Thursday, August 23, 2012

Drinking Bees

The waterfall at our outdoor classroom attracts more than just people.  It's the ideal place for some insects to stop for a drink.  There must be a honeybee hive somewhere near the school, because our waterfall has become a bee watering hole!
Honeybee drinking water on an algae-coated rock.
Honeybees are my #1 top favorite insect, which is ironic since I was scared of them as a child.  Once I learned about them, I grew to love them best of all.  Not only do honeybees make honey to feed their offspring and feed themselves, but while they are collecting nectar to make the honey, they pollinate flowers.  Most of our agricultural crops need to be pollinated by insects, and honeybees are the best pollinators.  Honeybees are so helpful to humans that farmers often have honeybee hives on their farms to make sure their crops are pollinated.  If you like nuts, berries, apples, cherries, squash, tomatoes or avocados, thank the bees for making them possible.  I love to think of our pond as helping the bees.
Honeybees drinking on our waterfall.
We've all seen bees pollinating flowers, but I bet few of us have been able to watch honeybees drinking.  A good, clean water resource is incredibly valuable to bees, especially in the city where water is hard to find.  Bee keepers make sure their bees have access to clean water, or they provide water dishes to their bees.  Bees, like all creatures, need to drink water.  The bees use the water to make the fluids in their bodies, and they also sweat like we do to keep their bodies cool.  Bees carry water back to their hives to help keep the hives cool and to dilute the honey to feed their larvae.  Bees fan wet surfaces in their hives with their wings, causing the water to evaporate, which cools the wet surface and the hive.  You can observe this phenomenon if you dangle a wet towel in front of a fan. 
The top level of wet rocks is safest for bees to drink from.
Water is a tricky substance for small creatures like bees to deal with.  It might be strange to think about, but water is sticky to most surfaces.  In fact it's so sticky, that you have to use a towel to get it off of yourself after you shower.  The more surface something has, the more water sticks to it.  Think of how difficult it is to dry your hair, which has millions of surfaces all packed together, compared to drying your skin, which is one surface.  The stickiness of water is both helpful and dangerous to bees.

The good part about the stickiness of water for bees is that it's easy for bee mouth parts to soak up water.  Bees have a feathery tongue that sticks to water like hair does.  The bee just has to touch its tongue to water, and water wicks into it.  You can see the phenomenon of wicking if you touch the edge of a paper towel to water and watch how the water climbs further on to the paper towel.  Paper towels that are thicker with more microscopic fibers to provide more surface wick better than thin, smooth paper towels.  Bee's feathery tongues have lots of surface and are good wickers.   You can see a bee tongue sipping nectar on the flower from my garden in the picture below, but the picture is not magnified enough to tell that the tongue is feathery.
Honeybee soaking up nectar and pollinating chive flowers.  Note battered wing and pollen sack.
The dangerous part about water's stickiness is that bees' bodies can easily get stuck to open water.  If a bee lands on the surface of the pond, its body will stick and it won't be strong enough to get unstuck from the water.  The bee will likely drown unless someone scoops it out and sets it on dry land (careful - it will likely be stressed and possibly sting if you use your hand to do this).  To protect themselves, bees must stand on hard surface and drink from water that has seeped onto the surface.  Leaves and sticks on the surface of a pond are good platforms for bees to drink from.  The rocks in our waterfall are perfect surfaces from which bees can safely soak up water.

Monday, August 20, 2012

What is a Leaf Skeleton?

Leaf skeleton floating just below the surface in our pond.
For some reason, floating leaf skeletons are most visible on gloomy days.  Perhaps the filtered sunlight doesn't glare as much off the surface of the pond, and the light-colored skeletons stand out against the dark background of the pond depths.  Needless to say, leaf skeletons are strikingly beautiful, and they are lovely to find on a gray day.
Leaves ranging from living to dead floating in our pond.  The dead ones are starting to decompose.
The pond in our outdoor classroom has many tall trees towering over it.  As summer turns into fall, it is going to fill up with leaves, and we will hopefully have lots more floating skeletons.  Ponds provide the perfect habitat for production of leaf skeletons, because they allow for fast decomposition of soft plant tissues.  Aquatic conditions provide lots of snails, insects and microscopic organisms that attack a leaf as soon as it falls, since a newly fallen leaf has lots of nutrients to feed pond organisms.  The organisms eat the softest tissues and leave the leaf veins behind, allowing us to marvel at an important plant tissue.
Leaf skeleton from a hackberry leaf.
Leaf veins are a part of the transportation system within the plant.  The veins in leaves connect through the leaf stems into the main plant stems and all the way down to the roots.  Veins in plants are network of tubes for moving necessary substances from anywhere in the plant to any other part of the plant.  My mind can't help but compare leaf veins to our system of roads.  All our houses are connected to them, and we can use roads to get anywhere else.  I also think of our system of blood vessels - a similar network of tubes for moving necessary nutrients from one place to another within our bodies.
Leaf skeleton showing network of veins.
Plant vascular systems (vein systems) contain two types of tubes inside each vein.  One type of tube, called xylem (pronouned zy-lum), is rigid and only runs in one direction.  Xylem carries water and nutrients from the roots in the ground up to the leaves.  The second type of tube is called phloem (pronounced flow-um).  Phloem tubes are soft and flimsy, and they carry sugar, the product of photosynthesis, to wherever energy is needed in the plant.  Phloem tubes run in two directions.
Leaf veins in living leaves.
Leaf skeletons can be preserved by drying them pressed between newspaper or paper towels.  Their patterns can be revealed by covering them with paper and making a rubbing.  Different types of leaves have different patterns of leaf veins - highly branched, long parallel lines or radiating out from a center.  All three of these patterns of leaf veins can be found at our outdoor classroom.  Another fun trick for learning about the function of plant veins is to place a white carnation in water with food coloring.  After a few hours to a day, the xylem will carry the food coloring up to the petals.  The same thing would work in a leaf, but the green color of living leaves would make it difficult to see the food coloring.

