Plant Biology Flashcards
Explain the role of auxin in phototropism
auxin is a plant hormone;
produced by the tip of the stem/shoot tip;
causes transport of hydrogen ions from cytoplasm to cell wall;
decrease in pH / H+ pumping breaks bonds between cell wall fibres;
makes cell walls flexible/extensible/plastic/softens cell walls;
auxin makes cells enlarge/grow;
gene expression also altered by auxin to promote cell growth;
(positive) phototropism is growth towards light;
shoot tip senses direction of (brightest) light;
auxin moved to side of stem with least light/darker side
causes cells on dark side to elongate/cells on dark side grow faster;
Describe the process of mineral ion uptake into roots.
absorbed by root hairs / through epidermis
root hairs increase the surface area for absorption
uses active transport / uses ATP / uses energy
use of proteins / pumps to move ions across membrane
against concentration gradient / diffusion gradients into cell / root
can enter cell wall space / be drawn through cell walls / apoplastic pathway
selective / only specific ions absorbed
Describe how water is carried by the transpiration stream
transpiration is water loss (from plant) by evaporation;
flow of water through xylem from roots to leaves is the transpiration stream;
evaporation from spongy mesophyll cells;
replaced by osmosis from the xylem;
(diffusion of water vapour) through stomata;
water lost replaced from xylem / clear diagram showing movement of water from xylem through cell(s) (walls) to air space;
water pulled out of xylem creates suction/low pressure/tension; transpiration pull results;
water molecules stick together/are cohesive;
due to hydrogen bonding/polarity of water molecules;
xylem vessels are thin (hollow) tubes;
adhesion between water and xylem due to polarity of water molecules;
creates continuous column/transpiration stream;
Explain how abiotic factors affect the rate of transpiration in a terrestrial plant
less transpiration as (atmospheric) humidity rises
smaller concentration gradient ( of water vapour)
more transpiration as temperature rises
faster diffusion / more kinetic energy (of water molecules)
faster evaporation (due to more latent heat available)
more transpiration as wind (speed) increases
humid air / water vapour blown away from the leaf
increasing the concentration gradient (of water vapour)
more transpiration in the light
due to light causing stomata to open
wider opening with brighter light hence more transpiration
CAM plants opposite
narrower stomata with high carbon dioxide concentration hence less transpiration
adaptations of xerophytes
xerophytes are plants that live in dry conditions;
reduced leaves/spines to prevent water loss (by transpiration);
rolled leaves to prevent water loss / stomata on the inside / sunken stomata;
thick waxy cuticle/hairs on leaves to prevent water loss (by transpiration);
reduced stomata to prevent water loss (by transpiration) /
stomata on one side of leaf;
d
eep/widespread roots to obtain more water;
special tissue for storing water;
take in carbon dioxide at night / CAM plant to prevent water loss;
the role of the phloem in the active translocation
- living tissue
- composed of companion cells / sieve tube members
companion cells involved in ATP production - sucrose / amino acids / assimilate / products of photosynthesis transported
- bi-directional transport
- source / leaves to sink / fruits / roots /storage organs / named storage organ
- pressure flow hypothesis / movement of water into phloem causes transport
Explain the functions of the different tissues of a leaf
cuticle (produced by epidermis) prevents water loss
epidermis protects cells inside the leaf
stomata (in epidermis) for gas exchange
palisade parenchyma / mesophyll / layer for photosynthesis
spongy parenchyma / mesophyll / layer for photosynthesis
air spaces for diffusion of O2 / CO2 / gases
spongy mesophyll for gas exchange / absorption of CO2
xylem transports water / mineral salts / ions to the leaves
phloem transports products of photosynthesis / sugars (to flowers / new leaves / stem / roots / fruit)
stomata allow transpiration (which helps transport of mineral nutrients)
guard cells open and close stomata
guard cells close stomata to reduce transpiration
Outline the adaptations of plant roots for absorption of mineral ions from the soil.
mineral ions are absorbed by active transport;
large surface area;
branching (increases surface area);
root hairs;
root hair cells have carrier protein/ion pumps (in their plasma membrane);
(many) mitochondria in root (hair) cells;
to provide ATP for active transport;
connections with fungi in the soil/fungal hyphae;
Explain how abiotic factors affect the rate of transpiration in a terrestrial plant.
