Enzyme

The induced-fit hypothesis: The substrate molecule binds with the enzyme molecule and induces a change in shape of the enzyme molecule.

Enzyme Cofactors
A cofactor is the non-protein component of an enzyme essential for its catalytic activity.

Inorganic ions= Activators
can be loosely or firmly bound

Organic compounds:

1. firmly bound = prosthetic group
2. loosely bound = coenzymes

----Prosthetic group
----integral part, e.g. FAD

----Coenzymes
----carrier to transfer atom, e.g. NAD, NADP

Enzyme Inhibitions (nothing to do with cofactor)

Competitive inhibitors:
substance similar to substrate, compete for active site
+ substrate concentration, - degree of inhibition, vice versa
+ inhibitor concentration, + degree of inhibition, vice versa

Non-competitive inhibitors:
attach to parts other than active site, not compete for active site
+ substrate concentration, X degree of inhibition, vice versa
+ inhibitor concentration, + degree of inhibition, vice versa
binding affinity

Reversible inhibitors
Can be Competitive or Non-competitive
Effect on enzyme:
occupying active site/altering conformation of active site temporarily

Irreversible inhibitors
ONLY NON-COMPETITIVE
Effect on enzyme:
altering conformation of active site permanently

End-product inhibition

Metabolic pathway:
Step-wise reaction for

1. preventing vigorous reaction that a quick release of heat may damage the cells
2. allowing the energy released from the reactions to be utilized effectively
3. intermediate metabolites of pathway may be useful to other metabolic pathways

Negative feedback inhibition:
When end-product is in excess, end product itself act as an allosteric inhibitor and binds with the allosteric site of allosteric enzyme. This will temporary shut down the entire series of reaction.
All the intermediate metabolites and the end-product will not be formed.

Active transport

Unidirectional----substance are transported in one direction only
Carrier protein

For large particles
Phagocytosis

1. Invagination of the cell membrane/pseudopodia surround foreign particles
2. Cup-shaped cavity pinched off from cell membrane, it forms phagocytic vesicles/food vacuole
   
3. Vesicle migrates to the center of the cell
4. Lysosome fuses with the vesicle
5. Hydrolytic enzymes are discharged from lysosome to vesicle for digestion
6. Digested products are absorbed by the cytoplasm
7. Vesicle containing indigested matter moves towards the edge of the cell
8. Indigested matter removed when vesicle fused with the cell membrane

Pinocytosis
Similar to phagocytosis but differs in

1. liquids instead of solid are digested
2. pinocytic vesicles are much smaller than phagocytic vesicles

blood+neurone --71

animal cells and tissues: Epithelia

They are tissues that cover the surface of internal and external organ.
They give protection, secretion, absorption, gaseous diffusion, excretion etc.
connective tissue= basement membrane

Simple epithelia: Single layer of epithelial cell, e.g. Squamous, ciliated epithelium
compound epithelia: more than one layer, e.g. stratified epithelium

Squamous epithelium
Consist of flattened, plate-like cells with disc shape nucleus and wavy boundary.

features:
The thinness of the epithelium allows rapid diffusion/filtration of materials

Place found:
alveolar membrane, bowman's capsule

Ciliated epithelium
Consist of columnar cells with numerous cilia on the free surface. Goblet cells interspersed among columnar cells.
Columnar cells: tall and narrow shape, containing elongated nucleus.
Goblet cells: specialized epithelial cell that secret mucus

features:
Coordinated beating action produced facilitate movement of material(dust/ cell)

Place found:
inner surface of the oviduct, inner lining of trachea

Stratified epithelium:
Consist of basement membrane--germinative layer and layers of old cells

• Germinative layer is a site where active cell division takes place.
• Newly divided cells are pushed upwards to replace the old ones,while the old cells become gradually flattened near the surface.
• The outermost cells are usually dead, flattened and gradually sloughed off because they are kept away from the nutrient supply

features:
Protect the underlying tissues against abrasion.

