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#1
What is “oxidative phosphorylation”?
First, some basic definitions. When you take hydrogen ions or electrons away from a
molecule, you “oxidize” that molecule. When you give hydrogen ions or electrons to a
molecule, you “reduce” that molecule. When you give phosphate molecules to a
molecule, you “phosphorylate” that molecule. So, oxidative phosphorylation (very
simply) means the process that couples the removal of hydrogen ions from one
molecule and giving phosphate molecules to another molecule. How does this apply
to mitochondria?
As the Kreb’s cycle runs, hydrogen ions (or
electrons) are donated to the two carrier molecules in 4 of the steps. They are
picked up by either NAD or FAD and these carrier molecules become NADH and
FADH (because they now are carrying a hydrogen ion). They carry the hydrogen
ions to the inner mitochondrial membrane (cristae). This is where the electron
transport complexes are embedded in the membrane. The following cartoon shows
what happens next.
The NADH and FADH essentially serve as a ferry in the lateral plane of the
membrane diffusing from one complex to the next. At each complex site is a
hydrogen (or proton) pump which transfers hydrogen from one side of the
membrane to the other. This creates a gradient across the inner membrane with a
higher concentration of Hydrogen ions in the intercristae space (this is the space
between the inner and outer membranes).
In biochemistry and molecular biology, the tertiary structure of
a protein or any other macromolecule is its three-dimensional structure, as
defined by the atomic coordinates.[1]
Figure 3:Three structures of proteins are illustrated (A) primary structure, its amino acid
sequence; (B) secondary structure, polypeptide coiling or folding; (C) tertiary structure, the
overall shape of the polypeptide.
Hypertonicity
A hypertonic solution contains a greater concentration of
impermeable solutes than the solution on the other side of the
membrane.[1] When a cell’s cytoplasm is bathed in a hypertonic
solution the water will be drawn into the solution and out of the cell
by osmosis. If water molecules continue to diffuse out of the cell, it
will cause the cell to shrink.
Hypotonicity
A hypotonic solution contains a lesser concentration of impermeable
solutes than the solution on the other side of the membrane.[1] When
a cell’s cytoplasm is bathed in a hypotonic solution the water will be
drawn out of the solution and into the cell by osmosis. If water
molecules continue to diffuse into the cell, it will cause the cell to
swell.
Isotonicity
Isotonic solutions contain equal concentrations of impermeable
solutes on both sides of the membrane.
e taxonomic classification of the Red Panda has been controversial since it was discovered.
French zoologist Frédéric Cuvier initially described the Red Panda in 1825,
and classified it as a close relative of the Raccoon (Procyonidae),
even though he gave it the genus name Ailurus "cat" based on superficial
milarities with domestic cats. The specific epithet is the Latin adjective fulgens "shining".[20]
At various times it has been placed in Procyonidae, Ursidae, with Ailuropoda in Ailuridae,
and in its own family, Ailuridae. This uncertainty comes from difficulty determining
whether certain characteristics of Ailurus are phylogenetically conservative or
are derived and convergent with species of similar ecological habits.[21]
Evidence based on the fossil record, serology, karyology, behavior, anatomy,
and reproduction reflect closer affinities with Procyonidae than Ursidae.
However, ecological and foraging specializations and distinct geographical distribution
in relation to modern Procyonids support classification
in a separate family (Ailuridae).[21][22][23]
Recent molecular-systematic DNA research also
places the Red Panda into its own
family Ailuridae, which is in turn part of the broad superfamily Musteloidea that
also includes the Mephitidae (skunks), Procyonidae (raccoons),
and Mustelidae (weasels) families.[3][23][24]
It is not a bear, nor closely related to the
giant panda, nor a raccoon, nor a
lineage of uncertain affinities. Rather it is a basal lineage of musteloid,
with a long history of independence from its closest
relatives (skunks, raccoons, and otters/weasels/badgers).
A pulmonary vein is a large blood vessel of the human
circulatory system that carries blood from the lungs to the left
atrium of the heart. There are two pulmonary veins, two from
each lung. They carry oxygenated blood, which is unusual
since almost all other veins carry deoxygenated blood.
