Biology

Chapter 1

Biology

Scientific study of life

Lays the foundation for asking basic questions about life

and the natural world

Why Study Biology?

• To learn how organisms are constructed, how they function, where they live, and what they do

• To help develop, modify, and refine ideas about life

Molecules of Life

• All things are made up of the same units of matter

• Living things are made up of a certain subset of molecules:– Nucleic acids– Proteins– Carbohydrates– Lipids

DNA (deoxyribonucleic acid)

• Signature molecule of life

• Molecule of inheritance

• Directs assembly of amino acids

DNA and Inheritance

• Inheritance– Acquisition of traits by way of

transmission of DNA from parent to offspring

• Reproduction – Mechanism by which an organism

produces offspring – Governed by instructions in DNA

Nothing Lives without Energy

Energy = Capacity to do work

Metabolism = Reactions by which cells acquire and use energy to

grow, survive, and reproduce

Sensing and Responding

• Organisms sense changes in their

environment and make responses to

them

• Receptors detect specific forms of

energy (stimuli)

• Allows maintenance of homeostasis

Levels of Organization

Cell

Multicelled Organism

Population

Community

Ecosystem

Biosphere

Interdependencies among Organisms

ProducersMake their own food

ConsumersDepend on energy stored in

tissues of producers

DecomposersBreak down remains and wastes

Decomposers

Decomposers break down dead organisms and wastes and release the nutrients they contain into the soil, where they are again available to the roots of plants (producers).

In this way, decomposers play an important role in recycling nutrients and getting rid of waste.

Energy Flow

• Usually starts with energy from sun

• Transfer from one organism to

another

• Energy flows in one direction

• Eventually, all energy flows back to

the environment

Producers

Consumers, Decomposers

NUTRIENT CYCLING

ONE-WAY FLOW OF ENERGY

In time, all energy flows back to the environment.

ENERGY FROM SUN

Unity of Life

All organisms:

– Are composed of the same substances

– Engage in metabolism

– Sense and respond to the environment

– Have the capacity to reproduce based

on instructions in DNA

Diversity of Life

• Millions of living species

• Millions more now extinct

• Classification schemes attempt to

organize diversity

Scientific Names

• Devised by Carolus Linnaeus

• First name is genus (plural, genera)

– Homo sapiens - genus is Homo

• Second name is species within genus

Eubacteria(Bacteria)

Archaebacteria(Archaea)

Eukaryota(Eukaryotes)

3 Domains

Origin of life

EubacteriaArchaebacteria

Eukaryotes

Protistans Plants Fungi Animals

6 Kingdoms

• Single cells

• No nucleus or

organelles

• Smaller, less

complex

Prokaryotic Organisms

Eukaryotic Organisms

• Single- or multi-celled

• Nucleus and other

organelles

• Larger, more complex

Mutation: Source of Variation

• Mutation = change in structure of DNA

• Basis for the variation in heritable traits

• Most are harmful

Adaptive Trait

A trait that gives the individual an advantage in survival or reproduction,

under a given set of circumstances

Evolution

• Genetically based change in a line of descent over time

• Population changes, not individuals

Antibiotic Resistance

• Antibiotics are used to kill bacteria

• Mutations for antibiotic resistance exist or arise

• Antibiotic-resistant bacteria survive and reproduce better than nonresistant

• Over time, proportion of antibiotic-resistant bacteria increases

Scientific Method

• Observe phenomenon

• Develop hypotheses

• Make predictions

• Devise test of predictions

• Carry out test and analyze results

Role of Experiments

• Used to study a phenomenon under known conditions

• Allows you to predict what will happen if a hypothesis is not wrong

• Can never prove a hypothesis 100% correct

Experimental Design

• Control group

– A standard for comparison

– Identical to experimental group except for

variable being studied

• Sampling error

– Nonrepresentative sample skews results

– Minimize by using large samples

Scientific Theory

• A hypothesis that has been tested for its predictive power many times and has not yet been found incorrect

• Has wide-ranging explanatory power– Darwin’s theory of evolution by natural

selection

Biological Therapy Experiments

Can we use viruses that attack bacteria (bacteriophages) to fight infections?

Experiment 1

• Hypothesis - Bacteriophages can protect mice against infectious bacteria

• Prediction - Mice injected with bacteriophages will not die as a result of bacterial injection

Experiment 1 - Test

• Experimental group

Inject with bacteria and bacteriophage

• Control group

Inject with bacteria and

saline

Experiment 1 - Results & Conclusion

• Experimental group

All mice lived

• Control group

All mice died

• Conclusion - Bacteriophage injections

protect mice against bacterial infections

Experiment 2

• Prediction - Bacteriophage injections will be more effective treatment than single dose of the antibiotic streptomycin

• Test - Mice injected with bacteria, then with saline, streptomycin, or bacteriophage

Experiment 2 - Results

• With 2nd injection:

– Bacteriophage - 11 of 12 mice lived

– 60 mg/gm streptomycin - 5 of 12 lived

– 100 mg/gm streptomycin - 3 of 12 lived

– Saline - all mice died

• Conclusion - Bacteriophage treatment can be

as good or better than antibiotic

Minimizing Variables

• All mice were same age and sex, reared under same conditions

• Each mouse in each test group received exact same treatment

• All mice in control group received same amount of saline

• Variable tested was antibiotic treatment versus bacteriophage treatment

Limits of Science

• Scientific approach cannot provide answers to subjective questions

• Cannot provide moral, aesthetic, or philosophical standards

Scientists Raise Questions

The external world, not internal

conviction, must be the testing ground

for scientific beliefs