1. Plants and other autotrophs are the producers of the biosphere · 14/01/2019 · reactants of...

• Photosynthesis nourishes almost all of the living world directly or

indirectly.

• All organisms require two basic kinds of organic compounds 1) those used for energy and 2) those used for carbon skeletons to use to make other molecules.

• Autotrophs can produce their own organic molecules from CO2

and other inorganic raw materials obtained from the environment.

• Heterotrophs like ourselves can’t do this trick.

• Except…watch this sea slug 4 min.

1. Plants and other autotrophs are the

producers of the biosphere

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

https://www.youtube.com/watch?v=AcX2n1rC4W4

• Autotrophs can be separated by the source of

energy that drives their metabolism.

• Photoautotrophs use light as the energy source.

• Photosynthesis occurs in plants, algae, some other

protists, and some prokaryotes.

• Chemoautotrophs harvest energy from oxidizing

inorganic substances,

including sulfur and

ammonia.

• Chemoautotrophy is

unique to prokaryotes.


Fig. 9.1

• Heterotrophs live on organic compounds

produced by other organisms.

• These organisms are the consumers of the biosphere.

• The most obvious type of heterotrophs feed on plants

and other animals.

• Other heterotrophs, decomposers, feed on dead

organisms and on organic litter, like feces and fallen

leaves.

• Almost all heterotrophs are completely dependent on

photoautotrophs for food and for oxygen, a byproduct

of photosynthesis.


• Any green part of a plant has chloroplasts.

• There are about half a million chloroplasts per square

millimeter of leaf surface.

• The color of a leaf comes from chlorophyll, the

green pigment in the chloroplasts.

• Watch for 3 structural adaptations that enhance

function very similar to what we saw in

mitochondria.

2. Chloroplasts are the sites of

photosynthesis in plants


• Chloroplasts are found mainly in mesophyll cells

forming the tissues in the interior of the leaf.

• O2 exits and CO2 enters the leaf through

microscopic pores, stomata, in the leaf.

• Veins deliver water

from the roots and

carry off sugar from

mesophyll cells to

other plant areas.


Fig. 10.2

• Each chloroplast has two membranes around a

central aqueous space, the stroma.

• In the stroma are

membranous sacs,

the thylakoids.

• These have an internal aqueous space, the thylakoid lumen or thylakoid space.

• Thylakoids may be stacked into columns called grana.


Fig. 10.2

• One of the first clues to the mechanism of photosynthesis came from the discovery that the O2 given off by plants comes from H2O, not CO2.

• C.B. van Niel proposed this hypothesis.

• In the bacteria that he was studying, hydrogen sulfide (H2S), not water, is used in photosynthesis.

• They produce yellow globules of sulfur as a waste.

• Van Niel proposed this reaction:

• CO2 + 2H2S -> CH2O + H2O + 2SCopyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• He generalized this idea and applied it to plants, proposing this reaction for their photosynthesis.

• CO2 + 2H2O -> CH2O + H2O + O2

• Other scientists confirmed van Niel’s hypothesis.

• They used 18O, a heavy isotope, as a tracer.

• They could label either CO2 or H2O.

• They found that plants gave off oxygen molecules containing the 18O only when watered with the radioactive water.

• Essentially, plants split water molecules and the hydrogen is incorporated into sugar and the oxygen released to the atmosphere (where it will be inhaled and used in respiration).


• Photosynthesis is a redox reaction.

• It reverses the direction of electron flow in respiration.

• Water is oxidized and its electrons are transferred

with H+ to CO2, which is thus reduced to sugar.

• Light boosts the potential energy of electrons as they move from water to sugar.


Fig. 10.3

• The light dependent reactions convert solar energy

to chemical energy.

• The light independent reactions or Calvin cycle

incorporates (fixes) CO2 from the atmosphere into an

organic molecule and uses energy from the light

dependent reactions to reduce the new carbon piece

to sugar.