Triglycerides are formed from a single molecule of glycerol,
combined with three fatty
acids on each of the OH groups,
and make up most of fats digested by humans.
Triglycerides, as major components of
very low density lipoprotein (VLDL) and chylomicrons,
play an important role in metabolism as energy sources
and transporters of dietary fat. They contain more than twice as
much energy (9 kcal/g) as carbohydrates and proteins.
In the intestine, triglycerides are split into monoacylglycerol and free
fatty acids in a process called lipolysis, with the secretion of lipases
and bile, which are subsequently moved to absorptive
enterocytes, cells lining the intestines.
• The salivary glands in mammals are
exocrine glands, glands with ducts, that
produce saliva. They also secrete
amylase, an enzyme that breaks down
starch into maltose. In other organisms
such as insects, salivary glands are often
used to produce biologically important
proteins like silk or glues, and fly salivary
glands contain polytene chromosomes
that have been useful in genetic research.
• Decomposition of Organic Matter in Soil Fungi alongwith other microbes, chiefly bacteria
(including actinomycetes) play vital role in the
decomposition of organic matter in soil, thus
releasing the nutrients locked up in the dead
organic matter of plant, animal and microbial
matter and bringing about the recycling of
nutrients in nature.
In soil, microbes oxidise organic carbon to CO2
and liberate bound materials.
#11
Genetic
Infectious
Down Syndrome Malaria (blood/
(extra
mosquitoes)
chromosome)
Tay-Sachs (fatal Influenza (flu)
genetic lipid
storage disorder )
Ricketts (spotted
fever)
#12
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• #13 There were many important naturalists
in the 18th century.
– Linnaeus: classification system from kingdom to species
– Buffon: species shared ancestors rather than arising
separately
– E. Darwin: more-complex forms developed from lesscomplex forms
– Lamarck: environmental change leads to use or disuse
of a structure
#14
• Angiosperms, the flowering plants, represent the most advanced
condition among terrestrial plants. While their sexual organs flowers- are unquestionably their crowning achievement, their origin
remains a topic of considerable debate. There is general agreement
that the precursor to the ancestoral flower was a modified whorl of
leaves, and that extant flowers with multiple parts of indefinate
number probably represent the ancestoral condition. For an
interesting discussion on the origin of flowering plants, the reader is
referred to Peter Crane, et.al. (1995) (See references). The
angiosperm life cycle possesses the following advances over
conifers:
• Reproductive structures are flowers rather than cones.
• Ovules embedded in female sporophylls rather than lying bare on
the surface
• Gametophyte still further reduced
• Double fertilization to produce a diploidtriploid endosperm nutritive
material
• Seeds enclosed in fruits that develop from the ovary or related
structures
• The sporophyte is the dominant phase for
seed plants.
• The spore-producing plant is the mature sporophyte.
– sporophyte phase is diploid
– begins with fertilized egg
– spores produced through
meiosis
• The gamete-producing
plant is the mature
gametophyte.
– gametophyte
phase is haploid
– begins with spore
– gametes
produced through
mitosis
15 Learning is adaptive.
• Animals that can learn can better adapt to new
situations.
• In associative learning, a specific action is
associated with its consequences.
• Trial and error
• Conditioning is one type of associative learning
– Classical conditioning: previously neutral stimulus
associated with behavior triggered by different
stimulus
– Operant conditioning: behavior increased or
decreased by positive or negative reinforcement
Innate behaviors are triggered by
specific internal and external
stimuli. (instinct)
• An instinct is a complex inborn behavior.
• Instinctive behaviors share
several characteristics.
– innate, or performed
correctly the first time
– relatively inflexible
Many behaviors have both innate
and learned components.
• Learning takes many forms.
• Habituation occurs
when an animal
learns to ignore a
repeated stimulus.
• Imprinting is a rapid
and irreversible
learning process.
– critical period
– Konrad Lorenz
and graylag geese
• In imitation, animals learn by observing the
behaviors of others.
– young male
songbirds learn
songs by listening to
adult males
– snow monkeys and
potato-washing
behavior
• Unlike learning by trial-and-error, insight learning is
solving problems not based on actual experience (like
trial and error steps) but on trials occurring mentally.
