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Biology; Chemistry; Physics: Post your doubts here!

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asma tareen

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as the rate of respiration increase thn more oxygen is reqiured which allos more blood to be pumped and the breating ans pulse is increase
 
simranlalchand

simranlalchand

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explain that DNA controls the production of proteins?
state that each gene controls the production of one protein?
explain that genes may be transferred between cells (reference should be made to transfer between
organisms of the same or different species)?
 
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asma tareen

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well for the first two i guess its related to transcription and translation
about the third one i think its by the help of genetic engineering:oops:
 
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Anees2rehman

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asma tareen said:
well i guess both have the same amount of villi but as digestion requires some time thn till illeum the digestion is complete and absorption starts :oops:
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Adv
1. They kill the Bacteria without harming the human cells.

Disadvantage
1. Introduction of antibiotics in the body may result in some allergic reactions.
2. The antibiotics also kill the useful bacteria in the body i.e those which help in digestion.
3. Wrong dosage may result in the bacteria becoming resistant to the antibiotic.
4. The liver breaks the antibiotics, as a result malfunctions may occur in the liver.
 
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Khadija_1234

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Snowysangel said:
The dry mass of the food storage region would remain the same while that of the plumule and radicle would increase gradually, as the glucose acquired from photosynthesis would directly be transported to the growing regions and there wouldn't be any need for it to be stored. Since the plant is already getting glucose from photosynthesis, it doesn't need to utilize it from the storage organ ie cotyledon so it's mass remains the same..:I think :S
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The mark scheme says that the mass of storage region will decrease but slowly :/
 
K

Khadija_1234

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Snowysangel said:
Could someone explain 8 or to me? :S
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(a) animal could be any farm animal for increased meat production and cows for increased milk production
Plants can be cereals for their increased production or any crop to make it disease resistant

First the individuals showing the quality required are selected. They are used as breeding stock. The offsprings showing the desired quality to the greatest extent are selected, then the selected offsprings are used for breeding. This is continued for many generations.as a result greater profits are made. But there is danger as well, this inbreeding can increses the chances of two recessive alleles coming together. This can give rise to genetically-controlled deformity
 
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Snowysangel

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For separating soluble salts, when do we use evaporation to dryness and when, crystallisation? Is sodium chloride the only salt that we evaporate to dryness? And if so why? Doesn't it have water of crystallisation :s
 
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Snowysangel

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Draw two lines 5 cm each. Then make two 5 cm arcs by placing the compass at either end. The two arcs will intersect. Join their intersection point to the origin. The resultant velocity will be at a 45' angle from both the forces
 
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Snowysangel

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What happens in centrifuging? The insoluble solute forms a suspension in the solid and sinks to the bottom very slowly, but how does that separate it from the mixture?
Also, how do u make soluble and insoluble salts? Could soneone tell me ONE detailed method of each?
 
Enferno

Enferno

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Snowysangel said:
What happens in centrifuging? The insoluble solute forms a suspension in the solid and sinks to the bottom very slowly, but how does that separate it from the mixture?
Also, how do u make soluble and insoluble salts? Could soneone tell me ONE detailed method of each?
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when the particles settle, we slowly drain the water and the particles remain inside(although some small one may come with the water

Methods of making Salts which are water soluble
Soluble salts can be made in four different ways:
1) ACID + METAL  SALT + HYDROGEN
2) ACID + BASE  SALT + WATER
3) ACID + CARBONATE  SALT + WATER + CARBON DIOXIDE
4) ACID + ALKALI  SALT + WATER


Method 1 (Acid + Metal):
Not suitable for making salts of metals above magnesium, or below iron/tin in reactivity.
e.g. zinc + hydrochloric acid  zinc chloride + hydrogen
Apparatus used: (1) balance, measuring cylinder, beaker and glass stirring rod;
(2)beaker/rod, bunsen burner, tripod and gauze;
(3) filter funnel and filter paper, evaporating (crystallising) dish;
(4) evaporating (crystallising) dish. (ii) A measuring cylinder is adequate for measuring the acid
volume, you do not need the accuracy of a pipette or burette required in method (a).
* Add excess metal to (warm) acid. Wait until no more H2 is evolved.
*Filter to remove excess metal.
* Heat the filtrate to evaporate off water until crystallisation starts.
* Set aside to cool slowly and crystallise fully.

Method 2 (Acid + Base):
Useful for making salts of less reactive metals, e.g. lead, copper.
e.g. copper(II) oxide + sulphuric acid  copper(II) sulphate + water
*Add excess base to acid. Warm gently.
*Filter to remove excess base, then continue as in method 1…

Method 3 (Acid + Carbonate):
Useful particularly for making salts of more reactive metals, e.g. calcium, sodium.
e.g. calcium carbonate + nitric acid  calcium nitrate + water + carbon dioxide
*Add excess metal carbonate to acid. Wait until no more CO2 is evolved.
*Filter to remove excess carbonate, then continue as in method 1…

Method 4 (Acid + Alkali):
This is useful for making salts of reactive
metals, and ammonium salts. It is different
from methods 1-3, as both reactants are in
solution. This means neutralisation must be
achieved, by adding exactly the right amount
of acid to neutralise the alkali. This can be
worked out by titration
e.g. sodium hydroxide + hydrochloric acid -> sodium chloride + water
ammonia + sulphuric acid -> ammonium sulphate
(1) A known volume of acid is pipetted into a conical flask and universal indicator added. The
acid is titrated with the alkali in the burette
(2) until the indicator turns green.
(3). The volume of alkali needed for neutralisation is then noted, this is called the
endpoint. (1-3) are repeated with both known volumes mixed together BUT without the
contaminating indicator.
(4) The solution is transferred to an evaporating dish and heated to partially evaporate the
water.
(5) The solution is left to cool to complete the crystallisation.
(6) The residual liquid can be decanted away and the crystals can be carefully collected and
dried by 'dabbing' with a filter paper OR the crystals can be collected by filtration (below) and
dried (as above).

Making Insoluble Salts:
Insoluble salts cannot be prepared by acid-base reactions in the same way as soluble salts.
Insoluble salts are prepared by precipitation. This involves mixing solutions of two
soluble salts that between them contain the ions that make up the insoluble salt. Here is
an example:
barium chloride + magnesium sulphate  barium sulphate + magnesium chloride
(soluble salt) (soluble salt) (insoluble salt) (soluble salt)
BaCl2(aq) + MgSO4(aq)  BaSO4(s) + MgCl2(aq)
When the two solutions are mixed, a white solid precipitate of barium sulphate is
formed.
 
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