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Teaching about evolution

So, we’re supposed to teach our students about evolution – but where to start? What topics to cover? And in what order should we cover them? And for each topic, what are the relevant learning standards? This sequence works for me:

Chicken or the egg

Abiogenesis & spontaneous generation

Abiogenesis – modern discoveries

Charles Darwin’s Voyage of Discovery and Darwin’s notebook

Darwin’s finches

Fossils: Evidence of evolution over time and Dating of fossils

Convergent evolution and Homologous and analogous structures

Natural selection

Artificial selection

clades & phylogenies

clades rotate = equivalent phylogenies

Gradualism vs. Punctuated Equilibrium

Examples of evolution

Evolution of our kidneys

Evolution of humans

Evolution of whales

Where did the idea of evolution develop? How has the idea of evolution changed over time?

Advanced topics

Evolution of the first animals

Ontogeny and Phylogeny: Addressing misconceptions

Did nerves evolve twice?

Horizontal Gene Transfer and Kleptoplasty

Evolution and the 2nd law of thermodynamics

Scars of evolution

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Teaching about cells

So, we’re supposed to teach our students biology – but where to start? What topics to cover? And in what order should we cover them? And for each topic, what are the relevant learning standards? This sequence works for me:

Characteristics of Life
Organelles, an introduction
Organelles: In more depth

What is the role of enzymes in cells?

Diffusion

Osmosis

Endocytosis and exocytosis

Then we move on to types of cells

Bacteria

Archaea

Now the bitty-gritty: Cell reproduction

Mitosis

Asexual reproduction

Meiosis

For those teaching Honors Biology

Active transport across cell membranes

Ion channels and carrier proteins

Endosymbiosis: origin of eukaryotic cells from prokaryotes

Organelles in depth

Cell membrane

has 2 layers of lipids (fats); hence > lipid bilayer.

Often we see simplified 2D drawings, showing a small section of the lipid bilayer.

Here we see the two layers, and some proteins.

 

Cytoplasm

The thick viscous liquid filling the cell. All the organelles float in it; and it’s also filled with millions of enzymes and other chemicals.

Dancing Queen molecules in cytoplasm

Here is a (false color) visualization of proteins in a cell’s cytoplasm – notice how densely packed this is.

Densely packed proteins in cytoplasm

Nucleus

The command-and-control center of the cell.

Here we see a more realistic image of the nucleus (lower left); we see mRNA copies of DNA coming out of the nucleus through nuclear pores.

Nucleus to ribosomes to ER GIF Protein synthesis NPR

Nucleus to ribosomes to ER GIF from NPR: Protein synthesis

Chromosomes

If we magnify a cell, we can see “X” shaped chunks floating in the cell nucleus.
These chunks are called chromosomes. They are made of a chemical called DNA.

organism cell chromosome DNA 2

Here we see a cell nucleus being lysed (broken open) and all the chromosomes are spilling out on the right.

(The color was added by hand to make it easier to tell them apart.)

We can then cut-and-paste each of the chromosomes, number them, and line them up (lower left.)

In humans we find 23 pairs of chromosomes in every cell.

These X shaped chromosomes are not solid; they are like objects made of wound-up yarn.

A chromosome could be unwound into a long, thing string.

This string is made of DNA molecules.

chromosomes 1

Each section of the chromosome has difference sequences of DNA.

A complete sequence of DNA is called a gene; it is an instruction on how to build a protein.

 

Mitochondrion

and

 

The Endomembrane system

More details: The endomembrane system is composed of the different membranes that are suspended in the cytoplasm within a eukaryotic cell.

Endomembrane system by Mariana Ruiz Villarreal LadyofHats

Endomembrane system by Mariana Ruiz Villarreal, LadyofHats

Ribosomes

In this simplified diagram we note that ribosomes are very tiny compared to the size of a cell.

They are just seen as little black dots. They are way tinier than any of the other organelles.

plant and animal cell ribosomes

Here we see a more realistic 3D model of a cell;

On the right we can just barely see the ribosomes as small dots stuck to the ER.

On the left we see the ER magnified, and the ribosomes are a bit clearer. (Although they are still small; we don’t see any details.)

Darryl Leja, NHGRI Rough endoplasmic reticulum and ribosomes

Darryl Leja, NHGRI Rough endoplasmic reticulum and ribosomes

Some ribosomes also float freely in the cytoplasm.

Here we see mRNA copies of DNA coming out of a cell nucleus, and moving to a type of ribosome floating nearby.

