Myanmar Matriculation Biology flashcards

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

Fluid mosaic model

Model of the cell membrane in which a phospholipid bilayer is studded with proteins, cholesterol, and glycolipids that move within the layer, giving selective permeability.

Mitochondrion function

Organelle with a double membrane and folded cristae where aerobic respiration occurs, producing ATP; it contains its own circular DNA and 70S ribosomes.

Meiosis I reductional division

First meiotic division in which homologous chromosomes separate, halving chromosome number from diploid to haploid; crossing over in prophase I creates genetic variation.

Mitosis outcome

Nuclear division producing two daughter nuclei with the same chromosome number and identical genetic content as the parent cell, used for growth, repair, and asexual reproduction.

Osmosis definition

Net movement of water molecules across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration, requiring no energy input.

Benedict's test

Test for reducing sugars such as glucose: sample heated with Benedict's solution forms a brick-red precipitate of copper(I) oxide; colour change from blue indicates concentration.

Enzyme active site

Region of an enzyme where the substrate binds; its shape is complementary to the substrate, and distortion of this shape by heat or pH causes denaturation.

Competitive inhibition

Inhibitor molecule resembles the substrate and binds to the active site, blocking substrate access; increasing substrate concentration reduces the inhibition.

Peptide bond formation

Condensation reaction joining the amino group of one amino acid to the carboxyl group of another, releasing water and forming a covalent peptide bond in a polypeptide chain.

Triglyceride structure

Lipid formed by condensation of one glycerol molecule with three fatty acids joined by ester bonds; it is the main energy storage molecule in animals and plants.

Mendel's law of segregation

During meiosis the two alleles of a gene separate so each gamete receives only one allele; fusion at fertilisation restores the pair in the offspring.

Test cross purpose

Cross of an individual showing a dominant phenotype with a homozygous recessive individual; offspring ratios reveal whether the dominant parent is homozygous or heterozygous.

Codominance definition

Condition in which both alleles in a heterozygote are fully expressed in the phenotype, as in AB blood group where both A and B antigens appear.

X-linked recessive inheritance

Trait controlled by a recessive allele on the X chromosome; males with one copy are affected, while females need two copies, so the disorder is commoner in males.

Semi-conservative replication

DNA replication in which the double helix unwinds and each strand acts as a template, so every new DNA molecule contains one original and one new strand.

Transcription process

Synthesis of messenger RNA from the DNA template strand by RNA polymerase in the nucleus; the mRNA then leaves through nuclear pores to the ribosome.

Codon definition

Sequence of three bases on mRNA that specifies one amino acid or a stop signal; the genetic code is degenerate, non-overlapping, and nearly universal.

Frameshift mutation

Insertion or deletion of a number of bases not divisible by three, which shifts the reading frame and alters every subsequent codon, usually producing a non-functional protein.

Natural selection mechanism

Heritable variation exists in a population; individuals with favourable variations survive and reproduce more, so those alleles increase in frequency over generations.

Homologous structures

Structures in different species with the same basic origin and anatomy but different functions, such as the forelimbs of humans, whales, and bats; evidence for common ancestry.

Binomial nomenclature

Two-part scientific naming system: genus name capitalised and species name lower case, both italicised or underlined, giving every species a unique universal name.

Hardy-Weinberg principle

In a large random-mating population with no selection, mutation, or migration, allele and genotype frequencies remain constant; genotype frequencies are p squared, 2pq, and q squared.

Transpiration definition

Loss of water vapour from aerial parts of a plant, mainly through stomata; it drives the transpiration pull that moves water up the xylem.

Xylem adaptation

Vessels and tracheids are dead, hollow, lignified tubes with no cross walls, forming continuous pipes for water and mineral transport under tension.

Calvin cycle

Light-independent stage of photosynthesis in the stroma where carbon dioxide combines with RuBP using rubisco, and ATP and NADPH reduce the product to carbohydrate.

Guard cell action

Pairs of epidermal cells flanking each stoma; when they take up water and become turgid the stoma opens, and when they lose water it closes, controlling gas exchange.

Alveoli adaptations

Tiny air sacs in the lungs with a very large total surface area, thin one-cell walls, moist lining, and dense capillary network for efficient gas exchange by diffusion.

Selective reabsorption

Process in the kidney nephron where useful substances such as glucose, amino acids, and most water are returned from the filtrate to the blood, leaving urea to be excreted.

Negative feedback

Control mechanism in which a change from the normal level triggers a response that reverses the change, restoring conditions such as body temperature or blood glucose.

Double fertilisation

In flowering plants, one male gamete fuses with the egg to form the zygote and the second fuses with polar nuclei to form triploid endosperm.

Placenta function

Organ of exchange between maternal and fetal blood, supplying oxygen and nutrients and removing carbon dioxide and urea, while secreting hormones that maintain pregnancy.

Energy transfer in food chains

Only about ten percent of energy at one trophic level passes to the next, the rest lost as heat, movement, and undigested material, so chains are short.

Eutrophication sequence

Nutrient runoff causes algal bloom; algae die and decomposers multiply, using oxygen; oxygen levels fall and fish and other aerobic organisms die.

Genetic engineering steps

Isolate the desired gene using restriction enzymes, insert it into a plasmid vector with DNA ligase, transfer the vector into a host cell, then select and culture transformed cells.

Stem cell definition

Undifferentiated cell that can divide repeatedly and differentiate into specialised cell types; embryonic stem cells are pluripotent while adult stem cells are usually multipotent.

Micropropagation method

Tissue culture of meristem tissue on sterile nutrient medium containing auxin and cytokinin, producing many genetically identical plantlets quickly from one parent plant.