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Aerobic respiration finishes in the mitochondrion, where the Krebs cycle and oxidative phosphorylation produce most ATP. The inner membrane holds the electron transport chain and ATP synthase. Other organelles carry out different roles and are not the main ATP source.
Glycolysis splits glucose into two three-carbon molecules of pyruvate, with a net gain of two ATP and two NADH. Pyruvate may then enter the mitochondrion or be reduced to lactate under anaerobic conditions. Acetyl-CoA and citrate are formed later in aerobic respiration.
Messenger RNA is transcribed from DNA and carries the coding sequence to the ribosome. Transfer RNA delivers amino acids, and ribosomal RNA forms part of the ribosome itself. DNA normally remains in the nucleus.
Each recessive trait appears in one quarter of the offspring, so both together appear in 1/4 × 1/4 = 1/16. The 9:3:3:1 ratio describes the four phenotype classes. The value 9/16 corresponds to both dominant traits.
The pulmonary vein returns oxygenated blood from the lungs to the left atrium. It is unusual because it is a vein carrying oxygenated blood. The pulmonary artery carries deoxygenated blood away from the heart to the lungs.
The liver produces bile, which contains bile salts that emulsify fats into small droplets. Bile is stored in the gallbladder and released into the small intestine. The pancreas supplies lipase but not bile.
Ultraviolet light converts a cholesterol derivative in the skin into vitamin D3, which is later activated by the liver and kidney. This is why limited sun exposure supports vitamin D status. Vitamins A, C, and K must be obtained mainly from the diet.
Only about 10% of the energy at one trophic level is passed on to the next, because most is lost as heat, used in metabolism, or left in uneaten parts. This is why food chains rarely have many levels. The remaining energy is not transferred efficiently.
In a hypertonic solution, the solute concentration outside is higher than inside, so water leaves the cell by osmosis. The cell therefore shrinks. Swelling would occur in a hypotonic solution.
Competitive inhibitors resemble the substrate and bind reversibly to the active site. Raising substrate concentration outcompetes the inhibitor, restoring the reaction rate. Non-competitive inhibitors bind elsewhere and are not overcome by more substrate.
The proximal convoluted tubule reabsorbs most glucose, amino acids, and sodium from the filtrate. Damage here therefore impairs glucose reabsorption and can cause glucose in the urine. Filtration occurs earlier in the glomerulus.
Meiosis halves the chromosome number, producing haploid gametes. If the diploid number is 20, each gamete receives 10 chromosomes. The chromosome number is not doubled in gametes.
The man can pass either an A allele or a B allele, while the woman can pass only an O allele. Children therefore have genotype AO (group A) or BO (group B). Groups AB and O are not possible in this cross.
When oxygen is limited, the electron transport chain cannot regenerate NAD+ quickly enough. Reducing pyruvate to lactate regenerates NAD+, allowing glycolysis to keep producing ATP. This pathway does not increase oxygen supply or feed the Krebs cycle.
A silent mutation changes the nucleotide sequence but not the amino acid encoded, because the genetic code is degenerate. Here both codons specify phenylalanine, so the protein sequence is unchanged. Frameshift and nonsense mutations alter or truncate the protein.
A trait present in every generation and passed from affected fathers to both sons and daughters is characteristic of autosomal dominant inheritance. X-linked recessive traits affect males more often and are not passed from father to son. Y-linked traits affect only males.
The Calvin cycle fixes carbon dioxide, so it stops when carbon dioxide is unavailable. The light-dependent reactions can continue briefly because they depend on light and water, not on carbon dioxide directly. ATP and NADPH production may continue until electron acceptors are depleted.
Insulin promotes glucose uptake by cells and stimulates glycogen formation in the liver, lowering blood glucose. Glucagon, cortisol, and adrenaline all tend to raise blood glucose. Insulin is secreted by the beta cells of the pancreatic islets.
At high altitude, the partial pressure of oxygen is lower, so the kidneys detect reduced oxygen delivery. They secrete erythropoietin, which stimulates red blood cell production and improves oxygen-carrying capacity. Carbon dioxide and glucose levels are not the primary trigger.
A Tt × tt cross gives offspring in a 1 Tt : 1 tt ratio. Half of the offspring therefore receive two recessive alleles and are short. The 3/4 value would apply to a cross between two heterozygotes.
If q = 0.2, then p = 1 − 0.2 = 0.8. Heterozygote frequency is 2pq = 2 × 0.8 × 0.2 = 0.32. The value q² = 0.04 represents homozygous recessive individuals.
Calcium released from the sarcoplasmic reticulum binds troponin, moving tropomyosin away from the myosin-binding sites on actin. This allows cross-bridge formation. Acetylcholine release and T-tubule depolarization occur earlier in excitation-contraction coupling.
Daughters receive X^C from the mother and X^c from the father, so they are carriers with normal vision. Sons receive Y from the father and X^C from the mother, so they have normal vision. Colour blindness is X-linked recessive and cannot be expressed by these daughters.
By definition, Km is the substrate concentration at which the reaction velocity is half of Vmax. At [S] = Km, half of the enzyme active sites are occupied. Velocities above 0.5 Vmax require substrate concentrations greater than Km.
