15.1 and 15.2 Flashcards
Changes in levels of soil water, salt, and temp. → affect
plant’s growth, reproduction + survival
Plants are adapted to tolerate temporary stress→by
going dormant
Plants react to drought by saving water by
closing their stomata →slows down rate of transpiration
adaptations that let plants survive dry climate
-Cacti and succulent plants (Aloe vera) keep water in fleshy stems that help them to thrive in desert
-Succulent plants have thick fleshy leaves
-stems and leaves have a thick cuticle
-Some desert plants have waxy cuticles or an epidermis multiple layers thick
-Stomata of many plants are made inside epidermal pits + protected by epidermal hairs
adaptations that let plants survive in cold, dry arctic regions
-small needle-shaped leaves + grow low to ground
-reduces transpiration by reducing exposure to harsh, dry wind
adaptations that let plants survive wet habitats
-mangrove trees grow in coastal marshes, but their roots are slightly above ground →provide O2 for underwater roots→negative gravitropism
-plants not able to survive in aquatic habitats have to endure periods of waterlogged soil
adaptation for a salty habitat
Halophytes (salt-tolerant plants) have adaptations to remove salt from plant
- some plants have salt glands that remove salt from plant across leaf epidermis + rain washes it away
- e.g. salt marsh plant called Pickleweed takes extra salt to stems at tips of plant→pickleweed sheds stems→salt removed
adaptations that protect plants from infection
When infected→plants use chemicals to defend themselves
- Some chemicals can be used for defence or lignin production (lignin hardens cell walls around infected area + seals off pathogen from taking over
adaptations to protect themselves from herbivores
-physical defences (thorns, poisons)
-when in light, potato tubers make a bitter chemical called solanine→fungicide + insecticide
-solanine→natural defence that protects tubers
from being eaten
-chlorophyll can be a clue that tuber has been in
light + contains solanine
auxin
chemical messenger produced in shoot tip and is a plant growth hormone
plant hormones
Plant hormones: chemical signals made in small amounts in one section of plant that specifically affect another part of the plant
5 major plant hormones
Auxins, cytokinins, gibberellins, abscisic acid, and ethene
purpose and functions of auxin
Main purpose of auxin is to help plants grow →lengthening stem
Other functions:
-increase secondary growth of plant stem by promoting cell division in vascular cambium
-trigger process of making roots and leaves
-bringing plants to auxin can cause fruit to grow without any pollination or seed development
where is auxin made?
Made in apical meristems of plants at tips of shoots
process of auxin being used
Seedling gets light from one direction→auxin builds up on shaded side → triggers growth beneath tip→cells on shaded side exposed to more auxin→they lengthen, more than the cells on the lighted side
Uneven growth of cells on the two sides of plant make the shoot bend toward light (smaller on that side)
functions of cytokinins
help plants grow by triggering cell division
slows aging of flowers and fruits
encourages branching of plant
can trigger shoot formation
where are cytokinins made?
-growing tissues (embryos, roots, seeds, and fruits)
-roots (get to target cells in stems by going up xylem sap)
give an example of how effects of cytokinins are affected by concentration of auxins present?
e.g. cytokinins entering shoot system from roots encourage cell division in axillary buds
how can cytokinins be used in horticulture
-used in horticulture to make plants and leaves bigger
-e.g. gardeners pinch back terminal buds at growing tips of plant
-lowers auxin levels→plant branches more
-adding cytokinins to leaf, stem, or root cuttings can also trigger shoot formation
gibberellins functions
-important in plant growth and development
-increase stem growth by promoting cell division + cell elongation
-crucial to seed germination
When combined with auxins, gibberellins can cause
fruits to grow
what happens to plants with less gibberellins
Less gibberellin in plants→short, stiff stems + less leaves
how are gibberellins crucial to seed germination?
e.g. when in water, embryos in cereal grains (barley) let out gibberellins that trigger breakdown of nutrients held in endosperm
where are gibberellins made?
Made at tips of stems and roots
during what time is ABA made and taken through
xylem to shoots + leaves?
dormancy
Abscisic Acid functions
Stops cell division in buds + vascular cambium → stops primary + secondary growth
ABA has opposite effect of ______→causes dormancy in seeds
gibberellins
Give an example of how ABA acts like a stress hormone
e.g. plant doesn’t have enough water→ ABA builds up in leaves → stomata closes (reduces transpiration + water loss)
Spraying ABA on plants helps them …
survive drought stress in dry seasons
ethene
a gas let out when kerosene is burned
function of ethene
Natural plant hormone that helps ripen fruits
ethene promotes _____
leaf drop
describe leafdrop
Promotes leaf drop: leaves falling off deciduous trees every autumn
- Caused by sudden change in amounts of ethene + auxin in leaf petioles
