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Sunday, April 29, 2012

Transpiration Made Simple!

The plants always seem to get left out!

It is nearing the end of the school year, standardized testing is all anyone is talking about, the students are getting antsy to be out for the summer, and the biology teachers have to decide "what not to cover this year."  This always happens at the end of the year as we begin to run out of time.  For many biology teachers, a unit on plants is the first to go.

Teaching about plants is actually one of my favorite units, and I always find that my students are woefully lacking in knowledge about the plants.  I make it a priority each year to leave enough time at the end of the school year for my plant unit.  I like teaching plants at the end of the year because everything in our area is in full bloom!  Among the many activities I do with plants, I always have students germinate seeds.  It is mind-boggling to me how many of my students have never planted a seed! They love taking care of them in the lab and they get so excited to watch them grow.  Since the weather is nice, the students then take their seedlings home and plant them in their yards.  Many will report back to me at the start of the following year with news of their plant.

One of the labs I do that is so very easy to setup and clean up, is a transpiration lab. Transpiration is the loss of water through the leaves.  As the stomata open to allow carbon dioxide to enter the leaf for photosynthesis, water vapor escapes the leaf and enters the atmosphere.  For trees and other tall plants, it is tricky business to get the water up to the top of a very tall tree.  The major force in water transport is provided by the evaporation of water from the leaves during transpiration.  As water is lost, the movement of the water out of the leaf "pulls" water upward through the xylem all the way down to the roots.  This is called transpiration pull.

Measuring transpiration from the leaf is a very simple thing!  I went to Wal Mart and bought begonia plants.  The one tray contained 6 plants.  The begonia is a good choice because it has a thick and fleshy leaf.  Once back in my school lab, I placed plants in small (250 mL) beakers.  I watered them thoroughly.  Since I wanted to measure the amount of water lost from the leaves, I took a plastic sandwich bag and wrapped it very tightly around the beaker, and around the stem of the plant.  It is necessary to insure that no water evaporates from the dirt itself.

1)  Place plant in beaker.
2)  Wrap beaker tightly around plant, and tightly around the stem.  Only the leaf should be sticking out of the plastic bag.

The only way water is getting out of this beaker is through the leaves of this plant!

3)  Find the initial mass of the entire set-up and write the mass on a piece of masking tape which is then placed on the beaker.

Now for the testable variables!  What factors will cause an increase or decrease in the rate of transpiration?  We decided to test the following factors:

  • One plant will be placed in continuous light for 24 hours. 
  • One plant will be placed in front of a blowing fan for 24 hours.
  • One plant will be placed inside a plastic bag that had previously been spritzed with water (high humidity inside the bag). 
  • The fourth plant will serve as a control.

This plant was placed in the beaker, the beaker was covered with a plastic bag, and the initial mass was written on the outside.
The plant was then placed under a lamp and left for 24 hours.

This plant was placed in front of a blowing fan for the same 24 hour period of time.

The inside of this bag was misted with water and the plant was then sealed inside the bag for 24 hours.  This simulates a high humidity environment.

This is the control.  The plant is still transpiring, but without the additional influence of light, a blowing fan, and without the added humidity.  A true control would be the absence of transpiration, but we decided to use a plant at normal room conditions as our control.

Let the plants sit for 24 hours (or longer if you want!).  Each plant is massed again after a 24 hour period of time.  Students will be amazed at how much water has been lost through the leaves.  The results should be as follows:

Plant in Light:  This plant loses a good amount of water.  The light causes the plant to continuously carry on photosynthesis.  This requires a lot of carbon dioxide, so the stomata stay open for a longer period of time to let in the carbon dioxide.  While the stomata are open, the plant will lose water.  The heat from the light also plays a role.  The increase in heat will cause a higher rate of evaporation from the leaf.

Plant in front of fan:  The increased air movements across the surface of the leaf will cause a higher rate of evaporation from the plant.

Humidity:  Less water is lost from the plant when the humidity of the air surrounding the plant is high.

All masses should be compared to the control to see if the factor being tested causes an increase or decrease in the rate of transpiration.

Here are some ideas of how this might be used at different age levels:

Elementary:  It may be enough in the lower grades to just show that water is taken up by the roots and escapes from the leaf.  Students can be asked before the experiment to make predictions as to what they think the outcome will be.  They can form a hypothesis and go through the steps of the scientific method.

Middle Grades may add the following:  Have students calculate how much water is lost per minute in each plant.  Test an additional factor, such as complete darkness, or various temperatures.  Test different types of plants to see if the transpiration rate is the same in all types of plants.

High School Grades may add the following:  Remove the leaves and determine the surface area of each leaf.  Determine how much water is lost in a given amount of surface area.  Have students research the mechanisms of transpiration, such as cohesion, adhesion, capillary action, and transpiration pull.

