lecture 2: Water and Plant Cells

turgor pressure

Cell walls allow plant cells to build up large internal hydrostatic pressures, called __________________, which are a result of their normal water balance.

is essential for many physiological processes, including cell enlargement, gas exchange in the leaves, transport in the phloem, and various transport processes across membranes.

also contributes to the rigidity and mechanical stability of nonlignified plant tissues.

Water

the most abundant and the best solvent known

Transpiration

is an important means of dissipating the heat input from sunlight.

hydrogen bonds

The weak electrostatic attraction between water molecules is known as

true

true or false

When the temperature of water is raised, the molecules vibrate faster and with greater amplitude

Cohesion

the mutual attraction between molecules

Adhesion

the attraction of water to a solid surface

capillarity

the movement of water along a capillary tube

high tensile strength

Cohesion gives water a ________________, defined as the maximum force per unit area that a continuous column of water can withstand before breaking.

bulk flow

Also known as mass flow

Pressure driven

Occurs when an external force, such as gravity or pressure is applied

Movement of water by bulk flow is part of our everyday experience (for example, our faucets flow because of the pressure generated by gravity or water in a stream flow in response to the hydrostatic pressure by gravity)

Bulk flow also accounts for some water movement in plants, such as conducting cells of xylem tissue or the movement of water into the roots

diffusion

Directed movement from a region of higher concentration to a region of lower concentration

Diffusion is driven by concentration differences

Diffusion is a significant factor in the uptake and distribution of water, gases, and solutes throughout the plant

Diffusion is an important factor in the supply of CO2 for photosynthesis as well as the loss of water vapor from the leaves

osmosis

is the diffusion of water across a selectively permeable membrane

Transpiration

is the process by which water moves through a plant and evaporates from its aerial parts, including leaves, stems, and flowers.

Root pressure

is the force in plants that helps drive fluids upward into the waterconducting vessels (xylem).

Sandy soils

this type of soil have a relatively low surface area per gram of soil and have large spaces or channels between particles

clay soils

this soil have much greater surface areas and smaller channels between particles.

Water potential

is defined as the potential energy of water in a system relative to that of pure water, with pressure and temperature held constant

osmotic potential

The potential of water molecules to move from a hypotonic solution to a hypertonic solution across a semi-permeable membrane.

hydrostatic pressure

the pressure exerted by a fluid at equilibrium at any point of time due to the force of gravity".

true

true or false

Water has a high surface tension that tends to minimize air-water interfaces

bulk flow

Water moves up through the soil by ________

Soil hydraulic conductivity

is a measure of the ease with which water moves through the soil, and it varies with the type of soil and water content

true

true or false

As the water content (and hence the water potential) of a soil decreases, the hydraulic conductivity decreases drastically.

Root hairs

are microscopic extensions of root epidermal cells that greatly increase the surface area of the root, thus providing greater capacity for absorption of ions and water from the soil

apoplast, transmembrane, and symplast pathways

Water moves in the root via the ______________, ______________ , and ______________

APOPLAST PATHWAY

water moves exclusively through the cell wall without crossing any membranes.

apoplast

the continuous system of cell walls and intercellular air spaces in plant tissues

Casparian strip

At the endodermis, water movement through the apoplast pathway is obstructed by the __________.

Casparian strip

a band of radial cell walls in the endodermis that is impregnated with the wax-like, hydrophobic substance called suberin.

Suberin

acts as a barrier to water and solute movement.

TRANSMEMBRANE PATHWAY

the route followed by water that sequentially enters a cell on one side, exits the cell on the other side, enters the next in the series, and so on.

SYMPLAST PATHWAY

water travels from one cell to the next via the plasmodesmata

plasmodesmata

The symplast consists of the entire network of cell cytoplasm interconnected by the ______________

xylem

is plant's vascular tissue that conveys water and dissolved minerals from the roots to the rest of the plant and also provides physical support

Tracheids and Vessel elements

2 types of tracheary elements in the xylem

TRACHEIDS

Present in both angiosperms and gymnosperms, in ferns, and other vascular plants

Tracheids

are elongated, spindle-shaped cells that are arranged in overlapping vertical files.

pits

Water flows between tracheids by means of the numerous ________ in their lateral walls.

are microscopic regions where the secondary wall is absent and the primary wall is thin and porous

pit pairs

Pits of one tracheid are typically located opposite pits of an adjoining tracheid, forming ____________.

pit membrane

The porous layer between pit pairs, consisting of two primary walls and a middle lamella, is called the ____________

VESSEL ELEMENTS

Found only in angiosperms, a small group of gymnosperms, and germs

Vessel elements and perforation plate

________________ tend to be shorter and wider than tracheids and have perforated end walls that form a ___________ at each end of the cell.

vessel

the perforated end walls allow vessel members to be stacked end to end to form a larger conduit called a ________

10 cm

Maximum vessel lengths range from _______ to many meters.

waxy cuticle

the __________ that covers the leaf surface is a very effective barrier to water movement.

diffusion and stomatal apparatus

Almost all of the water lost from typical leaves is lost by ___________ of water vapor through the tiny pores of the _____________, which are usually most abundant on the lower surface of the leaf

Guard cells

this regulate the diameter (and diffusional resistance) of the stomatal aperture