- D4 ✏︎ Ecosystems -
D4.1 - Natural Selection (SL/HL)
LECTURE VIDEO
DESCRIPTION
Evolution isn’t a goal—it’s a filter. Organisms don’t “try” to get better. They just randomly show up with traits, and nature either vibes with them or throws them in the bin. Over millions of years, you get giraffes, guppies, and somehow still mosquitoes.
This video watches nature play favorites:
- Natural Selection: The Brutal Talent Show – Variation exists. Some traits help you survive and reproduce. Those get passed on. Others don’t. The end. No judges. No second chances. Just stats.
- Lamarck vs. Darwin: The Clown vs. The Legend – Lamarck thought giraffes stretched their necks and passed on the stretch. Adorable. Wrong. Darwin said giraffes with slightly longer necks ate more leaves, lived longer, had more babies. Repeat for millions of years. Lamarck’s theory died. Darwin’s became biology. RIP stretchy neck energy.
- Heritable vs. Acquired Traits: Heritable = built into your DNA. Eye color, blood type, potential to lose your keys daily. Acquired = stuff that happens to you. Muscles from the gym. Losing a finger. Scars. Your kids don’t inherit your gym gains. Sorry. Lift for yourself.
- Modeling Selection Pressures (The Guppy Saga): Put guppies in a pool with predators. Dull guppies survive. Bright ones get eaten. Move them somewhere safe? Suddenly bright colors attract mates and dull ones die lonely. Same fish. Different pressure. Different outcome. Evolution in real time, just wetter.
Understand why your gym membership won’t help your future kids, how Darwin roasted Lamarck without even trying, and why guppies are basically the lab rats of evolutionary fashion.
TIMESTAMPS
STUDY RESOURCES
00:00 – Outline Of This Video
00:40 – Natural Selection Overview
04:20 – Step1: Overproduction Of Offspring
06:17 – Step 2: Genetic Variation Within The Population
12:46 – Step 3: Struggle For Survival
17:57 – Step 4: Differential Survival
18:51 – Step 5: Reproduction
20:55 – Darwinism V.S Lamarckism
23:06 – Heritable V.S Acquired Traits
25:04 – Guppies & Sexual Selection
31:18 – Guppies & Predator Selection
34:00 – Guppies Summary
35:18 – Questions & Answers
NOTES – All you need to know in one place!
QUESTIONS – Test your Big Brain!
D4.1 - Natural Selection (HL)
LECTURE VIDEO
DESCRIPTION
Evolution isn’t just “survival of the fittest.” It’s about which genetic versions stick around, which ones get kicked out, and how a math equation can expose whether a population is evolving or just really bad at statistics. Also, moths pulled a full outfit change because people couldn’t stop burning coal.
This video tracks the genetic scorecard of life:
- Gene Pools & Allele Frequencies: The gene pool is every allele in a population. Think of it as the genetic group chat. Allele frequency is just how many members have a specific trait. Over time, these numbers shift. That’s evolution. Not magic. Just math with consequences.
- The Peppered Moths: The Original Fashion Influencer – White moths on clean trees? Hidden. Black moths on soot-covered trees? Hidden. Then the Industrial Revolution said “let’s make everything black.” White moths got eaten like snacks. Black ones thrived. Frequency flipped. Moths invented outfit changes before it was cool.
- Antibiotic Resistance: Bacteria Are Playing 4D Chess – You take antibiotics. Most bacteria die. But that one random resistant mutant? It throws a party and invites all its friends. Now the whole infection is resistant. Congrats, you just speedran evolution by forgetting to finish your prescription.
- Selection Types: Nature’s Drama Filters – Directional selection puts one extreme in the spotlight—bigger beaks get the girls, smaller beaks get leftovers. Stabilizing selection says average is safe—too big or too small dies, medium is the dream. Disruptive selection lets both extremes thrive while the middle gets absolutely wrecked. Nature has no chill.
