Luyện nói tiếng Anh bằng Shadowing qua video: Stroll Through the Playlist (a Biology Review)

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Petunia, we have so many videos now.

Every once in a while, I'll come across one of your pictures and be reminded all about the topic again.

I love them so much.

Aw, thanks.

Remember the danger guppy?

I love the danger guppy.

Which video was that for?

Classification!

Remember we were talking about how a scientific name is much more reliable than a common name?

Especially a made-up common name.

Oh, yeah.

Sometimes I forget what I've drawn.

You forget?

Well, every video has, like, 200 pictures.

If I don't go back and watch the videos, I tend to forget.

And I mean, we have, like, more than 50 videos, so that would take a long time.

I guess I'd be more inclined to do that if we had, like, a TLDR version.

A what?

You know, too long, didn't read, a summary of sorts.

Like a refresher, just covering the main points.

A refresher?

Now wait a minute, I didn't mean that we actually need to create a- We do!

I mean, we've made quite a few videos now in our biology playlist.

And if someone was reviewing, we could have this recap video, this stroll through the playlist.

Yeah, but- Now this one video would be way longer than our short videos, obviously, but it could be a useful study tool to connect the main pieces of the content together.

Granted, it would only have main points, not everything.

I guess that would be helpful.

I just don't think we, uh- Also, this stroll would be meant to be paused a lot.

There's so much vocabulary in biology.

We'll get Gus in on this.

He can hold up the pause sign so people know

when to pause the video so we can even ask the viewer questions.

And if the questions are difficult to answer, that may be a good indicator to check out the video it corresponds to.

Are you ready to stroll, Petunia?

Actually, this is going to be kind of a brisk stroll.

And because it only covers a short part of each concept, never forget biology is full of more exceptions and details than we can cover.

But that's great for more exploring.

We start with the characteristics of life.

What makes an organism alive?

Or not alive, anyway?

Life is difficult to define, and there are so many exceptions in looking at characteristics of life.

We went through some characteristics between my bathtub-grown pony and a real pony, but we didn't want to put numbers on the characteristics of life

because we didn't want to suggest that these are the only characteristics that one could argue.

So here's your first pause question.

Can you think of some characteristics of life to include?

We also note it in the video that they could certainly be titled differently, but here they are.

But this may get you to thinking of what's alive and what's not.

When studying biology, the study of life, it's important to understand the biological levels of organization.

Meaning these levels start small.

The smallest living unit being the cell.

That's part of the cell theory after all.

The cell theory includes that the cell is the smallest living unit in all organisms, that all living organisms are made up of cells, and what else?

Ah yes, that all cells come from pre-existing cells.

So cells combined together make up tissues.

Tissues make up organs.

Organs make up organ systems.

Organ systems are part of an organism.

An individual organism.

Individuals can be part of a population.

They're all the same species.

A community can you keep leveling up?

So the next larger level after community would be ecosystem.

At that level you're including abiotic factors which are non-living factors.

Rocks or temperature.

Next level is biome.

And then with biomes combined, all parts of the living world?

The biosphere.

Let's focus on living organisms.

are part of living organisms.

We mentioned four of these major macromolecules.

Can you name them here with their building blocks?

Carbohydrates, lipids, proteins, and nucleic acids.

And here are their building blocks.

Monosaccharides, fatty acid and glycerol, amino acids, and nucleotides.

These building blocks are considered true monomers for carbs, proteins, and nucleic acids.

Can you think of some important functions for any of these biomolecules?

Okay, Petunia, bring out some functions.

These are just some functions.

We wouldn't exist without these large molecules of life.

And their structures are just beautiful.

We included a popular mnemonic to remember some of the major elements they contain in their structures as well.

Most enzymes are made of proteins.

Can you describe some of the vocabulary associated with the enzyme?

Well, you can see this enzyme has an active site where a substrate binds.

Enzymes can speed up reactions.

Enzymes have the ability to break down or build up the substrates that they act upon. And ta-da!

Products.

An example of why we care?

Well consider the specific different digestive enzymes that are specific for breaking down fats or sugars or proteins.

But enzymes typically have a specific temperature and pH range that they need to be in to work correctly.

And what happens if enzymes can't stay in their ideal temperature or pH range?

That's right, they can denature.

Enzymes play a major role within cells.

We have oh so many videos on cells that you may wish to explore.

We explain the differences between prokaryotic cells and eukaryotic cells using the popular mnemonic

that pro rhymes with no and u rhymes with do, but what does that actually reference to?

cells have no nucleus, nor the other fancy membrane-bound organelles.

But ewe rhymes with do, and eukaryotic cells do have a nucleus and other membrane-bound organelles.

Prokaryotes include bacteria, anarchaea.

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Eukaryotes include plants, animals, protists, and fungi.

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Can you think of some things that prokaryotic cells would have in common with eukaryotic cells?

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So just to name a few, DNA, cytoplasm, ribosomes, and a cell membrane would be included in both.

