Exam Review


1. 🔬 Doing Science

Your professor wants you to understand the scientific process, hypotheses, variables, graphs, and error bars.

Scientific process

Think:

Observation → Question → Hypothesis → Prediction → Experiment → Data → Conclusion

Example:

Observation: Plants near a window grow taller.
Question: Does more light increase plant growth?
Hypothesis: If plants receive more light, then they will grow taller.

Hypothesis

A hypothesis is a testable explanation for an observation.

It must be something you can actually test.

❌ "Plants like sunlight."

✅ "Increasing the amount of sunlight a plant receives will increase its growth."

Independent vs. dependent variable

Easy trick:

Independent = I change it
Dependent = Data I measure

Example: You're testing whether temperature affects plant growth.

  • Independent variable: Temperature

  • Dependent variable: Plant growth

On a graph:

X-axis = Independent
Y-axis = Dependent

Error bars

Error bars show variation/uncertainty around a mean.

For your class, the important idea is:

  • Little/no overlap → means may be significantly different

  • Lots of overlap → probably not significantly different

Be careful: in real statistics, whether overlap establishes significance depends on what the error bars represent and the statistical test. For your exam, follow the method your professor taught.

2. 🌎 Global Climate Patterns

This is a BIG section. Your study guide specifically lists convection currents, bodies of water, El Niño, upwelling, seasons, the Coriolis effect, mountains, and elevation vs. latitude.

☀ Convection currents

Remember:

Warm rises → cool sinks

The Sun heats Earth's surface unevenly.

  1. Sun warms the ground.

  2. Ground warms the air.

  3. Warm air expands and rises.

  4. Rising air cools.

  5. Cool air sinks.

  6. The cycle repeats.

That circulation is a convection current.

Easy memory:

🔥 HOT = UP
❄ COLD = DOWN

🌪 Coriolis Effect

Earth rotates, so moving air and water appear to curve instead of traveling completely straight.

Northern Hemisphere

Deflects RIGHT

Southern Hemisphere

Deflects LEFT

🧠 Remember:

Northern = Right

The Coriolis effect helps create global wind and ocean-current patterns.

🌊 How large bodies of water affect climate

Water changes temperature more slowly than land.

That means areas near oceans often have more moderate temperatures.

Think:

Ocean = temperature buffer

Coastal areas often have:

  • cooler summers

  • warmer/milder winters

  • smaller temperature changes

🌊 Upwelling

This one is important biologically.

Upwelling = deep, cold, nutrient-rich water rises to the surface.

Think:

⬆ Cold water
⬆ Nutrients
⬆ Phytoplankton growth
⬆ Food for consumers
⬆ Productivity

So upwelling can support highly productive marine communities and fisheries.

🌊 El Niño

Normally, winds help push warm surface water westward across the tropical Pacific, allowing cold, nutrient-rich water to upwell along western South America.

During El Niño, those normal wind/ocean patterns weaken or change.

That can cause:

Less upwelling → fewer nutrients reaching the surface → lower primary productivity → effects throughout the food web

☀ What Causes the Seasons?

🚨 Very important misconception:

Seasons are NOT caused by Earth being closer/farther from the Sun.

They're primarily caused by:

Earth's axial tilt ≈ 23.5°

When a hemisphere is tilted toward the Sun:

☀ More direct sunlight + longer days → summer

When tilted away:

☀ Less direct sunlight + shorter days → winter

🏔 Mountains and Climate

Mountains can create a rain shadow.

Moist air approaches mountain:

🌊 → 💨 → 🏔

Air rises → cools → water condenses → precipitation

After crossing the mountain:

Air descends → warms → becomes drier

So:

Windward side = wetter

Leeward side = drier

Why are high elevations similar to high latitudes?

Because both tend to be colder.

Going:

⬆ Higher elevation → colder

⬆ Higher latitude (toward poles) → colder

So mountaintops can have communities similar to places much farther north or south.

