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Date Created: 08/21/15
Biochemistry Water has high speci c heat has a high heat of vaporization is the universal solvent exhibits strong cohesion tension and ice oats because it is less dense than water Bicarbonate ion is the most famous buffer substance that resists changes in pH Structural isomers differ in the arrangement of their atoms cistrans isomers differ only in spatial arrangement around double bonds enantiomers are molecules that are mirror images of each other Structural polysaccharides cellulose makes up plant cell walls plants chitin makes up exoskeletons of arthropods animal Storage polysaccharides starch amylose and amylopectin plants glycogen stored in liver and skeletal muscles of humans A fatty acid is a hydrocarbon chain w a CARBOXYL group at one end saturated unsaturated Lipid functions energy storage major components of cell membranes endocrinehormone Phospholipids hydrophilic headfatty acid tails Proteins growth and repair signaling from one cell to another hormones such as insulin lower blood sugar catalyze reactions allow for movement Amino acids carboxyl group and amine group and R groups Primary structure unique linear sequence of amino acids slight change big consequence secondary structure results from hydrogen bonding within the polypeptide molecule alpha helixbeta pleated sheet tertiary structure intracite threedimentional shape of the protein determines the speci city of a protein includes hydrogen bonding ionic bonding hydrophobic interactions van der waals disul de bonds quaternary structure proteins that consist of more than one polypeptide chain pH salt concentration and temperature affect the folding of a protein denaturation nucleotide consists of pentose sugar nitrogen base ACGTU and phosphate rst law of thermodynamics energy cannot be created or destroyed only transformed from one form to another second law during energy conversions the universe is more disordered exergonic reactions power endergonic ones coupling anabolism building up molecules catabolism breaking down molecules induced t model NOT lock and key as the substrate enters the active site it induces the enzyme to alter its shape so it ts better enzymes often require the assistance from cofactors inorganic or coenzymes vitamins competitive inhibition compounds resemble molcules and reduce the chance of substrate binding to enzyme CAN be overcome by increasing substrate noncompetitive bind to a different site and change the shape of active site CANNOT overcome the cell theory of endosymbiosis eukaryotic cells emerged when mitochondria and chloroplasts once freeliving prokaryotic cells took up permanent residence in larger cells all cells contain plasma membrane cytosol ribosomes and DNA prokaryotes no nuclei or internal membranes have nucleoid nonmembrane bound no ER nuclear membrane mitochondria vacuoles or other organelles naked DNA ribosomes are small metabolism is anaerobic or aerobic no cytoskeleton unicellular eukaryotes contain organelles DNA wrapped around histone proteins into chromosomes ribosomes are larger metabolism is aerobic cytoskeleton is present mainly multicellular with differentiation of cell types ribosomes protein factories free ribosomes are associated w protein production for cell39s own use attached ribosomes are for export out of the cell peroxisomes contain cataase which converts hydrogen peroxide into water and oxygen also detoxi es alchol nucleus contains chromatin network nuclear envelope and pores ER rough ER is studded w ribosomes and produces proteins smooth ER assists in the synthesis of hormones stores calcium ions in muscle cells detoxi es drugsposions Golgi process package secrete proteins Lysosomes hydrolytic enzymes that are the principal site of intracellular digestion autophagy and apoptosis Mitochondria contain christae their own DNA and are the site of cellular respiration double membrane Vacuoles membranebound structures used for storage derived from ERGA Chloroplast contain chlorophyll that absorbs light and synthesizes sugar inner membrane system called thylakoids own DNA double membrane Cytoskeleton maintains cell shape controls positions of organelles by anchoring cytoplasmic streaming enchors the cell in place Microtubules hollow tubes made up of tubulin that make up cilia agella spindle bers that help separate chromsomes during mitosis and meiosis Micro laments from actin laments allow animal cells to form cleavage furrow during cell division streaming contracting of muscles Plasma membrane selectively permeable uid mosaic phospholipid bilayer amphiphatic contain integral proteins nonpolar regions that span the hydrophobic interior of the membrane Peripheral proteins loosely bound to surface of membrane Cholesterol molecules stabilize the membrane imbedded in the layer Functions of proteins in the plasma membrane transport enzymatic activity signal transduction celltocell recognition attachment to cytoskeletonmatrix Passive transport diffusion simple doesn39t involve protein channels nephronscountercurrent exchange facilitated requires hydrophilic protein