chicken sperm Flashcards

Question

explain how nerve impulses pass from one neuron to another neuron (8)

Answer 1

action potential reaches the pre-synaptic membrane Ca channels open & Ca2+ diffuse into pre-synaptic neuron neurotransmitter vesicles fuse with the plasma membrane & releases the neurotransmitters by exocytosis synapse = gap between neurons neurotransmitters diffuse across the synaptic cleft & binds with the receptors on the post-synaptic membrane ion channels open & Na+ enters → post-synaptic neuron depolarises neurotransmitters are broken down by enzymes → stop effects on post-synaptic membrane

Answer 2

the resting membrane is polarised interior is -70 mV & is relatively negative compared to outside more Na+ outside + more K+ inside nerve impulses are action potentials propagated along the axons of neurons neurotransmitter attaches to receptor site → initiating transmission opens Na+ channels → Na+ rush into cell → depolarisation Na+ channels shut and K+ channels open → K+ rush out of cell → restore polarised state of membrane sodium-potassium pumps maintain polarity and restore resting potential process is repeated along the length of the neuron Na+ diffuse between region with action potential and region at resting potential myelin permits saltatory conduction → speed up transmission

Answer 3

follicle-stimulating hormones (FSH) released from pituitary gland stimulates follicle growth in the ovary oocytes mature cells of growing follicle produce estrogen stimulates more FSH receptors on follicle cells so respond more to FSH positive feedback signals endometrium to thicken final maturation of follicles rapid ↑ levels of estrogen stimulates secretion of luteinizing hormone (LH) LH spike stimulate ovulation stimulate remaining follicle to develop into corpus luteum stimulate corpus luteum to secrete progesterone progesterone stimulate maintenance of endometrium in prep for embryo implantation no pregnancy → corpus luteum disintegrates ↓ in progesterone → breakdown in endometrium progesterone inhibit FSH and LH release neg feedback

Answer 4

DNA replication is semi-conservative 1 new strand + 1 strand from parent molecule helicase uncoils double helix → separates 2 strands by breaking H bonds between bases DNA primase adds primer short length of RNA primer allows attachment of DNA polymerase III → starts to replicate DNA by adding free nucleotides in the cell in a 5' – 3' direction complementary base pairing Adenine=Thymine Guanine≡Cytosine leading strand: built up continuously towards the replication fork lagging strand: built up in Okazaki fragments DNA polymerase I removes RNA primers and replaces them with DNA DNA ligase seals gaps between Okazaki fragments by making sugar-phosphate bond 2 phosphates are lost to gain the required energy to add nucleotides

Answer 5

RNA polymerase binds to a promoter on the DNA unwind the DNA strands bind nucleoside triphosphates to the antisense strand of DNA in a 5' – 3' direction complementary pairing Adenine=Uracil Guanine≡Cytosine lose 2 phosphates to gain the required energy to add nucleoside triphosphates until a terminator signal is reached RNA polymerase detaches from the DNA many RNA polymerases can follow each other mRNA detaches from the template DNA rewinds introns have to be spliced in eukaryotes to form mature mRNA

Answer 6

translation involves initiation, elongation, translocation and termination ribosome slide along mRNA in 5' – 3' direction to start codon AUG → code for methionine tRNA activating enzymes link amino acids to a specific tRNA A, P, E binding sites are on the large subunit of the ribosome ribosome binds tRNA at the P site with the mRNA anticodon of tRNA pairs with codon on mRNA using complementary base pairing 2nd tRNA binds at the A site peptide bond forms between amino acids: polypeptide is transferred to the tRNA in A site translocation occurs as the ribosome moves down the mRNA tRNA in A site holding the growing polypeptide moves to P site tRNA in P site moves to E site tRNA in E site without its amino acid detaches another tRNA moves into A site proceeds until stop codon is reached polypeptide is released mRNA detach from ribosome subunits of ribosome separate

Answer 7

lower activation energy: energy needed to overcome energy barrier that prevents reaction ↑ rate of reaction substrate joins with enzyme at active site → form enzyme-substrate complex active site specific for a particular substrate induced fit model: change in enzyme conformation when enzyme-substrate complex forms → substrate more reactive enzyme binding with substrate brings reactants closer tgt to facilitate chemical reactions remains unchanged at the end of reaction

