1
Q
Autotrophs and Heterotrophs
A
Autotrophs:
- self sufficient without eating other organisms
- plants, algae, some prokaryotes
- use photosynthesis to make organic molecules from water and CO2
Heterotrophs:
- live on compounds produced by other organisms
- humans, cows, etc
2
Q
Choroplasts
A
- in leaves
- where photosynthesis occurs
- contain thylakoids
- thylakoids stack into grana
- stoma outside thylakoids
3
Q
Photosynthesis Equation
A
6CO2 + 6H2O —–(light energy)—–> C6H12O6 + 6O2
water oxidised and carbon dioxide reduced
4
Q
Light Reaction
A
- first phase of photosynthesis
- convert solar energy (physical) to the chemical energy of ATP and NADPH
5
Q
Pigments
A
Chlorophyll A
- main photosynthesis pigment
Chlorophyll B
- accessory pigment
- absorbs different wavelengths of light
- passes energy to chlorophyll A
Carotenoids: other accessory pigments
6
Q
Photosystems
A
- composed of a reaction centre surrounded by a number of light-harvesting complexes
- these complexes consist of pigment molecules bound to proteins
- funnel energy of photons to reaction centre
- when chlorophyll in reaction centre absorbs energy one of its electrons gets bumped up to the primary electron acceptor
- thylakoid membrane contains two types of photosystems, I and II
7
Q
Electron Flow During Light Reactions
A
- lost electrons replaced by splitting water into two protons and an oxygen
- 2 electrons from oxygen atom replace lost electrons
- oxygen and protons are a by-product
- electron reaches primary receptor and indirectly produces ATP (thylakoid fills with protons)
- electron is low energy when it reaches next photosystem
- pumped up by another photon
8
Q
Calvin Cycle
A
- dark reaction (doesn’t need light)
- uses ATP and NADPH from light reaction to convert CO2 to sugar
- occurs in stroma outside the thylakoids
- input of CO2 which in incorporated by rubisco
- output is sugar
9
Q
Leaf Structures
A
- complex
- surrounded by cuticles which makes leaves impermeable
- structures allow opening and closing of access to leaf by opening or closing these cells
- can control what comes in and out
- stomata open —> CO2 enters, O2 exits and water evaporates
- plants close stomata in hot, dry weather
- conserves water but limits CO2 access
- buildup of O2 results in photorespiration
- rubsico incorporates O2 instead of CO2
- energy consumed not produced
- photosynthetic rate is reduced
10
Q
C4 plants
A
- minimise cost oh photorespiration
- spatially confines calvin cycle to very internal cells
- Co2 incorporated into 4 carbon organic acids in mesophyll cells by PEP carboxylase (not by rubisco)
- PEP carboxylase isn’t sensitive to CO2/O2 ratios and can incorporate CO2 at low concentrations
- C4 exported to bundle of sheath cells where they release CO2 used in calvin cycle
11
Q
CAM Plants
A
- use temporal separation instead of spatial deparation
- open stomata at night
- incorporate as much CO2 as possible and incorporate CO2 into organic acids
- close during day and CO2 released from organic acids for use in calvin cycle
12
Q
Three basic organs of plants
A
roots, stems, leaves
13
Q
Roots
A
- anchors plants
- absorbs minerals and water through root hairs
- often stores nutrients
14
Q
Stems
A
- alternating system of nodes where leaves attach
- internodes, stem segments b/w nodes
- auxiliary buds: structures with potential to form lateral shoot of branch
- terminal bus: located near shoot tip, causes elongation of shoot
15
Q
Leaf
A
- main photosynthetic organ of vascular plants
16
Q
Tissue System
A
dermal tissue:
- protection
vascular tissue:
- long distance transport of materials
- two tissues: xylem and phloem
ground tissue:
- specialised cells for functions such as storage, photosynthesis and support
17
Q
Tissue Organisations of Stems
A
In most eudicots (two cotyledons), vascular tissue consists of vascular bundles arranged in a ring
In most monocot stems, vascular bundles scattered throughout ground tissue instead of forming a ring
Epidermal barrier in leaves is an impermeable cuticle to liquid and gas
Interrupted by stomata to allow exchange of CO2 and O2
Ground tissue sandwiched between upper and lower epidermis
Vascular tissue continuous of stem
18
Q
Xylem
A
- empty dead cells forming tubes
- transport water and dissolved minerals upward from roots into shoots
19
Q
Phloem
A
- live cells
- transports organic nutrients from where they are made to where they are needed
20
Q
Tissue Organisation of Leaves
A
epidermal barrier is impermeable to liquid and gas