2. Photosynthesis occurs in two steps:


2.A.2.d. Explain the products and

reactants of the light-dependent

reactions of photosynthesis in

eukaryotes and the purpose of the

reaction.

2.A.2.d.5. Explain how the products of

the light reactions are connected to the

production of carbohydrates from

carbon dioxide in the Calvin cycle be

sure to include where each occurs.

• Light, like other forms of electromagnetic energy, travels in rhythmic waves.

• The distance between crests of electromagnetic waves is called the wavelength.

• Wavelengths of electromagnetic radiation range from less than a nanometer (gamma rays) to over a kilometer (radio waves).

3. The light dependent reactions convert solar

energy to the chemical energy of ATP and

NADPH: a closer look


• The entire range of electromagnetic radiation is the

electromagnetic spectrum.

• The most important segment for life is a narrow

band between 380 to 750 nm, visible light.

• It is also the most abundant segment available.


Fig. 10.5

• When light meets matter, it may be reflected,

transmitted, or absorbed.

• Different pigments absorb photons of different

wavelengths.

• A leaf looks green

because chlorophyll,

the dominant pigment,

absorbs red and blue

light, while transmitting

and reflecting green

light.


Fig. 10.6

• A spectrophotometer measures the ability of a

pigment to absorb various wavelengths of light.

• It beams narrow wavelengths of light through a solution

containing

a pigment and

measures the

fraction of light

transmitted at

each wavelength.

• An absorption

spectrum plots a

pigment’s light

absorption versus

wavelength.


Fig. 10.7

• The light dependent reaction can perform work

only with those wavelengths that are absorbed.

• In the thylakoid are several pigments that differ in

their absorption spectrum.

• Chlorophyll a, the dominant pigment, absorbs best in

the red and blue wavelengths, and least in the green.

• Other pigments

with different

structures have

different

absorption

spectra.


Fig. 10.8a

Here’s why some leaves change color.

http://www.scientificamerican.com/video/why-do-autumn-leaves-change-color-2013-10-03/

• Collectively, these photosynthetic pigments

determine an overall action spectrum for

photosynthesis.

• An action spectrum measures changes in some aspect of

photosynthetic activity (for example, O2 release) as the

wavelength is varied.


Fig. 10.8b

• The action spectrum of photosynthesis was first

demonstrated in 1883 through an elegant

experiment by Thomas Engelmann.

• In this experiment, different segments of a filamentous

alga were exposed to different wavelengths of light.

• Areas receiving wavelengths favorable to

photosynthesis should produce excess O2.

• Engelmann used the

abundance of aerobic

bacteria clustered

along the alga as a

measure of O2

production. Neat, eh?


Fig. 10.8c

2.A.2.d.1. During

photosynthesis, describe the

purpose of chlorophylls.

2.A.2.d.2. Describe the

location and connection

between Photosystems I and

II.

• Photons are absorbed by photosystems,

clusters of pigment molecules in the thylakoid

membranes.

• The energy of the photon is converted to the

potential energy of an electron raised from its

ground state to an excited state.

• In chlorophyll a and b, it is an electron from

magnesium in the porphyrin ring that is

excited.

• Look at the structure of chlorophyll.



Fig. 10.9

• In the thylakoid membrane, chlorophyll is organized

along with proteins and smaller organic molecules

into photosystems.

• A photosystem acts like a light-gathering “antenna

complex” consisting of a few hundred chlorophyll a,

chlorophyll b,

and carotenoid

molecules.


Fig. 10.11

• When any antenna molecule absorbs a photon, it is

transmitted from molecule to molecule until it

reaches a particular chlorophyll a molecule, the

reaction center.

• Next to the reaction center is a primary electron

acceptor, a molecule which removes an excited

electron from the reaction center chlorophyll a.

• This starts the light dependent reactions.

• Each photosystem - reaction-center chlorophyll

and primary electron acceptor surrounded by an

antenna complex - functions in the chloroplast as a

light-harvesting unit.


• There are two types of photosystems.

• Photosystem I has a reaction center chlorophyll,

the P700 center, that has an absorption peak at

700nm.