Often the solution is learned suddenly, such as when a
person is in a problem for a period of time and suddenly
learns the way to solve it.
• This was observed in the experiments of Wolfgang
Kohler in 1900s involving chimpanzees. Kohler found
that chimpanzees could use insight learning instead of
trial-and error to solve problems. In one example, a
banana was placed high out of reach that the
chimpanzees found a way to reach it. They stack boxes
on top of each other to reach it and used sticks to knock
the banana down.
16
• In biochemistry,
• allosteric regulation is the regulation of
an enzyme or other protein by binding an
effector molecule at the protein's allosteric
site (that is, a site other than the protein's
active site). Effectors that enhance the
protein's activity are referred to as
allosteric activators, whereas those that
decrease the protein's activity are called
allosteric inhibitors.
17
• Lysosomes are spherical organelles that contain enzymes (acid
hydrolases). They break up food so it is easier to digest. They are
found in animal cells, while in yeast and plants the same roles are
performed by lytic vacuoles.
• The size of lysosomes varies from 0.1–1.2 μm.[2] At pH 4.8, the
interior of the lysosomes is acidic compared to the slightly alkaline
cytosol (pH 7.2). The lysosome maintains this pH differential by
pumping protons (H+ ions) from the cytosol across the membrane
via proton pumps and chloride ion channels. The lysosomal
membrane protects the cytosol, and therefore the rest of the cell,
from the degradative enzymes within the lysosome. The cell is
additionally protected from any lysosomal acid hydrolases that leak
into the cytosol as these enzymes are pH-sensitive and function less
well in the alkaline environment of the cytosol.
• Hydrolysis is a chemical reaction during which molecules of water
(H2O) are split into hydrogen cations (H+) (conventionally referred
to as protons) and hydroxide anions (OH−) in the process of a
chemical mechanism.[
18
19
• An adaptive radiation is a rapid evolutionary
radiation characterized by an increase in the
morphological and ecological diversity of a
single, rapidly diversifying lineage. Phenotypes
adapt in response to the environment, with new
and useful traits arising.[1] This is an
evolutionary process driven by natural
selection.
•
• Four of the 14 finch species found on the
Galápagos Archipelago, are thought to have
evolved by an adaptive radiation that diversified
their beak shapes to adapt them to different
food sources.
20
• Cephalization is an evolutionary trend,
whereby nervous tissue, over many
generations, becomes concentrated
toward one end of an organism. This
process eventually produces a head
region with sensory organs.[1]
• Cephalization is intrinsically connected
with a change in symmetry.
• The solubility of oxygen in water is temperature21
dependent, and about twice as much (14.6 mg·L−1)
dissolves at 0 °C than at 20 °C. To illustrate, recall
bubbles forming in a pot of water right before it begins to
boil; these bubbles are oxygen that was dissolved at
room temperature, but is being ejected as the
temperature rises. Oxygen can slip into the crevasses or
“holes” that exist in the loose hydrogen-bonded network
of water molecules without forcing them apart. A very
physical perspective on solubility of oxygen in water is
that when the water is colder, the water molecules move
less, and the oxygen remains trapped in the aqueous
solution.
22
• Proteins are made on the ribosomes which
are located on the rough ER.
• Then they move to the Golgi apparatus/
complex that packages them and ships
them out
• They go to a vesicle and then plasma
membrane
23
• A laboratory centrifuge is a piece of laboratory
equipment, driven by a motor, which spins liquid
samples at high speed. There are various types
of centrifuges, depending on the size and the
sample capacity.
• Like all other centrifuges, laboratory centrifuges
work by the sedimentation principle, where the
centripetal acceleration is used to separate
substances of greater and lesser density.
24
• Dicotyledonous plants (dicots)
are the second major group of
plants within the
Angiospermae division
(flowering plants with seeds
protected in vessels). The
other major group is the
monocots.
• In contrast to monocots, dicots
have an embryo with two
cotyledons, which give rise to
two seed leaves. The mature
leaves have veins in a net-like
pattern, and the flowers have
four or five parts.
