LGCSE Biology (0180) flashcards

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

Cell theory

The principle that all living organisms are composed of cells, that the cell is the basic unit of structure and function, and that new cells arise from pre-existing cells by division.

Prokaryotic cell

A cell lacking a membrane-bound nucleus and membrane-bound organelles, with a single circular DNA molecule, 70S ribosomes and often a cell wall, plasmids and flagella.

Osmosis

The net movement of water across a partially permeable membrane from a region of higher water potential to a region of lower water potential, without the input of energy.

Active transport

The movement of substances across a membrane against a concentration gradient using energy from ATP and carrier proteins, as in mineral ion uptake by root hair cells.

Enzyme active site

The specific region of an enzyme where the substrate binds; its shape is complementary to the substrate, and high temperature or extreme pH alters it, denaturing the enzyme.

Limiting factor

The factor in shortest supply that restricts the rate of a process such as photosynthesis; increasing any other factor produces no further increase in rate.

Tissue

A group of similar cells that are adapted to perform a particular function, such as muscle tissue or photosynthetic palisade mesophyll tissue in a leaf.

Villus

A finger-like projection of the small intestine lining that increases surface area for absorption and contains a thin epithelium, capillaries and a lacteal.

Double circulation

A circulatory arrangement in which blood passes through the heart twice per complete circuit, once through the lungs and once through the body, maintaining high pressure.

Transpiration

The loss of water vapour from the aerial parts of a plant, mainly through stomata, which draws water up the xylem and cools the leaves.

Negative feedback

A control mechanism in which a change in a condition triggers a response that reverses the change, restoring the internal environment towards its set point.

Allele

One of the different versions of a gene that can occupy the same locus on homologous chromosomes, contributing to variation between individuals of a species.

Monohybrid cross

A genetic cross following the inheritance of a single characteristic controlled by one gene, often used to predict offspring ratios with a Punnett square.

Codominance

A situation in which both alleles in a heterozygote are fully expressed in the phenotype, as in the AB blood group, so neither allele masks the other.

Mutation

A random change in the base sequence of DNA that may produce a new allele, and can be silent, harmful or beneficial to the organism.

Food chain

A sequence of organisms showing the direction of energy transfer, beginning with a producer and followed by primary, secondary and tertiary consumers.

Decomposer

An organism such as a bacterium or fungus that breaks down dead organic matter, releasing mineral ions and carbon dioxide back into the ecosystem.

Carrying capacity

The maximum population size of a species that an environment can support indefinitely, determined by available resources and other limiting factors.

Eutrophication

Nutrient enrichment of water causing algal blooms; decomposers then deplete dissolved oxygen, killing fish and other aerobic organisms.

Meiosis

A type of cell division that halves the chromosome number from diploid to haploid and produces four genetically different gametes through independent assortment and crossing over.

Fertilisation

The fusion of a haploid male gamete nucleus with a haploid female gamete nucleus to form a diploid zygote, restoring the full chromosome number.

Placenta

An organ formed in pregnancy that allows exchange of oxygen, nutrients and waste between the maternal and fetal blood without the two blood supplies mixing.

Reflex arc

The nervous pathway for a rapid involuntary response, involving a receptor, sensory neurone, relay neurone, motor neurone and effector, bypassing conscious thought.

Synapse

A junction between two neurones where a chemical neurotransmitter diffuses across the gap to transmit the impulse from one neurone to the next.

Auxin

A plant hormone produced in shoot tips that promotes cell elongation on the shaded side of a shoot, causing phototropism, and inhibits elongation in roots.

Natural selection

The process by which individuals with inherited characteristics suited to their environment survive and reproduce more successfully, so advantageous alleles increase in frequency.

Adaptation

An inherited feature of an organism that increases its chance of survival and reproduction in its environment, and may be structural, behavioural or physiological.

Antibiotic resistance

A heritable trait in bacteria, arising from random mutation, that allows survival in the presence of an antibiotic; antibiotic use selects and spreads these resistant bacteria.

Species

A group of organisms with similar characteristics that can interbreed to produce fertile offspring, and which is reproductively isolated from other such groups.

Independent variable

The variable deliberately changed by the investigator in an experiment, whose effect on the dependent variable is being measured.

Reliability

The extent to which repeated measurements give consistent results; it is improved by taking repeat readings and calculating a mean.

Accuracy

How close a measured value is to the true value; it is affected by the quality of the apparatus and by systematic errors in the method.