9 Plant Biology (HL) Flashcards
Define transpiration
Loss of water vapour from stems and leaves of plants
Define the transpiration stream
Water absorbed by the roots travels along a pressure gradient up the xylem
What causes stomata to close?
Abscisic acid is released triggering an efflux of K+ from guard cells, decreasing water pressure (less turgor) -> flaccid guard cells
What do turgid guard cells mean?
Open stomata
What do flaccid guard cells mean?
Closed stomata
What components of the xylem do all vascular plants have?
Tracheids
Describe a tracheid
Tapered cells that exchange solely via pits (pores) (slow water transfer)
What components of the xylem do only some vascular plants have?
Vessel elements with fused end walls that form a continuous tube (faster water transfer)
What lignin pattern is followed on vessel elements of the xylem?
Annular
What lignin pattern is followed on tracheid elements of the xylem?
Spiral
In which 3 ways can minerals be uptaken into plants?
Passive diffusion
(Indirect active transport) H+ ion pump displaces positive ions in the soil to allow them to diffuse in
(Indirect active transport) H+ ions bind to anions and are reabsorbed
In which 2 ways can water move through a root?
Symplastically
Apoplastically (through cell walls)
Describe the symplastic route of water through the roots
Water travels through the cytoplasm of cells which are connected via plasmodesmata
Describe the apoplastic route of water through the roots
Water travels through the cell wall (through the epidermis and cortex)) until reaching the Casparian strip into the endodermis cytoplasm and the pericycle cytoplasm until reaching the xylem
What are the 4 sections of the root?
Epidermis
Cortex
Endodermis
Pericycle
Define xerophytes
Plants that can tolerate extreme dryness
Define halophytes
Plants that can tolerate extreme salinity
Name some xerophytic adaptations
Reduced/rolled leaves
Thick waxy cuticle
Stomata in pits with hairs
CAM physiology (open stomata at night)
Lower growth to ground
Name some halophytic adaptations
Altered flowering schedule
Sequestration of ions in vesicles
Sectioning of salty leaves which can drop off
Excretion of salt through salt glands
Restricting entry of ions at roots
Define translocation
Movement of organic compounds from sources to sinks
What are the principle products in the phloem?
Sap primarily composed of:
Sugars (mostly sucrose)
Amino acids etc…
What are the two primary components of phloems?
Sieve element cells
Companion cells
What is the purpose of companion cells?
Provide metabolic support for sieve element cells and facilitate loading and unloading of materials at source and sink
Describe monocotyledon roots
Stele is large and vessels form a radiating circle around the central pith
Xylem more internal, phloem more external
Describe dicotyledon roots
Stele is very small and xylem is located centrally (usually X shaped) with the phloem surrounding (filling in the gaps)
Describe monocotyledon stems
Vascular bundles scattered throughout the arrangement with phloem externally and xylem internally
Describe dicotyledon stems
Vascular bundles are arranged in a circle around the centre (pith)
Xylem (inside) and phloem (outside) will be separated by the cambium
Describe phloem loading at the source
Active transport of the solute into the phloem make the sap hypertonic causing osmosis into the phloem from the xylem
This creates a hydrostatic pressure moving the sap to wherever there is lower hydrostatic pressure (sink)
Describe phloem unloading at the sink
Solutes are unloaded by companion cells unto the sink which becomes hypotonic causing water to be drawn back into the xylem (maintaining low hydrostatic pressure)
How can rate of translocation be measured?
Aphids and cut of the stylets
Define meristem cells
Undifferentiated cells capable of indeterminate growth (totipotent)
Where can apical meristems be found?
Shoot and root tips
What are apical meristems responsible for?
Primary growth - lengthening
Where can lateral meristem cells be found?
At the cambium
What are lateral meristems responsible for?
Secondary growth - widening
Name one of the main plant hormones involved in root and shoot growth
Auxin
What is the function of auxin?
Promotes growth in the shoot apex but prevents lateral growth - apical dominance
Why do plants have apical dominance?