The two parental combinations, grey long and black vestigial, are far more frequent than the recombinant combinations. This excess of parental types indicates that the two genes are linked on the same chromosome. Independent assortment would produce roughly equal numbers of all four classes.
Lysosomes are membrane-bound vesicles containing acid hydrolases that break down ingested material and damaged organelles. This recycling role is why they are often called the cell's digestive system. Ribosomes and mitochondria carry out protein synthesis and ATP production instead.
A condensation reaction between an amino group and a carboxyl group releases water and links the two residues by a peptide bond. Repeated peptide bonds form the primary backbone of a polypeptide. Glycosidic and ester bonds join sugars and fatty acids respectively.
The epiglottis is a flap of cartilage that tilts backwards during swallowing and seals the laryngeal opening. This prevents food and liquid from entering the trachea. The glottis is the opening itself, which the epiglottis covers.
These organisms are unicellular eukaryotes without the tissue organisation of plants, animals or fungi, so they are classified in the kingdom Protoctista. Monera contains prokaryotes such as bacteria. Fungi are eukaryotic but heterotrophic with chitinous walls and body forms distinct from these protists.
In C4 plants, PEP carboxylase attaches CO2 to phosphoenolpyruvate, giving the four-carbon acid oxaloacetate in the mesophyll. 3-phosphoglycerate is the first product of RuBP carboxylation and is characteristic of C3 fixation.
Water potential is the sum of solute potential and pressure potential, so −0.8 + 0.3 = −0.5 MPa. Solute potential is always negative and turgor pressure raises the value towards zero. Water therefore enters such a cell from any solution with a water potential below −0.5 MPa.
Depolarisation of the presynaptic membrane opens voltage-gated calcium channels, and the resulting calcium influx causes synaptic vesicles to fuse with the membrane and release acetylcholine. Sodium entry generates the action potential itself, but calcium is the direct trigger for exocytosis.
Activated B lymphocytes proliferate and differentiate into plasma cells, which are packed with rough endoplasmic reticulum and release antibodies specific to the antigen. T cells act through cell contact or cytokine signals rather than antibody secretion.
Both parents are heterozygous RW, so the offspring segregate as 1 RR : 2 RW : 1 WW. Roan animals therefore make up 2 out of 4, that is one half. The 1:2:1 ratio is typical of codominance, where both alleles are expressed in the heterozygote.
Oxygen accepts electrons and protons at the end of the chain, forming water and keeping electrons flowing so that ATP synthesis can continue. NAD⁺ is an electron carrier that delivers electrons to the chain rather than accepting them at its end.
Pancreatic amylase secreted into the duodenum breaks the glycosidic bonds of starch, releasing the disaccharide maltose. Maltase, bound to the intestinal epithelium, then splits maltose into glucose. Pepsin and lipase act on proteins and fats respectively.
Antidiuretic hormone inserts aquaporins into the membranes of collecting duct cells, so more water is reabsorbed and a small volume of concentrated urine is produced. Glucose reabsorption occurs in the proximal tubule and is unaffected by this hormone.
One turn of the cycle yields three NADH, one FADH₂ and one ATP (or GTP) by substrate-level phosphorylation, along with two molecules of carbon dioxide. Because one glucose produces two acetyl groups, these figures are doubled per glucose. The other combinations misassign the redox carriers.
One map unit equals a 1% recombination frequency, so 12 map units corresponds to about 12% recombinants. Twelve per cent of 400 is 48 offspring. The remaining 352 are parental types, distributed equally between the two parental combinations.
Because the genetic code is read in non-overlapping triplets, removing one base shifts the reading frame from that point onward. All later codons are misread, usually producing a truncated or non-functional polypeptide. Only deletions of complete triplets leave the frame intact.
The mass number is the sum of protons and neutrons, while the atomic number equals the number of protons. For sodium-23, neutrons = 23 − 11 = 12.
Moles are found by dividing mass by molar mass: 36 g ÷ 18 g mol⁻¹ = 2.0 mol.
Across period 3 the nuclear charge rises while electrons enter the same shell, so the attraction on the outer electrons increases. First ionisation energy therefore increases from sodium to silicon.
Hydrogen and chlorine share an electron pair, giving a covalent bond. Because chlorine is much more electronegative, the shared pair is pulled towards it, making the bond polar.
Hydrochloric acid is a strong monobasic acid, so [H⁺] equals the acid concentration, 1 × 10⁻² mol dm⁻³. pH = −log(10⁻²) = 2.0.
Mass is obtained by multiplying moles by molar mass: 0.50 mol × 58.5 g mol⁻¹ = 29.25 g.
Alkanes are saturated hydrocarbons in which every carbon forms four single bonds, so the hydrogen count is two more than twice the carbon count. Hence the general formula is CnH2n+2.
Charles's law states that at constant pressure the volume of a gas is directly proportional to its temperature in kelvin. Boyle's law instead relates pressure and volume at constant temperature.
Increasing pressure favours the side of the equation with fewer gas molecules. Four moles of gas on the left become two moles on the right, so the equilibrium shifts towards ammonia.
For CH₄ + 2O₂ → CO₂ + 2H₂O, use ΔH = ΣΔHf°(products) − ΣΔHf°(reactants). This gives [−394 + 2(−286)] − (−75) = −891 kJ mol⁻¹.