plasma membrane and cell wall

Question 1

why is cell membrane a absolute requirement?

Answer 1

maintains the relationship of a cell and the outside world

Question 2

which cell was used to study plasma membrane before the invention of electron microscope?

Answer 2

erythrocytes or RBCs

Question 3

what is a plasma membrane composed of?

Answer 3

they are composed of lipids in the bilayer. the hydrophilic head(polar) face in the outer side and the hydrophobic head(non-polar) facing the inner side, this ensures that the hydrophobic tail is protected from the aqueous environment. The plasma membrane also contains protein and carbohydrates.

Question 4

what is the protein-lipid ratio of the plasma membrane in human erythrocytes(RBC)?

Answer 4

52% protein 40% lipids

Question 5

what are the different type of protein present in the plasma membrane ?

Answer 5

1) peripheral protein:-lie one surface of the membrane
2) integral protein:-they are partially or totally buried in the membrane. the integral protein that runs through the membrane are called tunnel protein or trans membrane protein. removal of these proteins require crude methods like detergent treatment

Question 6

explain the fluid mosaic model?

Answer 6

its is an improved model of the plasma membrane proposed by singer and Nicholson(1792). According to it the quasi-fluid nature of lipid enables the lateral movement of protein within the overall bilayer .this ability to move is measured by fluidity

Question 7

what has been the plasma membrane been described as?

Answer 7

protein ice bergs floating in sea of phospholipids.

Question 8

what is the function of the plasma membrane?

Answer 8

1) the fluid nature of the help in functions like cell growth, formation of the intercellular junction, secretion, endocytosis, cell division etc.
2) plasma membrane is selectively permeable and allows the transport of some molecules across it.
3) the two methods of transport are: -passive: transport of molecules without any energy requirement, along the concentration gradient. Downhill movement. eg: diffusion
- active: it is an uphill movement, against the concentration gradient(low to high) with energy requirement.
eg: Na+/k+ pump in animal cells.

Question 9

explain the movement of water across the blipped layers?

Answer 9

water move from high concentrate to low concentrate by diffusion through cell membrane called osmosis.as polar molecules cannot pass through non polar lipid bilayer, they need a carrier protein to facilitate their transport.

Question 10

what are cell walls?

Answer 10

they are rigid non living structure present in algae , fungi and plants.

Question 11

what is the cell wall of a fungi composed of?

Answer 11

the are genrally composed chitin , N-acetylegleucosa(NAG)

Question 12

what is the cell wall of a algae composed of?

Answer 12

thy are generally compose of cellulose , n= mannons, calcium carbonate, galactans.

Question 13

what is the cell wall of a plant composed of?

Answer 13

they are composed of cellulose , hemi cellulose ,protein ,pectin.

Question 14

what are the three layer of plant cell all

Answer 14

1) primary wall
2) secondary wall
3) middle lamella

Question 15

explain the structure of primary wall?

Answer 15

they are found in young plants.its a single layer of cell material capable pof expansion in growing cells.it grows in addition to already existing wall material . meristematic and parenchymatous cell wall only have primary wall.

Question 16

explain the structure of secondary wall?

Answer 16

in mature cell more layers are added to the pre existing primary wall internally which results in the thickening of cell wall. this mainly occurs in lignified and suberized cell walls. Primary wall gradually diminishes with maturity

Question 17

explain the structure of middle lamella?

Answer 17

it is a thin, sticky, amorphous layer of cementing material that holds together adjecent cells. its mostly made up of calcium pectate and magnesium pectate.
it may be traversed by plasmodesmata which connects the cytoplasm of adjacent cells.

Question 18

what happens to middle lamella in fruits?

Answer 18

they solubilize to form a jelly like substance making the fruit soft.

Question 19

what are the functions of cell wall?

Answer 19

1) maintains shape
2) protects from mechanical injury
3) wards off attacks from pathogens like bacteria, viruses and fungi
4) allows materials in and out of the cell
5) prevents the entry of undesired macromolecules
6) helps in the cell to cell interaction.

Question 20

what are pits?

Answer 20

cell walls are unevenly thickened since the secondary wall are not laid down in some areas and these areas are called pits. pits of adjacent cell usually lie opposite to each other forming a pit pair.

Question 21

what are the 2 types of pits?

Answer 21

1) simple pit :- pits that are in uniform diameter

2) bordered pit:- pits that have a flask shaped cavity as in tracheids

Question 22

what are plasmodesmata?

Answer 22

they are living components of dead wall. a large number of plasmodesmata or cytoplasmic strands are present inb the pits through which the cytoplasm of a cell keeps contact with the other. They are lined by plasma membrane and contain fine tubules called desmotubules.ER plays a role in the formation of plasmodesmata. they form the symplastic system

Question 23

what is the symplastic system?

Answer 23

it is a system of interconnected cells that that linked by plasmodesmata.