Qualification > Sciences
IGCSE BIOLOGY DOUBTS HERE !!!!
Deadly_king:
--- Quote from: Ivo on October 13, 2010, 06:03:31 pm ---Xerophytes (Desert plants)
They are plants that are able to exist in conditions where water is scarce. Cacti are xerophytes that survive in hot, dry (arid) desert regions. Cacti reduce water loss and conserve water in the following ways:
1) Their leaves are reduced to spines. This reduces the surface area of the leaf over which water can be lost.
2) A thick waxy cuticle covers the plant's surfaces and reduces transpiration.
3) They have swollen stems containing water-storage tissue.
4) They have a shallow, spreading root system to absorb quickly any water from rain and overnight condensation.
5) Many cacti have a round compact shape which reduces their surface area so there is less surface through which water can be lost.
6) They have shiny surfaces which reflect heat and light.
7) Their stomata are closed during the day to reduce water loss. They open their stomata at night to absorb the carbon dioxide which they store for use in photosynthesis during the day. Photosynthesis occurs in the outer layers of cells in their stems.
Hydrophytes (Pond plants)
(eg. Water lilies, Nymphaea sp.)
They are plants that grow submerged or partially submerged in water. Living in water has both its costs and benefits.
Buoyed up by water and with no need for water transport, floating plants save energy since they produce little or no xylem tissue.
Roots, if present, are for anchorage and since there is no need for the roots to absorb water or mineral ions, there are no root hairs. The leaves and stems of hydrophytes have little or no cuticle, since there is no need to conserve water.
The problem for hydrophytes is that carbon dioxide, which is needed for photosynthesis, diffuses through the water much more slowly than it does through air. The same applies for oxygen, needed for plant respiration, since it is not very soluble in water. Therefore many hydrophytes have an extensive system of air spaces in their stems and leaves through which gases diffuse quickly. These air spaces provide buoyancy to keep the plants close to the light and are a resevoir of oxygen and carbon dioxide.
Mesophytes (Garden plants)
(eg. Coleus, Solenostemon spp. - brightly coloured garden plants)
Garden plants are grown for their colourful, scented flowers, for their subtle leaf colours, for shade and to provide an attractive environment.
Mesophytes are terrestrial plants that usually have enough water and do not have such extreme adaptations to reduce water loss like those of xerophytes, Many garden plants are mesophytes, as gardeners can provide them with enough water even in parts of the world that might be dry for much of the year.
--- End quote ---
Nice piece of research buddy ;)
+rep
acash09:
thanks man! good to have you helping moi!
acash09
MKL:
Quick question: describe the use of microorganisms in the food industry, with reference to yoghurt and single cell protein.
Thanks in advance
Deadly_king:
--- Quote from: MKL on October 19, 2010, 04:21:40 am ---Quick question: describe the use of microorganisms in the food industry, with reference to yoghurt and single cell protein.
Thanks in advance
--- End quote ---
1.Two species of bacteria Lactobacillus bulgaricus and Lactococcus thermophilus in approximately equal proportions, are used to make yoghurt.
NOTE : You need not know the names of the bacteria. I just mentioned it ;)
Commercial producers pasteurize and homogenize the milk before adding the starter. After stirring, the mixture is then incubated for 3-6 hours at 40-450C. At this temperature the two bacteria have a mutually stimulating effect on one another.
Protolytic enzymes from L. bulgaricus break down milk proteins into peptides. These stimulate the growth of L. thermophilus which, in turn, produce formic acid and carbon dioxide, growth stimulants for L. bulgaricus. As the incubation proceeds, L. bulgaricus converts the lactose to lactic acid and the pH falls to 4.2-4.4 which leads to the coagulation of proteins by lactic acid and the thickening of the yoghurt.
Further processing involves the addition of flavour, colour, fruit pulp and heat treatment to kill off any bacteria.
2.The most common single-celled protein is yeast. It is used in the manufacture of bread and beer.
The principal dry ingredients used in bread-making are wheat flour, salt, sugar, ascorbic acid, and the yeast Saccharomyces cerevisiae. Water or milk is added to produce a thick, sticky dough which is repeatedly folded or kneaded, to create nuclei for gas production and expansion. The mixed dough is rested, folded, and moulded and in a humid atmosphere at 34-350C, it is left for 10 minutes to ‘prove’.