• Photosystem II has a reaction center with a peak

at 680nm. Which is more energetic, 680 or 700?

• The differences between these reaction centers (and their absorption spectra) lie not in the chlorophyll molecules, but in the proteins associated with each reaction center.

• These two photosystems work together to use light

energy to generate ATP and NADPH.


Untested:

✘ Specific steps, names of enzymes and intermediates of the

pathways for these processes are beyond the scope of the course and

the AP Exam.

✘ Memorization of the steps in the Calvin cycle, the structure of the

molecules and the names of enzymes (with the exception of ATP

synthase) are beyond the scope of the course and the AP Exam.

✘ Memorization of the steps in glycolysis and the Krebs cycle, or of

the structures of the molecules and the names of the enzymes

involved, are beyond the scope of the course and the AP Exam.

✘ The names of the specific electron carriers in the ETC are beyond

the scope of the course and the AP Exam.

✘ No specific cofactors or coenzymes are within the scope of the

course and the AP Exam

• During the light reactions, there are two possible routes for

electron flow: cyclic and noncyclic.

• Noncyclic electron flow, the predominant route, produces

both ATP and NADPH. Let’s watch

1. When photosystem II absorbs light, an excited electron is captured by the primary electron acceptor, leaving the reaction center oxidized. For more detail, Watch

2. An enzyme extracts electrons from water and supplies them to the oxidized reaction center.

• This reaction, photolysis, splits water into two hydrogen ions and an oxygen atom, which combines with another to form O2.


../Animations/Photosynthesis Virtual Cell.wmv

../Animations/PhotosystemII virtual cell.wmv

Mystery solved!!!

• The thing that grabs electrons from water causing

the release of oxygen was a mystery for a good

while. In 2006, Vittal Yachandra at Berkeley

figured it out to be a complex of 4 manganese

held by 5 oxygens and a calcium, all held in place

by proteins in Photosystem II.

• Artificial reproduction of this could one day help

solve the energy crisis.

3. Photoexcited electrons pass along an electron

transport chain before ending up at an oxidized

photosystem I reaction center.

4. As these electrons pass along the transport

chain, their energy is harnessed to produce ATP.

• The mechanism of noncyclic photophosphorylation is

similar to the process of oxidative phosphorylation.


2.A.2.d.3. Explain how an

electrochemical gradient of

hydrogen ions (protons) across the

thykaloid membrane is established.

2.A.2.d.4. Describe how the

formation of the proton gradient is

a separate process, but it is linked

to the synthesis of ATP from ADP

and inorganic phosphate.


Fig. 10.12


Fig. 10.16

5. At the bottom of this electron transport chain,

the electrons fill an electron “hole” in an oxidized

P700 center.

6. This hole is created when photons excite

electrons on the photosystem I complex.

• The excited electrons are captured by a second primary

electron acceptor which transmits them to a second

electron transport chain.

• Ultimately, these electrons are passed from the transport

chain to NADP+, creating NADPH.

• NADPH will carry the reducing power of these high-

energy electrons to the Calvin cycle.


2.A.2.c. Explain how different

energy-capturing processes use

different types of final electron

acceptors

- NADP+ in photosynthesis

- Oxygen in cellular respiration

• Under certain conditions, photoexcited electrons

from photosystem I, but not photosystem II, can

take an alternative pathway, cyclic electron flow.

• Excited electrons cycle from their reaction center to a

primary acceptor, along an electron transport chain, and

returns to the oxidized P700 chlorophyll.

• As electrons flow along the electron transport chain,

they generate ATP by cyclic photophosphorylation.

• But they don’t get passed to NADP, so no NADPH is

made. Watch here

• This may sound like a bad thing, but wait…


http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter10/animations.html

• Noncyclic electron flow produces ATP

and NADPH in roughly equal quantities.

• However, the Calvin cycle consumes more

ATP than NADPH.

