talk nine: plants that feed the world chapter 13 biology today (biol 109)
TRANSCRIPT
Talk Nine:Plants that feed the world
Chapter 13
Biology Today (BIOL 109)
Plants that feed the world• Hunger, starvation, and malnutrition are
endemic in many parts of the world today.
• Rapid increases in the world population have intensified these problems!
• ALL of the food we eat comes either directly or indirectly from plants.
• Can’t just grow more plants, land for cultivation has geographic limits– Also, can destroy ecosystems!
Figure 9.1Plants that feed usThe Earth is currently experiencing the most population increase in Humanhistory.
2.5 billion in 1955 to 7 billion in 2012
At current rate, will double within 30 years!
Fastest growing nations have growth rates at or above 4% - this will double the countries population every 17 years
Plants to feed the world• At the latest count there are between 250,000
and 400,000 plant species on the earth.
• But three - maize, wheat and rice - and a few close runners-up, have become the crops that feed the world. All produce starch, helping to provide energy and nutrition, and all can be stored.
• Maize converts the sun’s energy into sugar faster, and potentially produces more grains, than any of the other major staples.
Figure 11.13Increasing crop yields
• To feed the increasing population we have to increase crop yields.
• Fertilizers - are compounds to promote growth; usually applied either via the soil, for uptake by plant roots, or by uptake through leaves. Can be organic or inorganic
• Have caused many problems!!
• Algal blooms pollute lakes near areas of agriculture
Figure 11.13Increasing crop yields
• Algal blooms - a relatively rapid increase in the population of (usually) phytoplankton algae in an aquatic system.
• Causes the death of fish and disruption to the whole ecosystem of the lake.
• International regulations has led to a reduction in the occurrences of these blooms.
Figure 11.17Chemical pest control
• Each year, 30% of crops are lost to insects and other crop pests.
• The insects leave larva, which damage the plants further.
• Fungi damage or kill a further 25% of crop plants each year.
• Any substance that kills organisms that we consider undesirable are known as a pesticide.
• An ideal pesticide would:-– Kill only the target species– Have no effect on the non-target species– Avoid the development of resistance– Breakdown to harmless compounds after a short time
Figure 11.17Chemical pest control
• DDT was first developed in the 1930s
• Very expensive, toxic to both harmful and beneficial species alike.
• Over 400 insect species are now DDT resistant.
• As with fertilizers, there are run-off problems.
• Affects the food pyramid.– Persist in the environment
Figure 11.18Chemical pest control
• DDT persists in the food chain.
• It concentrates in fish and fish-eating birds.
• Interfere with calcium metabolism, causing a thinning in the eggs laid by the birds – break before incubation is finished – decrease in population.
• Although DDT is now banned, it is still used in some parts of the world.
What comes from plants
Popular stimulants like coffee, chocolate, tobacco, and tea.
Simple derivatives of botanical natural products; for example, aspirin is based on the pain killer salicylic acid which originally came from the bark of willow trees.
Most alcoholic beverages come from fermenting plants such as barley (beer), rice (sake) and grapes (wine).
What comes from plants
• Plants also provide us with many natural materials– hemp, cotton, wood, paper, linen, vegetable oils, some
types of rope, and rubber.
• The production of silk would not be possible without the cultivation of the mulberry plant.
• Sugarcane, rapeseed, soy and other plants with a highly fermentable sugar or oil content have recently been put to use as sources of biofuels, which are important alternatives to fossil fuels
A few of the many medicinal plants
Plants to feed the world
• The term Green Revolution is used to describe the transformation of agriculture in many developing nations that led to significant increases in agricultural production between the 1940s and 1960s
• Scientists bred short plants that converted the sun’s energy into grain rather than stem, so preventing the mass starvation in the developing world predicted before the 1960s, at a cost of higher inputs from chemical fertilizers and irrigation.
Plants to feed the world
• Disease-resistant wheat varieties with high yield potentials are now being produced for a wide range of global, environmental and
cultural conditions.
• The Green Revolution has had major social and ecological impacts, which have drawn intense praise and equally intense criticism.
Plants to feed the world
• Agriculture has changed dramatically, especially since the end of World War II.
• Food and fiber productivity soared due to new technologies, mechanization, increased chemical use, specialization and government policies that favored maximizing production.
• These changes allowed fewer farmers with reduced labor demands to produce the majority of the food and fiber in the U.S.
Plants to feed the world
• Has had major social and ecological impacts, which have drawn intense praise and equally intense criticism.
• In fact, many regions of the world peaked in food production in the period 1980 to 1995
• Are presently in decline, since desertification and critical water supplies have become limiting factors in a number of world regions.
