II: Chemical Context of Life

Question 1

What are organisms composed of?

Answer 1

They are composed of matter, which is anything that takes up space and has mass

Question 2

What is matter?

Answer 2

matter is made up of chemical elements, substances that cannot be broken down to other substances by chemical reactions

-> 118 elements which 94 exist in nature

Question 3

What is a compound?

Answer 3

a substance consisting of two or more elements in a fixed ratio
- characteristics differ from its elements

Question 4

What are the elements that make up 96% of living matter?

Answer 4

Oxygen 65% > carbon 18%> hydrogen 9% > nitrogen 3.3%

Question 5

Which element is the most common element in the human body?

Answer 5

hydrogen

Question 6

What are the elements that make up the rest 3.7% of the human body?

Answer 6

• calcium
• phosphorus
• potassium
• sulfur
• sodium
• chlorine
• magnesium

Question 7

What are trace elements?

Answer 7

= Spurenelemente
the elements required by an organism in only minute quantities
-> make up less than 0.01% of human body weight

eg iron, iodine, selenium

some are required by all forms of life (eg Fe), others are required only by certain species

Question 8

What is the evolution of tolerance to toxic elements?

Answer 8

Some species can become adapted to environments containing toxic elements
- eg some plant communities are adapted to serpentine

Question 9

What are the properties of an element?

Answer 9

properties depend on the structure of its atoms

• each element consists of a unique atom that is different from those of other elements

Question 10

what is an atom?

Answer 10

the smallest unit of matter that still retains the properties of an element

• subatomic particles

Question 11

what do the different subatomic particles determine?

Answer 11

• protons determine the element
• neutrons determine the isotope
• electrons determine the chemical behaviour

Question 12

What are the mass of the subatomic particles?

Answer 12

• neutrons and protons are measured in daltons (=atomic mass unit)
  -> 1.7 x 10^-24 = 1 dalton
• electrons are considered negligible
  -> 1/2000 dalton

Question 13

what is the atomic number?

Answer 13

• the number of proton in the nucleus
• unique to each element
• written as subscript
• equal to number of electrons
• determines the elements properties

Question 14

What is the mass number?

Answer 14

• same as atomic mass
• protons + neutrons
• approximation of atomic mass in dalton
• written as superscript

Question 15

What are isotopes?

Answer 15

two atoms of an element that differ in the number of neutrons in the nucleus, but have the same number of protons

Question 16

What are radioactive isotopes?

Answer 16

spontaneously give off particles and energy

Question 17

What are some applications in biological research for radioactive isotopes?

Answer 17

• dating fossils
• tracing atoms through metabolic processes
• diagnosing medical disorders
• used with sophisticated imaging instruments
• used in PET scanners -> monitor metabolism of cancers

Question 18

What is energy?

Answer 18

the capacity to cause change

Question 19

What is potential energy?

Answer 19

the energy that matter possesses due to its location or structure
- the further away the electrons are from the nucleus, the more their potential energy

• matter has a natural tendency to move toward the lowest possible state of potential energy

Question 20

What are electron shells?

Answer 20

the energy level of an electron associated with the average distance from the atomic nucleus

• electrons are found in different electron shells
• 1st shell has the lowest potential energy

Question 21

How can changes in electron potential energy occur?

Answer 21

an electron can change the shell by absorbing / losing an amount of energy equal to the difference in potential energy between its position in the old shell and that in the new shell

• when e absorbs energy, it moves a shell higher
• when e loses energy, the energy lost is usually released to the environment as heat

Question 22

What are valence electrons?

Answer 22

= outermost electrons

• determine the chemical behaviour of an atom
• involved in chemical bonds between atoms
• elements with a full valence shell are chemically inert

Question 23

What are electron orbitals?

Answer 23

• 3D space where an electron is found 90% of the time
• each shell consists of a specific number of orbitals -> no more than 2 electrons can occupy a single orbital
• atoms interact in a way that completes their valence shells and become stable

Question 24

What are Covalent bonds?

Answer 24

The sharing of a pair of valence electrons by two atoms

• the shared electrons count as part of each atom’s valence shell
• intra- and intermolecular

Question 25

What types of covalent bonds exist?

Answer 25

a molecule consists of two or more atoms held together by covalent bonds - single bond: sharing of one e pair - double bond: sharing of two e pairs

Question 26

What is a compound?

Answer 26

a combination of two or more different elements held together by covalent bonds

Question 27

What is the bonding capacity called?

Answer 27

atom's valence

Question 28

What is electronegativity?

Answer 28

an atom's attraction for the electron in a covalent bond - the more electronegative, the more strongly it pulls shared electrons toward itself

Question 29

What is a non-polar covalent bond?

Answer 29

when the atoms have similar electronegativities, they share the electrons equally

Question 30

What is polar covalent bond?

Answer 30

when the atoms have differing electronegativities and share the electrons unequally -> causes partial positive / negative charge for each atom or molecule

Question 31

What kind of bonds do the H and O atoms have in water?

Answer 31

polar covalent bonds - shared electrons are pulled more toward oxygen ( more electronegative) - oxygen is partially negative, hydrogen is partially positive

Question 32

What are ionic bonds?

Answer 32

when the atoms strip electrons away from their bonding partners - transfer of electrons between to atoms -> oppositely charged atoms = ions - an attraction between anions and cations

Question 33

What are ions?

Answer 33

atoms with more or fewer electrons than usual -> charged atoms - anion = negatively charged ion - cation = positively charged ion

Question 34

What are ionic compounds?

Answer 34

compounds formed by ionic bonds - Salts - often found in nature as crystals - most salts are quite stable when dry, but dissociate quite easily in water

Question 35

What are weak chemical bonds?

Answer 35

- Hydrogen bonds, dipole-dipole bonds, van der waals force - many large biological molecules are held in their functional form by weak bonds -> considered very important for biological science - reversible

Question 36

What are hydrogen bonds?

Answer 36

- weak bond - form when h atoms covalently bonded to electronegative atom is also attracted to another electronegative atom - in living cells, the electronegative partners are usually oxygen and nitrogen eg hydrogen atom in water with nitrogen atom in ammonia internet: interaction involving a hydrogen atom located between a pair of other atoms having a high affinity for electrons

Question 37

What are van der Waals interactions?

Answer 37

if electrons are distributed asymmetrically in molecules or atoms, they can result in hot spots of positive or negative charge - van der waals are individually weak attractions between molecules that are close together as a result of these charges -> attractions between molecules that are very close together - can be strong due to strength in numbers ( eg gecko's toe hairs and wall surface)

Question 38

What is the molecular shape and its function?

Answer 38

a molecular shape is determined by the positions of its atom's orbitals - specific molecular shaped could be created by the hybridisation of the s and p orbitals in a covalent bond - weak chemical bonds reinforce the shapes of the large molecules and help molecules adhere to each other - the precise size and shape is vital for the function in cells, eg shape of proteins -> molecular shape determines how biological molecules recognize and respond to one another in an environment

Question 39

What are chemical reactions?

Answer 39

- the making and breaking of chemical bonds -> leads to changes in the composition of matter reactants -> products

Question 40

What are reversible chemical reactions?

Answer 40

products of the forward reaction become reactants for the reverse reaction

Question 41

What is the chemical equilibrium?

Answer 41

is reached when the forward and reverse reaction rates are equal and occur at the same time - at equilibrium, the relative concentrations of reactants and products do not change