20) Photosynthesis and environmental management Flashcards
Give 5 key adaptations of chloroplasts
- thylakoid stacking - large surface area for light dependent reactions
- organisation of photosynthetic pigments into photosystems - maximises efficiency of light energy absorption
- grana surrounded by stroma - products from light-dependent reactions can pass directly to enzymes catalysing light-independent reactions
- inner membrane less permeable than outer and is embedded with transport proteins - control over substances entering stroma from cell cytoplasm
- contain own DNA and ribosomes - can produce some of their photosynthetic proteins rather than importing them from the cell cytoplasm
Define grana (granum sing.)
thylakoid stacks; site of light-dependent stage
Define thylakoid
flattened membrane compartment
Define stroma
fluid-filled matrix with enzymes; site of light-independent stage
State 6 key parts of a chloroplast
grana thylakoid stroma intergranal lamella outer membrane inner membrane
Describe the 4 steps of the light-dependent stage
- photosystem converts light energy into chemical energy (photons of light are absorbed by pigment molecules and energy is funnelled down the light-harvesting complex to a chlorophyll a molecule which is oxidised and transfers electrons (excited to a higher energy) to a primary acceptor and subsequent electron carriers
- energy is released as the electron transport chain progresses (as each new electron carrier occupies a lower energy level) and is used to pump protons across the thylakoid membrane, establishing a proton gradient
- protons flow through ATP synthase (chemiosmosis) enabling the regeneration of ADP -> ATP, used in the Calvin cycle (light independent)
- protons reduce NADP in the stroma to NADPH, used in the Calvin cycle
Define photophosphorylation
the harnessing of light energy to produce ATP
Define photolysis
an enzyme-catalysed reaction of photosynthesis that uses light energy to split water
Give an equation for photolysis
2H2O -> 4H+ + 4e- + O2
Where do the electrons produced by photolysis go?
replace those lost by the oxidation of chlorophyll a in photosystem II
Where does the oxygen produced by photolysis go?
diffuses out of the leaves through stomata or is used by plant cells in aerobic respiration
Describe the 7 steps of the light-independent reaction (Calvin cycle)
- carbon dioxide diffuses into the stroma
- ribulose bisphosphate, RuBP (5C) is converted to 2 molecules of glycerate 3-phosphate, GP (3C) - catalysed by the enzyme RuBisCO
- 2 x GP are reduced – (ATP -> ADP + Pi) –> 2x triose phosphate, TP (3C)
- this provides the reducing power to regenerate NADP from NADPH, which then returns to the light-dependent stage
- some TP, as a source of common respiratory substrates, is converted to useful molecules
- majority of TP is used to regenerate RuBP, which requires an extra ATP -> ADP + Pi
Give a term to describe what happens to CO2 in the Calvin cycle
CO2 is fixed - converted from a gas to organic molecules
How many molecules of ATP are required in the Calvin cycle and what for?
3 molecules overall
for carbon fixation reactions and the production of carbohydrates
Describe what may happen to the small amount of TP that is converted into useful molecules
2TP -> 6C sugars e.g. glucose + fructose
converted to glycerol which forms triglycerides with fatty acids
Define limiting factor
a variable that limits the rate of a particular process
State 6 limiting factors of photosynthesis
light intensity, wavelength and duration
CO2 concentration
temperature
pH
Explain light intensity as a limiting factor of photosynthesis
- positive correlation with rate of ATP + NADPH production in light dependent reactions;
- GP concentration increases; RuBP and TP concentrations decrease with increased light intensity
Explain light wavelength as a limiting factor of photosynthesis
in some environments and laboratory conditions plants might not receive all wavelengths to an equal extent
Explain light duration as a limiting factor of photosynthesis
daylight hours
Explain CO2 concentration as a limiting factor of photosynthesis
- RuBP increases, GP limited with increasing concentration of CO2
- optimum = 0.1%, atmospheric = 0.04%
Explain temperature as a limiting factor of photosynthesis
- high temperatures increase kinetic energy > denatures enzymes
- little effect on light-dependent stage as few enzymes required, except photolysis
- whereas, each light-independent reaction is catalysed by an enzyme so temperature has a more significant impact
Explain pH as a limiting factor of photosynthesis
can denature proteins
Describe the use of a photosynthometer as a method for investigating the factors affecting photosynthesis
- rate of oxygen production is used as a measure of photosynthetic rate
- O2(g) bubbles collected in capillary tube and volume of O2 evolved (length of bubble x Pi x r^2) per unit time calculated
- adding sodium hydrocarbonate to water generates CO2
Define DCPIP (2,6-dichlorophenol-indophenol)
a blue dye that acts as an electron-acceptor which becomes colourless when reduced
How can DCPIP be used to investigate the factors affecting photosynthesis?
