Cell: Cell wall, endomembrane system

Question 1

what is a cell wall

Answer 1

it is a non living rigid layer forming an outer covering of plasma membrane in plant cells. It is completely permeable.

Question 2

functions of cell wall

Answer 2

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.

Question 3

what is the composition of cell wall in diff cells

Answer 3

prokaryotes: peptidoglycan( protein+carb)
fungi: chitin
algae: cellulose, mannans, galactans minerals like caco3
plants: cellulose, hemicellulose, prtoeins and pectins

Question 4

what is the primary wall characs

Answer 4

it is thin and elastic.
it diminishes as cell matures
capable of growth
cellulose/hemicellulose/pectins

Question 5

secondary wall characs

Answer 5

divided into 3 distinc layers
thick and rigid
absent in meristematic cells
formed towards the inner side of primary wall due to deposition
cellulose/hemicellulose/pectins

Question 6

what is the middle lamella

Answer 6

The middle lamella is a layer mainly of calcium pectate(and mg pectate, more ca pecttate ) which holds
or glues the different neighbouring cells together

Question 7

what is the plasmodesmata

Answer 7

these are cytoplasmic connections between adjoining cells
present as pores on cell wall
mainly used for signalling

Question 8

what is the endomembrance system? why/?

Answer 8

While each of the membranous organelles is distinct in terms of its structure and function, many of these are
considered together as an endomembrane system
because their functions are coordinated. The
endomembrane system include endoplasmic
reticulum (ER), golgi complex, lysosomes and
vacuoles. Since the functions of the mitochondria,
chloroplast and peroxisomes are not coordinated
with the above components, these are not
considered as part of the endomembrane system.

Question 9

what is the er? how does it divide cell?

Answer 9

it is a network of tubular structure mainly close to the nuclear membrane.
The endoplasmic reticulum divides the intracellular space into 2 distinct compartments:
-luminal compartment- inside er
-extraluminal compartment- outside er in cytoplasm

Question 10

types of endoplasmic reticulum

Answer 10

The endoplasmic reticulun
bearing ribosomes on their surface is called rough
endoplasmic reticulum (RER). In the absence of
ribosomes they appear smooth and are called
smooth endoplasmic reticulum (SER).
RER is frequently observed in the cells actively
involved in protein synthesis and secretion. They
are extensive and continuous with the outer
membrane of the nucleus.
The smooth endoplasmic reticulum is the major
site for synthesis of lipid. In animal cells lipid-like
steroidal hormones are synthesised in SER

Question 11

what is the golgi bodie?

Answer 11

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 (Figure 8.6). These are
stacked parallel to each other.Varied number of
cisternae are present in a Golgi complex.

Question 12

what are two parts of golgibodies

Answer 12

The Golgi
cisternae are concentrically arranged near the
nucleus with distinct convex cis or the forming face and concave trans or the maturing face.
The cis and the trans faces of the organelle are entirely different, but
interconnected.

Question 13

what is the function of golgi bodies? why is it close ot er?

Answer 13

The golgi apparatus principally performs the function of packaging
materials, to be delivered either to the intra-cellular targets or secreted
outside the cell. Materials to be packaged in the form of vesicles from
the ER fuse with the cis face of the golgi apparatus and move towards
the maturing face. This explains, why the golgi apparatus remains in
close association with the endoplasmic reticulum. A number of proteins
synthesised by ribosomes on the endoplasmic reticulum are modified
in the cisternae of the golgi apparatus before they are released from its
trans face. Golgi apparatus is the important site of formation of
glycoproteins and glycolipids.

Question 14

what are the functions of cis and trans face

Answer 14

cis face: inlet of products/materials from the endoplasmic reituclum which passes through a series of cisternae to undergo modification before reaching the trans face

trans face:
packaged material is released in the form of a vesicle here.

Question 15

what is a lysosome

Answer 15

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

Question 16

what does lysosome contain

Answer 16

The isolated lysosomal vesicles
have been found to be very rich in almost all types of hydrolytic
enzymes (hydrolases – lipases, proteases, carbohydrases,nucleases) optimally active at the acidic pH. These enzymes are capable of digesting carbohydrates, proteins, lipids and nucleic acids.

Question 17

what is the vacuole

Answer 17

The vacuole is the membrane-bound space found in the cytoplasm. It contains
water, sap, excretory product and other materials not useful for the cell. The
vacuole is bound by a single membrane called tonoplast. In plant cells the
vacuoles can occupy up to 90 per cent of the volume of the cell. It maintains the turigidity of the cell

Question 18

what is the function of tonoplast

Answer 18

In plants, the tonoplast facilitates the active transport of a number of ions
and other materials against concentration gradients into the vacuole(region of low concentration outside cell to high concentration vacuole), hence
their concentration is significantly higher in the vacuole than in the
cytoplasm.

Question 19

how are vacuoles in animal cells

Answer 19

In anial cellls, vacuoles are tiny and temporary
In Amoeba the contractile vacuole is important for osmoregulation
and excretion. In many cells, as in protists, food vacuoles are formed by
engulfing the food particles.