Plant Cell Definition
Plant cells, which are the fundamental units of the members of the plant kingdom, are eukaryotic cells. This means that they are having a true (membrane-bound) nucleus in them. In addition to the nucleus that is enveloped by a membrane, the plant cells are also containing other organelles. Here, the organelles can be defined as the tiny cellular structures. There are several organelles within a plant cell with each one carrying a specific function.
Functions of Plant Cells
The functions of the nucleus and organelles are necessary for the cell operation. The plant cells can be differentiated from the cellular structures of other organisms by the following three components:
- Cell walls
- Chloroplasts
- Central vacuole
Plant Cell Structure
Cell Wall
As the name suggests, the cell wall is the outer covering of the plant cell. The primary function of the cell wall is to protect the inner components of the plant cell. But, this is not its only function. This component is also giving the plant cell its shape. In the plant cell, the constituents of the cell wall are mainly:
- Cellulose
- Hemicellulose
- Pectin
- Lignins
Although animal cells are also eukaryotic, they do not contain a cell wall. Thus, it can be said that cell wall is a salient feature of the plant cells. In a plant cell, there will a primary cell wall – the flexible layer on the outer side of a developing plant cell and a secondary cell wall – the tougher and the thicker layer on the inner side. The secondary cell wall can be seen only in the matured cells.
Chloroplasts
Chloroplasts are the places where photosynthesis takes place in the plant cell. These chloroplasts will have chlorophyll – the green pigment to absorb the energy from sunlight. Photosynthesis is a biological process that converts water, light energy, as well as carbon dioxide into plant nutrients. As such, the chloroplasts are oval-shaped with two membranes – the outer and inner membranes. Within the chloroplasts, there will be a fluid called stroma with a circular DNA. There will be several flattened disks within the chloroplasts that are called as thylakoids. These molecules would contain a higher concentration of chlorophyll and carotenoids. These thylakoids will be stacked one above the other in vascular plants. This setup is called as grana.
Central Vacuole
This is the organelle of the plant cell that is known to provide support to the cell by sustaining the turgid pressure against plant cell wall. In addition, the central vacuole will take part in various cell functions like:
- Storage
- Detoxification
- Protection
- Growth
In a mature plant cell, the central vacuole will occupy 30% to 80% of the total volume of the plant cell. This large vacuole will be surrounded by a membrane called tonoplast. Within the vacuole, there will be fluid, ions, and molecules. Although vacuole is present in the cells of various organisms, the plant cell vacuole is unique because of its larger size.
Apart from the above-mentioned three unique components of the plant cell, there are several other organelles too. They are as follows:
Cell Membrane
This is a thin and a semi-permeable membrane that encloses the cell’s contents. This thin lining will be present at the inner side of the plant cell wall.
Cytoplasm
This is a gel-like fluid that is found within the cell membrane. This will contain various elements like:
- Water
- Enzymes
- Salts
- Organelles
- Organic molecules
Cytoskeleton
This is basically a bundle of fibers that are found throughout the cytoplasm. The role of the cytoskeleton is to help the cell maintain the shape. It also provides support to the cell.
Endoplasmic Reticulum
This is a wide network of membranes. There are two types of regions in endoplasmic reticulum – one with ribosomes and other without ribosomes. The former is called rough endoplasmic reticulum and the latter is called smooth endoplasmic. The main function of this organelle is protein and lipid synthesis.
Golgi complex
This apparatus, which is found in all eukaryotic cells, is involved in distributing macromolecules to different parts of the cell.
Microtubules
These are the hollow rods whose primary function is to provide support, as well as shape to the cell. These have important roles to play in the chromosome movement during plant cell division.
Mitochondria
This is the “powerhouse” of the cell meaning that this generates energy for the cell through the process called respiration.
Nucleus
As mentioned earlier, this is the membrane-bound organelle and contains the cell’s DNA. The nucleus contains nucleolus that helps in the production of ribosomes and nucleopore that allows the transport of nucleic acids and proteins from and to the nucleus.
Peroxisomes
These are small structures, which are enveloped by a single membrane that contains the enzyme. The peroxisomes will be involved in plant processes like photorespiration.
Plasmodesmata
These are the channels that are located between cell walls, which allow for the molecules and signals to pass between the plant cells.
Ribosomes
These are the organelles that contain RNA and protein elements. As such, the ribosomes will be responsible for the protein assembly. Within the plant cell, the ribosomes are either found to be adhering to the endoplasmic reticulum or floating in the cytoplasm.