Answer 8

link reaction: pyruvate combines with coenzyme A → coenzyme A accepts acetyl group to form acetyl CoA oxidative decarboxylation: pyruvate oxidised to NADH NADH and carbon dioxide are formed with each decarboxylation involves oxidation and a release of energy Krebs cycle acetyl CoA releases acetyl group acetyl group is joined to a 4-C molecule → 6-C molecule → 5-C molecule → 4-C molecule → original 4-C molecule ATP formed by substrate level phosphorylation oxygen accepts electrons each pyruvate produces 2 carbon dioxide, 3 NADH, 1 FADH2 & 1 ATP

Answer 9

occurs during aerobic respiration oxidative phosphorylation = ATP production using energy from oxidising foods during electron transport chain chemiosmosis = formation of proton gradient by the movement of H+ NAD & FAD is reduced by gaining 2 electrons NADH delivers electrons to electron transport chain in the inner mitochondrial membrane electrons release energy as they are passed between carriers along the chain oxygen is the final electron acceptor electron carriers act as proton pumps protons pumped into cristae against conc gradient → generate proton gradient ATP synthase in inner mitochondrial membrane ATP synthase generates ATP due to kinetic energy from movement of H+ as it diffuses through by chemiosmosis phosphorylates ADP: ADP + Pi → ATP

Answer 10

water only plays a role in non-cyclic photophosphorylation cyclic photophosphorylation: electron returns to photosystem I chemiosmosis = formation of proton gradient by the movement of H+ photophosphorylation = production of ATP chlorophyll in photosystem II absorb light → photoactivation produce excited electrons electrons pass along a series of carriers in thylakoid membrane in electron transport chain require electrons from photolysis photolysis = splitting of water produce oxygen and H+ oxygen is released as a waste product protons pumped across thylakoid membrane → H+ gradient small thylakoid space enhances gradient ATP synthase generates ATP due to kinetic energy from movement of H+ as it diffuses through by chemiosmosis ATP synthase = protein complex in thylakoid membrane ADP + Pi → ATP electrons from photosystem II passed to I → photoactivation produce excited electrons electrons from photosystem I passed to NADP+ NADP+ accepts H+ → NADPH produced → passed to light-independent reactions ATP and NADPH are used by light independent reactions in the stroma carbon fixation to RuBP produces glycerate 3-phosphate in Calvin cycle ATP and NADPH are used to transform glycerate 3-phosphate to triose phosphate

Answer 11

occurs in stroma ATP & NADPH provided by light-dependent reactions Calvin cycle carboxylation of RuBP by rubisco → forms unstable 6C compound split into 2 glycerate 3-phosphate → reduction using NADPH → triose phosphate → converted → glucose most triose phosphate used for regeneration of RuBP use ATP

Answer 12

factor furthest from its optimum is limiting ↑ a limiting factor with other factors constant → ↑ rate ↑ a non-limiting factor with other factors constant → no effect on rate light intensity is limiting at night photosynthesis directly proportional to intensity up to plateau affects the light-dependent reactions chloroplast molecules are working at optimal pace temp limiting at low & high temp photosynthesis directly proportional to temp up to optimum temp low temperatures: limit the rate of light-independent reactions high temperatures: rubisco denatured → does not fix carbon dioxide carbon dioxide conc is limiting in bright light & warm temp photosynthesis directly proportional to CO2 conc up to plateau low CO2 conc limits carbon fixation chloroplast molecules are working at optimal pace

Answer 13

transpiration = loss of water vapour from stomata water lost from the diffusion of water vapour through stomata + evaporation from spongy mesophyll cells → replaced by water from osmosis through xylem vessels water pulled out of xylem creates suction → transpiration pull xylem vessels are hollow tubes cellulose wall with rings of lignin give strength to resist pressure due to polarity of water molecules water molecules are cohesive + adhesion between water and xylem → creates transpiration stream root hairs provide a large surface area for water uptake