Place found:
inner lining of virgina
epidermis of skin

• the outer cells are keratinized (layer of keratin)
• horny and waterproof layer provides excellent protection from mechanical injury and dehydration

Phloem and Xylem

Phloem
composed of sieve tube elements, companion cells, parenchyma, sclereids and fibres

sieve tube element:
tubular cell
fuse together end to end to form continuous tube--sieve tube
Its maturity:

• nuclear degenerates
• cytoplasm restricted to the edge of the cell
• end wall perforated--sieve pore
• keep alive by companion cell<---connected via plasmodesmata

Xylem
composed of tracheary elements, fibres and parenchyma

Tracheary elements:
Elongated cells that transport water and minerals.
provide high mechanical strength to withstand the high tension of the uprising columns of water give support to the plant

two kinds: -----vessel element -------------- tracheid
different-aaaa------shorter-------------------longer
aaaaaaaaaaaaa---larger lumen---------------smaller

common- Thick and highly lignified
----------When extensively lignified, it would be deprived of water,
----------nutrient supply and die off, cell content degenerates
---------- leaving empty lumen to facilitate the transport of water
-----------and minerals.

vessel element:
align as hollow tubes called xylem vessel
primary wall area covered by secondary wall material--

• first occur as rings or helices called annular thickening and spiral thickening
• next more extensive deposit of lignin reticulate thickening and pitted thickening

Tracheid:
similar to sclerenchyma
tapered end wall overlapping each other
passage of water from cell to cell is facilitate by bordered pits, through pit membranes


Fibres
similar to sclerenchyma but with thicker cell walls
do not involved in conduction of water
provide additional mechanical support

Ground tissues:Parenchyma, Collenchyma, Sclerenchyma

hardness:
P < C < S PCS

Parenchyma
Place: Found in cortex and pith of stem and cortex of root and mesophyll of leaves.

features:made up of thin-walled living cell, metabolically active and capable of division, capable of elongation, potentially meristemic(modified to form epidermal cell)

functions:
1.mechanical support of non-woody plant,
2. facilitate gas exchange,
3. contains chloroplast for photosynthesis

Collenchyma
place: under the epidermis of stems and around the midrib of leaves.

features: similar to parenchyma, with additional deposits of cellulose at the coners of the cell walls .

functions:
1. mechanical support to young, actively glowing stems and leaves.

Sclerenchyma
features: dead cells with cell contents lost----thickened and impermeable to water, evenly thickened cell wall

secondary thickening: laying down of secondary cell wall which is highly lignified on the primary cell wall except at the pit. It formed when the cell growth is stopped.

functions:
1. high mechanical strength provided by high tensile strength and compressional strength of lignin.

Fibres:
elongated and tapering cells
found in vascular tissues(phloem...), behind epidermas

Sclereids:
shorty and relatively spherical
behind epidermas, cortex, fruits, seeds

Lysosome

Single membrane bounded vesicle pinched off from the releasing face of Golgi Apparatus.

NOT secretory vesicle! They are retained in the cytoplasm.

Function:

1. Breaking down unwanted molecules.
2. Digesting material taken up from outside
   
3. Breaking down worn -out organelles
4. Destroying the whole cell when the cell is severely damaged
   
5. reabsorbing unnecessary tissue by releasing enzyme outside the cell.
   

Functional relationshiop between nucleus, ER, Ribosomes and Golgi apparatus

Golgi apparatus

Structure:
Forming face----convex end next to ER----form new cisternae by vesicle budding off rER
Releasing face----concave end----secretary vesicles and lysosomes are pinched off

Function:

1. Storage, chemical modification, packing and export of proteins
2. enzyme production
3. lysosome formation
4. synthesizing and exporting of polysaccharides, e.g. celloluse

Ribosomes

Made up of ribosomal RNA and proteins.

They are attached to rough ER or suspended freely in cytoplasmic matrix.

They synthesis protein

Endoplasmic reticulum

Structure:

• single membrane-bounded

• highly folded in to flattened sacs and tubes which is
  

----cisternae

system of channel extends throughout cytoplasm, from outer nuclear membrane to cell
membrane. It is an extension of the outer nuclear membrane without pore. It filled with fluid containing enzymes for metabolic activities.
Tubular cisternae continuously pinched off to form Golgi Apparatus.