Nucleus to ribosomes to ER GIF Protein synthesis NPR

Nucleus to ribosomes to ER GIF from NPR: Protein synthesis

And now you’ll always remember this:

Beyonce look like the rough ER

 

Cytoskeleton

and a photo

 

Golgi body

Golgi GIF

and

Endomembrane system by Mariana Ruiz Villarreal LadyofHats

Endomembrane system by Mariana Ruiz Villarreal, LadyofHats

ER

Rough ER GIF

and

Darryl Leja, NHGRI Rough endoplasmic reticulum and ribosomes

Darryl Leja, NHGRI Rough endoplasmic reticulum and ribosomes

lysosome

Lysosome GIF

vacuoles

Vacuole GIF

chloroplasts

and

Chloroplast structure Thylakoid Granum

cell wall

Animal cell versus plant cell

and

Plant cell has a wall adapaproject

Plant cell has a wall adapaproject

large central vacuole

 

External resources

http://www.amoebasisters.com/gifs.html

Biology MCAS exams

Previous MCAS exams from the Massachusetts Department of Elementary and Secondary Education

massachusetts-dese-learning-standards

Feb 2017 Biology MCAS

Feb 2016 Biology MCAS

Feb 2015 Biology MCAS

Feb 2014 Biology MCAS

Feb 2013 Biology MCAS

Below you will find each released short-response question, open-response question, and writing prompt that was included on High School Biology MCAS tests; the scoring guide for each question; and a sample of student work at each score point for that question. Taken together, these provide a picture of the expectations for student performance on the MCAS tests.

 

 

 

.

 

Organelles

A car is a working machine – made from smaller systems working together.

A cell is an organic, living machine – made from organelles working together.

No part of a car, by itself, is functioning.

No part of a cell, by itself, is alive.

What we a “functioning car” is the way that parts work together.

What we call “life” is the way that organelles work together.

Let’s compare the parts of a car with the parts of a cell

 

Consider: The transmission, the axles and the engine.

Yet disconnect just one of these systems, and we effectively no longer have a car.

We’d just have an inert 2000 pound block of metal and plastic.

A car is not a car unless the parts are connected and working together.

The same is true for cells.

drive-train-transmission xpertechautorepair

Inside the engine, what would happen if we removed or froze the pistons?

We’d effectively no longer have an engine.

The same is true for organelles inside cells.

four-stroke-engine-gif

Similarly, consider the ways that organelles and organic molecules are interacting within our cells:

What would happen if we removed some of these parts?

We’d effectively no longer have a living cell.

Nucleus to ribosomes to ER GIF Protein synthesis NPR

Nucleus to ribosomes to ER GIF from NPR: Protein synthesis

You’ve seen parts inside cars. Now let’s look at the organelles (parts inside cells)

First, a note of caution about artwork: Many books simplify what a cell looks like, with a 2D black & white drawing, like this. This picture is “true” – but simplified.

In reality cells are 3D.

Organelles are suspended in cytoplasm throughout the cell.

c6026-animal252bcell252blabeled252bblue252blavendar

 

Now let’s learn the job of each organelle using analogies:

 Organelle

 Function

 Analogy

 lipid bilayer  Controls which molecules go in/out of the cell  Walls and doors
 cytoplasm  Suspends and holds all the organelles  the factory floor, where all the work is done.
 nucleus  Chromosome (DNA) storage  Control center
 chromosomes
(made of DNA)
 Instructions for building and running the cell  blueprints and instructions
 mitochondrion  Converts energy from food molecules into a form usable by the cell  Powerhouse
 ribosomes  biological protein synthesis (translation)  Workers on the assembly line, building our product.
 cytoskeleton  gives the cell its shape and mechanical resistance to deformation  Walls & studs, support and structure
golgi body  Packages proteins into vesicles inside the cell, and send them to their destination.  Receives product from ER. Like UPS, its packages and distributes the products.
endoplasmic reticulum
(ER)
 Manufactures lipids and proteins  Assembly line which makes our products
 lysosome  Contain enzymes that can break down virtually all kinds of biomolecules.  garbage disposal
 vacuoles  Multiple uses, often related to storing molecules.  Storage

 

Organelles unique to plant cells (TDB)

section coming soon:

chloroplasts

cell wall

large central vacuole

Organelles: The Details!

Cell membrane (lipid bilayer)

cytoplasm

nucleus

chromosomes

mitochondrion

ribosomes

cytoskeleton

golgi body

ER

lysosome vacuoles

chloroplasts

cell wall

large central vacuole

Endomembrane system

More details: The endomembrane system is composed of the different membranes that are suspended in the cytoplasm within a eukaryotic cell.

Endomembrane system by Mariana Ruiz Villarreal LadyofHats

Endomembrane system by Mariana Ruiz Villarreal, LadyofHats

Learning Standards

2016 Massachusetts Science and Technology/Engineering Curriculum Framework

6.MS-LS1-2. Develop and use a model to describe how parts of cells contribute to the cellular functions of obtaining food, water, and other nutrients from its environment,
disposing of wastes, and providing energy for cellular processes.

2006 Massachusetts Science and Technology/Engineering Curriculum Framework

Biology High School Standards: Cells have specific structures and functions that make them distinctive. Processes in a cell can be classified broadly as growth, maintenance, and reproduction.

