Plant Cell Definition
Any cell of a plant is called a plant cell. The plant cell act as a structural and functional unit for all plants. The green algae are considered as earliest plant cell that first occurred in the early Palaeozoic era. An English natural philosopher, Robert Hooke first discovered the plant cell under the microscope.
Hooke observed some pores that resembled a honeycomb and named them “cell”. They were thought empty cells by Hooke in earlier days but the discovery of advanced microscopes make it easy to observe these cells.
Later, the living components of plant cells were observed by scientists. The plant cell is bounded by a selectively permeable membrane, called the plasma membrane. The cell is filled with the fluid-like component names cytoplasm.
Plant Cells vs Animal Cells
A cell is classified into two types: Prokaryotic cell and eukaryotic cell. The eukaryotic cell consists of plant cells and animal cells whereas prokaryotic cells are found in bacteria and archae. Eukaryotic cells have a well-defined nucleus and membrane-bound cytoplasmic organelles that are absent in prokaryotes.
The plant cell differs from the animal cell in some structural properties. A rigid cell wall is present in the outermost layer of a plant cell that is not found in an animal cell. The plant cell has a large central vacuole that occupies much space whereas in the animal cell the size of the vacuole is much smaller and numerous.
The plant cell consists of a green-colored photosynthetic pigment called chlorophyll that is absent in animals. The presence of chlorophyll enables the plant cell to make their food by the process of photosynthesis in presence of sunlight. The animal cell cannot perform photosynthesis and get their food from plants.
Plant Cell Structure
A typical plant cell consists of various cellular organelles and cytoplasmic structures embedded in the cytoplasm of the cell and covered by the cell membrane and cell wall. The cellular organelles in plant cells consist of plastids, nucleus, mitochondria, endoplasmic reticulum, and Golgi apparatus.
The nucleus is called the control house of the cell is modulates all the metabolic activities in the cell. The genetic material is also present in the nucleus; however, the semi-autonomous organelles such as mitochondria and chloroplast also have the genetic material.
Plant Cell Labelled Digram
The chemical energy, e.g. ATP is synthesized in the mitochondria and the chloroplast contains chlorophyll that plays a significant role in photosynthesis. The chloroplast uses light energy and converts inorganic substances such as CO2, water into complex organic molecules.
Some other plastids like chromoplast and leucoplast. Chromoplasts are involved in photosynthesis as accessory pigments and the leucoplast contains stored food. The cellular functions require proteins that are synthesized by the endoplasmic reticulum along with the ribosome.
These proteins are transported to the Golgi apparatus where they are packaged and transported to various intracellular and extracellular parts. The cytoskeleton is also present throughout the cytoplasm and provides a definite shape to the cell.
The cytoskeleton consists of three types of cells that are microtubules, microfilaments, and intermediate filaments. Lysosomes are involved with the digestion of wastes material of the cell. All these cytoplasmic organelles are suspended in the fluid called cytosol.
The vacuole also plays an important role in osmoregulation. The cell is covered by a selectively permeable membrane called the plasma membrane. In-plant cell, the cell membrane is covered by a rigid cell wall that provides strength, mechanical support, and turgidity to the cell. The cell wall is mainly composed of cellulose, however, the secondary cell wall is made up of lignin.
There are several cells present in a plant that form plant tissues and organs that perform particular functions. Based on the structure and functions, plant cells are classified into different types. The common cell types include- Meristematic cells, Parenchyma cells, Collenchyma cells, Sclerenchyma cells, Reproductive cells.
i. Meristematic cells: The cells of meristem are called meristematic cells. These cells can divide and give rise to any plant cell type therefore they are also called stem cells of a plant.
ii. Parenchyma Cells: These cells form the parenchyma tissues. They do not have secondary cell wall deposition and therefore have thin walls. The main functions of parenchyma cells are photosynthesis, food storage, phloem loading, and secretion.
The parenchyma cells are the most common cell type and are found in the vascular bundles, leaves, and epidermis of the plant. Some common examples of parenchyma cells are guard cells, chlorenchyma cells (involved in photosynthesis).
iii. Collenchyma Cells: Collenchyma tissues are made of collenchyma cells. They also do not have a secondary cell wall, therefore, remain alive at maturity. The parenchyma cells have thin walls whereas the thickening of walls is irregular in collenchyma cells. The growing shoots and leaves are made up of collenchyma cells.
iv. Sclerenchyma Cells: Sclerenchyma cells from sclerenchyma tissues. The cell wall of the sclerenchyma cell is composed of secondary tissues and lignin composition therefore it has thick cell walls. At maturity, these cells remain dead and lose their protoplast. They are found in sclerenchyma fibres, sclereids, and bast fibers.
v. Reproductive Cells: Most of the plants complete their life cycle in two generations. The generation is followed alternatively and called “alteration of the generation”. The sporophyte generation produces spores in sporangia that are in haploid condition. The gametophyte is produced by haploid spores or reproductive cells.
A gametophyte is a haploid cell and bears gametangia that produce gametes. These gametes are involved in sexual reproduction and are called reproductive cells. The plant consists of two types of sex cells that are male sex cells (sperm) and female sex cells (egg cells).
Biological Importance of Plant Cell
Plants are the most important part of the ecosystem. They are the primary producers in the food chain and autotrophic organisms. They can synthesize organic molecules by photosynthesis therefore heterotrophic organisms also depend on plants for nutrition.
Some of the plant cells are also important commercially, For example- Fibers are collected and used to prepare different products. Example- Hemp, flax, jute, ramie, etc.