	Rough ER	Smooth ER
Appearance	ribosome attached	no
cisternae	nothing special	more tubular
function	Synthesize protein(secretary,membrane)	synthesize lipid and steroids

Function of all ER:

1. Extensive membrane system acts as cytoskeleton for support
2. Intricate channel of ER facilitate transport .
3. ER membrane provide a large surface area for attachment of enzyme

Example:
rough ER: pancreatic islet cells
smooth ER:sebaceous gland cells

AL Biology: Cell membrane

Made up of phospholipid bilayer, hydrophobic hydrocarbon chain face inward to each other----suit aqueous environment on both sides of the cell membrane and to accommodate the hydrophobic hydrocarbon chains.

it is in the form of fluid mosaic model----phospholipid and protein molecules can move side way within the bimolecular leaflet, movement is restricted by cholesterol but still in liquid form.
Function
Permeable to fat soluble substances
Carrier protein permeable to aqueous substance

The membrane protein:
outer or inner surface----peripheral protein(pp)
extended into leaflet----integral protein(ip)
penetrate both surface----transmembrane protein(tp)

type	location	function
enzymes	pp	[speeding up metabolic reactions]
recognition proteins	pp(outer)	[cell recognition(distinguishing foreign molecules from self molecules)]
receptor proteins	tp	[allowing the cell to recognize a signal and trigger corresponding reactions ]
channel proteins	tp	[forming channels through which small polar molecules may pass]
carrier proteins	tp	[for active transport and facilitated diffusion]

ERRCC

The surface carbohydrates:
mostly conjugated with membrane protein to form glycoprotein.

Differentiation in cell membrane:
Microvilli---- finger-liked projections which increases the surface area of the cell for absorption of material, facilitate absorption and secretion due to presence of contractile filament eg. intestine epithelial cell.
pseudopodia----foot-like membrane extensions found in cell capable of changing shape. It facilitate phagocytosis, pinocytosis or movement for itself.

Functions of the cell membrane
1. Maintains the integrity of the cell.
2.Controls the movement of material in and out of the cell by channel protein etc.
3.Protects the cell from harmful material outside such as hydrolytic enzyme
4.Recognition proteins perform cell recognition.
5.Receptor proteins allow the cell to recognize a signal and trigger corresponding reaction.
6.subcellular membranes divide the cell into compartments so that metabolic reactions can take place without interference.
7. Provides surface for attachment of enzyme
8. Provide electrical insulation(myelin sheath)
9. Enable movement, phagocytosis and pinocytosis.

resources from Advance level biology for Hong Kong

AL Physics: no change in percentage error for mutiple/division

the t for a number of complete oscillations is taken. It is found that the time for 20 complete oscillations is 36.5+-0.2s.

% error in T =% error in t although t=T/20
So 0.2/36.5 =(delta)t/t

Example:
The period of oscillation, T, of a simple pendulum is related to its length, l, by the formula T=2pi sqrt(l/g). To find experimentally the accerleration of free fall by using in simple pendulum, a student takes the following measurements:

time for 10 oscillations: 13.8+-0.2s
length of the pendulum: 0.472+-0.001m

ANS:9.8+-0.3m s^2

CE Biology: location of area in the brain

CE Biology:the degrees of movement of vertebral column and a joint in relation to their structure

Compare the degrees of movement of vertebral column and a joint in relation to their structure?

(6 marks)

Vertebral column is made up of many pieces of vertebrae.	1
Intervertebral discs lie between adjacent vertebrae in the spine. Each disc forms a cartilaginous joint to	1
allow slight movement of the vertebrae, and acts as a ligament to hold the vertebrae together.	1
A joint is a junction where two or more bones meet together.	1
At the joint, the bones are held together by tough sheets of elastic fibres called ligaments.	1
As they are elastic, the bones can moved with a larger degree of movement in a controlled way at the joint.	1

CE Mathematics: Polar coordinate

Q=(a,b)

polar coordinate of Q=(SQRT(a^2+b^2), tan^-1(b/a) degree)

CE Chemistry: detection and analysis

To distinguish sodium carbonate and sodium hydrogencarbonate, we cannot add water as both of them dissolve. We will heat the solid and the one remains stable is sodium carbonate while the one decompose on heating to release a colourless gas which can turn lime water milky is sodium hydrogencarbonate.