channel and osmosis Solvent substance that does the dissolving solute substance that dissolves hypotonic having lesser concentration of solute than another solution hypertonic having greater concentration of solute than other solutions Osmotic potential the tendency of water to move across a permeable membrane into a solution Water potential pure water zero the addition of solute lowers water potential to a value less than zero water moves across a membrane from the solution w higher water potential to solution w lower water potential Active transport sodium potassium pump pumps 2 K ions for every 3 Na ions electron transport chain contractile vacuole Receptor mediated endocytosis allows a cell to take up large quantities of speci c substances ligands attach to receptors and become coated cells Tight junctions belts around epitahlial cells that serve as a barrier to prevent leakage into or out of the organs urinary bladder Desosomes rivet cells together light spot welds gap junctions permit the passage of materials from the cytoplasom of one cell to the cytoplasm of another cell heart like plasmodesmata Autocrine signals diffuse from one part of a cell to another part of the same cell synaptic signaling neutrotransmitter is the singlaing molecule endocrine singals travel anywhere in the blood to reach target cells Cascade effect ampli es the signal and provides multiple opportunities for coordination and regulation STP evolved hundreds and millions of years ago in a common ancestor Cellular respiration Two types of cellular respiration anaerobic and aerobic Oxygen is not present anaerobic respiration then glycolysis is followed by either alcoholic fermentation or lactic acid fermentation If oxygen is present glycolysis is followed by the Krebs cycle ETC and oxidative phosphorylation Glycolysis breaks down one molecule of glucose into 2 threecarbon molecules of pyruvate and releases four molecules of ATP net gain of 2 wout oxygen ATP is produced by substrate level phosphorylation direct transfer of a phosphate to ADP Facultative anaerobes can tolerate the presence of oxygen but don39t use it obligate anaerobes cannot live in an envionrment containing oxygen Fermentation can generate ATP AS LONG AS there is an adequate supply of NAD to accept electrons during glycolysis NOTE fermentation consists of glycolysis AND the reactions that regenerate NAD Alchol fermentation cells convert pyruvate from glycolysis into ethyl alchol and carbon dioxide in the absence of oxygen and also oxidize NADH to NAD Lactic acid fermentation pyruvate from from glycolysis into lactate and also oxidize NADH to NAD Citric acid cycle 1 acetyl coA combines with oxaoacetic acid to produce citric acid 2 each molecule of glucose is broken down to 2 moecues of pyrivate during glycolysis so each molecule of glucose results in 2 turns 3 pyruvate must combine w coenzyme A to form acetyl coA which enters the Krebs cycle produces 2 NADH 4 each turn of the Krebs cycle releases 3 NADH 1 ATP 1 FADH and C02 5 during the Krebs cycle ATP is produced by substratelevel phosphorylation Krebs cycle takes place in the matrix ETC takes place in the cristae membrane NAD is the oxidized form NADH is the reduced form ETC 1 a collection of molecules embedded in the cristae membrane of the mitochondria 2 thousands of copies due to the extensive folding ETC carries electrongs delived by NAD and FAD from glycolysisKrebs cycle to oxygen the nal electron acceptor through a series of redox reactions Reduction one atom gains electrons or protons oxidation one atom loses electrons 3 highly EN oxygen pulls oxygen through the ETC 4 NADH delivers electrons to higher energy level in the chain than FADH2 Oxidative phosphorylation 1 it is powered by the redox reactions of the ETC 2 proteins are pumped from the matriz to the outer compartment by the ETC 3 a proton gradient is created bt the outer compartment and the inner matrix 4 protons cannot diffuse across the christae can only go through ATP synthase chemiosmosis as protons ow through these channels they generate energy to phosphorylate ADP to ATP Oxygen is the nal hydrogen acceptor forming water SEQUENCE glucose l NAD and FAD l ETC lchemisomosis lATP Photosynthesis Cell Division Functions in growth repair and reporudction Mitosis produces two genetically identical daughter cells and is diploid meiosis results in cells that are haploid A replicated chromosome consists of two sister chromatids copies of each other centromere is the region that holds the two chromatids together kinetochore is the disc shaped protein that attaches the chromatid to the spindle Two factors limit cell size and promote cell division the ratio of the colume of a cell to the SA and the capacity of the nucleus to control the entire ce Cell cycle phases Gl intense growth S replication of DNA 62 cell continues to grow an prepares for cell divion interphase mitosis cytokinesis Mitosis Prophase nuclear membrane disintegrates strands of chromsomes condense nuceous disappears mitotic spindle begins to form Metaphase chromsomes line up along the equator centrosomes are positioned at the opposite