3. 🌳 Where Species Live

Your professor wants you to understand biotic factors, abiotic factors, dispersal, and habitat selection.

Abiotic factors

A = Away from life

Nonliving environmental conditions.

Examples:

  • Temperature

  • Water

  • Sunlight

  • Soil

  • Salinity

  • pH

  • Oxygen

Biotic factors

Bio = life

Living interactions.

Examples:

  • Predators

  • Competitors

  • Parasites

  • Food

  • Mates

  • Disease

Dispersal vs. Habitat Selection

Dispersal

Can the organism GET there?

Movement from one location to another.

Example:

A bird species could survive on an island, but the island may be too far away for the birds to reach.

Habitat selection

Does the organism CHOOSE to live there?

Organisms may select habitats based on food, shelter, mates, predators, etc.

🧠 Remember:

Dispersal = GET there

Habitat selection = STAY there

4. 🐰 Population Ecology

This section includes dispersion, population dynamics, r, K, exponential/logistic growth, density-dependent/independent factors, and the Allee effect.

Population

A population = individuals of the same species living in the same area.

Dispersion Patterns

Dispersion describes how individuals are distributed.

1. Clumped

Individuals live in groups.

🐟🐟🐟 🐟🐟

Very common in nature.

Causes include:

  • resources occurring in patches

  • protection

  • social behavior

2. Uniform

Individuals are evenly spaced.

🌳 🌳 🌳 🌳

Can result from:

  • territorial behavior

  • competition

3. Random

No predictable spacing.

🌳 🌳
🌳 🌳

Can occur when individuals neither strongly attract nor repel one another and resources are fairly uniform.

📈 Population Change

This is the equation you were asking me about earlier:

r = b − m

In a simplified population with no immigration/emigration:

r = per-capita population growth rate

b = birth rate

m = death rate

So:

If:

b > m → r is positive → population grows

b = m → r = 0 → population stable

b < m → r is negative → population decreases

🧠 Remember:

r = rate of increase

📈 Exponential Growth

Occurs when resources are essentially unlimited.

Produces a:

J-shaped curve

Population grows faster and faster.

Basic model:

dN/dt = rN

Where:

  • N = population size

  • r = per-capita growth rate

  • dN/dt = change in population size over time

Think:

🐰 → 🐰🐰 → 🐰🐰🐰🐰 → 🐰🐰🐰🐰🐰🐰🐰🐰

📈 Logistic Growth

Resources are limited.

Produces an:

S-shaped curve

Population grows quickly initially but eventually slows as it approaches:

K = Carrying Capacity

K = maximum population size the environment can sustainably support under those conditions.

So:

r = growth rate

K = carrying capacity

Density-Dependent Factors

Their effects become stronger as population density increases.

Examples:

👥 Competition
🦠 Disease
🪱 Parasites
🐺 Predation

More individuals → stronger effect.

Density-Independent Factors

Their effects aren't determined by population density.

Examples:

🔥 Fire
🌪 Hurricane
❄ Freeze
🌊 Flood
☀ Drought

A hurricane can affect a population whether it's large or small.

👥 Allee Effect

This happens when a population becomes so small that individuals have difficulty surviving/reproducing successfully.

Examples:

  • difficulty finding mates

  • reduced group protection

  • reduced cooperative hunting

So:

Very small population → lower individual success → population may decline further

5. 👶 Demography & Life History

Your professor expects you to interpret survivorship curves and distinguish reproductive strategies, life-history strategies, semelparity/iteroparity, and r/K-selected strategies.

Demography

Study of characteristics of populations such as:

  • Birth rates

  • Death rates

  • Age structure

  • Survival

  • Reproduction

📉 Survivorship Curves

These show how survival changes with age.

Type I

Most survive until old age, then mortality rises.

Example:

👶 → 🧑 → 👵 → 💀

Often associated with humans and other large mammals.

Type II

Approximately constant mortality rate throughout life.

Example often used: some birds.