Features
Monocotyl
edon
Dicotyle
don
Leaf
Parallel
structure
veins
Network
veins
Roots
Fibrous
roots
Tap roots
Stem
Soft
Hard
No. of
cotyledo
ns
1
2
25
• In biology, anaerobic respiration is a way for an
organism to produce usable energy without the
involvement of oxygen; it is respiration without
oxygen.[1] Respiration is a redox reaction that processes
energy in a form usable by an organism, chiefly the
process of producing ATP,[2] the "universal energy
currency of life".[3] It employs an electron transport
chain, with inorganic molecules other than oxygen used
as a final electron acceptor. Anaerobic respiration should
therefore not be confused with fermentation, as in
ethanol fermentation and lactic acid fermentation.
26 AIDS/HIV
• The virus, entering through which ever route, acts
primarily on the following cells:[70]
• Lymphoreticular system:
–
–
–
–
CD4+ T-Helper cells
Macrophages
Monocytes
B-lymphocytes
• Certain endothelial cells
• Central nervous system:
–
–
–
–
Microglia of the nervous system
Astrocytes
Oligodendrocytes
Neurones – indirectly by the action of cytokines and the gp-120
27
• Chemo: chemical
• Auto: self
• Tropic: feeding
• Deep sea vents have no light. Chemoautotrophs
generally only use inorganic energy sources. Most are
bacteria or archaea that live in hostile environments such
as deep sea vents and are the primary producers in such
ecosystems. Evolutionary scientists believe that the first
organisms to inhabit Earth were chemoautotrophs that
produced oxygen as a by-product and later evolved into
both aerobic, animal-like organisms and photosynthetic,
plant-like organisms.
28
• Plants have a mitochondria and a
chloroplast
29
•
•
Egg
Frogs and Toads tend to lay many many eggs because there are many
hazards between fertalization and full grown frogness! Those eggs that die
tend to turn white or opaque. The lucky ones that actually manage to hatch
still start out on a journey of many perils.
Life starts right as the central yolk splits in two. It then divides into four, then
eight, etc.- until it looks a bit like a rasberry inside a jello cup. Soon, the
embryo starts to look more and more like a tadpole, getting longer and
moving about in it's egg.
Usually, about 6-21 days (average!) after being fertilized, the egg will hatch.
Most eggs are found in calm or static waters, to prevent getting too rumbled
about in infancy!
Some frogs, like the Coast foam-nest treefrog, actually mate in
treebranches overlooking static bonds and streams. Their egg masses form
large cocoon-like foamy masses. The foam sometimes cakes dry in the sun,
protecting the inside moisture. When the rain comes along, after
developement of 7 to 9 days, the foam drips down, dropping tiny tadpoles
into the river or pond below.
30
• The light-dependent reactions produce ATP.
– hydrogen ions flow through a channel in the thylakoid
membrane
– ATP synthase attached to the channel makes ATP
•
• A molecule of glucose is formed as it stores
some of the energy captured from sunlight.
– carbon dioxide molecules enter the Calvin cycle
– energy is added and carbon molecules are rearranged
– a high-energy three-carbon molecule leaves the cycle
The second stage of
photosynthesis uses energy from
the first stage to make sugars.
• Lightindependent
reactions occur
in the stroma
and use CO2
molecules.
Glycolysis is needed for cellular
respiration.
• The products of glycolysis enter cellular
respiration when oxygen is available.
– two ATP molecules are used to split glucose
– four ATP molecules are produced
– two molecules of NADH produced
– two molecules of pyruvate produced
• The Krebs cycle produces energy-carrying
molecules.
31
•
•
•
•
Atoms: smallest piece of matter
Molecules: two or more atoms
Cells: smallest living unit
Organism: living thing made of one or
more cells
• ecosystem: An environment made of both
biotic and abiotic factors.
32 Analogous structures
• Two structures in biology are
said to be analogous if they
perform the same or similar
function by a similar
mechanism but evolved
separately.
• Similar structures may have
evolved through different
pathways, a process known
as convergent evolution, or
may be homologous.
The wings of pterosaurs (1), bats (2) and birds (3) are analogous: they serve the same
function and are similar in structure, but each evolved independently.
Homologous structures
• homology refers to any similarity between
characteristics of organisms that is due to
their shared ancestry.