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In our Intro to Cells video, we explore a lot of membrane-bound organelles that would be found exclusively in eukaryotes such as the nucleus,

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endoplasmic reticulum, Golgi apparatus, and mitochondria.

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Plant cells and animal cells can have some differences between them as well.

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Let's consider the cell membrane, also known as a plasma membrane.

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It is a part of all living cells, so why is it so important?

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Remember all cells have a membrane, regardless of whether or not they may have a cell wall.

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The membrane is a big deal for homeostasis because it controls what goes in and out of the cell.

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The membrane is made up of these phospholipids which have polar heads and nonpolar tails.

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Some molecules move passively through the membrane without a need for added energy.

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That's called passive transport.

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Simple diffusion and facilitated diffusion, which is through a protein, are examples of passive transport.

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In those cases, solutes travel with the gradient.

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Active transport, though, can involve using ATP to force molecules to move in the opposite direction of the gradient.

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So is this example simple diffusion, facilitated diffusion, or active transport?

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And how do you know?

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Well, it's not active transport because you can tell the molecules are traveling with the gradient without a need for ATP.

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It's not simple diffusion because it does seem to require a protein.

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It's facilitated diffusion, and that's passive.

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Water molecules can travel directly across a semi-permeable membrane, as they are so small.

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Or they can travel through proteins called aquaporins.

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That is more efficient.

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Water traveling through the membrane is called osmosis.

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In peak diffusion, water molecules do travel from an area where there is a

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high concentration of water molecules to an area of low concentration of water molecules.

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But we mentioned there's another way to look at osmosis.

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You can also look at it as water traveling to areas where there is a higher solute concentration, as the water concentration is less there.

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So to determine the net movement of water in osmosis, look for the hypertonic area.

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The areas of high solute concentration.

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A cell that is placed in a salty solution can lose water

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because the net movement of water is to the area of high solute concentration.

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One reason why you should not drink a lot of salt water.

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It's very dehydrating.

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Check to see if you can explain this graphic using the vocabulary hypertonic, hypotonic, and isotonic.

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Let's move beyond the membrane here and take a look at these organelles.

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the mitochondria and chloroplast.

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In eukaryotes, cellular respiration involves the mitochondria and photosynthesis involves the chloroplast.

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Cellular respiration involves the breakdown of glucose to yield ATP.

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All organisms must make ATP in some way or another.

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Yes, this includes plants and amoebas.

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If oxygen isn't available, some organisms like bacteria or yeast can do anaerobic respiration or fermentation to make their ATP.

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So what do these chemical equations have in common?

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Well one thing that is interesting is that these reactants and products are switched here, although that doesn't mean they are simply the reverse of each other.

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Keep in mind that they have different steps within them that make them very different.

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produces glucose.

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Sugar.

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Using sunlight energy.

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Not everything can do photosynthesis.

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In eukaryotic cells it occurs in the chloroplast.

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So moving beyond the mitochondria and chloroplast, let's take a look at this nucleus of a eukaryotic cell.

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Guess what's in here?

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DNA.

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DNA is a nucleic acid and nucleic acids are one of the types of biomolecules.

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It contains your genetic information and your entire DNA code is found in almost all of your cells, although genes can be turned on or off in different cells.

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Let's zoom into the monomer of DNA, a nucleotide.

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Nucleotides have a phosphate, deoxyribose, and a nitrogenous base.

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Which part of this nucleotide do you think is critical for determining genetic information?

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Yep, the base.

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Well that is the sequence of them.

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And this mnemonic, apples in the tree, cars in the garage, can help you remember that the bases adenine and thymine pair together.

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Cytosine and guanine pair together.

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DNA can be tightly coiled and condensed into these units called chromosomes.

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The number of chromosomes in humans is 46.

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How many do you receive from each parent?

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Well you would receive 23 from the female parent and 23 from the male parent.

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That's really important later on when we talk about cell division because chromosomes are more portable when it comes to cells dividing.

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Zooming back out, DNA is made up of two anti-parallel strands.

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One strand runs 5' to 3' and the other strand runs 3' to 5'.

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Now your body cells have to make copies of their DNA.

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Why?

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When you make a new body cell, which you make body cells for growth and repair, you need DNA to go into that new body cell as that is its genetic material.

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Hence the need for DNA replication.

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Making more DNA.

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We have some major key player enzymes here.

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Can you remember what these key players do?

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DNA must be unwound by an enzyme called helicase.

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Primase is an enzyme that sets down primers.

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Primers are needed because another enzyme, called DNA polymerase, requires them in order to start building.

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DNA polymerase builds a new strand in the 5' to 3' direction only.

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And because of that directional building, one of these new strands will be a lagging strand as

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DNA polymerase has to keep racing up here next to where the unwinding is going on.

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This causes fragments on the lagging strand known as okazaki fragments.

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Ligase can eventually be involved in sealing those fragments together.

