Hey this is Mr. W. Welcome to Episode One of
Thinking Biologically: Biology's Big Ideas. This is the first episode of a weekly
series that I'll be doing this year. My goal is to help you succeed in your biology
course and learn more than you ever thought imaginable. Throughout this series I'll be
emphasizing the College Board's four big ideas.
Why? Because they're a fantastic
intellectual scaffold that you can use to organize all of the information in this very
information-rich subject. Here's what they are: evolution, information storage and
transmission, energy and matter flow, and systems and system interactions. And
they're all right here in this Apple. Evolution is the process by which living things
change over time.This Apple is a Gala or a Gala depending on how you like to pronounce it. It's
a cultivated variety of a wild undomesticated apple that first evolved in Central Asia.
If
you could go back in time and went back just a hundred years you wouldn't find a Gala Apple.
This variety has only been cultivated for about a hundred years. It's one of hundreds of Apple
varieties each with different appearances and tastes that humans have created through selective
breeding. Evolution is a process that unfolds over time you can use a diagram like this— it's
called a phylogenetic tree— to represent the evolutionary history of any organism, including
apples. Apples have a common relatively recent ancestor with crab apples. They're more distantly
related to fruit like pears. Apples, crab apples, and pears are part of an enormous group
of species called the flowering plants that first emerged over a hundred million
years ago in the time of the dinosaurs. A more ancient ancestor gave rise to
plants with seeds but no flowers about 350 million years ago. You can push further
back to seedless plants, and eventually you reach an ancestor that wasn't a plant at all.
Before
450 million years ago there was no life on land. There were no plants. At that point the apple's
ancestor was some kind of aquatic photosynthetic algae If you go wide enough you're looking at all
of evolutionary history — essentially the tree of life. Here's the group that apples belong to: the
plant kingdom. Here's our group the animals. Note that we and apples have an evolutionary ancestor
in common. The apple is our evolutionary cousin, as is every other living thing. Is there evidence
for that astounding claim? Of course: it's embedded in our genes, our selves, our metabolism.
We'll get there later in this series. Evolution produces adaptations: structures with functions
that help organisms to survive and to reproduce. The skin of this apple is an adaptation that
evolved to attract animals by letting the apple be seen against a sea of green leaves. That's a
trait that co-evolved with color vision in fruit loving primates like ourselves.
The apple's skin
also protects the apple's flesh from bacteria and fungi. The flesh is an adaptation that evolved
to be a reward for animals that would eat the fruit and swallow the seeds. The seeds themselves
have other adaptations including a protective seed coat that allows the seeds to pass through an
animal's gut without being broken down by the acids in an animal's stomach. This allows the
seeds to be deposited somewhere where they can grow into new apple trees. Adaptations come about
through a process called natural selection. In any population there's variation in traits. Among
the apple seeds there are going to be some that have thicker coats and some that have thinner
coats. Some of that variation is determined by genes. Variants that are unsuccessful — which
means that they're not very good at promoting survival and reproduction — are going to
wind up being removed from the population. An apple seed that has a coat that's too thin is
going to wind up being dissolved in the stomach as it's being dissolved.
The genes for that trait
are also going to be dissolved and that means that those genes won't wind up being represented in the
next generation's gene pool. The opposite is going happen to traits that are more adaptive (that help
an organism to survive and reproduce). So over time natural selection shapes adaptations. It's
that simple. The second big idea in our course is information storage and transmission.
Again,
think about this apple. You plant an apple seed, you get a new plant. What the seed is transmitting
is information about how to build a new tree. That information is genetic information and
it's stored in a molecule called DNA. Let's think about DNA in the context of a cell.
DNA is in the cell's nucleus and it sends a message that goes to particles that are
called the ribosomes. Those ribosomes are unbelievable because what they can do is they
can take information sent by DNA and translate it into protein. Protein determines the
characteristics of cells. And in fact, through many complex mechanisms, proteins will
wind up determining the characteristics of the entire organism. And that information has
been changing over evolutionary time. In fact you can think of evolution as a change in the
genetic information carried within a population's gene pool. The third theme is energy and matter
flow. This apple was built by cells using solar energy. Photosynthesis is one of the great energy
reactions of living things.