2NaHCO3(s) --> Na2CO3 +H2O + CO2
-----------------------------------------------------

To distinguish sulphate and sulphite solution, we can add acidified barium nitrate solution. The one which forms white precipitate is sodium sulphate while the solution which does not show observable change is sodium sulphite.
*barium sulphite is insoluble in water but redissolve in dilute nitric acid.
-----------------------------------------------------
To test for the presence of silver ions, add excess ammonia solution to see whether colourless solution form.

CE Chemistry: reagent store in brown bottle

Concentrated nitric acid, potassium permanganate solution, silver nitrate and chlorine water is usually kept in a brown bottle. It is because they are easily decompose by light.

ethanol, ethyl ethanote and 1,1,1-trichloroethene should be heat under water bath because they are flammable.

物理試後感

千年道行一朝喪！莫道不銷魂！

CE Physics: conservation of energy cannot be applied to the question of inelastic collision

Two pendula of the same length are arranged as bob A of mass M at the equilibrium position and bob B of mass 2M hang aside of vertical height 0.45m . Bob B is relased and hit the other boba at the equilibrium position. Finally the two ball stick together. Find the common velocity of the bobs just after collision.

If you use the formula: potential energy of B at original position=Kinetic energy of B at the equilibrum= kinetic energy after collision, then you are wrong. Kinetic Energy is not conserve in the system of inelastic collision. So better find the velocity of B just before collision and use conservation of momentum to reach the answer.

CE Physics: force of impact...

A ball of mass 3kg drops from rest to the ground from a height of 5m. After the impact it rebounds to the same height. Assume that the time of impact between the ball and the ground is 0.2s. What is the rorce of impact acting on the ground surface by the ball?

The answer is 330N, not 300N. 300 is the net force acting on the ball during impact. Talking about impact force acting on the ground surface by the ball, it is action force acting on the ground by the ball in other words, so we have to include weight in the calculation.

CE Physics:notes on atomic physics

In alpha particle scattering experiment, when gold foil is in 1mm thickness, The number of particles detected at the opposite side of the source becomes zero but not just decreases. (92Q7)

Usually a radioactive source with X to 1X hours half life emitting gamma radiation is used for injection in patient. The reasons include:
1.The half-life is long enough for doctor to diagnose the patient.
2.The half-life is short so that the radiation will not retain inside the body for a long time causing little harm to the body
3.Gamma ray get high penetrating power so that it can be detected outside the body.
(93Q7)

CE Physics: copper is not a magnectic material

93Q5(ai)
Describe a method to find the magnetic field pattern on the cardboard using iron filings.
Ans.Sprinkle iron filings on the board and tap the board gently. The magnetic field pattern is shown by the pattern of the filings.

How about using copper filings?
Copper, though being a metal, is not a magnetic material. So we cannot use copper filings.

CE physics: conservation of energy 的真諦

設一架過山車在A點(設離地100米) 以30m/s 移動，向下滑動後再上B 點，那麼B點可否超過A點的高度?(超過離地100米?) 假設friction 可以neglected.

答案是可以。如果單純看potential energy，車在B點的potential energy高於A，那麼energy 便不conserved了?這是因為看漏了kinetic energy，留意車在A點是在移動，那麼只要車在B點的速度少於A點，彌補多出的potential energy，兩者整體的energy(KE+PE) 都是一樣，energy is conserved 。

CE Biology: MC knowledge

1.Female sex hormone can maintain pregnancy.
2.Cotyledons in seeds do not carry out photosynthesis.
3.Small mammals have bigger surface area to volume ratio so that more heat is lost.
4.Sweat gland can only be found in mammal.
5.Concentration of urea and salt in glomerular filtrate is the same as plasma.
6.The highest concentration in glomerular filtrate is sodium chloride not urea.
7.Vertebral column consist of many small bone to enable body to bend.
8.Axon presents in the central nervous system are non-myelinated.
9.Both red blood cell and plasma involve in transportation of carbon dioxide towards the lung.
10.Calcium, which can be removed by sodium oxalate in solution, takes parts in blood clotting.
11.Double circulation maintain higher blood pressure and prevent the mixing of oxygenated and deoxygenated blood.
12.Canine absents in some mammals.
13.The widespread distribution of veins give mechanical support to the flattened blade of the leaf.
14.The vascular bundles of a dicotyledonous root are usually presence at the central core to provide better anchoring effect to act against the uprooting stress of wind or by-passing animals.
15.The vascular bundles of a dicotyledonous stem are usually presence along the periphery to provide better strengthening effect to act against the bending stress of wind.
16.At night, the accumulation of carbon dioxide stimulate sugar in the guard cell changing to starch thereby raise the water potential there and causing water to be drawn to be drawn to the surrounding which cause the stomata to close.
17.Each time before the level of the coloured water in the graduated U glass tube is measured, the leveling arm has to be moved up and down until the water levels in both the leveling arm are the same. This is to ensure that each time the volume of the gas trapped in the sample chamber is measured under the same pressure.
18.Contour ploughing prevents gully erosion.
19.Warm water decrease the solubility of gases and this make less oxygen available in water.this may lead to suffocation of certain aerobic life.
20.Carbon dioxide can be utilized by aquatic animals to combine with calcium for the formation of calcareous shells.
21.Bacteria carry out sexual reproduction conjugation.