Try this...It works like a charm.  And have fun teaching plants!

Here are some additional resources:

Look for video segments from "The Private Life of Plants"by David Attenborough.  There are quite a few of these on YouTube.  Each is very short - about 3 to 5 minutes - and my students really enjoy them.

Lab: Leaf Structure and Function
Lab:  Living Flowers
Photosynthesis: Complete Unit Plan/Bundle
Lab: Pigment Chromatography 
Lab:  Stomata - Gateways into the Leaf

Thursday, April 26, 2012

Reviewing for the AP Biology Exam

Click picture to download PowerPoint.

The key to success is REVIEWING!!

If you have taught AP (Advanced Placement) Biology, then you know that the amount of material that must be covered before the exam is daunting.  I have had great success with my AP exam scores.  I normally have between 60 to 80 students take the exam each year.  For the 2011 exam, I had 65 students sit for the exam, and we had an average score of 4.3.  Admittedly, this is one of the best years I have ever had.  It was a great group of students who were highly motivated.  Those kids absorbed everything I threw at them.  They then dug deeper and deeper on their own outside of the regular class time.

The group I have this year makes me very proud!  I will have 61 taking the 2012 exam.  They are every bit as motivated and talented as the group I had last year.  They have such potential to do well!!  I just have to convince them how important it is to study and review for the exam.

I am convinced that the key to success is how you review the material with your students.  I began to review with my students on February 1.  I am most fortunate to have a 70 minute class each day.  I give a prayer of thanks for this each and every day, and I realize that most AP teachers do not have this luxury.  Beginning on February 1, I use the first 10 to 15 minutes of class to review a topic that we have previously covered earlier in the school year.  The remaining class time is used to cover new material.  The day before the AP exam in May, I am still reviewing and still covering new material!!

We have to convince our students that they must review, review, review before the exam.  I have written a set of powerpoints that I use for review. These are not teaching powerpoints.  These are just slide after slide of question and answer.  The students are not going to remember every little detail, so I try to make sure that they are solid on the basic facts.

Here is one of my review PowerPoints that I hope you will download.  It covers the characteristics of carbon and the organic compounds.

AP Review: Carbon and Organic Compounds ---- It's FREE!!  I hope you find this useful for your classroom.

Happy Teaching and good luck on the AP exam!

Monday, April 23, 2012

Everything About Enzymes!! (and a free lab!)

Recently, I was required to attend a system-wide inservice meeting for all the science teachers in our district.  In attendance were science teachers of grades 7 through 12.  These events are fun and interesting, mostly because I have been teaching for 28 years, and it is nice to see science teachers from other schools that I have known for years, but rarely get to see.  After joining up with a group of old acquaintances, the inevitable question came up:  "What have you been doing in your biology classes?"

I responded with, "I have just finished teaching a unit on enzymes to our biology 1 students."  One of the other teachers immediately responded with, "I don't really teach that in my class."

What????  How do you NOT teach about enzymes in a biology class????  As soon as I returned home that day, I promptly sent her all of my teaching materials on enzymes.

Enzymes are the stuff of life.  No cell would be alive without the action of enzymes.  Life in a cell is made possible through the hundreds of chemical reactions that occur there.  If these chemical reactions proceed too slowly, the activities of the cell would come to a screeching halt.  You see, enzymes are biological catalysts. They speed up the chemical reactions of the cell.  Without these enzymes, the reactions of the cell would proceed so slowly that they would be of no use to the cell, and the cell would die.

When is the best time to teach about enzymes?  I begin teaching about enzymes when I teach biochemistry.  When teaching about carbohydrates, lipids, and proteins, it is a natural fit to talk about enzymes as you discuss the structure and functioning of proteins.  I also teach about enzymes when I cover photosynthesis, respiration, replication, transcription, digestion..... This list could go on and on since enzymes are involved in every single biological process!

Be sure to cover all the basic points about enzymes:
  • Enzymes are biological catalysts that speed up the chemical reactions of the cell.
  • Enzymes are proteins.
  • Enzymatic reactions occur faster and at lower temperatures because enzymes lower the activation energy for that chemical reaction.
  • Enzymes are never consumed or used up during the reaction. They can do their job over and over again.
  • Enzymes are highly specific for just one substrate.  The enzyme has an active site with a unique 3-D shape into which this substrate must fit.  
  • Enzymes catalyze both the forward and the reverse of the same reaction.
  • Enzymes can be denatured by temperatures and pH levels outside the optimal range for that particular enzyme.
Enzymes are truly amazing proteins that play a vital role inside every living cell.  Please don't leave this out of your curriculum!

Okay.... I did promise you a freebie.  This is a lab that I have done for years, and it remains a favorite with my students year after year.

