General Biology Study Notes: Evolution, Biological Themes, and Chemical Context of Life

Chapter 1: Evolution, Themes of Biology, Scientific Inquiry

Unifying Themes in Biology

Biology is the scientific study of life, and several unifying themes help organize our understanding of living systems.

• Organization: Biological systems are structured at multiple levels, from molecules to the biosphere.

• Information: Genetic information is stored and transmitted within organisms, primarily through DNA.

• Energy and Matter: Life requires the transfer and transformation of energy and matter.

• Interactions: Components of biological systems interact to ensure smooth functioning.

• Evolution: Evolution explains both the unity and diversity of life.

Levels of Biological Organization

Life can be studied at different levels, from molecules to the entire living planet.

• Biosphere

• Ecosystem

• Communities

• Populations

• Organisms

• Organs

• Tissues

• Cells

• Organelles

• Molecules

The Cell

The cell is the smallest unit of organization that can perform all activities required for life.

• Cell Theory: All living organisms are made from cells.

Expression and Transmission of Genetic Information

Within cells, structures called chromosomes contain genetic material in the form of DNA (deoxyribonucleic acid).

• DNA directs development: DNA is transcribed into RNA, which is then translated into protein.

• Gene expression: The process of converting information from gene to cellular product.

Genomics: Large-Scale Analysis of DNA Sequences

Genomics involves the rapid analysis of large sets of DNA data, often using high-throughput technology.

Energy and Matter in Biological Systems

Life requires the transfer and transformation of energy and matter.

• Producers: Organisms that generate chemical energy (e.g., plants).

• Consumers: Organisms that feed on other organisms or their remains (e.g., animals).

Interactions in Biological Systems

Interactions between system components ensure smooth integration of all parts.

Evolution: Unity and Diversity of Life

Evolution accounts for the unity and diversity of life. Living organisms are modified descendants of common ancestors.

• Unity: Shared DNA, similar skeletons, and common ancestry.

• Diversity: Adaptations and modifications over time.

Darwin and Natural Selection

Charles Darwin proposed that species show evidence of "descent with modification" from common ancestors. Natural Selection is the mechanism behind descent with modifications.

The Scientific Method

The scientific method is a systematic approach to inquiry in science.

1. Make an observation and ask a question about it.

2. Develop a testable explanation called a hypothesis.

3. Design experiment to test the hypothesis.

4. Include a control.

5. Determine dependent and independent variables.

6. Do the experiment, collect and analyze data.

7. Draw a conclusion.

8. Communicate methods, results, and conclusions.

9. A scientific theory is an explanation supported by a large amount of evidence.

Chapter 2: The Chemical Context of Life

Atoms, Elements, and Compounds

All matter is made up of atoms, which join together to form compounds.

• Element: A substance that cannot be broken down to other substances by chemical reactions.

• Compound: A substance consisting of two or more elements in a fixed ratio.

The Elements of Life

About 20-25% of the 92 natural elements are essential for life. Four elements—carbon, hydrogen, oxygen, and nitrogen—make up 96% of living matter. Most of the remaining 4% consists of calcium, phosphorus, potassium, and sulfur.

Element	Symbol	% of Body Mass
Oxygen	O	65.0%
Carbon	C	18.5%
Hydrogen	H	9.5%
Nitrogen	N	3.3%
Calcium	Ca	1.5%
Phosphorus	P	1.0%
Potassium	K	0.4%
Sulfur	S	0.3%
Sodium	Na	0.2%
Chlorine	Cl	0.2%
Magnesium	Mg	0.1%

Atoms and Subatomic Particles

An atom is the smallest unit of matter that retains the properties of an element. Atoms are composed of subatomic particles:

• Neutrons: No electrical charge

• Protons: Positive charge

• Electrons: Negative charge

Neutrons and protons form the atomic nucleus. Electrons form a "cloud" of negative charge around the nucleus. Neutron mass and proton mass are almost identical and are measured in Daltons. Electrons are so small they are ignored when calculating the total mass of an atom.

Atomic Number and Mass

• Atomic number: The number of protons in its nucleus.

• Mass number: The sum of protons plus neutrons in the nucleus.

• Atomic mass: The atom's total mass, can be approximated by the mass number.

Isotopes

All atoms of an element have the same number of protons but may differ in the number of neutrons.

• Isotopes: Two atoms of an element that differ in the number of neutrons.

• Radioactive isotopes: Decay spontaneously, giving off particles and energy.

Radioactive Traces and Radiometric Dating

• Radioactive tracers: Used as diagnostic tools in medicine; can track atoms through metabolism.

• Radiometric dating: Measures the ratio of different isotopes and calculates how many half-lives have passed since the fossil or rock was formed.

Half-life equation:

$N = N_0 \left( \frac{1}{2} \right)^{t / t_{1/2}}$

Where $N$ is the remaining quantity, $N_0$ is the initial quantity, $t$ is time elapsed, and $t_{1/2}$ is the half-life.

The Energy Levels of Electrons

Energy is the capacity to cause change. Potential energy is the energy that matter possesses because of its location or structure. Matter tends to move toward the lowest possible state of potential energy.

Covalent Bonds

Atoms with incomplete valence shells can share or transfer valence electrons with certain other atoms.

• Covalent bond: The sharing of a pair of valence electrons by two atoms.

• Molecule: Consists of two or more atoms held together by covalent bonds.

• Single covalent bond: Sharing one pair of electrons.

• Double covalent bond: Sharing two pairs of electrons.

Electronegativity and Polar Covalent Bonds

Electronegativity is an atom's attraction for the electrons in a covalent bond. In a polar covalent bond, one atom is more electronegative, and the atoms do not share the electrons equally, resulting in partial charges.

Ions and Ionic Bonds

Atoms sometimes strip electrons from their bonding partners, resulting in oppositely charged ions.

• Cation: Positively charged ion

• Anion: Negatively charged ion

• Ionic bond: Attraction between anion and cation

Weak Chemical Interactions

Weak bonds, such as hydrogen bonds and van der Waals interactions, are important in biological systems.

• Hydrogen bond: Forms when a hydrogen atom covalently bonded to one electronegative atom is attracted to another electronegative atom.

• Van der Waals interactions: Attractions between molecules that are close together as a result of these charges.

Molecular Shape and Function

Molecular shape determines how biological molecules recognize and respond to one another. For example, opiates and endorphins have similar shapes and bind to the same receptors.

Chemical Equilibrium

Chemical equilibrium is reached when the forward and reverse reactions occur at the same rate.

Additional info: These notes cover foundational topics in general biology, including the scientific method, cell theory, genetic information, chemical elements, atomic structure, and chemical bonding, which are essential for understanding biological processes.