enables reducing agents produced in the light-dependent reactions of photosynthesis to be detected
Give a method for the use of DCPIP to investigate the factors affecting photosynthesis
- grind leaves in ice-cold sucrose 2% solution
- centrifuge to form a pellet (high chloroplast concentration) and supernatant (low chloroplast concentration)
- store leaf extract in ice-cold water bath
- DCPIP solution + leaf extract pellet (light) -> generates electrons, DCPIP decolourises, green colour of chloroplasts
Give 4 controls that could be used when using DCPIP to investigate the factors affecting photosynthesis
DCPIP solution + leaf extract pellet (dark)
DCPIP solution + sucrose solution (light)
distilled water + leaf extract pellet (light)
DCPIP solution + supernatant (light)
What may you observe when using the control, DCPIP solution + supernatant (light), when using DCPIP to investigate the factors affecting photosynthesis? Why?
decolourise slowly
may contain a low concentration of chloroplasts
Define compensation point
the light intensity at which the rate of photosynthesis matches the rate of respiration
Above compensation point…?
CO2 is taken up
plants increase in biomass
Below compensation point…?
CO2 is given out
When is compensation point normally reached?
in early morning and evening
In relation to compensation point, why will increased daylight hours increases growth rates?
compensation point is exceeded for longer periods when day length increases
How can you investigate compensation point?
with hydrocarbonate indicator solution
atmospheric CO2 concentration = red
below compensation point, pH drops = yellow
above compensation point, pH rises = blue
Nitrogen cycle: nitrogen in atmosphere -> ammonium ions
nitrogen fixation by free-living bacteria using Azotobacter
Nitrogen cycle: nitrogen in atmosphere -> nitrogen-containing molecules e.g. proteins in producers
nitrogen fixation by mutualistic bacteria e.g. Rhizobium (live in mutualistic relationships with plants and fix N with enzyme nitrogenase in return for carbohydrates)
Nitrogen cycle: ammonium ions -> nitrite ions, NO2 -
nitrification by nitrifying bacteria, Nitrosomonas
oxidation reaction releases energy
Nitrogen cycle: nitrite ions, NO2 - -> nitrate ions, NO3 -
nitrification, Nitrobacter
oxidation reaction releases energy
Nitrogen cycle: nitrate ions, NO3 - -> nitrogen in atmosphere
denitrification by denitrifying bacteria (anaerobic and favour waterlogged soils lacking O2)
poorly aerated soils with high H2O concentration reduce availability of N containing compounds and limits growth rate
Define denitrification
conversion back to N(g)
Define nitrogen fixation
atmospheric N is converted into N-containing compounds e.g. ammonia, by nitrogen-fixing bacteria
Nitrogen cycle: nitrate ions, NO3 - -> nitrogen-containing molecules e.g. proteins in producers
absorption
Nitrogen cycle: nitrogen-containing molecules e.g. proteins in producers -> nitrogen-containing molecules e.g. proteins in consumers
feeding and digestion
Nitrogen cycle: nitrogen-containing molecules e.g. proteins in producers -> ammonium-containing molecules e.g. proteins in decomposers (saprobiotic microorganisms)
death
Nitrogen cycle: nitrogen-containing molecules e.g. proteins in consumers -> ammonium-containing molecules e.g. proteins in decomposers (saprobiotic microorganisms)
death and excretion
Nitrogen cycle: ammonium-containing molecules e.g. proteins in decomposers (saprobiotic microorganisms) -> ammonium ions
ammonification by saprotrophic bacteria
Define ammonification
breakdown of proteins, nucleic acids and vitamins from dead organisms and nitrogenous waste to produce NH3 and NH4 + and add them to soils
Define histology
microscopic tissue structure
The histology of a root nodule can be studied by…?
treating a thin section with crystal violet and observing under a light microscope
the central region stained purple contains nitrogen-fixing bacteria and is surrounded by a cortex
Define bioluminescence
visible light generated by an organism
What does a food chain illustrate?
the transfers of energy between organisms within an ecosystem
Define ecosystem
the organisms and non-living components of a specific area and their interactions
Producers convert _ energy -> _ energy and are eaten by _.
light
chemical
primary consumers
Define trophic level
each stage within a food chain
Give an equation for energy transfer
energy transfer = (energy available after transfer / energy available before transfer) x 100
Why is some energy lost between trophic levels?
inedible / indigestible parts
excretory waste
heat from respiration
Define ectotherms, give an example and how they affect their food chain
organisms which rely on external sources of heat to regulate body temperature
fish
improve the efficiency of energy transfer in their food chain
Give two ways of improving efficiency and sustainability in food production
fish farming / aquaculture
promoting consumption of species low in the food chain
Define ruminants
animals that digest plant material slowly, in specialised stomachs, and regurgitate food to chew it a second time
A ruminant stomach is an ecosystem with _?
