Chapter 8 Flashcards
Transport in plants (16 cards)
State the functions of xylem and phloem
xylem – transport of water and mineral ions,
and support
phloem – transport (translocation) of sucrose and amino acids fro sources to sinks
Adaptive structures of xylem vessels
thick walls with lignin: waterproof, strong
cells joined end to end with no cross walls to form a long continuous tube with no cell contents to allow smooth continuous flow of water
Structure of vascular bundles in root, stem, and leaf
!! refer to images of vascular bundles !!
root – star shaped inner xylem outer phloem
stem – petal-like inner xylem outer phloem
leaf – circular with xylem on top of phloem
Outline the pathway taken by water through the
root, stem and leaf
root hair cells → root cortex cells → xylem → mesophyll cells
Describe the structure and function of root hair cells
Root hair cells are tiny, tube-like outgrowths that form on young roots. They are very numerous and increase the surface area of the root for absorption of water (via osmosis) and mineral ions (via active uptake)
Investigate the pathway of water through the above-ground parts of a plant
use a plant shoot that has soft tissue (Impatiens, daffodil stalk with flower, or a stick of celery works well)
place in a beaker of dilute stain (eg. food coloring)
leave for 24 hrs
remove shoot and section stem with scalpel
blue xylems veins absorbed dye
Describe transpiration
loss of water vapour from leaves
State the pathway of water vapour
water from a thin layer evaporates from the surfaces of the mesophyll cells into the air spaces increasing conc. gradient – diffuses out of the leaves through the stomata as water vapour; this causes suction, which pulls
water up the stem – transpiration pull
Explain how water vapour loss is related to internal sa and stomata
The large air spaces provides the spongy mesophyll cells with a large surface area, allowing faster diffusion, a large number and size of stomata allow an easy pathway of water vapour out the leaf
Explain the mechanism by which water moves
upwards in the xylem
transpiration in the leaves lowers the pressure creating a suction that pulls up columns of water molecules held together by forces of attraction between water molecules (cohesion)
Explain the effects of factors on the rate of transpiration
Temperature: increase in temp causes increase in KE of water vapour particles; move faster y3ni faster diffusion
Humidity: if conc. of water vapour particles outside the leaf is higher than inside, the conc gradient gets reduced slower diffusion, if humidity too low conc. gradient very steep so a lot of water is lost – stomata close to prevent wilting
Wind speed: as water is lost, wind carries it away maintaining conc gradient
Explain how you would investigate the effects of these factors on the rate of transpiration
Use a !!potometer!! (see diagram)
weight: measuring the weight loss of a plant over time
bubble: movement of the bubble is recorded over time
Explain how and why wilting occurs
the water in each cell is applying a turgor pressure outwards on the cell wall. This pressure forces some water out of the cell wall, evaporating into the air space between the cells, ifthe amount of water lost from the leaves is
greater than the amount taken into the roots – the turgor pressure decreases, making the cells flaccid (no long rigid) causing wilting
What is translocation
the movement of sucrose and amino acids in phloem from sources to sinks
What are sources and sinks
sources: parts of plants that release sucrose or amino acids
sinks: parts of plants that use or store sucrose or amino acids
Explain why some parts of a plant may act as a source & a sink at different times
During the life of a plant, a region that originally acted as a sink may become a source. For example, sugars stored in the leaves of a bulb in the summer (acting as sink) may be translocated to a growing flower bud or stem the following spring. The bulb is now acting as a source.