- Artificial Selection: Humans Playing God With Vegetables – Wolves that didn’t bite became dogs. Cows that gave more milk got more babies. Broccoli, cauliflower, kale, cabbage? Same plant. Humans just kept picking the weird-looking versions until dinner became a science experiment. Selective breeding is just evolution with a shopping list and commitment issues.
- Hardy-Weinberg Equation (p² + 2pq + q² = 1):The equation that tells you if a population is evolving. It assumes no selection, no mutation, no migration, giant population, random mating. Basically it assumes a perfect world that doesn’t exist. When reality doesn’t match the math? Evolution is happening. You caught it red-handed.
Understand how bacteria outsmart us, why moths are fashion icons, and how one equation has been humbling biology students at 2 a.m. since 1908.
TIMESTAMPS
STUDY RESOURCES
00:00 – Overview Of This Video
00:23 – Genome
04:42 – Gene Pool
11:58 – Evolution & Allele Frequencies
16:16 – The Peppered Moths
19:47 – Antibiotic Resistance & Natural Selection
26:01 – How doctors find the right antibiotic for you?
29:00 – Type Of Selection
34:13 – Artificial Selection
36:48 – Hardy Weinberg Equilibrium
42:07 – The Hardy Weinberg Equations
48:00 – Worked Examples Using Hardy Weinberg Equations
54:22 – Questions & Answers
NOTES – All you need to know in one place!
QUESTIONS – Test your Big Brain!
D4.2 - Stability & Change (SL/HL)
LECTURE VIDEO
DESCRIPTION
Ecosystems are constantly walking a tightrope between stability and chaos. One keystone species gets removed? Whole thing collapses. Too much fertilizer runs into a lake? Everything dies. Plastic shows up? It stays forever. But don’t worry—humans also invented rewilding and tiny artificial ecosystems to study our mess.
This video watches nature try to keep it together:
- Sustainable Ecosystem: An ecosystem that can maintain itself indefinitely. No handouts. No bailouts. Just recycling nutrients, capturing energy, and not collapsing. Basically the financial independent friend you wish you were.
- Keystone Species: The one organism holding everything together. Remove it and the whole system implodes like a Jenga tower with one too many moves. Sea otters? Keep urchins in check. Wolves? Keep deer from eating everything. Be humble, keystone species. The weight of the world is on you.
- Sustainability of Resources & Agriculture: Taking resources at a rate they can replenish. Fishing? Don’t take all the fish. Farming? Don’t destroy the soil. It’s not rocket science. It’s just not being greedy. Apparently that’s hard.
- Eutrophication: When Fertilizer Kills Everything – Excess nutrients (usually from farms) wash into lakes. Algae goes crazy. Blooms everywhere. Then algae dies, bacteria decomposes it, and uses up all the oxygen. Fish suffocate. Lake becomes dead zone. Congratulations, your lawn fertilizer murdered a whole ecosystem.
- Biomagnification: Toxins Get More Concentrated Up the Food Chain – Tiny amounts of toxin in water? Plankton absorb it. Small fish eat lots of plankton. Big fish eat lots of small fish. Top predator eats lots of big fish. Now the predator has a toxic overdose. DDT. Mercury. Forever chemicals. They don’t go away. They just climb.
- Microplastic Pollution: The Forever Trash –Plastic breaks down. Into smaller pieces. And smaller. And smaller. Now it’s everywhere—oceans, soil, your blood, probably your brain. We’ve made the planet into a plastic soup and we’re just now figuring out that’s bad.
- Rewilding: Letting Nature Take the Wheel – Stop managing everything. Bring back keystone species. Let forests grow. Let rivers meander. Nature actually knows what it’s doing. Who knew?
- Mesocosms: Tiny Ecosystems for Science – Want to study an ecosystem without the whole planet? Build a mini one. A tank. A pond in a bucket. A sealed forest in a glass ball. Control everything. Watch it burn or thrive. Science is just god with smaller ambitions.
Understand how ecosystems balance on a knife’s edge, why your laundry is shedding plastic into the ocean, and how tiny fake ecosystems help us predict the future of the real one.