less transpiration as (atmospheric) humidity rises
smaller concentration gradient ( of water vapour)
more transpiration as temperature rises
faster diffusion / more kinetic energy (of water molecules)
faster evaporation (due to more latent heat available)
more transpiration as wind (speed) increases
humid air / water vapour blown away from the leaf
increasing the qconcentration gradient (of water vapour)
more transpiration in the light
due to light causing stomata to open
wider opening with brighter light hence more transpiration
CAM plants opposite
narrower stomata with high carbon dioxide concentration hence less transpiration
List abiotic factors which affect the rate of transpiration in a typical mesophytic plant.
light
temperature
wind
humidity
transpiration
is the germ given to the loss of water vapour from leaves and other aerieal parts of the plant which is replaced by water absorption
cuticle
- outermost layer of a leaf
- protects the plant from water loss and insect invasion
epidermis
secondary outermost leayer that protects the plant
vascular tissue
-phloem
-xylem
together in vascular bundles
xylem
- brings water to the leaves
- its red and dead
phloem
- carries the products of photosynthesis to the rest of the plant
palisade mesophyll
- densely packed region of cylindrical cells in upper portion of leaf
- contain many chloroplasts for photosynthesis
spongy mesophyll
- loosely packed cells with few chloroplasts
- many air spaces for gas exchange
stomata
are pores that are on the bottom of the leaf surface for oxygen and carbon dioxide exchange between leaf and surrounding environement
- on bottom to allow for less light/temperature to minimize water loss
guard cells
specialized cells that control the opening and closing of the stomata
- have uneven cell wall thickness
tracheids
dead cells in the xylem that taper at the ends and connec to one another to form a continious column
xxlem vessel elements
cells involving water transport; also dead and have thick lignified secondary walls
xylem transport + function
- transports water from roots to upper parts of the plant and supports the plant (by transpiration)
- any water lost used to cool leaves and stems
xylem primary walls
pits and pores for lateral water movement
xylem secondary walls
lignin often interupted by areas of the primary walls
lignin
complex organic compounds that greatly strengths cell wall of vascular plant
- also water profs plant and add protection against pathogens
- primary cell wall made up of cellulose; in some plants they form a secondary cell wall of lignin
stomata and guard cell action
- stomata can only be closed on short-term basis in reponse to turgor pressure of the surrounding guard cells
- when water enters the cell, guard cells bulge and their cell wall thickens which opens the stoma
- when the plant loses water; guard cells sag and that closes the stoma
hormone involved in stomata action
abscisic acid; plant hormone that causes potassium ions to diffuse rapidly out of guard cels for stomatal closure
-produced in roots during times of water deficiency
how does water loss/gain occur in the guard cell
-water loss/gain is due to potassium ion transport that triggers ATP pumps (solute concentration causes osmosis)
what affects stomatal opening and closing?
- Carbon dioxide levels
- Circadian rhythms
- Hormonal changes
- Humidity and droughts
- Temperature
turgor definition
refers to pressure in a cel that liquid exerts on the membrane and/or cell wall
cohesion-tension theory
- explains the movement of water vertically in the plant using intermoleculer attraction like cohesion and adhesion
transpiration process
- water moves down concentration gradient (spaces within leaf have high water vapour concentration so water moves to atmosphere where there is a lower water concentration); water leaves by evaporation
- water lost by transpiraiton replaced by water from vessels (replacing water from vessels maintains a high water vapour concentration in air spaces of leaf)
- the vessel water column is manintained by cohesion and adhesion (cohesion involves hydrogen bonds between water molecules and adhesion involves hydrogen bonds between water molecules and xylem vesel sides)
- tension occurs in the columns of water in the xylem
(loss of water in leaves replaced by water xylem so water flow is continous because of cohesion and adhesion) - water is pulled from the root cortex into xylem cells
(cohesion and adhesion mantain columns under tension by transpiration) - water is pulled from the soil into roots, root hair cells and roots have large surface area and water enters by osmosis
(as a result of the tension created by transpiration and continiious maintenance of a continious column of water)
root and fluid movement in plant
Water moves into root hairs through plasma membranes from soil due to the higher solute concentration within the roots (osmosis) and into the vascular cylinder (phloem and xylem)
function of roots
provide mineral ion and water uptake for plant (absorbtion)
why are roots efficent?
