Bio 173 - Exam #2 Textbook Assigned reading notes

4/26/24 - 29.5 & 46.4

• Uptake of water and nutrients by roots

  • plants obtain nutrients from the soil

    

  • nutrient uptake by roots is highly selective

    • uptake of water and nutrients takes place in actively growing roots, the root hairs

    • the endodermis and Casparian strip prevent any unwanted material to travel through the xylem and phloem

  • nutrient uptake requires energy

    • the mitochondria of the root cell must respire at a high rate to provide the energy needed for nutrient uptake

    • root and root hairs need to elongate because both structure increase the volume of soil from which a root can obtain nutrients when the diffusion is not being driven in the plant’s favor

    • soil is more likely to bind to positively charged molecules which are necessary components to the plant so it will release compounds that make the rhizosphere more acidic to obtain the highly immobile nutrients

  • mycorrhizae enhance nutrient uptake

    • ectomycorrhizae & endomycorrhizae

    • fungal networks have better access between soil particles since they are very thin, greatly increase the absorptive SA in contact with the soil

    • the fungi can secrete enzymes that make soul nutrients more available

    • these associations can be costly: 4%-20% of C supply

• symbiotic nitrogen-fixing bacteria supply nitrogen to both plants and ecosystems

  • nitrogen fixation is a process that some bacteria and archaea convert N2 gas from the atmosphere into ammonia

  • a root nodule is formed when chemicals in the soil trigger the root cells to divide where the nitrogen-fixing bacteria are housed to supply the plant with a source of nitrogen while it receives carbohydrates (25%) in return

• nitrogen availability has a large impact on agricultural productivity

• Nitrogen-Cycle

  • assimilation: primary producers converting atmospheric N2 to nitrate, ammonia, or ammonium in the soil

  • ammonification: the return of biological nitrogen to the environment as ammonia during the breakdown of organic matter by decomposers

  • denitrification: the process in which bacteria use nitrate as an electron acceptor in CR (anaerobic) to release N2 to the environment

  • nitrification: the process by which chemoautotrophic bacteria oxidize ammonia to nitrite and then nitrate

  • anammox: energy metabolism found in some bacteria in which ammonium ions are oxidized by nitrite with N2 gas as a byproduct

    • anaerobic ammonia oxidation

  

• Phosphorus cycle

  • mainly found in rocks, does not provide electron donors or electron acceptors for energy metabolism

  • enters the food web as phosphate ions released by rocks from chemical weathering and then assimilated by primary producers

  • transferred from organisms by consumption and decomposition until to returns to geologic reservoirs by accumulation in sediments

4/30/24 & 5/2/24 - 30.4, 30.5, 30.6

• plant hormones

  • hormones affect the growth and differentiation of plant cells

    • two roles: they help establish and maintain basic patterns of the plant body plan and they coordinate growth in different parts of the plant in response to both external and internal factors

    • an example includes leaf arrangement and branch formation and the length of elongation for the internodes

  

  • polar transport of auxin guides the development of vascular connections between leaves and stems

    • this hormone has a role in patterning results that is controlled by the net movement of this hormone creates region of high and low conc

  • gibberellins stimulate internode elongation by reducing the force needed to cause cell walls to expand

  • cytokinin’s control the outgrowth of branches

    • this hormone is produced in the plant meristems and axillary buds

    • the shoot apical meristems suppress the growth of axillary buds (apical dominance)

• the environmental context of growth and development

  • plants rely on photoreceptors to provide information of their surroundings

    • photoreceptors sense the availability of light needed to drive photosynthesis

    • mechanical receptors sense physical influences

    • chemical receptors detect the presence of certain chemicals / chemical gradients

  • plants orient the growth of their stems and roots by light and gravity

    • trophism: the bending of an organism in response to a directional signal such as light of gravity

    • plant stems are positively phototrophic (toward the light)

    • plant stems are negatively gravitropic (growth upward against gravity)

    • plant roots are positively gravitropic and negatively phototrophic

  • the photoreceptors that trigger phototropism absorb blue wavelengths of light

    • if only exposed on one side of the plant, only photoreceptors that side are activated

    • conc of auxin will be higher on the side with more shade and lower on the side intercepting the blue light (this is because auxin stimulates cell expansion in stems so the shoot grows faster on the shaded side than the illuminated side ~ causes the bend TOWARDS light)

  • the accumulation of auxin on the lower surface causes stems to bend up and roots to turn down

    • plants are able to tell which way is down due to starch globules called statoliths that are specialized gravity-sensing cells in the root cap which orient the growth of the root downwards

  • seeds can delay germination if they detect the presence of plants overhead

    • as sunlight passes through leaves, the plant absorbs the red wavelength by the chlorophyll but the far-red wavelengths aren’t

    • the plant can detect higher levels of competition if the far-red wavelengths are being reflected by other plants around it

    • phytochrome is a photoreceptor that switches back & forth between two stable forms red light wavelength: Pr and Pfr (active form)

    • Pfr is converted to Pr very slowly at night by moving from the cytoplasm to the nucleus where it gets altered of gene pattern expression

  • plants grow taller and branch less when growing in the shade of other plants

  • roots elongate more and branch less when water is scarce

    • roots penetrate further into the soil when no available water at their current location and being deeper in the substrate increases the plant’s chances of reaching moister soil

    • if there is a water shortage or conditions alike a drought, the roots will secrete abscisic acid which stimulates the stomata to close and conserve the water supply

  • exposure to wind results in shorter and stronger stems

    • the movement of the stem by external factors triggers an increase in the ethylene hormone which makes the plant having wider diameter stem

    • thigmotropism is a developmental response to a mechanical stimulus arising from physical contact

• timing of developmental events

  • flowering time is affected by day length

    • photoperiodism is the effect of the day length on physiological or developmental processes ~ the effect of day length on flowering

    • a short-day plant is a plant that flowers only when the day length is less than a critical value and they measure the length of the dark period (usually bloom late-summer)

    • a long-day plant is a plant that flowers only when the duration of the light period exceeds a critical value and they measure the length of the dark period (usually bloom late spring or early summer)

    • a day-neutral plants is a plant that flowers independently of any change in the day length

  • vernalization prevents plants from flowering until winter has passed

    • vernalization is a long prolonged period of exposure to cold temps necessary to induce flowering in some plants

    • these plants “remember” winter conditions due to chromatin modifications

  • plants use day length as a cue to prepare for winter

    • day length can trigger developmental events like the change of seasons prompts the plant to form storage organs in their roots or overwintering buds to prepare for winter

    • the plant will stop producing photosynthetic tissue and instead form bud scales which accompanies a metabolic change in the plant that allow meristems to remain dormant over winter

5/3/24 - 40.2

• excretion of wastes

  • excretion is the elimination of waste products and toxic compounds from the body

  • the kidneys function to maintain water & electrolyte balance and they eliminate waste products

  • the excretion of nitrogenous wastes is linked to an animal’s habitat and evolutionary history

    • one form of nitrogenous waste is ammonia NH3 which can disturb the pH balance of cells and damage neurons, can be very toxic

    • animals had to evolve biochemical pathways to convert ammonia to a less toxic form, urea which requires energy to dilute

    • ammonia can also be converted to uric acid which is the form of N waste reptiles and birds excrete which eliminates any water loss or need to dilute their waste with their water supply

  • excretory organs work by filtration, reabsorption, and secretion