Animal and Plant Biology Flashcards
Briefly explain how the evolution of plants contributed to the diversity of life on the planet
The evolution of land plants triggered a fall in atmospheric CO2 and global temperature. This also enabled plants to evolve larger, broader leaves.
The success and diversification of plants led to further reduction in CO2 and temperatures, as well as further increases in atmospheric O2 enabling animals to establish themselves on land.
Later, the evolution and diversity of Angiosperms, or flowering plants, had a significant impact on the number and diversity of insects and terrestrial arthropods by
producing more diverse opportunities of food and nutrition (such as seeds and nectar)
Briefly describe an example where experimental evidence has been used to demonstrate that increased pollination efficiency promotes outbreeding
A good example is an experiment using Antirrhinum which has flowers that are relatively large and can be only opened by bees.
Antirrhinum emit a volatile ester called methyl benzoate, the scent exclusively attracts bees.
The scent is produced in the highest quantities when bees are most active at midday. The scent is produced from petal tissue closest to the opening of the flower,
which encourages bees to enter the corolla tube.
The peak of scent production coincides with the dehiscence of the anthers and ripening of the pollen grains, and prior to the stigma becoming receptive to pollen.
This strategy is also successful because it targets a single pollinator. Bees show an increase in the frequency of visits to a different Antirrhinum plants that is dependent on these scent emissions, transferring pollen between different individual plants to promote
outbreeding
Briefly describe and explain a mechanism that enables plants to avoid inbreeding
Geranium columbinum operates a mechanism of 3 phase protogyny; in phase 1 stigmas are open to favour cross pollination, in phase 2 the first five anthers open
this again favours cross pollination (because pollen is likely transferred to other plants), but is also a fail mechanism because the stigma are still open and receptive, in phase 3 the sigmas wither after pollination, but another five anthers mature and release pollen
promoting outbreeding with other flowers. This strategy demonstrates that phased release of pollen can favour outbreeding by increasing the amount of available pollen to plants of this species via the pollinators they attract and at a point at which the female reproductive structures are receptive to pollen.
Briefly describe the experimental approach and conclusions from the original experiment that demonstrated that plants can develop systemic acquired resistance to a virus
This experiment was carried out by Frank Ross in 1961. He hypothesised that plants can gain immunity from infection by a virus to resist further attack and spread of a disease. A single leaf from a plant is infected with a virus. One week later a different leaf from the same plant is infected with the same virus. The first leaf that is infected shows necrotic lesions form the hypersensitive response. The second leaf shows no visible sign of infection or disease. Conclusion the plant has acquired immunity to the virus that is transmitted to
previously undamaged parts of the plant.
Briefly describe the experimental evidence that explains why some wild populations of chilli pepper taste ‘hot’ and others do not
It has been shown that wild chilli peppers are adapted to different environments and phenotypic variation is important in wild populations of chillies.
This variation appears balanced between different environments due to an evolutionary trade-off between the hotness of chilli peppers (due to the amount of capsaicin present in the fruit), and the density of stomata in the leaves.
Pungent plants have been shown to be much more resilient to fungal attack than non-pungent plants in wet or humid conditions. This has been examined further and evidence also suggests that even though pungent plants produce fewer seeds, they have a fitness advantage in humid or wetter climates.
In drier climates a lower stomatal density is much more advantageous because it reduces water loss. In areas where pathogens are much less prevalent, it has been shown that populations of non-pungent chilli peppers benefit more than pungent plants.
In these conditions non-pungent plants appear to use limited water resources more efficiently than than
pungent plants.
Briefly describe how CO2 uptake and water loss in plants are linked and how this
is regulated.
CO2 is taken up into the plant by the stomata and water is lost by the same route. Stomata close in response to low water sensed at the roots and open in response to light.
Consider 2 plant species, one that has short, unbranched roots and the other with a large, finely branched root system. Briefly compare the trade-offs each plant species is making between nutrient uptake and growth
The main point of this answer is demonstrate that you understand how investment in non-photosynthetic tissues such as roots, may affect growth.
The plant with a large root system invests a lot of carbon in root, but in doing so, increases surface area, and will take up enough nutrients to fuel photosynthesis and growth.
The plant with a poor root system may lose less carbon to growing roots but if soil nutrient concentrations are high, then growth and photosynthesis should not be affected. Alternatively, these species are more likely to spend additional carbon on nutrient acquisition methods, eg mycorrhization or cluster roots
Describe how the arrival of action potentials at a chemical synapse leads to neurotransmitter release.
The arrival of action potentials leads to the opening of voltage-gated calcium ion channels. Calcium ions enter the axon terminal, and the increased calcium ion concentration leads to the fusion of vesicles containing neurotransmitter molecules with the presynaptic membrane, thereby releasing the neurotransmitter.
Explain how exposure of the postsynaptic membrane to neurotransmitter molecules can inhibit the generation of action potentials in the signal-receiving neuron.
Binding of neurotransmitter molecules to receptors at the postsynaptic membrane leads to the opening of ion channels. If the opening of these channels allows an
outflux of positively charged ions or an influx of negatively charged ions, this leads to membrane hyperpolarisation. The hyperpolarisation counteracts any depolarisation that could trigger the generation of action potentials.
What are the three key characteristics of a reflex?
A reflex is an automatic, rapid and predictable response to a stimulus
How does the formation of 4-carbon organic acids increase the efficiency of water use in both CAM and C4 plants?
CAM plants open their stomata at night when rates of evaporation are low and close during the day to conserve water. At night CO2 is combined with 3-carbon PEP to form 4-carbon organic acids that are stored in the vacuole. During the day these 4-carbon organic acids are converted back to PEP and CO2, providing CAM plants with a source of CO2 for photosynthesis, even though their stomata are closed.
The production of 4C organic acids by C4 plants results in an increase in the concentration of CO2 in the bundle sheath cells. The high concentration of CO2 in the cells makes it unlikely that rubisco will use O2 as a substrate, preventing the loses in energy and reduced carbon association with photorespiration.
How do the male and female gametophyte generations differ in seed plants?
The male gametophyte develops within the spore wall, forming pollen. Following pollination, the male gametophyte develops a pollen tube that grows through the ovule to deliver male gametes to the egg.
The female gametophyte grows to fill the entire sporangium and is never dispersed.
Seed plant gametophytes are never free-living all of the resources that fuel the growth of both male and female gametophytes come from the sporophyte generation
Name three advantages of seeds over spores in terms of the probability that the next sporophyte generation will become successfully established.
Compared with spores, seeds can store more resources, slow down their metabolism, and exhibit dormancy, all of which aid their dispersal.
From what plant structure(s) is a fruit derived?
A fruit forms from the ovary that encloses the seeds, and in some plants it also forms from other parts of the flower such as the petals and sepals.
Describe the process by which stomata open
- Light falls onto guard cell
- H+/ATPase pump is activated in plasma membrane causing H+ to move out of the cells and K+ to move in
- Starch is metabolised to glucose and malate
- Both result in a fall in water potential for the cell
- Water moves into the cell via osmosis - causing them to swell
- Unequal thickening of the cell walll causes the guard cells to expand outwards, opening the stomatal pore