Plant Basics• Roots – absorb water from the soil
as well as many mineral nutrients
• Xylem – transports water from the roots to the rest of the plant
• Phloem – transports sugars made in the leaves via photosynthesis to the pest of the plant
• Leaves – Site of gas exchange CO2 brought in and O2 out. Have structures called Stomata which also control water loss.
Plants and water• Water is the essential medium of life.
• Land plants faced with dehydration by water loss to the atmosphere
• There is a conflict between the need for water conservation and the need for CO2 assimilation
– This determines much of the structure of land plants
– 1: extensive root system – to get water from soil– 2: low resistance path way to get water to leaves –
xylem– 3: leaf cuticle – reduces evaporation
– 4: stomata – controls water loss and CO2 uptake
– 5: guard cells – control stomata.
Water across plant membranes• There is some diffusion
of water directly across the bi-lipid membrane.
• Auqaporins: Integral membrane proteins that form water selective channels – allows water to diffuse faster– Facilitates water
movement in plants
• Alters the rate of water flow across the plant cell membrane – NOT direction
• Xylem:– Main water-conducting tissue
of vascular plants.– arise from individual
cylindrical cells oriented end to end.
– At maturity the end walls of these cells dissolve away and the cytoplasmic contents die.
– The result is the xylem vessel, a continuous nonliving duct.
– carry water and some dissolved solutes, such as inorganic ions, up the plant
Water transport in Plants
Water and plant cells• 80-90% of a growing plant cell is
water– This varies between types of plant cells– Carrot has 85-95% water– Wood has 35-75% water– Seeds have 5-15% water
• Plant continuously absorb and lose water– Lost through the leaves
• Called transpiration
Water
Water• (A) Hydrogen
bonds between water molecules results in local aggregations of water molecules
• (B) Theses are very short lived, break up rapidly to form more random configurations
• Due to temperature variations in water
Osmosis and Tonicity
• Osmosis is the diffusion of water across a plasma membrane.
• Osmosis occurs when there is an unequal concentration of water on either side of the selectively permeable plasma membrane.
• H2O CAN cross the plasma membrane.
• Tonicity is the osmolarity of a solution--the amount of solute in a solution.
• Solute--dissolved substances like sugars and salts.
• Tonicity is always in comparison to a cell.
• The cell has a specific amount of sugar and salt.
Tonic Solutions
• A Hypertonic solution has more solute than the cell. A cell placed in this solution will give up water (osmosis) and shrink.
• A Hypotonic solution has less solute than the cell. A cell placed in this solution will take up water (osmosis) and blow up.
• An Isotonic solution has just the right amount of solute for the cell. A cell placed in this solution will stay the same.
Plant cell in hypotonic solution• Flaccid cell in 0.1M sucrose solution. • Water moves from sucrose solution to cell – swells up –
becomes turgid• This is a Hypotonic solution - has less solute than the cell.
So higher water conc.• Pressure increases on the cell wall as cell expands to
equilibrium
Plant cell in hypertonic solution
• Turgid cell in 0.3M sucrose solution
• Water movers from cell to sucrose solution
• A Hypertonic solution has more solute than the cell. So lower water conc
• Turgor pressure reduced and protoplast pulls away from the cell wall
Plant cell in Isotonic solution
• Water is the same inside the cell and outside
• An Isotonic solution has the same solute than the cell. So no osmotic flow
• Turgor pressure and osmotic pressure are the same
Photosynthesis
The (very) Basic facts
Photosynthesis•Very little of the Sun’s energy gets to the ground
gets absorbed by water vapor in the atmosphere
•The absorbance spectra of chlorophyll.
Absorbs strongly in the blue and red portion of the spectrumGreen light is reflected and gives plants their color.
•There are two pigments•Chlorophyll A and B
General overall reaction
6 CO2 + 6 H2O C6H12O6 + 6 O2 Carbon dioxide Water Carbohydrate Oxygen
Photosynthetic organisms use solar energy to synthesize carbon compounds that cannot be formed without the input of energy.
More specifically, light energy drives the synthesis of carbohydrates from carbon dioxide and water with the generation of oxygen.