Tuesday, April 17, 2012

The Importance of Environmental Influences on Gene Expression

All students know that their hair color and their eye color is a result of the alleles that they have inherited from their parents.  But do your students know that the environment plays a role in the expression of these alleles?

The phenotype of an individual often depends on the influences from the environment.  A snowshoe rabbit has white fur in the winter months and brownish fur in the summer months.  Why?  If the rabbit is white in the winter, it will be camouflaged  and will have a greater chance of survival.  The same is true of a brown rabbit in the summer months.  A particular allele codes for coat color in these rabbits.  During the winter, the snowshoe rabbit will have white fur because these pigment producing genes do not function in cold weather.  When the weather warms in the spring and summer, the genes function to produce pigments and the coat becomes brown.

The million dollar question is this:  Is heredity or environment more important in determining the kinds of traits that appear in the offspring?

I recently had my students explore this very question in a laboratory activity.  Students were given 10 corn seeds to plant.  Half of the students were asked to leave their container of planted seeds near a window in our lab.  The other half of the class was asked to place their container of corn seeds in complete  darkness.    The seeds were watered as needed and left to grow.

The trait the students were asked to observe was the color of the stem and leaves.  Did the seeds grow into plants with green stems or into plants that were albino?  Stems are green due to the production of chlorophyll.  Chlorophyll production is controlled by a dominant allele.  The absence of a dominant allele results in a plant that is albino.

The students were given seeds that were the offspring of heterozygous parents.  Therefore, it is expected that 3/4ths of the seeds will grow into corn plants that are green, and 1/4th of the seeds will grow into plants that are white or albino.

After allowing the seeds to grow into seedlings, students return to the lab to count their offspring.

In the above photos, both trays of corn were grown in the light.  As you can see, some of the plants have green stems, while other plants have albino stems.  Class data was tabulated and we were very close to the expected 3:1 ratio of green to albino stems.

Take a look at the plants in the photo to the right.  The plants on the right side of the photo were grown in complete darkness.  All of these plants are termed albino.  The expected 3:1 ratio was not supported.  100% of the plants grew into albino plants.  What is the difference between the albino plants grown in the light and the albinos grown in the dark?   The albino plants that were grown in the light are albino due to their genetics.  These plants have two recessive alleles for chlorophyll production.  Without the dominant allele, chlorophyll production is not possible.  The albino plants that were grown in complete darkness are albino because of their environment.  Some of these plants may have the dominant allele, but in the absence of sunlight, the dominant allele is not expressed.  

To make this argument just a bit stronger, all students were asked to let their seedlings continue to grow for another 24 hours, and all trays of seedlings were left in the light.  Plants that were initially grown in the dark, were left in the light for 24 hours.  At the second observation, 3/4ths of these albinos had developed chlorophyll and were green.

So back to the original question...... Is heredity or the environment more important in gene expression?  Every student in my class now knows that having the dominant allele is not always enough for the trait to be expressed.  Sometimes the dominant allele and the proper environmental condition work together in the expression of the trait.

Give this lab a try.  Your students will love it!
Happy Teaching!

PS - I am proud to display the 5-Star Blogger award.  Check out the Five-Star Blogger Challenge posted on The Organized Classroom Blog to see some awesome Five-Star Blogs!

Thursday, April 12, 2012

The Giant Corpse Flower

A giant flower that smells of rotting flesh??

Yep, this is the Giant Corpse Flower, or scientifically speaking,  Amorphophallus titanum.  (Appropriate name, huh?)

This recently caught my attention when I was on my daily prowl on the internet searching for fun and interesting bits of science news to share with my students in my biology classroom.   It seems that Cornell University has a giant corpse flower that recently bloomed.  It was only one of 140 plants to bloom in cultivation in recorded history.

As you know, in angiosperms, the flower is the reproductive organ of the plant.  For true land plants reproduction is tricky business.  In order to be adapted to life on land, the plant must find a way to get its sperm to the egg of a different (but of the same species) plant.  Sperm cells are placed inside pollen grains, and then pollen grains must be effectively delivered to nearby flowers.  Pollen can be carried by wind or water, but many plants depend upon the insect pollinators to deliver their sperm cells.  The flower that can best attract these pollinators has the best chance of having its eggs fertilized.

Now back to the giant corpse flower.  This plant produces one of the largest flowers on record.  When it opens, the smell is said to be horrific, mimicking the odor of dead, rotting flesh.  The smell attracts dung beetles and flies that feed on carrion.   When the insects crawl into the flower, their bodies are covered with pollen.  The insects exit the flower, and move on to the next flower, transferring pollen from flower to flower as they go.