Special thanks to Y.K.To, author of Complete Multiple choice Biology

Circle touching each other

When you come across this situation, DRAW TANGENT at the point touching each other

CE Mathematics: cancel out the given impossible option in probability

There are 3 balls in a bag, they are black(B), red(R) and white(W) respectively. Suppose the probability of drawing B is 0.1, R is 0.4 and W is 0.5. You draw a ball and it is known that it is black or red(that means it cannot be white). What is the probability of drawing a black ball?
Originally: 0.1+0.4+0.5=1
As drawing white ball is impossible, we cancel it out and it becomes
0.1+0.4=0.5......(*)
(*) x 2 to have one as the utimate possibility 1
0.2+0.8=1

Thus the probability of drawing a black ball is 0.2.

CE Chemistry: describing cleaniness of fuels

low carbon content + complete combustion =clean fuels
high carbon content + incomplete combustion and particulates/CO/...= not clean fuels

CE Physics:machanics- newton's law and the definition of power

When situation is at rest or in constant acceleration, use newton's first law.
Accelerating, use second law.
Two objects, use third law.
They are some points in the (*) questions.

Power is the rate of change in energy, no matter it is potential energy, kinetic energy,etc
It can be express as P=Fv.
Sometimes differentiation can help solve the problem.

MC for finding LCM in mathematics

2004 NO.38
Find the LCM of (2-b) (4-b^2) (8-b^3).

There must be at least one that can factorized into another form. In this question we consider the middle one first.
(4-b^2)=(2^2-b^2) =(2+b)(2-b)
then the third one
(8-b^3) =(2^3-b^3) =(2-b)(2^2+2xb+b^2)
...
You can then work out the answer.

Take out variable instead of cancel out in solving equations

How many roots does the equation tan x =2sinx have? For 0<=x<=360 in degree.
sinx/cosx = 2sinx
sinx = 2sinx cosx

Now if you cancel out the term sinx, and the equation becomes 1=2cosx, you will miss 3 answers.

The correct steps are as follow:
0 = 2sinx cosx -sinx
0 = sinx(2cosx -1)
when sinx =0, x can be 0, 180, 360 in degree.
when cosx=0.5, x can be 60, 300 in degree.

There are 5 answers. This technique is very important in both math and A-math. Especially dueling with =0 or trigo problem.

Using Acidified silver nitrate solution to test for the presence of halides

Acidified silver nitrate can test for halides to give precipitate. Remember it do give positive result for halides, not only chloride ions.

(pale) Yellow precipitate forms when iodide (bromide) ions is used, white precipitate forms when there are chloride ions.

Here are the reasons why silver nitrate has to be acidified for testing purpose from Wikipedia:
Silver nitrate are typically acidifed with dilute nitric acid to remove interfering ions, e.g. carbonate ions and sulfide ions. This step avoids confusion of silver sulfide or silver carbonate precipitates with that of silver halides. Addition of AgNO3 to the resulting solutions produces a precipitate in the presence of halides. The color of precipitate varies with the halide.

Misconception on Alkene

The statement' It can decolorize acidified potassium dichormate solution ' has two mistakes:

1. Acidified potassium dichormate solution will change from orange to green when being reduced. NOT decolorize
2. Acidified potassium dichormate is not strong enough to oxidize alkene to alkanediol.

