JCE 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. Convert both measurements to the same unit before dividing. Rearranged, actual size equals image size divided by magnification.

Osmosis definition

Net movement of water molecules across a partially permeable membrane from a region of higher water potential (less negative) to a region of lower water potential (more negative), without energy input.

Enzyme denaturation

Above the optimum temperature or away from optimum pH, bonds holding the enzyme's active site break, changing its shape so the substrate no longer fits and the rate falls sharply.

Mitosis outcome

One diploid parent cell divides to produce two genetically identical diploid daughter cells. It is used for growth, repair of tissues and asexual reproduction in eukaryotic organisms.

Limiting factor

The factor in shortest supply that restricts the rate of a process such as photosynthesis. Raising other factors has no effect until the limiting factor is increased.

Photosynthesis equation

Carbon dioxide plus water, using light energy absorbed by chlorophyll, produces glucose and oxygen: 6CO2 + 6H2O -> C6H12O6 + 6O2.

Benedict's test

Detects reducing sugars such as glucose. Add Benedict's solution to the sample and heat in a water bath; a blue solution turns brick-red if reducing sugar is present.

Nitrate ion function

Plants use nitrate ions to make amino acids, which build proteins for growth. Deficiency causes stunted growth and yellowing of older leaves.

Transpiration definition

Loss of water vapour from leaf surfaces, mainly through stomata, by evaporation. It creates the pull that draws water up the xylem from roots to leaves.

Xylem versus phloem

Xylem carries water and minerals upward in dead, lignified vessels. Phloem carries sucrose and amino acids in either direction in living cells, requiring energy for translocation.

Anaerobic respiration in muscle

Glucose is broken down without oxygen to lactic acid, releasing much less energy than aerobic respiration. Lactic acid builds up and causes muscle fatigue.

Kidney reabsorption

After filtration at the glomerulus, the kidney tubule reabsorbs all glucose, some salts and most water back into the blood. Excess water, salts and urea remain in urine.

Reflex arc

A rapid, automatic response pathway: stimulus, receptor, sensory neurone, relay neurone in the spinal cord, motor neurone, effector. It does not require conscious brain processing.

Insulin and glucagon

Insulin lowers blood glucose by promoting uptake and glycogen storage in liver and muscle. Glucagon raises blood glucose by breaking glycogen down. Both act by negative feedback.

Negative feedback

A control mechanism in which a change from the set point triggers a response that reverses the change, restoring the normal level, as in temperature and blood glucose regulation.

Synapse function

A small gap between neurones. An impulse triggers release of a neurotransmitter that diffuses across and stimulates the next neurone, slowing and directing impulse transmission.

Menstrual cycle hormones

FSH matures the follicle; oestrogen thickens the uterus lining; an LH surge causes ovulation; progesterone maintains the lining. Falling progesterone triggers menstruation.

Placenta function

An organ in pregnancy where maternal and fetal blood come close but do not mix. It exchanges oxygen, nutrients and waste, and secretes progesterone to maintain the pregnancy.

Asexual versus sexual reproduction

Asexual reproduction gives genetically identical offspring from one parent and is fast. Sexual reproduction fuses gametes, producing genetic variation in offspring.

Seed germination requirements

Seeds germinate when supplied with water for enzyme activation, oxygen for aerobic respiration, and a suitable temperature. Light is not required by all seeds.

Monohybrid cross ratio

Crossing two heterozygotes (Aa x Aa) gives genotype ratio 1 AA : 2 Aa : 1 aa and phenotype ratio 3 dominant : 1 recessive, shown in a four-square Punnett grid.

Test cross

Crossing an individual showing a dominant phenotype with a homozygous recessive individual. A 1:1 ratio of phenotypes reveals the unknown is heterozygous; all dominant offspring means homozygous.

Codominance

Both alleles are fully expressed in a heterozygote, producing a combined phenotype, as in human AB blood group where A and B antigens both appear.

Sex chromosomes

Human females have XX and males have XY. The father's sperm determines the sex of the offspring because it may carry either an X or a Y chromosome.

Energy transfer efficiency

Only about 10 percent of energy at one trophic level passes to the next. The rest is lost through respiration, heat, movement, excretion and egestion, limiting food chain length.

Capture-recapture estimate

Population size equals (number marked in first sample times total in second sample) divided by number of marked individuals recaptured. Assumes random mixing and no migration.

Decomposer role

Bacteria and fungi break down dead organisms and waste, releasing carbon dioxide and mineral ions back into the soil so nutrients are recycled through the ecosystem.

Quadrat sampling

A square frame placed at random positions in a habitat. Counting organisms within each quadrat gives an estimate of population density and distribution.

Active versus passive immunity

Active immunity involves antibody production and memory cells after infection or vaccination, giving long-lasting protection. Passive immunity is short-lived antibody transfer, such as across the placenta.

Vaccination principle

Vaccines introduce weakened or inactive antigens, triggering an immune response and memory cells. A later infection with the real pathogen then produces antibodies rapidly.

Independent and dependent variables

The independent variable is deliberately changed by the investigator. The dependent variable is measured as the outcome. All other variables must be controlled to keep the test valid.

Antibiotic limitation

Antibiotics kill or inhibit bacteria but have no effect on viruses, which lack the cellular structures antibiotics target. Viral infections need other treatments or vaccination.