The news about the blooming of the flower at Cornell University was perfect timing for me.  I was in the process of teaching angiosperm reproduction to my biology students.  I did a quick YouTube search and found two short, but excellent videos to show my classes.  The first is called "Corpse Flower Blooms at Zoo" and is about a blooming that occurred at the Cleveland Zoo.  It has wonderful photography and my students were captivated by it.

The second video was a clip from The Private Life of Plants by David Attenborough.  This clip is called "The Largest Flower in the World."  This video is just a few minutes longer, and contains information about other plants, as well as the corpse flower.  But anything by Attenborough gets shown in my classroom....I may be his biggest fan!  Now, here is the neatest bit of information about the corpse flower being used in The Private Life of Plants.  Sir David felt that the constant use of the scientific name (Amorphophallus titanum) during his documentary would be inappropriate, so he invented the popular name of "titan arum" to use during the filming of his show.

To wrap up this lengthy post, here are a few fun and interesting facts about the giant corpse flower:

  • It is referred to as the corpse flower because it emits an odor resembling dead, rotting flesh.
  • Flowers are either male or female.  The female flower opens first.  A few days later the male flower open.  This prevents self-pollination.
  • The titan arum grows in the wild only in the equatorial rainforests of Sumatra, Indonesia.
  • The plant blooms rarely in the wild, and even less often when cultivated.
  • In 2003, the tallest bloom in cultivation was achieved at the Botanical Garden of the University of Bonn in Germany.  The bloom was 2.74 m (8 ft 11 in) high, and was recorded in the Guinness Book of World Records.
  • This record was broken in June of 2010 when a flower reached the size of 2.74 m (8 ft 11 in) high in a nursery in New Hampshire.

Sunday, April 8, 2012

The Koala "Bear"

I recently had the opportunity to visit the Dallas Zoo.  It was my first visit to Dallas and my first visit to the Dallas Zoo.  It was a wonderful zoo!  Since spring arrived in the south so early this year, all of the vegetation was lush and in bloom.  I have never been to a zoo that had koala "bears", so I made a beeline straight for their enclosure.

I was not disappointed.  The koalas were magnificent!

The koalas are such amazing animals, so I thought I would look up the stats and statistics for them:

  • Koalas are often called bears, but this is not correct.  Koalas are marsupials.
  • Koalas weigh between 9 and 20 pounds.
  • Koala fur is thick and soft and pleasant to touch.
  • Koalas can live up to 17 years.
  • Koalas spend up to 75% of each day sleeping.  They become active at sunset.
  • Koalas survive solely on a diet of eucalyptus leaves.
  • Koalas seldon drink water.  The eucalyptus leaves are about 50% water.
  • Koalas have a very slow metabolism due to their nutrient poor diet.
  • Koalas breed once a year.  The gestation period is only 35 days.
  • The baby is born hairless and blind, is less than one inch long and weighs less than one ounce.
  • Unaided, the baby must crawl to its mother's pouch, relying only on its sense of smell to do so.
  • Once inside the pouch, the baby will remain for 6 months, drinking milk from the mother.

This was my first encounter with the koala.  I watched them for quite some time, and left very satisfied with the experience!

Tuesday, April 3, 2012

Myths and Misconceptions About Genetics

If you teach genetics, I KNOW you have encountered these misconceptions before!

It is the time of the year that I teach genetics to my students.  It's a great time of the year.... I love teaching genetics and the students love learning about genetics......for the most part!  But have you noticed that even the students that seem to really "get it" will often ask a question that just stops you in your tracks?  You think to yourself, "How in the world did they get so mixed up on the concepts I have been teaching?"

A few weeks ago I noticed a post that Carolina Biological had posted on their facebook page.  It really caught my eye when I read "Five Common Misconceptions in Genetics."  A link was provided with the post, so I quickly clicked on it and began to read.  I am giving complete credit to this article to Crystal Jeter,  Product Developer for Carolina Biological.  Before reading further, click on the link above and read what she had to say.  The article is short and to the point and really packs a punch!  I deal with these five misconceptions EVERY SINGLE YEAR!  (I am in no way affiliated with Carolina Biological, but I am a huge fan of this company!)

I am not going to repeat any of her article here, but if you read it, I am sure you are nodding your head in agreement.  It is so nice to have my frustrations validated!  I am overjoyed to know that these are misconceptions that are very common and I am not the only one who deals with this each year.  Seeing the five misconceptions so neatly outlined in her article will make it much easier to address them in my class.  

I enjoyed her article very much, and I will keep an eye open to her future writings.

Happy Teaching!

Sunday, April 1, 2012


Congratulations to Denise, who is the winner of the $25 shopping spree from my TpT store called Science Stuff!  The giveaway was from Krystal's blog, Lessons From the Middle.  Thank you, Krystal, for including me in your giveaway.

I have been out of town and traveling for the last 5 days, so forgive me for not updating recently.  Stay tuned..... a new article is in the works!