Answer 14

plants absorb mineral ions bound to soil particles through roots e.g. potassium, sodium, calcium minerals dissolve in water mass flow causes movement of minerals with movement of water through soil minerals can be absorbed by facilitated diffusion movement of ions down concentration gradient minerals absorbed by active transport against a concentration gradient requires ATP occurs through carrier proteins proton pump transports H+ out of cell → creates electrochemical gradient → +ve mineral ions to diffuse into root cells -ve mineral ions cross membrane linked to H+ moving down gradient increase surface area for absorption of minerals branching of roots root hair cells fungal hyphae

Answer 15

sugars and amino acids are transported inside plants by phloem tissue glucose → sucrose loaded into the phloem in sources and translocated to sinks, where they are unloaded by active translocation: active transport → require ATP through sieve tubes: plasmodesmata provide a path between sieve tubes and companion cell sources: parts of the plant where photosynthesis is occurring stems and leaves storage organs where the stores are being mobilised sinks: roots, growing fruits, developing seeds sucrose → starch → stored in sinks high solute concentration causes water to enter by osmosis at source high hydrostatic pressure causes mass flow from source to sink

Answer 16

auxin = plant hormone produced by the shoot tip make cells enlarge alter gene expression to promote cell growth cause transport of H+ from cytoplasm to cell wall H+ pumping breaks bonds between cell wall fibres → flexible phototropism is growth towards light shoot tip senses direction of light auxin moved to darker side of stem → cause cells on dark side to elongate

Answer 17

flowering affected by light phytochrome exists in 2 interconvertible forms: active Pfr & inactive Pr Pr (red/660 nm absorbing) → Pfr (far-red/730 nm absorbing) in daylight sunlight contains more red than far red light so Pfr predominates during the day gradual reversion of Pfr to Pr in darkness long-day plants: flowering induced by dark periods shorter than a critical length Pfr remains in long-day plants at the end of short nights to stimulate flowering Pfr acts as promoter of flowering short-day plants: flowering induced by dark periods longer than a critical length enough Pfr converted to Pr at the end of long nights to stimulate flowering Pfr acts as inhibitor of flowering

Answer 18

one homologous chromosome is from the mother and one from the father prophase I: homologous chromosomes pair up → crossing over occurs recombination of linked genes’ alleles many possible points of crossing over occur at random positions where 2 chromatids crossing over aren’t identical metaphase I: random orientation of homologous chromosomes anaphase I: chromosomes move to opposite poles → independent assortment meiosis II: separates alleles further 2n combinations: 4 genetically different nuclei gametes from each meiosis

Answer 19

independent assortment of unlinked genes unlinked genes are on different chromosomes genes are inherited independently presence of one allele does not influence presence of other allele metaphase I: random orientation of homologous chromosomes orientation of one bivalent does not affect orientations of others evidence seen in dihybrid crosses all allele combinations (AB, Ab, aB, ab from AaBb) in gametes phenotypic ratio of 9:3:3:1 in double heterozygous cross shows equal probability of all gametes

Answer 20

directional selection natural selection favours one end of the range of variation progressive change in a population in that direction isolated population subjected to directional selection while rest of the species aren’t species change sufficiently over time → can’t interbreed → different species disruptive selection extreme types selected for → adapted to different niches reproductive barriers become established between extreme types polyploidy having 3(+) sets of chromosomes sometimes occurs due to an error in meiosis many new species formed as tetraploids triploids are infertile: tetraploids and diploids do not produce fertile offspring tgt

Answer 21

1+ gene control same characteristic: combination of alleles determines the phenotype no. of genes ↑ → possible no. of phenotypes ↑ allows for continuous variation of skin colour phenotypes do not follow simple Mendelian ratios of dominance and recessiveness incomplete dominance skin colour due to the amount of melanin in the skin the more recessive alleles there are the lighter the skin colour the environment also affects gene expression of skin colour sunlight/UV light stimulate melanin production if need 2nd example: grain colour in wheat + allele promote pigment production or not

