The document explains the transport processes in plants, focusing on xylem for water movement and phloem for nutrient translocation. It details the role of transpiration, the adaptations of xerophytes and halophytes for water conservation, and the mechanisms of meristems in growth. Additionally, it discusses flowering and reproduction, including the influence of photoperiods and mutualism with pollinators.

1. 9,1 Transport in the Xylem of Plants
Transpiration
● Transpiration​: loss of water vapour from the leaves and stems (occurs as a
consequence of gas exchange)
● Guard cells​ (located on either side of the stomata) minimise transpiration
by control the opening of the stomata (pores)
Using a potometer
● Potometer​: device used to measure water uptake in plants (measuring rate
of transpiration)
Xylem structure helps withstand low pressure
● Xylem​ (vessel which transports water) walls are thick and contain lignin → ​withstand low pressure without collapsing
● Water is attracted to each other (​cohesion​) and is also attracted to hydrophilic parts of the cell wall (​adhesion​) →
supports water uptake
Tension in leaf cell walls maintains the transpiration stream
● Water evaporates​ from leaves → adhesion and cohesion causes ​water uptake
● Low pressure generates pulling force upwards (transpiration-pull)
Active transport of minerals in roots
● Active transport of mineral ions into root hairs allow osmosis​ to occur (from soil to roots)
● Because some ions move through soil slowly, some ​fungi grow on plants roots to absorb these ions for them
Transport of water from roots to leaves
1. (Water evaporates from leaves)
2. Water moves from soil into roots through osmosis
3. Water gets into xylem through cell walls
4. Water climbs up xylem (adhesion and cohesion)
5. Water evaporates from leaves
Xerophytes and halophytes adaptations for water conservation
● Xerophytes​: plants adapted to growing in dry habitats (e.g. cacti)
● Cacti adaptations (xerophyte):
○ Reduced leaf​ (spines) → prevent transpiration
○ Swollen stems​ → water storage
○ Pleats (folds)​ → allow for rapid contraction/expansion
○ Thick waxy cuticle​ → prevent evaporation of water
○ Stomata on stem​ which opens up during night instead of day →
slower transpiration (CO​2​ stored as malic acid at night and is
used during day for photosynthesis)
● Marram grass (right) adaptations (xerophyte):
○ Rolled leaves​ → prevent water loss
○ Stomata in pits​ → prevent water loss
○ Hairs​ inside leaves → prevent air movement
● Halophytes​: plants adapted to growing in saline soil
● Halophytes adaptations:
○ Reduced leaves
○ Leaves shed off​ in dry conditions, stems take over photosynthesis
○ Water storage structures
○ Thick cuticle​ and ​multiple epidermis
○ Sunken stomata
○ Long roots​ → seek for water
○ Structures for removing salt​ build-up
Drawing xylem vessels
● Larger phloem​ located outside with ​smaller xylem​ inside
● Xylem vessels: large lumen and thickened cell walls

2. 9.2 Transport in the Phloem of Plants
Translocation
● Translocation​: transport of organic solutes (amino acids, carbohydrates) in a plant (from ​source​ [site of
production/storage] to ​sink​ [site of usage]) by phloem
● Sinks and sources can interchange → phloems must be able to transport in either directions
Phloem loading
● Phloem loading​: ​actively transporting​ organic compounds
(sucrose) into phloem
● Process (​phloem loading​ [apoplast route]):
1. H​+​
ions​ are actively pumped (ATP) from​ companion
cell​ to ​source
2. (Because of high ​H​+​
concentration in ​source​) ​H​+​
flows
out from ​source​, simultaneously carrying ​sucrose ​into
companion cell
3. Sucrose ​transported into phloem
● Process (​translocation​)
4. Sucrose​ enters sieve tubes from the ​source​ ​→ high solute
concentration
5. Osmosis​ occurs from corresponding ​xylem to sieve tubes
6. High water pressure​ near source causes movement of phloem
content from ​source ​to ​sink
Sieve tube structure and function
● Sieve tube cells are living​ (unlike vascular elements of xylem) →
membranes control concentration of organic molecules
● Sieve tube cells associated with companion cell​ → companion cells perform
genetic and metabolic functions for sieve tube cell (which has smaller
cytoplasm and no nucleus)
● Plasmodesmata​ (opening in cell wall) connecting sieve tube cell and
companion cell → allow movement of carbohydrates and genetic materials
between the 2 cells
● Infolding of plasma membrane​ (companion cell) → increases phloem loading
● Rigid cell wall​ → building up high pressure for internal flow
● Pores in sieve plates​ → prevent reducing the flow speed
Using aphid stylets to measure phloem transport rate
● Aphids use a stylet (part of mouth) to penetrate the stem and to feed on the
phloem sap
● Scientists cut the stylet off while the aphid is feeding on the sap to measure
the rate of flow and composition of the phloem sap
Identifying xylem and phloem in light micrographs
● Xylems are larger than phloem
● Phloems are located closer towards the outside and xylems closer to the inside
● Dicot​ if the vascular bundles are aligned in a ring shape, ​monocot​ if scattered
9.3 Growth in Plants
Meristems
● Meristems​: region in plants undergoing ​active cell division​ by ​undifferentiated cells​ (​region of growth​)
● Apical meristems​: growth occurring at the ​root or stem tip​ (shoot)
● Lateral meristems​: growth occurring at the ​cambium​ (thickening)
Mitosis in plant growth
● Root apical meristem
○ Responsible for growth of ​root
● Shoot apical meristem
○ Produces both cells for ​stems​ and ​leaves/flowers
○ One daughter cell remains in the meristem whereas the other one increases in size and differentiates into a
specific cell

