Chemical Context of Life

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Chapter 2

The Chemical Context of Life

PowerPoint Lectures for Biology, Seventh Edition
Neil Campbell and Jane Reece

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Overview: Chemical Foundations of Biology

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• The bombardier beetle uses chemistry to defend itself

Figure 2.1
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• Concept 2.1: Matter consists of chemical elements in pure form and in combinations called compounds

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Elements and Compounds
• Organisms are composed of matter, which is anything that takes up space and has mass

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• A compound
– Is a substance consisting of two or more elements combined in a fixed ratio – Has characteristics different from those of its elements

+

Figure 2.2

Sodium

Chloride

Sodium Chloride

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Essential Elements of Life • Essential elements
– Include carbon, hydrogen, oxygen, and nitrogen – Make up 96% of living matter

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• A few other elements
– Make up the remaining 4% of living matter

Table 2.1
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• The effects of essential element deficiencies

Figure 2.3

(a) Nitrogen deficiency

(b) Iodine deficiency

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• Trace elements
– Are required by an organism in only minute quantities

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• Concept 2.2: An element’s properties depend on the structure of its atoms

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• Each element
– Consists of a certain kind of atom that is different from those of other elements

• An atom
– Is the smallest unit of matter that still retains the properties of an element

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Subatomic Particles • Atoms of each element
– Are composed of even smaller parts called subatomic particles

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• Relevant subatomic particles include
– Neutrons, which have no electrical charge – Protons, which are positively charged – Electrons, which are negatively charged

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• Protons and neutrons
– Are found in the atomic nucleus

• Electrons
– Surround the nucleus in a “cloud”

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• Simplified models of an atom
Cloud of negative charge (2 electrons) Nucleus Electrons

(a) This model represents the
electrons as a cloud of negative charge, as if we had taken many snapshots of the 2 electrons over time, with each dot representing an electron‘s position at one point in time.

(b) In this even more simplified
model, the electrons are shown as two small blue spheres on a circle around the nucleus.

Figure 2.4

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Atomic Number and Atomic Mass • Atoms of the various elements – Differ in their number of subatomic particles

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• The atomic number of an element
– Is the number of protons – Is unique to each element

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• The mass...
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