During the process of ‘proving’, fermentation of sugars in the dough, catalysed by enzymes from the yeast cells, produces carbon dioxide. As this gas cannot escapes from the sticky mass, it fills the gas nuclei and causes the dough to “rise” or increase in volume. This process is sometimes is called ‘leavening’. The overall effects of leavening are to make the dough lighter, more digestible, and of better flavour following from the production of organic acids, alcohols and esters by yeast cells. The role of enzymes in the process are summarized as follows:
maltase
a) Maltose ---------------› glucose
(in flour) (from yeast)
invertase
b) Sucrose-----------------› glucose + fructose
(added) (from yeast)
zymase
c) Glucose + fructose----------------› alcohol + carbon dioxide
(from yeast)
The yeast fermented bread have better flavour and texture as compared to the one prepared by using baking powder therefore in the commercial production of bread, Baker’s yeast is used. The living cells of aerobically grown Saccharomyces cerevisiae are collectively referred to as baker’s yeast.
Baker’s yeast is commercially available either as a dried powder i.e. dry yeast with about 95% dry weight or in the form of cakes (about 25-30% dry weight). In recent years, some workers have reported the development of genetically engineered strains of Saccharomyces cerevisiae with improved fermentation properties.
NOTE : Again you need not know the names of the yeast.
Hope it helps :)
MKL:
--- Quote from: Deadly_king on October 19, 2010, 05:53:48 am ---1.Two species of bacteria Lactobacillus bulgaricus and Lactococcus thermophilus in approximately equal proportions, are used to make yoghurt.
NOTE : You need not know the names of the bacteria. I just mentioned it ;)
Commercial producers pasteurize and homogenize the milk before adding the starter. After stirring, the mixture is then incubated for 3-6 hours at 40-450C. At this temperature the two bacteria have a mutually stimulating effect on one another.
Protolytic enzymes from L. bulgaricus break down milk proteins into peptides. These stimulate the growth of L. thermophilus which, in turn, produce formic acid and carbon dioxide, growth stimulants for L. bulgaricus. As the incubation proceeds, L. bulgaricus converts the lactose to lactic acid and the pH falls to 4.2-4.4 which leads to the coagulation of proteins by lactic acid and the thickening of the yoghurt.
Further processing involves the addition of flavour, colour, fruit pulp and heat treatment to kill off any bacteria.
2.The most common single-celled protein is yeast. It is used in the manufacture of bread and beer.
The principal dry ingredients used in bread-making are wheat flour, salt, sugar, ascorbic acid, and the yeast Saccharomyces cerevisiae. Water or milk is added to produce a thick, sticky dough which is repeatedly folded or kneaded, to create nuclei for gas production and expansion. The mixed dough is rested, folded, and moulded and in a humid atmosphere at 34-350C, it is left for 10 minutes to ‘prove’.
During the process of ‘proving’, fermentation of sugars in the dough, catalysed by enzymes from the yeast cells, produces carbon dioxide. As this gas cannot escapes from the sticky mass, it fills the gas nuclei and causes the dough to “rise” or increase in volume. This process is sometimes is called ‘leavening’. The overall effects of leavening are to make the dough lighter, more digestible, and of better flavour following from the production of organic acids, alcohols and esters by yeast cells. The role of enzymes in the process are summarized as follows:
maltase
a) Maltose ---------------› glucose
(in flour) (from yeast)
invertase
b) Sucrose-----------------› glucose + fructose
(added) (from yeast)
zymase
c) Glucose + fructose----------------› alcohol + carbon dioxide
(from yeast)
The yeast fermented bread have better flavour and texture as compared to the one prepared by using baking powder therefore in the commercial production of bread, Baker’s yeast is used. The living cells of aerobically grown Saccharomyces cerevisiae are collectively referred to as baker’s yeast.
Baker’s yeast is commercially available either as a dried powder i.e. dry yeast with about 95% dry weight or in the form of cakes (about 25-30% dry weight). In recent years, some workers have reported the development of genetically engineered strains of Saccharomyces cerevisiae with improved fermentation properties.
NOTE : Again you need not know the names of the yeast.
Hope it helps :)
--- End quote ---
Thanks heaps man!
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