Flashcards in The Wood-wide Web Deck (67):
What allows the transfer of organic compounds between trees in the wood wide web? What might the implications be?
Fungal strands between organisms below ground. It allows the pooling of responses across communities.
What are the survival implications from pooling resources via the wood wide web on seedlings?
Seedlings may be able to absorb nutrients from more mature plants nearby. While they are shaded and unable to successfully photosynthesise themselves.
Is their any evidence for plants displaying altruism?
This is a source of some debate. Some scientists believe trees may know when they are growing near a close relative (so compete less) by virtue of root exudates.
Briefly explain the development of plant-fungus mutualism.
Plants may benefit from pooled resources via fungus. If fungus receive nutrients, but if they take too much they are harmful and repelled. A balance must be struck.
Explain mutualism, including it's symbol.
(+ +) mutualism positively affects both species involved
An organism which lives on another organism as a parasite, causing disease to the host
Explain predation and parasitism including its standard symbol.
(+ -) one species gains while the other looses. This is the standard 'predator hunts prey' interaction. The predator is a consumer.
Explain commensalism including its standard symbol.
(+ 0) one species benefits but the other isn't affected. For example, bromeliads on tree branches.
Explain the difference between competition and amenalism.
Competition (- -) is an interaction where both species have the potential to out-compete each other. Amenalism (- 0) is where one species is harmful to others without gaining. Walnut trees secrete toxins preventing other plants from growing near by.
What main similarity does fungus have with animals?
The presence of the biological polymer chitin. This is found in fungal cell walls and insect exoskeletons, but not in plants
List the major fungal groups
Zygomycota, Glomeromycota, Ascomycota, Basidiomycota & Chytridiomycota.
Outline the defining features of Chytridiomycota.
Fungi evolved from this early free-swimming form. Zoospores still display the single flagellum. Found in the guts of rumen where they aid digestion. Also know to cause disease in frogs.
Outline the defining features of Zygomycota fungus.
Second stage in fungal evolution. Poses characteristic hyphae with multiple nucleus within the single very long cell. Hyphae grow radially as central resources are depleted giving rise to 'fairy rings' of mushrooms.
The characteristic of some fungi in which multiple cells coalesce to form a continuous cytoplasm containing multiple nuclei.
Define Glomeromycota fungus.
Usually live in association with plant roots. Most often mutualistically but occasionally as pathogens. They spread out for many meters in the soil and also penetrate plant roots where they occasionally form storage organs called arbuscule.
Outline the similarities between the fungal orders Ascomycota & Basidiomycota
They are the mushrooms and toadstools we commonly know best, producing large fruiting bodies to disperse their spores, their myliecal threads spread for meters under the soil unseen.
Outline the reproductive differences between the fungal orders Ascomycota and Basidiomycota
Ascomycota create their spores internally then inject them into the atmosphere. Basidiomycota create their spores externally and release them gently via gravity until they are carried by the wind.
Amoebozoa, Opisthokonts and possibly Apusozoa. Single celled eukaryotes with flagellum or ameboid movement.
What is the main difference in how fungi and animals absorb nutrition?
Fungi absorb nutrients through their cell walls rather than through ingestion. They secrete enzymes straight into the medium they are growing through.
Name the three main types of fungus nutrition
Saprotrophy, necrotrophy & biotrophy.
The use of dead organic matter for nutrition. Method of nutrition by deco posers such as fungus and bacteria.
Fungus which kill living cells in order to digest them. Moulds on fruit.
Fungal consumption of nutrients out of living cells without killing them. For example, oral thrush & athletes foot.
Explain the origin of the concept of the wood wide web
The discovery made that organic compounds move in both directions between different organisms. (The examples studied were the Douglas fir and paper birch)
Outline the coevolution of plants with biotrophic fungus
Coevolution generates the adaptation of defence mechanisms. Plants produce anti fungal toxins which interfere with fungal metabolism or enzymes which degrade fungal cell walls.
What are phytoalexins?
Anti fungal toxins produced in the tissues of plants.
Explain hypersensitive fungal response in plants
Plants produce acute anti fungal toxins, such as hydrogen peroxide, which kill both fungal cells & the plants own tissue around the site of infection. This isolates the fungal spread.
Why is humidity important in determining the rate at which fungus digest organic matter?
Extracellular enzymes require sufficient moisture in the substrate to allow them to diffuse and for the products of hydrolysis to diffuse back to the hyphae.
Contrast the relative extent of relative surface area of fugal hypha to plant roots
Fungal hyphae are longer and thinner, they may have many thousands of times more surface area, gram for gram, than tree roots. This makes them far more efficient at nutrient uptake.
What chemical do all higher organisms (eukaryotes) use as their main energy source?
ATP. Adenosine triphosphate.
What is special about the molecule ATP which allows it to be used as an energy source?
The bond which holds the third phosphate group requires substantial energy to create it. This bond can be broken to release the energy.
