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Chapter 2

BIO152H5 Chapter Notes - Chapter 2: Nuclear Fallout, Environmental Factor, Radiometric Dating

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Maria Arts

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Chapter 2: The Chemical Context of Life
Concept 2.1: Matter consists of chemical elements in pure form in combinations called compounds
Elements and compounds
o Element- substance that cannot be broken down to other substances by chemical reactions
o Compound- substance consisting of two or more different elements combined in a fixed ratio
The elements of life
o Essential elements- elements that an organism needs to live a healthy life and reproduce
Humans need about 25
Plants need 17
C, H, O, N, Ca, P, K, S
o Trace elements- required by an organism in only minute quantities
Iron required, the others depend on the organism
In vertebrates, iodine is an essential ingredient of a hormone produced by the
thyroid gland
Concept 2.2: An element’s properties depend on the structure of its atoms
Subatomic particles
o Atom- smallest unit of matter that still retains the properties of an element
o Neutrons- found in nucleus, no charge
o Protons- found in nucleus, positive charge
o Electrons- surround the nucleus; negative charge, form clouds
Atomic number and atomic mass
o All atoms of a particular element have the same number of protons in their nuclei
Referred to as atomic number
2He means that there are 2 atoms in the nucleus
o Mass number refers to the sum of protons and neutrons in the nucleus
o Atomic mass is an approximation of the total mass of an atom
o Same number of protons but different number of neutrons
o Radioactive isotopes
Unstable nucleus results in radioactive decay
Gives off particles and energy
Decay leads to a change in the number of protons
o Transforms atom to an atom of a different element
Carbon-14 can decay into nitrogen
Radioactive tracers
Used as diagnostic tools in medicine
Cells given radioactive isotopes use radioactive atoms as they would use
nonradioactive isotopes of same element
Can be readily detected so track atoms through metabolism
o Certain kidney disorders can be diagnosed by injecting small doses of
substances containing radioactive isotopes
o Measure amount of tracer excreted in the urine
o Also used in combination with sophisticated imaging instruments
PET scanners monitor chemical processes such as those
involved in cancerous growth
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