All questions of Cell: Structure, Types & its Components for JAMB Exam

Middle lamella is the outermost layer of plant cell. It was thick & non elastic.so it connect the adjacent plant cell.

Eukaryotes are the organisms which have membrane bound cell organelles as well as membrane bound nucleus. All the kingdoms except kingdom monera are eukaryotes. Monera is a kingdom of prokaryotes.

Centriole is present exclusively in animal cells.in plant cells vacuole occupies about 90% of space plant cell wall is made up of cellulose and plastids are present in plants.

Middle lamella acts as a cementing material between the adjacent cells in a tissue and is generally made up of calcium pectate.

Characteristics of Prokaryotic Cells

Prokaryotic cells are a type of cells that lack a true nucleus and membrane-bound organelles. They are typically smaller in size compared to eukaryotic cells and are found in organisms such as bacteria and archaea. One of the characteristic features of prokaryotic cells is the presence of circular DNA.

Presence of circular DNA
Prokaryotic cells have a single, circular DNA molecule that contains the genetic information of the cell. This circular DNA is located in the cytoplasm of the cell and is not enclosed within a nucleus. The circular DNA is often referred to as the prokaryotic chromosome. It carries the essential genes necessary for the survival and reproduction of the cell.

This circular DNA is distinct from the linear DNA found in eukaryotic cells, which is packaged into multiple chromosomes and located within a membrane-bound nucleus. The circular DNA in prokaryotic cells allows for efficient replication and gene expression.

The presence of circular DNA is a characteristic feature of prokaryotic cells and is one of the key differences between prokaryotic and eukaryotic cells. This circular DNA is also smaller in size compared to the total amount of DNA found in eukaryotic cells.

Other characteristics of prokaryotic cells
- Lack of membrane-bound organelles: Unlike eukaryotic cells, prokaryotic cells do not have membrane-bound organelles such as a nucleus, mitochondria, or endoplasmic reticulum. Instead, the cellular components are dispersed throughout the cytoplasm of the cell.
- Small size: Prokaryotic cells are generally smaller in size compared to eukaryotic cells. They range in size from 1 to 10 micrometers in diameter.
- Cell wall: Prokaryotic cells have a cell wall that provides structural support and protection. The composition of the cell wall varies among different types of prokaryotes.
- Simple internal structure: Prokaryotic cells have a simpler internal structure compared to eukaryotic cells. They lack complex membrane systems and have a less-developed cytoskeleton.
- Rapid reproduction: Prokaryotic cells can reproduce rapidly through binary fission, a process in which a single cell divides into two identical daughter cells.

In conclusion, the presence of circular DNA is a characteristic feature of prokaryotic cells. This circular DNA, along with other unique characteristics such as the absence of membrane-bound organelles and smaller size, distinguishes prokaryotic cells from eukaryotic cells.

Understanding the Levels of Biological Organization
In biology, the levels of organization refer to how living organisms are structured, from the simplest to the most complex. One important level is the organ level, which plays a crucial role in the functionality of multicellular organisms.
Integration of Tissues
- Organs are formed by the combination of different types of tissues.
- Each tissue type has a specific function, and their collaboration allows organs to perform more complex tasks.
Examples of Organs
- Heart: Composed of cardiac muscle tissue (for contraction), connective tissue (for structural support), and nervous tissue (for regulating heartbeats).
- Liver: Contains hepatocytes (liver cells), connective tissues, and blood vessels, all working together for detoxification and metabolism.
Functionality of Organs
- Organs are specialized to carry out specific functions that are vital for the organism's survival.
- For instance, the stomach aids in digestion by integrating muscular, epithelial, and connective tissues to break down food.
Conclusion
Choosing option 'C' as the correct answer highlights the significance of organs in the biological hierarchy. They represent a complex level of organization where diverse tissues collaborate, enabling the organism to perform intricate functions that are essential for life. Understanding this level of organization is fundamental in fields like anatomy, physiology, and medicine, as it lays the groundwork for comprehending how systems operate within living organisms.

The correct answer is option 'B', Flagella.