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So we mentioned that you have to replicate DNA before you make new cells.

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It's a controlled event that happens in something known as the cell cycle.

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Do you remember the cell cycle phases often shown in a pie chart like this?

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The cell cycle includes G1 , S phase synthesis of DNA that's when the DNA replicates,

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G2 cell grows some more to prepare for dividing, and then M phase which includes mitosis and phytokinesis.

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G1S and G2 are all part of interphase, so the cell is not dividing during that time.

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But once it enters M phase, it divides.

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There are checkpoints it controls whether a cell can continue through the cycle.

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If a cell doesn't meet the checkpoint requirements, it is either fixed or it must undergo apoptosis, which means the cell destroys itself.

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This highly regulated cell cycle is controlled by many different proteins.

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Some that we mentioned included CDK, cyclin, and p53.

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Cancer cells are body cells that do not respond correctly to these checkpoints and tend to divide out of control.

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They can also have other problems such as making too much of their own growth factors, not anchoring properly, and not functioning correctly.

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Now we mentioned this cell cycle has emphase which includes mitosis.

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So what is mitosis?

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Mitosis is part of cell division.

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What kind of cells does it make?

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In humans and many other organisms, it makes identical body cells.

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Like skin cells making skin cells or stomach cells making stomach cells.

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Great for growth of an organism or replacement of worn out cells.

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During mitosis, chromosomes, which are condensed forms of DNA and protein, can be moved more easily into the newly formed daughter cell.

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We went over the PMAT mnemonic to remember the stages.

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Prophase, metaphase, anaphase, and telophase.

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Cytokinesis splits the cytoplasm and completely divides the actual cell.

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What's really easy to confuse with mitosis?

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Meiosis.

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Kind of wish they didn't sound so close.

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Anyway, what kind of cells does meiosis make?

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In humans and many other organisms, meiosis makes gametes, which are critical for sexual reproduction, otherwise known as sperm and egg cells.

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These gametes have half the number of chromosomes as a body cell.

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Gametes are haploid, meaning they have one set of chromosomes.

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Body cells are diploid, meaning they have two sets of chromosomes.

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PMAT happens twice here in meiosis.

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You have your starting cell here, which is diploid, it goes through prophase 1, metaphase 1, anaphase 1, and telophase 1.

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Then cytokinesis happens and it makes two cells.

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Then those cells go through prophase II, metaphase II, anaphase II, and telophase II.

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After cytokinesis, this results in four haploid cells, as these sperm cells shown here.

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These cells are all different from each other due to independent assortment and a process known as crossing over.

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So what is crossing over again and when does it happen?

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over happens during prophase I and it's when pairs of homologous chromosomes can transfer information between each other.

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So since meiosis is an important process for making sperm and egg cells for sexual reproduction in humans and many other organisms,

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how is this involved with the alleles and genes that a baby organism may inherit?

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Remember that in humans, a sperm cell has 23 chromosomes and an egg cell has 23 chromosomes.

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When they come together in a fertilized egg, that is 46 chromosomes.

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Portions of the chromosomes are genes that can code for specific traits.

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Many traits actually involve multiple genes.

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Genes can come in varieties known as alleles.

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Alleles are forms of a gene.

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For example, we talk about the trait of tasting or not tasting the chemical PTC.

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If treating this as a single gene trait, we would say the gene is a PTC tasting gene.

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But the allele that could be on a chromosome, which is a form of a gene,

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could be tasting or non-tasting In Mendelian inheritance,

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recessive alleles are expressed if the dominant allele is not present.

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So someone who inherits a homozygous dominant genotype of T, T would have a phenotype that is PTC tasting.

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What would the phenotype be of these other two?

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Someone who inherits a heterozygous Tt genotype would have a phenotype that is also PTC tasting.

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Only someone who inherits a homozygous recessive little t, little t genotype would have a phenotype that is non-PTC tasting.

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Again assuming it's a single gene trait, and as we mentioned in the video, it may be more complex than that.

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So speaking of alleles and genes, it's time for the super brisk stroll through different types of genetics that we have covered.

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We started with basic Mendelian, monohybrid, and dihybrid crosses.

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Could you explain, in your own words, how to complete these Punnett squares and how to write out the genotype and phenotype ratios of the offspring?

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To get help with the answer to these questions, check out the videos on these two topics specifically because there are multiple steps to solving these.

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Then we talked about some non-Mendelian inheritance including sex-linked traits and multiple alleles.

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If these look unfamiliar, you might want to review these videos as well.

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We also mentioned incomplete dominance and codominance.

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What is the difference between incomplete dominance and codominance?

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This graphic may help.

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Notice in codominance both alleles are expressed.

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In incomplete dominance, you can see how the phenotype can have an almost in-between

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appearance of the two traits there is not complete dominance when both of these alleles are present.

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Finally, we have a video on pedigrees.

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Pedigrees can be used to track a trait of interest, whether it be a sex-link trait or an autosomal trait.

