chapter 3-exe (ans)

8/11/2019 Chapter 3-Exe (Ans)

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Chapter 3 : Movement of Substances across Plasma Membrane

Section A

1.

(a) (i) Fluid-mosaic model

(ii) Give 2 reasons why this membrane is given the name as mentioned inai!

- The phospholipids molecules, protein molecules & other components are not

rigid or static, they can move thus giving the membrane fluidity.

- The protein are scattered in the phospholipids bilayer giving it a mosaic

appearance.

(b) A phospholipids molecules

! integral protein (carrier protein)

" e#trinsic protein

$ cholesterol

(c) "#plain how the molecules in structure A are arranged in a bilayer$

- %ydrophilic head of phospholipids molecule points outards (attract to ater).

- %ydrophobic tail faces inards (aay from ater)

- The phospholipids molecules are arranged in bilayer structure.


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(d) State the importance of molecule % in the maintenance of the fluidity of animal

cell membrane at

(i) &'(C

At moderately high temp) molecule % reduce e#cessive membrane

fluidity by preventing free movement of phospholipids molecules$

(ii) *'(C

At low temp) molecule % prevents close pac+ing of phospholipids

molecules , prevent solidification of the membrane$

(e) State 3 differences between simple diffusion , active transport.

Simple diffusion

$oes not re'uired energy.

ove from a region of higher concentration to a region of loer concentration

ove don a concentration gradient

'uilibrium reach

$oes not re'uire carrier protein

Active transport

*eed energy

ove from a region of loer concentration to a region of higher concentration

ove against the concentration gradient

+esults in accumulation or elimination

A carrier protein is needed


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.

(a) "#plain why osmosis is considered as a special type of diffusion$

Movement of -2. molecules only

/rom a region of high 0 1 to a region of low 0 1

hrough partially permeable membrane

Move down 0 1 gradient until euilibrium reach

(b) 4hat will happen to the potato cylinder , air bubbles when the potato is in

contact with the distilled water5

-2. diffuses into the potato cells osmosis!

%istilled -2. is hypotonic to the cell sap of potato

he volume of -2. in the capillary tube 6

he air bubbles moves towards the left

(c) A second similar apparatus was set up using a fresh potato cylinder but using a

different liuid 7$ he air bubble remained stationary$ "#plain the

observation$

8iuid 7 is isotonic to the potato cell sap

9o net movement of -2. in , out of the cell


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-2. diffuse in , out at the same rate

(d) A third e#periment was set up using another fresh potato cylinder , using a

different liuid $ he air bubble moved to the right in the capillary tube$

(i) 4hat has happened in the third set of apparatus5

8iuid is hypertonic to the potato cell sap

More -2. diffuse out from potato cells osmosis!

;olume of -2. in capillary tube

*$ he spinach strips A) >) C! were placed in Petri dishes containing sucrose

solution of different concentration) *?) @?) 3'?$ he remaining spinach strip

%! was placed in a dish without sucrose solution$


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a! i! -ypotonic solution

The solution ith loer solute hen compared ith other solution.

ii! sotonic solution

%as the same solute as the other solution.

iii! -ypertonic solution

The solution ith higher solute hen compared ith the other solution.

(b)

(c) "#plain what happen to each of the following spinach strips after 3' minutes$

i! Strip A

"uticle layer is impermeable to %/

%/ diffuses fr the hypotonic solution through the cut surface


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The spinach cells near the cut surface e#pand

The strip curves outards

ii! Strip >

0sotonic solution

+ate of %/ diffuses into the spinach cells rate of %/ diffuses out fr the

cells

*o change in the length & shape

iv! Strip C

%/ diffuses out fr the spinach cells into the hypertonic solutions

pinach cells plasmolysed & contract

pidermis is protected by a cuticle layer (impermeable to %/)

trip curves outards

v! Strip %

%/ evaporates fr the cells through the cut surface

trip $ curves inard

trip $ curves less than strip ". %/ lost more rapidly by osmosis in strip

" than evaporation of %/ from strip $ to atmosphere.