Flagella are long, whip-like structures that protrude from the surface of prokaryotic cells and enable them to move. These structures are composed of a protein called flagellin. Prokaryotes can have one or multiple flagella, depending on the species and their mode of movement.

Flagella Structure:
- The flagellum consists of three main parts: the filament, the hook, and the basal body.
- The filament is the long, helical portion of the flagellum that extends outward from the cell. It is made up of many flagellin proteins arranged in a spiral pattern.
- The hook connects the filament to the basal body and allows for flexibility and rotation.
- The basal body is embedded in the cell membrane and is responsible for the rotation of the flagellum.

Flagella Movement:
- Prokaryotic cells use the rotation of the flagella to move in their environment.
- The basal body acts as a motor, utilizing energy from ATP to rotate the flagellum.
- The rotation of the flagella creates a whip-like motion, propelling the cell forward.
- By controlling the direction and speed of flagellar rotation, prokaryotic cells can move towards or away from certain stimuli, such as light or chemical gradients.

Advantages of Flagella:
- Flagella allow prokaryotic cells to move towards favorable conditions, such as nutrients or light, and away from harmful substances or unfavorable environments.
- They enable prokaryotes to explore their surroundings and find suitable habitats for growth and survival.
- Flagella also play a role in the colonization of host organisms by pathogenic bacteria, allowing them to move within tissues and evade the host immune system.

In conclusion, flagella are important structures that enable prokaryotic cells to move. They provide motility, allowing cells to navigate their environment and respond to stimuli. Understanding the structure and function of flagella is crucial for studying the behavior and characteristics of prokaryotic organisms.

Plant Cell Wall Components

The plant cell wall serves as a protective barrier and provides structural support to the plant cell. It is composed of various components, including pectin, hemicellulose, cellulose, and in some cases, lignin. However, calcium carbonate is not present in the plant cell wall.

Pectin:
- Pectin is a complex polysaccharide that is present in the middle lamella and primary cell wall of plant cells.
- It plays a crucial role in cell-to-cell adhesion, as it forms a gel-like substance that holds adjacent cells together.
- Pectin also acts as a water-binding agent and helps regulate cell wall porosity.

Hemicellulose:
- Hemicellulose is a group of polysaccharides that are present in the plant cell wall, primarily in the secondary cell wall.
- It provides structural support and contributes to the flexibility of the cell wall.
- Hemicellulose also serves as a matrix for cellulose microfibrils and helps in cell wall expansion during growth.

Cellulose:
- Cellulose is the main component of the plant cell wall and forms a network of long, linear chains of glucose molecules.
- It provides rigidity and strength to the cell wall, making it resistant to osmotic pressure.
- Cellulose microfibrils are organized in a crisscross pattern, providing structural integrity to the cell wall.

Calcium Carbonate:
- Calcium carbonate is not present in the plant cell wall.
- It is commonly found in the shells of marine organisms and in some rocks.
- While calcium ions (Ca2+) play important roles in plant cell signaling and various physiological processes, calcium carbonate is not a component of the plant cell wall.

In conclusion, among the given options, calcium carbonate is not present in the plant cell wall. The plant cell wall mainly consists of pectin, hemicellulose, and cellulose, which provide structural support, flexibility, and rigidity to the cell wall, respectively.

Protein Synthesis in Prokaryotic Cells
Protein synthesis in prokaryotic cells primarily occurs in the ribosomes. Here is an explanation in detail:

Ribosomes
- Ribosomes are the cellular organelles responsible for protein synthesis in prokaryotic cells.
- They are composed of ribosomal RNA (rRNA) and proteins.
- Ribosomes read the messenger RNA (mRNA) and use the information to assemble amino acids into proteins.
- In prokaryotic cells, ribosomes can be found both free-floating in the cytoplasm and attached to the cell membrane.

Nucleus
- Unlike eukaryotic cells, prokaryotic cells do not have a nucleus where DNA is housed. Instead, the DNA is located in the nucleoid region of the cell.
- Since prokaryotic cells lack a nucleus, protein synthesis occurs in the cytoplasm directly by the ribosomes.

