CSEC Biology flashcards

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

Cell membrane

A partially permeable phospholipid bilayer surrounding the cell that controls the movement of substances into and out of the cell and contains proteins for transport and recognition.

Nucleus

The membrane-bound organelle containing chromosomes made of DNA; it controls all cell activities and is the site of DNA replication and transcription in eukaryotic cells.

Mitochondrion

An organelle with a folded inner membrane where aerobic respiration occurs; it releases energy as ATP from glucose and oxygen and is abundant in active cells such as muscle.

Chloroplast

A green organelle containing chlorophyll where photosynthesis takes place; it absorbs light energy to convert carbon dioxide and water into glucose and oxygen.

Ribosome

A small organelle found free in the cytoplasm or attached to rough endoplasmic reticulum; it is the site of protein synthesis, joining amino acids according to mRNA instructions.

Vacuole

A fluid-filled sac bounded by a membrane; plant cells have a large permanent central vacuole storing cell sap that maintains turgor, while animal vacuoles are small and temporary.

Diffusion

The net passive movement of particles from a region of higher concentration to lower concentration, down a concentration gradient, until equilibrium is reached.

Osmosis

The net movement of water molecules across a partially permeable membrane from a dilute (high water potential) solution to a concentrated (low water potential) solution; a passive process.

Active transport

Movement of ions or molecules across a cell membrane against a concentration gradient, requiring energy from ATP and carrier proteins, as in root hair uptake of mineral ions.

Enzyme

A protein biological catalyst that speeds up reactions by lowering activation energy; it is specific to its substrate and is denatured by high temperature or extreme pH.

Photosynthesis equation

6CO2 + 6H2O -> C6H12O6 + 6O2, occurring in chloroplasts with light and chlorophyll; light, carbon dioxide and temperature can limit the rate.

Aerobic respiration

The breakdown of glucose using oxygen to release energy: C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy; occurs mainly in mitochondria and releases more energy than anaerobic.

Anaerobic respiration

Breakdown of glucose without oxygen, releasing less energy; in muscle it produces lactic acid, and in yeast it produces ethanol and carbon dioxide (fermentation).

Mitosis

Cell division producing two genetically identical diploid daughter cells; it is used for growth, repair and asexual reproduction and maintains the chromosome number.

Meiosis

Reduction division producing four genetically different haploid gametes; it halves the chromosome number and introduces variation through crossing over and independent assortment.

Binomial nomenclature

The two-part naming system for organisms: Genus name with a capital letter followed by species name in lowercase, both italicised, for example Homo sapiens.

Classification hierarchy

The ordered grouping of organisms: Kingdom, Phylum, Class, Order, Family, Genus, Species; each level contains fewer organisms with more shared characteristics than the level above.

Food chain

A sequence showing energy transfer from producer to consumers; arrows point in the direction of energy flow, and energy is lost as heat at each trophic level.

Trophic level

The feeding position of an organism in a food chain (producer, primary consumer, secondary consumer); only about 10 percent of energy passes to the next level.

Decomposer

An organism such as bacteria or fungi that breaks down dead organic matter and waste, releasing mineral ions and nutrients back into the soil for reuse.

Nitrogen fixation

Conversion of atmospheric nitrogen gas into nitrogen compounds such as ammonia by nitrogen-fixing bacteria (for example in root nodules of legumes) or by lightning.

Transpiration

Loss of water vapour from the leaves of plants through stomata; it is driven by evaporation and pulls water up the xylem, and is affected by humidity, wind and temperature.

Xylem

Vascular tissue of dead, hollow, lignified cells that transports water and dissolved mineral ions upward from the roots to the leaves; flow is driven mainly by transpiration.

Phloem

Living vascular tissue that transports dissolved sugars and amino acids from sources such as leaves to sinks such as roots and fruits; transport is bidirectional.

Homeostasis

The maintenance of a stable internal environment within narrow limits despite external change, controlled by negative feedback and including temperature, blood glucose and water balance.

Negative feedback

A control mechanism in which a change in a factor triggers a response that reverses the change, restoring the value towards a set point, as in thermoregulation and blood glucose control.

Reflex action

A rapid, automatic, involuntary response to a stimulus via a reflex arc (receptor, sensory neurone, relay neurone, motor neurone, effector) that protects the body from harm.

Hormone

A chemical messenger secreted by an endocrine gland into the blood, which travels to target organs with specific receptors to regulate processes such as growth, metabolism and reproduction.

Natural selection

The process by which individuals with advantageous inherited variations survive and reproduce more successfully, so those alleles increase in frequency in later generations.

Genotype and phenotype

Genotype is the combination of alleles an organism possesses for a gene; phenotype is the observable characteristic resulting from genotype and environmental influence.

Dominant allele

An allele that expresses its phenotype even when only one copy is present; the recessive phenotype appears only in homozygotes carrying two recessive alleles.

Genetic engineering

Deliberate transfer of a gene from one organism to another, for example human insulin genes inserted into bacteria using plasmids; it produces useful products and modified crops.