List some of the types of protein which can break the ATP third phosphate bond (so release energy)
Enzymes used for metabolic reactions. Transporter proteins driving active transport across cell membranes. Structural proteins which contract to drive movement (I.e. Muscles)
What is the formula for photosynthesis?
Water (H2O) + carbon dioxide (CO2) + energy (light) = Carbohydrate (CH2O) + oxygen (O2)
How have photosynthetic plants overcome the problem of storing ATP for use over night during darkness.
What is PGA? (Within the process of photosynthesis)
Phosphoglyceric acid. A simple three carbon molecule used as theraw material to build more complex carbohydrates.
Outline the different reactions taking place in plants in sunlight and in the dark.
During sunlight prosy thesis splits water molecules, releasing oxygen and retaining hydrogen. In the dark that hydrogen is then used to convert carbon dioxide into carbohydrate.
What is the Calvin cycle?
The cycle of reactions occurring in the dark during photosynthesis. Carbon dioxide is reduced and converted into sugars.
Name the enzyme used in the c3 pathway
Ribulose-biphosphate carboxylase/oxygenase. Otherwise known as Rubisco.
What is Rubisco?
Ribulose-bisphosphate carboxylase/oxygenase. The enzyme responsible for catalysing the reaction in which carbon dioxide is fixed during photosynthesis.
What is the most abundant protein on earth?
Why is rubisco referred to as the 'gatekeeper' between the organic and inorganic worlds?
It drives the primary conversion of inorganic carbon to the biosphere. It is the first major step of carbon fixation, converting atmospheric carbon dioxide into glucose.
How does rubisco incorporate carbon dioxide into the Calvin cycle? (The actual chemical process)
It adds CO2 to a five carbon sugar, RuBP (ribulose biphosphate) to produce two molecules of PGA (phosphoglyceric acid)
Why is the c3 cycle called the c3 cycle?
Because the initial product of co2 fixation is a 3 carbon molecule (PGA)
What are bryophytes?
Liverworts and mosses
Why is rubisco such an abundant protein?
It is actually rather inefficient and catalyses at a much slower rate than most metabolic reactions. It is the factor limiting the rate of photosynthesis.
What would happen if an organism mutated a more effective form of rubisco?
They would be able to convert sunlight to glucose at a far higher rate and outcompete other photosynthetic life forms. They could essentially take over the earth.
What is photorespiration?
Process by which sugar is converted back into carbon dioxide. Not for energy liberation, like in respiration, but to provide the raw materials needed by photosynthesis machinery as protection against damage during excessive light.
What is another term for the C2 cycle?
Why is the C2 cycle historically referred to as photorespiration?
It absorbs oxygen and releases carbon dioxide. It only occurs during daylight.
What causes the loss of roughly 1/4 of the carbon dioxide fixed by rubisco?
The oxygenase activity of the same enzyme (rubisco)
What is photoinhibition?
Reduction in photosynthesis resulting from excess light energy. (Causing excess ATP molecules, hydrogen ions & high energy electrons)
What defence mechanisms do plants have against photoinhibition?
The C2 cycle. Providing rubisco with enough co2 ensures the process can continue without damage.
What would render the C2 cycle redundant?
The C4 cycle, keeping the photosynthetic equipment so well supplied with co2 that dark reactions match the speed of light reactions.
Give examples of C4 plants
Maize and sugar cane.
What is the C4 pathway?
Relies on PEP carboxylase for initial fixation of co2 instead of rubisco. Works efficiently at lower concentrations of co2. Produces a 4-carbon molecule.
Why is the C4 cycle called C4? Name the molecule it produces.
It produces the 4 carbon molecule oxaloacetic acid (OAA)
Why is the C2 cycle called C2? Name the molecule it produces.
It produces the 2 carbon molecule phosphoglycolate.
What gives rhubarb and under-ripe apples their acidic taste?
OAA gives rhubarb it's flavour, OAA undergoes chemical reduction to form malic acid which causes the flavour in the apples.
What does the c4 cycle produce?
OAA (oxaloacetic acid) which reduces to form another organic acid, maltic acid.
What is the limitation of the c4 cycle?
OAA and maltic acid cannot directly enter the Calvin cycle. Plants still have to rely on rubisco to get the carbon into biosynthesis. 4 carbon molecules from c4 must be broken down to release the co2.
What benefit do c4 plants gain over c3? What is the penalty for this benefit?
They effectively eliminate the c2 cycle by keeping rubisco in their bundle sheath cells saturated with co2. The penalty is the high energy expenditure of moving malic acid.
The breaking down of a molecule into smaller molecules, usually involving the release of energy. Catabolism may be aerobic or anaerobic. Catabolism and biosynthesis together constitute metabolism.
Name the two processes which make up metabolism
Catabolism & biosynthesis.
What is radiation in an evolutionary context?
The process by which a single ancestral line gives rise to a large number of species that each specialise in a separate niche.
What cycle do all eukaryotes use for respiration, to oxidise carbohydrate into co2?
Tricarboxylic acid cycle (TCA cycle).
What is the name of the initial stage of carbohydrate respiration that occurs in the cytosol?