. he figure shows the beginning , the end of an e#periment to illustrate a

physical process$


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(a) %escribe briefly the physical process as shown :

0s a simple diffusion

At the beginning, copper sulphate crystals are placed at the bottom of the

bea2er. There are no copper sulphate molecules in the distilled ater.

A different in of copper sulphate molecules at the bottom of the bea2er &

in the distilled ater.

"opper sulphate molecules diffuse from an area of high to an area of lo

, don a gradient until an e'uilibrium reach.

At the end, a uniformly blue colour is observed 3 simple diffusion has

occurred & sulphate molecules are uniformly

istributed in the distilled ater.

(b) "#plain the principles involved in the various stages of the food preservation$

The fish is placed a hypertonic salt solution.

4ater diffuses fr the fish into the surrounding hypertonic solution.


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4ater also diffuses from the bac (found on the fish) into the hypertonic solution.

The bacterial cells are plasmolysed.

$rying under the sun causes evaporation of ater & the fish becomes dehydrated.

This prevents the groth of bac.

(c) Plant cell immersed in different concentration of sucrose solution , distilled

water$

"#plain what happens to the plant cell at stage B) and S$

Stage B

The sucrose solution is isotonic to the plant cell sap.

*o osmotic gradient beteen the plant cell sap & its surrounding solution.

The rate of ater diffuses into & out the cell is e'uals.

*o change in the shape of the cell5 volume of the vacuole.

Stage

The sucrose solution is hypertonic to the plant cell sap.

4ater molecules diffuse out fr the cell sap & cytoplasm of the plant into the

surrounding sucrose solution.

A decrease in the volume of vacuole. The plasma membrane & cytoplasm start to

pull aay fr the cell all.


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Stage S

4hen a cell at plasmolysis is placed in distilled ater again, the distilled ater is

hypotonic to the cell sap.

4ater molecules diffuse fr the distilled ater into the plant cell by osmosis.

"ytoplasm presses against the cell all.

The cell becomes fully turgid.

The plant cell is deplasmolysed.

Section C

*$ (a)

Structure of plasma membrane based on the model proposed by S$D Singer ,

G$9icolson$

6lasma membrane consists of a phospholipids bilayer.

The hydrophilic heads of phospholipids molecules point outards.

Attracted to the atery surroundings.

The hydrophobic tails of phospholipids molecules face inards.

Aay from ater.

The phospholipid molecules can move laterally or change places. This gives the

membrane its fluidity.

There are different types of protein molecules scattered in the membrane, giving it a

mosaic pattern.

There are e#trinsic proteins on the outer & inner surfaces of the membrane.

ome intrinsic proteins are embedded partially in the membrane & others penetrate

through the membrane.

"holesterol molecules are found beteen phospholipid molecules to stabili7e

membrane structure & regulate membrane fluidity.


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ome protein molecules have short-branched carbohydrate chains attached ith them

to form glycoproteins.

(b) %escribe the different methods by which these mineral ions can move across

plasma membrane into the animal cells$

CellConcentration of mineral ions mol per dm3!

Sodium ion Potassium ionAnimal cell 89.: 81:

Tissue fluid 8;< .:

Facilitated diffusion (passive transport, does not re'uire energy)

*a=diffuse fr a region of higher to a region of loer , move don a

gradient.

*a=move through the membrane protein pore (channel protein) into the cell.

>= diffuse from a region of loer to a region of higher .

>=move against a gradient.

This process is aided by carrier protein.

The binding of >=to the carrier protein causes the protein molecule to alter its

shape.

The >=are released into the cell.

The process is active transport. nergy is re'uired (provided by AT6).

2$ (b)"#plain why the application of e#cessive fertili=ers by farmers causes the

wilting of the crop plants$


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Addition of e#cessive fertili7ers causes the soil solution to become concentrated.

The soil solution is hypertonic to the root cells.

%/ diffuses out from the root cells by osmosis, don a %/ concentration.

This causes the cells to be plasmolysed.

The root cells cannot absorb %/ & mineral salts from the soil solution.

%/ & mineral salts are not transported to the aerial part of the plant. The leaves

ilt, no photosynthesis & the plant dies.

chapter 3-exe (ans)

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