• A little cyclic electron flow allows the

chloroplast to generate enough surplus

ATP to satisfy the higher demand for ATP

in the Calvin cycle.

• See, plants are pretty smart.


• Chloroplasts and mitochondria generate ATP by the

same mechanism: chemiosmosis.

• An electron transport chain pumps protons across a membrane as electrons are passed along a series of more electronegative carriers.

• This builds the proton-motive force in the form of an H+ gradient across the thylakoid membrane.

• ATP synthase molecules (the lollipops) harness the proton-motive force to generate ATP as H+ diffuses back across the membrane.

• Mitochondria transfer chemical energy from food

molecules to ATP and chloroplasts transform light

energy into the chemical energy of ATP.



Fig. 10.14

• The proton gradient, or pH gradient, across the thylakoid

membrane is substantial.

• When illuminated, the pH in the thylakoid space drops

to about 5 and the pH in the stroma increases to about 8.

How much difference in H+ concentration is that?

• The light-reaction “machinery” produces ATP and

NADPH on the stroma side of the thylakoid.

• The structure of the chloroplast contributes to the

efficiency of the light dependent reactions in three ways,

similar to the mitochondrion and respiration.

• Can you explain two of them that we have encountered

so far????



Fig. 10.16

• Noncyclic electron flow pushes electrons

from water, where they are at low

potential energy, to NADPH, where they

have high potential energy.

• This process also produces ATP.

• Oxygen is a byproduct.

• Cyclic electron flow converts light energy

to chemical energy in the form of ATP.


Like the Krebs Cycle, the Calvin cycle regenerates its starting material after molecules enter and leave the cycle.

• CO2 enters the cycle and leaves as sugar.

• The energy of ATP and the reducing power of electrons carried by NADPH are used to make the sugar, and their energy is thus captured in its bonds.

• The actual sugar product of the Calvin cycle is not glucose, but a three-carbon sugar, glyceraldehyde-3-phosphate a.k.a. PGAL, or G3P.

4. The Calvin cycle uses ATP and NADPH to

convert CO2 to sugar: a closer look

../Animations/Animation 10.3 Calvin Cycle.MOV

Untested:



the AP Exam.











• Each turn of the Calvin cycle fixes

one carbon.

• For the net synthesis of one

G3P/PGAL molecule, the cycle must

take place three times, fixing three

molecules of CO2.

• To make one glucose molecule would

require six cycles and the fixation of

six CO2 molecules.


• The Calvin cycle has three phases.

• In the carbon fixation phase, each CO2 molecule is

attached to a five-carbon sugar, ribulose

bisphosphate (RuBP).

• This is catalyzed by RuBP carboxylase or rubisco, the

most abundant protein in the world.

• The six-carbon intermediate splits in half to form two

molecules of 3-phosphoglycerate, or PGA, per CO2.



Fig. 10.17.1

• Using energy from ATP and

a pair of electrons from

NADPH, the PGA is

changed to G3P/PGAL.

• Had enough of this

chemistry? Just wait…



Fig. 10.17.2

• If our goal was to produce one PGAL net, we

would start with 3 CO2 (3C) and three RuBP

(15C).

• After fixation and reduction we would have six

molecules of PGAL (18C).

• One of these six PGAL (3C) is a net gain of

carbohydrate.

• This molecule can exit the cycle to be used by the

plant cell.

• The other five (15C) must remain in the cycle to

regenerate three RuBP (15C).


• In the last phase, regeneration of the CO2

acceptor (RuBP), these five TP/PGAL

molecules are rearranged to form 3 RuBP

molecules.

• To do this, the cycle must spend three

more molecules of ATP (one per RuBP) to

complete the cycle and prepare for the

next. (This is why more ATP than

NADPH is needed).



Fig. 10.17.3

• The PGAL from the Calvin cycle

is the starting material for

metabolic pathways that

synthesize other organic

compounds, including glucose and

other carbohydrates, as well as

lipids and parts of proteins and

nucleic acids.


Back to my infatuation with themes…

• Can you now explain a third way in which the structure of the chloroplast enhances its function?

