Test: Cell Organelles:Structural unit of Life - NEET MCQ

A plant cell has rigid wall on the outside. It has plastids and a centrally located large vacuole. All of these are absent in an animal cell.

Line in NCERT: "Plant and animal cells are different as the former possess cell walls, plastids and a large central vacuole which are absent in animal cells."

Golgi complex consists of a stack of cisternae which are curved to give definite polarity to the Golgi apparatus. The convex side (forming/cis face) receives vesicles from endoplasmic reticulum. The concave side (maturing /transface) buds off vesicles as secretion.

Line in NCERT: "The Golgi cisternae are concentrically arranged near the nucleus with distinct convex cis or the forming face and concave trans or the maturing face."

Ribosomes may-occur singly as monosomes or in rosettes and helical groups called polyribosome. The different ribosomes are connected with a 10-20A thick strand of mRNA. They are formed during periods of active protein synthesis when a number of copies of the same polypeotide are required.

Line in NCERT: "Several ribosomes may attach to a single mRNA and form a chain called polyribosomes or polysome."

Cell wall is the outer rigid protective and supportive covering of plant cells,fungi and some protists. Cell membrane is covering of protoplasm which occurs inside the cell wall. 

Line in NCERT: "Plant cells have a cell wall outside the cell membrane."

Ribosomes are naked ribonucleoprotein protoplasmic particles (RNP) which function as a site for protein synthesis.

Line in NCERT: "Ribosomes are non-membrane bound organelles found in all cells – both eukaryotic as well as prokaryotic. Within the cell, ribosomes are found not only in the cytoplasm but also within the two organelles - chloroplasts (in plants) and mitochondria and on rough ER."

- Option a is true because both plastids and mitochondria have their own DNA and ribosomes, allowing them to produce some of their own proteins.
- Option b is false; in plant cells, spindle fibers do not perform the function of centrioles, which are more common in animal cells for cell division.
- Option c is true, as mitochondria are known as the powerhouse of the cell because they generate ATP, the energy currency of the cell.
- Option d is incorrect; plastids do not contain lysosomes.

Line in NCERT: "Plastids and mitochondria possess single circular DNA molecule, a few RNA molecules, ribosomes (70S) and the components required for the synthesis of proteins." "Organelles which generate ATP are mitochondria."

Energy currency of cell is ATP that is generated in a double membraned structure called mitochondria. The inner membrane of the mitochondria plays the most prominent role in generating ATP.

Line in NCERT: "The inner membrane forms a number of infoldings called the cristae (sing.: crista) towards the matrix. The cristae increase the surface area. Mitochondria are the sites of aerobic respiration. They produce cellular energy in the form of ATP, hence they are called 'power houses' of the cell."

Plasmodesmata are cytoplasmic bridges between adjacent plant cells which develop in minute pores of their walls. They form a protoplasmic continuum called symplast.
It provides channels for controlled passage of small sized particles between adjacent cells as well as transfer of some specific signals.

Line in NCERT: "The cell wall and middle lamellae may be traversed by plasmodesmata which connect the cytoplasm of neighbouring cells."

The lipid molecules are amphipathic, i.e., they possess both polar hydrophilic (water loving) and nonpolar hydrophobic (water repelling) ends. The hydrophilic region is in the form of a head occurring at outer surface while the hydrophobic part contains two tails of fatty acids. Hydrophobic tails usually occur towards the centre of the membrane. It results in the formation of a lipid bilayer. Most common lipid in the bilayer is phospholipid.

Line in NCERT: "The major lipids are phospholipids that are arranged in a bilayer. Also, the lipids are arranged within the membrane with the polar head towards the outer sides and the hydrophobic tails towards the inner part."

Lysosomes are single membrane bound vesicles which contain hydrolytic enzymes. They are believed to be formed by the joint activity of ER and Golgi complex. Precursors of hydrolytic enzymes are synthesized at RER and are transferred to the forming face of Golgi complex. These precursors are then changed to enzymes. Enzymes are packed in larger vesicles and are pinched off at maturing face. These vesicles combine with endosomes to produce lusosomes.

Line in NCERT: "These are membrane bound vesicular structures formed by the process of packaging in the golgi apparatus."

The SER provides surface for the synthesis of  including phospholipids, cholesterol, steroid hormones and hormones, adrenal corticoid hormones), ascorbic acid are visual pigments.

Line in NCERT: "The smooth endoplasmic reticulum is the major site for synthesis of lipid. In animal cells lipid-like steroidal hormones are synthesised in SER."

Succinate dehydrogenase, anenzyme complex involume in TCA cycle, is located in inner mitochondrial membrare.

