Cytoplasm: Structure and Functions, Practice Problems and FAQs

You must have seen that many people have artificial ponds in their gardens that enhance the aesthetic beauty of the space. What do you think are the things used to build such an artificial garden pond? We may add some pebbles, some plants, some plumbing mechanisms to keep the water fresh and clean, some fishes, a proper fence, clean water etc. All these components have their own significance in maintaining the ecosystem of this artificial pond. The water inside the pond is the major component which supports all the life forms in it. Now, let us compare this pond with our cell. Can you find any similarities?

Fig: Garden pond and an animal cell

Our cell also has some important components inside it, which help in the metabolic processes of our body. They are the cell organelles. So just like the water holds all other components inside the pond, the cell organelles are also dispersed inside a semi-solid medium or matrix called cytoplasm. How are these cell organelles dispersed in it? Is cytoplasm the same for both prokaryotic and eukaryotic cells? What are the major functions of this cytoplasm? Let’s discuss and find out the answers to all these questions through this article.

Table of contents:

• Cytoplasm
• Composition of cytoplasm
• Structure of cytoplasm
• Functions of cytoplasm
• Practice Problems
• FAQs

Cytoplasm

The intracellular matrix inside a cell is called cytoplasm. It is a colourless, translucent and homogenous jelly-like matrix in which all the cell organelles are suspended. It is the quasi fluid, continuous phase of the protoplasm that remains after the removal of all the major particulates and organelles from the cell.

Fig: Cytoplasm and cell organelles of animal cell

Structure of cytoplasm

The ground substance of cytoplasm, that is, the cytosol or hyaloplasm contains biomolecules such as amino acids, carbohydrates, proteins, enzymes, vitamins, nucleotides, tRNAs etc. As the proteins in the cytosol exist as colloidal particles, they make it a crystallo colloidal system which has water as its dispersion medium. Cytoplasm is also a major depository of many elements of the periodic table that are called biogenic elements and are crucial for the metabolic reactions of the cell. The exact proportions of these biomolecules in the cell cytoplasm varies from one cell type to another.

Being a crystallocollodial system, the cytoplasm exists in two forms:

• Sol or plasmasol - non-viscous fluid like cytoplasm
• Gel or plasmagel - viscous and jelly like cytoplasm

These two forms of cytoplasm are interchangeable and help in the cytoplasmic movements. The cytoplasm and the structures in it are always in a constant motion and it is called cyclosis or streaming movement.

The components suspended in the cytoplasm are different in prokaryotic and eukaryotic cells. The prokaryotic cell being simple and ancient, has a simple cytoplasm. But eukaryotic cells have a complex cytoplasm.

Fig: Structure of prokaryotic and eukaryotic cell

Cytoplasm of prokaryotic cell

A prokaryotic cell is the cell without a defined membrane bound nucleus (eg: bacterial cell). It lacks membrane bound organelles such as endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria, microfilaments etc. The cytoplasm of a prokaryotic cell contains gas vacuoles, a variety of inorganic and organic molecules including glycogen granules, lipid droplets, sulphur and phosphorus granules etc. It also has certain actin and tubulin related proteins which serve as cytoskeletal elements. Most of the biochemical or metabolic reactions of a prokaryotic organism occur in the cytoplasm.

Fig: Structure of a bacterial cell

Structures in prokaryotic cytoplasm

The major structures present in the prokaryotic cytoplasm are as follows:

• Ribosomes
• Mesosomes
• Photosynthetic pigments
• Nucleoid
• Plasmids

Ribosomes

70S ribosomes are present with 50S and 30S subunits. They are the major site of protein synthesis. A group of ribosomes on the mRNA are called polysomes.

Fig: Prokaryotic ribosomes

Mesosomes

The infoldings of plasma membranes, called mesosomes, extend into the cytoplasm. They contain respiratory pigments which help in respiration.

Fig: Mesosome

Photosynthetic pigments

Photosynthetic pigments such as bacteriochlorophyll, bacteriopheophytin, carotenoids are present in the spherical bodies called chromatophores which lie in the cytoplasm.

Fig: Chromatophores in cyanobacteria

Nucleoid (genetic material)

The double stranded, spirally coiled, circular DNA which is highly folded is called nucleoid and it lies naked in the cytoplasm.

Plasmids

The small and circular extra chromosomal DNA molecules called plasmids are found in the cytoplasm of prokaryotic cells.

Fig: Nucleoid and plasmids

Cytoplasm of eukaryotic cell

The cells with membrane bound nucleus and other membrane bound cell organelles are called eukaryotic cells. In unicellular eukaryotes like protozoans, the cytoplasm has two major parts as follows:

• Ectoplasm - outer narrow and relatively firm zone
• Endoplasm - inner fluid mass

Fig: Cytoplasm of Amoeba

Structures in eukaryotic cytoplasm

The ground substance of the cytoplasm is the cytosol which is a mixture of dissolved molecules, colloidal proteins and water.

Fig: Cytoplasm of eukaryotic cell

The major components suspended in the cytosol can be classified as:

• Cell organelles
• Cell inclusions

Cell organelles

The specialised structures in the cytoplasm which performs specific functions are called cell organelles. There are two types of cell organelles:

• Membrane bound organelles - nucleus, endoplasmic reticulum (SER and RER), Golgi apparatus, lysosomes, mitochondria, microbodies are present in animal cells.

Fig: Membrane bound cell organelles in animal cell

In the cytoplasm of a plant cell other organelles like chloroplast and large vacuoles can be observed too.

Fig: Membrane bound cell organelles in plant cell

• Non-membrane bound organelles - 80S ribosomes (made up of larger 60S and smaller 40S subunits), cytoskeletal elements such as microtubules, microfilaments and intermediate filaments and centrioles (in animal cells).