Overall Perspective• Light reactions:
– Harvest light energy– Convert light energy
to chemical energy
• Dark Reactions:– Expend chemical energy
– Fix Carbon [convert CO2 to organic form]
Photosynthetic pigments• Two types in plants:• Chlorophyll- a• Chlorophyll –b
• Structure almost identical,– Differ in the composition of a
sidechain – In a it is -CH3, in b it is CHO
• The different sidegroups 'tune' the absorption spectrum to slightly different wavelengths– light that is not significantly
absorbed by chlorophyll a, will instead be captured by chlorophyll b
The chemical reaction of photosynthesis is driven by
light• The initial reaction of
photosynthesis is:– CO2 +H2O (CH2O) +
O2 – Under optimal conditions
(red light at 680 nm), the photochemical yield is almost 100 %
– However, the efficiency of converting light energy to chemical energy is about 27 %
• Very high for an energy conversion system
The Chloroplast• Membranes contain chlophyll
and it’s associated proteins– Site of photosynthesis
• Have inner & outer membranes• 3rd membrane system
– Thylakoids
• Stack of Thylakoids = Granum
• Surrounded by Stroma
• During photosynthesis, ATP from stroma provide the energy for the production of sugar molecules
The light reactions
• Step 1 – chlorophyll in vesicle membrane capture light energy
• Step 2 – this energy is used to split water into 2H and O.
• Step3 – O released to atmosphere. Each H is further split into H+ ion and an electron (e-).
• Step 4 – H+ ion build up in the stacked vesicle membranes.
The light reactions• Step 5 – The e- move
down a chain of electron transport proteins that are part of the vesicle membrane.
• Step 6 – e- ultimately delivered to the molecule NADP+ - forming NADPH
• Step 7 - Some membrane proteins pump H+ into the interior space of the vesicle– Stored energy
• Step 8 – These make ATP!
Summary of light reactions• Plants have two reaction centers:
– PS-II• Absorbs Red light – 680mn• makes strong reductant (& weak oxidant)• oxidizes 2 H2O molecules to 4 electrons, 4 protons
& 1 O2 molecule• Mostly found in Granum
– PS-I• Absorbs Far-Red light – 700nm• strong oxidant (& weak reductant)• PS-I reduces NADP to NADPH• Mostly found in Stroma
• The NADPH and ATP move into the liquid environment of the Stroma.
• The NADPH provides H and the ATP provides energy to make glucose from CO2.
• The Calvin cycle thus fixes atmospheric CO2 into plant organic material.
The Carbon reactions
Overview of the carbon reactions
• The Calvin cycle:• The cycle runs six
times:– Each time incorporating a
new carbon . Those six carbon dioxides are reduced to glucose:
– Glucose can now serve as a building block to make:• polysaccharides • other monosaccharides • fats • amino acids • nucleotides
Photorespiration • Occurs when the CO2 levels inside a leaf become low•
– This happens on hot dry days when a plant is forced to close its stomata to prevent excess water loss
• If the plant continues to attempt to fix CO2 when its stomata are closed
– CO2 will get used up and the O2 ratio in the leaf will increase relative to CO2 concentrations
• When the CO2 levels inside the leaf drop to around 50 ppm, – Rubisco starts to combine O2 with Ribulose-1,5-
bisphosphate instead of CO2
The C4 carbon Cycle• The C4 carbon Cycle occurs in 16 families
of both monocots and dicots. – Millet– Sugarcane– Maize
• There are three variations of the basic C4 carbon Cycle – Due to the different four carbon
molecule used
The C4 carbon Cycle• This is a biochemical pathway
that prevents photorespiration • C4 leaves have TWO chloroplast
containing cells– Mesophyll cells– Bundle sheath (deep in the leaf
so atmospheric oxygen cannot diffuse easily to them)
• C3 plants only have Mesophyll cells
• Operation of the C4 cycle requires the coordinated effort of both cell types– No mesophyll cells is more than
three cells away from a bundle sheath cells
• Many plasmodesmata for communication
Genetically modified crops• All plant characteristics, such as size, texture, and
sweetness, are determined on the genetic level.
• Also:• The hardiness of crop plants.• Their drought resistance. • Rate of growth under different soil conditions. • Dependence on fertilizers.• Resistance to various pests and diseases.
• Used to do this by selective breeding
Edible VaccinesTransgenic Plants Serving Human Health Needs
• Works like any vaccine • A transgenic plant with a pathogen protein gene is developed• Potato, banana, and tomato are targets• Humans eat the plant • The body produces antibodies against pathogen protein• Humans are “immunized” against the pathogen• Examples:
DiarrheaHepatitis BMeasles
Ah, the big hitters!
maize, wheat and rice
Maize (Corn)• Represents the most
remarkable plant breeding achievement in
the history of agriculture.
• The modern manifestation of this ancient plant bears very little resemblance to its original ancestor, a wild grass from southern Mexico called teosinte.
Photo courtesy of Raúl Coronado
Maize• Teosinte is a tall, drought-
tolerant grass that produces, instead of a cob, spikes close to the ground, filled with two rows of small, triangular-shaped seeds within an enclosed husk
• A hard shell around each seed protects them once they fall to the ground
• This transformation from an inconspicuous grass to a diverse, highly evolved and productive food plant spans thousands of years
• A story of co-evolution and interdependence between humans and corn unprecedented in nature
Maize• 100 years after discovering that teosinte
was edible, people began selecting spikes to plant near their homes, which were close to irrigation sources.
