Biological Science Course Introduction

Biological Science Course Introduction

• Biology is the study of life
• Living organisms share five fundamental characteristics:
  • Cells: All organisms are made of membrane-bound cells
  • Replication: All organisms can reproduce
  • Information: Organisms process hereditary information (genes) and environmental information
  • Energy: Organisms acquire and use energy
  • Evolution: Populations of organisms evolve over time

Theories

• Theory: A general explanation for a class of phenomena supported by evidence
  • Differs from everyday use (e.g., a "guess") in science
• Cell Theory: Explains the composition of organisms
• Theory of Evolution by Natural Selection: Explains the origins of organisms
• Chromosome Theory of Inheritance: Explains the transmission of hereditary information

Life is Cellular and Replicates through Cell Division

• 1665: Robert Hooke used a microscope to discover and name cells
  • Observed small compartments in cork
• 1600s: Anton van Leeuwenhoek built microscopes with greater magnification
  • Observed single-celled organisms ("animalcules")
• 1800s: Cell theory developed:
  • All organisms are made of cells
  • All cells come from preexisting cells

All Organisms are Made up of Cells

• Cells are highly organized compartments separated from their environment by a membrane barrier.
• The first part of the cell theory was the understanding that all organisms are made up of cells
• All cells come from pre-existing cells.

Terminology

• Theory: Explains broad patterns
• Hypothesis: A testable statement explaining an observation
• Experiment: Allows researchers to test the effect of a factor on a phenomenon
• Prediction: Measurable or observable result that must be correct if the hypothesis is valid

Cell Theory vs Spontaneous Generation

• Cell theory challenged spontaneous generation
  • All-cells-from-cells is a hypothesis
  • Cells grow and divide to produce new cells
• Spontaneous generation: The belief that organisms can arise spontaneously under certain conditions

The Spontaneous Generation and All-Cells-From-Cells Hypotheses Were Tested Experimentally by Louis Pasteur

• Pasteur's experiment demonstrated that cells arise from cells and not from spontaneous generation
  • Straight-necked flasks: Cells appeared due exposure to air, resulting in the growth of microbes.
  • Swan-necked flasks: Cells did not appear due to the filter-like curve in the flask, preventing microbes from entering the flasks.

Life Replicates Through Cell Division

• Cells must replicate for life to exist
• All cells in multicellular organisms descend from previously existing cells

How is Hereditary Information Encoded and Passed During Cell Division?

• Chromosomal theory of inheritance:
  • Hereditary information is encoded in genes
  • Genes are located on chromosomes
• DNA is the hereditary material
  • DNA is made of deoxyribonucleic acid molecules
• Genes are segments of DNA coding for cell products

DNA is a Double Helix

• Rosalind Franklin, James Watson, and Francis Crick proposed that DNA is a double-stranded helix
• DNA is made of four building blocks: A, T, C, and G
• The sequence of these blocks (A, T, C, G) carries information for an organism's growth, development, and reproduction
• DNA strands are bonded based on specific pairings:
  • A pairs with T
  • C pairs with G

The Central Dogma Describes the Flow of Genetic Information

• DNA codes for RNA which codes for proteins
• RNA (ribonucleic acid) carries out specialized functions in cells
  • Messenger RNA (mRNA) translates DNA code into protein production
• Proteins are crucial for carrying out cell tasks; forming structural components and promoting chemical reactions

DNA is Copied to Pass Genetic Information

• Copying DNA is accurate
• DNA changes (mutations) could lead to changes in proteins
• DNA changes lead to heritable variations and diversity

Life Requires Energy

• Organisms have two fundamental nutritional needs:
  • Acquiring chemical energy (ATP)
  • Obtaining molecules for building blocks (DNA, RNA, proteins)
• How organisms get energy is key to diversification of life

Life Evolves

• Evolution is the change in characteristics of a population over time, reflecting relatedness of species by common ancestry.
  • Modifications from generation to generation are called descent with modification

Evolution and Natural Selection

• Evolution: Change in characteristics of a population over time where species arise from a common ancestor
• Population: Group of individuals of the same species
  • Natural Selection: Explains evolution in that individuals vary in heritable characteristics; certain versions help individuals reproduce more than others.

Natural Selection and Evolutionary Change

• Certain heritable traits lead to increased success in producing offspring; these traits become more common over time
• Natural selection acts on individuals
• Evolutionary change occurs in populations
• Speciation occurs when populations diverge to form new species

The Phylogenetic Tree of Life

• Phylogenetic tree: Used to show relationships between species
  • Branches that share a recent common ancestor represent species closely related; those further apart are more distantly related
  • Data for the tree is often determined from genetic data.

How is Genetic Variation Analyzed?

• Biologists study RNA and DNA sequences from different organisms to compare building blocks (A, T, C, G)
  • Fewer variations indicate closer evolutionary relationships.

The Tree of Life Was Produced by Comparing Genetic Sequence Data

• Three major groups of organisms are shown in the tree (Domains): Eukaryotes (have a nucleus), Bacteria, and Archaea (both prokaryotes, lack a nucleus).

Doing Biology

• Science is based on asking questions that can be answered by collecting and analyzing data.
• Formulating a hypothesis is important
• Use of a control group helps in isolating the effect of the factor under investigation
• Experimental conditions and large sample size are crucial for valid findings.

How Do Foraging Desert Ants Navigate?

• Desert ants meander to find food, then return to the nest in a straight line
• The question is how do they find their way back?

Pedometer Hypothesis for How Ants Navigate

• Pedometer hypothesis: Ants track steps taken and stride length to know their distance from the nest.
• Null hypothesis: Stride length and number of steps have no effect on how the ant finds its way back to the nest; another mechanism is used for navigation.

Experimental Setup

• Ants were divided into three groups: stumps (shorter leg length), normal, and stilts (longer leg length) to understand whether stride length affects navigation

Do Desert Ants Use a "Pedometer"?

• Experiments were conducted as a test of the pedometer hypothesis.
  • Data was collected to see if the manipulation of leg length affect their ability to find their nest.