Plants Flashcards
Plants
● Multicelled, eukaryotic, photosynthetic autotrophs
● Their cell walls are mad of cellulose, and their surplus carbohydrate is stored as starch
Sporopollenin
● A tough polymer, is resistant to almost all kinds of environmental damage and protects plants in a harsh terrestrial environment
- Found in the walls of spores and pollen
Gametangia
● A protective jacket of cells that gametes and zygotes form within some plants
● Prevents them from drying out
Cutin
● The waxy coating on the leaves
● Helps prevents water loss
Stomates
● Open to exchange gases
● Close to minimize water loss
Mycorrhizae
● A symbiotic fungus that lives on some roots
● Increases hte amount of water hte plant absobrs
Lignin
● Embedded in xylem and other plant cells
● Provides support
Leaf
● Organized to maximize sugar production while minimizing water loss
● Epidermid is covered by a waxy cuticel made of cutin to minimize water loss
- Guard cells control the opening of the stomates
● Inner part consists of palisade and spongy mesophyll
- Vascular bunders/veins are located here
Guard cells
● Modified epidermal cells that contain chloroplasts
● Photosynthetic
● Control the opening of the stomates
Palisade mesophyll cells
● Photosynthesis
● Pakced tightly
Spongy mesophyll cells
● Photosynthesis
● Packed loosely to allow for diffusion of gases into and out of these cells
Vascular bundles/veins
● Loaed int he mesophyll cells
● Carry water and nutrients from the soil to the leaves
● Carry sugar, the product of photosynthessi, from the leaves to the rest of the plant
Bundle sheath cells
● Specialized mesophyll cells
● Surround the veins and separate them from the rest of mesophyll
● Involved in special C4 photosynthesis
Stomatal crypts
● Some platns have stomates nestled in these
● THey further minimize exposure of the stomate to air
● This reduced water loss even more
Osmosis
● The diffusion of water across a membrane
● The direction in which water idffuses in determined by water potential
● Responsibled for short-distance transport of water
Water potential
● Free water, water not bound to solutes, diffuses from regions of higher water potential to lower water potential
Aquaporins
● Speical transport proteins that facilitate the rapid osmosis of water across emmbranes
● THe opening and closing of these selective channels affect the rate at which water flow, not its direction
Bulk flow
● The movement of liquid in response to pressure gradient
● Always occur from higher to lower pressure
● Independent of slolute concentration
● Occur within vascular tissue (phloem and xylem)
Phloem
● Transports sugars produced by photosyntehssis from leaves to all parts of a plantf or immediate use or storage
Xylem
● Transports fluid, water and minerals from the soil, rises in a platn against gravity but requires no energy
● The fluid can be pushed up by root pressure or pulled by transpirational pull
Root pressure
● Results from water flowing into the stele from the soil as a result of the high mineral content in the root cells
● It push xylem sap upward only a few yard
● Known as guttation
Transpirational pull
● Evaporation of water from leaves
● Causes negative pressure (tension) to develop int eh xylem tissue from the roots to the leaves
● The cohesion of water due to strong attraction between water molecules makes it possible to pull a column of water from above within the xylem
● The absorption of usnlight drives this
Transpirational pull-cohesion tension theory
● States that for each molecule of water that evaporates from a leaf by transpiration, another molecule of water is drawn in at the root to replace it
Plant hormones
● Help coordinate growth, development, and responses to environemntal stimuli
● Produced in very small quantities, but they have a profound effect ont eh plant because the hormone signal is amplified
Signal transduction pathway
● amplify the hormonal signal and connect it to specific cell responses
Tropism
● Growht of a plant toward or away from a stimulus
● Examples are thigmotropism (touch), geotropism or gravitropism (gravity) and phototropism (light)
Positive tropism
● A growth of a plant toward a stimulus
Negative tropism
● A growth of a plant away from a stimulus
Phototrpism
● Result from an unequal distribution of one category of plant hormones called auxins htat accumulate on teh side of the plant away from the light
● Cells ont he shady side of the plant enlarge and the stem bends toward the light
Auxin
● Cause primary growth (in length)
Geotropism
● Results from an interaction of auxins and statoliths
Statoliths
● Specialized plastids containing dense starch grains
Photoperiod
● The environmental stimulus a plant uses to dtect the time of year
● THe relative lengths of day and night
Circadian rhythm
● Biological clock set to a 24-hour day
Photoperiodism
● Physiological response to the photoperiod
- Such as flowering
Long-day plants
● Plants that flower only when the light period is longer than a certain number of hours
● Plants respond to the legnth of darkness not the length of light
Short-day plants
● Plants that flower only when the light period is shorter than a certain number of hours
● Plants respond to the legnth of darkness not the length of light
Day-neutral plants
● Plants that flower regardless of the length of day
Phytochrome
● Photoreceptor pigment responsible for keeping track of the length of day and night
● Two forms Pr and Pfr
Pr/red-light absorbing
● A form of phytochrome
● Phytochromee is synthesized in the Pr form
● It is in Pr form in dark
Pfr/Infrared light absorbing
● A form of phytochrome
● Phytochrome is converted to Pfr when exposed to light
What are the strategies that enabled plants to move to land?
● Cell walls made of cellulose lend support to the plant whose cells, unsupported bby a watery environemtn, must mainttain their own shape
● Roots and root hairs absorb water and nutrients from the soil
● Transport tissue, xylem and phloem, can move fluid great distances
- Also enables plants to grow tall
● Stomates
● Cutin
● Gametangia
● Sporopollenin
● Seeds and pollen are a meanas of dispersing offspring with protective coat that prevents dessication
● Mycorrhizae
● Lignin
What happens when water is introduced to guard cells and why?
● Cellulose microfibrils are oriented in such a direction that when the guard cells absorb water by osmosis and become turgid, they curve like hot dogs, causingt he stomate to open
● Wehn guard cells lose water and become flaccid, the stomate clses
What controls short-distance movement of substances into and out of cells?
Selective permeability of plasma membranes
What are the factors that affect the rate of transpiration?
● High humidity slows down transpiration, while low humidity speeds it up
● Wind can reduce humidity near the stomates adn thereby increase transpiration
● Increased light intensity will increase photosynthesis and thereby increase the amount of water vapor to be transpired and increase the rate of transpiration
● Closing sotmates stops transpiration
How does plant keep track of time?
● The conversion from one from of phytochrome to another
● Plant is able to sense the concentrations of the two phytochromes and respond accordingly
