SPM Biology flashcards

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

Light-dependent stage

Stage of photosynthesis occurring on thylakoid membranes where light energy splits water, releasing oxygen and producing ATP and reduced NADP for the Calvin cycle.

Limiting factor

The environmental factor in shortest supply, such as light intensity or carbon dioxide concentration, that restricts the rate of photosynthesis even when others increase.

Transpiration

Loss of water vapour from plant leaves through stomata, creating a pull that draws water up the xylem from roots to shoots.

Translocation

Energy-requiring movement of sugars and amino acids through phloem sieve tubes from source leaves to sinks such as roots, fruits and growing shoots.

Guard cell mechanism

Guard cells take up water and become turgid, bowing outward to open the stoma; losing water makes them flaccid and closes the pore.

Auxin and phototropism

Auxin accumulates on the shaded side of a shoot, promoting greater cell elongation there so the shoot bends towards the light.

Magnesium deficiency

Shortage of magnesium prevents chlorophyll synthesis, producing yellowing between leaf veins and reduced photosynthesis.

Prokaryote versus eukaryote

Prokaryotes lack a nucleus and membrane-bound organelles and have 70S ribosomes; eukaryotes have a nucleus, organelles and 80S ribosomes.

Magnification formula

Magnification equals image size divided by actual size; both measurements must be converted to the same unit before dividing.

Surface area to volume ratio

Ratio that falls as an object grows larger; a high ratio speeds diffusion, so small or flattened cells exchange substances more efficiently.

Osmosis

Net diffusion of water across a partially permeable membrane from a region of higher water potential to a region of lower water potential.

Active transport

Movement of ions or molecules across a membrane against their concentration gradient using energy from ATP and carrier proteins.

Enzyme denaturation

High temperature or extreme pH alters the enzyme's active site shape, so the substrate no longer fits and the reaction rate falls irreversibly.

Meiosis outcome

Two divisions producing four genetically different haploid cells, with crossing over and independent assortment creating variation in gametes.

Bile function

Bile emulsifies fats into small droplets, increasing lipase action, and neutralises acidic chyme from the stomach for small intestine enzymes.

Alveolus adaptations

Alveoli provide a large surface area, thin walls, moist lining and dense capillaries, maintaining a steep gradient for fast gas exchange.

Left ventricle adaptation

The left ventricle has the thickest muscular wall because it pumps oxygenated blood at high pressure around the whole body.

Synapse transmission

A neurotransmitter diffuses across the synaptic gap between neurones, ensuring impulses travel in one direction only.

Insulin action

Insulin lowers blood glucose concentration by stimulating liver and muscle cells to convert glucose into glycogen and store it.

Vasodilation

Arterioles near the skin surface widen, increasing blood flow and heat loss by radiation, lowering body temperature.

Kidney reabsorption

Useful glucose, ions and water are reabsorbed from kidney tubules into blood, leaving urea and excess water and ions in urine.

Monohybrid cross ratio

Crossing two heterozygous parents gives a 3:1 phenotype ratio and a 1:2:1 genotype ratio in the offspring.

Test cross

Crossing an individual of unknown genotype with a homozygous recessive individual; offspring ratios reveal whether the unknown was homozygous or heterozygous.

Frameshift mutation

Insertion or deletion of bases changes every subsequent codon, altering the whole amino acid sequence and usually the protein's function.

Restriction enzyme role

Enzyme that cuts DNA at a specific base sequence, producing sticky ends used to insert a gene into a plasmid vector.

DNA ligase

Enzyme that joins the sugar-phosphate backbones of DNA fragments, sealing a gene into a plasmid vector during genetic engineering.

Gel electrophoresis

Technique separating DNA fragments by size; smaller fragments move faster and further through the gel, producing a banding pattern.

Recessive pedigree clue

A trait appearing in offspring of unaffected parents indicates recessive inheritance, because both parents must carry the hidden allele.

Energy transfer efficiency

Only about 10 percent of energy passes to the next trophic level; the rest is lost as heat, in uneaten parts and in waste.

Eutrophication

Excess nitrates and phosphates cause algal blooms; decomposing algae use up oxygen, killing fish and other aerobic organisms.

Pyramid of energy

Diagram showing energy at each trophic level; it is always upright because energy decreases at every transfer along a food chain.

Indicator species

Organism whose presence or absence reveals environmental conditions, such as lichens for clean air or mayfly larvae for unpolluted water.