- extension branching patterns and specialised epidermal structures (such as root hairs cells that increase surface area)
what is the role of the root cap?
protects the apical meristem during primary growth of the root in the soil
zones of cell development in root zones
area of cell division
area of elongation
area of maturation
area of cell division in root
newly undifferentiated cells are formed in M phase of the cell cycle
area of elongation in root
where cells enlarge in size (G1)
area of maturation in root
where cells become functional party of plant
what proceses allow for mineral ions to enter the root?
- diffusion of mineral ions and mass flow of water in soil that carries these ions
- action of fungal hyphae
- active transport
what affects diffusion rate?
- difference in concentration
- length of diffusion path
- surface area
what is the action of fungal hyphase?
- symbiotic relationship between root and fungi where fungi increase surface area for absorbiton and in return hav e a place to live
active transport action in roots
ions use transport proteins in membrane due to size or polarity
- protons pumps are used to pump
- represents a form of chemiosmosis
effect of light on transpiration
Speeds up transpiration by warming the leaf and opening stomata
effect of humidity on transpiration
Decreasing humidity increases transpiration because of the greater difference in water concentration
effect of wind on transpiration
Increases the rate of transpiration because humid air near the stomata is carried away
effect of temperature on transpiration
Increasing temperature causes greater transpiration because more water evaporates
effect of soil water on transpiration
If the intake of water at the roots does not keep up with the transpiration, turgor loss occurs and the stomata close, and the transpiration rate decreases
effect of carbon dioxide on transpiration
High CO2 levels in air around plant usually close the guard cells to lose turgor and the stomata to close
xerophyte
plants that live in arid climates (desertes and little water)
xerophyte LIFE CYCLE ADAPTATION
Perennial plants bloom only in wet season
Dormant seed can survive for many years until optimum growth conditions
Plants shed leaves/become dormant in dry season
xerophyte METABOLIC ADAPTATIONS
CAM plants: CO2 is absorbed at night and stored as a 4 carbon compound
During the day, photosynthesis is optional
Stomata can close during day
xerophyte PHYSICAL ADAPTATIONS
Fewer leaves and stomata
Rolled leaves and spikes, smaller leaves (decrease surface area of leaves)
Stomata in pits with hairs to increase humidity near stomata
Deeper roots to reach water
Cacti can store water in fleshy watery stems
Waxy cuticle that reduces evaporation
halophyte
plants adapted to grow in water with high levels of salinity
-some being used for net generation of biofuel as the don’t compete with food crops for resources
halphyte adaptations
- Many have become succulent by storing water, thus diluting salt concentrations
- Several species (like mangroves) secrete salt through salt glands
- Some species are able to compartmentalize Na+ and Cl- in the vacuoles therefore preventing NaCl toxicity
- Sunken stomata on thickened leaves reduce water loss by creating a higher humidity near the stomata. The thickened leaves often include a more developed cuticle to minimize water loss
- Surface of area of the leaves is reduced
phloem function
transports organic molecules throughout the plant from source to sink (products of photosynthesis)
sink
plant organ that uses or stores sugar
e.g. roots, buds, stems, seeds, fruits
source
plant organ that is the net producer of sugar, either by photosynthesis or starch hydrolysis
e.g. leaves
phloem structure
made up of living cells (sieve plate with pores)
a companion cell with a nucleus and dense cytoplasm
connected to the sieve tube by plasmodesmata
and a sieve tube that lacks a nucleus or cytoplasm
pressure-flow hypothesis
hydrostatic pressure cuases contents of phloem to flow towards sink
translocation process
- Loading of sugar into the sieve tube at the source reduces the relative water concentration in the sieve tube members, causing osmosis from surrounding cells.
