The cell of photosynthesis (Plant cell)- Erakina

The plant cell is the simplest, organizational unit of any plant. It is distinct from all other living cells due to the presence of certain characteristic features.

Plants and their basic features

All plants are eukaryotic, multicellular organisms. Plants are present ubiquitously, in a multitude of habitats. They can be categorised based on the following characteristics-

• Presence of a well-differentiated root and shoot system.
• Presence of a well-developed vascular system.
• Production of covered seeds.
• Seed production is further characterised by the presence of one or two cotyledons. 

Plants are responsible for the production of oxygen through the process of photosynthesis which makes them essential supporters of all life forms on earth. Plants are also responsible for the circulation of water and the prevention of soil erosion. A vast majority of natural resources which are obtained from plants are as follows-

• Food in the form of fruits, vegetables and cereals.
• Medicines are extracted from the shoots, leaves and flowers of various plants.
• Wood is required for the building of urban and rural structures.
• Oxygen is the main driving force behind all life forms on earth.

The resources and services that plants provide us with are invaluable. Apart from the feature of immobility which makes plants distinct from animals, they also possess a variety of microscopic, cellular features which make them distinct from other life forms.

The plant cell: An overview

Plant cells are eukaryotic and are characterised by the presence of membrane-bound organelles and a well-defined nucleus. Apart from these two commonalities, the following organelles are found in both plant and animal cells-

Nucleolus and the nucleus

• Ribosomes 
• Smooth and rough endoplasmic reticulum.
• Golgi apparatus
• Vesicles 
• Vacuoles 
• Mitochondria 
• Lysosome 

Centrioles which are part of the centrosomes of animal cells are absent in plant cells. Some of the distinct features of plant cells are as follows-

• • Presence of a cell wall. The plant cell wall is usually composed of cellulose and pectin and provides structural integrity to the cell.
  • Plant cells possess large vacuoles which are rarely seen in animal cells. Vacuoles act as storage organelles that store cell sap, oils and pigments. Vacuoles also store water which in turn maintains the turgor pressure of the cell. 
  • All plant cells are characterised by the presence of plastids. These are membrane-bound organelles that store pigments. Chloroplasts are those plastids that store the pigment chlorophyll which is essential for the process of photosynthesis.

Functional organisation of a plant cell

A plant cell is complex in nature and its structure and function go hand in hand. The functions of various plant cell organelles are as follows-

• The plant cytoskeleton is composed of microtubules and intermediate filaments. These cytoskeletal structures provide the plant cell with structural integrity and enable the transportation of cellular substances. 
• Plasmodesmata are cellular channels that are responsible for the transportation of proteins and nucleic acids within the cell. These channels also work in cooperation with phloem vessels for the transportation of nutrients. 
• Mitochondria is responsible for energy production and is hence known as the powerhouse of the cell. This is where metabolism takes place via the Kreb’s cycle which is also known as the Tricarboxylic cycle (TCA). 
• The rough endoplasmic reticulum is covered by ribosomes which are responsible for the translation of proteins. The RER is also responsible for the assembly of proteins for proper utilization within the cell.
• The smooth endoplasmic reticulum is responsible for the synthesis of lipids and cell membranes. It is also responsible for the storage of carbohydrates.
• Inert organelles called storage granules are present in plant cells and are primarily responsible for the storage of starch granules. They are also responsible for the instigation of various metabolic processes. 
• The Golgi apparatus is found next to the endoplasmic reticulum and is hence responsible for the modification and packaging of the proteins synthesized by the RER.
• Peroxisomes are responsible for the degradation of hydrogen peroxide within the cell. They also regulate metabolic processes and are part of the defence system of plant cells.
• The presence of lysosomes within plant cells is still debated as they are not present as conventional bags containing hydrolytic enzymes as seen in animal cells. The enzymes performing the same functions are present in the Golgi bodies and vacuoles.

Conclusion 

Plant cells are distinct from animal cells and possess certain unique features. The various cell organelles work together in tandem to perform various cellular functions which are necessary for the survival of the organism. Plant cells are characterised by the presence of a cell wall composed of cellulose and chloroplasts. These two features are seen only in plants.