Introduction
Plants are one of the most important living organisms on earth. They have huge benefits for both humans and animals. A plant is made up of numerous parts. Distinct parts serve different purposes. The shoot system refers to the portion of the plant that protrudes above ground level, whereas the root system refers to the portion buried beneath the soil.
The essential parts of a plant are:
- Roots
- Stem
- Leaves
- Flowers
- Fruits
The study of plant organ tissue and cellular structure is known as plant anatomy. Cells serve as the fundamental building block of plants. Cells are organised into tissues, which are then organised into organs. Plant organs differ from one another in terms of their internal structure. The monocots and dicots are also observed to have diverse anatomical structures within angiosperms. Internal structures also exhibit environmental adaptations.
Table of Contents
Anatomy of Root
All vascular plants have important structures called roots. A root system is the collective unit of a plant’s roots. Most vascular plants have two types of roots: primary roots that develop downward and secondary roots that branch out to the sides.
Root Systems
Plants have two types of root systems: taproot systems and fibrous root systems.
Tap Root System
A taproot’s main central root is surrounded by a network of smaller, lateral roots known as root hairs. The taproot might penetrate as many as 60 metres (almost 200 feet) underneath the ground surface. It can access extremely deep water sources and store a large amount of food to assist the plant in withstanding drought and other environmental conditions. Additionally, the plant’s taproot firmly secures it in the soil. Examples of taproot systems include mustard, beetroot, carrot, china rose, parsley, china rose, and dicotyledons.
Fibrous Root System
On the other hand, fibrous roots are branched, bushy roots that originate from the stem and have thin, moderately branched roots. Though fibrous roots bind the plant less firmly, the large number of threadlike roots improves the surface area for water absorption and minerals. The fibrous root system is present in many plants, including monocotyledons, rice, maize, wheat, marigolds, and bananas.
Types of Roots
With almost 2,000 000 species, angiosperms are the most varied group of plants. Herbs, shrubs, and trees that reproduce sexually through seeds fall under this category. Angiosperms can be classified as monocot or dicot plants, depending on how many cotyledons are present in the seed. The plants that grow from monocotyledonous seeds and those that grow from dicotyledonous seeds differ significantly from one another.
Dicotyledonous Root
- Taproot systems are seen in dicot plants.
- Epidermis is the topmost layer. Epidermal cells can occasionally protrude, appearing as root hairs.
- Endodermis, or the inner layer of the cortex, is densely populated with barrel-shaped cells.
- Following the epidermis is the multilayered cortex, which is loosely formed of parenchyma cells with intercellular gaps.
- Phloem and xylem range from two to four.
- Conjunctive tissue is a layer of parenchymatous cells surrounding the xylem and phloem.
- The pericycle, consisting of several layers of thick-walled parenchyma cells, comes after the endodermis.
- Dicots lack a clear central pith.
- The cambium separates the xylem and phloem during secondary growth. The pericycle, vascular bundles, and pith merge in dicots to form the stele.
Monocotyledonous Root
The monocot root and dicot root have many similar characteristics in terms of anatomy.
- Monocot plants have a lateral root system.
- The epidermis is the uppermost layer, like in dicots, followed by the cortex, pericycle, endodermis, vascular bundles (xylem and phloem), and pith (random order).
- A prominent and noticeable pith is present.
- Six or more xylem bundles are present in monocots.
- The monocot plants do not exhibit secondary growth.
Transformation of Roots
- Roots are modified for storage, nitrogen fixation, aeration, and support.
- The taproot of carrot, turnip and sweet potato expands to store food.
- As Rhizophora thrives in swampy environments, it has pneumatophores, which help obtain oxygen for breathing.
Anatomy of Stem
Stems are the parts of vascular plants that hold plants upright so they may receive the necessary sunshine and air. The stems can also produce cones, flowers, leaves, and secondary stalks. Node points are where secondary stems grow. A meristem tissue bud at each node can divide and specialise in developing a specific structure.
Plants cannot survive in the air high above the ground without a connection between the roots and the leaves. Transporting food from leaves to the rest of the plant and water and minerals from roots to leaves are two other essential functions performed by stems. Stems of many plants can also serve as winter or summer-time food or water reserves.