poles of the cells spindle bers run from centrosomes to kinetochores in the centromeres Anaphase centromeres of each chromosome separate as spindle bers pu apart sister chromosomes Telophasse chromsomes cluster at oppsite ends of the cell and nuclear membrane forms Cytokinesis cleavage furrow w actin and myosin for animal cells cell plate w sticky middle lamella for plant cells Density dependent inhibition cells grow and divide until they become too crowded anchorage dependence to divide a cell must be attached to a surface cancer cells show neither Meiosis I reudciton division process by which homologous chromsomes separate meiosis sister chromatids separate into different cells Meiosis I Prophase I synapsis the pairing of homogogues crossing over the exchange of homogous bits of chromosomes chiasmata visible manifestations of crossing over Metaphase homoogus pairs of chromsomes are lined up DOUBLE le along the metaphase plate spindle bers are attached to centromeres Anaphase separation of homogous chromsomes as they are pulled by spindle bers Telophasse homogous pairs continue to separate until they reach the poles of the cell Cytokinesis same time as teophase Meiosis same steps as mitosis The types of genetic variation result from meiosis and fertilization independent assortment of chromosomes corssing over and random fertilization Cell cycle control system checkpoints at 61 restriction point if it receives the goahead the cell will complete cell divison otherwise it enters G zero phase 62 M Protein kinases signal transduction catalyze the phosphortylation of target proteins that regulate the cell cycle CDKs are activated by binding to cyclin which activates the molecule The activity of a CDK rises and falls with the concentration of its cyclin partner Peaks in MPF activity correspond to rises in cyclin Cyclin rises during S and 62 and falls during the M phase MPF triggers ce39s passage from 62 into M Purpose of apoptosis no longer needed cells too much genetic damage and may lead to cancer defense against infection for plant cells excessive protein misfolding conserved evolutionary mechanism Heredity Multiplication rule to nd the probability to two independent events happening addition rule when more than one arrangement of events producing the speci ed outcome is possible Law of dominance when two organisms homozygous for two opposing traits are crossed the offspring that are hybrid exhibit only the dominant trait and the hidden trait is recessive Law of segregation during the formation of gametes the two traits carried by each parent separate Ttle and t Law of independent assortment a cross a carried out bt two individuals hybrid for two or more traits that are not on the same chromosome during gamete formation the allele of a gene for one trait such as height Tt segregates independently from the alleles for another trait seed color Yy Incomplete dominance blending codominance blood types both traits show Multiple allles when there are more than two allelic gorms of a gene Pleiotropy the ability of one single gene to affect an organism in several or many ways Epistasis two separate genes control one trait but one gene masks the expression of the other gene 934 Polygenic blending of several genes that vary along a continuum height skin color etc Penentrance the proportion of individuals in a group with a given genotype actaually show the expected phenotype Linked genes genes on the same chromsomes that are inherited together and don39t assort indpenendtly Of 46 human chromsomes 44 are autosomes and 2 are sex chromsomes Traits on the X chromosome are sex linked If a sex linked trait is due to a recessive mutation a female will express the phenotype only if she carries two mutated genes if she carries only one mutated X linked gene she will be a carrier If a sex linked trait is due to a dominant mutation a female will express the phenotype with only one mutated gene If a male inherits a mutated X linked gene he will express the gene Recesive sexlinked traits include color blindness hemophilia muscular dystrophy All daughters of affected fathers are carriers Sons cannot inherit a sex linked trait from the father because the son inherits the Y chrosome from the father A son has a 50 chance of inherited a sex linked trait from a carrier mother There is no carrier state for males it is uncommon for a female to have a recessive sex linked condition One map unit on a chromosome is the distance within which recombination occurs 1 percent of the time Determining recombination frequencies number of recombinantstota offspring x 100 Autosomal recessive PKU cystic brosis Taysachs sickecell Autosomal dominant huntington s Sexlinked recessive hemophilia color blindness muscular dystrophy Down syndrome 47 chromsomes due to trisomy 21 turner39s syndrome XO Klinefelter39s syndrome XXY Deletion fragment is lost during cell division inversion reattaches in reverse orientation translocation chromosome fragment becomes attached to a non homolgous chromosome Genomic imprinting variation in phenotype depending on whether a trait is inherited from mom or dad Molecular Basis