Nature – Page 10 – Dr. How's Science Wows

"Mammy I hatched an egg!"

April 3, 2013July 5, 2014nao

As a mother of three young children I have had many charming moments that I feel I will remember forever…. first steps, first words, how they pronounced a certain word, the list is endless. Memories to cherish for a lifetime…. and then I forget!! Startling but true! More moments forgotten than remembered. However, certain things will stay with me forever…. like when my daughter was five and we got chickens for the first time; she was beginning to learn the joy of finding and collecting the eggs each day. One day she came to the back door with her bounty only to trip at the step and drop an egg. The poor thing burst into tears with the dramatic exclamation…

……………………………….”MAMMY, I HATCHED AN EGG!

Image credit: Graham Ettridge

I will never forget that one! It was hard to keep a straight face as I tried to console my sobbing child. With all the egg activities and treats of the Easter it has certainly got us talking and thinking about eggs in this house, have you ever wondered about these marvels of nature?

WHAT IS AN EGG MADE OF?

Firstly, what exactly is an egg made of and what purpose does each component have?

Image source: http://www.exploratorium.edu

The shell: the egg shell is made of calcium carbonate (95%), just like the enamel of our teeth (see previous post). The other 5% of the egg shell is made up of calcium phosphate, magnesium carbonate and proteins. Although the shell gives the egg it’s strength you might be surprised to learn that it actually contains up to 7,000 tiny holes (pores); these pores allow air and moisture pass through the shell.

The bloom/cuticle: this is a protein coating outside the egg shell that acts as a natural barrier to bacteria and dust while reducing moisture loss.

The membrane: there are two layers of membrane just inside the shell called the outer and inner membrane. These membranes are like layers of skin and contain a protein called keratin, which is found in our own nails and hair!

The yoke: the yellow of the egg contained within a membrane called the vitelline membrane. The yolk is the part of the egg that feeds the developing embryo – it has a very high protein content and is also rich in vitamins and minerals. The yolk contains all of the egg’s fat and cholesterol. The yolk is the primary food store for the developing chick.

The Albumen: this is the white of the egg; it has a high protein and water content. The albumen cushions the developing chick and keeps it moist while still in the egg.

The air cell: this is a pocket of air at the wide end of the egg, created between the outer and inner membrane. The air cell gets bigger as the egg ages.

The chalazea: these are spiral ropes of egg white that keep the yolk in place.

WHAT ANIMALS LAY EGGS?

Animals that lay eggs are called oviparous and they include birds, fish, amphibians, many reptiles, many arachnids and insects, some molluscs and two mammals – the echidna and the platypus. Mammals that lay eggs are referred to as momtremes.

A BIT OF EGG EVOLUTION

The reptile is credited as inventing the egg shell, allowing their young to develop outside the mother’s body. All true dinosaurs are reptiles and they all laid eggs. The development of the egg shell has been a fundamental step in evolution as it allowed the embryo develop in self contained egg, without the requirement for water. This removed animals’ dependence on water for breeding.

HOW IS AN EGG MADE?

In the hen it takes about 24 to 26 hours to produce an egg. An egg is made from the inside out, starting with the yolk which is released from the hens ovary and moves through various parts of the body where another element of the egg is added until finally the finished egg reaches the vent and the egg is laid. Within 30 minutes of laying an egg, the process will start for the hen all over again.

SO WHAT GOES ON INSIDE THE EGG?

The embryo has started to develop in the egg while it is still being made within the body of the hen. Once the egg is laid the development of the embryo will only continue if conditions are correct. If the temperature and humidity levels are right (temp approx 22oC, relative humidity 50% ) the development of the embryo will continue after the egg is laid. This process continues for approximately 21 days. If the egg is being hatched under a broody hen then the hen must turn the eggs regularly.

THE HATCHING PROCESS

Image credit: http://www.waldeneffect.org

Finally, when the time is right, its time to crack out and see the world. The young of many egg-laying species are equipped with an egg tooth – a tooth like projection on the end of a beak (birds) or protruding from a jaw (reptiles) that helps the young animal tear through the membrane and break through the hard shell. The egg tooth will eventually be reabsorbed or fall off.

Chicks and many other animals will hatch from the larger, rounded side of the egg. That is because this is the end where the air cell is usually located. Once the chick becomes too larger to receive enough oxygen from inside the egg it will use it’s egg tooth to pierce through the inner membrane into the air cell space. This provides them with an extra supply of oxygen, just enough to sustain them as they continue the hatching process and crack and break though the egg shell.

We have been lucky enough to hatch a few broods of chicks over the years and it is always so exciting to meet the little ones for the first time.

This is chips – one of our brood!

So the only other question to be addressed is “which came first – the chicken or the egg?” but I think that’s a blog in itself, perhaps for another day!

AN EXPERIMENT TO TRY – HOW STRONG IS AN EGGSHELL?

You would be amazed how strong an egg shell is, although you might want to try this one over a sink!
Hold a raw egg between your thumb and first finger, holding at the two ends and then apply pressure – as hard as you can! You might be surprised to notice that the egg doesn’t break!

If you repeat this but apply the pressure to the sides of the egg, things might not go so well and you might find yourself covered in egg!

So why is this? Although an egg shell can be very fragile, it’s shape can provide it with great strength. This is because the egg is dome shaped at the top and the bottom, just like a bridge structure; this structure means that when you apply pressure the force is distributed evenly over the shell, not just on one point, hence the egg does not crack!

Further reading:
Anatomy of an egg
Eggshell
Poultry reproduction and incubation

The Thorn bug

April 2, 2013July 5, 2014nao

Week 1st – 7th April 2013

Did you guess this weeks CAN YOU NAME THIS CREATURE?