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In a pedigree, individuals that are females are represented by circles, males are represented by squares,

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and individuals that have the trait being tracked are represented by circles or squares that are shaded.

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Now, when we're talking about these fascinating traits, you might wonder, How does DNA actually code for your traits?

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Well DNA can code for proteins and proteins are involved with many traits.

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Proteins are involved in transport, in structure, in acting as enzymes that make all kinds of materials, in protecting the body, and so much more.

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Your eye color is due to proteins involved in pigment production.

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So protein synthesis, that is, making proteins, is a big deal.

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Do you remember the two major steps in protein synthesis?

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The first step is transcription, which makes mRNA within the nucleus.

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The second step is translation, which takes place in the ribosome and makes a chain of amino acids known as a polypeptide.

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Proteins can be made up of one or more of these polypeptide chains.

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We also mention other forms of RNA, such as rRNA and tRNA,

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as well as how to read a codon chart to determine which amino acids are produced.

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Proteins often need folding to be fully functional.

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We have a video clip on protein structure and folding too.

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Now, on the subject of this codon chart, you will notice that the bases are read in 3s to determine a specific amino acid.

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These three bases on the mRNA are known as a codon.

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tRNA has an anti-codon on it that complements the mRNA codon.

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tRNAs also carry the corresponding amino acid.

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But what if there is a mutation in the DNA or mRNA?

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When we talk about mutations, we first mention gene mutations.

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This can include substitution, deletion, or insertion.

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Do you remember which of these are more likely to result in a frameshift mutation?

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A frameshift is a shift in the reading frame.

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Bases are read in 3s, so a frameshift mutation is more commonly caused by an insertion or deletion.

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If you add or delete a base, it's possible to change the entire reading frame, depending on where it occurs.

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With substitution, you typically would only affect one codon.

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Now not every change in the base means the amino acid will be different.

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See how all of these codons still code for the amino acid leucine?

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We also discussed chromosomal mutations.

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Can you name and describe some chromosomal mutations?

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We mentioned duplication, deletion, inversion, and translocation.

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As mentioned, mutations can be neutral.

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They can also be harmful or potentially even beneficial.

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But the mutations are random.

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The organism doesn't will itself to mutate or have some certain trait.

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This is a good time to talk about natural selection.

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Take these frogs sitting on logs.

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They are all the same species.

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There can be variety, though, within the species due to processes like independent assortment and crossing over during meiosis or from mutations.

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The frogs in this population with a darker color blend into this particular environment more easily.

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A predator may have a higher chance of consuming the lighter, easier to see green frogs.

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The darker green frogs may have more fitness than the lighter frogs.

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Fitness in the biological sense is determined by not how strong they are or how long they live, but by how many offspring they have.

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These darker green frogs pass down their DNA to their offspring.

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The new baby frogs will have DNA from their parents.

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The lighter green frogs are being selected against since they are easier to see in this particular habitat.

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Over a long period of time, you could expect to see a higher frequency of darker frogs in the population.

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This mechanism of evolution is known as natural selection, which acts on populations.

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So how does natural selection compare to genetic drift?

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Well, both genetic drift and natural selection are mechanisms of evolution.

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In natural selection, organisms of traits that result in high reproductive fitness tend to be more frequent in a population over time.

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But with genetic drift, the organisms that survive and have offspring were randomly selected.

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They are not necessarily more biologically fit.

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Instead it's more that the organisms won the game of chance from an event.

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Check out the bottleneck effect and founder effect, which are forms of this.

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We mention in our natural selection video an example involving bacteria

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and antibiotic resistance that continues to be a great concern in our world.

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But let's talk more about bacteria in general.

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Bacteria are unicellular prokaryotes.

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Some can make their own food, they're autotrophs, and some consume organic material, they're heterotrophs.

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Being prokaryotes, they don't have a nucleus or other membrane-bound organelles, but they still have genetic material, cytoplasm, and ribosomes.

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Bacteria can come in a range of shapes.

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Bacteria often get a reputation for being bad pathogens, and there are many that can be, although not all bacteria are harmful,

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bacteria can also be very helpful for organisms and ecosystems.

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Can you think of some examples of bacteria being helpful?

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Some examples of helpful bacteria roles include breaking down food in our digestive system, acting as decomposers, making some foods that we eat,

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and fixing nitrogen for plants.

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But as for harmful bacteria, they can be treated with antibiotics.

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Examples of bacterial infections include strep throat, tooth decay, or tetanus.

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When we start thinking about bacteria, our minds may wander to viruses.

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How are bacteria and viruses similar, and how are they different?

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If you watch our viruses video, you will hear some reasons why viruses are not considered to be living organisms.

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Although debate still exists on calling them non-living.

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Unlike bacteria, viruses are not prokaryotes.

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Viruses don't even consist of cells.

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But viruses do have genetic material, DNA or RNA.

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Viruses typically have a protein coat known as a capsid.