2.1 Relate cell parts/organelles (plasma membrane, nuclear envelope, nucleus, nucleolus, cytoplasm, mitochondrion, endoplasmic reticulum, Golgi apparatus, lysosome, ribosome, vacuole, cell wall, chloroplast, cytoskeleton, centriole, cilium, flagellum, pseudopod) to their functions. Explain the role of cell membranes as a highly selective barrier (diffusion, osmosis, facilitated diffusion, active transport).

Benchmarks for Science Literacy, AAAS

By the end of the 12th grade, students should know that

  • Every cell is covered by a membrane that controls what can enter and leave the cell. 5C/H1a
  • In all but quite primitive cells, a complex network of proteins provides organization and shape and, for animal cells, movement. 5C/H1b
  • Within the cells are specialized parts for the transport of materials, energy capture and release, protein building, waste disposal, passing information, and even movement. 5C/H2a

SAT Biology Subject Area Test

Cellular and molecular biology: Cell structure and organization, mitosis, photosynthesis, cellular respiration, enzymes, biosynthesis, biological chemistry

External links

Wayback archive of RegentsPrep.Org on Cells

Amoeba Sisters.com gifs

Khanacademy Eukaryotic-cells

tablesgenerator.com

Evolution of the first animals

Animals probably evolved from marine protists, although no group of protists has been identified from an at-best sketchy fossil record for early animals.

Cells in primitive animals (sponges in particular) show similarities to collared choanoflagellates as well as pseudopod-producing amoeboid cells.

Multicellular animal fossils and burrows (presumably made by multicellular animals) first appear nearly 700 million years ago, during the late precambrian time….

All known Vendian animal fossils had soft body parts: no shells or hard (and hence preservable as fossils) parts.

Animals in numerous phyla appear at (or in many cases before) the beginning of the Cambrian Period ( 540 million years ago)

from http://www2.estrellamountain.edu/faculty/farabee/BIOBK/BioBookDiversity_7.html

Nicole King explains “All animals, from sponges to jellyfish to vertebrates [animals with a backbone], can be traced to a common ancestor. So far, molecular and fossil evidence indicate that animals evolved at least 600 million years ago. The fossil record does not reveal what the first animals looked like or how they lived. Therefore, my lab and other research groups around the world are investigating the nature of the first animals by studying diverse living organisms….. Choanoflagellates are a window on early animal evolution. Both cell biological and molecular evidence indicate that choanoflagellates are the closest living relatives of multicellular animals.

http://www.actionbioscience.org/evolution/king.html

————————————–

http://www.wired.com/2014/08/where-animals-come-from/

Between 620 and 550 million years ago (during the Vendian Period) relatively large, complex, soft-bodied multicellular animals appear in the fossil record for the first time. While found in several localities around the world, this particular group of animals is generally known as the Ediacaran fauna, after the site in Australia where they were first discovered.

The Ediacaran animals are puzzling in that there is little or no evidence of any skeletal hard parts i.e. they were soft-bodied organisms, and while some of them may have belonged to groups that survive today others don’t seem to bear any relationship to animals we know. Although many of the Ediacaran organisms have been compared to modern-day jellyfish or worms, they have also been described as resembling a mattress, with tough outer walls around fluid-filled internal cavities – rather like a sponge.

http://sci.waikato.ac.nz/evolution/AnimalEvolution.shtml

A new study mapping the evolutionary history of animals indicates that Earth’s first animal–a mysterious creature whose characteristics can only be inferred from fossils and studies of living animals–was probably significantly more complex than previously believed… the comb jelly split off from other animals and diverged onto its own evolutionary path before the sponge. This finding challenges the traditional view of the base of the tree of life, which honored the lowly sponge as the earliest diverging animal. “This was a complete shocker,” says Dunn. “So shocking that we initially thought something had gone very wrong.”

But even after Dunn’s team checked and rechecked their results and added more data to their study, their results still suggested that the comb jelly, which has tissues and a nervous system, split off from other animals before the tissue-less, nerve-less sponge.

The presence of the relatively complex comb jelly at the base of the tree of life suggests that the first animal was probably more complex than previously believed, says Dunn.

http://www.astrobio.net/topic/origins/origin-and-evolution-of-life/earths-first-animal/

http://news.nationalgeographic.com/news/2014/05/140521-comb-jelly-ctenophores-oldest-animal-family-tree-science/

Is this possible? for this to be true, it would seem that complex structures – neurons – have evolved twice! Independently? See here for more amazing details:

Did neurons evolve twice? The curious case of comb jellies

What kinds of radiation cause cancer

An infographic on the intersection of physics and health:

For most people the biggest cancer risk from radiation hovers in the sky above us giving us all warmth and light. There is no cancer risk from Wi-Fi or microwaves.

Wear sunscreen, but use WiFi without fear. (Image: Spazturtle/SMS (CC))

What is radiation, and where does it come from? nuclear chemistry

What is cancer? How is caused?  Cancer

Microwaves, Radio Waves, and Other Types of Radiofrequency Radiation: American Cancer Society

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