Andalusia PAU Biology key terms

Water chemical potential expressed relative to a defined pure-water reference, often in pressure units. Pure water at reference conditions is assigned zero; positive pressure can raise potential, and water moves toward lower potential.

The net movement of water across a partially permeable membrane from a region of higher water potential to one of lower water potential. It is passive and driven by the water potential gradient.

The component of water potential caused by dissolved solutes, always negative or zero. More concentrated solutions have more negative solute potentials and so attract water.

Shrinking of the protoplast away from the plant cell wall when a cell loses water in a hypertonic solution. It occurs because the protoplast contracts while the rigid wall stays in place.

Passive movement through membrane channels or carriers down an electrochemical gradient. The transport step does not directly hydrolyze ATP, although other processes may use energy to establish the gradient.

Energy-coupled movement against an electrochemical gradient. Primary transport can use ATP directly; secondary transport uses a gradient established by another energy-dependent process.

The description of membranes as a phospholipid bilayer with proteins and other molecules embedded in or attached to it, able to move laterally. It explains selective permeability and membrane flexibility.

The first stage of mitosis, when chromosomes condense, the nuclear envelope breaks down and spindle fibres begin to form. Each chromosome is already duplicated into two sister chromatids.

The mitotic stage in which condensed chromosomes line up along the cell equator, attached to spindle fibres at their centromeres. This alignment ensures one chromatid from each pair goes to each pole.

The mitotic stage in which spindle fibres shorten and pull sister chromatids apart to opposite poles. Each pole therefore receives one complete set of identical chromosomes.

The final mitotic stage, when chromosomes reach the poles, decondense and new nuclear envelopes form. Cytokinesis usually follows, dividing the cytoplasm to produce two separate cells.

Nuclear division producing two daughter nuclei genetically identical to the parent cell and to each other. It underlies growth, repair and asexual reproduction in eukaryotes.

Reduction division that, in a canonical diploid life cycle, produces haploid nuclei through two successive divisions. Subsequent cell fates vary: products may become gametes or spores, and animal oogenesis does not make four equivalent ova.

Exchange of corresponding segments between non-sister chromatids of homologous chromosomes during prophase I. It breaks linkages between alleles and produces recombinant chromosomes.

Random orientation of homologous chromosome pairs at the equator in meiosis I, so maternal and paternal chromosomes are distributed independently into gametes. It generates many possible allele combinations.

A pair of chromosomes of similar size and shape carrying the same gene loci, one inherited from each parent. They pair during meiosis but may carry different alleles at a locus.

One of the two identical DNA copies of a replicated chromosome, joined at the centromere. Chromatids separate at anaphase so each daughter nucleus receives one copy of every chromosome.

The constricted region of a chromosome where the two sister chromatids are held together and where spindle fibres attach. It ensures correct segregation of chromatids during nuclear division.

An alternative DNA-sequence form at a locus. A diploid individual ordinarily carries one copy on each homolog, while haploid and polyploid organisms have different numbers of copies.

The particular combination of alleles an organism carries at one or more loci, which together with environmental influences and interactions among genes determines the observable phenotype.

The observable traits of an organism, such as morphology, physiology, or behavior, resulting from the interaction of its genotype with environmental conditions during development.

RNA synthesis from a DNA template by RNA polymerase. Nuclear-gene transcription occurs in the eukaryotic nucleus; organelles have additional systems, and prokaryotic transcription can be coupled to translation.

The process at the ribosome in which messenger RNA codons are read and matched to transfer RNAs, assembling amino acids into a polypeptide in the order specified by the genetic code.

Small, single units that join end to end in long chains, such as amino acids forming proteins or nucleotides forming nucleic acids. Their structure determines the properties of the polymer built from them.

A large molecule made of many similar subunits linked in sequence, such as starch from glucose or a protein from amino acids. Its behaviour depends on chain length, branching and folding.

A joining reaction in which two molecules bond and a small molecule, usually water, is released. It builds glycosidic, peptide and ester bonds when smaller units are assembled into larger biological molecules.

A splitting reaction in which a water molecule is used to break a bond between subunits. Digestion of starch, proteins and lipids depends on it, and it reverses condensation.

The bond formed between the hydroxyl groups of two monosaccharides with the loss of water. Its orientation, alpha or beta, changes whether a polysaccharide coils or forms straight strands.

A storage polysaccharide of alpha-glucose found in plant cells, made of amylose and amylopectin. It is compact, insoluble and easily hydrolysed to release glucose for respiration.

A structural beta-glucose polysaccharide forming straight chains associated into strong plant-wall microfibrils. Most animals lack their own cellulase enzymes, while some obtain cellulose digestion through symbiotic microorganisms.