The Leaf: Students who want to understand everything about the leaf can check out the detailed explanation provided by Embibe experts. Plants have a crucial role in ecology. Plants are necessary for all life on earth, whether directly or indirectly. The leaf is the most important of all the components of a plant.
The two primary purposes of leaves are photosynthesis and transpiration. In some plants, leaves also bear the burden of reproduction.
Let us find out more about the morphology of leaves, their components, wide varieties, and their variations.
The Structure of a Leaf
The thin, flat structures called leaves are in charge of photosynthesis in plants. At the node, it develops laterally. It comes from shoot apical meristems and is a crucial component of the shoot system.
The following is a detailed description of a leaf’s structure:
Parts of a Leaf
Typically, the basic components of a leaf are the leaf base, petiole, and lamina.
The base of the leaf is where it joins to the stem. Stipules are two tiny, leaf-like structures at the base of leaves. This broad leaf base conceals the stem in monocotyledon plants like rice, wheat, and other species.
The petiole, which connects the leaf blade to the stem, is a long, thin stalk.
The leaf blade is another name for lamina. It is the leaf’s flat, emerald-green surface. It is made up of veinlets and a small branching vein. Midrib refers to the vein that runs down the centre of the lamina. The midrib splits the lamina’s surface into two. These veins and veinlets offer the leaf blade stiffness and help transport water and other substances.
The arrangement of veins and veinlets in leaves is known as venation. Different plants exhibit various venational patterns. There are typically two types of venation:
Reticulate venation: A reticulate venation is made up of a complicated network of veinlets that are randomly placed. A rose plant is an example of a dicotyledonous plant.
Parallel venation: In a parallel venation, the veinlets run parallel to each other. Ex: In monocotyledons like paddy.
Simple and compound leaves are divided into separate groups according to their size, shape, placement on the stem, whether they are on flowering or non-flowering plants, and a number of other physical characteristics.
A plant has two different kinds of leaves, which are as follows:
A leaf is referred to as simple when a petiole joins only one lamina and the main stem. A simple leaf can have any depth of incision, but the midrib or petiole cannot be reached. Example: Guava leaves
A leaf with two or more leaflets is referred to as a compound leaf. A single petiole connects the several leaflets that branch off from the midrib of a complex leaf. For example, Palm leaves, peas, etc.
The following leaf types are included within the category of compound leaves:
Palmately Compound Leaf
The leaflets of a palmately complex leaf are joined at the petiole’s tip like silk and cotton. These can be classified as follows:
Unifoliate: These types of leaves have one leaflet. Example Citrus
Bifoliate: These leaves have only two leaflets. Example Balanites
Trifoliate: These leaves contain three leaflets emerging from the same point. Example Oxalis
Quadrifoliate: These leaves contain four leaflets arising from the same point. Example Marsilea
Multifoliate: This type of leaf contains many leaflets arising at a common pint. Example Bombax
Pinnately Compound Leaf
In a pinnately complex leaf, the midrib is divided into several leaflets, each of which is attached to the other by a single axis. Like Neem. These can be further classified as follows:
Pinnate: A pinnate leaf is a complex leaf with an axis on each side of the midrib.
Unipinnate: A leaf that is unipinnate has leaflets on both sides of the axis, as in Cassia.
Bipinnate: In this case, the primary axis generates a secondary axis that bears the leaflet as in Acacia.
Tripinnate: Here, the secondary axis gives way to a tertiary axis that bears leaflets as in Moringa.
Decompound: A leaf with more than three pinnates is known as Decompound. Old coriander leaves, for instance
Parapinnate: A leaf that is parapinnate lacks a terminal leaflet as in Cassia
Imparipinnate: A leaflet at the terminal node is unusual. Example Pea
The term “Phyllotaxy” refers to the patterns of leaf arrangement on the stem. Plants display three different types of phyllotaxy: alternating, opposite, and whorled.
It is an alternative type of phyllotaxy when just one leaf grows alternately at each node.
Opposite phyllotaxy is the development of two leaves facing one another at each node.
Consider guava plants.
It is known as whorled phyllotaxy when more than two leaves grow at the nodes to produce a whorl of leaves. Consider Alstonia.
Modification of Leaves
We are aware that photosynthesis is a specialised task for leaves. They also provide other important functions, such as support, food storage, defence, etc. They have been altered into various shapes for each of these purposes.
For instance, pea tendrils, cactus spines, onion bulbs, insectivorous plant leaves, etc., are all examples of modified leaves. Let’s take a closer look at some of the leaf modifications:
The thick, succulent leaves of xerophytic plants and members of the Crassulaceae family store water in their tissues. These leaves’ parenchymatous cells have sizable vacuoles that are filled with hydrophilic colloids. The plant can withstand desiccation thanks to this alteration.