ground tissue sandwiched between upper and lower epidermus
vascular tissue continuous of stem
21
Q
Meristems
A
Generate cells for new organs
Apical meristems:
- located at tips of roots and buds of shoots
- elongate shoots and roots through primary (vertical) growth
Lateral meristems:
- adds thickness to woody plants throgh secondary growth
- cork cambium
- vascular cambium
- form ring
22
Q
Primary Growth of Roots
A
- root tip covered by root cap
- protects the delicate epical meristem as root pushes through hard soil during primary growth
- hard cells of root cap multiply to move upwards
- cells left behind are stem cells which go through elongation then maturation
23
Q
Primary Growth of Shoots
A
A shoot apical meristem
- differentiate when left behind
- dome shaped mass of dividing cells at tip of terminal bud
24
Q
Secondary Growth
A
occurs in stems and roots if woody plants but rarely in leaves
the secondary plant body consists of the tissues produced by the vascular cambium and cork cambium. vascular cambium adds secondary xylem inside and phloem outside. cork cambium adds secondary dermal tissue for more protection
25
Genetic Control of Flowering
flower formation:
- phase change from vegetative to reproductive
- triggered by combo of environmental cues and internal signals
- transition from vegetative to flowering is associated with switching on of floral meristem identity genes
26
Stem Cells to Flower
Flower contains four concentric whorls:
1) sepals
2) petals
3) stamens
4) carpels
3 genes control formation, A, B and C
```
A = 1 and 2
B = 2 and 3
C = 3 and 4
```
A = sepal
A + B = petal
B + C = stamens
C = carpels (end of flower)
Create mutants without certain genes:
- no C = no end = confused plant
- roses are mutants --> multiple petals --> type C gene mutants
27
Short-distance transport
passive and active transport
three pathways:
1) transmembrane: out of cell, across wall and into another cell
2) symplast (continuum of cytosol connected by plasmodesmata)
3) apoplast (continuum of cell walls and extracellular fluid)
28
Long-distance transport
Vascular tissue transports nutrients throught a plant
Through bulk flow and transpirational pull
29
Bulk Flow
- long distance transport
| - movement of xylem and phloem driven by pressure difference at opposite ends of xylem vessels and sieve tubes
30
Endodermis
- innermost layer of cells in root cortex
- surrounds vascular cylinder
- functions as last checkpoint for selective passage from cortex to vascular tissue
- waxy casparian strip of endodermal wall blocks apoplastic transfer of minerals from cortex to vascular cylinder
31
Transpiration Pull
- water vapour in airspaces of leaf exits leaf via stomata
- transpiration produces negative pressure (tension) in leaf which exerts pulling force on water in xylem, pulling water into leaf
- transpirational pull affects xylem sap
- xylem sap transmitted from leaves to root tipis and even into soil solution
- facilitated by cohesion between H2O and adhesion to walls of xylem tissue
- stomata help regulate rate of transpiration
- leaves generally have broad surface area
- stomata are major pathway for water loss (90% water leaves through stomata, replaced by roots)
32
Light Reactions
- occur on thylakoid membrane of chloroplast
- convert solar energy to chemical energy of ATP and NADPH
1) chloroplasts in photosystem 1 absorb light energy. electrons are excited to higher energy levels. energised electrons passed down electron transport chain and form NADPH
2) energised electrons from photosystem 2 passed through another electron transport chain. used to pump H+ from stroma into thylakoid compartment to create concentration gradient
3) electrons leaving photosystem 2 enter photosystem 1 to replenish electrons. photosystem 2 replenishes it's electrons by splitting water, generating oxygen gas
4) potential energy from concentration gradient harvested by ATP synthase. energy used to make ATP
5) ATP and NADPH used in sugar making process of calvin cycle
33
Calvin Cycle (Dark Reactions)
- takes place in stroma of chloroplast
- ATP and NADPH from light rxn used to form sugar
- 3 CO2 added added to 3 RuBP (5-carbon sugar) to give 6 3-PGA (3 carbon molecules)
- high energy phosphate molecules from 6 ATP added to 3-PGA
- 6 NADPH molecules oxidised and electrons reduce 3-PGA to give 6 G3P
- 5 G3P reshuffled to reform RuBP
- process repeats, and two G3P's combined to make glucose
34
What is the physical basis of the phototropic response?