Line in NCERT: "The two membranes have their own specific enzymes associated with the mitochondrial function."

The lysosomes may be called "suicide bags’ of the cell in view of their autolytic role, or "disposal units’ of the cell because they digest the incoming food materials and remove the foreign bodies, toxic molecules, and debris, or "recyling centres" as they break down worn out cells cell organelles to component molecules for building organelles and cells.

Line in NCERT: "These enzymes are capable of digesting carbohydrates, proteins, lipids and nucleic acids."

Nucleolus is a dense, rounded, dark-staining, granular structure without a limiting membrane. It consists largely of RNAs and proteins. Nucleolus syntesizes and stores RNA. It also receives ribosomal proteins from the cytoplasm for storage. It forms ribosomal subunits by wrapping the RNAs with nitosomal proteins. The ribosomal subunits later have the nucleus through the nuclear pores.

Line in NCERT: "The nucleoli are spherical structures present in the nucleoplasm. It is a site for active ribosomal RNA synthesis."

A covering membrane is absent around ribosomes, centrioles and nucleolus.

Line in NCERT: "Ribosomes are non-membrane bound organelles found in all cells – both eukaryotic as well as prokaryotic."

• Extranuclear inheritance refers to the transmission of genes that exist outside the cell nucleus.
• The primary organelles involved are mitochondria and chloroplasts, both of which contain their own DNA.
• Mitochondria are inherited maternally since sperm contribute little to the embryo's mitochondria during fertilization.
• This type of inheritance is crucial for understanding traits that are passed down through maternal lineage.
   

• Nuclear inheritance

  Involves passing on genetic information from parents to offspring through nuclear chromosomes. This is the type of inheritance that is usually referred to when the term "heredity" is used.

• Extranuclear inheritance

  Also known as cytoplasmic inheritance, this involves passing on genes from outside the nucleus of a cell. These genes are usually found in organelles like mitochondria and chloroplasts, or from cellular parasites like bacteria or viruses.

Topic in NCERT: Mitochondria and Chloroplast

Line in NCERT: Mitochondria : The matrix also possesses single circular DNA molecule, a few RNA molecules, ribosomes (70S) and the components required for the synthesis of proteins. The mitochondria divide by fission.

Chloroplast:The stroma of the chloroplast contains enzymes required for the synthesis of carbohydrates and proteins. It also contains small, doublestranded circular DNA molecules and ribosomes

Ribosomes are granular structures which were discovered by Robinson and Brown (1953) in plant cell and by Palade (1955) in animal cell. Palade (1955) also coined the term ribosomes hence, they are also called Palade particles. Ribosomes occur in both prokaryotic and eukaryotic cells.

Topic in NCERT: Ribosomes

Line in NCERT: "Ribosomes are the granular structures first observed under the electron microscope as dense particles by George Palade (1953)."

Acentriole possesses a whorl of nine peripheral fibrils. Fibrils are absent in the centre. The arrangement is, therefore, called 9 + 0. Flagella contains an axoneme of a peripheral doublet fibrils and 2 central singlet fibrils. This arrangement is called 9 + 2 or 11 stranded.

Line in NCERT: "The axoneme usually has nine doublets of radially arranged peripheral microtubules, and a pair of centrally located microtubules. Such an arrangement of axonemal microtubules is referred to as the 9+2 array."

Camillo Golgi discovered the Golgi apparatus as reticular structure. Typically it is 0.5 - 1.0 pm in diameter but its shape and size depend upon the physiological state of the cell.

Line in NCERT: "Camillo Golgi (1898) first observed densely stained reticular structures near the nucleus. These were later named Golgi bodies after him. They consist of many flat, disc-shaped sacs or cisternae of 0.5μm to 1.0μm diameter."

Topic in NCERT: Cell Wall
 - Regulation of the Cell Cycle:
- This is not a function of the cell wall. The cell cycle is regulated by various cellular mechanisms and structures within the cell, particularly involving the nucleus, cytoplasm, and specific proteins and enzymes.

- Plasmodesmata Connection:
- The cell wall and middle lamella can be traversed by plasmodesmata, which allow cytoplasmic connections between neighboring plant cells.

- Turgidity:
- The cell wall permits plants to become turgid by maintaining structural integrity when the cell takes up water.

- Mechanical Strength:
- The cell wall provides mechanical strength and support, protecting against damage and maintaining cell shape.

Line in NCERT: "Cell wall not only gives shape to the cell and protects the cell from mechanical damage and infection, it also helps in cell-to-cell interaction and provides barrier to undesirable macromolecules." 
The cell wall and middle lamellae may be traversed by plasmodesmata which connect the cytoplasm of neighbouring cells.