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Some viruses have envelopes.

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And some diseases that viruses cause include the common cold, HIV, or influenza .

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Unlike bacteria, though, viruses don't respond to antibiotics.

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While bacteria can reproduce by splitting in something called binary fission, viruses actually require a host to reproduce.

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Viruses reproduce using the lytic or lysogenic cycle.

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Definitely something to revisit if you have forgotten.

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While viruses are not considered to be living organisms, bacteria are.

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So are archaea, protists, fungi, plants, and animals.

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We mentioned that archaea are unicellular prokaryotes and many can live in extreme environments.

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They can be either autotrophs or heterotrophs.

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Protists are mostly unicellular but can be multicellular.

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This diverse group can be made up of autotrophs or heterotrophs.

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Fungi are typically multicellular but they can be unicellular.

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Fungi are heterotrophs.

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Many can act as decomposers.

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We'll get to plants and animal systems a bit later.

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So how do we classify living organisms?

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First of all, all of life can be organized into three domains.

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Can you recall what those domains are?

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Those domains are bacteria, archaea, and eukarya.

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Consider looking at the classification video to refresh your memory of characteristics of these domains.

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But we can get more specific than domains, right?

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Can you remember those taxonomy levels that come after domain?

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They are Kingdom, Phylum, Class, Order, Family, Genus, and Species.

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And this was our mnemonic to help you remember, but you may have one that is more memorable.

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The thing about classification is that it is changing as we learn more about relatedness from DNA evidence.

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Scientific names tend to be able to be used everywhere, often having Latin or Greek roots,

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and they're definitely more reliable than common names which can vary by language or location or in this case, be completely made up.

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Let's take some time to focus on a kingdom that provides a significant amount of the oxygen that we breathe.

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A talented kingdom of autotrophs, which means they make their own food.

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Plants.

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And if they are going to make their own food using photosynthesis, they are definitely going to need to have structure that helps them to do so.

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To do photosynthesis, plants need water.

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How do they get water?

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Non-vascular plants get their water by osmosis kind of like soaking up water like a sponge.

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How is that different from a vascular plant?

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Vascular plants have two major types of vessels, the xylem which carries water, and the phloem which can carry photosynthesis products such as sugar, throughout the plant.

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How about light?

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We mentioned that plant cells have chloroplasts to capture light energy.

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To do photosynthesis, plants need carbon dioxide.

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Many plants have these fascinating little openings, Pores really called stomata.

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Stomata have a major role in gas exchange.

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Gases like carbon dioxide can flow in through these openings.

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Guard cells can control the opening and closing of the stomata.

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When might stomata need to be closed?

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One example is on a very hot day when the plant has low water.

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So staying on the topic of plants, how do they reproduce?

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Well, many plants can reproduce asexually as mentioned with my spider plants.

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But many plants, spider plants included, can reproduce sexually.

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We only covered sexual reproduction in flowering plants at the time of this stroll, otherwise known as reproduction in angiosperms.

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Angiosperms typically have petals to attract pollinators and many offer nectar to attract them as well.

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Many angiosperms have sepals which protect the developing flower bud.

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Okay, so do you remember the male and female parts that can be within a flower structure?

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Male parts of the flower include the anther and filament.

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This whole thing here is the stamen.

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Female parts of the flower include the stigma, style, and ovary.

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The whole thing here is the pistil.

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Can you describe the pollination and fertilization process in angiosperms using those terms?

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Simplified a bit, pollen is brought from an anther to the sticky stigma possibly by a pollinator.

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That's pollination.

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Next comes fertilization.

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For this to happen, a pollen tube is formed.

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A generative cell from the pollen can divide into two sperm cells,

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which can travel down the stile to the ovary into an ovule where one sperm cell will fertilize an egg, giving rise to a zygote.

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Inside the ovule, another sperm cell will fertilize two polar nuclei, which gives rise to the endosperm.

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The endosperm provides food for the the baby plant.

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Because this fertilization process involves sperm cells joining two different things, the egg and the polar nuclei, we call this double fertilization.

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These fertilized ovules can develop into seeds.

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The ovary can give rise to a fruit, and that fruit can be very useful for helping the seeds get dispersed.

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But while angiosperms bear fruit, keep in mind it may not be how you might imagine a fruit.

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So we talked about plant structure and how some plants reproduce.

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We already mentioned how plants provide a lot of oxygen that we breathe.

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But it's not just about oxygen.

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Plants are also critical as part of food chains and food webs.

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As autotrophs, plants are producers.

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If you remember in a food chain we start with producers, then we move into consumers which are heterotrophs.

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Heterotrophs have to consume other things.

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So we have primary consumers, secondary consumers, tertiary consumers, we could keep going.

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The arrows point to the direction of the energy flow.

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We could arrange this into an energy pyramid.

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The producers at the base here in TLE 1 actually contain the most energy.

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The primary consumers here in TCl2 actually only receive approximately 10% of the energy from the level below.