of Inheritance Grif th discovered that bacteria have the ability to transform harmless cells into virulent ones by transferring some genetic factor from one bacteria cell to another bacterial transformation Avery provided direct experimental evidence that DNA not protein was the genetic material Hershy and Chance proved that DNA from the viral nuecleus not protein from the viral coat was infecting bacteria Watson and Crick proposed the double helix structure of DNA Meselson and Stahl proved that DNA replicates in a semiconservative fashion DNA replication steps 1 Helicase unwinds our double helix into two strands 2 Polymerase adds nucleotides to an existing strand 3 Ligase brings together the Okazaki fragments 5 Topoisomerase cuts and rejoins the helix 6 RNA primase catalyzes the synthesis of RNA primers DNA AAA TAA CCG GAC mRNA UUU AUU GGC CUG tRNA AAA UAA CCG GAC STEPS of transcription NO Helicase NO RNA primaseRNA primers Three stages of transcription are initiation elongation and termination NUCLEUS Initiation Transcription factors attach to the promoter Then RNA polymerase II binds to the promoter TATA box and pries the two strands of DNA apart Note the whole complex of RNA polymerase II and transcription factors bound to the promoter transcription initiation complex Elongation RNA polymerase II moves down links together RNA nucleotides complementary to a DNA template strand in a 53 direction DNA retwists into double helix Termination The RNA transcript premRNA not nished yet is released when it nears the polyadenylation signal AAUAAA RNA polymerase II detaches from the DNA RNA processing INCLUDES RNA splicing The 539 end of the premRNA receives a 539 cap a modi ed guanine basically guanine with three phosphates The 339 end receives 50 250 adenine nucleotides polyA tail The premRNA contains BOTH introns intervening sequences and exons expressed sequences snRNPs small nuclear ribonucleoproteins catalyze splicing and recognize splice sites join with other proteins to form a spliceosome SPLICES the intron and LINKS the exons the intron degrades premRNA becomes mRNA which only contains exons STEPS of translation Translation has three stages initiation elongation both of which require GTP termination Initiation a small ribosomal subunit binds to a molecule of mRNA in a bacteria the mRNA binding site on this subunit recognizes a speci c nucleotide sequence on the mRNA The intitator tRNA anticodon UAC basepairs with the start codon AUG thus tRNA carries the amino acid methionine The arrival of the large ribosomal subunit completes the initation complex Proteins called intitation factors are required to bring all translation compnents together Hydrolysis of GTP provides the energy for the assembly The intitator tRNA is in the P site the A site is available to the tRNA bearing the next amino acid Elongation Codon recognition the anticodon of an incoming aminoacyl tRNA basepairs w the complementary mRNA codon in the A site hydrolysis of GTP increases ef ciency many different aminoacyl tRNAs are present but only the one w the proper anticodon will bindallow the process to continue Peptide bond formation an rRNA molecule of the large ribosomal subunit catalyzes the formation of peptide bond bt amino group of new amino acid A site and carboxyl end of growing polypeptide P site Polypeptide removed from tRNA P site and attaches it to amino acid on the tRNA in the A site Translocation the ribosome translocates the tRNA in the A site to the P site At the same time the empty tRNA in the P site is moved to the E site where it is released the mRNA moves along w its tRNAs bringing the next codon Termination when a ribosome reaches a stop codon on mRNA UAG UAA or UGA the A site of the ribosome accepts a release factor a peotein shaped like a tRNA instead of an aminoacyl tRNA The release factor promotes hydrolysis of the bond bt tRNA in the P site and last amino acid of the polypeptide thus freeing the polypeptide from the ribosome The two ribosomal subunits and the other compnents dissociate Bacteriophage Lytic cycle a type of phage replicative cycle resulting in the release of new phages by lysis and death of the host cell Lysogenic cycle a type of phage replicative cycle in which viral genome becomes incorporated into the bacterial host chromosome as a prophage is replicated along with the chromosome and does not kill the host Retroviruses viruses that contain RNA instead of DNA and replicate in an unusual way reverse the usual ow of information from DNA to RNA Although bacteria can reproduce through a primitive method called conjugation the main mode of reproduction is binary ssion F plasmid contain genes for the production of pilia that lead to conjugation R plasmid leads to resistance of speci c antibiotics Operon a set of genes and switches that controls the expression of those genes inducible lac operon and repressible tryptophan operon Tryptophan Operon consists of promoter and 5 adjacent structural genes that code for separate enzymes that are necessary to synthesis tryptophan Without RNA polymerase attached to DNA at the promoter transcription ceases tryptophan