General Biology: Life, Scientific Method, Ecology, and Global Climate Change

Biology: The Study of Life

What is Life?

Biology is the scientific study of life. To define life, biologists use several key characteristics that all living things share.

• Reproduction: Life reproduces, grows, and develops. Reproduction can be either asexual or sexual.

• Growth and Development: Organisms grow and develop from a single cell into multicellular forms with specialized organs.

• Energy Use: Life requires energy, which is brought in, converted to useful forms, and expelled. Example: Heat is lost every time energy is transferred.

• Cells: All living things consist of cells.

  • Unicellular: Organisms made of one cell.

  • Multicellular: Organisms made of trillions of cells.

• Order: Life is organized in hierarchical levels: biosphere → ecosystem → community → population → organism → organ system → organ → tissue → cell → organelle → molecule → atom.

• Response to Environment: Life maintains internal constancy (homeostasis). Example: Elephants have an "internal thermostat" to maintain temperature homeostasis.

• Evolution: Life evolves over time. Example: Seahorses that blend in are more likely to survive and reproduce.

The Nature of Science

Attributes of Science

Science is defined by its testable, repeatable, and falsifiable nature.

• Testable: Scientific claims can be tested through observation and experimentation.

• Repeatable: Experiments and observations can be repeated with similar results.

• Falsifiable: Scientific ideas can be proven wrong if evidence contradicts them.

Scientific Method

The scientific method is a systematic approach to investigating phenomena.

• Observation: Gathering data about the world.

• Question: Asking why or how something occurs.

• Hypothesis: Proposed explanation that can be tested.

• Experiment: Testing the hypothesis through controlled investigation.

• Results: Collecting and analyzing data.

• Conclusion: Drawing inferences from the results.

Scientific Facts, Hypotheses, and Theories

• Fact: Observation that has been repeatedly confirmed.

• Hypothesis: Proposed explanation for an observation that can be tested.

• Theory: Highly probable, well-tested, and substantiated explanation based on a large collection of observations and experiments.

What Science is NOT

• Not a solution to all problems and questions.

• Not infallible or unbiased.

• Does not prove anything absolutely.

Ecology and Global Climate Change

Ecology

Ecology is the study of interactions between organisms and their environment.

• Ecosystem: All biotic (living) and abiotic (non-living) components of a particular environment.

• Ecosystem Processes:

  • Energy flow

  • Biogeochemical cycling

Greenhouse Gases and Climate Change

Greenhouse gases trap heat in the atmosphere, leading to global temperature rise and climate change.

• Main Greenhouse Gases:

  • Methane

  • Nitrous oxide

  • Water vapor

  • Carbon dioxide

• Effects:

  • Global temperatures rise

  • Sea level rise

  • More extreme weather events

  • Ocean acidification (CO2 dissolves in water, forming carbonic acid)

Common Misconceptions

• "The earth has experienced high CO2 concentrations before, so what's the big deal?" Reality: Slow change in the past allowed adaptation; current changes are abrupt and can cause mass extinction events.

• CO2 Persistence: Most carbon dioxide stays in the atmosphere for at least 50-200 years; about half is removed within 30 years.

Population Ecology

Population ecology studies how populations of organisms change over time and space.

• Exponential Growth: Rapid, unlimited growth producing a J-shaped curve. $N(t) = N_0 e^{rt}$

• Logistic Growth: Growth slows as population reaches carrying capacity, producing an S-shaped curve. $N(t) = \frac{K}{1 + \frac{K-N_0}{N_0}e^{-rt}}$

• Carrying Capacity (K): Maximum population size that an environment can sustain.

Community Ecology

Community ecology examines interactions between species and how these affect the organization of communities.

• Mutualism: Both species benefit (e.g., plant-pollinator interactions).

• Competition: Both species are harmed (e.g., alpine plants moving to higher elevations due to warming).

• Parasitism: One species benefits, the other is harmed (e.g., Zika virus in mosquitoes).

Trophic Structure and Food Webs

Trophic structure describes feeding relationships within a community and the flow of energy and nutrients.

• Producers: Obtain energy from sunlight (photosynthesis).

• Primary Consumers: Eat producers.

• Secondary Consumers: Eat primary consumers.

• Tertiary Consumers: Eat secondary consumers.

• Quaternary Consumers: Eat tertiary consumers.

Food Web: Multi-branched and interconnected food chains reflecting complexity in trophic structure.

Species Diversity

Species diversity refers to the variety of species that live in a community.

• Species Richness: Number of different species.

• Relative Abundance: How abundant a particular species is compared to others.

Ecological Footprints and Sustainable Energy

Ecological Footprints

An ecological footprint measures the amount of resources (land, water, fuel) required to sustain one person.

• Carrying Capacity: Connected to ecological footprint; higher footprints reduce carrying capacity.

Barriers to Sustainable Energy

• Location: Decentralized energy sources require transmission infrastructure.

• Storage: Energy must be stored for later use; accessibility and reliability are key.

• Fossil Fuels: Oil, natural gas, and coal are traditional energy sources but contribute to climate change.

• Biofuels: Fuels created from biomass (living stuff), such as ethanol and biodiesel.

Photosynthesis and Cellular Respiration

Photosynthesis and cellular respiration are fundamental biological processes for energy transformation.

• Photosynthesis: Converts energy from sunlight into chemical energy (sugars).

• Ingredients: Sunlight, carbon dioxide, water.

• Products: Sugars, oxygen.

• Location: Chloroplasts in plant cells; chlorophyll is the light-absorbing pigment.

Stages of Photosynthesis:

• Light Reactions: Capture energy, split water, release oxygen, transfer energy to Calvin cycle.

• Calvin Cycle: Uses energy from light reactions to convert carbon dioxide into sugar.

Cellular Respiration: Breaks down sugars to release energy for biological processes. Ingredients: Sugars and oxygen. Products: Carbon dioxide, water, energy.

Biofuels

• 1st Generation Biofuels: Produced from food crops (e.g., ethanol from sugar cane, biodiesel from vegetable oils).

• 2nd Generation Biofuels: Produced from non-food biomass.

• 3rd Generation Biofuels: Produced from algae and other advanced sources.

Energy Source	Origin	Examples
Fossil Fuels	Extracted from plants and seeds (ancient)	Oil, coal, natural gas
Biofuels	Modern primary producers	Ethanol, biodiesel

Additional info: Equations for photosynthesis and cellular respiration:

Photosynthesis:

$6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2$

Cellular Respiration:

$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy}$