AqBot Exam 2: Photoreceptors/Intro to nutrients (Lecture 11)

list and define the 3 types of photoreceptors

• type 1 = single layer of photoreceptive molecules

• type 2 = multilayered membrane structure

• type 3 = very specialized

what organisms are considered to have Type 1 photoreceptors?

Chlorophyta, Ochrophyta, Cryptophyta, Haptophyta, Dinoflagellates

what organisms have type 2 photoreceptors?

Euglenophyta and Ochrophyta (Chrysophyceae)

what organisms have type 3 photoreceptors?

Dinoflagellates (Warmowiales)

what are the structures of Type 3 photoreceptors?

• Warnowiales have an Ocelloid = eyespot/photoreceptor

• Hyalosome = lens

• Cornea = derived from mitochondria

• Retinal body = derived from plastid

• *overall, detects light to detect prey

define phototaxis

when is it positive and negative?

• phototaxis = response to direction and intensity of light

  • positive = toward light

  • negative = away from light

define photophobia

response to rapid change in light intensity => swims backward, then in new direction

define gliding

moves along surface

Phototaxis: what affects the rate of flagella?

rate of flagella beats depending on cytoplasm Ca2+ concentration and flagella response is unique to each

Phototaxis: describe the process of flagella movement based on algae movement.

As the algae moves through the water, the light intensity changes so different amounts of light are reflected onto the photoreceptor => rhodopsin changes membrane potential => change in Ca2+ into the cell => changes beat of flagella

what determines strength of response?

intensity and wavelength of light determines strength of response - temperature modulates

what is the secretion of mucus affected by?

secretion of mucus helps movement towards light = desmids => positive phototaxis

Chlorophyta cell structure:

• where is the photoreceptor located?

• what is the composition of the Chlorophyta cell?

• photoreceptor is located in the plasma membrane above eyespot

• composition = rhodopsin (protein specific to different algae)

  • chromophore = 11 cis-retinal => conformation changes from cis (day time) to trans (dark) by photons

  • absorbs light by 500 nm

what is the purpose of the eyespot for photoreceptors?

• shading device bc location prevents light from coming in certain directions from reaching receptor

• structural

• contains carotenoids

what is the purpose of photoreceptive proteins for photoreceptors?

• photosensitive proteins = rhodopsin

• structural

what is the purpose of sampling strategies for photoreceptors?

• behavioral

• single receptor

• small cells are hard to compare

• swimming in helical motion helps w/ light detection

what is the purpose of trajectory control for photoreceptors?

• behavioral

• depends on swimming behavior

• asymmetrical has sharper adjustments while symmetrical is more smooth

what is the purpose of single transmission for photoreceptors?

• physiological

rhopdopsin

• what is it?

• what drives it?

• what does it use?

• what is it limited by?

• sensory protein

• light driven-proton pumps

• different from chlorophyll

• uses retinal to transport H => creates a gradient to synthesize ATP (chemical alternative to photosynthesis)

• iron-limited adaptation (bc Chl-photosynthesis requires iron)

list and define the 2 forms or Rhodopsin

• Rhodopsin A =

  • absorbs max 510 nm

  • saturates at high light intensity

  • photophobic response = won’t cross light/dark border

• Rhodopsin B =

  • absorbs 470 nm max

  • saturates at low light intensity

  • phototaxis

describe the phototactic response for Volvox spp. (a palmelloid algae in which the colony is stuck in a mucus membrane) for dark and light side

• dark side = cells of colony have normal flagellar beat frequency while cells on the light side of the colony stop/slow flagellar beating = this provides the chance so that all cells can have contact w/ light

• overall, causes the colony to spin and swim at 5mph

describe the phototaxis of Spirogyra.

• aligns toward blue light

• gliding movement along filaments

• filaments form parallel bundles, curve, form larger mat => this can be an issue if there are too many spirogyra creating mats

eyespots

• define (include appearance, location)

• describe positive/negative phototaxis

• eyespots = flagellar swelling in the transition zone b/w canal and reservoir, indicated by an orange-red lipid droplet due to beta-carotene located at the anterior portion of the cell

• phototaxis is negative w/ bright lights and positive w/ dim lights (so does NOT like bright light)

circadian phototaxis

• when does it work?

• what is it due to?

• describe migration?

• phototaxis only works during light period, SO light during dark period doesn’t cause phototaxis

• this is probably due to cell division that occurs during the dark period causing the flagella to be lost during mitosis

• migration toward the surface of mud during daylight and low tide occurs

what are the 3 types of eyespots?

1. lipid globules in cytoplasm

2. lipid globules in plastid-like structure

3. complex eyespots = Oscelloids

can phototaxis occur in organisms w/out eyespots?

yes

Cryptophyta

• describe flagella?

• describe eyespots?

• describe phototaxis?

• flagellates have an asymmetric shape

• eyespots are present in some genera = lipid granules inside chloroplast envelope

• positive phototaxis in some spp.

What are the general 4 types of nutrients plankton need?

nitrogen, phosphorous, silicon, and iron

what are the forms of nitrogen plankton need?

inorganic nitrogen = atmospheric N (N2), ammonium (NH4+), nitrate (NO3-), nitrite (NO2-)

organic nitrogen

what are the forms of phosphorous plankton need?

inorganic phosphate (PO4)

organic phosphate

what organisms are most reliant on silicon and iron?

dinoflagellates, silicaflagellates, and cocoliths

what promotes the induction of N, P, Si, and Fe in plankton environments?

fertilizers

how is nutrients important for algal spp. composition?

• the form of nutrient is important to associating spp.

• the ratio of nitrogen to phosphorous or nitrogen to silicate is important => red field ratio

what are the 5 steps of the nitrogen cycle?

1. nitrogen fixation = atmospheric nitrogen is pulled from the atmosphere into the water to undergo fixation via cyanobacteria, etc. into ammonium (NH4) or ammonia (NH3)

2. nitrification = when NH3/4 is used or converted into nitrite (NO2)

3. assimilation = NO2 is then converted into nitrate (NO3)

4. ammonification = NH3/4 and NO3 are consumed/released through excretion and byproducts

5. denitrification = low oxygen converts nitrate to atmospheric oxygen

what are the 3 general steps of the phosphorous cycle?

1. weathering = rocks are broken down

2. assimilation = organisms take the nutrients in

3. decomposition = release into the sediment

besides weathering, what are 2 other sources of phosphorous?

fertilizers and humans

what is a limiting nutrient

a nutrient that is important but is limiting bc in low supply

why are limiting nutrients limiting?

it’s such a necessity that it doesn’t last, once it’s present it’s gone and taken up

what happens when limiting nutrients spike?

all plankton will explode in population, then the resource will be diminished due to high demand and will be gone

describe the Mississippi Phosphate?

the MS Phosphate fertilizer plant made massive mounds of physical phosphorous byproduct as well as an acidic liquid form so when a hurricane hit, the sea level rose and washed out the mounds which caused blooms and destroyed the environment => became of Superfund Site by EPA => solution: closure turf (synthetic grass) closed the mounds to keep it from running off (this is only temporary)

define Superfund Site by EPA

uncontrolled or abandoned location contaminated by hazardous waste that poses significant risk to humans and environment