UNIT 9 - Plant Biology Flashcards
List the main parts of the plant distingusihing the shoot system from the root system.
SHOOT SYSTEM
- reproductive shoot (flower)
- apical bud
- node
- internode
- vegetative shoot
- axillary bud
- stem
LEAF
- blade
- petiole
ROOT
- taproot
- lateral (branch) roots
State the function of the stem
supports leaves in the sunlight and transports organic materials, ions and water between roots and leaves
State the location and function of the terminal and axillary bud
terminal bud - top of the stem
axillary bud - axil of each leaf
new cells are produced at these growing points
State the general function of the leaf
photosynthesis
State the general function of the root
anchors the plant and is the site of absorption of water and ions from the soil
List the four main functions of stems
- support for and the elevation of leaves, flowers and fruits - keep the leaves in light
- transport of fluids between the roots and shoots in the xylem and phloem
- storage of nutrients
- production of new living tissue - through meristems
List the tissues present in the stem
- epidermis
- cortex (chlorenchyma)
- fibre cap (sclerenchyma)
- phloem
- xylem
- pith (parenchyma)
Define epidermis
outer layer of wax-coated cells that provides protection and covering
Define cortex
primary tissues of a stem externally bound by the epidermis and internally by the phloem
Define xylem vessels
dead cells with no cytoplasm with varying degrees of lignin thickening in their walls with end walls dissolved leaving a continuous tube
Define and state the function of lignin
tough impermeable material that can be laid down in the primary cellulose wall to strengthen the cell and provide support
What two components is xylem composed of and what is their function
- tracheid’s (all vascular plants) - tapered cells that exchange water solely via pits leading to a slower rate of water transfer
- vessel elements (in only certain vascular plants) - the end walls have becomes fused to form a continuous tube, resulting in a faster rate of water transfer
State the two ways of lignin deposition in xylem vessels
- circular rings in annular vessels - equal distance from each other
- helix/coil in spiral vessels
XYLEM COMPONENTS
- vessel element
- tracheid
LIGNIN ARRANGEMENTS
- annular
- spiral
State how does water and minerals from the soil enter the xylem
through the epidermis of roots, cross the root cortex and pass into the vascular cylinder -> it’s called xylem sap.
Define the phloem tissue
living tissue consisting of sieve tubes and companion cells, responsible for active translocation of sucrose and amino acids from the source (photosynthetic tissues and storage organs) to sink (fruits, seeds and roots)
State what does phloem tissue consist of
it’s a living tissue consisting of sieve tubes and companion cells.
Describe the structure of sieve tubes
narrow, elongated elements
end walls (sieve plates) perforated by pores
cytoplasm has no nucleus
State the function of phloem tissue
active translocation of sucrose and amino acids from source (photosynthetic tissues and storage organs to sink (fruits, seeds, roots)
State the adaptation of the sieve-tube elements
reduction in cell contents enabling the nutrients to pass more easily through it
like the pored sieve plates
State the function of companion cells and define them in phloem
nonconducting cell which is connected to the sieve tube by numerous plasmodesmata
help load sugars into the sieve tube elements
and its nucleus and ribosomes serve for the adjacent sieve tube element
Describe the external structure of a leaf
- leaf blade
- petiole - leaf stalk
- stipules - leaf-like appendages at the base of the leaf
Describe the internal structure of a leaf
- epidermis - outer layer of tissues
- cuticle - waxy protective outer layer of epidermis
- leaf hairs - part of the epidermis
- stomata - natural opening in leaves and herbaceous stems that allow for gas exchange
- guard cells - specialized kidney-shaped cells that open and close the stomata
- palisade layer - tightly packed layer of parenchyma tissues filled with chloroplasts for photosynthesis
- chloroplasts
- vascular bundle - xylem and phloem tissues
- spongy mesophyll - layer of parenchyma tissues loosely arranged to facilitate movement of gases
State the function of the root system
mineral ion and water uptake
State the adaptation for its function of the root system
huge surface area increased by branching of roots and root hairs
Define root hairs
extensions of individual epidermal cells
Describe the tissue distribution in the root and how it relates to the uptake of materials absorbed
materials absorbed diffuse across the cortex and towards the central stele (where xylem is)
the stele is surrounded by a layer of endodermis impermeable to the passive flow of water and ions (Casparian strip) and so they need to be pumped across this barrier by specialized cells allowing for the control of the process.
List the three main ways in which water and minerals are absorbed from root hairs to the xylem.