Thursday, August 16, 2012

Invasion of the Blue Dasher Dragonflies

Blue dasher dragonfly.  Are those aviator sunglasses?
The outdoor classroom and back field of our school has been a-buzz with these miniature blue helicopter-like insects.  They are a type of dragonfly called blue dashers (scientific name Pachydiplax longipennis, which means double-thick long wings, by the way), and they are beautiful!  The one above is an adult male, which you can tell from the bluish color of his abdomen.  Females and young adult males have brownish-black abdomens.  Both males and females have brown and yellow wavy stripes on their mid-section, or thorax.  Blue dashers all have a white head with bluish-green eyes.  In the picture above, the white patch on the head is the upper and lower mandible, which the dragonfly uses to bite its prey.

Dragonfly eyes are amazing.  They cover most of the head and provide the dragonfly with a 360 degree view of their world.  Dragonflies need excellent vision of their surroundings because they can fly and maneuver so quickly.  If they couldn't see in all directions, they'd constantly be smashing into things.  Dragonflies fly quickly because they need to catch their prey, which consists of insects that can also fly.  Blue dashers specialize in mosquitoes, gnats and flies, but they also eat butterflies and grasshoppers.  

Blue dasher demonstrating its helicopter shape, with a long abdomen to balance the head.
Since dragonflies are so big and fast, sometimes people are afraid of them.  The good news is that dragonflies are harmless to humans.  They do not bite or attack humans, and the long, pointy abdomen does not sting.  The shape of the abdomen serves as a counter-weight to the head, keeping the body of the insect level as it is suspended by its wings in flight.  If you look at the picture above, you can see how the head and tail appear to balance each other out under the wings.  Blue dashers are particularly useful on the school grounds because they keep other biting insects away from the kids' outdoor areas.

All dragonflies lay their eggs in water, and we probably have blue dasher nymphs in our pond at school.  After being deposited in the water, dragonfly eggs hatch into nymphs (underwater larvae), which grow and eat other aquatic insects and tiny fish until they are big enough to metamorphose into adults.  When a dragonfly becomes an adult, it crawls out of the water onto a stem or rock, splits its exoskeleton, and drags itself out of the shed skin as a fully-formed adult.  Blue dasher nymphs are particularly tolerant of poor water conditions, which makes them ideal for living in an urban environment.  They are widespread around the United States and in southern Canada in all variety of habitats. 
Dragonfly nymph exoskeleton. (Photo: Mary Entrekin Agee)

Tuesday, August 14, 2012

Green Algae

The school where I work has an outdoor classroom that invites nature into our urban schoolyard and creates a peaceful outdoor space for students to learn about life.  We have trees, wildflowers, and a pond, each hosting their share of associated organisms.  I'll be doing some nature blogging about the outdoor classroom for use by teachers at our school, and I'm posting the first outdoor classroom blog post here:

Welcome!  I'm excited about starting an outdoor classroom blog.  I can't wait to see what we find in our little urban nature oasis.  The subject of our first post is green algae.

If you look under the surface of the pond, you see a very busy ecosystem indeed!  There are plants, fish and insects, and those are just the visible organisms.  There are way more microscopic organisms than big ones, which I'll save for a future post.

Green algae growing just below the surface of our pond.
The strangest macroscopic (big enough to see) organism is the filamentous green alga that forms clouds of soggy green cotton candy.  But what on earth are green algae?  They seem a lot like plants: they photosynthesize, they have cell walls, and they have chloroplasts (green structures that photosynthesize).  There are also some features of green algae that we don't usually associate with plants: they live entirely under water; they don't form roots, leaves or stems; and some of the microscopic ones can swim!  Scientists have wavered a bit about whether algae are actually plants or protists.  The discovery of how to sequence DNA has allowed algal geneticists to confidently classify green algae as plants, though the other colors of algae (red, brown and blue-green) are not classified as plants.  I have had to re-learn my green algae taxonomy!

Interconnected strands of green algae pulled up from under the surface.
Our green alga (alga, hard g, is singular, and algae, soft g, is plural) is a filamentous type, meaning it grows in long strands.  The filaments (strands) of green algae are only one-cell thick, which is surprising considering how tough they are.  Each algal cell is cylindrical like a soup can, and the filament is arranged like an infinite strand of soup cans glued end to end.

