Cell - The Unit of Life Test - 9

The cell walls of bacteria are composed of a macromolecule peptidoglycan which is a repeating framework of long glycan chains having alternate N-acetyl glucosamine and N-acetyl muramic acid; these glycan chains are cross-linked by short peptide fragments to provide a strong but flexible support framework. This makes option A correct. The green algal cell wall is composed mainly of cellulose which makes option B incorrect. Chitin is common constituent of cell walls of all type of fungi; option C is incorrect. The yeast cell wall itself is mainly composed of glucans (β$-glucans), mannoproteins and chitin; option D is incorrect. Thus, the correct answer is option A.

Growth of the Cell Wall:

It has been stated that primary cell wall is soft and plastic. It is composed of cellulose and pectic substances. The pectic matters are hydrophilic colloids; they can absorb and hold water.

Due to softness and plasticity the primary wall gets considerably stretched during the growth of the cell, when new cell wall materials are deposited on the primary wall.

Two processes of the growth of cell wall have been described, viz., growth by intussusception and growth by apposition. The first method, though rather difficult to explain, involves wedging in or interpolation of new cell wall materials between the existing ones of the stretched primary wall. This process brings about growth in surface area.

It's simple Plasmodesmata are protoplasmic connect... moreions between adjacent cells.These R threads like structure of protoplasms which travel from protoplasm of one cell to protoplasm of nearest adjacent cell crossing cell wall.These Plasmodesmata connects the protoplasm of adjacent cells.These are charastically found out only in plant cells and ABSENT IN ANIMAL CELLS ..

Vessels are made of a subtance called lignin . they have lignified cell wall. The lignin makes the cell wall impermeable so they are in effect waterproof.

Around 30 enzymes are present in cell membrane, for example-ATPases, G-3-phosphate dehydrogenase.

Plasma membrane or cell membrane is the outer covering of all cells but it is present below the cell wall in animal cells. It is mainly composed of phospholipid bilayer structure with embedded proteins and some carbohydrates. Thus, the correct answer is option D.

Formation of ATP occur at thylakroid membrane so ATPase enzyme present at surface.

The plasma membrane or cell membrane is the outer covering of all cells but in a plant cell, it is present below the cell wall. It is mainly composed of phospholipid bilayer structure with the embedded proteins. The membrane proteins are extrinsic (on the surface of the membrane) and intrinsic (across the membrane i.e., cross the bilipid layer). About 70% of the proteins of the plasma membrane are intrinsic proteins. The intrinsic proteins, as their name implies, are firmly embedded in the phospholipid bilayer. Almost all intrinsic proteins contain special amino acid sequences.

Cell wall was discovered by Robert Hooke, in 1665, when he saw an empty box like compartments in a very thin slice of cork under his microscope. He wrote a book Micrographia and coined the term Cellula which was later on changed into cells. Robert Hooke thought cells to be passages for conducting fluids. Actually, he had observed compartments made up of the cell wall and not true living cells.

Cell wall is always dead but suberin or lignin is not diposited in it to make it impermeable .Cell wall is always permeable..

Glycoprotein --> carbohydrate + protein ...So your ans is glycoprotein.

In plant cells, Golgi apparatus consists of a number of isolated units called as dictyosomes while in animal cells it occurs as single compact or loose complex. The dictyosomes are engaged in secretory activities (because secretory materials are produced in dictyosomes) and rapid divisions (because wall materials are synthesized in dictyosomes). 

Tonofibrils are cytoplasmic protein structures in epithelial tissues that converge at desmosomes and hemidesmosomes. They consist of fine fibrils in epithelial cells that are anchored to the cytoskeleton.

Torus is composed of suberin. Torus is the thickened part of a stem, the receptacle, from which the flower and fruit parts grow. Torus, a structure of the xylem. Suberin is highly hydrophobic and a somewhat rubbery material. Its main function is to prevent water from penetrating the tissue. In roots, suberin is deposited in the radial and transverse cell walls of the endodermal cells.
Thus, the correct answer is option A.