- mass flow through the interconnecting free spaces between the cellulose fibres of the plant cell walls
- diffusion through the cytoplasm of cells
- osmosis from vacuole to vacuole of the cells
State and explain the alternative name for the mass flow way of water transport from root hairs to the xylem
apoplast
as it entirely avoids the living content of cells while also including the water-filled spaces of dead cells.
State and explain the alternative name for the diffusion through the cytoplasm of cells way of water transport from root hairs to the xylem.
Symplast.
Explanation here
Define a Casparian strip and its function
a belt made of suberin (waxy material)
because it’s impermeable to water and dissolved materials they must cross the selectively permeable membrane of an endodermal cell before they enter the vascular cylinder and thus keeps many unneeded or toxic substances out and prevents leakages back into soil solution.
Distinguish between the symplast an apoplast in short
apoplast - the continuum of cell walls and extracellular spaces
symplast - the continuum of cytosol connected by plasmodesmata
Describe briefly and define the cohesion tension theory
the most widely accepted explanation of water movement
transpiration provides the pull for the ascent of xylem sap and thus the cohesion of water molecules transmits this pull along the entire length of the xylem from shoots to roots
List the steps of the cohesion tension theory of water transport
- Light absorbed by leaf increases the temperature
- water evaporates through stomata
- evaporated water is being replaced by water from mesophyll cells
- constant loss of water creates a lower water potential in the leaf cells than in the other cells and thus the water is being pulled though the plant along a decreasing gradient in water potential.
- the cohesive and adhesive properties create an unbroken column of water through the plant
- root pressure is created in the soil
Define root pressure
water entering the stele from the soil creates a week “push” effect for the water’s upward movement through the plant
State one possible consequence of root pressure
guttation
forcing of water droplets from some small plants under certain conditions
List the three main ways allowing mineral ions to pass from the soil to the roots
- active transport - when concentration of ions in the soil is much lower than inside root cells
- fungal hyphae symbiosis
- diffusion of mineral ions and mass flow of water in the soil carrying these ions
Describe the two methods of mineral ion uptake by active transport
- indirect - proton pumps establish electrochemical gradients
- direct - membranes actively transporting a particular mineral
Describe the indirect method of active mineral absorption
- Hydrogen pumps of the plasma membrane actively pump hydrogen ions out into the soil water creating membrane potential of -120 mV.
- The negative ions are carried across the plasma membrane in conjunction with H+ ions as the ions diffuse down their concentration gradient (co-transport mechanism).
- H+ displace cations from the clay particles so that they are free to move down an electrochemical gradient by facilitated diffusion.
Describe the direct method of active mineral absorption.
The specific membrane pumps for different cations take up actively the cations which are free in the solution in the soil.
Describe the phloem tissue and it’s structure.
living tissue consisting of sieve tubes and companion cells.
Describe the adaptation of phloem to transport.
reduction in cell concents (sieve-tube elements lack a nucleus, ribosomes, cytoskeletal elements) allowing the nutrients to pass more easily
the end walls between the sieve tube elements (sieve plates) have pores facilitating the flow of fluid from cell to cell along the sieve tube
a nonconducting companion cell along each sieve tube element providing the sieve-tubes with nucleus, ribosomes etc
State the two functions of phloem companion cells.
sharing the cell contents with the sieve-tube elements
in leaves helping to load the sugars into the sieve tube elements which are then transported to other parts of the plants
Define translocation
the movement of manufactured food (sugars, amino acids) mainly occurring in the phloem tissue of the vascular bundle
Describe the bulk flow by positive pressure in a sieve tube
- The active transport of solutes (such as sucrose) into the phloem by companion cells makes the sap solution hypertonic
- This causes water to be drawn from the xylem via osmosis (water moves towards higher solute concentrations)
- Due to the incompressibility of water, this build up of water in the phloem causes the hydrostatic pressure to increase
- This increase in hydrostatic pressure forces the phloem sap to move towards areas of lower pressure (mass flow)
- Hence, the phloem transports solutes away from the source (and consequently towards the sink
Describe the loading of sucrose into phloem
sucrose manufactured in mesophyll cells can travel into sieve tube elements via symplast or sometimes through apoplast
Apoplastic loading of sucrose into the phloem sieve tubes is an active transport process that requires ATP expenditure
- Hydrogen ions (H+) are actively transported out of phloem cells by proton pumps (involves the hydrolysis of ATP)
- The concentration of hydrogen ions consequently builds up outside of the cell, creating a proton gradient
- Hydrogen ions passively diffuse back into the phloem cell via a co-transport protein, which requires sucrose movement
- This results in a build up of sucrose within the phloem sieve tube for subsequent transport from the source
List the factors affecting translocation rate
concentration of dissolved sugars in the phloem primarily which is affected by:
- rate of photosynthesis
- rate of cellular respiration
- rate of transpiration
- diameter of sieve tubes
Define meristematic tissue
made up of small unspecialized cells that undergo mitosis and result in growth of the plant
List and differentiate between the types of meristems
shoot and root apical meristems - causes primary growth (lengthening), occurs at tips of shoots and roots, produces new leaves and flowers.
