topic 9 ib biology

what are the two forces mediated by capillary action?

Cohesion (water molecules stick together by H-bonding) Adhesion (water molecules adhere to the xylem wall)

why do Leaves contain chloroplasts and stomatal pores?

for photosynthesis and gas exchange

why are Roots highly branched

with a high SA:Vol ratio?

why do Stems transfer essential materials in vascular bundles?

transpiration of water and translocation of nutrients

A leaf possesses two layers of inner tissue

Palisade mesophyll
Spongy mesophyll

What is the palisade mesophyll?

upper layer of tightly packed cells that are rich in chloroplasts (⇧ light absorption)

What is the spongy mesophyll?

lower layer of cells interspersed by space and located near the stomata (⇧ gas exchange)

what is the Root systems?

Fibrous (adventitious) root systems contain many branching roots that are thin and very spread out
Tap root systems have a deeply penetrating central root (for stability) with many connected lateral branches

why do The root epidermis additionally have many small extensions called root hairs?

to further increase available surface area

what vessels do vascular plants have?

xylem and phloem and they are arranged into bundles that extend from the roots to the shoots
The organisation of these vascular bundles differ according to the plant section (root vs stem) and plant type (monocot vs dicot)

Roots

Vascular bundles are radially arranged within a big stele in monocots

Stems

Vascular bundles are scattered haphazardly in monocots

What is transpiration?

Transpiration is the loss of water vapor from a plant

how dose transpiration work?

Active uptake of ions by roots promotes water uptake
Water moves up the stem of a plant by mass flow
Water is evaporated from leaves (via stomatal pores)

what features do xylems contain?

The vessel elements form a continuous tube
The remnants of fused end walls are shown as indents
The xylem lining contains pits and pores
It is reinforced with lignin (spiral or annular)

root uptake via soil

Soil contains anionic clay particles to which minerals attach • Examples of cationic minerals include K+

Roots pump H+ ions into the soil to displace the minerals

Displaced minerals diffuse into root (indirect active transport) • Water follows mineral ions into the root via osmosis

how dose Water moves up the stem via the xylem?

Pressure is high in root (water in) and low in leaf (water out)
The pressure differential results in the mass flow of water

how are Xerophytes (desert plants): adapted?

Reduced leaves (lowers evaporative surface area)
Thick

how are Halophytes (salt water plants) adapted?

Cellular sequestration (salt is stored within the vacuoles)
Tissue partitioning (abscission of leaves containing salt)
Salt excretion (salt is actively removal from the plant)
Root level exclusion (roots avoid salt uptake)

What is evaporation?

light absorbed by a leaf is transformed into heat
heat converts water into vapor

The vapor diffuses out of stomata

resulting in transpiration

Water transport in xylems can be modeled in various ways

Capillary tubing (water moves along tubing via surface tension) Filter paper (absorbs water due to adhesive properties)
Porous pots (semi-permeable containers can model osmosis)

Transpiration rates in plants are measured with potometers

Potometers measure movement of air bubble /meniscus
More movement represents increased transpiration rate

what is source and sink?

Source: Photosynthetic tissues (e.g. leaves)
Sink: Storage organs (e.g. fruits

What are companion cells?

Phloem cells that surround sieve tube elements

how is water drawn into the phloem via the xylem?

osmosis

how is sap made?

The active loading of solutes at the source creates high solute concentrations within the viscous phloem fluid (sap)

how is pressues gradient/ mass flow generated?

The closeness of water causes the sap volume to be increased

how are solute concentrations lowered?

Organic molecules are actively unloaded at the sink

how are Carbohydrates usually transported?

in the phloem as sucrose

Xylem versus Phloem

XYLEM PHLOEM
Process Transpiration Translocation
Materials Water

Translocation rates can be measured using aphid stylets. what are aphid stylets?

Aphids are insects that feed on the sap in phloem via a protruding mouthpiece called a stylet

how dose aphid stylets work?

If the stylet is severed

What are meristems?

The areas in plants where growth occurs

Meristematic tissue can be characterised as either?

Apical - Occurs in shoots and roots and is responsible for primary growth (i.e. lengthening) and leaf development
Lateral - Occurs at the cambium and is responsible for secondary growth (i.e. widening) and the production of bark

what dose auxin do?

Plant hormones (specifically auxins) control growth in the shoot apex by stimulating or inhibiting cell division (mitosis)

What do auxin efflux pumps do?

set up concentration gradients of auxin in plant tissues to allow for differentiated growth rates

how is auxin released?

by the shoot apical meristem and coordinates both apical growth and directional growth (tropism)

how dose Auxin influences cell growth?

by changing the pattern of gene expression within the plant tissue

what dose Growth in the shoot apex allow?

for the extension of the stem and the development of leaves (primary growth)

where dose growth occurs in the stems?

in sections called nodes

What is apical dominance?

Auxins promote growth in apex but inhibit growth in buds

what is a tropism?

A tropism is the turning of an organism in response to a directional external stimulus (e.g. light \= phototropism)

what is plant tropism caused by?

caused by the differential elongation of plant cells (plant turns away from side with cell elongation)

how may Tropisms differ according to the type of plant tissue?

In plant shoots

What is micropropagation?

Micropropagation is an in vitro technique used to produce large numbers of identical plants (i.e. clones) from a selected stock plant

how dose micropropagation work

Tissue sample (explant) is grown in agar and treated with growth hormones
Growing shoots are divided and transferred to soil to form new plants

what are Micropropagation used for?

used for the rapid bulking up of new plant varieties

Flowers are the reproductive organs of certain types of plants. how do they develop?

develops from changes to gene expression in the shoot apex

what are the three key stages Sexual reproduction in flowering plants?

Pollination - The transfer of pollen from the anther to the stigma (usually occurs between different plants)
Fertilisation - The fusion of the male gamete nuclei (in pollen) with the female gamete nuclei (in ovule)
Seed Dispersal - The fertilised ovule (seed) moves away from the parent plant to reduce the competition for growth

Most flowering plants will employ a mutualistic relationship with pollinators (e.g. birds

bees) in order to reproduce how would this work?

how are Flowering plants controlled?

photoperiodism - The response of a plant to the length of day or night

Flowering is regulated by phytochrome in what 2 forms?

Inactive red form (Pr ) absorbs red light (to become Pfr)
Active far red form (Pfr) absorbs far red light (forms Pr )

Sunlight contains more red light so:

The active far red form is predominant during the day \n Reverts to mainly the inactive red form at night

what do Long Day Plants: do?

Pfr activates flowering in long-day plants
Flowering induced when night length is short (⇧ Pfr)

what do short Day Plants: do?

Pfr inhibits flowering in short day plants
Flowering induced when night length is long (⇩ Pfr)

What is germination?

Germination is the process by which a seed emerges from a period of dormancy and sprouts (forming a new plant)

Germinating seeds require what conditions?

Oxygen (to produce ATP via aerobic respiration)
Water (to metabolically activate the cells)
Suitable temperature and pH (for enzyme activity)