• Hint – like the other two examples you came up with a few slides back, this is also very similar to a way in which the mitochondrion’s structure aided in it’s function, but this has to do with the Calvin Cycle.

• The comparison with respiration should help you remember them, yes?

And how about this scientific method

connection????

• Limiting factors are things that can affect a

process for better or worse (which is where the

term “limiting” comes from).

• Just for fun, come up with three factors that could

limit the rate of photosynthesis and explain why

and how they have their effect.

Untested:



the AP Exam.











How about a little comic relief, you say?

• I happen to have just the

thing - a video on C4

plants!!!

• NOT on this test, but a good

example of adaptation.

• One of the major problems facing terrestrial plants is

dehydration.

• At times, solutions to this problem conflict with other

metabolic processes, especially photosynthesis.

• The stomata are not only the major route for gas exchange

(CO2 in and O2 out), but also for the evaporative loss of water.

• On hot, dry days, plants close stomata to save water, but this

means a CO2 shortage for photosynthesis.

5. Alternative mechanisms of carbon fixation

have evolved in hot, arid climates


• In most plants (C3 plants) initial fixation of CO2

occurs via rubisco and results in a three-carbon compound, GP/PGA).

• These plants include rice, wheat, and soybeans.

• When their stomata are closed on a hot, dry day, CO2 levels inside the chloroplast drop as CO2 is consumed in the Calvin cycle.

• At the same time, O2 levels rise as the light reaction converts light to chemical energy.

• While rubisco normally accepts CO2, when the O2/CO2 ratio increases (on a hot, dry day with closed stomata), rubisco can add O2 to RuBP.


• When rubisco adds O2 to RuBP, RuBP splits into a

three-carbon piece and a two-carbon piece in a

process called photorespiration.

• The two-carbon fragment is exported from the

chloroplast and degraded to CO2 by mitochondria and

peroxisomes.

• Unlike normal respiration, this process produces no

ATP, nor additional organic molecules.

• Photorespiration decreases photosynthetic output

by siphoning organic material from the Calvin

cycle, so no TP/PGAL (therefore no glucose) is

made.


• Photorespiration can drain away as much as 50% of the carbon fixed by the Calvin cycle on a hot, dry day.

• Certain plant species have evolved alternate modes of carbon fixation to minimize photorespiration.

• The C4 plants fix CO2 first in a four-carbon

compound, not three carbon GP/PGA like C3 plants.

• Several thousand plants, including sugercane and corn

and crabgrass use this pathway.


• C4 plant’s leaves have a different internal structure.

• mesophyll cells incorporate CO2 into organic molecules.

• The mesophyll cells have the key enzyme PEP carboxylase,

not rubisco.

• PEP carboxylase adds CO2 to phosphoenolpyruvate (PEP) to

form 4-carbon oxaloacetetate (where have you seen that

before?)

• PEP carboxylase has a very high affinity for CO2 and can

fix CO2 efficiently when rubisco cannot - on hot, dry days

with the stomata closed.

• So there is not the competition between O2 and CO2 that

leads to photorespiration with rubisco involved.


• The mesophyll cells pump these four-carbon

compounds into bundle-sheath cells.

• The bundle sheath cells strip a CO2 from the four-

carbon compound and return the three-carbon remainder

(your friend, pyruvate) to the mesophyll cells.

• The bundle sheath cells then use rubisco with this

abundant supply of CO2 to start the Calvin cycle.

• The Calvin cycle works just as it does in C3 plants, the

only difference is how CO2 is delivered to it.



Fig. 10.18

• In effect, the mesophyll cells pump CO2 into the bundle

sheath cells, keeping CO2 levels high enough for rubisco to

accept CO2 and not O2.

• Because the mesophyll cells don’t have rubisco to grab O2

instead of CO2, and because they surround the bundle

sheath cells, therefore blocking O2 from getting to them, C4

photosynthesis minimizes photorespiration and enhances

sugar production.