lateral meristems - causes secondary growth (widening), occurs are cambium, produces bark on trees
List and define the additional meristems the shoot apical meristem gives rise to
- protoderm - creates epidermis
- procambium - produces vascular tissues
- ground meristem - produces pith and cortex
- leaf primordia - young leaves
State and define the two types of lateral meristem (cambium)
vascular cambium - produces secondary xylem or phloem
cork cambium - produces the bark layer of a stem
Define a hormone
signaling molecule produced in tiny amounts and transported to different parts of an organism where it binds to a specific receptor and triggers responses in target cells and tissues
Define plant hormones
organic compounds (natural or synthetic) that control or modify one or more specific physiological processes within a plant
List the major plant hormones, where they are produced in the plant and their major functions
- auxin (IAA) - shoot apical meristems - stem elongation, suppression of lateral buds
- cytokinin’s (Kinetin) - produced in roots - stimulation of cell division, determination of differentiation
- gibberellins - apical roots and shoots - stem and internode elongation, mobilization of enzymes during seed germination
- ethylene - leaves, stems, young fruits - controls abscission of leaves fruits flowers, retardation of lateral bud elongation, hastening of fruit ripening
- abscisic acid - mature leaves, fruits, roots - suppression of bud growth, stomatal openings, leaf senescence promotion
Describe the main functions of auxin
stimulates stem elongation
promotes the formation of lateral and adventitious roots
regulates fruit development
phototropism and gravitropism regulation
promotes vascular differentiation
Describe the function of auxins with relation to tropism
In shoots, high auxin concentrations promote cell elongation, meaning that:
- The dark side of the shoot elongates and shoots grow towards the light (positive phototropism).
- The lower side of the shoot elongates and roots grow away from the ground.
In roots, high auxin concentrations inhibit cell elongation, meaning that: - The dark side of the root becomes shorter and the roots grow away from the light (negative phototropism).
- The lower side of the root becomes shorter and the roots turn downwards into the earth.
Define tropism
growth toward or away from a directional stimulus in the environment.
List and define two tropisms popular in plant
phototropism - growth toward light exhibited by many plant shoots
gravitropism - growth of roots towards gravity and shoots away from gravity
Describe in detail the auxin mechanism behind positive phototropic response of the shoots
- when sunlight is overhead, the IAA molecules produced by the apical meristem are distributed evenly in the shoot.
- once the sunlight shines on the shoot at an angle, the IAA molecules move to the far side and induce the elongation of cells on that side.
- cell elongation results in the bending of the shoot toward the light.
What is the underlying mechanism of auxin regulation of plant growth
the auxin efflux pumps that set up concentration of gradients within tissues changing the distribution of auxin within the plant
the pumps can then control the direction of plant growth through determining which regions of plant tissue will habe higher auxin levels
the pumps can both change position within the membrane and be activated by various factors
Explain the mechanism behind the auxin promotion of plant growth via cell elongation (acid growth hypothesis)
it actiates a proton pump in the plasma membrane which causes the secretion of H+ ions into the cell wall
that increase in pH allows the cellulose fibres to loosen within the cell wall (by breaking bonds between them)
also auxin upregulates the expression (activates) of expansins which also increase the elasticity of the cell wall (through breakinf the hydrogen bonds between cellulose microfibrils and other constituents)
the influx of water causes the more flexible cell walls to increase in size
Define statoliths, what do they indicate and their effect on plant behavior
dense cytoplasmic components that settle under the influence of gravity to the lower portions of the cell (in vascular plants they are specialized plastids containing dense starch grains)
they detect gravity and are a result of gravitropism
triggers a redistribution of calcium causing lateral transport of auxin within the root
both calcium and auxin accumulate on the lower side of the root’s zone of elongation thus inhibiting the cell growth on the roots lower side and increasing the elongation on the upper side -> the root grows straight downward
Define micropropagation of plant
in vitro procedure that produces large number of identical plants
Describe the technique of micropropagation of plants
- small pieces (explants) are cut from the stock plant (e.g. shoot apical meristem).
