Classification of Plants: Herbs, Shrubs, and Trees

Plants exhibit a vast variety in size, shape, colour, and structure. They exist all around us, from small green patches on the soil to towering trees. To understand this diversity, plants are often classified into different categories based on their characteristics, particularly the nature of their stem and branches.

Based on these characteristics, most plants can be classified into three main categories: herbs, shrubs, and trees. Two other categories, creepers and climbers, describe plants with weak stems.

---

Herbs

Herbs are plants with green and tender (soft) stems. They are typically short in height and may have few or no branches. Due to their non-woody stems, they are generally easy to bend.

Examples: Tomato, Mustard, Mint (Pudina), Coriander (Dhania).

---

Shrubs

Shrubs are medium-sized plants. Their key features include a hard stem that is not very thick. In shrubs, the branches typically arise from the base of the stem, giving them a bushy appearance.

Examples: Lemon, China Rose (Hibiscus), Jasmine.

---

Trees

Trees are tall and large plants. They are characterized by a hard and thick, woody stem known as the trunk. The branches on a tree typically grow from the upper part of the stem, much above the ground.

Examples: Mango, Neem, Banyan.

---

Creepers and Climbers

These categories include plants with weak stems that cannot stand upright on their own.

• Creepers: These plants spread out on the ground. Their stems are too weak to support their weight. Example: Pumpkin, Watermelon.
• Climbers: These plants take support from neighbouring structures (like walls, fences, or other plants) and climb up. Examples: Money plant, Grapevine, Bean Stalk.

---

Summary of Plant Categories

Plant Name	Stem Characteristics (Tender/Hard, Thick/Thin)	Where do branches appear?	Category
Tomato	Green, Tender	Few branches	Herb
Lemon	Hard, Not very thick	At the base of the stem	Shrub
Mango	Hard, Thick (Trunk)	Higher up on the stem	Tree

The Stem

The stem is the main axis of a plant that typically grows above the ground. It is a crucial part of the plant's shoot system. The stem bears various parts of the plant, including:

• Leaves
• Branches
• Buds
• Flowers
• Fruits

Stems provide structural support to the plant, holding the leaves up to the sunlight.

---

Function of the Stem: Conduction

One of the primary functions of the stem is to act as a transport system for the plant. It conducts water and minerals from the roots to the rest of the plant parts and transports food from the leaves to other parts.

Upward Movement of Water

The stem contains narrow tubes or vessels that act like straws, helping in the upward movement of water. An activity with a soft stem placed in coloured water demonstrates this function.

Observation: If a plant with a soft stem is placed in a glass of water mixed with red or blue ink, after some time, the colour rises in the stem. If left for a longer period, coloured lines (veins) appear in the leaves as well. An enlarged view of the cut stem shows small coloured dots, which are the ends of the tubes that carry water.

Conclusion: This activity shows that the stem conducts water and dissolved minerals upwards from the roots to the leaves and other parts of the plant.

Two-Way Transport System

The stem functions like a two-way street. It transports water and minerals up from the roots to the leaves, and it transports the food (prepared in the leaves) down to be stored in the roots, fruits, and other parts of the plant.

The Leaf

The leaf is a vital part of a plant, typically green, flat, and attached to the stem. It is the primary site for photosynthesis.

---

Parts of a Leaf

A typical leaf consists of two main parts:

• Petiole: The stalk-like part of the leaf that attaches it to the stem.
• Lamina: The broad, flat, green part of the leaf.

---

Leaf Venation

The design made by the lines on a leaf is called leaf venation. These lines are called veins, and the prominent line running through the middle of the leaf is the midrib. There are two main types of venation:

1. Reticulate Venation: In this type, the veins form a net-like or web-like pattern on both sides of the midrib. This is common in dicot plants like mango, rose, and peepal.
2. Parallel Venation: In this type, the veins run parallel to one another from the base to the tip of the leaf. This is common in monocot plants like grass, wheat, maize, and banana.

---

Functions of the Leaf

1. Transpiration

Transpiration is the process by which plants release excess water into the air in the form of water vapour. This process mainly occurs through tiny pores on the leaf surface called stomata.

Observation: If a leafy branch of a healthy plant is enclosed in a transparent polythene bag and left in the sun, after a few hours, tiny droplets of water appear on the inner surface of the bag. An empty bag kept alongside shows no such droplets.

Conclusion: This shows that leaves release water vapour, which then condenses on the cooler surface of the bag to form water droplets.

