UEE Biology flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Magnification formula

Magnification equals image size divided by actual size. Both measurements must be in the same unit; convert micrometres to millimetres by dividing by one thousand before calculating.

Water potential equation

Water potential equals solute potential plus pressure potential. Solute potential is always zero or negative; water moves by osmosis from higher to lower water potential across a partially permeable membrane.

Competitive versus non-competitive inhibition

Competitive inhibitors bind the active site, so more substrate overcomes them and Vmax is unchanged while Km rises. Non-competitive inhibitors bind elsewhere and lower Vmax without changing Km.

Enzyme denaturation

Heat or extreme pH breaks hydrogen and ionic bonds holding the enzyme's tertiary structure. The active site changes shape, so the substrate no longer fits and the rate falls irreversibly.

Semi-conservative replication

DNA helicase unwinds the double helix and DNA polymerase adds complementary nucleotides in the 5' to 3' direction. Each new molecule keeps one original strand and one new strand.

Frameshift mutation

Insertion or deletion of a number of bases not divisible by three shifts every later codon. All downstream amino acids change, usually producing a non-functional protein.

Chi-squared test

Chi-squared equals the sum of (observed minus expected) squared divided by expected. Compare the result with the critical value at n minus one degrees of freedom to accept or reject the null hypothesis.

Test cross

An organism showing the dominant phenotype is crossed with a homozygous recessive individual. Offspring ratios reveal whether the unknown parent was homozygous dominant or heterozygous.

Sex-linked recessive inheritance

A recessive allele carried on the X chromosome is expressed in males with only one copy. Affected fathers cannot pass the allele to sons, only to daughters as carriers.

Transpiration pull mechanism

Water evaporates from leaf mesophyll through stomata. Cohesion between water molecules and adhesion to xylem walls let the resulting tension pull a continuous water column upward.

Phloem translocation

Sucrose is actively loaded into phloem at the source, lowering water potential so water enters. Pressure rises and mass flow carries solutes to the sink, where they are unloaded.

Limiting factor in photosynthesis

The factor in shortest supply sets the rate. At low light intensity light limits rate; once light saturates, carbon dioxide concentration or temperature becomes limiting.

Auxin phototropism

Auxin redistributes to the shaded side of a shoot, promoting cell elongation there. The shaded side grows faster, so the shoot bends towards the light source.

Countercurrent gas exchange

Blood in fish gill lamellae flows opposite to the water current. A diffusion gradient is maintained along the whole gill, so more oxygen is absorbed than with parallel flow.

Cardiac output

Cardiac output equals heart rate multiplied by stroke volume, giving the volume pumped per minute. Exercise raises both factors, increasing delivery of oxygen to muscles.

Negative feedback homeostasis

A receptor detects a change from the set point, a coordinator processes the information, and an effector produces a response that reverses the change and restores the norm.

Selective reabsorption in nephron

In the proximal convoluted tubule, glucose, amino acids and most water are reabsorbed by active transport and osmosis. The collecting duct adjusts water reabsorption under ADH control.

Antibody action

Antibodies are proteins produced by lymphocytes that bind specific antigens on pathogens. Binding neutralises the pathogen and marks it for destruction by phagocytes.

Hardy–Weinberg equations

Allele frequencies p plus q equal one. Genotype frequencies are p squared plus 2pq plus q squared equal one, where q squared is the frequency of homozygous recessives.

Allopatric speciation

A geographical barrier separates populations, which then experience different selection pressures and mutations. If they become reproductively isolated, they form separate species.

Homologous versus analogous structures

Homologous structures share a common ancestor but may differ in function, such as forelimbs of mammals. Analogous structures have similar function but evolved independently, such as wings of birds and insects.

Stabilising selection

Individuals with intermediate phenotypes are favoured and extremes are selected against. The mean stays the same while variation in the population is reduced.

Binomial naming system

Each species has a two-part Latin name: the genus, capitalised, followed by the species, lower case. Both are italicised in print or underlined when handwritten.

Three-domain classification

Organisms are grouped into Bacteria, Archaea and Eukarya, based largely on ribosomal RNA and cell structure. Archaea resemble bacteria but have distinct biochemistry and membrane lipids.

Species definition

A species is a group of organisms with similar features that can interbreed to produce fertile offspring. Sterile hybrids, such as the mule, indicate separate species.

Mark–recapture estimate

Population size is estimated as marked individuals multiplied by the second sample total, divided by marked recaptures in that sample. Assumes random mixing and no deaths or migration.

Energy loss between trophic levels

Only about ten per cent of energy passes to the next trophic level. The rest is lost as heat from respiration, in movement and in undigested excreted material.

Eutrophication sequence

Fertiliser runoff adds nitrates and phosphates, causing an algal bloom. Decomposers break down dead algae and use up dissolved oxygen, so fish and other aerobes die.

Nitrogen fixation

Nitrogen-fixing bacteria convert atmospheric nitrogen gas into ammonia compounds usable by plants. Legumes host these bacteria in root nodules, supplying the plant with nitrogen.

Vaccination mechanism

A vaccine introduces antigens from a pathogen without causing disease. Lymphocytes produce antibodies and memory cells, so a later infection is fought off rapidly.

Type 1 versus type 2 diabetes

Type 1 results from insufficient insulin secretion by pancreatic cells. Type 2 involves body cells responding poorly to insulin; both raise blood glucose concentration.

Reliability and validity

Reliability is how consistently a method gives repeatable results, improved by repeats. Validity is whether the investigation measures what it claims to measure, requiring controlled variables.