operon is known as a repressible operon meaning it is always on unless the repressor is activated Three enzymes must be synthesized to break down lactose into glucose and galactose coded for by the lac operon so that Ecoi can use lactose as an energy source To transcribe these genes a repressor must be prevented from binding to the operator and RNA polymerase must bind to the promoter Allolactose is the inducer that facilitates this process by binding to the active repressor and inachaUngit REMEMBER tryptophan absent repressor inactive operon ontryptophan produced Tryptophan present repressor active operon off Lactose present repressor inactive operon on Lactose absent repressor active operon off VOCAB RNA polymerase enzyme that transcribes new RNA chain Operator sequence of nucleotides near the start of an operon to which the active repressor can attach which prevents RNA polymerase from attaching to the promoter and transcribing the operon39s genes Promoter nucleotide sequence of DNA that is the binding site of RNA polymerase Repressor protein that inhibits gene transcription binds to the operator Regulator gene gene that codes for a repressor located some distance from operon and has its own promoter Prions misfolded versions of protein normally found in the brain PCR a automated technique by which DNA can be rapidly copied or ampli ed cDNA Dna produced by retroviruses CHARRRRRRRRRRRRT Domain Bacteria prokaryotes decomposers pathogens diseasecausers carry out conjugation have cell walls with peptidoglycan some carry out photosynthesis no introns viruses are placed here Domain archea unicellular prokaryotic include extremophiles methanogens obtain energy in a unique way by producing methane from hydrogen halophiles thrive in environments w high salt concentration thermophiles introns in some genes no peptidoglycan Domain Eukarya includes Protista fungi plants animals contain organelles and nucleus no pep Complex animals are triploblastic contain ectoderm outermost layer skin nervous system endoderm innermost layer guts mesoderm middle layer bloodbones ln bilateral symmetry the body is organized along a longitudinal axis Sensory apparatus and a brain are clustered at the anterior while digestive and excretory are located in the posterior the coelom is a uid lled body cavity that arises from within the mesoderm no coelom acoleomates pseudocoelomates have a uid lled tube between the endoderm and the mesoderm sponges have no symmetry do not move consists of ectoderm and endoderm connected by mesoglea have no true tissues or organs reproduce asexually by fragmentation as well as sexually hermaphrodites hydra and jelly sh invertebrate radial symmetry upside down bowlshaped contains exederm and endoderm have a gastrovascular cavity where extracellular digestion occurs Also carry out intracellular digestion inside body cells tapeworms invertebrates simplest animals with bilateral symmetry an anterior end three distinct cell layers and cephalization have true tissues and organs acoelomate the body is very at and the digestive cavity is branched roundworms invertebrate bilateral symmetry little sensory apparatuspseudocoeom parasitic Earthworms invertebrates protostome coelomates digestive tract is a tube within a tube closed circulatory system hermaphroditic hemoglobin in blood Clams snail squid invertebrate soft body bilateral symmetry with three distinct body zones headfoot sensors visceral mass digestion excretion reproduction mantle surrounds everything open circulatory system have gills PC crab invertebrate PC segmented into head thorax abdomen has more sensory apparatus exoskeleton open circulatory system trachea lung Star sh invertebrate DC slow moving endoskeleton water vascular system reproduces by fragmentation and regeneration sh mammals either endoderm or ectoderm DC vertebrate dorsal hollow nerve cord notochord a rod that extends the length of the body mammals mothers nourish their babies with milk have hair or fur placental marsupial monotremes egglaying Evolution fossil record uses radiometric dating and half life to accurately measure the age of fossils homologous structures have a common origin and re ect a common ancestry analogous structures have the same function but do not descend from a common ancestor vestigial structures are structures that are no longer used comparative embryology and comparative biochemistry molecular biology and biogeography are evidence of evolution in binomial nomenclature every organism has a name consisting of a genus and a species Cuvier studied fossils and believed that a series of catastrophes were responsible for the changes on earth James Hutton published the theory of gradualism which stated that the Earth has been molded by sudden violent events Lyle stated that geological change resulted from slow continuous actions lamarack proposed the inheritance of acquired characteristics and use and disuse Wallace published an essay discussing natural selection like darwin TENETS OF NATURAL SELECTION 1 populations tend to grow exponentially overpopulate and exceed their resources 2 overpopulation it results in competition