PLANT CELL AND ITS FUNCTION

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Plant Cell

 

Plant cells are eukaryotic cells or cells with membrane bound nucleus. Generally, plant cells are larger than animal cells and are mostly similar in size and are rectangular or cube shaped.  Plant cells are similar to animal cells in being eukaryotic and they have similar cell organelles.

 

What is a Plant Cell?

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Plant cells are eukaryotic cells i.e., the DNA in a plant cell is enclosed within the nucleus. The most important distinctive structure of plant cell is the presence of the cell wall outside the cell membrane. It forms the outer lining of the cell. The cell wall mostly constitutes of cellulose and its main function is providing support and rigidity. Plants cells also contain many membrane bound cellular structures. These organelles carry out specific functions necessary for survival and normal operation of the cells. There are a wide range of operations like producing hormones, enzymes, and all metabolic activities of the cell. 

Diagram of Plant Cell

Distinctive Features of Plant Cell

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The features that are distinctive in plant cells are as follows:  

Plant cells contain cell structures like cell wall, plastids, and large vacuoles.

Cell wall provide plant cells rigidity and structural support and cell to cell interaction.

Plastids help in storage of plant products. 

Chloroplasts aid in carrying out the process of photosynthesis to produce food for the plants. 

Vacuoles are water-filled, membrane bound organelles which stores useful materials. 

Plants have specialized cells in order to perform certain functions for the survival of plants. Some cells manufacture and store organic molecules, others transport nutrients throughout the plant. 

Some specialized plant cells include: parenchyma cells, collenchyma cells, sclerenchyma cells, water conducting cells and food conducting cells.

Parts of Plant Cell

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Plants cell constitute of membrane bound nucleus and many cellular structures. These organelles carry out functions that are necessary for the proper functioning and survival of the cell. The cell organelles of the plant are enclosed by a cell wall and cell membrane. The constituents of the cell are suspended in the cytoplasm or cytosol. 

The parts of the plant cell are as follows: 

Cell wall is the outermost rigid covering of the plant cell. It is a salient feature of plant cell. 

Cell membrane or the plasma membrane is the outer lining of the cell inside the cell wall. 

Cytosol or cytoplasm is the gel-like matrix inside the cell membrane which constitutes all other cell organelles.

Nucleus is the control center of the cell. It is a membrane bound structure which contains the hereditary material of the cell - the DNA 

Chloroplast is a plastid with green pigment chlorophyll. It traps light energy and converts it to chemical energy by the process of photosynthesis.

Mitochondria carries out cellular respiration and provides energy to the cells.

Vacuoles are the temporary storage center of the cell.

Golgi body is the unit where proteins are sorted and packed.

Ribosomes are structures that assemble proteins.

Endoplasmic reticulum are membrane covered organelles that transport materials.

Plant Cell Structure and Function

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All parts of the plant play a significant role in the proper functioning of the cell. Unlike animals, plant cells are surrounded by a rigid cell wall.

Cell wall: The cell wall is a rigid layer that surrounds the plant cells. It is made up of cellulose.  Cell wall is a characteristic feature to cells of plants. Plant cell walls are primarily made up of cellulose. Plant cell wall consists of three layers: the primary cell wall, secondary cell wall and the middle lamella. It is located outside the cell membrane whose main function is to provide rigidity, strength, protection against mechanical stress and infection. Cell wall is made up of cellulose, pectins,glycoproteins, hemicellulose and lignin.

Cell membrane: It is the outer boundary of the cell, it encloses the cytoplasm and the organelles of the cells. In plants cells it is inside the cell wall. The cell membrane is semi permeable, allowing only specific substances to pass through and blocking others.

Chloroplasts: It is an elongated or disc-shaped organelle containing chlorophyll. They have two membranes and have structures that look like stack of coins. They are flattened structures which contain chemical chlorophyll. The process of photosynthesis occurs in this region of the plant cell. The chlorophyll is a green pigment that absorbs energy from sunlight to make food for the plants by converting light energy into chemical energy. 

Cytoskeleton: It is a network of fibers made up of micro-tubule and micro-filament. They maintain the shape and gives support to the cell.

Microtubules: They are hollow cylinder like structures found in the cytoplasm of the cells. Its function is transport and structural support.

Microfilaments: Microfialments are solid rod like structures whose primary function is structural support.

Plasmodesmata: They are microscopic channels which traverse the cell walls of plant cells and enables transport and communication between them.

Vacuole: Vacuoles are known as cells storage center. Plant cells have large membrane bound chamber called vacuole. Its main function is storage. Vacuoles are found in the cytoplasm of most plant cells. They are membrane bound organelles, they perform functions of secretion, excretion and storage. 