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Meaning, let's say you have plants here that had 10,000 kilocalories of energy.

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Can you complete the rest of the pyramid with approximately how much of the energy would be within each TCl?

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Well the next level here, the primary consumers in TCl2, would only receive 1,000 kilocalories of energy.

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The secondary consumers in TLC3 would receive 100 kcal of energy.

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Tertiary consumers in TLC4 would receive approximately 10 kcal of energy.

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Energy can be lost as heat or undigested.

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Ecosystems typically do not have a single food chain.

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Instead they tend to have a food web.

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A food web is made up of multiple food chains that interact together.

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This can show the importance of biodiversity.

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variety of organisms living in a given area.

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Biodiversity can contribute to the sustainability of a community, but how do they develop?

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This takes us to our ecological succession video.

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Ecological succession is a process, over time, of organisms in an ecological community.

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In primary succession, the area this is happening in generally is brand new without soil.

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An example could be a volcano lava flow that has cooled and left behind this new area with and no soil present.

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Usually you have a pioneer species which is a name for the species it colonizes first.

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Lichen or moss, for example.

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After pioneer species colonize the area, they slowly break down rock into smaller,

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more plant-friendly substrate, and over time contributing more organic matter in newly formed soil which will support plants.

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Small vascular plants like grasses can come in, shrubs can follow, then trees.

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continue to move into the area.

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How long this takes can vary, but it's often hundreds of years before you get a climax community going.

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So how is this different from secondary succession?

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With secondary succession, you're talking about an area that once had plants and animals and an ecological community going on.

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But then there is an ecological disturbance such as a forest fire or human activity.

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The soil is still there and that's kind of the big key point here

444

because your initial species starting out could be small plants as there is already soil there.

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Secondary succession can then follow a similar sequence to primary succession after that point.

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See our video for more details and an understanding of why this succession sequence tends to happen.

447

Communities make up ecosystems and in order for these ecosystems to function, we've got to have cycling.

448

You probably learned about the water cycle in elementary school.

449

Learning about the carbon cycle and the nitrogen cycle tends to be explored later on in junior high or high school.

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So let's recap that from our nitrogen and carbon cycle video.

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Carbon is often known as a building block in life.

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You will find it in the four big biomolecules.

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Can you think of examples where you might find carbon?

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Some examples.

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Carbon is dissolved in the ocean.

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It is in rocks and fossil fuels.

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It is in living organisms.

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It can be in the atmosphere.

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There's carbon dioxide in the atmosphere.

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It is taken in by organisms that perform photosynthesis.

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If the photosynthetic organism is eaten by an animal, it becomes part of that animal too.

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And the animal that eats that animal.

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Both the plants and animals do cellular respiration which releases carbon dioxide.

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When the plants and animals die, the carbon can be released and stored in sediment.

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Over a very long time, they can even be converted into fossil fuels.

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The burning of fossil fuels produces carbon dioxide, and this has also led to the concern of excessive carbon dioxide in the atmosphere.

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Now for nitrogen.

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Nitrogen is important in building proteins and nucleic acids.

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Let's look at how it can cycle.

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Nitrogen can be found in the atmosphere, but it needs to be fixed before it can be used well.

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Some plants have nitrogen-fixing bacteria living in their roots.

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The nitrogen is fixed by these bacteria into a form of nitrogen known as ammonia and ammonium.

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Nitrifying bacteria in the soil can convert the ammonium to nitrates and nitrites, forms of nitrogen that plants can also easily use and assimilate.

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Animals can eat those plants and obtain nitrogen.

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When both plants and animals decompose, decomposers help return ammonia and ammonium to the soil in a process known as ammonification where it can be reused again.

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There are also denitrifying bacteria.

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In denitrification, they can convert nitrates and nitrites back into nitrogen gas.

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This is just one example of cycling.

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But keep in mind that this happens in both aquatic and terrestrial environments.

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So you can see there's a balance with these elements and living organisms in an ecosystem.

481

Let's talk about some of the ecological relationships among living organisms.

482

In the ecological relationships video, I mentioned my fascination with antlions.

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Antlions are predators of ants.

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Ants are their prey.

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This is known as predation.

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Antlions have to compete with other predators like this jumping spider, for example.

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Competing for a food resource is an example of competition.

488

We also mentioned three symbiotic relationships.

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Symbiotic relationships are specific types of relationships where different species live together.

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Can you recall what occurs in the three symbiotic relationships that we mentioned?

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In commensalism, one organism benefits and the other is neither helped nor harmed.

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It's neutral.

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Many barnacle species can attach themselves to moving things.

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On a free whale ride, this barnacle can get access to food since it's a filter feeder and the whale may travel to nutrient-rich waters.

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However, in this example, with this particular whale and these barnacles, the whale was neither are helped nor harmed.

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In parasitism, one organism benefits and the other one is harmed by a parasite.

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Parasites can live inside or on their host.

