In depth notes for OCR A for first year A-level biology, including diagrams, and different sub-headings, an easy read from a biology student.
ISBN of the book used is 0802, as well as some contrast from save my exams
Biological molecules
Molecular bonding
Condensation reactions- When 2 molecules are joined together and water is removed/ formed
from that formation
Hydrogen bonding- Weak interactions between slightly negatively charged oxygen atoms and
slightly positively charged hydrogen atoms
Hydrolysis reaction- Reaction that occurs when a molecule is split into 2 smaller molecules with
the addition of water to carry out the reaction
Monomer- Small molecule that can bind to other molecules to form a polymer
Polymer- Large molecule formed from many monomers
Proteins (C, H, O, N and S) Amino acids Polypeptides and proteins
Nucleic acids (C, H, O, N and P) Nucleotides DNA and RNA
Properties of water
Liquid:
- Provides habitats for living things in rivers, lakes and seas
- Forms a major component of tissues in living organisms
- Provides a reaction medium for chemical reactions
- Provides e ective transport medium
Density:
Ice is less dense than water at room temperature because the hydrogen bonds form a lattice
when water is frozen
- Aquatic organisms have a stable environment in which they can live in during winter
- Ponds and other bodies of water are insulated against extreme cold, a layer of insulation
Solvent:
- Molecules and ions can move around and react together in water
- Molecules and ions can be transported around living things whilst dissolved in water
Cohesion and surface tension:
- Hydrogen bonding pulls molecules together, they’re more attracted to the water molecules
beneath them than the air molecules above of them
- Columns of water in plants, including the xylem in the vascular bundle
- Pond skaters can walk on water
High speci c heat capacity:
Causes a lot of energy to break the hydrogen bonds, so water doesn’t cool down or heat up so
easily
- Living things need a stable temperature for enzyme controlled reactions
- Aquatic organisms need a stable environment to live in
High latent heat of vaporisation:
Helps molecules to break away from each other and a large amount of energy is needed to
evaporate water molecules.Water can cool living things and keep their temperature stable
Reactant:
In photosynthesis and hydrolysis reactions and is important in digestion and synthesis of large
biological molecules.
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, Carbohydrates
Monosaccharides
- Could exist as rings or in cyclic forms
- Could have di erent number of carbons, hexoses and pentoses
Name of Displayed formula Molecular formula Role in the body Type of sugar
monosaccharide
A-glucose C6H12O6 Energy source, Hexose
component of starch,
glycogen, two types of
energy stores in plants
and animals respectively
B- glucose C6H12O6 Energy source, Hexose
component of cellulose
and used for structural
support. In cellulose
Ribose C5H10O5 Component of RNA, Pentose
ATP and NAD
Deoxyribose C5H10O4 Component of DNA Pentose
Disaccharides
- Maltose and lactose are reducing sugars whereas
sucrose is a non-reducing sugar
- Disaccharides when monosaccharides are formed
together by a glycosidic bond during a
condensation reaction
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