To promote growth upwards to become more competitive for light
What does auxin do at the shoots?
Stimulates cell elongation
(high concentrations promote growth)
What does auxin do at the roots?
Inhibits cell elongation
(high concentrations limit growth)
What is the mechanism of auxin in shoots?
Auxin activates an H+ pump into the membrane which decreases pH (increased wall elasticity) and causes H20 to enter for elongation
Define tropisms
The growth or turning movement of a plant in response to a directional external stimulus
Define phototropism
Growth movement in response to light
Define geotropism (gravitropism)
Growth movement in response to gravitational forces
How do geotropism and auxin relate?
Auxin will accumulate on the lower side due to gravity
In shoots: elongation of the lower side (growth upwards)
In roots: Inhibition of the lower side (growth downwards)
How do phototropism and auxin relate?
Auxin will accumulate on the darker side
In shoots: elongation of the dark side (growth towards light)
In roots: Inhibition of the dark side (growth away from light)
Define micropropagation
A technique used to produce large numbers of identical plants
Describe micropropagation
Specific plant tissue is selected and sterilised
The sample is grown in nutrient agar gel
The explant is treated with hormones
The growing shoots can be continuously separated to form new samples
Once the root and shoot are developed the plant can be transferred to soil
Name three uses of micropropagation
Rapid bulking
Virus-free strains
Propagation of rare species
What are 3 ways in which plants can reproduce?
Vegetative propagation
Spore formations
Pollen transfer
What are the three stages of sexual reproduction in plants?
Pollination
Fertilisation
Seed dispersal
Describe pollination
Transfer of pollen grains from an anther (male) to a stigma (female)
This can be self-pollination or cross pollination
Describe fertilisation
Fusion of a male gamete (pollen) with a female gamete (ovule) nuclei to form a zygote
Describe seed disperasal
Fertilisation of gametes results in seed formation
This can occur via wind, water, fruits or animals
Why is seed dispersal important?
So parent and offspring do not need to compete for resources
What are the male components of the flower?
Stamen composed of: anther and filament
What are the female parts of the flower?
Pistil composed of stigma, style and ovule
What non male or female reproductive structures are there in flowers?
Petals
Sepal
Peduncle
What is the function of an anther?
Pollen producing organ of the flower
What is the function of a filament?
Slender stalk supporting the anther
What is the function of the stigma?
Sticky, receptive tip responsible for catching pollen
What is the function of the style?
Tube shaped connection between the stigma and ovule
What is the function of the ovule (plant)?
Structure that contains the female reproductive cells and becomes the seed
What is the function of petals?
Attract pollinatros
What is the function of a sepal?
Outer covering which protects the flowed when in bud
What is the function of the penduncle?
Stalk of the flower
What is the function of photochromes?
Absorb light to determine day length
What are the two types of photochrome?
Active (Pfr) and inactive (Pr)
When is photochrome far red active and inactive?
Pfr is active until it absorbs far red light and is broken down to the inactive form
When is photochrome red active and inactive?
Pr is inactive until it absorbs red light and convers into the active form
Which wavelength does Pfr absorb?
~730 nm
Which wavelength does Pr absorb?
~660 nm
When is active photochrome Pfr reverted to inactive Pr?
Night as there is less red light
What is the function of Pfr in short day flowering plants?
Inhibits flowering
What is the function of Pfr in long day flowering plants?
Activates flowering
Name the different components of a seed?
Testa
Micropyle
Cotyledon
Plumule
Radical
What is the Testa (flower)?
Outer seed coat that protects the embryonic plant
What is the Micropyle (flower)?
Small pore on the outer covering allowing the passage of water
What is the cotyledon (flower)?
Contains the food stored for the seed and forms embryonic leaves
What is the plumule (flower)?
Embryonic shoot
What is the radical (flower)?
Embryonic root
Which 4 conditions must be correct for germination?
O2 levels
Water
Temperature
pH