cell elongation
35
Phototropism
auxin moves to side of stem opposite light and causes cells to elongate
direction of elongation controlled by orientation of cellulose microfibrils within cell wall
auxin increases activity of proton pumps to decrease cell pH. this causes enzymes to activate, cleaving cross-linking polysaccharides in cell wall to allow elongation
36
Photosynthesis in Dry Climates
- C3 plants
37
C3 vs C4 vs CAM
- C4 photosynthesis uses two extra ATPs
- C4 plants have a lot less photorespiration
- optimum temp for C4 is higher than C3
- C3 more efficient than C4 at lower temperatures
PHOTOSYNTHESIS:
C3: CO2 captured by Rubisco and added to RuBP to produce 3-PGA
C4/CAM: CO2 reacts with PEP to give oxaloacetate (4 carbon). steeper concentration gradient ---> smaler openings at guard cells ---> reduced water loss
SEPARATION OF CO2 FIXATION AND CALVIN CYCLE
C3: no separation (in chloroplasts)
C4: between mesophyll cells and bundle sheath cells (in space)
CAM: between day and night (in time)
STOMATA OPEN
C3: day
C4: day
CAM: night
BEST ADAPTED TO:
C3: cool, wet environments
C4: hot, sunny environments
CAM: very hot, dry environments
38
Photorespiration
- takes place in hot, dry conditions
- rubisco uses O2 instead of CO2
- wastes energy and does not produce sugar
39
Co-transport: Nitrate
- transport protein couples passage of one solute to passage of another
- cell accumulates NO3- anions by coupling their transport to inward diffusion of H+ through a cotransporter
40
Co-transport: Sugars
- "coat tail" effect
- responsible for uptake of sugar sucrose by plant cells
- plant cells can also accumulate a neutral solute, sucrose, by co-transport H+ down steep concentration gradient
41
Control of Stomata Opening and Closing
- each stomata flanked by guard cells which control the diameter of the stomata by changing shape
- changes in turgor pressure open and close stomata
- results from the reversible uptake and loss of potassium ions by guard cells (K+ channels)
42
Sources & Sinks
Source: plant organ that produces sugar e.g. mature leaves
Sink: organ that is a net consumer or storer os sugar e.g. roots, growing buds, stems, growing leaves
43
Sugar Transport
- sugar moves by symplastic and apoplastic pathways
- phloem loading requires active transport
- proton pumping and co-transport of sucrose and H+ allows cell to accumulate sucrose
44
Pressure Flow
- sap moves through a sieve tube by bulk flow
- driven by positive pressure in phloem (xylem = neg. pressure)
- pressure flow hypothesis explains why phloem sap always flows from source to sink
45
Etiolation
Morphological adaptations for growing in darkness
46
Cytokinis
- stimulate cell division
- produced in actively growing tissues (roots, embryos, fruits)
- work with auxin in apical dominance
- retard ageing of some plants
47
Gibberellins
- stem elongation, fruit growth and seed germination
- after water is imbibed, release of gibberellins from embryo signal seed to germinate
1) water enters seed, GA released, signals to aleurone
2) aleurone releases digestive enzymes which hydrolyse stored nutrients
3) nutrients feed embryo ---> growth
48
Brassinosteroids
- similar to sex hormones in animals
| - induce elongation
49
Abscisic Acid (ABA)
- many effects
- seed dormancy (inhibit germination)
- survival value: only germinates in optimum condition
- drought tolerance: control stomata
50
Ethylene
- produces in response to stresses (drought, flooding, pressure, injury, infection)
- alerts nearby plants to danger
- apoptosis (programmed cell death)
- fruit ripening
- slows primary growth (not secondary)
- in climacteric fruits, ethylene increases ripening
- biosynthetic pathway: Met ---(adomet synthetase)---> AdoMet ---(ACC synthase)---> ACC ---(ACC oxidase)---> ethylene
- ACC synthase regulates whole route
- block ACC synthase gene to control ripening
51
Photomorphogenesis
effects of light on plant morphology
52
Plants and Light (Photoreceptors)
- plants can see light colour, direction and intensity
- phototropic bending toward light is caused by photoreceptor
- sensitive to blue and violet light (high energy)
Blue-Light Photoreceptors: elongation, stomata opening and phototropism
Phytochromes: regulate plants response to light throughout life
53
Phytochromes
- photoreceptor responsible for the opposing effects of red and far-red light
- two identical subunits bonded to a non-protein pigment (chromophore)
- exist in two reversible states, Pr and Pfr
synthesis ---> Pr ---(red light)---> Pfr ---> enzymatic destruction
Pfr ---(far-red light / slow conversion in darkness)---> Pr
54
Photoperiodism and Responses to Seasons
Photoperiod - relative lengths of night and day
- used to detect time of year
- developmental processes (flowering) require a certain photoperiod
- short day plants trigger flowering in short day season (autumn/winter)
- long day trigger in spring/summer
- flowering controlled by night length
plants also respond to:
- gravity
- environmental stresses
- enemies
- mechanical stimuli
55
Mechanical Stimuli
touch (wind) ---> short induction of ACC synthase gene ---> short burst of ethylene ---> primary growth stopped for short period --> secondary growth continues ---> shorter and thicker trees
56
Genetic Modification: Argo Transformation
- argobacterium tumefaciens bacterium transfers genes to plants
- causes "crown gall" disease
- Ti plasmid only in pathogenic strains
- fragment of plasmid DNA
- transferred into plant cells
- flanked by border sequences
Process taken advantage of:
1) cut out T-DNA
2) insert DNA that we want to transfer
3) Argo will infect plant tissue
- effective on dicots (fruits, cotton) but now monocots (wheat, rice)
- transforms few cells
- introduce survival gene into T-DNA so untransformed cells can be killed
57
Genetic Modification: Gene Gun
- shoots micro-projectiles coated with DNA into cell
- effective on monocots
- transforms few cells
- introduce survival gene into T-DNA so untransformed cells can be killed