What photosynthetic cells can do is take free energy in sunlight (free
energy is available energy that can be harvested to do work) and they use that energy to combine
carbon dioxide (a gas in the air) and water to create carbohydrates. Those carbohydrates are full
of chemical energy that plants can use to power their own life processes. These carbohydrates
also provide the matter—the carbon, hydrogen, and oxygen atoms— that plants use to build
themselves. Now that energy can also pass to animals like you and me. What we do is we take
chemical energy and combine it with oxygen, releasing energy we need to sustain our life
processes. We breathe out the exhaust carbon dioxide and water vapor. The entire process
is called cellular respiration and it's life's other great energy related process.
So we
have energy flow from the sun into plants and then into animals like you and me. Note that
this is a one-way flow. The energy isn't lost, but it starts out as useful free energy and by
the time living things are done with it it's useless heat. Energy flows and dissipates.
In almost every ecosystem on Earth, life is sustained by a constant flow of energy from the
Sun. Matter works differently: it's recycled. Carbon, for example, will move from carbon dioxide
in the air into plants like apple trees. Plants, in addition to doing photosynthesis, also do
cellular respiration and that returns some carbon dioxide into the air. The carbohydrates made
by plants can then pass to animals. We perform cellular respiration and that again returns
CO2 to the air. When living things die they're decomposed by bacteria and fungi. Decomposition
returns carbon dioxide to the atmosphere, so the same atoms have been cycling on planet
Earth for billions of years. Idea number four is that life is composed of complex interacting
systems. A system is a group of connected things that form a larger whole. You know that phrase
"the whole is greater than the sum of its parts?" That's what systems are all about.
The systems
that we'll look at most in this course are cells, the building blocks of life. Earlier we looked
at the Tree of Life. You can see here that the tree has a common stem and then there are
three major branches. Each branch is a Domain. That's the biggest classification category
and it's based on cell type. Simpler, smaller cells are found in bacteria
and archaea. Much more complex cells, like the one in this Paramecium, are found in
our Domain, the eukaryotes. Apple trees are composed of eukaryotic cells that are like this.
These cells interconnect to form tissues like the photosynthetic tissue in this leaf. Interacting
tissues form organs like the leaf itself. At every level new properties emerge as the system grows
more complex. Organisms, whether they're made of one cell like this Paramecium or trillions of
cells like you and me, are open systems.
That means that they have input and outputs. The inputs
in terms of cellular respiration are things like fuel food and oxygen. The outputs are things like
carbon dioxide, water and other wastes. Systems interact when I took a bite out of this Apple
that was one organism consuming another organism. That's an important kind of interaction. Living
systems are also embedded within other systems. An apple tree, for example, is part of a wider
ecosystem composed of interacting populations and the nonliving matter and energy that sustain
them and all ecosystems are part of the biosphere, the living system that includes all life on Earth.
How are you going to learn this? I'm not referring just to this video but to the entire course.
Learning requires interaction and that's why I put together an interactive biology curriculum
and my website, sciencemusicvideos.com. So go there now You're gonna find flashcard. You're
going to find multiple-choice quizzes. You'll find the interactive diagrams: ways that you can
interact to really remember what you've learned. Go there now there's a card above
there's a link below.
Complete the activities and you will learn more than
you ever thought possible and you'll have fun doing it because it's not passive
learning. It's active you'll have a great sense of accomplishment. So go do it! It does
require a subscription. It's a great bargain, and you can also get your teacher to purchase
a site license so that all the students in your class can be learning together. Got a
question? Please leave it in the comments below. But right now we're going to sign
off. I'll see you at sciencemusicvideos.com and I'll see you here next week the next
episode of Thinking Biologically. Thanks..