• C4 plants thrive in hot, dry regions with intense sunlight.

• This is why crabgrass grows better than St. Augustine

grass (a C3 plant) when it is hot and dry.


• A second strategy to minimize photorespiration is found in

succulent plants like cacti and pineapples.

• These plants, known as CAM plants for crassulacean

acid metabolism (CAM), open stomata during the night

and close them during the day, the opposite pattern of other

plants.

• Temperatures are typically lower at night and

humidity is higher, so water loss is minimized.

• During the night, these plants fix CO2 into a variety of

organic acids in mesophyll cells, kind of like C3 plants.

• During the day, the light reactions supply ATP and

NADPH to the Calvin cycle and CO2 is released from

the organic acids.


• Both C4 and CAM plants add CO2 to organic

intermediates before it enters the Calvin cycle, thus

avoiding the photorespiration that happens when

O2 competes with CO2 for the rubisco active site.

• In C4 plants, carbon fixation and the Calvin cycle are

spatially separated.

• In CAM plants, carbon fixation and the Calvin cycle are

temporally separated.

• Both eventually use the Calvin cycle to incorporate

light energy into the production of sugar.



Fig. 10.19

• In photosynthesis, the energy that enters the

chloroplasts as sunlight becomes stored as chemical

energy in

organic

compounds.

6. Photosynthesis is the biosphere’s

metabolic foundation: a review


Fig. 10.20

• Sugar made in the chloroplasts supplies the entire

plant with chemical energy and carbon skeletons

to synthesize all the major organic molecules of

cells.

• About 50% of the organic material is consumed as fuel

for cellular respiration in plant mitochondria.

• Carbohydrate in the form of the disaccharide sucrose

travels via the veins to nonphotosynthetic cells.

• There, it provides fuel for respiration and the raw

materials for anabolic pathways including synthesis of

proteins and lipids and building the extracellular

polysaccharide cellulose.


• Plants also store excess sugar by synthesizing

starch.

• Some is stored as starch in chloroplasts or in storage

cells in roots, tubers, seeds, and fruits.

• Heterotrophs, including humans, may completely or

partially consume plants for fuel and raw materials.

• On a global scale, photosynthesis is the most

important process to the welfare of life on Earth.

• Photosynthesis is your friend (until you have a test

on it).


NOT on this test

• But we will study it later and it is definitely

connected to what we are doing, so let’s take a

look.

• No extra charge

• An ecosystem consists of all the organisms living in a community as well as all the abiotic factors with which they interact.

• The dynamics of an ecosystem involve two processes: energy flow and chemical cycling.

• Ecosystem ecologists view ecosystems as energy machines and matter processors.

• We can follow the transformation of energy by grouping the species in a community into trophic levels of feeding relationships.

Introduction


• The autotrophs are the primary producers, and are

usually photosynthetic (Photoautotrophs, which can

be either ?, or ?, or?), but could be ?????

• They use light energy to synthesize sugars and other

organic compounds.

• Chemoautotrophs are the producers in some ecosystems,

like deep sea vents (they are strictly prokaryotic).

1. Trophic relationships determine the

routes of energy flow and chemical cycling

in an ecosystem


• Heterotrophs are at

trophic levels above

the primary

producers and

depend on their

photosynthetic

output.

• Decomposers, or

detritivores, feed on

dead organisms of all

types, helping

recycle nutrients.


Fig. 54.1

• An ecosystem’s main decomposers are fungi and

prokaryotes, which secrete enzymes that digest

organic material and then absorb the breakdown

products, defining them as saprotrophs.


Fig. 54.2

• The law of conservation of energy applies to

ecosystems.

• We can potentially trace all the energy from its

solar input to its release as heat by organisms.

• The second law of thermodynamics allows us to

measure the efficiency of the energy conversions.

3. The laws of physics and chemistry apply

to ecosystems


• The amount of light energy converted

to chemical energy by an ecosystem’s

autotrophs in a given time period is

called primary production, and is

measured in the DRY mass of

autotroph tissue made in a certain

amount of time.