Green algae out of the water.
The color of green algae comes from the pigment chlorophyll, just like in other plants.  Chlorophyll is the molecule that can catch light to allow plants to use its energy to build food.  Green algae cells contain structures called chloroplasts that hold the chlorophyll plus all the other machinery needed to conduct photosynthesis.  All plants' cells contain chloroplasts.

I looked at the algae from our pond using a microscope that magnified what I saw by a factor of 100.  In the picture below, you can see the cell wall between adjacent algal cells, just above the pointer.  Cell walls are rigid structures made of cellulose (a strong, rigid molecule), and they give plant cells their shape.  Paper is made by starting with plant material and getting rid of everything but the cellulose, meaning that paper is essentially squished, dried plant cell walls.
The pointer rests on a filament of green algae.  A broken alga releases its cell contents. 100x
Another interesting thing in the picture above is the broken cell.  A chloroplast is slipping out of the broken plant cell in the center of the picture.

Below is another view under the microscope, with one normal filament and one filament with shrunken cell contents.  The chloroplasts and other structures have been compressed into a central structure in each cell.  The strange filament may be undergoing reproduction or it could be stressed, but either way, you can see the beautiful cylindrical shape of each individual cell.

Shrunken cell contents in the lower filament allow you to see the cell walls.  The round object is an air bubble. 100x
In our pond, the algae seem to be growing quickly.  There is ample sun for food, plus decomposing leaves and insect/fish excrement providing nutrients, the equivalents of vitamins in our food.  When you see a pond with lots of algae in it, you can assume that there are a lot of nutrients in the water, either from natural sources or from pollution.

Tuesday, August 7, 2012

Why Do Sunflowers Follow the Sun?

Blooming sunflower.
It feels good to look at, doesn't it?  Something about bright yellow and radial symmetry is so pleasing to the eyes and mind.  Perhaps the visual buzz we get from gazing on sunflowers is due to the arrangement of the flower parts in what is known as Fibbonaci spirals, which I will not attempt to explain to you, but which you can learn about here in a fascinating animation.  No matter how much you understand Fibbonaci spirals, sunflowers are captivating.

The top picture shows a recently-opened sunflower inflorescence, or group of flowers.  Each dot in the face of the sunflower is actually a single flower, and the picture above shows sunflowers at the stage of pollination.  After pollen has been transported from the male parts of the flower to the female parts of the flower, the female parts of the flower begin to grow into what we know of as sunflower seeds.  In the two photographs below, you can see a mature sunflower inflorescence transitioning to sunflower seeds.
Sunflower finishing blooming and turning to seed.
Sunflower seeds not yet turned black arranged in a Fibbonaci spiral, allowing for maximum packing of seeds.
Above, you can see whitish green sunflower seeds packed together with their pointy end in.   The Fibbonaci spiral arrangement allows the plant to pack as many seeds as possible into the space available.  As this sunflower matures, the seeds will turn striped white and black like what we're accustomed to seeing in the grocery store or birdfeeder.  For a more detailed description of sunflower floral structures, see my older post on aster-type flowers, written when I wrote catchier though less-internet-searchable titles for my posts.

Sunflowers also do that amazing sun-following trick that makes these plants seem to possess some mystical powers.  Well, if you'd like to maintain your sunflower mysticism, I suggest you skip the rest of the text in this post and just look at the pretty pictures.
Sunflowers facing the sun.
What's really going on here is something called heliotropism, and lots of plants do it.  Heliotropism means moving toward the sun.  If you've ever repositioned yourself periodically during an afternoon of misguided youthful tanning in order to get even sun exposure on all parts of your previously cancer-free skin, you've done heliotropism yourself.  The puzzle with sunflowers is, why do the flowers need to face the sun?  To even out tan lines? To look good in a white dress?  To appear thinner?  To fit in with their friends?  Read on.

The truth is, the stems of all actively growing sunflower parts - flowers and leaves - grow to face the sun in order to maximize photosynthesis.  During the day, the stems elongate on the side away from the sun, tilting leaves and immature flowers toward the sun throughout the day and ending up facing west at sunset.  When there's no light (so...night time), the other side of the stem grows, pushing the leaves and flowers back to the east where they will be facing the sun at sunrise.  Growing leaves and immature flowers are green and actively photosynthesizing, and heliotropism provides them with 10-15% more sunlight than just sitting still.

Take a look at the picture below.  On the right, you can see an immature sunflower inflorescence covered in green bracts, which are obviously photosynthesizing since they are filled with chlorophyll and appear green.  The younger sunflower has immature leaves held up and facing the sun as well.  The lower leaves on the younger sunflower, as well as all parts on the older sunflower, have matured, and though they are generally facing up, they are not facing the sun.  The older sunflower is drooping from the weight of the developing seeds.
Young sunflower parts following the sun, old sunflower parts stuck in place.
So just-opened sunflowers like the gorgeous ones in the vase below (if they weren't cut off from their stalks) are still growing some, so they still face the sun.  As soon as they mature, they usually end up facing east and staying there.
Bouquet of sunflowers