Chap 35-37 - Plants Flashcards
Meristem
Tissue that remains embryonic through a plant’s entire life.
Allows indeterminate growth.
Primary vs Secondary growth
Primary - growth in length.
Secondary - growth in thickness.
Vascular & Cork cambium
Lateral meristem tissue arranged in a ring.
Allows secondary growth.
Vascular arises from procambium, cork cambium arises from ground meristem.
Pneumatophores
Oxygen-absorbing roots that poke out of the ground - eg. in mangroves where the plant grows in oxygen-poor substrate.
Mycorrhizal associations
Connection between plant roots and mycelium; exchanges nutrients between the two.
Fibrous root system
Roots are arranged in a dense, shallow mat. Found in plants that are frequently grazed on by vertebrate herbivores.
Rhizomes vs Stolons vs Tubers
Rhizomes - horizontal shoots just below soil surface.
Stolons - “runner” stems above the soil, as in strawberries/mint.
Tubers - enlarged rhizomes or stolons (not roots).
Three main types of tissue in plants
Dermal (epidermis & periderm)
Vascular (xylem & phloem)
Ground tissue
Periderm
The ‘woody’ cells that replace epidermis. Produced by cork cambium, and contains a lot of lignin for strength.
Pith vs Cortex
In Eudicots:
Pith - ground tissue that is found internally of the vascular tissue.
Cortex - ground tissue that is between vascular and dermal tissue.
Major cell types in plants
(5)
Parenchyma cells - default, does everything.
Collenchyma cells - scaffold.
Sclerenchyma cells - woody (lignin)
Xylem & phloem cells
Parenchyma cells
A ‘normal’ plant cell:
- Thin, flexible primary cell wall; no secondary.
- Big central vacoule.
- Starch-storing amyloplasts.
- Able to divide and differentiate into other cell types.
Collenchyma cells
Quick, effective scaffolding in young plants:
- Elongated, with thickened but still flexible primary cell wall.
- Just beneath epidermis in young stems.
Sclerenchyma cells
Woody, basically:
- Big secondary cell wall with lignin for strength.
- Two types; boxy sclereids & elongated fibres.
Xylem cells
(two types)
Water and minerals from ground up:
- Dead at maturity.
- Tracheids; Elongated, with tapered end that overlaps with the next tracheid cell. Pits in the secondary cell wall in these overlapping regions allows water to move to the next cell.
- Vessel elements; Shorter & wider than tracheids, aligned end-to-end instead of tapered. Perforation plates with holes allows water movement between elements.
Phloem cells
(two types, kind of three?)
Sugars from leaves
- Alive at maturity!
- Made of sieve cells in gymnosperms & plants without seeds.
- In angiosperms, built from sieve-tube element cells. Sieve-tube elements have no nucleus/ribosomes/cytoskeleton.
- Elements connected through sieve plates with holes.
- A companion cell is next to each element, connected by lots of plasmodesmata. The companion’s nucleus/ribosomes serves the element cell.
Vascular cambian
- Layer that is single cell thick.
- Forms phloem on outside.
- Xylem on inside.
Root cap
“cap” of dead cells on the tip of a growing root. Made and constantly replenished by the meristem. Protects the meristem and softens the soil with mucous to help grow through it.
Pericycle
Outermost layer of cells of the stele (vascular bundle) in plant roots. Non-vascular, but controls the inputs/outputs of stuff into the vascular bundle.
Also propagates development of lateral roots.
Vascular rays
Radial lines of parenchyma cells that connect secondary xylem and phloem cells.
- Moves stuff between the vascular cells.
- Stores carbohydrates.
Dendrochronology (just for fun)
Science of analysing a tree’s growth rings.
Sapwood vs Heartwood
Sapwood - outer, younger layers of secondary xylem that transports xylem sap.
Heartwood - older, inner layers that no long transport xylem sap. Darker in colour.
Lenticels
Small areas with more space between cork cells.
Allows cells on the inside to exchange gases for respiration.
