Eye Eye, Dissection Club!

Sheep eyes are disappointingly small, unlike their testicles which we dissected last week.  If you can get hold of cow eyes or bull eyes, they are much more rewarding.  

We trimmed the muscle and fat off initially.   Then inspected the outside of the eye; the clear front (cornea), the white (sclera) and the optic nerve, which is like a nodule sticking out of the back.

The sclera of the eye is surprisingly tough. We really had to use our scissors with a lot of force to cut through this connective tissue.

We were able to remove the dark circle of tissue which is the iris and behind this was the jelly like lens. The humours (liquid) oozed out and became quite inky and messy.

Finally we turned the eyeball inside out to observe the shiny reflective tapetum lucidum, which looked like a pool of black oil with rainbows.

Dissection Club: Sheep Testicles

We dissected sheep testicles today. They were lovely specimens and an interesting tissue to dissect, being so dense.  

We first looked at the outer appearance and noted the shiny outer testis.  Exiting at the upper end is the epididymis head. The tail of the epididymis leading to the vas deferens or sperm tube is pressed against the ball sac all the way down then up again to the top.  Here we have cut through the thin membrane that attaches it to the testis and released it. We can see the associated blood vessels.

We cut into the testis and removed the outer tunica like a bag.  It was a very shiny, smooth and tough tissue with no elasticity.

Finally we cut into the testicular tissue.  When we divided it we could see the lobes or septate nature of the seminiferous tubules.

Caesarian Sections influencing Evolution

Birth weight is always the classic example of Stabilising Selection in Evolutionary Biology.  Basically, humans have difficulty giving birth; there is a trade off between large human heads and small fused pelvises required for bipedalism and human babies get stuck in the birth canal.  

Selection operates on survival of the fittest, or death of not fit.  Those babies that are too small may be born easily but are so underdeveloped they are unlikely to survive. Those babies that are too big may be well developed but they get stuck during birth, and are unlikely to survive either by being starved of oxygen or fatally haemorrhaging their mother.

So the perfect size is in the middle and selection makes sure that these individuals survive, reproduce and put their genes into the next generation.

This is an interesting article that shows that interventions in birth, ie Caesarian sections, is causing directional selection, not stabilising, and birth weight is increasing.

http://www.bbc.co.uk/news/science-environment-38210837

Is it a Bird? Is it a Dinosaur?

I had planned to teach, yet again, about muscles and bones.  Just the other week we dissected chicken legs to separate out the muscles that are attached to the tendons that operate the individual toes, and had gruesome fun making the toes wiggle in turn.  

Sometimes teaching is led by the students.  Today the student noticed the resemblance of the bird legs and toes to images he has seen of dinosaurs.  Thus ensued a brilliant discussion on the evolutionary relationship between reptiles and birds. 

Archaeopteryx was a fossil found in Germany in the 1860 s that has since been called 'the transition fossil'.  It is thought to represent a species from about 150 million years ago which is half dinosaur and half bird, indicating that the one evolved into the other.

From Muscles to Mussels - Dissection Club

You wouldn't have thought there was much to a bivalve, but when we opened up the shell, we found the soft tissue of the mantle also opened up to reveal the tiny structures inside. We could identify the muscular foot, the gills and the siphons.

Puff ball puffing

I came across this common puffball,  

Lycoperdon perlatum, at Calke Abbey today

Immediately obvious is the apical pore, and I could not resist stamping on it.  Prior to this I took a deep breath and shouted 'Run!' To the bemusement of the family.  Lo and behold a thick black puff of spores was exuded.  You really would not want to breathe them in; lycoperdonosis is an unpleasant lung disease.

Dissection Club - Octopi

The mantle is like a pouch that is open on the underside.  Water is taken in and squirted out to provide propulsion.

Just where the tentacles are attached is the mouth which contains the beak.  The beak is the only tough material in this soft bodied animal.  It is used to lever open bivalves.

Underneath the mantle can be found the heart, reproductive organs and in this case, egg, as seen here.

Egg-like fungus

This is amazing!  It is the volva or immature fruiting body of a fungus.  The recognisable stem and cap are encased in this gelatinous material, and they are usually found just below the ground.  This was found in an area where I have found stinkhorns previously, so I think it must be the same species, Phallus impudicus

Dissection Club - Lovely Lilies

Today we looked at the Reproductive organs of flowers, which are large and easy to see in the Lily.  The colours and scent of flowers attracts insects which are useful in the dispersion of pollen for reproduction.

Flowers reproduce sexually and have both male and female organs, although to prevent self-fertilisation they mature at different times.  In the photo we can see the central female organs (the stigma, style and ovary), surrounded by a number of male anthers (brown).  The specimen on the left is from an open flower, and the one on the right is from a bud.

The male sex cells are the pollen and these are small cells that are dispersed by the wind or by insects that come to feed on the sugary nectar that exudes from the female stigma.

The stigma is sticky so that foreign pollen which lands on it will bond.  A pollen tube grows down the long style to the ovary which is at the base.  Fertilisation takes place when the male sex cell (pollen) fuses with the female sex cell (ovule) becoming a seed.

The flowers' petals drop away as their job is done, but the ovary swells and becomes a fruit to protect the seed as it too falls to the ground.  In some species, the swelling is large, colourful and packed with sugar which is attractive as a food source for animals, including birds. When they eat the fruit, the seed will pass unharmed (protected by a seed case) through the digestive system, eventually being egested. In this way the seeds will have been dispersed far from the parent plant and will be able to colonise new areas, thus ensuring the success of the species

Leaf pigments

The colours of my Soomack are stunning.  

Leaves are usually green in the growing season, of course, and brown when they are dead! But as the temperatures drop in autumn and the rate of photosynthesis declines,  the leaves transition through a very beautiful sequence of green, orange, yellow and red before they fall off the trees.
Two pigments, chlorophyll a and chlorophyll b, are responsible for the green colour.  They absorb red and blue wavelengths of light, but reflect green, so that is the colour we observe. The light energy absorbed is what is converted into the chemical energy of glucose, made in the process of photosynthesis.    It is also required to make chlorophyll, so when the light starts to fade at the end of summer, so too does the chlorophyll molecule.
Other pigments may be present in the leaf to maximise the amount of light energy that can be absorbed.  A second group of pigments are carotenoids, which absorb blue-green pigments and reflect the red end, hence they look orange in colour. These pigments are a little more stable than chlorophyll and last a bit longer into the autumn.  So as the green colour fades, the oranges and yellows come through.
Some leaves have a third pigment, the red anthocyanin.  These are compounds that are in the cell sap and are synthesised from sugar.  The higher concentration of glucose, the more purple the anthocyanin.
As chemical reactions are involved, many variables influence the reaction; different species, sugar concentration, pH of cell sap, and external factors such as light wavelength, light intensity, temperature, and so on.  Which is why there is such a wonderful spectrum of colour at this time of year.  Enjoy.

Forever fungi

 Lycoperdon excipuliforme

Fungi are not autotrophs like plants. They do not make their own food.  No, fungi are heterotrophs, which means their food has to be digested and absorbed (like in animals, although, clearly, only in this respect!).  Fungi perform Extracellular digestion.  Their enzymes are secreted outside of their body. The enzymes digest the large and insoluble organic molecules (eg wood) into small and soluble ones like glucose.  This can be absorbed into the body and assimilated into more complex materials for growth such as proteins.  Hence fungi are found growing through their food source, eg a tree stump.

Phallus impudicus, the common Stinkhorn

Phallus impudicus was named by the father of taxonomy, Carl Linnaeus, himself.  The common Stinkhorn can be both seen and smelt in the woodland at this time of year.  It is said that Darwin's granddaughter, Etty Darwin, was so upset by them that she attacked them with a cudgel at dawn.

A ten minute walk in the woods on my way home from work yielded a great array of fungi.  I highly recommend getting out and about to observe the vast number of species of every shape, form and colour that pop up in the autumn.

Conkers bonkers

When I was a kid,  nothing could be more thrilling than finding conkers under a horse-chestnut tree in autumn.  The nut, up to 4 cm in diameter, is shiny and smooth, with a scar on one side.   The spiky fruit opens as if it has been scored with a knife, so straight is the cut,  and the conker tumbles out of the fruit, usually one but sometimes two or three.

The horse-chestnut tree is a huge beast.  Massive boughs, five to seven sprigged gigantic leaves, large white  towers of flowers with small pink dots on the petals, and of course, a big scent.  Wrongly called a chestnut, though might be poisonous to horses. The conker does contain toxic saponins.  However, whether there is any truth to the belief that they keep away spiders is not known.

Aesculus hippocastanum

Dissection Club; the Locust

We dissect all sorts at this club, and today it was the turn of the Locust, a fairly large representative of the class Insecta.

Insects are Arthropods with jointed legs, segmented bodies and an exoskeleton made of chitin.

They have three body regions; the head, thorax and abdomen.

The main reason for dissecting insects for A level Biologists is to observe the Gas Exchange system.  Locusts cannot get enough oxygen to their cells by diffusion alone.  (Only fairly small organisms with a relatively large surface area to volume ratio can get enough oxygen through their surface) . 

Insects have a simple tubular system  in which oxygen can enter the body through holes called Spiracles, and can move down a concentration gradient through tubules called tracheoles to the respiring tissues.

Compression of the body brought about by the movements of the legs can aid gas exchange.

Geo-caching challenge

At this time of year, the grey squirrel is incredibly busy, running up and down trees, running madly around woodland, risking life and limb crossing busy roads, all in a frenzy to collect as many nuts as possible as they rain from the skies.  Autumn is indeed bounteous on the nut front, and squirrels behave as if they are on Supermarket Sweep.
What to do with so much food?  Evidence of them eating as many as possible is everywhere, with half eaten nuts strewing the paths.

But they can also be seeing hiding them in caches.  Squirrels do not hibernate but they may sleep for long periods in the winter.  When they wake up, they will be hungry, and their well-developed spatial memory, as well as their excellent sense of smell, will lead them straight to breakfast.

Sexual Selection: how the female mind works

I spent a lovely afternoon at Gwydir Castle in North Wales last weekend.  Gracing the beautiful gardens were a number of peacocks and peahens.
Peacocks (the males) are well known for displaying their magnificent long tail feathers in a fan.  The brown feathers have shimmering tips of blue and green and a pattern that resembles an eye.  It is not difficult to see why a peahen would be impressed by that tail.

In evolutionary biology terms, the dimorphism of the peacock/peahen is because of a form of sexual selection.  Sexual selection is when the female gets to select her mate and the father of her offspring.  Obviously she will choose the one that is the most fit; big, strong, healthy, so that he can pass these genes on to her offspring and make them successful.

How does the elaborate peacock tail indicate his fitness as a father?  The theory is rather bizarre.  Peacocks are native to the rainforest, and to be honest a very long brightly coloured tail could be considered a hindrance; it makes you very conspicuous to predators, and it really hampers your movement through dense vegetation. 

And that is just it! Any individual who survives in spite of this handicap must have good genes, and therefore will make a good father!

It's raining Slugs....

Arion rufus

Not many people like Slugs! Ugly, and slimy, and resembling doggy doo! But like all organisms, they have their role in the ecosystem, and somebody has to do the dirty work; the decomposition.  Slugs are omnivores, consuming a large variety of organisms.  Their exceptional suite of digestive enzymes is testament to this: not just amylase and invert awe, to digest starch and sugar respectively, but also proteases (protein), chitinases (the material of insect exoskeletons), and xylemases and ligninases to digest the woody stems of plants.

The other interesting thing about slugs that everybody knows is that they are hermaphrodite.  But did you know how intricate and beautiful the reproductive organs of a slug or snail are?  Best thing I ever dissected at university, and so I think we must introduce this to Dissection Club. Watch this space...