module 4 Flashcards
Provide argument suggesting multicellularity arose independently in plants and animals
Propose possible steps leading to multicellularity
- Divided and stayed in a cluster
- inter and intracellular communication
- differentiation and specialisation
- specialised cells seperate into groups
Benefits of multicelluarity
- cell specialisation allows cells to adopt new functions
- integration and co-operation between cells allowing for the development
- structurally and fucntionally complex bodies
- creation of a stable internal environment
- increase in size
- more efficient gathering of resources and adapting to specific environment
Primary and secondary growth
Primary is vertical and secondary is radical
Role of expansin
allows slippage between cellulose microfibrils by temperarily disrupting non-covalent bonds of celluse and glycan, hemicellulose and pectin
difference between primary and secondary cell division
primary cell wall is sem-rigid and can expand whereas secondary cell wall is thick, rigid, rich in lignin and cannot expand
Auxin hormone and its role in regulating phototropism and gravitropism
-auxin is a growth hormone in plants
-phototropism: auxin accumulates on the exposed side
-gravitropism: auxim accumulated on the lower side
Key steps in plant embryogenesis
- asymmetrical division of zygote into a smaller apical cell and a larger basal cell
- octant stage: apical cell further divides to become the embryo and basal cell divides to form the suspensor
- heart stage: cell expansion and division
- mature embryo: embryo fold over in the seed
Shoot apical and root apical meristem
shoot apical meristem generates aerial structures (leaf, axillary bud, internode)
root apical merstem: subterranean structures (roots)
Tissue systems in plants - dermal tissue system
single layer of cell forming the epidermis
epidermal cells can differentiate into stomata, trichomes and root hairs
Tissue systems in plants - Ground
makes up most of plant tissue and is located between dermal and vascular tissue
classifications based on cell wall structure
1. parenchyma: round cell, thin cell wall
2. collenchyma: flexible structural support
3. sclerenchyma: have a secondary cell wall, rigid tissue and thicken cell wall
Tissue systems in plants - vascular
Network of transporting systems
Xylem: carrier for water and mineral ions from roots to shoots
- dead cells with secondary walls
pholem: move sugar and nutrients from shoot to roots
- living cells
- sieve tuble element cells
companion cells
Water potential
refers to the tendency of a solution to take up water from pure water across a selectively permeable membrane
water always moves for high to low potential reigons
Water uptake by root cells
- water enters root via osmosis and moves through symplast or apoplast
- when reaching the casparian strip, water and solute in apoplast forced into endothermal cells
- water and solute remain in the symplast
solute is actively transportd out of the cell and into apoplast and follows passively by osmosis
difference between apoplast and symplast
apoplast: rapid and unregulated movement on interconnected cell wall and intercellular spaces between cells
symplast: slow and regulated movement in interconnected cytoplasm via plasmodesmata