its own specific abiotic conditions (anaerobic environment)
Name 4 key parts of a ruminant stomach
rumen
reticulum
omasum
abomasum
Describe the rumen of a ruminant stomach
contains microorganisms able to digest cellulose and carbohydrates -> disaccharides and monosaccharide, other bacteria convert these molecules into fatty acids
Describe the abomasum of a ruminant stomach
acts like a human stomach by secreting hydrochloric acid and protease enzymes, which digest bacterial proteins into amino acids
Define primary productivity / gross primary productivity, GPP
the energy fixed by photosynthesis over the course of one year (MJm-2 yr-1)
Define net primary productivity, NPP
the rate of production of new biomass in producers (mass per unit area per year)
Give an equation for net primary productivity
NPP = GPP - respiration loss
State 7 manipulating factors which increase energy available to consumers
light temperature water nutrients competition pests disease
Explain how light can be a manipulating factor which increases energy available to consumers
- under light banks in greenhouses (constant, optimal light intensity and duration)
- timing of sowing (max. leaf area during optimum conditions photosynthesis)
- sowing density (prevent overshadowing)
Explain how temperature can be a manipulating factor which increases energy available to consumers
regulated warm
Explain how water can be a manipulating factor which increases energy available to consumers
irrigation drought-resistant variants genetically modified (GM)
Explain how nutrients can be a manipulating factor which increases energy available to consumers
rotate crops
nitrogen-fixing crops (replenish nitrate levels in soil within rotation cycle)
application of fertilisers (if organic, increase water-holding capacity and structure)
State how competition can be a manipulating factor which increases energy available to consumers
herbicides
Explain how pests can be a manipulating factor which increases energy available to consumers
pesticides - maintain leaf area for photosynthesis
GM pest-resistant plants (Bt gene)
Explain how diease can be a manipulating factor which increases energy available to consumers
fungicides
GM disease-resistant crops
Define secondary productivity
the rate at which animals convert the chemical energy in the plants that they consume into their own biomass
State and explain 5 factors to increase secondary productivity
- antibiotics - reduce energy expenditure of immune systems by reducing infections
- zero grazing (limiting movement) - increase energy into growth
- maintenance of a constant temperature - reduce energy for thermoregulation
- selective breeding - increase productivity
- harvesting animals before adulthood - invest a greater percentage of energy into growth than adults
Intensive rearing of livestock produces large quantities of _ that requires _
waste safe storage (prevent leaking and eutrophication
Extensive farming requires less _ than intensive farming?
chemicals
money
labour
Give 4 methods to conserve ecosystems
crops (seeds and nectar) to attract birds, bees + butterflies maintain hedgerows (shelters and food sources) maintain dry stone walls (habitat for moss and lichen) creating buffer strips between intensive agriculture and natural habitats
Define succession
natural development of an ecosystem / directional change in a community of organisms over time
Define deflected succession
the changes resulting from human activities (land management, farming) that can prevent a climax community from forming and instead produce a stable community, plagioclimax
Succession: _ conditions, _ species diversity + _ -> _ conditions, _ species diversity + _
hostile low instability less hostile high stability
State a typical sequence of succession
barren land -> pioneer species / primary colonisers e.g. lichen -> secondary colonisers e.g. mosses -> tertiary colonisers e.g. grasses -> scrubland e.g. shrubs + small trees -> climatic climax e.g. forest
State a typical sequence of deflected succession
barren land -> pioneer species / primary colonisers e.g. lichen -> secondary colonisers e.g. mosses -> tertiary colonisers e.g. grasses -> plagioclimax e.g. farmland
Give 3 reasons for the deforestation of deciduous woodland
non-native trees (timber and fuel)
agricultural spaces
deteriorated soil dominated by heather
Suggest 3 reasons why plants cannot use the ATP produced in the light-dependent stage of photosynthesis as their only source of ATP
photosynthesis only occurs in the light
the rate of production is insufficient to supply plant with concentrations of ATP required
some plant cells lack chloroplasts and would not be able to generate ATP
Name two useful molecules that can be produced from GP and describe one way in which a plant can use each molecule
fatty acids uses (when combined with glycerol) include: plasma membrane formation; waterproofing e.g. waxy cuticles; energy source
amino acids uses: protein formation e.g. enzyme production
Suggest the role of DNA and ribosomes in a chloroplast
produce photosynthetic pigments
DNA codes for genes/proteins (e.g. enzymes used), for electron carriers, ATP synthase
Explain how the 3 reaction pathways, glycolysis, Calvin cycle and Krebs cycle are able to work independently of each other in the same leaf cell
compartmentalisation take place in different parts / organelles: glycolysis - cytoplasm Calvin cycle - chloroplast Krebs cycle - mitochondria