*HOWEVER, acidified potassium dichormate solution can oxidize methanol and ethanol to methanoic acid and ethanoic acid repectively. Further down the homologous series propan-1-ol and Butan-1-ol need a more stronger oxidizing agent that is acidified potassium permanganate.

Question on alpha paricle scattering experiment

Option (3) is not correct because the positive charge of the nucleus of the gold atom will repell the positively charged alpha particle. Instead, the alpha particle should bend downward.

Nucleons = neutrons + protons.

Electrostatics: Charge 不變定則before earthing

在一幅圖內，不論charge 如何induce，圖內的total charge 是不會改變的，在earthing之前而言。
(稍後會附圖解釋。)

當earthing 發生後，圖內的total charge 是 0 。

是就整體而言，非指個別物體。

Electrostatics: Earth 的獨特性

接下來要說明的物理學重點頗為抽像，用中文解釋可以幫助香港學生理解。

一樣沒有被earth的普通conductor 是不可以discharge 一個帶charge 的 insulator(當接觸時).只有像Earth 那般巨大的物體才可以做到share 所有的charge.

如要discharge 一個insulator，可以用火去燒。

adding line to the given graph to solve equation

y= x^2 -2x -3 is given, to solve 2x^2 -6x -3 =0, what straight line should be added in order to solve the equation?

1.make the equation contains =0 to be like the y=... equation. NOT VICE VERSA.
x^2 -3x-3/2 =0

2.duel with the y= equation, substitute the line equation into y so that it becomes the treated
equation in procedure 1
x^2 -2x -3 = x -3/2

The equation of the line is y= x -3/2.

arithmatic sequence

given sum of first n of the arithmatic sequence= n^2, find T(10).

Difference between two consecutive arithmatic sequence is the last term:T(n)=S(n)-S(n-1)
e.g. T10 =S10-S9 = 10^2 - 9^2 =19

This technicque is quite useful .
----------------------------------------------------------------------------------
reminder:
T(n)= a + (n-1)d to find T(10).
sum of arithmatic sequence is 頭加尾乘項數除2.

solving trigo equation

cos x = cos 2x
cos x = 2 (cos x)^2 -1
2(cos x)^2 - cos x - 1=0
(2cos x +1)(cos x - 1)=0
.
.

The skill is to make similar trigo terms, e.g. with cos x and cos 2x, you should convert cos 2x in terms of cos x.

Probability

Two dice are thrown, what is the probability of getting one '6'?

(1/6 x 5/6) x 2,
(1st=6 and 2st<>6) or (1st<>6 and 2st=6)

Not 1/6 + 1/6 !
Every time you due with the question concerning probabilty,
think of the combination first!

Getting at least one '6'?

(1/6 x 5/6) x 2 + (1/6 x 1/6)
(1st=6 and 2st<>6) or (1st<>6 and 2st=6) or (1st=6 and 2st=6)

Questions concerning Fossil Fuels, carbon compound, and corresponding products

Question for simple lab method to prepare Ethyl ethanoate.

Sulphuric acid in the condensation of ester act as dehydrating agent and catalyst.
HCL cannot be used because water presence will reverse the reaction.











Essay type question for oil spillage









Acid rain:

• Why rain is usually more acidic during water?

ANS: Decreasing temperature will increase the solubility of gases in water. Therefore more sulphur dioxide and nitrogen dioxide would dissolve in water during winter.
Besides, more fuels is burnt to meet the greater energy demand in winter.

• Use scrubbers in industry to remove SO2.
• Use electrostatic precipitator to remove dust/particulates.
• use catalytic converter in car exhaust system.
  

Convenience of crude oil over coal:

• Crude oil is convenient because it is in liquid state so that it is easy to transport.

Method to remove excess water:

• Adding calcium oxide.

Function of reflux condenser(Leibig's condenser) in preparing ethanoic acid from ethanol.

• Due to volatile intermediate product, a reflux condenser is used.
• If the condenser is arranged in a sloping position to a receiver(the set up for distillation of sea water), the product obtain would be ethanal instead of the desired ethanoic acid.
• the first product ethanal after oxidation of ethanol is very volatile and will escape on heating. If so, there would be no chance for the ethanal to be further oxidized to ethanolic acid.
• *Please refer to the previous post for the heat under reflux set up.
• After reflux, use fractional distillation to seperate ethanoic acid from the mixture.