Divergent evolution
• Divergent evolution is the accumulation
of differences between groups which can
lead to the formation of new species,
usually a result of diffusion of the same
species adapting to different
environments, leading to natural selection
defining the success of specific mutations.
Adaptive radiation
• An adaptive radiation is a rapid evolutionary
radiation characterized by an increase in the
morphological and ecological diversity of a
single, rapidly diversifying lineage.
• Four of the 14 finch species found on the
Galápagos Archipelago, are thought to have
evolved by an adaptive radiation that diversified
their beak shapes to adapt them to different food
sources.
Punctuated Equilibrium
• Punctuated equilibrium is a theory in
evolutionary biology which proposes
that most sexually reproducing species
will experience little evolutionary
change for most of their geological
history (in an extended state called
stasis). When evolution occurs, it is
localized in rare, rapid events of
branching speciation (called
cladogenesis). Cladogenesis is simply
the process by which species split into
two distinct species, rather than one
species gradually transforming into
another.
33
•
•
The formal system of naming species
is called binominal nomenclature
(especially in zoological circles),
binary nomenclature (especially in
botanical circles), or the binomial
classification system[citation
needed]. The essence of it is that each
species name is in (modern scientific)
Latin and has two parts, so that it is
popularly known as the Latin name of
the species, although this terminology
is avoided by biologists and
philologists, who prefer the term
scientific name. He adopted the
binominal nomenclature scheme,
using only the genus name and the
specific name or epithet which
together form the species name.
For example, humans belong to genus
Homo and their specific name is
sapiens. Humans as a species are
thus classified as Homo sapiens.
Kingdom
World
Phylum
USA
Class
CA
Order
Genus
Panorama
City
Van Nuys
Blvd
8015
Species
A306
Family
#35
• Natural selection can take one
of three paths.
– Stabilizing selection favors the
intermediate phenotype.
• Natural selection can take
one of three paths.
– Disruptive selection favors both
extreme phenotypes.
Gas exchange occurs in the alveoli
39
of
the
lungs.
• Oxygen and carbon dioxide are carried by
the blood to and from the alveoli.
– oxygen diffuses from alveoli into capillary
– oxygen binds to hemoglobin in red blood cells
– carbon dioxide difuses from capillary into alveoli
GAS EXCHANGES
ALVEOLI
capillary
alveolus
Co2 diffuses
into alveolus.
co2
o2
capillaries
O2 diffuses
into blood.
#41
KEY CONCEPT
The endocrine system produces
hormones that affect growth,
development, and homeostasis.
• Hormones are chemical signals that
influence cell’s activities.
– produced by glands
– travel through the circulatory system
– affects cells with matching receptors
target cell
hormone
bloodstream
receptor
not a target cell
• There are steroid hormones and nonsteroid
hormones.
– Steroid hormones enter the cell.
– Nonsteroid hormones do not enter the cell.
Steroid hormone
Steroid hormone
diffuses through the
cell membrane
Nonsteroid
hormone binds to
receptor on the
cell membrane.
Non-steroid
hormone
receptor
Steroid hormone
binds to a receptor
within the cell.
receptor
nucleus
The hormone and
receptor enter the
nucleus and bind
to DNA
DNA
Steroid hormone
causes DNA to
make proteins.
proteins
Receptor stimulates
a second messenger
with in the cell.
Second messenger
starts a series of
chemical reactions
in the cytoplasm.
Second messenger
reactions activate
enzymes.
second
messenger
Chemical
reactions
activated
enzymes
Endocrine glands secrete
hormones that act throughout the
body.
• There are many glands located throughout
the body.
HYPOTHALAMUS
PITUITARY
THYROID
THYMUS
ADRENAL GLANDS
PANCREAS
FEMALE GONADS
:OVARIES
MALE GONADS : TESTES
– Hormones travel through the bloodstream to cells with
matching receptors.
The hypothalamus interacts with
the nervous and endocrine
systems.
• The hypothalamus is a gland found in the brain.
– a structure of both the nervous and
endocrine systems
– produces releasing hormones,
sent to pituitary gland
• The pituitary gland is found below
the hypothalamus in the brain.
