Structure And Functions Of Cell

 

Life begins with a cell hence it is the basic structural and functional unit of all life forms. Each organism is unique as they vary in their structure, organization pattern, function and its relationship with the surrounding.

Definition of cel

A cell is the structural and functional unit of life on which life survives. Cells are responsible for all of life’s processes.” Within the cellular cytoplasm, a fluid-like material is found. All the cell organelles are afloat on the cytoplasmic fluid. The cytoplasm is enclosed by an inner cell membrane and an outer cell wall.  The cell wall and cell membrane vary in their structural integrity, thickness, and functions. Alongside the cell organelles,  many biomolecules such as proteins, nucleic acids, and lipids are found. The biomolecules assist in nourishing the cytoplasmic organelles during cellular processes. For the first time, Robert Hooke- a famous Biologist has discovered the microscopic nature of cells. 

 

Order of structural organization in animals      

Even though the cell is a smaller unit, sub-units such as nucleus, genes, DNA, and chromosomes are tightly packed within this space. At the very basic level, DNA and Chromosomes are present. DNA  is a genetic material responsible for the structural and functional integrity, uniqueness and complexity of each individual.  Each individual is unique, it is simply because the DNA varies in its organizational pattern of each individual. DNA is found in a double-helical model, tightly coiled within the nucleolus. Around the nucleolus, there is a nucleus. Within the cytoplasm, there are multiple biomolecules that nourish and regulate the metabolic activities of the body. Biomolecules are the intracytoplasmic nutritional components floating in a ground material, matrix. Biomolecules are made up of carbohydrates, lipids, nucleic acids, and proteins. The structural and functional organization of the nucleolus,  nucleus, cytoplasmic content, and organelles together form a complete cell. Many cells join together to form a tissue. Tissues are mainly divided into epithelial, muscular, nervous and connective tissues. When tissues are arranged in a desired pattern, they form organs help in performing specific roles. Some of the organs are the stomach, kidneys, brain, liver, and lungs. Many organs combine to form a system, for instance, the digestive system is formed by stomach, liver, intestine, and so on.

 

Characteristics of Cells

  1. Cells are  unique in their structural and functional aspects. Cells behave in a certain way depending upon the necessities and demands that the organs signal to them.  For instance, intestine demands  peristalsis and the peristalsis  is a result of the specific pattern of cellular organization within the intestine ,consequently, the wavy motions will push the food material forward. 

  2. Cells work in a specific, well-organized pattern, based on the system they belong to. For example, a neuron cannot behave like a nephron as they both have to perform different functions differently.

  3. Cells vary in their size, shape, structure and this is the reason we have a variety of  different tissues, organs, and systems in our body.

  4. Some of the cells provide structural framework and support necessary for the tissues and organs , for example,  muscles and bones.

  5. Every cell has a lifespan through which they form and die, for example, RBCs live for a maximum of 120 days. However,  there is a balance between the rate of formation and the number of cells die each day. On the other hand, any injury to the cells within the nervous system can cause irreversible damage.

  6. Every cell has an organized cytoplasm within which, multiple organelles and biomolecules float 

  7. Cell wall and the cell membrane are the outermost layers of a cell. Plant cells are unique because they possess both cell walls and cell membranes but animal cells lack cell walls.

  8. The nucleus is the central body of a cell that regulates most of the cellular processes such as protein synthesis, genetic functions.

  9. Mitochondria is a double membrane-bound organelle vital for the survival of the cell because they act as the storehouse of energy.

  10. Lysosomes are the organelles responsible for digesting unwanted materials in the cell.

  11.  The endoplasmic reticulum plays a major role in the internal organization of the cell by synthesizing selective molecules. They assist in processing, directing and sorting the cellular components in their appropriate locations.

 

Types of Cells

Based on cellular advancement and internal complexity, cells are classified as prokaryote cells and eukaryote cells. Prokaryotes are present in most of the primitive organisms like microbes and the megakaryocytes are present in mammalian, reptile, and vertebral organisms.

 

Structural and functional organization of cell

1. Cell Wall 

It is the outermost layer of plant cells. The cell wall is a tough and most prominent layer made up of cellulose, hemicellulose, and pectin.  Cell wall so made that they play a vital role in safeguarding and protecting the cell from external threats and foreign bodies. It also provides shape and support to the cells.