TIMESTAMPS
STUDY RESOURCES
00:00:00 – Overview Of This Video
00:00:24 – A Sustainable Ecosystem
00:10:55 – The Amazon Rainforest
00:17:22 – Keystone Species (Sea Star Example)
00:20:46 – Keystone Species (Wolves)
00:25:27 – Sustainable Resource Harvesting (Aquatic Example)
00:29:31 – Sustainable Resource Harvesting (Terrestrial Example)
00:32:27 – Agriculture Sustainability
00:44:12 – Eutrophication
00:48:08 – Biomagnification E.g., Mercury
00:55:11 – Biomagnification E.g., DDT
00:58:36 – Plastics
01:00:56 – Rewilding
01:03:46 – Mesocosms
01:08:24 – Calculating Percentage Change
01:11:34 – Questions & Answers
NOTES – All you need to know in one place!
QUESTIONS – Test your Big Brain!
D4.2 - Stability & Change (HL)
LECTURE VIDEO
DESCRIPTION
Imagine a bare rock. No soil. No life. Just vibes. Now wait a few hundred years. Somehow, there’s a forest. That’s not magic—it’s succession. Nature’s slowest, most determined home makeover.
This video watches barren landscapes slowly turn into ecosystems:
- Primary Succession: Starting From Absolute Zero – No soil. Nothing. Just rock. Lichens move in first because they’re desperate and have no standards. They die, leave a little organic matter. Mosses arrive. Then grasses. Then shrubs. Then trees. Each stage paves the way for the next. It takes centuries. Nature is not on a deadline.
- Secondary Succession: The Comeback Story – Soil already exists. Maybe a fire wiped out the forest. Maybe a farmer abandoned a field. Plants sprint back. Grasses first. Then weeds. Then shrubs. Then baby trees. Then forest again. Much faster than primary succession. The soil did all the hard work already.
- Cyclical Succession: The Revolving Door – Some ecosystems just cycle through the same stages on repeat. Heaths burn, regenerate, burn again. Grazing keeps grasslands from becoming forests. It’s not a straight line to a “climax community.” Sometimes nature just vibes in a loop.
Understand how life colonizes bare rock, why abandoned fields don’t stay empty, and how some ecosystems are just stuck in a biological hamster wheel.
TIMESTAMPS
STUDY RESOURCES
00:00 – Outline Of This Video
00:10 – Primary Succession
07:49 – Secondary Succession
09:57 – Summary Page (Primary V.S Secondary Succession)
10:42 – Cyclical Succession
14:34 – Questions & Answers
NOTES – All you need to know in one place!
QUESTIONS – Test your Big Brain!
D4.3 - Climate Change (SL/HL)
LECTURE VIDEO
DESCRIPTION
Imagine Earth as a temperature-controlled greenhouse. Humans added extra insulation, turned up the heat, and now the whole planet is sweating. The ice is melting, corals are bleaching, and animals are relocating like it’s a bad rental situation. But sure, let’s keep burning stuff.
This video watches the planet slowly lose its cool:
- The Greenhouse Effect: Earth’s Cozy Blanket (Now Too Thick) – Greenhouse gases trap heat. Always have. Without it, we’d be a frozen rock. Problem? Humans keep adding more blanket. Now Earth is sweating and can’t kick it off. Too many blankets. Global warming isn’t a theory. It’s a sleeping bag emergency.
- Positive Feedback Cycles: When Nature Panics and Makes It Worse – Ice melts. Dark ocean exposed. Dark ocean absorbs more heat. More ice melts. That’s positive feedback. Not “good” positive. “Oh no, this is accelerating” positive. Permafrost thaws? Releases methane. More warming. More thawing. Nature is in a doom spiral and can’t stop.
- Coral Reefs: The Ocean’s Fever Dream – Water warms one degree too much. Corals freak out and kick out their algae roommates. They turn white. Bleaching. If temps don’t drop, they die. Entire ecosystems gone because the ocean got too spicy. Corals did not sign up for this.
- Polar Habitats: Where “Cool” Is Literal – Walruses need sea ice to rest between dives. Ice is melting. Giant blubbery creatures with nowhere to sit. It’s sad and also slightly ridiculous. Penguins? Also struggling. The North Pole is having a meltdown. Literally.