Golgi Apparatus
- The Golgi apparatus is responsible for modifying, sorting, and packaging proteins for secretion or for use within the cell.
- While the Golgi apparatus plays a crucial role in protein processing and transport in eukaryotic cells, it is not directly involved in protein synthesis in prokaryotic cells.

Lysosome
- Lysosomes are membrane-bound organelles containing digestive enzymes that break down cellular waste and debris.
- They are not involved in protein synthesis but rather in the digestion of macromolecules within the cell.
In conclusion, the ribosomes are the organelles responsible for protein synthesis in prokaryotic cells, highlighting their essential role in the cellular machinery of these organisms.

Prokaryotic Cell Structures

Prokaryotic cells are simple, single-celled organisms that do not have a membrane-bound nucleus. They have a few key structures that help them carry out essential functions, but they lack some of the more complex organelles found in eukaryotic cells.

Cell Wall

- Prokaryotic cells have a rigid cell wall that provides structure and protection to the cell.
- The cell wall is made of peptidoglycan in bacteria and other unique materials in archaea.

Plasma Membrane

- The plasma membrane is a semi-permeable barrier that surrounds the cell and controls the flow of molecules in and out.
- It is made of a lipid bilayer with embedded proteins that help with various cellular processes.

Ribosomes

- Ribosomes are the cellular machinery responsible for protein synthesis.
- Prokaryotic cells have ribosomes that are smaller than those found in eukaryotic cells, but they still perform the same function.

Mitochondria

- Mitochondria are membrane-bound organelles that are the powerhouse of eukaryotic cells, producing ATP through cellular respiration.
- Prokaryotic cells do not have mitochondria; instead, they generate energy through other means, such as glycolysis or fermentation.

In conclusion, prokaryotic cells do not have mitochondria, which is a key organelle found in eukaryotic cells for energy production. This distinction is an important characteristic that helps differentiate prokaryotic cells from eukaryotic cells.

Cell wall is a non living rigid structure, it's present in bacteria, fungi , plants etc. It's selectively permeable and averts infections. so the option c is appropriate choice.

The correct answer is option 'D': Mitochondria.

Prokaryotic cells are a type of cell that lack a nucleus and membrane-bound organelles. They are typically found in bacteria and archaea. Unlike eukaryotic cells, prokaryotic cells are much simpler in structure. They contain a few essential structures that carry out basic cellular functions. Let's discuss each of the structures mentioned in the options and why mitochondria is not found in prokaryotic cells.

a) Cell wall:
The cell wall is a rigid outer layer that provides support and protection to the cell. It is found in both prokaryotic and eukaryotic cells. However, the composition of the cell wall differs between prokaryotes and eukaryotes. In prokaryotic cells, the cell wall is mainly composed of peptidoglycan, a unique molecule that provides strength to the cell wall. On the other hand, eukaryotic cell walls can be made of various materials such as cellulose (in plants), chitin (in fungi), or silica (in diatoms).

b) Plasma membrane:
The plasma membrane is a thin, flexible barrier that surrounds the cell and separates the internal environment from the external environment. It is present in both prokaryotic and eukaryotic cells. The plasma membrane is composed of a phospholipid bilayer with embedded proteins that regulate the passage of molecules into and out of the cell.

c) Ribosomes:
Ribosomes are small cellular structures that are responsible for protein synthesis. They can be found in both prokaryotic and eukaryotic cells. However, there are slight differences in the structure of ribosomes in prokaryotes and eukaryotes. Prokaryotic ribosomes are smaller and have a different composition compared to eukaryotic ribosomes.

d) Mitochondria:
Mitochondria are membrane-bound organelles found in eukaryotic cells. They are often referred to as the "powerhouses" of the cell because they generate most of the cell's energy through the process of cellular respiration. Mitochondria have a double membrane structure and contain their own DNA. They are thought to have originated from symbiotic bacteria that were engulfed by a primitive eukaryotic cell.

In summary, mitochondria are not found in prokaryotic cells. They are a characteristic feature of eukaryotic cells and play a crucial role in energy production. Prokaryotic cells, on the other hand, have a simpler structure and lack membrane-bound organelles such as mitochondria.

After the discovery of electron microscope , the structure of cell was analyzed in detail because of its high resolution and magnifying power.