Fig: Non-membrane bound organelles

Some cells have extracellular organelles such as cilia and flagella for locomotion and these structures have their basal granules in the cytoplasm.

Fig: Examples of cilia and flagella in animals

Cell inclusions

The non living or cytoplasmic structures in the cytoplasm are called cell inclusions. They reserve food in the form of fat globules, starch grains, glycogen granules or protein grains. They also have pigment granules, secretory products and excretory products.

Functions of cytoplasm

The major functions of cytoplasm are as follows:

• Intracellular distribution - distribution of metabolites, enzymes and nutrients within the cell.
• Exchange of materials between different cell organelles.
• Pathways of glycolysis (breakdown of glucose), anaerobic respiration and pentose pathway takes place in cytoplasm.
• Biosynthesis of proteins, fatty acids and nucleotides.
• Cell division is determined by the nucleo-cytoplasmic interaction.
• Cytoplasmic streaming or cyclosis helps in the movement of cell organelles.
• In ameboid cells cytoplasm helps in the ingestion and movement of cells by pseudopodia.

Practice Problems

Q1. Which of the following statements are wrong about the cytoplasm of a cell?

A. It is the colourless, translucent and homogenous intracellular matrix inside a cell.
B. The cell organelles in the cytoplasm are referred to as the hyaloplasm.
C. The cytosol is crystallo-colloidal in nature.
D. The constant motion of the cytoplasm is called cyclosis or streaming movement.

Solution: The intracellular matrix inside a cell is called cytoplasm. It is a colourless, translucent and homogenous jelly-like matrix in which all the cell organelles are suspended.

The ground substance of cytoplasm, that is, the cytosol or hyaloplasm contains biomolecules such as amino acids, carbohydrates, proteins, enzymes, vitamins, nucleotides, tRNAs etc. The cell organelles remain suspended in the cytosol. It is a crystallo colloidal system which has water as its dispersion medium. The cytoplasm and the structures in it are always in a constant motion and it is called cyclosis or streaming movement.

Hence the correct option is b.

Q2. Which of the following cell organelles are not seen in a prokaryotic cytoplasm?

A. Ribosomes
B. Nucleoid
C. Plasmids
D. Endoplasmic reticulum

Solution: A prokaryotic cell is the cell without a defined membrane bound nucleus (eg: bacterial cell). It lacks membrane bound organelles such as endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria, microfilaments etc. The cytoplasm of a prokaryotic cell contains gas vacuoles, a variety of inorganic and organic molecules including glycogen granules, lipid droplets, sulphur and phosphorus granules etc. The major structures present in the prokaryotic cytoplasm are ribosomes, mesosomes, photosynthetic pigments, nucleoid and plasmids. Hence the correct option is d.

Q3. Match the following column A with column B.

1. I-i, II-ii, III-iii, IV-iv
2. I-ii, II-i, III-iv, IV-iii
3. I-i, II-ii, III-vi, IV-iii
4. I-ii, II-i, III-iii, IV-iv

Solution: The cells with membrane bound nucleus and other cell organelles are called eukaryotic cells. In unicellular eukaryotes like protozoans, the cytoplasm has two major parts and they are ectoplasm (outer narrow and relatively firm zone) and endoplasm (inner fluid mass).

The cytoplasm is a crystallocollodial system with water as the dispersion medium. There are two forms of cytoplasm and they are sol or plasmasol (non-viscous fluid like cytoplasm) and gel or plasmagel (viscous and jelly like cytoplasm). These two forms of cytoplasm are interchangeable and help in the cytoplasmic movements. Hence the correct option is b.

Q4. Which of the following is not a function of cytoplasm?

i)Intracellular distribution
ii) Biosynthesis of proteins, fatty acids and nucleotides.
iii) Oxidative phosphorylation during respiration.
iv) Helps in the ingestion and movement of cells by pseudopodia.

1. i, ii and iii
2. i, iii and iv
3. Only ii
4. Only iii

Solution: The major functions of cytoplasm are; Intracellular distribution - distribution of metabolites, enzymes and nutrients within the cell, exchange of materials between different cell organelles, pathways of glycolysis (breakdown of glucose), anaerobic respiration and pentose pathway takes place in cytoplasm, biosynthesis of proteins, fatty acids and nucleotides, cell division is determined by the nucleo-cytoplasmic interaction, Cytoplasmic streaming helps in the movement of cell organelles. In ameboid cells cytoplasm helps in the ingestion and movement of cells by pseudopodia.

Oxidative phosphorylation during respiration occurs in the mitochondria. Hence the correct option is d.

FAQs

Q1. What happens when a cell does not have cytoplasm?
Answer: If cytoplasm is not present in the cell, the transportation of waste material out of the cell will not be possible. The total functionsing of the cell will get affected, like the shape of the cell and the movement of the cell of unicellular organisms. The organelles can not be suspended inside the cell and they can not function properly.

Q2. What is the difference between cytoplasm, nucleoplasm and protoplasm?
Answer: The contents inside the nucleus is called nucleoplasm. The contents inside the cell except the nucleus and the nucleoplasm is called cytoplasm. Protoplasm includes both cytoplasm and nucleoplasm.

Q3. Who coined the term cytoplasm?
Answer: The term cytoplasm was coined by Rudolf Von Kolliker, who is a Swiss biologist. Earlier the term cytoplasm was considered as the synonym of protoplasm.

Q4. What is the reason for most reactions taking place in the cytoplasm?
Answer: Cytoplasm has all the cell organelles and it contains many enzymes. Hence most chemical reactions take place in the cytoplasm.

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