2/ This is achieved by active transport, energy provided by the companion cells
- The uptake of water at the source causes a positive hydrostatic pressure in the sieve tube, resulting the the bulk flow of phloem sap
- Hydrostatic pressure is reduced by sugar removal at the sieve tube at the sink. The sugars are changed at the sink to starch, which is insoluble and has no osmotic effect
- Xylem recycles the pure water by carrying it from the sink back to the source.
How can aphids be used to calculate phloem transport rates?
Aphids are insects that use their stylet to pierce the phloem and eat the sap.
- Plant grown in lab and is exposed to radioactive CO2
- Incorporated in photosynthesis which produces radioactive sucrose
- Apid put on a plant
- Their sylhet is cut off so phloem fluid flows out
- The time taken for the sucrose to come out of the cut through leaf measure the rate of phloem sap movement
types of plant tissue
- dermal tissue
- ground tissue
- vascular tissue
- meristamatic tissue
dermal tissue
outer covering against physical and pathogenic agents
-prevents water loss
ground trissue
thin-walled cells for storage, photosynthesis, support and secretion
vascular tissue
phloem and xylem for water, mineral, nutrient support
-provide support
meristimatic tissue
derived of aggregates of small cells with the same function as stem cells; undifferentiated and used for growth
apical meristems
- differentiated based on position in plant (primary meristem)
occurs at roots and stems
shoot apex; apical meristem and surronding tissue which uses mitosis and cell division
stem growth increase with light and carbon dioxide exposre
lateral meristems
growth in plant thickness (secondary meristem growth)
occurs at cambium; often in trees and shrubs
vascular cambium; procues secondary vascular tissue
cork cambium; produces cork cells of outer bark in trees
plant hormones
Plant developments depends on communication within the plant
hormone types:
- auxin
- abscisic acid
Factors that affect plant growth and development:
Environmental factors (day length and water availability)
Receptors (which allow plants to detect environmental factors)
Genetic makeup of plant
Hormones; chemical messengers (move through phloem or cell to cell)
tropism?
phototropism?
Tropism: the growth or movement to directional external stimuli (can be positive or negative)
Phototropism: responses/growth to light
auxin?
a plant growth hormone that affects the gene expression in shoots; causes cell elongation and development.
Found in the embryo of seeds, meristems of apical buds and young leaves. Only work on plants with auxin receptors.
how does auxin work?
Affects the patterns of gene expression
Redistribution of available auxin to the side of the stem away from the light source.
Plant Auxin is called indoleacetic acid (IAA)
Auxin efflux pumps that move auxin out of cells closer to light (using ATP) to create a high auxin concentration in the space between cells
As a result, auxin moves down the concentration gradient into adjacent cells until (auxin influx) there is a greater conc. Of auxin in darker cells resulting in the elongation of the stem away from the light
Elongation of cells is caused by the expansion of the cell walls
Sequence of events in stem causing it to bend towards a light source
- auxin produced by all cells in stem towards light source
- auxin moves by efflux pump action into nuclei of cells on the side of the stem opposite to light
- auxin + receptor in nuclei form a complex that activates a proton pump
- proton pump moves protons into spaces of cell wall
- these protons cause a pH drop; results in Hydrogen Bonds between cellulsoe fibres of cell wall breaking
- results in elongation of cell wall away from light source
what are auxins involved in?
- cell division stimulation in most meristamtic tissue
- xylem and phloem differentiation
- lateral root development in tissue cultures
- lateral bud growth suppresion when present in apical bud
- growth of flower parts stimulation
- fruit production without pollination induction
micropropagation
Using knowledge of hormones and meristems to clone plants to produce large numbers of progeny
- involves placing shoot apexes into nutrient agar gels with growth hormones to get a certain quantitiy of cloned plants
- allows for altering of gene expression in plants to help humanity
angiosperm
flowering plants
co-evolve with a pollinator species (bats, insects, birds)
sepals
protect developing flower while inside bud
petals
often coloful to attract pollinators
anther
part of the stamen that produces male sex cells
filament
stalk of the stamen that holds up the anther
stigma
sticky top of the carpel where pollen lands
style
structure of carpel that supports stigma
ovary
base of carpel; where female sex cells develop and fertilization occurs
male part and female part
male; stamen
female; carpel
monocot
- parallel venation (system of veins) in leaves
- three flower parts/multiple of three
- seeds contain only one cotyledon
- vascular bundles arranged throughout stem
- root system mainly fibrious
- pollen grain with one opening
dicot
- netlike venation pattern in leaves
- four or five flower parts/multiples of four or five
- seeds contain two cotyledons
- vascular bundles arranged as a ring in the stem
- root system involves a taproot (main root)
- pollen grain with three openings
polllination
act of transferring pollen grains from the male anther to a flower to the female stigma
pollination process
Male pollen carried by pollinators or wind to style
Most flowering plants have a mutualistic relationship with pollinators in sexual reproduction (reward pollinators with nectar)
How do plants attract pollinators?