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Mutualism is an example of a symbiotic relationship where both organisms involved benefit.

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Our example had been an acacia tree being protected by acacia ants.

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The acacia tree provides a home and possibly nutrients.

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But you know, one of my favorite examples of mutualism is the good bacteria.

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We can live in our digestive system and help us digest our food.

503

So speaking of systems in the human body, our short video on that topic only goes into basic functions of 11 body systems.

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Here they are up here for you in alphabetical order.

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Can you give a general function for each of these?

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The circulatory system helps transport gases and nutrients.

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The digestive system is involved with both the mechanical and chemical breakdown of food.

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The endocrine system is involved with producing important signals known as hormones.

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The excretory system is involved with excreting waste material as done by the kidneys or skin.

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The immune lymphatic system helps defend our body against pathogens such as viruses and harmful bacteria.

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The integumentary system, long fancy word for a large organ, your skin, can protect against water loss and serve as a barrier.

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The muscular system is involved with allowing for movement.

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The nervous system coordinates both voluntary and involuntary responses.

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The reproductive system allows for the ability to reproduce.

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The respiratory system is involved with gas exchange.

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And the skeletal system is critical for structure and support.

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Those are very basic functions mentioned, and of course this doesn't include structures.

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But the big takeaway we hope you have from our body systems video is that these systems don't work in isolation.

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They work together.

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If you're nervous about a test, which we hope you're not because we have confidence that you're going to do great, but if you were nervous, you can get an adrenaline rush.

521

Your endocrine system secretes adrenaline, a hormone that can cause your heart involved in the circulatory system to speed up its beating.

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Your breathing rate, which is involved with your respiratory system, can increase.

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These are all systems working together.

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And that's relevant for the end.

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Because in this stroll through our playlist, you've seen how we've been connecting these concepts together.

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Because that's the thing that is so cool about biology.

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It's all connected.

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We hope this video helps you identify your strengths and areas that you might want to go back and explore.

529

We also hope that you recognize that beyond any test you're studying, it is so important to be able to answer, why does this content matter?

530

If there is a topic in this video that still doesn't seem to matter beyond just studying for a test, please check out our full video on that topic because that's something

531

that we really try to address in each and every video.

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Don't forget we also have a video with study strategies that you might want to check out, and we have helpful gif animations and comics on our website that you might find useful.

533

And if you are studying for something big, it is our sincere amoebic wish that you will feel confident about your learning.

534

Well, that's it for the Amoeba Sisters, and we remind you to stay curious.

535

Thank you.

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✨ Video gợi ý

109 câu

Từ vựng và ghi chú luyện nói cho bài học này

Bài luyện nói trình độ B2 này dựa trên video “Stroll Through the Playlist”. Những từ được nhắc lại nhiều nhất trong bài: cell, plant, organism, dna, bacteria. Video này có 535 câu và 6317 từ để luyện shadowing. Phần lời nói dài 41:19. Người nói nói với tốc độ tự nhiên, khoảng 153 từ mỗi phút, gần với hội thoại hằng ngày. Chỉ 76% số từ nằm trong 3.000 từ tiếng Anh thông dụng nhất, nên từ vựng khá khó.

Từ vựng quan trọng trong video

15 từ khó nhất trong video, kèm phiên âm và nghĩa:

Từ	Phiên âm	Nghĩa
organism danh từ	/ˈɔɹ.ɡəˌnɪz.əm/	sinh vật
bacterium danh từ	/bækˈtɪəɹ.ɪəm/	vi khuẩn, vi trùng
trait danh từ	/tɹeɪt/	đặc điểm, đặc tính
membrane danh từ	/ˈmɛm.bɹeɪn/	màng
enzyme danh từ	/ˈɛn.zaɪm/	enzim, men tiêu hoá
chromosome danh từ	/ˈkɹoʊməˌsoʊm/	chất sinh sắt, nhiểm sắc thể
nitrogen danh từ	/ˈnaɪ.tɹə.d͡ʒən/	nitơ, đạm khí
mutation danh từ	/mjuˈteɪʃən/	đột biến
molecule danh từ	/ˈmɑ.lɪ.kjul/	phân tử
photosynthesis danh từ	/ˌfoʊ.toʊˈsɪn.θə.sɪs/	quang hợp
stroll động từ	/stɹoʊl/	đi dạo, dạo
characteristic danh từ	/ˌkæɹ(ə)ktəˈɹɪstɪk/	đặc điểm
heterotroph danh từ	/ˈhɛtəɹəˌtɹoʊf/	sinh vật dị dưỡng
meiosis danh từ	/maɪˈoʊ.sɪs/	giảm phân
mitosis danh từ	/maɪˈtoʊ.sɪs/	nguyên phân

Cụm động từ bạn sẽ nghe

Từ	Nghĩa
check out động từ	tính tiền, trả phòng
break down động từ	hỏng, hỏng hóc
go back động từ	trở lại

Những câu đáng luyện lại

Các câu ngắn, trọn ý trong video mà bạn có thể dùng lại khi giao tiếp hằng ngày:

A community can you keep leveling up?
Can you name them here with their building blocks?
An example of why we care?
How many do you receive from each parent?
Can you remember what these key players do?