Type III

Many die young, but individuals that survive early life may live much longer.

Example:

🐟 Fish
🦪 Oysters
🌱 Many plants

🧠 Easy:

I = die late

II = constant

III = die young

🥚 Semelparous vs. Iteroparous

Semelparous

Reproduce once, often with a large reproductive effort.

Example: Pacific salmon.

Iteroparous

Reproduce multiple times during life.

Example: humans.

🧠 Think:

Itero = iterate = repeat

r-selected vs. K-selected Strategies

r-selected

Emphasize rapid reproduction.

Typically:

  • Many offspring

  • Small offspring

  • Early reproduction

  • Less parental investment

  • Often associated with unpredictable/disturbed environments

Think:

🐭🐭🐭🐭🐭🐭🐭

K-selected

Typically:

  • Fewer offspring

  • Larger offspring

  • Later reproduction

  • Greater parental investment

  • Often associated with populations living nearer carrying capacity

Think:

🐘 👶

Important: Tradeoffs

An organism has limited energy.

Energy spent on:

growth + survival + reproduction

can't all be maximized simultaneously.

Example:

Producing many offspring may mean investing less energy into each offspring.

6. 🧔 Darwin & Evolution

Your professor wants you to understand how other scientists, competing theories, fossils, homology, artificial selection, and Darwin's observations contributed to descent with modification.

Charles Darwin

Darwin proposed evolution by:

Natural Selection

He traveled aboard the HMS Beagle and made observations of organisms, fossils, and geographic patterns.

🪨 Charles Lyell

Lyell wrote:

Principles of Geology

His work helped establish the idea that geological processes operating gradually over enormous periods could produce major changes.

This helped Darwin think:

Earth is very old → enough time exists for biological change to accumulate.

👥 Thomas Malthus

Malthus wrote:

An Essay on the Principle of Population

Core idea:

Populations have the potential to produce more offspring than available resources can support.

Darwin connected this to nature:

Too many offspring

↓

Limited resources

↓

Competition/struggle

↓

Some individuals reproduce more successfully

↓

Their traits become more common

🦴 Fossil Record

Fossils showed that:

  • Organisms in the past differed from organisms today.

  • Species have appeared and disappeared over Earth's history.

  • Some fossils resemble living organisms.

This helped support the idea that life has changed over time.

🦴 Homology

Homologous structures share an underlying structural similarity because of common ancestry, even when their functions differ.

Example:

🧑 Human arm
🐳 Whale flipper
🦇 Bat wing

Different functions, but similar underlying bone organization.

🐶 Artificial Selection

Humans choose which organisms reproduce based on desired traits.

Example:

Humans breeding dogs for particular characteristics.

Darwin realized:

If humans can cause populations to change by selecting traits...

the environment could also "select" traits over generations.

That's natural selection.

🌳 Descent With Modification

Organisms descend from ancestral populations but accumulate changes across generations.

Over long periods, this can produce the diversity of life we see.

🦎 Adaptation

An adaptation is a heritable trait that increases reproductive success in a particular environment.

Important:

❌ Individuals don't develop adaptations because they "need" them.

Instead:

Variation already exists → environment favors certain heritable variants → individuals with them leave more offspring → variants become more common.

7. 🧬 Natural Selection

This is likely one of your highest-priority concepts because your professor specifically wants the three requirements, sources of genetic variation, phenotype, environment, and relative fitness.

⭐ Three Requirements for Natural Selection

Memorize these.

1⃣ Variation

Individuals in a population must differ in traits.

Example:

🐰 Fast rabbit
🐰 Medium rabbit
🐰 Slow rabbit

2⃣ Heritability

At least some of that variation must be genetically heritable.

Parents must be able to pass relevant genetic variants to offspring.

3⃣ Differential Reproductive Success

Different variants lead individuals to leave different numbers of surviving, reproducing offspring in the particular environment.

That's closely related to:

Relative fitness

Relative fitness = reproductive success relative to other individuals/genotypes in the population.