Answer 22

antibodies are necessary for immunity to disease produced by beta lymphocytes many types of lymphocytes in the body, each produce 1 specific antibody each antibody corresponds to a specific antigen macrophage recognises and engulfs pathogens by endocytosis presentation of antigen by macrophage on membrane helper T-cell are complementary to antigen: binds to macrophage activated → binds to complementary inactive B-cell → activated → increases in size and clones by mitosis plasma cells grow → ↑ no. of rough ER/Golgi apparatus plasma cells begin to produce antibodies to the specific antigen antibodies secreted through membrane by exocytosis antibody binds to antigen and destroy them after the infection clear → most lymphocytes disappear but some persist → memory cells can quickly form clones of itself if the pathogen is re-encountered allows long-term immunity

Answer 23

nerve impulse arrives at end of motor neuron → stimulate contraction neurotransmitter released cause action potential in muscle fibre sarcoplasmic reticulum releases Ca2+ → bind to troponin → cause tropomyosin to expose binding sites on actin myosin heads bind to sites on actin → form cross-bridges myosin head moves actin filament by ATP actin moved towards M line → shorten sarcomere + light bands narrow ATP binding → break cross bridge conversion of ATP to ADP and Pi → myosin heads change angle cycle repeated during muscle contraction

Answer 24

``` function of the kidney: osmoregulation osmoregulation = control of water balance in blood nephron is the functional unit of the kidney ``` most small soluble molecules, glucose and ions removed from blood in Bowman's capsule through ultrafiltration in the glomerulus high pressure in glomerulus due to larger afferent than efferent arteriole basement membrane act as filter proteins, blood cells and large molecules remain in blood selective reabsorption of glucose by active transport in proximal convoluted tubule all glucose and amino acid is reabsorbed, none should remain most water reabsorbed through osmosis urea remain in the filtrate → conc ↑ microvilli ↑ surface area loop of Henle creates solute conc gradient in medulla → enhance water reabsorption active transport of Na+ out of ascending limb ascending limb is impermeable to water reabsorbed in descending limb distal convoluted tubule adjust conc of Na+/K+/H+/Cl– osmoregulation occurs in collecting duct water is reabsorbed permeability of membrane regulated by ADH depending on blood solute conc water conc in urine is variable to maintain homeostasis in blood water unabsorbed → urine

Answer 25

``` function of the kidney: osmoregulation osmoregulation = control of water balance in blood nephron is the functional unit of the kidney ``` water passes into the kidney tubules by ultrafiltration → glomerular filtrate collected by Bowman's capsule reabsorbed in proximal convoluted tubule, descending limb of loop of Henle and collecting duct by osmosis transport of salts into kidney’s medulla → maintains hypertonic conditions in medulla so water is reabsorbed ADH regulates water level and solute concentration monitored by hypothalamus pituitary secretes ADH when water in blood too low and the solute concentration of blood is too high ↑ aquaporins in collecting duct cell membranes → ↑ permeability collecting duct passes through medulla medulla is hypertonic → ↑ water is reabsorbed from collecting duct ↓ urine is produced + ↑ conc urine no ADH secreted when solute concentration is too low higher flow rates → less time for water reabsorption dilute and large vol of urine produced

Answer 26

spermatogenesis = process where male gametes are produced spermatogonia undergo mitosis to keep a supply of germinal cells present some spermatogonia grow larger to become primary spermatocytes primary spermatocyte → meiosis I → secondary spermatocytes → meiosis Il → spermatids spermatid differentiate → grow tail & reduce cytoplasm → sperms associated with Sertoli cells: provide nourishment detach from Sertoli cells → enter lumen of seminiferous tubule testosterone produced by Leydig cells stimulates sperm production

Answer 27

oogenesis = process where female gametes are produced begins during fetal development large number of oogonia formed by mitosis oogonia undergo cell growth → primary oocytes begin 1st meiotic division but stop in prophase I until puberty at puberty: some follicles develop each month in response to FSH primary oocyte completes meiosis I → 2 cells with unequal cytoplasm distribution polar body eventually degenerates secondary oocyte begin 2nd meiotic division but stop in prophase II cell fertilised → meiosis II complete ovum and 2nd polar body form

chicken sperm Flashcards

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