Plant biology Flashcards
(43 cards)
1
Q
What is transpiration?
A
- water evaporation during gas exchange in plants
- water is lost
- in stomata
- water potential is lower in air
2
Q
What are stomata?
A
- pores in epidermis of a plant
- gas exchange
- CO2 can’t pass through waxy cuticle
3
Q
Where is water loss controlled?
A
- guard cells
- in pairs (on each side of stoma)
- control aperture of stoma
- thin outer walls and thick inner walls
4
Q
How is the water loss controlled?
A
- guard cells
- potassium pumps
- light activated
- K+ from epidermis move to guard cells
5
Q
When does wilting occur?
A
- transpiration → water uptake
- stoma closes (flaccid)
6
Q
How is water replaced?
A
- transpiration = water loss
- plant uptakes water from soil through roots
- water gradient created by active transport of minerals into roots
- water travels through cell walls and cytoplasm to xylem
7
Q
How does transport of water occur?
A
- xylem structure
- thickened walls
- low pressure (negative)
- water properties
- adhesion (travels up the xylem) and cohesion (continuous stream)
8
Q
What is transpiration-pull?
A
- water is pulled up
- adhesion
- low pressure in xylem
- the higher, the lower the pressure is
- energy comes from heat (transpiration)
- cavitation = liquid unable to resist water pressure, xylem vessels break
9
Q
How is water gradient in roots created?
A
- mineral ions go through protein pumps
- active transport
- relationship with fungus
- as it attaches to the roots it absorbs ions creating gradient
10
Q
What are xerophytes?
A
- plants growing on deserts and dry habitats
11
Q
How do xerophytes adapt to hot environment?
A
- reduced leaves
- lower area of transpiration
- fleshy leaves
- water storage
- silver or shiny surface
- reflecting sun, low transpiration
- CAM metabolism
12
Q
What is CAM metabolism?
A
- CO2 is absorbed at night
- low transpiration
- stored as malic acid (C4H8O5) in vacuoles
- stomata closed during day
- photosynthesis still occurs
13
Q
How do xerophytes absorb water?
A
- deep root system
- water from ground layers
- high concentration of ions in roots
14
Q
How does Marram grass adapt?
A
- rolled leaves
- thick outer layer
- stomata in pits
- water vapour saturation
- more diffusion shells
- water vapour saturation
15
Q
How do halophytes adapt to salty environment?
A
- reduced leaves
- leaves are shed
- stems preform photosynthesis
- water storage in leaves
- thick cuticle and layered epidermis
- sunken stomata
- long roots
- structures removing salt build-up
16
Q
What are the factors affecting transpiration?
A
Environmental: relative humidity, temperature, air movement, atmospheric pressure, water supply, light intensity
Intrinsic: leaf surface, thickness of epidermis and cuticle, stomatal frequency, size and position
17
Q
What is a potometer?
A
- transpiration rate measured
- rate of water loss: uptake
- movement of water (air bubble) measured
18
Q
Where are carbohydrates transported in plants?
A
- from source to sink
- source (storage): leaves, green stems,
- sink (uses): roots, shoots
19
Q
What is translocation?
A
- transport of organic solutes in plants
- phloem links parts that need supply
20
Q
How is transport in phloem possible?
A
- due to pressure gradients solutes move
21
Q
What is the structure of phloem?
A
- sieve tubes
- sieve tube cells and plates
- no nucleus
- huge vacuole
- companion cells
- nucleus
- support for sieve tube members
- control active transport
- mitochondria
22
Q
Apoplastic phloem loading
A
- carbohydrates into phloem
- sucrose = most prominent in phloem sap
- not readily used for metabolism
- good to transport
- active transport
- H+ gradient created outside companion cells (apoplast)
- as the H+ moves back it creates energy
- sugar into sieve tube
- sugar co-transporter
- H+ gradient created outside companion cells (apoplast)
23
Q
Symplastic phloem loading
A
- through plasmodesmata
- connections between cells
- converted to oligosaccharide in companion cells to maintain sucrose gradient
24
Q
How is osmotic pressure created in phloem?
A
- high concentration of solutes
- osmotic pressure created
- water taken from xylem
- solutes are unloaded into sink
- water returns to xylem
25
How is hydrostatic pressure created?
- water is incompressible
- uptake of water = increased volume
- build-up of pressure
- water moves down (to the sink)
26
How are phloem transport rates measured?
