Unit 1
Essential Questions:
 What is the relationship between structure and function in living systems?
 How is matter and energy transformed and transferred in living systems?
Biology is the study of living things (Bios = greek for living; ology = the study of). Living things are also referred to
as organisms.
How are living things organized?
The cell is the basic building block of all living organisms. Some organisms will remain single celled, while others will
multiply into highly specialized, multicellular organisms.
Cells themselves are made up of lots of chemicals grouped in different ways, and the cells and the chemicals that
make them are all highly organized, from simple to complex:
Atoms: This is the basic unit of any chemical, such as Carbon, Hydrogen, Oxygen
Molecules: Groups of atoms can be joined to create molecules, for example, two
hydrogen atoms and one oxygen atom will join together to create a water
molecule.
Macromolecules: Some simple molecules join together to form large complex
molecules, such as amino acids that join together to make proteins.
Organelles: Macromolecules combine to form structures in cells, such as
membranes and mitochondria, with each organelle carrying out a specific job or
function.
Cells: The basic unit of all living organisms, such as a muscle cell, leaf cell, nerve
cell.
Tissues: A group of similar cells. All the cells in a tissue look the same and do
the same job.
Organs: A group of tissues working together, such as the heart, stomach, lungs.
Systems: Different organs work together as part of an organ system, for
example, the heart and blood vessels work together as the circulatory system.
Organisms: All of the organ systems together make an organism, like a human or
a plant.
Water is composed of one oxygen atom and two hydrogen atoms. Each
hydrogen atom is covalently bonded to the oxygen via a shared pair of
electrons. Oxygen also has two unshared pairs of electrons. Water is a
"polar" molecule, meaning that there is an uneven distribution of
electron density. Water has a partial negative charge ( ) near the
oxygen atom due the unshared pairs of electrons, and partial positive
charges (
) near the hydrogen atoms.
An electrostatic attraction between the partial positive charge near the
hydrogen atoms and the partial negative charge near the oxygen results
in the formation of a hydrogen bond as
shown in the illustration. Hydrogen bonds
are much weaker than covalent bonds,
however, when many hydrogen bonds form
between two molecules (or parts of the
same molecule), they can form a very strong bond.
Water
About two-thirds of the weight of cells is accounted for by water. The properties of water are vital to living
organisms and allow it to behave in a number of ways:



As a solvent
As a molecule with cohesive properties
As an environment
Water as a solvent
Because water is polar, water molecules pull apart [dissolve] compounds composed of positive and negative ions
[such as salt]. Water dissolves so many compounds [solutes] that it is called the "universal solvent". When water
dissolves a substance it pulls it apart ion by ion. Once the solute is dissolved the water acts as a transport medium.
e.g.:
 Transport of dissolved substance in blood and lymph
 Removal of metabolic wastes, such as urea
 Movements of minerals to lakes and seas
Water as a molecule with cohesive properties
The hydrogen bonds in water mean that the water molecules have considerable
cohesive properties. This cohesion allows plants to pull water up from the roots
to the leaves. It is also important in the formation of surface tension which enables insects such as pond skaters
to move across the surface of the water without sinking.
Water as an environment
Ice is less dense than water and therefore in cold weather it forms an insulating layer on the top of ponds, etc.
this means that the water beneath the ice stays in the liquid state, a property vital to aquatic life.
MACROMOLECULES
1. Carbohydrates
Carbohydrates are organic molecules containing just Carbon, Hydrogen & Oxygen.
In living organisms, the primary role of carbohydrates is the storage and supply of energy to metabolic processes,
such as respiration.
In addition, the complex carbohydrate, cellulose, is used as a structural material by plants.
Carbohydrates can be classified according to their structure:
Monosaccharides
These are ‘simple sugars’. The commonly occurring monosaccharide sugars contain between 3 and 7 Carbon atoms.
They are the monomer units which form polysaccharides. (Building blocks)
The monosaccharides most frequently found are sugars, such as glucose and fructose. The name usually ends in
“ose.”
Polysaccharides
These are chains of ‘many sugars’, built up from 3 or more sugars. The chains can be variable in length, linear,
branched, straight or coiled.
Functions of carbohydrates:
Glucose
The best known monosaccharide is glucose,
which contains six C atoms. The diagram here shows how
the atoms are arranged in glucose:
Polysaccharides
In polysaccharides, the monosaccharides are linked together to form polymer chains hundreds of units long.
They can be divided into two groups according to their function:
 Storage polysaccharides
 Structural polysaccharides
Storage polysaccharides
A food storage molecule mustn’t take up too much space in a cell. The most important storage polysaccharides are
STARCH and GLYCOGEN. Starch is the glucose store in plants and glycogen is the animal equivalent.
Structural polysaccharides
The most important member of this group is the polysaccharide that makes up every plant cell wall, CELLULOSE.
2. Lipids
Lipids are not polymers like carbohydrates, but are made of fatty acids and glycerol.
 Lipids are fats, oils, waxes, sterols [such as cholesterol and hormones] and soaps. At room temperature fats
are solid and oils are liquid.
 Lipids are generally hydrophobic [water-fearing].
Triglycerides that contain long, saturated fatty acids tend to form hard fats like lard and butter. Triglycerides
that contain shorter, unsaturated fatty acids tend to form oils which are liquid at room temperature, e.g.:
sunflower oil. Unsaturated fats have a lower melting point because the double bonds in the fatty acids produce
kinks in the C chain. This means the molecules cannot lie so close to each other and therefore unsaturated fats are
more fluid.
Functions of lipids:
Lipids are important sources of energy. Energy is stored in the body as fat – these energy stores also serve as
insulation layers (fat tissue).
Lipids are important in the structure of cell membranes – they combine with phosphoric acid to form phospholipids.
3. Proteins
The structure of proteins determines their properties and consequently their uses in living organisms. Proteins are
used for growth & repair, support & movement (muscle, collagen etc), transport oxygen (using hemoglobin),
immunity (antibodies) and coordination (hormones).
The basic building blocks, or monomers, of which proteins are made, are amino acids. There are 20 known amino
acids.
The structure of a protein creates the specific shape the protein needs to carry out its function. E.g.: enzymes are
protein molecules which need to be exactly the right shape to catalyse specific reactions.
A protein with a particular shape:
4. Nucleic Acids
DNA and RNA
Every cell in your body uses DNA for an instruction
manual on how to make proteins. DNA is just a long
spiral chain of nucleotides
So you get all of those nucleotides in two long chains
that twist around each other. That twisting shape is
called a double-helix.
RNA is a copy of DNA – it allows proteins to be made
by sending the instructions out the nucleus.