– controls growth and water
levels in blood
– produces releasing hormones
• Releasing hormones stimulate other glands
to produce hormones.
– allow glands to
communicate with one
another
– are used in temperature
regulation
#44
• The human body wants blood
glucose (blood sugar) maintained in
a very narrow range. Insulin and
glucagon are the hormones which
make this happen. Both insulin and
glucagon are secreted from the
pancreas, and thus are referred to as
pancreatic endocrine hormones. The
picture on the left shows the intimate
relationship both insulin and
glucagon have to each other. Note
that the pancreas serves as the
central player in this scheme. It is
the production of insulin and
glucagon by the pancreas which
ultimately determines if a patient has
diabetes, hypoglycemia, or some
other sugar problem.
• Insulin is normally secreted by the
beta cells (a type of islet cells) of the
pancreas. The stimulus for insulin
secretion is a HIGH blood
glucose...it's as simple as that!
45 Offspring =success
r-selection (unstable environments)
• In unstable or unpredictable environments, r-selection predominates as the ability to
reproduce quickly is crucial. There is little advantage in adaptations that permit
successful competition with other organisms, because the environment is likely to
change again. Traits that are thought to be characteristic of r-selection include: high
fecundity, small body size, early maturity onset, short generation time, and the ability
to disperse offspring widely. Organisms whose life history is subject to r-selection are
often referred to as r-strategists or r-selected. Organisms with r-selected traits range
from bacteria and diatoms, through insects and weeds, to various semelparous
cephalopods and mammals, especially small rodents.
K-selection (stable environments)
• In stable or predictable environments, K-selection predominates as the ability to
compete successfully for limited resources is crucial and populations of K-selected
organisms typically are very constant and close to the maximum that the environment
can bear (unlike r-selected populations, where population sizes can change much
more rapidly). Traits that are thought to be characteristic of K-selection include: large
body size, long life expectancy, and the production of fewer offspring that require
extensive parental care until they mature. Organisms whose life history is subject to
K-selection are often referred to as K-strategists or K-selected. Organisms with Kselected traits include large organisms such as elephants, trees, humans and whales,
but also smaller, long-lived organisms such as Arctic Terns.
46
47
The excretory system eliminates
nonsolid wastes from the body.
• Nonsolid wastes are
eliminated through
lungs, skin, and
kidneys.
• Lungs exhale carbon
dioxide and water
vapor.
• Sweat glands in skin
release excess water
and salts.
skin
lungs
kidneys
ureters
urethra
urinary bladder
• Kidneys have three basic functions in maintaining
homeostasis.
– remove waste from blood
– help to maintain electrolyte, pH, and fluid balances
– release key hormones
• Nephrons clean the blood in a three-step process.
• The first step is filtration of the blood.
1 FILTRATION
Glomerulus
Bowman’s capsule
Water,electrolytes,aminoacids,
glucose,urea, and other small
molecules diffuse out of the
blood,creating the filtrate.
48
• Plasmodesmata
(singular:
plasmodesma)
are microscopic
channels which
traverse the cell
walls of plant cells
and some algal
cells enabling
transport and
communication
between them.
49
• Chemiosmosis is the diffusion of ions across a
selectively-permeable membrane. More
specifically, it relates to the generation of ATP by
the movement of hydrogen ions across a
membrane during cellular respiration.
• ATP synthase is the enzyme that makes ATP by
chemiosmosis. It allows protons to pass through
the membrane using the kinetic energy to
phosphorylate ADP making ATP. The generation
of ATP by chemiosmosis occurs in chloroplasts
and mitochondria as well as in some bacteria.
50
• Wildfires are critical to maintaining the integrity of forest
and grassland ecosystems. Forest and grass fires,
usually started by lightning, act as an ecologically
renewing force by creating necessary conditions for plant
germination and continued healthy growth to occur. The
primary goal of fire management is to simulate the
revitalizing aspects of natural fire cycles. Fire
management also attempts to prevent large catastrophic
wildfires from occurring by removing accumulated debris
from forests. Seen throughout the American West every
summer, these extremely intense fires are caused
primarily by decades of fire suppression, which has
allowed heavy fuels-accumlated debris-to build up.