Dicotyledonous Stem
The dicotyledonous stem is generally solid. The following parts make up the transverse section of a typical young dicotyledonous stem:
- The epidermis, protected by a thin cuticle layer, is the outermost layer.
- Trichoid and a few stomata are present in the epidermis.
- The epidermis and pericycle are sandwiched by the multilayered cells that make up the cortex.
- The parenchyma, collenchyma, and sclerenchyma cells of the stem are three basic cell types in charge of metabolism, wound healing, and starch storage.
- The pericycle, made up of semilunar patches of sclerenchyma, is located next to the endodermis.
- Only dicot stems have vascular bundles arranged in a “circle” or “ring.”
- Pith is apparent and is made of parenchymatous cells.
Monocotyledonous Stem
The monocot stem has a sclerenchymatous hypodermis, scattered vascular bundles encased in sclerenchymatous bundle sheaths, and a large, visible parenchymatous ground tissue. Vascular bundles are joined and closed. Vascular bundles at the periphery are usually smaller than those in the centre. Water-containing cavities can be found inside the vascular bundles, but the phloem parenchyma is absent.
Transformation of Stems
- Rhizome: Rhizomes are non-green and have identifiable internodes and nodes. They are brown in colour. For example, ginger.
- Climbers: Tendrils are modified stems that resemble leafless, threadlike structures. They are designed for climbing. For example, Passiflora.
- Tuber: A tuber is a fleshy component of the plant that stores food. For example, potato.
- Bulb: The bulb might be tunicated. The tunicate bulb was shielded by a layer of dry membranous scale leaves. For example, onion.
- Stolon: They first develop in an airborne state for a while before bending to the earth. The stem’s base is where the stolon emerges. For example, Jasmine.
Anatomy of Leaf
Plant leaves produce nourishment for plant and animal life, which helps to sustain life on earth. In plants, photosynthesis takes place on the leaf. Producing food in the form of sugars through photosynthesis involves utilising the energy from sunshine.
Plants rely on their leaves to function as leading food chains’ primary producers. In addition to producing food, leaves also contribute significantly to the carbon and oxygen cycle in the environment by producing oxygen during photosynthesis. In addition to stems and flowers, leaves are a part of the plant’s shoot system.
Leaves can have various shapes and sizes. The blade, petiole, and stipules are the three primary parts of the leaves of flowering plants (angiosperms). The epidermis, the mesophyll, and the vascular tissue are the three primary tissues of leaves. Layers of cells make up each form of tissue.
Some plants have additional, highly specialised functions in addition to photosynthesis. Examples include plants that can “eat” insects and are carnivorous. Some creatures, such as the Indian Leafwing Butterfly, imitate leaves to hide from predators.
Dorsiventral or Dicotyledonous Leaf
- The epidermis, mesophyll, and vascular system can be seen in the vertical section through the lamina of a dorsiventral leaf.
- A noticeable cuticle on the epidermis covers the leaf’s upper (adaxial epidermis) and lower (abaxial epidermis) surfaces.
- The term “mesophyll” refers to the tissue that lies between the top and lower epidermis. Parenchyma makes up the chloroplast-containing mesophyll, which performs photosynthesis.
- Vascular bundles, visible in the veins and the midrib, are part of the vascular system. The size of the veins affects the size of the vascular bundles.
- Dicot leaves have reticulate venation, which has veins of varying thicknesses. A layer of densely packed bundle sheath cells encircles the vascular bundles.
Isobilateral or Monocotyledonous Leaf
In many ways, the anatomy of the isobilateral leaf resembles that of the dorsiventral leaf. It displays the following characteristic variations:
- Both the adaxial and abaxial epidermis have stomata.
- The mesophyll lacks a defined palisade and spongy parenchyma.
- There are bulliform cells, which are a development of adaxial epidermal cells and veins.
- Large, empty cells called bulliform cells cause leaves to curl to prevent excessive water loss.
Transformation of Leaf
In some plant species, such as peas, leaves are modified to serve additional purposes. For example, in cacti, leaves are transformed into spines for defence.
Related Links:
- Parts of Plants
- Modifications of Stem
- MCQs on Plant Anatomy
- MCQs on Internal Structure of Root Stem and Leaf
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