Plants with flimsy stems have leaf tendrils. Tendrils, which resemble threads, are created from the leaves. These tendrils sustain the plant by climbing a neighbouring pole or wall. Lathyrus aphaca, for instance, transforms the entire leaf into tendrils. Pisum sativum’s top leaflets change into tendrils.
Plants with Leaf Spines Some plants have changed their leaves to form spines that resemble needles. Spines serve as protective structures. Additionally, they reduce water loss because of transpiration. For instance, the leaves of Opuntia have been changed to become spines.
These have a brownish or colourless look and are thin membrane structures without stalks. They guard the nearby auxiliary bud in their axil. Onion scale leaves are meaty and substantial.
Some plants develop hook-like appendages on their terminal leaflets to aid them in climbing. Consider Bignonia unguiscati.
A few plants can transform one of the nodes’ leaves into adventitious roots, allowing them to float above the water, such as Salvinia.
In some plants, the petiole flattens out, becomes the form of a leaf, and turns green. This is known as Phyllode. Australian Acacia, for instance.
Few plants actually need nitrogen to grow. Such plants have modified leaves that can capture and consume insects. Below are a few of the modifications:
Leaf Pitcher: The leaf lamina is altered to resemble a pitcher in a few plants, such as Nepenthes. The bug is broken down inside the pitcher’s inner walls, which then release a digestive fluid into the pitcher’s interior chamber.
Leaf Bladder: The leaf segments are transformed into bladders on these plants. In water, several plants can be found. Digestive glands are present on the inner wall, which aid in breaking down the captured insect. Consider Utricularia.
In Drosera, the lamina is covered in many hairs, each of which has a gooey globule with digestive enzymes at the tip. When an insect perches on the lamina, the hair totally encases the bug.
The Functions of Leaves
The functions of the leaves are as follows:
Leaf function is mostly based on photosynthesis. They use the process of photosynthesis to turn carbon dioxide, water, and UV light into glucose.
Transpiration is the process by which plants release extra water into the atmosphere. The opening of the stomata found in the leaves causes this.
Guttation is the process of removing extra water from the xylem at the leaf’s margins when the stomata are closed.
Photosynthetic activity occurs on leaves. They do this by storing nutrients and water. The thick, succulent leaves are specially adapted to storing water.
Some leaves are modified into spines to protect them from being damaged or eaten by animals. Think of Opuntia.
The photosynthetic pigment chlorophyll is present in leaves located at the stem’s nodes.
The leaf base, leaf lamina, and petiole are the three major components of a leaf.
Simple leaves and compound leaves are the two distinct types of leaves. Accicular, linear, lanceolate, orbicular, elliptical, oblique, central cordate, etc., are some of the additional leaf types.
They assist in removing extra water from the plant’s aerial sections and carry out the process of photosynthesis.
They have been modified to include scales, tendrils, hooks, and spines, which help their ability to adapt to different habitats.
FAQs on the Leaf
Check out some of the frequently asked questions on the leaf.
Q.1 What do you mean when you refer to a leaf’s morphology?
Ans: Science’s study of morphology is concerned with an organism’s shape and structure. The study of a leaf’s structural elements and components is known as morphology.
Q.2 What varieties of leaves are there?
Ans: Simple and compound leaves are the two different types of leaves. Simple leaves do not form discrete leaflets; they are lobed or split. In contrast, a complex leaf has distinct leaflets that are separated by a small petiole.
Q.3 What role do leaves play that is most crucial?
Ans: The primary activity carried out by leaves is photosynthesis. They produce glucose and energy by converting carbon dioxide, water, and sunshine.
Q.4 What significance do the leaf veins have?
Ans: Xylem and phloem, two types of vascular tissues, line the veins in the leaves. Phloem carries food via the leaf to the rest of the plant, whereas xylem moves water from the roots to the leaves.
Q.5 Why are leaves such a crucial component of plants?
Ans: The primary catalyst for photosynthesis, the mechanism by which plants sustain themselves, is leaves. Additionally, they aid in getting food and water to various areas of the plant. They so significantly contribute to a plant’s ability to survive. Additionally, they aid in the exchange of gases through the opening and closing of stomata and assist the plant in evaporating extra water through transpiration.
Q.6 What is Wilting?
Ans: Wilting is when a plant’s leaves dry out, wilt, and droop as a result of a lack of water, excessive transpiration, or vascular disease.
Q.7 What different modifications have leaves undergone?
Ans: Spines that decrease water loss and serve as a defence can be added to leaves. Some are altered to become tendrils to sustain the plant. Some leaves are thick, which aids in the storage of water. Some have been altered to capture and consume insects.
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