activities make the concepts of plant structure and function clear to students.

(A) Comparison of Root Systems 🌱

• Take a pea plant (tap root system) and a grass plant (fibrous root system).
• Wash the roots carefully and observe.
• Observation:
• Pea → One main root with side branches (tap root).
• Grass → Many roots of equal size forming a cluster (fibrous root).

(B) Storage Stem 

• Show examples of potato, onion, ginger.
• Cut them to show stored food inside.
• Explain: These are stems modified to store food.

---

(C) Iodine Test for Starch Formation in Leaf 🍃

• Keep a potted plant in dark for 1–2 days (to remove starch).
• Then keep it in sunlight for few hours.
• Pluck one leaf, boil it in water, then in alcohol to remove green colour.
• Add iodine solution.
• Observation: Blue-black colour appears → proves starch formation by photosynthesis.

(D) Parts of a Flower 🌸

• Bring different flowers (e.g., hibiscus, pea, marigold).
• Ask students to identify:
• Sepals (green, outermost)
• Petals (coloured, attractive)
• Stamens (anther + filament)
• Carpel/Pistil (stigma, style, ovary)

 

🔹 10. Evaluation Questions

1. Write differences between Tap Root and Fibrous Root.

Tap Root	Fibrous Root
One main root grows deep into the soil with side branches.	Many roots of equal size arise in a cluster near the base of the stem.
Example: Pea, Mango, Carrot.	Example: Wheat, Grass, Onion.

---

2. List the raw materials required for photosynthesis.
• Sunlight
• Chlorophyll (green pigment in leaves)
• Carbon dioxide (from air)
• Water (from soil)

3. Explain the function of xylem and phloem.
• Xylem → Transports water and minerals from roots to other parts of the plant (upward).
• Phloem → Transports prepared food from leaves to other parts of the plant (both upward and downward).

4. Name and explain the parts of a seed.
• Seed Coat → Outer protective covering.
• Cotyledons → Seed leaves, store food.
• Embryo → Baby plant inside the seed, which develops into a new plant.

5. What are the types of pollination?
• Self-Pollination → Pollen grains from anther fall on stigma of the same flower or same plant.
• Cross-Pollination → Pollen grains from anther of one flower are transferred to stigma of a different flower of the same species (by wind, water, insects, birds).

 

🔹 11. Homework

1. Diagram Work
• Draw a neat, labelled diagram of a plant.
• Label the parts (Root, Stem, Leaf, Flower, Fruit, Seed).
• Write one main function of each part.
2. Short Note
   “Can animals survive without plants?”
• No, animals cannot survive without plants.
• Plants provide oxygen for respiration, food directly or indirectly, and shelter.
• They also maintain ecological balance.
• Thus, plants are essential for the survival of all living beings.

🔹 12. Conclusion

• Each part of the plant performs special and important functions:
• Roots absorb water and minerals and give support.
• Stem transports water, minerals, and food, and provides support.
• Leaves prepare food by photosynthesis and help in respiration and transpiration.
• Flowers are reproductive organs and produce fruits and seeds.
• By studying plant structure and functions, we understand the importance of plants and the interdependence of life on Earth.