Chapter 7: Transport In Plants Flashcards
What is the name of the main transport system in plants?
The vascular system
What are the two types of main vascular tissue in the vascular system?
The xylem and the phloem
What are the cells in the xylem
- Xylem vessel element
- sclerenchyma (fibre)
- Parenchyma
- tracheid
What are the cells in the phloem?
- Sieve tube element
- Companion cells
- Parenchyma
- sclereids (stone cells, sclerenchyma)
How do xylem vessel elements join up to form the xylem vessel?
Xylem vessel element join end to end to form the xylem vessel
How do the sieve tube elements form the sieve tube?
They join end to end
What is the function of xylem tissues thickening?
- for transport of water and dissolved mineral ions
- for mechanical support
What are the structural adaptations of the xylem vessel for transport?
- Hollow lumen (with no cytoplasm)
- No end walls
- lignified walls
- Arranged end to end
- Pitted
What properties of the xylem elements aid in mechanical support of the plant structure?
- Lignin thickenings (5 types)
- primary cell wall is made up of cellulose
- secondary cell wall (during differentiation, lignin is formed as an additional layer beneath the primary cell wall)
Define dicotyledonous
Plants that produce seeds that contain
two cotyledons. They have two primary
leaves.
Why do plants require a transport system?
● To ensure all cells receive a sufficient supply of the
nutrients they require
● Especially important as a plant must be able to
transport substances up their stem, against gravity
What is the xylem?
A non-living, heavily lignified plant transport
vessel responsible for the transfer of water
and minerals from the roots to the shoots and
leaves.
What is the phloem?
A living plant transport vessel responsible for
the transfer of assimilates to all parts of the
plant. The phloem consists of sieve tube
elements and companion cells.
State what is meant by the term “vascular bundle” in
plants.
The vascular system in dicotyledonous
plants. It consists of two transport
vessels, the xylem and the phloem.
Relate the structure of the xylem to its function.
● Long, continuous columns made of dead tissue, allowing
transportation of water
● Contains pits which allow sideways movement of water
between vessels
● Thickened with a tough substance called lignin which
provides structural support
Relate the structure of the phloem to its function.
● Sieve tube elements transport sugars around the plant
● Companion cells designed for active transport of sugars
into tubes
● Plasmodesmata allow flow of substances between
cytoplasm of different cells
Describe the arrangement of the vascular bundle in
dicotyledonous roots.
● Vascular bundle enable transport as well as structural support
● Xylem vessels arranged in an X shape in centre of vascular bundle. This
enables plant to withstand various mechanical forces such as pulling
● X shape arrangement of xylem vessels is surrounded by endodermis, an
outer layer of cells which supply xylem vessels with water
● Inner layer of meristem cells known as the pericycle
Describe the arrangement of the vascular bundle in
dicotyledonous stems.
● Xylem located on inside in non-wooded plants to provide
support and flexibility to stem
● Phloem found on outside of vascular bundle
● Layer of cambium in between xylem and phloem. This is made
of meristem cells which are involved in production of new xylem
and phloem tissue
Describe the arrangement of the vascular bundle in
dicotyledonous leaves.
● Vascular bundles form the midrib and veins of a leaf
● Dicotyledonous leaves have a network of veins,
starting at midrib and spreading outwards which are
involved in transport and support
Draw a labelled diagram of the
arrangement of the vascular bundle in
the root and stem of dicotyledonous
plants.
(see diagram in pmt notes)
State the importance of water potential (ψ) in the
movement of water from roots to shoots.
● Water moves down a ψ gradient
● Roots have a high concentration of minerals. Water moves from the
soil into the root, down its ψ gradient
● ψ decreases as you move up the plant. This results in a ψ gradient,
facilitating the movement of water through the plant by osmosis
Define transpiration.
● The evaporation of water from the leaves of a
plant via open stomata
● Consequence of gaseous exchange. Occurs
when the plant opens the stomata to exchange
oxygen and carbon dioxide
Name the factors that affect the rate of transpiration.
● Increased light increases transpiration
● Increased temperature increases transpiration
● Increased humidity decreases transpiration
● Increased air movement increases transpiration
● Waxy cuticle prevents transpiration
How can we measure transpiration rate?
● Using a potometer
● Plant cutting placed in a water-filled tube that
contains an air bubble. Rate of transpiration is
calculated by measuring the movement of the air
bubble over time
Explain what is meant by the apoplastic pathway.
● One of three pathways by which water and minerals move
across the root
● Water moves through intercellular spaces between cellulose
molecules in the cell wall
● Water reaches the casparian strip (impermeable layer made of
suberin) and is forced through the symplastic pathway
Explain what is meant by the symplastic pathway.
● One of three pathways by which water and minerals move
across the root
● Water enters the cytoplasm through the plasma membrane
and moves between adjacent cells via plasmodesmata
● To begin this pathway, water must be actively transported
into cells
Explain the cohesion-tension theory.
● Water molecules form hydrogen bonds with each other,
causing them to ‘stick’ together (cohesion)
● The surface tension of the water also creates this sticking
effect, preventing water slipping down the xylem. As water is
lost through transpiration, more can be drawn up the stem
from the roots
Define the term xerophyte.
Plants that are adapted to live and
reproduce in dry habitats where water
availability is low, e.g. cacti.
Give adaptations of xerophytes that allow them to
live in dry conditions.
● Small/rolled leaves ● Densely packed mesophyll ● Thick waxy cuticle ● Stomata often closed ● Hairs to trap moist air
State what is meant by “source to sink”.
The movement of plant assimilates from a
producing or storage region, the “source”
(e.g. leaves) to a region of requirement, the
“sink” (e.g. developing fruits).
Define translocation.
The bulk movement of organic
compounds in plants from sources to
sinks via the phloem.
Summarise the mechanism of translocation.
● Companion cells actively transport H+ to surrounding tissue, establishing a
concentration gradient
● H+ flows down their concentration gradient via a cotransporter (facilitated diffusion)
along with sucrose
● Sucrose builds up in companion cells and diffuses into sieve tube elements via
plasmodesmata
● This lowers ψ, causing water to move in from xylem (increasing hydrostatic pressure)
● Assimilates move along sieve tube towards areas of lower hydrostatic pressure (sink).
Sucrose diffuses into surrounding cells where it is needed
what is mass flow
the mass flow of water from the source to the sink down the
hydrostatic pressure gradient is a means of supplying assimilates such as sucrose to where
they are needed.