Carbohydrates which are present in the cell membrane take part in cell recognition. Cell recognition is defined as an active process giving rise to a specific response.
Cell adhesion is a good example of cell recognition when it can be demonstrated that the adhesion is mediated by molecules having specific binding properties. Such cell adhesion molecules have now been identified in several cellular systems. Carbohydrates, or sugars, are sometimes found attached to proteins or lipids on the outside of a cell membrane. That is, they are only found on the extracellular side of a cell membrane. Together these carbohydrates form the glycocalyx. The glycocalyx of a cell has many functions. It can provide cushioning and protection for the plasma membrane, and it is also important in cell recognition. Based on the structure and types of carbohydrates in the glycocalyx, your body can recognize cells and determine if they should be there or not.

The plasma membrane or cell membrane is the outer covering of all cells but in a plant cell, it is present below the cell wall. It is mainly composed of phospholipid bilayer structure with the embedded proteins. The fluid nature of membranes is due to the lipids. The lipids can be saturated or unsaturated. More the unsaturation in lipids more the fluidity of the membrane.

A plant cell is characterized by a well developed cellulosic cell wall which is dead at maturity and consists lignin. Since cell wall is dead at maturity it does not take part in any physiological or biochemical process and may not allow passing molecule across it. Therefore, the correct answer is option C.

Middle lamella is the cementing material between two cells. It is mostly amorphous, thin and made up of calcium and magnesium pectate. The pectin present in this layer is a heteropolysaccharide which helps to bind the two cells together. It also helps in cell growth and cell wall extension. Thus, the correct answer is option D.

Tight junctions, also known as occluding junctions or zonulae occludentes (singular, zonula occludens) are multiprotein junctional complexes whose general function is to prevent leakage of transported solutes and water and seals the paracellular pathway.

Epithelial cells are compactly arranged and thus to provide mechanical support and keeping the cells together desmosomes are in abundance. Tight junctions are coming found in columnar epithelium to stop leakage across a tissue.

A plant cell is characterised by a cellulosic cell wall. The cell walls are separated by a middle layer or middle lamella. The middle lamella is actually a cementing layer between two plant cells. It is absent on the outer surface. Middle lamella is made up of calcium and magnesium salts of pectin. Pectins are mucopolysaccharides that occur in plant cell walls. Pectic acid is polymer of D-galacturonic acid.

Plant cell is characterised by a well developed cellulosic cell wall which is dead at maturity. Three major algal groups (Chlorophyceae, Rhodophyceae and Phaeophyceae) are included in plant kingdom. Hence, algae have well developed cell wall. A bacteria or prokaryotic cell also has a well developed cell wall but it is not made up of cellulose. Bacterial cell wall is made up of peptidoglycans.
So, the correct answer is 'All of the above'.

Phospholipids are a class of lipids that are a major component of all cell membranes. They can form lipid bilayers because of their amphiphilic characteristic. The structure of the phospholipid molecule generally consists of two hydrophobic fatty acid "tails" and a hydrophilic "head" consisting of a phosphate group.

Plasma membrane or cell membrane is the outer covering of all the cells and made up of phospholipid bilayer structure with embedded proteins. The thickness of the plasma membrane ranges from 7.0nm to 10nm or 75A˚ to 100A˚. Thus, the correct answer is option B.

Robertson proposed unit membrane concept for biological membranes. According to this concept, the biological membrane is a lipid bilayer surrounded on either side by proteins with a difference in their type for the outer and inner side. All biomembranes have a trilaminar structure with an electron transparent lipid bilayer (35A˚) lying sandwiched between electron dense protein layers (20A˚ each).

Pits are discontinuities in the secondary cell wall. there are two main types of pits – simple and bordered. All pits have two essential components – the pit cavity and the pit membrane. In the simple pit, the cavity is nearly constant in width. In the bordered pit, the cavity narrows towards the cell lumen; typically, the membrane is arched over by the secondary cell wall. The pit membrane cosists of primary wall and middle lamella. As a rule, pits in the walls of adjoining cells appear in pairs called pit-pairs, and the common membrane is therefore composed of two primary walls and middle lamella.