OCR Biology Unit 2 Notes

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Biology Unit 2
Biological Molecules:
The main types of biological molecules found in organisms are water, proteins,
carbohydrates, lipids and nucleic acids which make up the structure and undergo
chemical reactions known as metabolic reactions (metabolism refers to the total sum
of all the chemical reactions taking place within the cells of an organism).
Water
It is the most abundant molecule in the body.
The uneven sharing of the covalently bonded electrons
causes polar bonds, making water a polar molecule which
means hydrogen bonds form between the molecules.
In ice, the hydrogen bonds hold the water in a rigid lattice
formation, with the molecules more spread apart, making it less dense than water.
It has a high specific heat capacity (amount of energy required to raise 1kg by 1
degrees Celsius), keeping the organisms temperature fairly constant as well as the
surroundings for organisms that live in water.
The hydrogen bonds give water a high boiling point and a high latent heat (amount of
energy required to change the state, not the temperature), which cools organisms
down as heat is removed from the organism as water evaporates out.
The delta charges on the molecule attract other charged ions or molecules, dissolving
them by surrounding them, making water a very good solvent, which helps metabolic
reactions to occur as most will only take place in solution as the dissolved molecule
have dissociated.
The solvent property, along with the fact water can flow due to cohesion and adhesion
caused by the hydrogen bonds, allow substances to be transported around organisms.
The hydrogen bonds make water very dense compared to most other liquids at 1.0 g
per cm cubed, which is similar to the density of organisms as they contain mainly
water, allowing them to swim (and many organisms can change their density slightly
to help them float or sink, e.g. inhaling).
The cohesion of water causes surface tension (as the surface molecules are only pulled
downward by hydrogen bonds, pulling them closer together), allowing small objects,
including some animals, to be able to stand/lay on top of a body of water.
Proteins
They are made up of a chain of amino acids.

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The amino acids are linked together on the ribosomes in a cell.
Peptide bonds are made between the amino acids when the OH from one molecule's
carboxyl group is removed with a H from the other molecule's amine group, making a
water molecule (a condensation reaction) and a CO-N bond.
This long chain is a polypeptide and protein molecules contain one or more chains of
these.
Polypeptides can be broken down (e.g. in digestion by protease enzymes) by hydrolysis
(breaking apart with water).…read more

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Carbohydrates
(Alpha glucose and beta glucose)
They are made up of sugar units (CnH2nOn).
They include sugars, starches and cellulose - sugars are soluble in water and taste
sweet, whereas starches and cellulose (polysaccharides) are insoluble in water and do
not taste sweet.
A carbohydrate with just one sugar unit is a monosaccharide, e.g. glucose, fructose
and galactose - glucose being the main respiratory substrate in cells and fructose being
found in fruits and nectar.…read more

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Non-reducing sugars can be detected by adding dilute hydrochloric acid and boiling for
a minute, before adding sodium hydrogencarbonate to neutralise the solution in which
the Benedict's solution will be added to, before boiling and shaking, which will turn
from blue to yellow to brick-red (precipitate).
Starch can be detected by adding I2 or KI, which will turn blue-black.…read more

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Lipids can be detected by adding ethanol, before shaking and adding water, which will
turn white (emulsion).
Nucleic Acids
Nucleic acid is the slightly acidic substance
found mostly in the nucleus of cells, made
up of DNA, which stands for
deoxyribonucleic acid.
Each nucleotide in a DNA molecule
contains a phosphate group, the
five-carbon sugar of deoxyribose and an
organic base.
The organic bases are adenine, guanine, thymine and cytosine.…read more

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They can be intracellular (like hydrolases in lysosomes or ATPase in mitochondria) or
extracellular (like amylase in the alimentary canal).
They have an active site, which is a region (usually a depression) to which another
molecule, the substrate, can bind, as the shape is specific to the substrate. Temporary
bonds are formed between the hydrophilic R groups of the enzyme and substrate,
creating an enzyme-substrate complex.…read more

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When more non-competitive inhibitor is added, the initial rate of reaction is decreased
no matter what the substrate concentration is whereas when more competitive
inhibitor is added, the initial rate of reaction is increased until the substrate
concentration is so high that the initial rate of reaction is not affected.
Sometimes enzymes require cofactors or coenzymes in order to function. They usually
work by binding briefly with the enzyme, altering its shape slightly so that it can bind
more effectively with its substrate.…read more

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The hardening
of the walls is called atherosclerosis.
2. A reduced lumen, reducing the oxygen supply to the heart, giving the
person chest pain called angina.
3. Stress and exercise can make the plaque break, allowing platelets to come
into contact with collagen, causing them to form a clot, which is called
coronary thrombosis.
4.…read more

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Food Sources
Selective breeding is chosing specific parents to breed together as they have the desired
characteristic and so they are most likely to produce an offspring with that
characteristic. It is generally carried out over several generations. It can be used to
grow crops with high yields, pest resistance (Russian aphid resistant wheat) and
disease resistance (leaf-rust resistant wheat), as well as domestic animals with high
productivity (milk and meat cattle).
As population grows, farming is becoming more intensive.…read more

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Microorganisms can however be used for food production, such as cheese and yoghurt.
A specific fungus can also make mycoprotein, which is rich in protein and low in fat,
and it mainly used as a meat substitute for vegetarians or for people on a diet.…read more

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