15 WJEC Biology AS Level - Marianne Izen - 2nd Edition Flashcards
Cohesion (Key Term)
The attraction of water molecules for each other, because of the dipole structure of water, producing hydrogen bonds between them.
Organic
Molecules that have a high proportion of carbon atoms.
Monosaccharide
An individual sugar molecule.
Triose
A monosaccharide containing three carbon atoms.
Pentose
A monosaccharide containing five carbon atoms.
Hexose
A monosaccharide containing six carbon atoms.
Isomers
Molecules that have the same chemical formula but a different arrangement of atoms.
What property of water helps to support the body of an insect on a pond’s surface?
In a pond, cohesion between water molecules at the surface produces surface tension so that the body of an insect, such as the pond skater, is supported.
What property of water allows water columns to be pulled to great heights? Describe how?
Cohesion.
Water molecules attract each other forming hydrogen bonds.
Individually these are weak but, because there are many of them, the molecules stick together in a lattice.
This sticking together is called cohesion.
It allows columns of water to be drawn up xylem vessels in plants.
1 - C
2 - A
3 - D
4 - B
Describe the property of water: high surface tension
Cohesion between water molecules at the surface produces surface tension.
At ordinary temperatures water has the highest surface tension of any liquid except mercury.
Describe the property of water: high density
Water is denser than air and, as a habitat for aquatic organisms, provides support and buoyancy.
Water has a maximum density at 4°C.
Ice is less dense than liquid water, because the hydrogen bonds hold the molecules further apart than they are in the liquid.
So ice floats on water.
Ice is a good insulator and prevents large bodies of water losing heat and freezing completely, so organisms beneath it survive.
Describe the property of water: transparency
Water is transparent, allowing light to pass through.
This lets aquatic plants photosynthesise effectively.
Describe carbohydrates.
Carbohydrates are organic compounds containing, as their name suggests, the elements carbon, hydrogen and oxygen.
In carbohydrates the basic unit is a monosaccharide.
Two monosaccharides combine to form a disaccharide.
Many monosaccharide molecules combine to form a polysaccharide.
Describe monosaccharides
Monosaccharides are small organic molecules and are the building blocks for the larger carbohydrates.
Monosaccharides have the general formula (CH2O)n and their names are determined by the number of carbon atoms (n) in the molecule.
A triose sugar has three carbon atoms; a pentose has five and a hexose has six.
The carbon atoms of monosaccharides make a ring when the sugar is dissolved in water, and they can alter their binding to make straight chains, with the rings and chains in equilibrium.