Tonoplast: A vacuole that is surrounded by a membrane is called tonoplast.

Plastids: Plastids are storage organelles. They store products like starch for synthesis of fatty acids and terpenes.  

Leucoplast: They are a type of plastid which are non-pigmented.

Chromoplast: They are plastids responsible for pigment synthesis and storage. They are found in photosynthetic eukaryotic species. They are found in colored organs of plants like fruits and flowers.  

Golgi complex: The Golgi bodies look like the endoplasmic reticulum and are situated near the nucleus. They are found in almost all eukaryotic cells. Their main function is to process and package macromolecules synthesized from other parts of the cell. The Golgi apparatus is referred to as the cell's packaging center.

Ribosomes: Ribosomes are smallest and the most abundant cell organelle. It comprises of RNA and protein. Ribosomes are sites for protein synthesis. They are found in all cells because protein are necessary for the survival of the cell. The ribososomes are known as the protein factories of the cell. 

Endoplasmic reticulum: Endoplasmic reticulum is a membrane bound compartment, which look like flattened sacs lined side by side. It is a large network of interconnecting membrane tunnels. It is composed of both rough endoplasmic reticulum and smooth endoplasmic reticulum. 

They are responsible for protein translation, and protein transport to be used in the cell membrane. They also aid in sequestration of calcium, and production and storage of glycogen and other macromolecules.

Mitochondria: Mitochondria are surrounded by two membranes. They are described as the 'power plants' of the cell as they convert glucose to energy molecules (ATP). They possess their own hereditary material which help in self duplication and multiplication. 

Lysosome: Lysosome contain digestive enzymes. They digest excess or worn out organelles, food particles and any foreign bodies.

Microbody: It is a single membrane bound organelle that comprises of degradative enzymes

Cytoplasm: It is a gel-like matrix inside enclosed by the cell membrane. The cytoplasm supports cell organelles and also prevents the cell from bursting or shrinking.

Nucleus: It is the control center of the cell. It is bound by a double membrane known as the nuclear envelope. It is a porous membrane, it allows passage of substances and is a distinctive characteristic of the eukaryotic cell. Most of the genetic material is organized as multiple long linear DNA molecules. The nucleus directs all the activities of the cell and also help in protein formation.

Plastids in Plant Cell

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Plastids are cell organelles that store specific things found only in plant cell but absent in animal cells.In plant cell they are found in the cytoplasm. Plastids are spherical or ovoid in shape. They are involved in manufacture and storage of certain important chemical compounds.

The term plastids was coined by Schimper in 1885 and was derived from a Greek word 'plastikas' which means formed or moulded.  

Plastids in plants include chloroplasts, chromoplasts, leucoplasts, amyloplast, elaioplast and proteinoplast/aleuronoplast depending on the function they play.

Chloroplasts

The word chloroplast is derived from the Greek word chloros meaning green and plast meaning form or entity. It is the most important plastid as they are involved in photosynthesis. The chloroplasts are situated near the surface of the cell and in parts where there is sufficient reception of sunlight. The shape of the cholorplast varies, it may be spheroid or ovoid or discoid. 

For a given cell type the size of plastid is constant but it differs from species to species.It is about 4-5 microns in length and 1-3 microns in thickness. The number of chloroplast may be 20 to 40 per cell may be upto 1000, the number varies from species to species but is constant for a plant.

Structure

Chloroplasts are disc-shaped and are enclosed by a double membrane.

Within the inner membrane is a protein-rich substance known as stroma, it is embedded in a membrane system. This membrane system forms membrane bound vesicles called thylakoids.

The thylakoids lie in stacks called grana. This contains the photosynthetic pigments - chlorophyll a and b and carotenoids. Lamellae are tubular membranes which interconnect the grana. 

Functions

Photosynthesis is carried out in the chloroplast.

The enzymes and co-enzymes necessary for photosynthesis is present. 

Chromoplast

Chromo means color; plast means living. Chromoplasts are colored plastids and they contain various pigments like yellow,orange and red. 

They are found commonly in flowers and fruits. The color is due ot pigement, carotenes and xanthophylls.

Functions

In flowers the main function is attract agents for pollination.

In fruits it is to attract agents for dispersal.

Leucoplasts

These  are colorless plastids and occur in parts of plants that are not exposed to light like roots and seeds. 

The absence of color is due to the lack of pigments.

Functions

Starch grain formations are seen in leucoplast.

Oils and proteins are synthesized here.