BIOL 1010 | Chapter 33 Definitions

herbivores

organisms that feed on plants, ranging from insects to large mammals, which exert selective pressure on plants to evolve defensive strategies

phytochromes

Photoreceptor proteins in plants that absorb red and far-red light → allows plant to detect light quality, duration, and changes in day length → regulating germination, flowering, and other light-dependent processes

photoperiod

the relative lengths of day and night that act as an environmental cue for plants, influencing seasonal developmental processes such as flowering, seed germination, and dormancy

short-day plants

plants that flower when the duration of night exceeds a certain number of hours, typically in late summer, fall, or winter, such as chrysanthemums and poinsettias

long-day plants

plants that flower when the duration of night is shorter than a certain number of hours, usually in late spring or early summer, such as spinach, lettuce, and radishes

circadian rhythm

an innate biological cycle of roughly 24 hours that regulates physiological and behavioural processes in organisms, persisting even in the absence of environmental cues

biological clocks

internal timekeeping mechanisms that generate and maintain circadian rhythms, allowing organisms to anticipate daily changes in the environment

clock genes

genes that encode proteins which regulate their own transcription through feedback loops, creating cyclic patterns of protein concentration that drive circadian rhythms

tropisms

directed growth responses in plants in which a part grows toward a stimulus (positive tropism) or away from a stimulus (negative tropism), allowing the plant to optimize access to resources such as light, water, or support structures

phototropism

growth of a plant organ in response to light, typically involving faster cell elongation on the shaded side of a shoot, causing it to bend toward light (a positive tropism)

gravitropism

directional growth of a plant in response to gravity → roots typically exhibit positive gravitropism (grow downward), and shoots exhibit negative gravitropism (grow upward)

thigmotropism

growth response of a plant to → touch or physical contact (tendrils coiling around a support) → allows climbing plants to secure structures while growing toward light

ethylene

gaseous plant hormone that triggers aging responses (fruit ripening, leaf abscission, and programmed cell death) → produced in response to stress (drought, flooding, injury, or infection)

abscission layer

specialized region at the base of a leaf stalk composed of thin-walled parenchyma cells, which is enzymatically weakened to allow leaves or fruits to detach while leaving a protective leaf scar

abscission

process by which plants shed leaves, fruits, or flowers, often in response to environmental cues or hormonal signals

abscisic acid (ABA)

plant hormone that slows growth, induces seed dormancy, and regulates responses to stress, particularly by reducing water loss during drought

seed dormancy

period in which a seed ceases growth and does not germinate until environmental conditions are favorable, ensuring survival through adverse seasons

gibberella

genus of fungi that can infect plants and cause hyperelongation of stems by producing excessive amounts of gibberellins

gibberellin

plant hormone that stimulates cell elongation, cell division, stem and leaf growth, bolting, seed germination, and fruit development, acting as a natural growth regulator

bolting

The rapid elongation of a plant’s floral stalk, often caused by high levels of gibberellin, which can make leafy vegetables like lettuce or parsley unpalatable

cytokinins

plant hormones produced in actively growing tissues such as roots, embryos, and fruits that promote cell division (cytokinesis), cell differentiation, and delay aging by inhibiting protein breakdown in leaves and flowers

terminal bud

The main growing tip at the apex of a shoot that directs vertical growth and can suppress the growth of lateral or axillary buds through apical dominance.

axillary bud

Buds located at the junctions of stems and leaves that have the potential to develop into lateral branches or flowers if not inhibited by apical dominance.

antagonistically

two hormones act antagonistically when the action of one counters the action of the other, such as auxins suppressing axillary bud growth while cytokinins promote it.

apical dominance

terminal bud inhibits growth of axillary buds, resulting in upward growth rather than lateral branching, largely controlled by the interaction of auxins and cytokinins

auxin

Any chemical substance that promotes elongation of seedlings and regulates multiple aspects of growth and development in flowering plants, including stem elongation, root formation, and branching patterns

indoleacetic acid (IAA)

primary natural auxin in plants that mediates cell elongation, division, and differentiation, and coordinates growth responses such as phototropism.

indolebutyric acid (IBA)

A naturally occurring auxin used to stimulate root development in cuttings and transplanted plant parts.

hormones

Chemical signals produced in one part of a plant that are transported to other parts, where they regulate growth, development, and responses to stimuli.