Ironically, by attempting to prevent natural fires, humans
have only increased their prevalence.
51
• True plants evolved through natural selection.
•
Life cycle phases look different
among
various
plant
groups.
Nonvascular plants have a dominant
gametophyte phase.
– moss gametophytes look like green carpet
– moss sporophytes shoot up as stalklike
structures
sporophyte (2n)
capsule
spores (1n)
gametophyte (1n)
• The sporophyte is the dominant phase for seedless
vascular plants.
– Fern spores form in sacs, sori, on underside of mature
sporophytes (fronds).
sporophyte (2n)
sori
• The sporophyte is the dominant phase for
seed plants.
52
Hardy-Weinberg equilibrium
describes populations that are
not evolving.
• Genotype frequencies stay the same if five
conditions are met.
– very large population: no genetic drift
– no emigration or immigration: no gene flow
– no mutations: no new alleles added to gene pool
– random mating:
no sexual selection
– no natural selection:
all traits aid equally
in survival
53
• Guard cells surround each stoma.
– Stomata open and close when guard cells
change shape.
– When stomata are open, water evaporates and
gas exchanges.
– Stomata close at night and when plant loses too
much water.
guard cells
stoma
54
• Geographic barriers can cause isolation.
– called geographic isolation
– physical barriers divide population
• Temporal barriers can cause isolation.
– called temporal isolation
– timing of reproductive periods prevents mating
• Mesophyll is between the leaf’s dermal
tissue layers.
cuticle
upper
epidermis
palisade
mesophyll
spongy
mesophyll
lower
epidermis
55
• Photorespiration and C4 Plants
• All plants carry on photosynthesis by
• adding carbon dioxide (CO2) to a phosphorylated 5carbon sugar called ribulose bisphosphate.
• This reaction is catalyzed by the enzyme ribulose
bisphosphate carboxylase oxygenase (RUBISCO).
• The resulting 6-carbon compound breaks down into two
molecules of 3-phosphoglyceric acid (PGA).
• These 3-carbon molecules serve as the starting material
for the synthesis of glucose and other food molecules.
• The process is called the Calvin cycle and the pathway
is called the C3 pathway.
•
•
•
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C4 Plants : the Calvin cylcle is confined to a bundle of sheathe cells.
Over 8000 species of angiosperms, scattered among 18 different families, have developed
adaptations which minimize the losses to photorespiration.
They all use a supplementary method of CO2 uptake which forms a 4-carbon molecule instead of
the two 3-carbon molecules of the Calvin cycle. Hence these plants are called C4 plants. (Plants
that have only the Calvin cycle are thus C3 plants.)
Some C4 plants — called CAM plants — separate their C3 and C4 cycles by time. CAM plants
are discussed below.
Other C4 plants have structural changes in their leaf anatomy so that
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These adaptations are described now.
The details of the C4 cycle
After entering through stomata, CO2 diffuses into a mesophyll cell.
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Being close to the leaf surface, these cells are exposed to high levels of O2, but
have no RUBISCO so cannot start photorespiration (nor the dark reactions of the Calvin cycle).
Instead the CO2 is inserted into a 3-carbon compound (C3) called phosphoenolpyruvic acid
(PEP) forming
the 4-carbon compound oxaloacetic acid (C4).
Oxaloacetic acid is converted into malic acid or aspartic acid (both have 4 carbons), which is
transported (by plasmodesmata) into a bundle sheath cell. Bundle sheath cells
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their C4 and C3 pathways are separated in different parts of the leaf with
RUBISCO sequestered where the CO2 level is high; the O2 level low.
are deep in the leaf so atmospheric oxygen cannot diffuse easily to them;
often have thylakoids with reduced photosystem II complexes (the one that produces O2).
Both of these features keep oxygen levels low.
Here the 4-carbon compound is broken down into
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carbon dioxide, which enters the Calvin cycle to form sugars and starch.
pyruvic acid (C3), which is transported back to a mesophyll cell where it is converted back into PEP.
• 56 An action potential is a moving electrical
impulse.
– It is generated by a stimulus.
– Na+ enters, and cell becomes
positively charged.
– K+ leaves, and area of positive
charge moves.
area of detail