and a struggle for existence 3 in any population there is variation and an unequal ability of individuals to survive and reproduce 4 only the best t individuals survive and get to pass traits on to their offspring 5 evolution occurs as advantageous traits accumulate in a population balanced polymorphism is the presence of two or more phenotypically distinct form of a trait out breeding is the mating of organisms within one species that are not closely related heterozygote advantage preserve multiple alleles in a population it is a phenomenon in which the hybrid individual is selected for because it has a greater reproductive success frequencydependent selection is also known as the minority advantage because it decreases the frequency of more common phenotypes genetic drift is change in the gene pool due to chance it limits diversity the bottleneck effect is when natural disasters such as res or earthquakes reduce the size of a population unselectively the founder effect is when a small population breaks away from a larger one to colonize a new area characteristics of the hardyweinberg principle the population must be very large the population must be isolated from other populations there must be no mutations random mating no natural selection allopatric speciation is caused by geographic isolation sympatric speciation include polyploidy habitat isolation behavioral isolation temporal isolation and reproductive isolation divergent evolution occurs when a population becomes isolated from the rest of the species becomes exposed to new selective pressures and evolves into a new species convergent evolution is when unrelated species occupy the same environment are subjected to the similar selective pressures and show similar adaptations parallel evolution is when two related species that have made similar evolutionary adaptation after their divergence from a common ancestor coevolution is the same as predator prey relationship and monarch butter y and milkweed plants adaptive radiation is the emergence of numerous species from a common ancestor introduce into an environment graduaism is the theory that organisms descended from a common ancestor gradually punctuated equilibrium is a theory that proposes that new species appear suddenly after long periods of stasis the endosymbiotic theory says the chloroplast and mitochondria have their own DNA DNA is more like prokaryotic DNA than eukaryotic DNA organelles have double membrane Plants Classi cation 1 Bryophytes non vascular plants including mosses horworts liverworts 2 Tracheophytes vascular plants seedless plants ferns that reproduce via spores seed plants gymnosperms cone bearing angiosperms owering plants monocotyledon dicotyledon characteristics xylem and phloem for transport ligni ed transport vessels to support the plant roots to absorb water and anchor the plant leaves that increase photosynthetic surface life cycle w dominant sporophyte generation 0 primary growth elongation of plant down into the soil and up into the air apical meristem secondary growth increases girth Plant tissue dermal tissue vascular tissue ground tissue dermal tissue protects the plant vascular tissue consists of the xylem the water and mineral conducting tissue and phloem carries sugars from the photosynthetic lease to the rest of the plant by active transport 0 Ground tissue functions mainly in support storage and photosynthesis parenchymal cells have primary cell walls that are thin and exible but lack secondary cell walls collenchymal cells have unevenly thickened primary cell wall but lacks secondary cell walls sclerenchymal cells have very thick primary and secondary cell walls forti ed with lignin The three functions of roots r to absorb nutrients from the soil anchor the plant and store food taproot skingle root that gives rise to branch roots brous root systems hold plants rmly in place adventitious roots are aboveground stems contain vascular bundles each bundle contains a xylem on the inside and a phloem on the outisde and meristem tissue in the middle monocots scattered dicots ring LEAF The epidermis is covered by a waxy cuticle made of cutin to minimize water loss guard cells are modi ed epidermal cells that contain chloroplasts and controls the opening of the stomates palisade and spongy mesophyll function in photosynthesis Vascular bundles carry water and nutrients from the soil to the leaves and also carries sugar from the leaves to the rest of the plant Xylem uid Rises through transpirational pull the evaporation of water off plant leaves 0 High humidity slows down transpiration wind reduces humidity and increases transpiration increased light intensity increases the rate closed stomates stop it o The sexual life cycle of plant is characterized by the alternation of generations in which a haploid and diploid generation alternates with each other The gametophyte n produces gametes through mitosis these gamete fuse during fertilization 2 yield diploid zygotes each they go to develop into a diploid sporophyte which produces haploid spores by meiosis each spore forms a new gametophyte completing the life cycle