- Range Shifts: Animals Moving Out – Species are packing up and heading toward the poles or up mountains. Looking for their comfort zone. Problem? Some hit coastlines. Some hit cities. Some hit extinction. It’s the world’s slowest, saddest migration.
- Ocean Current Changes: The Conveyor Belt Is Glitching – Ocean currents move heat around the planet. Currents slow down. Europe gets colder? Some places get weirder weather. The whole system is throwing error codes.
- Carbon Sequestration: Hiding the Evidence – Nature stores carbon. Forests. Oceans. Soil. Peat bogs. We keep digging it up and burning it. Solution? Stop digging. Plant more trees. Bury carbon. Let the ocean do its thing. Or invent expensive machines to suck CO₂ out. Either way, we’re cleaning up a mess we made.
Understand why Earth is overheating, why polar bears are running out of real estate, and how we might convince carbon to go back where it came from.
TIMESTAMPS
STUDY RESOURCES
00:00:00 – Overview Of This Video
00:00:28 – The Ultimate Greenhouse
00:04:25 – Greenhouse Effect On Earth
00:11:23 – Correlation & Causation
00:17:44 – Climate Change V.S Global Warming
00:21:24 – Positive Feedback Cycles In Global Warming
00:34:15 – Tipping Point & Taiga Biome
00:37:45 – Polar Habitat Change
00:41:04 – Coral Reef Change
00:49:00 – Range Shifts
00:52:12 – Ocean Current Basics
00:54:52 – El Nino Southern Oscillations (ENSO)
01:02:13 – Carbon Sequestration
01:05:02 – Questions & Answers
NOTES – All you need to know in one place!
QUESTIONS – Test your Big Brain!
D4.3 - Phenology (HL)
LECTURE VIDEO
DESCRIPTION
Nature runs on a schedule. Birds migrate, flowers bloom, caterpillars hatch—all timed to perfection. But the planet is warming, and now the calendar is glitching. Some species are adapting. Some are confused. Some are just showing up to an empty buffet.
This video watches nature miss its alarms:
- What Is Phenology?: The study of nature’s timing. When birds migrate. When trees leaf out. When bugs hatch. It’s nature’s daily planner, and everything is color-coded by season.
- Reindeer & Arctic Mouse-Ear: Reindeer calves used to arrive just when Arctic mouse-ear plants were most nutritious. Now warming springs mean plants peak earlier. Reindeer arrive on time, but the salad bar is already picked over. Hungry reindeer. Disappointed plants. Wrong place, wrong time.
- Great Tit & Caterpillars: Great tits time their egg hatching to match peak caterpillar season. Baby birds need protein. Caterpillars are the protein. But warmer springs mean caterpillars emerge earlier. Birds are still sitting on eggs. By the time chicks hatch, the caterpillars are gone. Hungry chicks. Stressed parents. Evolution needs to speedrun an adjustment.
- Spruce Beetle: The Invader That Loves Global Warming – Spruce beetles used to be kept in check by cold winters. Winters aren’t cold anymore. Beetles survive. Multiply. Kill forests. Vast stretches of dead trees. The beetle isn’t confused. It’s thriving. That’s the problem.
- Climate Change & Evolution: Tawny owls come in two colors—brown and grey. Grey ones used to blend better in snowy winters. Winters are milder now. Brown ones survive more. Brown owls are becoming dominant. Evolution in real time.
Understand why nature’s alarm clock is broken, why caterpillars and birds are in a toxic situationship, and how some owls are switching teams to keep up with the times.
TIMESTAMPS
STUDY RESOURCES
00:00 – Overview Of This Video
00:20 – What Is Phenology
06:20 – Reindeer & Arctic Mouse-Ear
15:45 – The Great Tit & Caterpillar
18:44 – The Spruce Beetle
24:36 – Climate Change & Evolution (Tawny Owls)
26:52 – Questions & Answers
NOTES – All you need to know in one place!
QUESTIONS – Test your Big Brain!