I got some correct responses…. it was a thorn bug ( a treehopper). These bugs can be found on all continents except Antartica. As you can see from the photo, they are excellent mimics of thorns on the plants and trees on which they feed.

These thorn-like protrusions on their backs act as a wonderful camouflage to prevent detection by predators. They also act as protective armour if attacked. These insects cut into the stem of the plant and feed on its sap. The females of most species cut into the bark to lay their eggs and often sit on their eggs to protect them. In some species there is even collaborative egg minding between females!

Another of nature’s wonderful creations!

Lacewing Larva

April 2, 2013July 4, 2014nao

Week 25th – 31st March

Last weeks “can you name this creature?” image was supplied by Molly, who is ten years old. Molly spotted this in her garden and, with the help of her Dad, Michael at Nature Learn, has shared it with me for this slot. A big thanks to Molly!!

Lacewing larva – photo credit Michael and Molly Bell

So did anyone guess what creature this is?

It is a LACEWING LARVA! A hard one this week I know, but we did give you some good clues!
I thought Molly did particularly well to spot this little guy as they only grow to between four to seven mm in length!

So now you know what it is do you want to learn some more?

These lacewing larva are a welcome addition to any garden as they like to dine on soft bodied insects, particularly aphids! They like to hang out in humid environments and can be a great gardening aid to any greenhouse or poly tunnel! They also feast on the eggs of certain other insects and spiders, as well as mites and mealy bugs. All in all a real asset to the garden!

Although the larva stage does not last more than two to three weeks these little guys certainly have a big appetite …. consuming up to 600 aphids during this period. The larva must make direct contact with it’s prey… injecting digestive enzymes into it and sucking back up the digested body parts once the enzymes have done their work!

Lacewing larvae are also experts in the art of camouflage, they often cover their bodies in debris to hide them from predators. This debris often includes bits of body parts from their own prey!

Sticky toes

January 28, 2013July 4, 2014nao

We are amassing quite a collection of geckos around our house these days. Not the organic variety of course, although that would really please the kids! No, our collection consists of ornaments, wall hangings, trinkets and even jewellery. It all started ten years ago when on honeymoon in Barcelona … the little guys were everywhere and we were drawn to them with fascination – especially their ability to scale any surfaces they encountered (even glass). So the collection started from there, anytime we come across a quirky gecko decoration or ornament we like, we purchase and add it to the collection!

Ten years on and our fascination has grown along with our collection. I was delighted to show my children a recent photo from National Geographic of a gecko. Of course that lead to the children asking questions, that lead to questions, that led to the ultimate… “How do they walk up walls?” After answering their questions I decided this might be a good topic to start my 2013 blog with. So…how do these amazing little creatures manage their “spiderman-like” feats? It truly is a marvel of nature but before I delve into that, I want to tell you a few other quirky facts about these lovely little creatures.

Geckos are a type of lizard. They are found on all continents except Antartica. They come in many shapes and sizes and are in fact the most species rich order among lizards. They are also among the most colourful lizards in the world.

Most species of geckos can actually sever part of their tail, usually to escape the hold of a predatory or threat. The released tail segment can keep wriggling as a distraction while the gecko escapes. PRETTY COOL DON’T YOU THINK? This process of severing the tail is called caudal autotomy!

photo credit: Tambako the Jaguar via photopin cc

Another very interesting fact about geckos is that nearly all species of geckos have no eye lids and can therefore not blink. Instead, they use their long tongues to clean any dust from their eyes.

Already you can begin to see how fascinating these creatures are, and that is before we have even looked at their ability to apparently defy gravity! DID YOU KNOW THAT A GECKO CAN SUPPORT ITS ENTIRE BODY WEIGHT ON ONE TOE?

So here is the science bit behind HOW THEY DO IT…the toes of a gecko are covered in hundreds of small ridges called lamellae. Each ridge is covered in millions of hairs called setae. Setae are much thinner that human hair (up to 30 times thinner). Each seta then splits at the top into tiny strands called spatulae – there can be up to 1000 spatulae on one seta (if you think you have problems with split ends, pity the poor gecko!). So you can begin to imagine how tiny these spatulae are, in fact, they are so tiny that they can bond with the molecules of the surface they are touching. This bonding is referred to as van der Waals interaction! The great thing about it is that it is what is called dry adhesion – it doesn’t require any sticky compounds or leave any messy residue.

photo credit: bernat... via photopin cc — photo credit: bernat… via photopin cc

This gives us an idea of how the gecko sticks to the surface, but HOW DOES IT UNSTICK? The adhesion (sticking) process is said to be one-directional…imagine sticking a piece of sticky tape to a surface and then taking hold of one edge and peeling it back to remove it… the gecko does something similar. Geckos toes bend in the opposite direction to humans so they can “peel” their toes off the surface from the tip backwards. Add to this the fact that geckos have rotating ankles and you start to understand how they can move in any direction.

As you can imagine this ability has captured the interest of Scientist for a long time. Imagine if we could copy this adhesion from the gecko… what could we do with the technology??? Robots that can scale any surface would be great in extreme or rescue situations, right? Or how about a suit we could wear to allow us to climb like a gecko? Did you know that geckos can climb in a vacuum? So now we can start thinking about using this technology in space! Or how about using the technology in bandages – inspired by the observation that geckos can climb in wet conditions… a bandage that stays on when wet.

Maybe YOU can think of another novel way to use gecko technology? If you have any ideas I’d love to hear them!

More on geckos…
Nat Geo Kids Creature Facts – Geckos
The dance of the disembodied gecko tail
Geckos evolved sticky feet many times