Tips For Biology Paper 5 Exam

Notes on tips for Biology Paper 5 Exam.

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Biology Paper 5 Notes

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CO2:

◦       Usually, most of the CO2 absorbents are with -OH eg: NaOH or KOH

◦       Sources of CO2 are usually those with the -CO3 eg: CaCO3, H2CO3

◦       a non-chemical source: gas cylinder

◦       the gas is supplied through a bubbler.

◦       to measure CO2 concentration: use probe with meter]

Temperature:

◦       method of controlling: use an electronic water-bath (a beaker of boiling water)-depends on the experiment

◦       use an electronic thermostat

◦       heat screen*/ heat filter

*for uniform distribution of heat.

◦       incubator

◦       digital/mercury thermometer

◦       for food tests, such as Benedict's test, the temp must be above 80'C.

Time:

Always mention:

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Physics - Revision Notes on Electric Fields

Electric field is a region in space where a stationary charge experiences a force

The direction of an electric field is defined as the direction in which a positive charge would move if it were free to do so

The electric field strength E, is defined as the force per unit charge acting on a small positive charge placed at that point,

 i.e.     E = F/Q  N C^-1

The force between charges according to coulomb is

proportional to the product of the charges and inversely proportional to the square of the distance between them

 i.e F = kQ₁Q₂/r²

  where k is a constant of proportionality, the value of which depends on the medium around the charges

•             this law applies to point charges but can be used for charged spheres provided their radii are small compared to their separation

The potential difference V_AB between two points A and B in an electric field is the work done W, in moving a unit positive charge from B of lower potential to A of higher potential against the direction of the line of action of the force on the unit charge.

That is V_AB = W/Q   i.e.  W = VQ   SI unit of V is Volts

But also, work done (which is energy)

W = Fd, therefore Fd = VQ with units of V C

·           Rearranging, F/Q = V/d,

·           but F/Q is the force per unit charge which is the definition of electric field strength E.

·           Hence for a uniform field, the field strength E = V/d V m^-1

·           E has 2 equivalent SI units, V m^-1 = N C^-1

From Coulomb’s Law, the force on a test charge Q₁, a distance r from the isolated point charge Q₂ is given by,

F = kQ₁Q₂/r²

The electric field E at the location of the test charge q, is given by

 E = F/q

Therefore the electric field due to the isolated point charge is

 F = kQ₁Q₂/r²

Electric field has been defined as the force per unit charge

Electric potential V, at a point in an electric field is defined as the work done or potential energy PE, in bringing unit positive charge from infinity to the point

 i.e V = PE/Q

The field strength is equal to the negative of the potential gradient at that point

V = PE/Q = (F x r)/q = (kQ1Q2/r2x r)/q   = kQ/r 

            where k = 1/4πε0r

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Handwritten Summary Notes on Remote Sensing - X-Rays

Short notes on X-rays under remote sensing. Please Like, Comment any questions or suggestions and Share. Thank you 😊😊

Organic Chemistry

Handwritten notes on Halogen Derivatives

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Tips for A Level Physics Paper 5

Tips for A Level Physics Paper 5 [with number of marks attached]

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Physics

Link to notes on:
Work, Energy and Power

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Biology Practicals

How to Prepare a Wet Mount Specimen/Microscopic Slide

Step One - Obtain a clean microscope slide.

Step Two - Place a drop of liquid on the slide. This is the “wet” part of the wet mount. The liquid used depends on the type of cell being viewed:

•  If examining a plant cell, tap water can be used. 

• If examining an animal cell, physiological saline (or contact lens solution) must be used, because if plain water is used, the cell will explode from osmotic pressure. Unlike plant cells and bacteria, animal cells have no cell wall to structurally support them.

Step Three - Obtain the specimen to be used. Some introductory biology classics for viewing include:

• Skin of an onion bulb: In order to view the cells, a very thin layer of skin must be obtained. Take a single layer of onion and bend it towards the shiny side. After it snaps, pull gently, and a transparent layer of skin, similar to Scotch tape, will appear.

• Elodea leaf: Elodea leaves are two cell layers thick. The cells in one layer are smaller than the cells in the other, so elodea leaves can be used to better understand a microscope's depth of field.

• Cheek cells: Human epithelial cells can be obtained by gently rubbing a toothpick on the inside of the mouth, and then swirling the toothpick in the physiological saline on the slide.

• Pond water: Obtaining some water from a pond makes wet mount preparation a breeze, since the water and the specimens are both included.

Step Four - Place the specimen into the liquid on the slide.

Step Five - If the specimen is transparent, such as onion skin or check cells, stain should be added to increase contrast. A drop of iodine or methylene blue is commonly used. Do not use stain if viewing photosynthetic cells (which already appear green due to chlorophyll), or living organisms, such as protozoans in pond water (stains will kill them).

Step Six - Place a cover slip over the specimen. This will sandwich the specimen between the slide and the cover slip. To avoid trapping air bubbles, set one edge of the cover slip on the slide, and then let the rest of the cover slip drop. As it drops from one side to the other, air will be pushed out, and this will reduce the number of bubbles in the wet mount. 

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