Pattern formation
Development of specific structures in specific locations - eg. dermal tissue on the outside, vascular on the inside.
Position-based mechanism
(pattern formation)
Plant cell differentiation is determined later in the cell’s life based on where it ends up, rather than early on like in animals.
Leaf primordium
Tiny groups of cells that form new leaves.
(Floral primordia form flowers)
ABC hypothesis
A model of three genes regulating the spatial pattern in flowers.
Morphogenesis (in growth)
Development of body shape and organisation.
Cell differentiation (in growth)
Differing gene activation allows cells to assume different functions.
Phyllotaxy
Arrangement of leaves on a stem.
Apoplast
Everthing external to plasma membrane - cell walls, extracellular spaces, interior of dead cells like tracheids.
Symplast
All cytosol and plasmodesmata.
Three routes of short distance transport
Apoplastic - extracellular spaces
Symplastic - within cells, through plasmodesmata
Transmembrane - within cells, crossing membranes
𝛙 definition
Water potential, with units of megapascals.
𝛙 equation
𝛙 = 𝛙s (solute potential) + 𝛙p (pressure potential)
Solute potential is negative; more solutes decrease water potential.
Pressure potential can be positive or negative, relative to atmospheric pressure.
Ion that controls guard cell opening/closing
K+
Three main factors that causes stomata to open
- Light
- Low CO2 within the leaf
- Internal circadian rhythm
Abscisic acid
Hormone released during drought stress. Causes stomata to close, and inhibits photosynthesis.
Xerophytes
Plant adapted to arid climates.
Translocation
Transport of nutrients in the phloem.
Soil horizon
Soil layers with distinct properties.
Topsoil is the A horizon.
Loams
Soil with somewhat equal amounts of sand/silt/clay, most fertile.
Charge in soil particles
Most soil particles are negatively charged.
This also means some nutrients (nitrate, phosphate & sulphate) are lost easily, since they won’t bind to negative particles.
Cation exchange
Positively charged minerals (bonded to negative soil particles) are released and made available by the plant when displaced by H+.
Role of phosphorous in plants
(3)
Component of:
- DNA/RNA
- ATP (phosphate)
- Phospholipids
Role of nitrogen in plants
(3)
Component of:
- DNA/RNA
- Amino acids
- Chlorophyll
Role of potassium in plants
(2)
- Cofactor of many enzymes
- Helps maintain turgor
9 macronutrients for plants
C, O, H
NPK
S, Mg, Ca
8 micronutrients for plants
Cl, Fe, Mn, B, Zn, Cu, Ni, Mo (molybdenum)
Chlorosis
Yellowing of leaves - usually issues with chlorophyll/chloroplast production.
Rhizosphere
Area of soil near plant roots, including the organisms living there.
Rhizobacteria
Prokaryotes that live in association with plants.
Rhizobacteria’s interactions with plants
- They depend on nutrient secretions from plants.
- Make antibiotics or growth-stimulating hormones, absorb toxic particles in soil.
- Fix nitrogen & increase nutrient uptake by changing soil properties.
Nitrogen fixing
vs
Nitrifying
Nitrogen fixing - N2 –> NH3
Nitrifying - NH4+ –> NO2- –> NO3-
Ammonifying
Amino acids in humus –> NH4+
Energy requirement of nitrogen fixing
An endergonic process; 16 ATP consumed per 2NH3
ATP supplied by decomposition in soil or from secretions from plants.
Rhizobium bacteria
A genus of bacteria associated with legumes for nitrogen fixing!
Two types of mycorrhizal associations
Ectomycorrhizae - less common, exterior.
Arbuscular myccorhizae - 85% of plants, interior.
Also known as Endomyccorhizae.
Ectomycorrhizae
A dense mantle of hyphae over surface of the root. Some into the apoplast of the root cortex, in and between the cell walls.
Arbuscular mycorrhizae
Hyphae forms branches on the interior of the cell wall, ‘poking’ the cell membrane. (Arbuscles) (membrane isn’t penetrated)
Creates high contact area.