So natural selection is ultimately about:

Who contributes more genes to future generations.

Not simply who lives longest.

🧬 Where Does Genetic Variation Come From?

A major original source is:

Mutation

Mutation creates new alleles.

Meiosis and sexual reproduction then reshuffle existing variation through processes such as:

  • Crossing over

  • Independent assortment

  • Random fertilization

🧬 Genotype vs. Phenotype

Genotype

Your genetic makeup.

Phenotype

Observable traits produced through genotype interacting with the environment.

Examples:

  • Body size

  • Color

  • Beak shape

  • Behavior

🚨 Natural selection acts directly on PHENOTYPE.

The environment doesn't "see" the genotype directly.

Think:

Genes → Phenotype → Environment selects → Reproductive success → Allele frequencies change

Why Can't Natural Selection Produce Perfect Organisms?

Natural selection works with:

Existing variation.

It doesn't intentionally design organisms.

Evolution is also constrained by:

  • Existing anatomy/evolutionary history

  • Tradeoffs

  • Available genetic variation

  • Changing environments

  • Chance

So adaptations can improve reproductive success without being "perfect."

🧬 MEIOSIS — Since You Asked About This Earlier

Your study guide specifically includes Chapter 13.3: meiosis among the exam topics.

First understand the purpose:

Mitosis

1 cell → 2 genetically similar cells

Used for:

  • Growth

  • Repair

  • Cell replacement

Meiosis

1 diploid cell → 4 haploid cells

Used to produce gametes for sexual reproduction.

Meiosis I vs. Meiosis II

This is the easiest way to remember it:

🧬 Meiosis I = Separate HOMOLOGOUS CHROMOSOMES

Homologous chromosomes pair.

Prophase I

⭐ Crossing over occurs

Homologous chromosomes exchange corresponding DNA segments.

This increases genetic variation.

Metaphase I

Homologous chromosome pairs line up.

Their orientation is random → independent assortment.

Anaphase I

Homologous chromosomes separate.

Telophase I

Cells divide.

Now you have 2 cells.

🧬 Meiosis II = Separate SISTER CHROMATIDS

It's somewhat similar to mitosis.

Prophase II

Chromosomes prepare.

Metaphase II

Chromosomes line up individually.

Anaphase II

⭐ Sister chromatids separate.

Telophase II

Cells divide.

Final result:

1 diploid cell → 4 genetically different haploid cells

⭐ The Exam Memory Sheet

If you only have a little time before the exam, memorize these connections:

Scientific method:
Observation → hypothesis → experiment → data → conclusion

Graph:
X = independent
Y = dependent

Convection:
Warm rises → cold sinks

Coriolis:
Northern = right
Southern = left

Seasons:
Earth's axial tilt

Upwelling:
Cold + nutrient-rich water rises

Abiotic:
Nonliving

Biotic:
Living

Dispersal:
Can it GET there?

Habitat selection:
Does it choose to LIVE there?

Dispersion:
Clumped / uniform / random

r:
Population growth rate

r = b − m:
birth rate − death rate

Exponential:
J curve

Logistic:
S curve

K:
Carrying capacity

Density-dependent:
Competition, disease, predation

Density-independent:
Weather/disasters

Allee effect:
Population too small → reproductive/survival problems

Survivorship:
I = die late
II = constant
III = die young

Semelparous:
Reproduce once

Iteroparous:
Reproduce repeatedly

Darwin:
Natural selection / descent with modification

Lyell:
Geology + gradual change

Malthus:
More offspring than resources can support

Homology:
Similarity due to common ancestry

Natural selection requires:
Variation + heritability + differential reproductive success

Fitness:
Relative reproductive success

Natural selection acts on:
Phenotype

New alleles originate through:
Mutation

Meiosis I:
Homologous chromosomes separate

Meiosis II:
Sister chromatids separate

Crossing over:
Prophase I

Final meiosis result:
4 genetically different haploid cells