Ngữ pháp trong video

Những cấu trúc người nói dùng nhiều nhất, kèm đúng cụm từ trong video:

Cấu trúc	Trong video
Câu bị động be + quá khứ phân từ — nhấn vào việc xảy ra, không phải người làm	be reminded · would be meant · be titled
Mệnh đề quan hệ who / which + mệnh đề — thêm thông tin về người hoặc vật	factors which are · phospholipids which have · diffusion, which is
Thì hiện tại hoàn thành have/has + quá khứ phân từ — việc đã xảy ra nhưng còn liên quan đến hiện tại	I've drawn · we've made · have covered

Phát âm cần chú ý

Người nói dùng 40 dạng rút gọn, ví dụ don't, you're, didn't. Hãy nói theo dạng ngắn đúng như bạn nghe.

Âm “th”: photosynthesis /ˌfoʊ.toʊˈsɪn.θə.sɪs/, synthesis /ˈsɪnθəsɪs/, anther /ˈæn.θɚ/
Âm “sh” và “zh”: mutation /mjuˈteɪʃən/, succession /səkˈsɛʃ.ən/, diffusion /dɪˈfju.ʒən/, respiration /ɹɛspɪˈɹeɪʃən/, reproduction /ˌɹiːpɹəˈdʌkʃən/
Từ dài — đặt trọng âm cho đúng: organism /ˈɔɹ.ɡəˌnɪz.əm/, photosynthesis /ˌfoʊ.toʊˈsɪn.θə.sɪs/, ecological /ˌiːkəˈlɒd͡ʒɪkl̩/, characteristic /ˌkæɹ(ə)ktəˈɹɪstɪk/, heterotroph /ˈhɛtəɹəˌtɹoʊf/

Những âm người Việt thường gặp khó:

Cụm phụ âm cuối — đọc đủ từng âm, đừng nuốt âm cuối: strand /ˈstɹænd/, chloroplast /ˈklɔːɹəʊˌplæst/, bind /ˈbaɪ̯nd/, dominance /ˈdɑmɪnəns/, gradient /ˈɡɹeɪdiənt/
Âm /tʃ/, /dʒ/ và /ʒ/ — tiếng Việt không có, đừng đọc thành “ch” hay “gi”: nitrogen /ˈnaɪ.tɹə.d͡ʒən/, diffusion /dɪˈfju.ʒən/, ecological /ˌiːkəˈlɒd͡ʒɪkl̩/, angiosperm /ˈæn.d͡ʒi.əˌspɝm/, digestive /daɪˈdʒɛstɪv/
Âm /æ/ — mở miệng rộng hơn âm “e”: bacterium /bækˈtɪəɹ.ɪəm/, characteristic /ˌkæɹ(ə)ktəˈɹɪstɪk/, angiosperm /ˈæn.d͡ʒi.əˌspɝm/, prokaryote /pɹoʊˈkæɹi.oʊt/, strand /ˈstɹænd/

Cách luyện với video này

Nghe hết video một lần, chưa cần nói, và ghi lại những từ bạn chưa biết.
Bắt đầu ở tốc độ 0,75×, nói đuổi từng câu, rồi quay lại tốc độ bình thường khi đã quen.
Ghi âm giọng mình rồi so với bản gốc, chú ý các từ như organism, bacterium, trait.

Phương Pháp Shadowing Là Gì?

Shadowing là kỹ thuật học ngôn ngữ có cơ sở khoa học, ban đầu được phát triển cho chương trình đào tạo phiên dịch viên chuyên nghiệp và được phổ biến rộng rãi bởi nhà đa ngôn ngữ học Dr. Alexander Arguelles. Nguyên lý cốt lõi đơn giản nhưng cực kỳ hiệu quả: bạn nghe tiếng Anh của người bản xứ và lặp lại to ngay lập tức — như một "cái bóng" (shadow) đuổi theo người nói với độ trễ chỉ 1–2 giây. Khác với luyện ngữ pháp hay học từ vựng bị động, Shadowing buộc não bộ và cơ miệng phải đồng thời xử lý và tái tạo ngôn ngữ thực tế. Các nghiên cứu khoa học xác nhận phương pháp này cải thiện đáng kể phát âm, ngữ điệu, nhịp điệu, nối âm, kỹ năng nghe và độ lưu loát khi nói — đặc biệt hiệu quả cho người luyện IELTS Speaking và muốn giao tiếp tiếng Anh tự nhiên như người bản ngữ.

Phương pháp shadowing: đọc hướng dẫn từng bước đầy đủ →

Luyện nói tiếng Anh bằng Shadowing qua video: Stroll Through the Playlist (a Biology Review)

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