Plant Cell: Parts and Structure With Functions

Plant cells are the basic unit and building blocks of life in organisms of the kingdom Plantae. They are cells that have a distinct nucleus and other cellular organelles enclosed within a membrane and thus are eukaryotic in origin.

A model of a typical plant cell is found to be rectangular in shape, ranging in size from 10 to 100 µm. Under the microscope, it shows many different parts. Each part, known as an organelle, works together to keep the cell functional.

 

1) Cell Wall

It is the outermost, protective layer of a plant cell having a thickness of 20-80 nm. Cell walls are made up of carbohydrates such as cellulose, hemicellulose, and pectin and a complex organic polymer called lignin.

Functions

• Providing mechanical strength, support, and rigidity to the cell
• Providing shape to the plant
• Allowing selective entry of small molecules inside the cell while preventing large molecules
• Protecting the delicate inner organelles from outer shock
• Providing turgidity to plants that allows movement of water and minerals throughout the plant body

2) Plastids

They are double membrane-bound organelles that have their own genetic material. Plastids are mainly of three types:

a) Chloroplasts: Found in the green parts of a plant and algae that contain the photosynthetic pigment, chlorophyll.

b) Leucoplasts: Found in the non-photosynthetic tissues of plants.

c) Chromoplasts: Colored plastics found in fruits and flowers of plants. Chromoplasts normally have red, orange, and yellow-colored pigments.

Functions

• Absorbing light energy (Chloroplast)
• Converting light energy into chemical energy to produce food in the form of carbohydrate by a process called photosynthesis (Chloroplast)
• Providing defense against infections (Chloroplast)
• Helping in the production of high energy phosphate molecules, ATP (Chloroplast)
• Storing of protein, lipid, and starch (Leucoplasts)
• Synthesizing and storing colored pigments (Chromoplast)

3) Central Vacuole

It is the large vesicle that make up almost 30 to 80% of the total plant cell volume. The central vacuole is often the largest organelle in the cell that is filled with fluid, ions, enzymes, and other molecules. Apart from plants, they are also present in algae.

Functions

• Maintaining turgidity of the cell that prevents plants from wilting
• Storing of reserve food, water, and waste materials of the cell
• Breaking of macromolecules into simpler ones using specific enzymes present inside them

4) Cell Membrane or Plasma Membrane

It is a thin, biological membrane having a thickness of 7.5-10 nm that separates the interior of the cell from the outside environment. The plasma membrane is selectively permeable in nature, which is mainly composed of lipids and proteins, with some carbohydrates attached to them.

Functions

• Protecting the cell from the outside environment and thus providing additional structural support
• Maintaining the shape of the cell
• Regulating the entry and exit of nutrients, essential minerals, and toxic waste products within the cell
• Helping in the formation of tissues
• Helping in cellular communication
• Regulating cell growth

5) Endoplasmic Reticulum (ER)

It is a series of membranes within the cytoplasm that forms connections with the nucleus on one side and cell membrane on the other. It is of two types: rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). The surface of RER has ribosomes attached to it, while they are absent in SER.

Functions

• Helping in the formation of nuclear membrane during cell division
• Producing trans-membrane proteins, lipids, glycogen and other steroids like cholesterol for its membrane and other parts of the cell
• Packaging and transporting of proteins and carbohydrates to other organelles
• Providing an increased surface area for cellular interactions
• Forming the skeletal framework of the cell

6) Golgi Apparatus

Also known as Golgi body or Golgi complex, they are stacks of five to eight membrane-covered sacs called cisternae. The Golgi apparatus acts as the post office of the cell by packaging and transporting proteins from their source RER to their destination. The number of Golgi apparatus varies in cells according to their functions.

Functions

• Synthesizing complex polysaccharides of the cell wall
• Processing, packaging. transporting, and secretion of the proteins produced in the rough endoplasmic reticulum
• Performing protein modifications such as phosphorylation and glycosylation
• Breaking down of proteins into simpler ones

7) Microfilaments or Actin Filament

They are a network of long and thin protein fibers present in the cytoplasm of the cell having a diameter of 3-6 nm. Microfilaments are composed of actin proteins that make them extremely strong and flexible.