Bright colors, scent
Food
pollinator types
Pollinators can be generalist or specialist (generally specialist pollinators are crossed with generalist plants and vice versa)
types of pollination
self pollination
cross pollination
self pollination
a pollen from the anther of the same plant falls upon its stigma (inbreeding + less variation)
cross pollination
pollen carried from anther of one plant to a stigma of different plants of same species (increases variation)
gametophyte generation
- haploid
- produces the plant gametes by mitosis
sporphyte generation
- diploid
- produces spores by meisosi
allergic rhinitis
- hay fever
- condition caused by pollen causing immune response in people
- usually happens from wind pollinated plants
fertilization
when the male and female sex cells unite in the ovule to form a diploid zygote
-When pollen grain adheres to stigma (covered in sticky substance) it grows a pollen tube
fertilization process
Process:
1. Pollen germinates to produce pollen tube
- Pollen tube grows down style
- Within the growing pollen tube is the nucleus that will produce sperm
- The pollen tube completes its growth and enters an opening at the bottom of the ovary
- The sperm moves from the tube to combine with egg in ovule and form a zygote
- Zygote develops into seed
seed dispersal
the method by which seeds are scattered from plant to a new place where they can grow and develop into a new plant
-porential new plant faces reduction in competition for limited resources by moving away from parent
Wind, water or animals can disperse seeds
testa
a tough, protective outer coat
cotyledons
seed leaves that function as a nutrient storage structure
microphyle
a scar at the opening where the pollen tube enters the ovule
embryo root and shoot
becomes the new plant when germination occurs
maturation process of seeds
- invoolves dehydration untill water content is low
- seeds usually in dormancy period; adaptive feature of seeds
- once conditions favourable; seeds will germinate
germination
development of the seed into a functional plant
conditions needed for germination
Water to rehydrate dried seed tissues
Oxygen for aerobic respiration to produce ATP
Appropriate temperature for enzyme action
Large amount of seeds due to plantlets fragility/dangers to germination
initial process of germination
- absorbtion of water
- release of plant growth hormone
- amylase is produce; hyydrolzes starch into maltose
- maltose hydrolyzed to glucose for cellular respiration
- early glucose may also convert into cellulose for cell wall production
photoperiodism
a plant’s response to light involving the relative lengths of a day and night which is an important factor in flowering control
long day plant conditions
- flowers when days are long and nights short
e. g. radish, spinach, lettuce
short day plant conditions
- flower when days are shorter
e. g. poinsettias and asters
day neutral plant factors
flower regardless of day length
e.g. roses, dandelions, tomatoes
phytocromes
pigment containing proteins; play an important role in plant regulation as they change back and forth between two isomeric forms
- they activate or inhibit gene transcription of flowering
Pr
absrobs red light and converts it to infrared during the daytime
PFr
absorbs infrared light and converts it to red light during the night time
e.g. sedd inhibited by infrared but promoted by red light
when do long day plants bloom?
- when nights are short
- less Pfr levels found and high Pr (Pr converted to PFr)
- high PFr binds to a protein which acts as a trancription factor switching on the gene for flowering
why wouldnt a short day plant bloom?
- high Pfr levels= inhibit flowering
example of short day plant
chrystanthemums; botanists will place a cloth over this flower over certain period of time to cause plant to flower