2. Cell Membrane 

The cell membrane is present in all organisms. It is also known as the plasma membrane that is capable of allowing the material in and out of the cell. Majority of the organelles such as the mitochondria, ribosomes are present in between the nucleus and cell membrane. Organelles and biomolecules together perform many cellular processes. The cell membrane plays a dual role in both the cell wall and plasma membrane in those cells where the cell wall is absent. The plasma membrane is a semi-permeable, porous membrane that is characterized by the selective absorption and movement of various substances to protect the health of the cell. 

3. Cytoplasm

Cytoplasm includes 3 parts, cytosol, organelles, and inclusions. Cytosol has a combination of protein filaments, soluble proteins, water, salt, cytoskeleton, and vaults. Cytosol also contains ions such as potassium, sodium, bicarbonate, chloride, calcium, magnesium and amino acids. Cellular organelles float across the fluid called cytosol or matrix.  In addition, cytosol also contains a mixture of molecules such as protein complexes and enzymes that assist in maintaining the metabolic functions inside the cytoplasm. This is made possible by allowing the cell organelles to interact with one another. In addition to the organelles and the cytosol, the cytoplasm also contains cytoplasmic inclusions such as lipid droplets, crystals, pigments, and glycogen. Most essential activities of the cell occur within the cytoplasm. Some of them are metabolism, waste management, maintenance and regulation of shape of the cell.

File:Plant cell structure-en.svg

Diagram showing plant cell-Image from wiki images

 

File:Animal cell structure en.svg

Diagrammatic presentation of animal cell-labelled source-wiki images

4. Nucleus

The nucleus contains the genetic material of the cell-like DNA and RNA in some cells. Nucleus is the controlling house for protein synthesis, cell division, and other principal functions of the cell. The nucleolus is the site of ribosome synthesis. Also, it is involved in controlling cellular activities and cellular reproduction. The nucleus is surrounded by made up of the Nuclear membrane and the central portion of the nucleus is the nucleolus. The nuclear membrane protects the nucleus by forming a boundary between the nucleus and other cell organelles. Inside the nucleolus, there are chromosomes that play a crucial role in determining the sex of an individual. Each human cells contain 23 pairs of chromosomes.

 

Functions of cells

Cell Component

Functions

Nucleus

Regulates all the cellular activities.

Cell wall

The outermost layer in animals acts as a protective covering.

Cell Membrane

It is made out of phospholipids and proteins act as a junction between the cytoplasm and the cell wall.

Mitochondrion

Metabolic powerhouse that produces energy by regulating the cellular respiration under certain conditions.

Lysosomes

Called as suicide sacks that contain digestive enzymes to digest unnecessary material

Rough Endoplasmic Reticulum

Contains Ribosomes, transports proteins and other materials

Smooth Endoplasmic Reticulum

It contains no ribosomes but it helps in storing proteins.

Golgi complex (apparatus)

Primarily participate in the processing and packaging of the proteins.

Nucleolus

Dark spot of chromatin in the nucleus where ribosomes are produced.

Cytoplasm

Colloid that contains water and nutrients to support the chemical process carried out by cell organelles.

Organelles

The parts of a cell with a particular function.

Prokaryotic

Cells with no true nucleus and no membrane-bound organelles

Eukaryotic

Cells that contain a true nucleus and membrane-bound organelles

Centrioles

Only in animal cells, aid in cell division

Ribosomes

Help in protein synthesis

Chloroplast

Found only in plants and it primarily assist in photosynthesis

Vacuoles

Large storage sacks found  in plant cells

Cell Wall

The outer layer of plant cells made up of cellulose. They help in protecting the cell.

Chromatin

Thin strands of DNA and proteins found inside the cell.

Cytoskeleton

Long protein filaments found in the cytosol. They support in keeping up the structural framework of a cell.

 

Further reading

1     

Structure of cell membrane

2

Cell cycle

3

Structure and functions of plant stem

4

Structure and functions of plant cell

 

Questions

  1. Explain the characteristics of Cells

  2. What prokaryotes and eukaryotes?

  3. What is the difference between a plant cell and animal cell based on the cell wall?

  4. What is cytoplasm? Explain briefly about components of cytoplasm?

  5. What are the functions of  cytoskeleton?

  6. How is rough and smooth endoplasmic reticulum different from each other?

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