Introduction


• The Global Energy Budget

• Every day, Earth is bombarded by large amounts

of solar radiation.

• Much of this radiation lands on the water and

land that either reflect or absorb it.

• Of the visible light that reaches photosynthetic

organisms, about only 1% is converted to

chemical energy.

• Although this is a small amount, primary

producers are capable of producing about 170

billion tons of organic material per year.


• Gross and Net Primary Production.

• Total primary production is known as gross

primary production (GPP).

• This is the amount of light energy that is

converted into chemical energy.

• The net primary production (NPP) is equal to

gross primary production minus the energy used

by the primary producers for respiration (R):

• NPP = GPP – R


Q8

• The net annual primary productivity of a

particular wetland ecosystem is found to be 8,000

kcal/m2. If respiration by the aquatic producers is

12,000 kcal/m2per year, what is the gross annual

primary productivity for this ecosystem, in

kcal/m2 per year? Round to the nearest whole

number.

Q8

• NPP=GPP-R

• 8,000 = GPP – 12,000

• 8,000+ 12,000= GPP

• 20,000=GPP

• Primary production can be expressed in

terms of energy per unit area per unit

time, or as biomass of vegetation added

to the ecosystem per unit area per unit

time.

• This should not be confused with the

total biomass of photosynthetic

autotrophs present at a given time,

called the standing crop.


• Different ecosystems differ greatly in their

production as well as in their contribution to the

total production of the Earth.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 54.3

• Production in Freshwater Ecosystems.

• Solar radiation and temperature are closely linked

to primary production in freshwater lakes.

• During the 1970s, sewage and fertilizer pollution

added nutrients to lakes, which shifted many lakes

from having phytoplankton communities to those

dominated by diatoms and green algae.


• This process is

called

eutrophication,

and has undesirable

impacts from a

human perspective.

• Hey, how about

explaining that to us.


• Obviously, water availability varies among terrestrial

ecosystems more than aquatic ones.

• On a large geographic scale, temperature

and moisture are the key factors

controlling primary production in

ecosystems.

3. In terrestrial ecosystems, temperature,

moisture, and nutrients limit primary

production


• The amount of chemical energy in

consumers’ food that is converted to their

own new biomass during a given time

period is called secondary production.

• In other words, how much of that double

cheeseburger and fries actually becomes

part of you is secondary production.

Introduction


• Production Efficiency.

• One way to

understand

secondary

production is

to examine the

process in

individual

organisms.

1. The efficiency of energy transfer between

trophic levels is usually close to 10%


Fig. 54.10

• Trophic Efficiency and Ecological

Pyramids.

• Trophic efficiency is the percentage

of production transferred from one

trophic level to the next.

• Pyramids of production represent

the multiplicative loss of energy from

a food chain.



Fig. 54.11

• Pyramids of biomass represent the ecological

consequence of low trophic efficiencies.

• Most biomass pyramids narrow sharply from

primary producers to top-level carnivores

because energy transfers are inefficient (10%)


Fig. 54.12a

• In some aquatic ecosystems, the pyramid is

inverted.

• In this example, phytoplankton grow,

reproduce, and are consumed rapidly.

• They have a short turnover time, which is a

comparison of standing crop mass compared

to production.Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 54.12b

• Pyramids of numbers show how the levels in

the pyramids of biomass are proportional to the

number of individuals present in each trophic

level.


Fig. 54.13

• The dynamics of energy through ecosystems have

important implications for the human population.


Fig. 54.14

So save money and get your heart in shape

• Eating more plants makes a lot of sense. Animal

rights activists would certainly agree. But…

• Seems like there are always fringe groups no

matter where you look. 4:30

http://www.youtube.com/watch?v=KmK0bZl4ILM

About time for another test, eh?

• Here’s one from the pep band

../Animations/Mellow Woes of Testing.mp3

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1. Plants and other autotrophs are the producers of the biosphere · 14/01/2019 · reactants of...

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