Unit 0 & 1 Review

Unknown Speaker

Hey everyone, welcome back to Biggie Bio. I’m Chloe, and Grady’s over here doodling in his notes, which means we’re definitely about to talk numbers whether he likes it or not. Today, let’s kick off with why statistics actually matter in biology—not just for teachers who want to put you to sleep!

Grady Killpack

Hey now, I’m actually prepping my favorite “mean, median, and mode” graph. My students always mix those up. I did, too, until I started teaching. So, central tendency: you hear that term, you mentally check out, right? But look, it’s just finding the center of a pile of data. Like, if you plant five tomato seeds and measure the height, you could get numbers like 65, 52, 71, 56, and 61 millimeters. The mean, or average, just adds 'em up—305 in this case—divide by five, you get 61. Bam, mean height.

Unknown Speaker

Exactly. But what happens if you—oops—accidentally measure one mutant tomato that hits 150 mm? That would seriously mess with your mean and make it way higher, right? That’s where median saves the day—lining up all your numbers, picking the one smack in the middle. Leave it to the median to ignore those wacky outliers. If there isn’t a single middle, average the two in the middle. Mode? Meh, unless there’s a number popping up over and over, it’s just kind of chilling in the background.

Grady Killpack

And mode’s perfect when you’ve got something like height data with a lot of repeats, or bimodal distributions, but most times, mean or median’s your MVPs. For data sets with wild values, use the median. Short and sweet.

Unknown Speaker

Okay, so let’s talk range—it’s not just for marathons. The range, simple as this: biggest number minus smallest. If your tomato plants were 71 mm and 52 mm, that’s 19 mm. But that doesn’t tell you everything. So, we dig into standard deviation—that’s how far each measurement strays from the mean. Lower number? Your tomatoes grew pretty evenly. Higher? Maybe you forgot to water one, or someone’s kid pulled a prank and replaced a tomato with a fake one (looking at you, Grady).

Grady Killpack

Ha—wouldn’t be the first time! Here’s where those error bars on graphs come in. Add standard error—tells you how confident you are that your sample mean represents the real mean for every tomato plant in the universe. If those error bars on two groups overlap, the difference isn’t statistically significant—so, don’t go publishing in Science just yet.

Unknown Speaker

If they don’t overlap, though, maybe there’s actually something cool happening worth a victory cheer. Oh—Grady, you’ve gotta tell your plant water vs. sports drink story. It’s the classic experiment for AP-style analysis!

Grady Killpack

Alright, so, picture eleven-year-old me, pumped full of curiosity and not nearly enough YouTube. I tested which helped plants more—plain water or a fancy sports drink. We measured the growth, plugged our data into some primitive Excel spreadsheet—mean, range, standard deviation. And when we graphed it, the error bars overlapped! So, no slam dunk for sports drinks; plants don’t care for electrolytes like I thought. But it convinced the science fair judges I understood data and how to interpret significance—and they didn’t care that my tomatoes tasted, well, weird. That’s how biology and stats actually tell a story, not just fill a page with numbers.

Unknown Speaker

That experiment was perfect for explaining the scientific method, honestly. Let’s run it down quick: you make an observation—like your tomato plants are growing differently. Next, make a hypothesis, usually starting with a null version. Something like “There will be no difference in plant height between those watered with water and those with sports drinks.” That’s H-naught! Then, you list alternative hypotheses—sports drink will increase it, or maybe even decrease it.

Grady Killpack

A classic. And every experiment’s got variables—the independent one is what you change (the drink type), the dependent variable is what you measure (plant height). Gotta keep the constants—like sunlight and soil—locked down, or you have no idea what actually mattered.

Unknown Speaker

Controls are a hill I’ll die on. Use both positive and negative controls if you can. Positive control’s something you know should cause an effect—like, if you’re testing painkillers, Tylenol’s your positive control because it definitely works for headaches. Negative control? Placebo, or plain water if you’re running the plant experiment. That’s how you catch bias, and it’s classic AP Bio. Last year, my class used placebo and Tylenol for a simulated headache relief lab—control group got the placebo, and one got actual Tylenol. If both reported feeling better, you check for outside factors before giving Tylenol all the credit!

Grady Killpack

And I always mess up explaining this: constants aren’t the same as controls. Constants never change—lighting, temp, same type of tomato, everything. The controls are your baseline for comparison. It kills interpretations when you skip them. And those classic AP questions love to mess with you on this detail.

Unknown Speaker

We also have to hit reasoning: inductive is generalizing from specifics, like “All the tomato plants I grew under the same light source hit about 61 mm, so maybe all tomato plants will.” Deductive is the reverse—taking general truths to make predictions about specifics, like if all plants need water, my tomato will, too. The AP exam will toss scenarios at you and ask, “Which kind of reasoning is this?” Stay sharp!

Unknown Speaker

Let’s bring it back to what’s actually inside those tomato plants—or you, or me! The chemistry of life starts with some wild water molecules. Water’s held together by polar covalent bonds between hydrogen and oxygen, which makes it a polar molecule, and then, every little water molecule forms hydrogen bonds with others. That’s why you get surface tension, the “walking on water” trick for pond bugs, and capillary action, which is literally how water gets to the top of trees.

Grady Killpack

Cohesion’s water molecules sticking together, adhesion’s when water sticks to a different thing, like the walls of a plant’s xylem tubes. Capillary action’s a combo—water “climbs” up the plant stem because adhesion to the walls beats out the water’s cohesion for itself. And high specific heat? Means it takes a whole lot of energy to heat water, so your iced tea and ocean temps both stay pretty stable. And here’s a good one—ice floats because hydrogen bonds expand as water freezes, making it less dense. Imagine if ice sank—marine ecosystems would be toast every winter.

Unknown Speaker

That’s a great visual! And since water’s the universal solvent, it dissolves stuff just by tugging on charged or polar molecules. Easy for nutrients to reach a plant cell, or for salt and sugar to dissolve in your sweet tea. That sets up life’s real stars—carbon and its specialty, organic chemistry. Carbon’s four valence electrons mean crazy chain options—single, double, triple bonds, branching, rings. That’s why you’ve got so many diverse molecules inside you.

Grady Killpack

And with carbon, you get functional groups, like hydroxyl or carboxyl, that can be swapped in and out, tweaking molecule behavior. Then the four macromolecules: carbs, proteins, nucleic acids, and lipids. Carbs are monosaccharides linked to make starch or cellulose; plants use starch to store energy, cellulose to build walls.

Unknown Speaker