- the explant is sterilized using sodium hypochlorite solution.
- the explant is transferred to culture plate containing nutrients and plant hormones in agar gel.
- culture plates are incubated (15-30 degrees) with 10-14 hours of light from 3-9 weeks.
- the developing callus contains undifferentiated cells.
- the new shoots are removed and placed in the new tissue culture and later grown in greenhouses before being planted outside.
- callus however is suspended in the liquid nutrient medium and broken up mechanically
State the function of flowers
used by flowering plants for sexual reproduction
List and state the function of the component parts of the flower
- sepals - protection of the flower bud during its development and at night when the bud closes
- petals - conspicuity; attracting insects and other small animals
- stamens - male parts of the flower: - anthers - housing pollen grains, - filament - stalk
- carpels - female parts: ovary - containing ovules, stigma - surface receiving pollen, connecting style
- nectar-secreting glands - attract insects, especially bees
Define pollination
transfer of pollen from mature anther to a receptive stigma
Define and state an example of a mutualistic relationship
when two organisms of different species “work together” each benefiting from the relationship
for example:
bee and the flower
bees collect nectar which they make into food benefiting the bees
flower gets some pollen from another flower pollinating it
List and define the two types of pollination
cross-pollination - pollen is delivered to a flower from a different plant
self-pollination - occurs when pollen from one flower pollinates the same flower or other flowers of the same individual
Define fertilization in plants
male and female gametes fuse to form a zygote
occurs in the ovule of the flower
Describe fertilization in the plant
- pollen arrives on the stigma
- they germinate and produce a pollen tube that grows down the style to the ovary
- tubes enter the ovary
- pollen nucleus passes down the tube to fuse with and fertilize the nucleus of the female gamete in the ovule
Define and state the consequence of double fertilization
fussion of gametes occuring after two sperm reaches the ovule where one sperm fertilises the egg forming a zygote and another combines with the two polar nuclei formin a triploid (3n) nucleus in the center of the large central cell of the ovule
this gives rise to endosperm (a food storing tissue)
Describe the structure of the seeds and the functions of their components
SEED PART
Testa:
- a tough, protective outer coat
Cotyledons:
- seed leaves that function as nutrient storage structures.
Micropyle:
- a scar at the opening where the pollen tube entered the ovule.
Embryo root and embryo shoot:
- become the new plant when germination occurs.
Define seed dispersal
the movement or transport of seeds away from the parent plant
depends on a variety of dispersal vectors (both abiotic and biotic) such as: gravity, wind, ballistic, water and animals
Define germination
growth of an embryonic plant contained within a seed results in the formation of the seedling
Describe the process of germination
- water absorption into the testa causes it’s splitting
- embryo produces gibberellic acid (GA)
- signals to the aleurone (outer layer of the endosperm) which responds by secreting digestive hydrolytic enzymes
- hydrolytic enzymes are produced converting stored starch to glucose and proteins to amino acids
- glucose and amino acids are translocated to growing points of stem and root fueling the growth
- breaking the coat of the seed and releasing the first root downwards (gravity) - radicle (the embryonic root)
- main root continues to grow
- main stem forces itself out and continues to grow in the opposite direction to the root
- main root shows signs of ramification
- first leaves develop - photosynthesis, plant begins to absorb water
- main root is ramificated for better absorption of water and nutrients
- leaves turn greener, plant grows all is good
State the three factors needed for a dormant seed to germinate
- water uptake - overcoming of dormancy - hydration of the cytoplasm of the cells of embryo
- ambient temperature - optimum range for enzyme action - production of GA by embryo cells
- oxygen - to sustain aerobic cell respiration
Define photoperiodism
physiological reaction of organisms to the length of day or night
List and define the classification of plant dependent on photoperiodism
short-day plants - flower as night become longer and days are shorter (late summer, autumn) - require a continuous period of darkness before flowering
For example: chrysanthemum, tobacco
long-day plants - flower when days are longest and the nights are short (NH: early summer, late spring) - require less hours of darkness to induce flowering
For example: carnation
Describe the reason for photoperiodism
the leaf-pigment phytochrome is exists in two inter-convertible forms inactive Pr and active Pfr
activation to Pfr occurs during daylight hours but in darkness revers slowly to the more stable Pr
Pfr - promotes flowering in long-day plants, through binding to the receptor promoting the transcription of genes needed for flowering, but inhibits it in short-day plants