Functions

• Helping in the contraction of muscles
• Helping in cell movement
• Aiding in cell division
• Maintaining cell shape
• Helping in the flow of cytoplasmic contents including nutrients within the cell (cytoplasmic streaming)

8) Microtubules

They are fibrous hollow rods composed of proteins called tubulin. Microtubules have an outer diameter of 23-27 nm and an inner diameter of about 11-15 nm. They can grow to as long as 50 µm and thus are highly dynamic.

Functions

• Maintaining the structure of the cell
• Helping in cell movement
• Participating in cell division
• Helping in the movement of cell organelles and nutrients within the cell (cytoplasmic streaming)
• Helping in cellular communication

9) Intermediate Filaments

They are made up of two proteins forming a coiled-coil structure. Intermediate filaments have a diameter of 8-10 nm that are intermediate in size to microfilaments and microtubules. Microtubules, together with microfilaments and intermediate filaments, form the cytoskeleton of the cell.

Functions

• Maintaining the structural integrity of the cell
• Maintaining cell shape
• Helping in the movement of cell organelles and nutrients within the cell (cytoplasmic streaming)

10) Mitochondria

It is a rod-shaped double membrane-bound organelle that contains its own DNA and ribosomes. Mitochondria are often called the ‘powerhouse of the cell‘, producing ATP that drives all cell-based metabolic activities. 

Functions

• Producing the energy currency of the cell, the ATP
• Helping in cellular respiration, which involves breaking down of nutrients to generate energy
• They maintain the concentration of Ca²⁺ within the cell by working closely with the endoplasmic reticulum

11) Nucleus

It is a spherical shaped double membrane-bound organelle that contains the genetic material of the cell, the DNA. A nucleus has four main parts:

Nuclear membrane or Nuclear envelope: A double-layered membrane that separates the nucleus from the cell cytoplasm.

Chromatin threads or Chromosomes: Genetic material of the cell that takes part in cell division

Nuclear sap or Nucleoplasm: Clear, homogeneous, and transparent liquid that contains the genetic material of the cell along with proteins, sugars, and enzymes.

Nucleolus: Membrane-less region where ribosome is manufactured

Functions

• Storing the genetic material of the cell
• Controlling cell growth and reproduction
• Controlling and coordinating center of the cell
• Transmitting genetic information to the next generation

12) Peroxisomes

They are single membrane-bound organelles with a diameter of 0.1-1 mm that houses a wide variety of digestive and oxidative enzymes. They vary widely in shape, size, and number depending upon the energy requirement of the cell.

Functions

• Performing oxygen-dependent breakdown of substrates such as fatty acids and glycerol
• Helping in the recycling of carbon, during cell metabolism

13) Ribosomes

They are particles that either remains attached to the endoplasmic reticulum or are found freely suspended in the cytoplasm. Ribosomes are the protein-synthesizing center of the cell.

Functions

• Synthesizing proteins required for all cellular activities including growth and reproduction

14) Cytoplasm

It is the semifluid substance that fills up the entire space of the cell and is enclosed by the cell membrane. The portion of the cytoplasm that is not enclosed by cell organelles is called the cytosol. The cytoplasm is mainly composed of water, salts, and proteins.

Functions

• Maintaining turgidity and thus helps in keeping cell shape
• Assisting several metabolic activities such as cell division, respiration and breaking down of waste products
• Keeping the cell organelles in their positions
• Providing the raw materials necessary for the chemical reactions within the cell

15) Plasmodesmata

They are small channels that form connections between the cytoplasm of adjacent plant cells. Plasmodesmata are formed through a close association between the plasma membrane and the endoplasmic reticulum of the cell.

Functions

• Allowing movement of water, nutrients and small signaling molecules between neighboring cells
• Transfering viral genomes between cells
• Helping in the cellular communication

Parenchyma cells: Living cells that are capable of division. Parenchyma cells in plants perform photosynthesis and help in gas exchange. They also store reserve food materials such as starch and proteins.

Collenchyma cells: Elongated cells with thick deposition of cellulose in their cell walls. Collenchyma provides support to growing parts of a plant.

Sclerenchyma cells: Dead cells that have very thick cell walls. Sclerenchyma cells provide mechanical support to the plant.

Xylem cells: Hard, water-conducting cells that help to transport water and nutrients absorbed by the roots to all parts of the plant.

Phloem cells: Cells that distribute food and sap, mainly in the form of sucrose from the leaves to all parts of the plant.