biology ocr unit 2 spec and explanation all u need

biology ocr unit 2 spec and explanation  all u need for unit 2

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Molecules, Biodiversity, Food and Health
Biological Molecules
Biological Molecules
(a) describe how hydrogen bonding occurs between water molecules, and relate this, and other properties of
water, to the roles of water in living organisms;
Water is a polar molecule. This is because the oxygen atom pulls the shared electrons towards it,
meaning that water is slightly negatively charged at the oxygen and positively charged at the
hydrogen ends, so they can form hydrogen bonds with each other. This are continuing breaking and
reforming, so the molecules can move around.
Property of water Importance Examples Hydrogen bonds
Solvent Metabolic processes in all 70-95% of cytoplasm is If the solute is slightly
organisms rely on chemicals water. Dissolved chemicals charged or ionic, they will
being able to react together take part in processes such as interact with water
in solution respiration and molecules. The water
photosynthesis in living molecules will cluster around
organisms the charged parts, keeping
solute molecules apart
Liquid The movement of materials Blood in animals and the Water remains liquid over a
around organisms, both in vascular tissue in plants use large temperature range and
cells and on a large scale in water as a liquid transport can act as a solvent for many
multicellular organisms medium chemicals
requires a liquid transport
Cohesion Water molecules stick to Transport of water in the A drop of water on the waxy
each other creating surface xylem relies on water surface of the leaf looks
tension at the water surface. molecules sticking to each almost spherical- it hardly
Cohesion also makes long, other as they are pulled up wets the leaf at all. This is
thin water columns very the xylem in the transpiration because hydrogen bonds pull
strong and difficult to break stream the water in at the surface.
This is cohesion, which also
Some small organisms make results in surface tension
use of surface tension to
`walk on water'
Freezing Water freezes, forming ice on Organisms such as polar Water is unusual because its
the surface. Water beneath bears live in an environment solid form is less dense than
the surface becomes of floating ice packs. its liquid form. As water
insulated and less likely to cools, its density increases
freeze Lakes tend not to freeze until the temperature drops
completely, so aquatic to 4°C, the density increases
organisms are not killed as again, so ice floats on water.
temperatures fall
Thermal stability Large bodies of water have Oceans provide a relatively The hydrogen bonds in liquid
fairly constant temperatures. stable environment in terms water restrict the movement
of temperature of the water molecules, so a
Evaporation of water can relatively large amount of
cool surfaces by removing Many land-based organisms water is needed to increase
heat. use evaporation as a cooling the temperature of water
mechanism, for example in
panting or sweating The evaporation of water
uses a relatively large
amount of energy, so water
evaporating from the surface
`removes' heat energy from
the surface
Metabolic Water takes part as a Water molecules are used in
reactant in some chemical hydrolysis reactions and in
processes the process of
(b) describe, with the aid of diagrams, the structure of an amino acid;
ALM June 2010

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Molecules, Biodiversity, Food and Health
(c) describe, with the aid of diagrams, the formation and breakage of peptide bonds in the synthesis and
hydrolysis of dipeptides and polypeptides;
The ­OH from one amino acid and the ­H from the ­COOH from the other are removed to
make water, and the C and the N join together via a peptide bond (CONH)
A water molecule is used to break the peptide bond.…read more

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Molecules, Biodiversity, Food and Health
(m) compare and contrast the structure and functions of starch (amylose) and cellulose;
Made up of -glucose
Straight chain
Tends to coil up
Plant storage polysaccharide
Made up of -glucose
In a chain, alternate glucose subunits are inverted
Forms straight chains
The -glycosidic bond can only be broken down by a cellulose enzyme, which herbivors
have, but humans do not
Forms plant cell walls
(n) describe, with the aid of diagrams, the structure of glycogen;
Mostly like amylase,…read more

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Molecules, Biodiversity, Food and Health
(r) describe how the concentration of glucose in a solution may be determined using colorimetry
Benedict's test reveals the presence of reducing sugars
It results in an orange-brown precipitate
The more reducing sugar there is present, the more precipitate will be formed and the
more Benedict's solution will be `used up'.…read more

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Molecules, Biodiversity, Food and Health
(c) describe, with the aid of diagrams, the mechanism of action of enzyme molecules, with reference to
The active site of an enzyme is a specific shape, depending on the reaction that it catalyses,
meaning that other molecules won't fit into the active site
active site,
The area on an enzyme to which the substrate binds
lock and key hypothesis,
The theory of enzyme action in which the enzyme active site is complementary to the
substrate molecule, like a…read more

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Molecules, Biodiversity, Food and Health
(e) describe how the effects of
A starch-agar plate is made up by mixing starch with agar. The mixture is poured into a
petridish and left to set. It forms a semi-rigid gel in the plate.…read more

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Molecules, Biodiversity, Food and Health
Small, organic, non-protein molecules that bind for a short period of time to the active site.
They may bind just before, or at the same time, as the substrate binds. In many reactions,
coenzymes take part in the reaction, and like substrate, are changed in some way. Unlike
the substrate, coenzymes are recycled back to take part in the reaction again.…read more

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Molecules, Biodiversity, Food and Health
Food & Health
Diet & Food Production
(a) define the term balanced diet;
A diet that contains all the nutrients of the nutrients requires for health and growth.
(b) explain how consumption of an unbalanced diet can lead to malnutrition, with reference to obesity;
Malnutrition is caused by an unbalances diet. Obesity is called by consuming too much energy and
the excess energy is deposited as fat in the adipose tissues.…read more

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Molecules, Biodiversity, Food and Health
(h) describe how the use of fertilisers and pesticides with plants and the use of antibiotics with animals can
increase food production;
Replace minerals in the soil which may have been removed by the previous crops. They
contain Nitrate, Phosphate and Potassium. They increase the rate of growth and the
overall size of crops
Kill organisms that cause diseases in crops. These organisms would reduce yield or kill the
crop.…read more

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Molecules, Biodiversity, Food and Health
(c) describe the causes and means of transmission of malaria, AIDS/HIV and TB (knowledge of the symptoms
of these diseases is not required);
If the host already has malaria, the female anopheles mosquito will suck the parasite
gametes into its own stomach
The gametes fuse and the zygotes develop in the mosquito's stomach
Infective stages are formed and these move to the mosquito's salivary glands
When the mosquito bites another person, it injects a little saliva as an anticoagulant…read more


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