The Anatomy of Plants: Understanding Their Structure and Function

There are 4 basic parts of plants: 

Leaf 

A leaf is a broad green outgrowth of the stem of vascular plants. Leaves come in a variety of shapes, sizes, venation, and colors. 

The function of the leaf: 

Leaves are a crucial part of plants. Leaves perform functions that are essential for the growth and reproduction of plants. 

1. Leaves are responsible for capturing sunlight
2. Leaves change this solar energy bracket sunlight  into mechanical energy In a process called photosynthesis
3.  Leaves prepare food for whole plants through the process of photosynthesis during the daytime.
4.  Gaseous exchange occurs through leaves.  They give off oxygen into the air and absorb carbon dioxide from the air.  This carbon dioxide is necessary for the process of photosynthesis. 
5.  Leaves also perform the process of transpiration and guttation. 

Leaf Structure: 

It has three parts, namely, the petiole, leaf base, and lamina or leaf blade. The leaf base is the portion where the petiole is attached to the leaf blade. Petiole is a stalk that connects the leaf blade to the stem. The leaf blade has a central vein called a midrib and smaller veins in various patterns that support the leaf and transport nutrients to it. 

Leaf Histology:  

The main tissues of a leaf include the dermal, ground, and vascular tissue systems. 

• Dermal system: 

Epidermis: The outermost layer of cells is the epidermis which may also secret the waxy cuticle layer. It has stomata through which gaseous exchange occurs. The upper surface of the leaf is called the adaxial surface whereas the other surface is called the abaxial surface. 

• Ground system: 

Mesophyll cells make the ground system. Mesophyll may be homogeneous or it may be differentiated into spongy parenchyma and palisade parenchyma. 

• Vascular system: 

The vascular system is present throughout the leaf blade. It forms a central thick midrib or midvein. The pattern of veins on the leaves is called venation. This system transports nutrients to plants and supports them. 

Stem: 

Function:

1. Stems Transport food from leaves to the other part of the plant and water from roots to the aerial parts of the plants.
2. Stem provides mechanical support to the plant And helps the plants stay upright
3. Underground stems help plants tide over unfavorable conditions of growth, help in vegetative propagation and help plants cover large surface area. 

Structure: 

Stem is usually a green, upright part of the plant that gives support to it. It consists of parenchyma cells but collenchyma and sclerenchyma cells are also present in it. Dicot stems are generally solid and have vascular bundles arranged in a ring shape. Monocots have scattered vascular bundles. 

Anatomy:

Stem too, just like leaves, is composed of three tissues i.e. dermal, vascular, and ground tissues. 

• Dermal tissues 

Epidermis is the outer layer surrounding the stem which has epidermal cells with cutin impregmentation of cell walls. It is bounded by a cuticle as the outer thin layer to reduce transpiration. 

The next layer is the Cortex which makes the ground tissues. Typically, it is composed of parenchyma cells and large intracellular spaces among them. 

Endodermis is usually the inner layer of the cortex. Pericycle is usually one or more cells thick layer between endodermis and vascular bundles

• Vascular tissues 

1. Primary Vascular Tissues comprising Primary Phloem and  primary Xylem 
2. Secondary Vascular Tissues comprising the secondary xylem and secondary phloem

Pith 

Pith is the center of the axis made up of parenchymatous cells which are often lignified. 

• Ground tissues

Pith and cortex make the ground tissues. 

Roots: 

The underground portion of the plant this called root. 

 Function

1. Roots help plants hold firmly to the ground
2. roots absorb water and nutrients from the ground and transport them to the aerial parts of the plant.
3. Roads may also store food and nutrients

Root anatomy:

A root cap is present at the tip of the root which protects its apical meristem and also helps in penetration into the soil.  

The Epidermis of the root is also termed as the Piliferous layer which is thin-walled and has no cuticle. Root hairs are the projections or outgrowths of the epidermal cells which absorb water and minerals.  The cortex is present inner to the epidermis and is composed of parenchyma cells. 

Then comes the endodermis layer. 

Stele; has the following layers

• Pericycle is made of parenchyma cells. 
• The vascular bundle is present in the central position in the roots. 
• Conjunctive tissue (parenchymatous) 
• Pith present in young stems only

Flower: 

Flowers are the reproductive part of a plant that performs significant roles.

Function

1. Flowers are vibrant so they are used to attract pollinators. 
2. Add to the beauty of the plant. 
3. Reproductive part of the plant
4. Contain nectar for insects and birds
5. Their ovary is converted into fruit 

Flower anatomy:

Flower has 4 main whorls, namely, 

1. Calyx 
2. Corolla
3. Androecium
4. Gynoecium  

Calyx is the outermost whorl composed of green sepals. Next whorl is the Corolla, which is composed of colorful petals then comes the reproductive whorls androecium (male reproductive part; stamens) and gynoecium (female reproductive part; carpels). Stamens have a long filament attached to an anther in which pollen grains are formed. The Carpel has 3 parts i.e. Style, stigma, and ovary. Ovary has ovules in it. Later, the ovary is converted into fruit after fertilization.