2. Photosynthesis

Photosynthesis is the process by which green leaves prepare food for the plant. The leaf uses water (supplied by the stem), carbon dioxide (from the air), and a green-coloured substance called chlorophyll in the presence of sunlight to make food (starch/sugar).

Equation:

$ \text{Carbon Dioxide} + \text{Water} \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} \text{Food (Starch)} + \text{Oxygen} $

Observation: An iodine test on a leaf that has been decolorized (by boiling in spirit) turns it blue-black. This confirms the presence of starch, which is the food prepared by the leaf.

The food prepared by the leaves is then transported through the stem and stored in different parts of the plant like roots, fruits, and seeds.

The Root

The root is the part of the plant that typically grows underground, in the soil. It is essential for the plant's survival and stability.

---

Functions of the Root

The roots perform two primary functions:

1. Anchoring the Plant: Roots help in holding the plant firmly to the soil. They act as an anchor, providing stability and preventing the plant from being uprooted by wind or water.
2. Absorption of Water and Minerals: Roots absorb water and essential minerals from the soil. These substances are then transported upwards to the rest of the plant through the stem.

An activity comparing a plant with roots to one without roots shows that the plant without roots wilts and dies, even if watered regularly. This demonstrates the crucial role of roots in absorbing water.

---

Types of Root Systems

Just like leaves and stems, roots also show variety. There are two main types of root systems:

1. Taproot System: This system consists of a main, thick primary root called the taproot, which grows straight down. Smaller, thinner roots, called lateral roots, branch out from this main root.
2. Fibrous Root System: This system does not have a main root. Instead, a cluster of thin, similar-sized roots grows from the base of the stem. It looks like a dense mat or bush of roots.

---

Relationship between Root Type and Leaf Venation

There is a very interesting and useful relationship between the type of root system a plant has and the type of venation in its leaves. This allows us to identify the root type of a plant simply by looking at its leaves.

• Plants with taproots usually have leaves with reticulate venation.
• Plants with fibrous roots usually have leaves with parallel venation.

Name of Plant	Type of leaf venation	Type of roots
Rose / Mango	Reticulate	Taproot
Wheat / Grass	Parallel	Fibrous

The Flower

The flower is the reproductive part of a plant. Flowers are often the most colourful and attractive part, playing a crucial role in producing seeds and fruits.

---

Parts of a Flower

A typical flower has four main parts or whorls, arranged in rings on the stalk.

1. Sepals

These are the small, green, leaf-like structures at the base of the flower. In the bud stage, the sepals enclose and protect the inner parts of the flower. They form the outermost whorl.

2. Petals

These are the usually bright and colourful parts of the flower, located inside the sepals. Their main function is to attract insects and birds for pollination. The number, colour, and shape of petals vary widely among different flowers.

3. Stamen (Male Reproductive Part)

The stamen is the male part of the flower. Each stamen consists of two parts:

• Anther: A sac-like structure at the tip of the stamen that produces and contains pollen grains.
• Filament: The thin stalk that supports the anther.

4. Pistil or Carpel (Female Reproductive Part)

The pistil is the innermost, female part of the flower. It consists of three parts:

• Stigma: The sticky tip at the top of the pistil, which receives the pollen grains.
• Style: The tube-like structure that connects the stigma to the ovary.
• Ovary: The swollen, lowermost part of the pistil. It contains small bead-like structures called ovules. After fertilization, the ovary develops into the fruit, and the ovules develop into seeds.

---

Structure of the Ovary

The internal structure of the ovary can be observed by cutting it either longitudinally (lengthwise) or transversely (cross-section). Inside the ovary, the ovules are visible as small, bead-like structures. These ovules contain the female egg cell and develop into seeds after fertilization.

---

Observations on Flowers

The structure of flowers is not always the same. The number, colour, and arrangement of sepals, petals, stamens, and pistils can vary greatly between different species. Some parts may even be absent in some flowers.

Flower Name	Rose	China Rose (Hibiscus)	Mustard
Number and colour of sepals	Many (Green)	5 (Green)	4 (Green)
Number and colour of petals	Many (Various)	5 (Red)	4 (Yellow)
Are sepals joined or separate?	Separate	Joined at base	Separate
Are petals joined or separate?	Separate	Separate	Separate
Stamens: free or joined?	Free	Joined (form a tube)	Free
Pistil: Present/Absent	Present	Present	Present

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer: