|How humans exploit fungi for food and drug
Brewing baking and wine making all require yeasts, Sacchromyces cervisiae is probably the most commonly used. Yeasts are
very active metabolically. The metabolism of the yeast produces CO2 that makes bread rise. It is a facultative anaerobe that ferments sugars to
alcohol when forced to live without oxygen. Winemakers used to use the native
yeasts growing on the grape skins for this purpose, but now they use
domesticated strains. Brewers add yeast to water and hops to make beer.
Agaricus bisporus has been in cultivation for some time and is an
important cash crop in some areas. Next in financial importance is shiitake and
matsuke mushrooms, they are considered delicacies in the east, and were
sometimes so expensive that they were sold singly. Recently they have been
cultivated commercially and the price has fallen, but the market has increased.
Truffles are the underground fruiting bodies usually found near oaks. In the
areas around the French/ Italian border they provide additional income in rural
areas. They have proved difficult to cultivate, but the French appear to have
succeeded in inoculating the roots of some seeding trees with the mycelium.
Mushroom are very popular and wild ones always taste best, recently
mushroom gathering has become so popular that in certain national forests in
the US you have to buy a licence to collect them, and in some places they are
considering banning mushroom picking altogether.
Various Penicillium spp. are used in the cheese industry, e.g. P. roquefortii is used in
making Roquefort cheese. Aspergillus niger is used by the soft drinks
industry for the fermentative manufacture of citric acid. Many fungi are used
in medicine and research. Yeasts being unicellular are used in cytological and
genetic research. Penicillium is an antibiotic, it hydrolyses the cell walls of
certain bacteria. P. griseofulvum is used to produce an antifungal
antibiotic to treat ringworm diseases including athletes foot. Claviceps spp. causes ergot in cereals and is cultivated for medical use. C.
purpurea is used in treating circulatory problems, low blood pressure, and
in stimulation of post-natal uterus contraction.
gramminis infects both barberry and wheat. On the upper surface of the
barberry leaf the basidio spores germinate to form spermogonium, these must be
cross-fertilized by insects for further development to proceed. A sticky, sweet
exudate attracts the insects. Aecia are formed on the lower surface of the
leaf, but the aeciospores cannot reinfect the barberry, they must find a grass
On wheat the aeciospores germinate and uredia are formed.
Urediospores are very small and light and can be blown 1000's of miles - from
Canada down the side of the Rockies to Mexico, and from Spain and Portugal to
the UK. This explains why P. gramminis can cause so much damage in the
US, but less damage in Europe, as the mountains from east to west usually get in the way
preventing the passage of urediospores.
Throughout the warm weather the
urediospores reinfect wheat. As the temperature drops telia are formed
releasing teliospores. These are two celled and can overwinter if the temp is
not too low - it usually is in UK. In spring the nuclei fuse (karyogamy),
meiosis takes place followed by formation of basidia, then haploid
basidiospores are released to infect barberry.
Control resistant varieties
have been produced, this takes time and money, and the resistance does not
persist because of the different strains of P. gramminis and its ability
Fungicide application using predictions based on climatic
conditions seems to be the best control. It is possible to forecast the likely
incidence of epidemics, and this info used in conjunction with systemic
fungicides, means the farmer can do minimum spraying for maximum effect.
Eradication of the barberry. As mentioned above, this can only be effective
when the urediospores cannot persist because of low temp. In Mexico, US and
Canada it is possible for asexual reproduction to continue throughout the year,
so eradicating the barberry is not very effective.
|Taste discrimination in blowflies
Flies taste with their feet, and on the last tarsal segment they have gustatory bristles and taste hairs. These hairs have a pore at the end into which a stimulus can enter to reach the sensory cells. There are five sensory cells in each hair; one mechanoreceptor which detects bending, two which respond to salts (one to anions the other to cations), one responds to sugar, and one to water (Barth 1991). The feet perform preliminary tasting of substances. If these substances are acceptable as food or water then the fly will extend its proboscis. This preliminary tasting prevents the fly from tasting harmful substances with its proboscis as the fly doesn't actually take in any food until it has passed the chemical tasting of its tarsal hairs and also the hairs around the edge of the labellum, which work in the same way as the tarsal taste hairs.
Barth, F.G. 1991. Insects and flowers, the biology of a partnership. Princeton University Press, New Jersey, USA.
|Life cycle of Black rust (Puccinia graminis)
1. Spores called basidiospores are dispersed into the air in spring.
2. Basidiospores land on barberry leaves, germinate, then grow inside the leaf cells.
3. The fungal cells multiply producing structures in which pycniospores develop.
4. Pycniospores are picked up by insects and carried on the insect body from one infected site to another enabling fertilisation.
5. The fertilised cell develops on the underside of the barberry leaf and produces aeciospores.
6. The aeciospores are liberated into the air.
7. The aeciospores land on wheat stems or leaves and grow in through the stomata.
8. On the stem or leaf, structures producing uredospores develop. The uredospores are liberated into the air to infect other wheat plants.
9. Late in the summer teliospores are produced. These are inactive, resting spores which remain attached to the wheat stem during the winter months.
10. The teliospores germinate as the weather warms up in the spring and produce basidiospores.
|How mosses obtain,
retain, and transport water
Mosses are poikilohydric, there are two
main growth habits, acrocarpous and pleurocarpous.
Acrocarpous have an
upright growth form. They are endo hydric, which means that most of their water
intake passes up the centre of the stem through rudimentary vascular tissue.
This can be seen at its most advanced in Polytrichum spp. which has
hydroids, sort of primitive tracheids. These are dead at maturity, and like
tracheids have inclined end walls. Acrocarpous mosses also have a thin cuticle
to help prevent water loss, the cuticle is also water repellant. However some
water can be lost by evaporation, to minimize such losses mosses grow together
in clumps creating their own microclimate. Fine hair points roughen up the
outline of a clump increasing boundary layer resistance as the air stream
passes over it. Water storage ability is 200-600% dried weight. Pleurocarpous
e.g. Hypnum cupressiforme have a prostrate growth form. they are
ectohydric, and so take in most of their water straight from the outside,
because of this they have no cuticle. They are usually branched and have
overlapping leaves, and can often be found growing in dense mats; and they have
capillary structures. All of these features make it easy for them to absorb
water in moist situations, and also to minimise water loss during drier times.
The have less water transportation ability than acrocarpous forms, but they
have less need, as absorption can occur over the whole surface of the plant.
Their water storage ability is greater than acrocarpous, being 600-1200% their
dried weight. Sphagnum spp. in addition to the above has special water
storage cells. These large water-filled cells account for the pale colour of
Is believed to have first occurred
when an anaerobic heterotroph ingested an aerobic heterotroph, but did not
digest it. This may have happened as the O2 began to increase in the
atmosphere, and this symbiosis would have enabled the two organisms to survive.
This is believed to have happened around 1900-1200 MYA, and was the origin of
the eukaryotes. Symbiosis is the organisation of two or more organisms for the
mutual benefit - though it is not clear what benefit the mitochondrion got -
perhaps just a controlled environment. Today mitochondria still have their own
DNA and divide in two when the cell does, though they depend on the nucleus for
instructions, and cannot exist on their own. Flagella are believed to originate
from motile anaerobes that formed a symbiotic relationship the with the
anaerobic heterotroph and mitochondrion. These three plus photoautrotriphic
cells combine in various combinations to form the different types of organisms
that exist today. Nostoc (a blue-green alga) is often found living in a
symbiotic relationship with a liverwort. Nostoc can fix nitrogen, and the
liverwort provides a protective environment. About 4/5 of all vascular plants
have a symbiotic relationship with mycorrhizae. Lichens are fungi and algae in
a symbiotic relationship, first reported by Beatrix Potter. And one of the most
fascinating symbiotic relationships is that between ants and acacias. The ants
obtain their food from the plant and in return kill any insects that attempt to
feed on the acacia and attack other plants that touch it.
|Pinus sylvestris. Alternation of generations refers to the manner in which in a life cycle the
sporophyte is succeeded by the gametophyte and then in turn by the sporophyte.
In the life cycle of Mnium hornum, and all other bryophytes, the haploid
gametophyte is the visible plant, the diploid sporophyte being dependant on the
gametophyte for nutrition etc. The main means if dispersal is when the haploid
spores are blown by the wind, the sperm are motile, but fertilisation and
transportation requires water. In Pinus, and most other plants, it is the
diploid sporophyte that is visible, the megaspore stays attached to the tree,
and is dependant on it for nutrients. The diploid seed falls to the ground
whilst still in the cone, further dispersal can occur by animals. The
microspores are tiny and may be dispersed great distances by wind.
||Pollination by deceit
Mimicry, e.g. the hammer orchid mimics a female wasp. Some European orchids mimic female bees.
Deception, Rafflesia sp. and other similar species smell like rotting meat so deceiving flies into thinking the plant is a food source for their larvae.
Prey mimics, Epipactis consimilis (orchid) has little bumps resembling aphids. Hoverfly larvae eat aphids, so the female hoverfly lays her eggs on the labellum and pollinates the flower.
Aggressive mimicry, some arums lure flies deep into the flower with the odour of decay. The flies are then trapped for some time during which the flower is pollinated, then the flies are released.
|Stephen Jay Gould on Natural Selection.
Stephen Jay Gould said that Darwin based the theory of Natural Selection on "two undeniable facts and an inescapable conclusion" - here they are:-
Fact 1. Individuals in a population vary in many heritable traits.
Fact 2. Every species or population has the potential to produce far more offspring than its environment can support with resources (food, space, etc.). This overproduction leads to an inevitable struggle for existence among individuals in the population/species.
Conclusion. Individuals with heritable traits best suited to the current local environmental conditions generally leave a disproportionately large number of offspring. This increases the representation of these heritable traits in the next generation. Darwin called this natural selection, and saw this as the cause of evolution.
Interactions between species and the effects.
+ = beneficial effects, - = harmful effects, 0 = neutral effects
Effect on species A
Effect on Species B
|Problems in designing new approaches to insect control
There are three main problems to overcome and no insecticide has overcome all three yet.
1) Avoidance of insect resistance.
2) Specificity. In some cases it would be preferable if the insecticides were species specific.
It is unlikely that a neurotoxic pesticide will ever be formulated to overcome all three problems for any length of time as resistance will always occur.
1) Avoidance of resistance. This can be done by not putting the insect under selection pressure to develop resistance, e.g. using a variety of insecticides in an integrated pest management programme where insecticide use is only one part of the programme.
2) Specificity to the degree of species is difficult and perhaps only pheromones and parasitoids will be species specific. Bacteria, e.g. Bacillus thuringiensis can be specific the the level of family, but even here resistance had arisen through incredibly bad pest control. A watercress crop was grown year-round in glasshouses for 3 -4 years. During this time 40-50 applications of Bt strain for Lepidoptera was sprayed - surprise, surprise the target moth began to show resistance!
3) Persistence can usually be induced by chemical means, but persistence is the reason DDT was banned. So persistence must be modified so that the insecticide is just persistent enough to harm the target and not be present in the food chain. Antifeedant, parasitic nematodes, chitin inhibitors, and polyhedrose viruses can be persistent as they harm only the target.
Another problem is the investment of time and money a company must make before its product can be sold on the open market and make a profit before resistance is found. It costs tens of millions of pounds to get one successful insecticide through the trials, then the advertising and marketing before it starts to make a profit.
|Adaptive value of animal colours.
1) Concealment from predators.
2) Advertisement; to frighten or startle potential predators, e.g. the eyespots of the peacock butterfly; to maintain territory or social rank, e.g. male peacock feathers; to announce sexual receptivity e.g. baboon rump patches.
3) Disguise as something unpalatable, e.g. the caterpillar of the comma resembles a bird dropping; or as something inanimate, e.g. stick insects.
|Stages in animal cell division.
Interphase. 2 pairs of centrioles form by replication from a single pair. Around these form microtubules. Chromosomes duplicate, but cannot be distinguished individually as they are still in the form of loosley-packed chromatin fibres.
Prophase. Nucleoli disappear. Chromatin fibres fold and coil until individual chromosomes become visible. Each chromosome has duplicated chromatids joined at the centromere. Mitotic spindle forms between 2 pairs of centrioles. Later the nuclear envelope fragments.
Metaphase. Centriole pairs are at opposite poles. Centromeres of all chromosomes are aligned with long axes at right angles to spindle axis.
Anaphase. Paired centromeres move apart separating sister chromatids. Kinetochore fibres shorten pulling chromosomes to either pole. Poles move further apart each having a complete collection of chromosomes.
Telophase. Polar fibres elongate. Nuclear envelopes form. Chromatin in each chromosome starts to uncoil. 2 nuclei.
Cytokinesis. Cytoplasm divides. Cleavage furrow pinches and divides cell into 2.
1. Chemoreception. This is the most primitive and universal sense in the animal kingdom. It can be split into two types; contact chemoreceptors which orient an animal away from or towards the source, and distance chemical receptors including the sense of smell and pheromones.
This includes touch, vibration and motion. These receptors allow the animal to move, feel and interact with its surroundings.
This is vision. These receptors can be simple, light-sensitive cells on the body surface of the animal, or more organised eyes such as the compound eyes of insects and cephalopods.
A species whose disappearance from a community tranforms the populations of the other species in the community. For example the sea urchin Diadema antillarum's die off in the Caribbean led to a huge increase in the algal community, and a decrease in productivity and diversity of the coral reef. The removal of the starfish Pisaster ochracecus from a Pacific coastal community led to a population explosion of the mussel Mytilus californicus and the disappearance of nearly all other animals and algae.