Lecture 1 Flashcards
(26 cards)
Define physiology.
Study of the normal functions of organisms and their parts which is related to structure in many ways. Everything in the normal life of an organism except morphology and reproduction.
Define homeostasis.
Tendency towards a relatively stable equilibrium maintained by physiological processes.
Define adaptation.
Heritable changes in genes through natural selection.
Define acclimation.
Changes in gene expression and metabolism, usually reversible and non-heritable.
What is water used for in plants?
Cell turgidity, photosynthesis, transpiration and transport of solutes. Makes up up to 95% of plant volume.
What is the aim of transpiration?
Water taken up by the roots, travels through the stems and is lost by the leaves. Transports solutes but not bigger molecules.
What directional does transpiration move in?
One, from roots to shoots through the xylem.
What effect does transpiration have on the world?
Accounts for %40 of global precipitation and water vapour is a more potent greenhouse gas than CO2.
What 2 components make up the vascular system?
Xylem and phloem.
Describe the structure of the xylem.
Open lignified tubes with no end wall between cells. Forms in rings or spirals.
Describe the function of the phloem.
Bi-directional transport of solutes (organic molecules) between sources and sinks.
Describe the structure of the phloem.
Living cells that need support so are in vascular bundles around the xylem. Have end walls that act as sieve plates between the cells.
What are the 4 different layers of root water must pass through to reach the xylem?
Epidermis, cortex, endodermis, pericycle.
Which section is the main body of the root?
The cortex.
Which section contains the Casparian strip?
The endodermis.
What is the function of the Casparian strip?
To force water into the symplastic pathway to increase control and prevent water loss out of the xylem.
What is the symplastic pathway?
Water moves through the cytoplasm of root cells to reach the xylem which are made selectively permeable using aquaporin channels.
How many aqauporins are there in Arabidopsis and humans?
35 in arabidopsis and 4 in humans.
What is the apoplastic pathway?
Water movement through cell walls, largely unrestricted.
How is leaf structure involved in the movement of water?
Water travels from xylem to the cytoplasm of mesophyl cells and then out of the stomata by transpiration.
What is the cohesion tension theory?
Water forms a continuous column in the xylem due to cohesive hydrogen bonding. Evapotranspiration pulls the column up through the xylem. Up to 30 MPa of pressure within the xylem.
What effect does the environment have on transpiration rates?
Higher humidity slows transpiration.
Higher wind increases transpiration.
Higher light increases transpiration.
Higher temperature increases transpiration,
What are the boreal forests?
Largest terrestrial biome made up of coniferous forests that cover 14% of the worlds surface in a circumpolar belt. Down to -70 degrees.
What problems does the cold create for water transport?
Creates a dry environment. As water freezes it loses gasses which form bubbles. Freeze-thaw cycles can cause embolisms to form in the xylem that break the water column.