3. Hormones in shoot growth
● Auxin​: hormone which can ​initiate root growth​, allow ​development of
fruits/leaves​, and also ​regulate leaf development​ (​inhibits growth in roots,
promotes growth in stems​)
● → Auxin produced by the ​shoot apical meristem​ inhibits growth of ​axillary
bud​ (shoots which form at plant nodes). At nodes further away from the
meristem, growth of​ axillary buds​ are not inhibited
● Cytokinins​: hormone which ​promote ​axillary bud​ growth
● → Levels of ​auxin and cytokinins determine ​axillary bud​ development
Plant tropisms
● Tropism​: directional growth responses to directional external stimuli (e.g.
gravity, light)
● Phototropism​: growth towards light
● Gravitropism​: growth in response to gravitational force
Auxin in gene expression
● Cells contain an ​auxin receptor
● Process:
1. Specific genes are transcribed when auxin ​binds to the receptors
2. Gene expression causes ​release of hydrogen ions
3. Hydrogen ions loosen the cellulose fibres → ​cell expansion
Intracellular pumps
● In phototropism:
1. Phototropins in tips of plants detects greater light intensity from a
particular direction
2. Auxin moves away from the light
3. Auxins cause the side with less light to grow (​promote growth​)
4. Stem curves towards the light source
● In gravitropism:
1. Root is placed on one side
2. Cell organelles (statoliths) accumulate at the bottom of the cell
3. PIN3 transport proteins move auxin to the lower side of the roots
4. Auxin causes ​inhibition of growth​ on lower side
5. Root curves downwards
Micropropagation of plants
● Micropropagation​: process of making large numbers of identical plants
from a stock plant
● Process:
1. Tissues (meristems) from stock plant are ​sterilised
2. Tissues are cut up into pieces (​explant​)
3. Explant is placed on sterilised ​growth medium​ (agar) with hormones (​auxin​ and ​cytokinins​)
a. 1 auxin​ : ​1 cytokinins​ forms undifferentiated mass (​callus​)
b. 1 auxin​ : ​10 cytokinins​ allows ​roots​ to develop
c. 10 auxin​ : ​1 cytokinins​ allows ​shoots​ to develop
4. Roots and shoots develop → planted in soil
● Advantages:
○ Produces ​virus-free​ strain of plants
○ Faster​ and consumes ​less space​ compared to traditional methods
○ Produce plants with ​desirable characteristics​ (preservation of rare species)
○ Micropropagated plantlets can be stored in liquid nitrogen for ​cryopreservation
9.4 Reproduction in Plants
Flowering and gene expression
● Vegetative phase​: seed germinates and the plant grows roots, stems, and leaves
● Reproductive phase​: plant forms flowers and produces seeds
● Floral initiation is caused by changes in ​temperature and light​ (changes as ​length of days​ change)
Photoperiods and flowering

4. ● Phytochrome​ are pigments in leaves which can switch between P​R ​and P​FR​ depending on the time of the day (used to
measure night length)
● Conversion of forms
○ P​R​ absorbs ​red light at 660 nm​ (more available) → becomes ​P​FR​ (more produced)
○ P​FR​ ​absorbs ​far-red light at 730 nm​ (less available) → becomes ​P​R​ ​(less produced)
○ P​FR​ ​converted back into ​P​R​ in the dark (because no light)
● Effect of phytochrome on flowering (​P​FR​ promotes flowering in ​long-day plants​, inhibits in ​short-day plants​)
○ Long-day plants​: ​P​FR​ remains (after short night) → binds to receptor → flowers
○ Short-day plants​: very little ​P​FR​ ​remains (after long night) → not enough to inhibit → flowers
Inducing plants to flower out of season
● Growers manipulate the ​length of days and nights​ to ​force flowering
● E.g. ​Chrysanthemums
○ Chrysanthemums don’t flower during ​summer
○ Plant is covered in ​opaque black cloth for 12-15 hours​ → floral initiation
Draw an animal pollinated flower
● Petals​: attract pollinators
● Sepal​: cover and protect developing flower (before blooming)
● Stamen (male)​:
○ Anther​: contains pollen
○ Filament​: supports anther
● Pistil (female)​:
○ Stigma​: Pollen landing site
○ Style​: has tubes to transport pollen from stigma to
ovary
○ Ovary​: contains ovules
○ Ovules​: contains egg nuclei, develops into seeds
Mutualism between flowers and pollinators
● Sexual reproduction in plants require transfer of pollen from one flower to another flower’s stamen
● Mutualism​: association between two organisms (​benefit from each other​)
Pollination, fertilisation and seed dispersal
● Process
1. Pollination​: pollen lands on stigma
2. Pollen tube carries male gametes to the ovary (through style)
3. Fertilisation​: Ovules fuse with pollen
4. Fertilised ovule develops into seed, ovary into fruit
5. Seed dispersal​: seed travels long distances (​prevent competition​ between offspring and parent)
Drawing structure of seeds
● Cotyledon​: contains ​nutrients​, serves as embryo leaves
(​dicotyledons have 2, monotorylegons 1​)
● Testa​: Seed coat
● Micropyle​: hole through which pollen fertilises ovule (before
fertilisation)
● Radicle​: embryo root
● Plumule​: embryo shoot
Factors affecting germination
● Water
○ Many seeds are dehydrated (cells need water)
○ Some have hormones which inhibits germination (water washes off hormone)
○ Growth of embryo and shoot requires water
● Oxygen​ for aerobic respiration to produce ATP
● Warmth​ for metabolic enzymes
● Gibberellin (hormone)​:
○ Stimulates mitosis and cell division
○ Stimulates production of amylase (break down ​starch into maltose​ for further catabolism)