• These selected plants continued to be developed in isolation from wild teosinte that was growing in the surrounding forests, and thus the process of developing corn had begun.
• The difference between Teosinte and maize is about 5 genes.
• About 5 regions of the genome (which could be single genes or groups of genes) seemed to be controlling the most-significant differences between teosinte and Maize
Maize• The oldest known corncobs,
distinctly different from teosinte, were found in the highlands of Oaxaca in southwestern Mexico and are estimated to be 5,400 years old.
• Maize cobs uncovered by archaeologists show the evolution of modern maize over thousands of years of selective
breeding.
• Even the oldest archaeological samples bear an unmistakable
resemblance to modern maize.
Maize• About two-thirds of the maize
grown in the United States goes into livestock feed. – Hogs eat almost half the corn
crop.
• Maize provides the base for many kinds of poultry feeds and dairy feeds.
• Maize and cornstalks are also made into silage, a fermented livestock feed.
• Americans eat about 45 pounds of Maize per person per year.
• Many kinds of food are made from the kernels.
• Maize also provides food indirectly, in the form of the meat and meat products that come from animals raised on it.
• Maize, in one form or another, makes up more of our diet than any other farm crop.
From: www.robinsonlibrary.com
Wheat• Wheat originated in the “cradle
of civilization” in the Tigris and Euphrates river valley, near what is now Iraq and the Ethiopian Highlands
• The Roman goddess, Ceres, who was deemed protector of the grain, gave grains their common name today – “cereal.”
• Wheat is the primary grain used in U.S. grain products — approximately three-quarters of all U.S. grain products are made from wheat flour.
Six classes bring order to the thousands of varieties of wheat. They are: hard red winter (HRW), hard red spring (HRS), soft red winter (SRW), hard white (HW), soft white
(SW) and durum.
Wheat Genetics• Wheat genetics is more complicated
than that of most other domesticated species.
• Some wheat species are diploid, with two sets of chromosomes. Many are stable polyploids, with four sets of chromosomes (tetraploid) or six (hexaploid).
• Genes for the 'dwarfing' trait, first used by Japanese wheat breeders to produce short-stalked wheat, have had a huge effect on wheat yields world-wide.
• Dwarfing genes enable the carbon that is
fixed in the plant during photosynthesis to be diverted towards seed production.
Wheat• Became known as Norin 10
• This grows to just two feet tall, instead of the usual four, which made it less prone to wind damage.– Other varieties grow too high,
become top-heavy, and lodge
• By 1997, 81% of the developing world's wheat area was planted to semi-dwarf wheats, giving both increased yields and better response to nitrogenous fertilizer.
• Norin 10 helped developing countries, such as India and Pakistan, to increase the productivity of their crops from approximately 60% during the Green Revolution.
Rice• This is the seed of the monocot
plants Oryza sativa (Asian rice) or Oryza glaberrima (African rice).
• Rice is the most important grain with regard to human nutrition and caloric intake, providing more than one fifth of the calories consumed worldwide by humans.
• Genetic evidence has shown that rice originates from a single domestication 8,200–13,500 years ago, in the Pearl River valley region of China.
•
Where is rice grown?• Rice is grown in eight
American States
• Arkansas
• California
• Texas
• Louisiana
• Minnesota
• Mississippi
• Missouri
• Florida From the Rice knowledge Bank
Rice• Rice cultivation is well-suited to countries
and regions with low labor costs and high rainfall, as it is labor-intensive to cultivate and requires ample water.– Rice can be grown practically anywhere,
even on a steep hill or mountain.
• The traditional method for cultivating rice is flooding the fields while, or after, setting the young seedlings.
• This simple method requires sound planning and servicing of the water damming and channeling, but reduces the growth of less robust weed and pest plants that have no submerged growth state, and deters vermin and many pathogens.
Rice Environmental impacts• Rice cultivation on wetland rice fields is thought to be responsible
for 6–21% of the annual methane emissions produced via Human interaction with the environment.– The Long-term flooding of rice fields cuts the soil off from
atmospheric oxygen and causes anaerobic fermentation of organic matter in the soil.
• Rice requires slightly more water to produce than other grains.
• As a result of rising temperatures and decreasing solar radiation during the later years of the 20th century, the rice yield growth rate has decreased in many parts of Asia.
• The reason for this falling yield is not fully understood– might involve increased respiration during warm nights, which
expends energy without being able to photosynthesize
The End.
Any Questions?