- aphid stylets experiment
- aphids get to phloem by stylets (mouth parts)
- stylets cut off
- phloem sap pumped by plant
- phloem sap content and flow rate investigated
- slow rate = close to sink
27
What is radiotracking?
- plant leaf exposed to C-14
- spread of radioactive tracker observed
- sink and source leaves distinguished
- photosynthate moves to younger plants above source
- potential source leaves removed
- photosynthate moves to younger leaves on the other side
28
What are meristems?
- plants have indeterminate growth
- plant tissues responsible for growth
- undifferentiated cells
- active cell division
- primary meristems = apical meristems
- tips of stems and roots
- length and thickness
29
What is the role of shoot apical meristems?
- division through mitosis and cytokinesis
- shoot apical meristems
- growth of stem
- group of cells that develop into leaves and flowers
- division = 2 cells
- one cell remains meristem
- the other increases and differentiates
- meristems produce additional meristems
- protoderm (epidermis)
- procambium (vascular tissue)
- ground (pith)
- young leaves at sides of shoot meristems
- small bumps = leaf primordia
30
How is growth in plants controlled?
- by hormones
- auxins
- initiation of growth of roots
- influencing the development of fruits
- regulating leaf development
- most abundant auxin = indole-3-acetic acid (IAA)
- elongation of stem
- stimulation of mitosis
- synthesised in apical meristem
31
What is apical dominance?
- axillary buds = shoots formed at junction (node) of base of a leaf
- regions of meristems are left in node
- no growth → auxins produced by shoot apical meristems
- the further from apical meristem, the more likely it is to grow
32
What is the role of cytokinins?
- hormones produced in root
- promotion of axillary bud growth
- relative ratio of cytokinins to auxins determines the growth
- gibberellins also contribute to growth
33
What are tropisms?
- directional growth
- towards light or gravity
- controlled by hormones
- towards light (phototropism) and opposite to gravity (gravitropism)
34
How does phototropism work?
- photoreceptors (phototropins) absorb wavelengths
- binding to receptors which control gene transcription
- genes involved are coding for auxin transporters (PIN3)
- more auxin on shadowed side → plant cells grow faster
- plant bends towards light
35
How does location of auxins influence growth?
- in roots auxins are at the bottom (gravity)
- prohibition of cell elongation
- top cells elongate faster
- root bends
- positive geotropism
- in stems auxins are at the top
- promotion of elongation
- stem grows
36
How does micropropagation of plants work?
- tissues from stock plants taken
- pieces = explants
- usually meristem
- explant placed in growth media
- plant hormones inside
- auxins to cytokinin ratio equal = undifferentiated mass (callus)
- auxin : cytokinin = 10:1 → root development
- less → stem development
- plant transferred to soil
37
Why is micropropagation used?
- transporting plants without risk of viruses
- usually in plasmodesmata
- apical meristem free of viruses
- preservation of species (orchids)
- difficult to germinate
- more efficient
- production of flowers with desirable features (artificial selections)
38
What are vegetative plants?
- seeds germinate
- young plants formed
- ends when reproductive phase begins
- meristems produce flowers instead of leaves
39
On what does reproductive phase depend?
Length of dark periods (night)
40
How do plants measure length of dark periods?
- photosensitive pigment: phytochrome
- two forms: PR and PFR
- mechanism
- PR absorbs red light (660nm) → PFR
- PFR absorbs far-red light (730nm) → PR
- in sunlight PR → PFR
- PR is more stable so at night PFR → PR
- PFR is the active form
- binds to receptor proteins in cytoplasm
- (long-day plants) at the end of short nights a lot of PFR remains = binding = transcription of genes needed for flowering
- (short-day plants) receptor inhibits transcription so at the end of long night
- high PFR = inhibition = no flowering
41
How is gene expression used for flowering?
- genes in shoot apex
- products trigger cell differentiation leading to flower production
42
How are plants induced to flower?
- manipulating amount of light a plant receives
43
What are the stages of plant reproduction?
- pollination
- delivery of pollen to the stigma of flower
- by pollinators (birds, bees, butterflies), wind or water
- mutualism --> pollinators get nectar
- fertilisation
- fusion of male gametes / nuclei (from pollen grain) with ovule
- zygote produced
- seed dispersal
- transport of seed in fruit to spread them
- wind, animals
