Transport in plants

LO:

• State the functions of xylem and phloem• Identify the position of xylem and phloem as

seen in sections of roots, stems and leaves, limited to non-woody dicotyledonous plants

• Identify root hair cells, as seen under the light microscope, and state their functions

• State the pathway taken by water through root, stem and leaf as root hair cell, root cortex cells, xylem and mesophyll cells

• Investigate, using a suitable stain, the pathway of water through the above ground parts of a plant

• Explain that the large surface area of root hairs increases the rate of the absorption of water by osmosis and ions by active transport

Uptake of water and minerals

• Water– supports the plant - reagent in many biochemical reactions - transport medium - by osmosis from the soil solution into the root cells

• Minerals – effect the water potential of plant tissues– absorbed in the form of ions– ion uptake depends on respiration (more oxygen = faster

absorbtion– by diffusion or active transport

• https://www.youtube.com/watch?v=g7HbmUnqGlM&t=85

Movement of water

Step 1: water loss from the leaves during transpiration

Step 2: water crosses the membrane and cytoplasm of cells of the endodermis

Step 3: water crosses the living cells of the cortex either by osmosis or by suction through the permeable cell walls

Step 4: water enters root hair cells by osmosis (water moves down the a water potential gradient)

Transport systems in plants

• Carried out by transport tissues:– Xylem

grouped into vascular bundles

– Phloem

Xylem and phloem tissue

Root structure

- Root hairs are extended cells of the epidermis

- Epidermis protects against infection by fungi

- Cortex (pith) can act as a winter store for starch

- Xylem and phloem form a strong central rod

• https://www.twig-world.com/film/root-hairs-4999/

Stem structure

• Vascular bundles in a ring with soft cortex in the centre

• Cortex – turgid cells, suports non-woody parts

• Epidermis protects against viruses and bacteria

LO:• State that water is transported from the roots to leaves

through the xylem vessels• Define the term transpiration• Explain how water vapour loss is related to the large surface

area of cell surfaces, interconnecting air spaces and stomata• Explain the mechanism by which water moves upwards in

the xylem in terms of a transpiration pull that draws up a column of water molecules, held together by cohesion

• Explain how and why wilting occurs• Explain the effects of variation of temperature and humidity

on transpiration rate

Transpiration

Loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata

= water movement through the plant – begins with the diffusion of water vapour out of the leaf and evaporation from the leaf surface (spongy mesophyll)- 98% of the water taken up by a plant is lost to the

athmosphere by transpiration

• Evaporation– From leaves– Greatest loss of water through the stomata

- Is affected by:- leaf structure may reduce transpiration(thick waxy cuticle, rolled

leaves, needle shaped leaves)- conditions in the atmosphere (wind, high temperature, low humidity,

high light intensity)

• Wind moves humid air away from the leaf surface and increases transpiration

• High temperature increase the water-holding capacity of the air and increase transpiration

• Low humidity increases the water potential gradient between leaf and atmosphere and increases transpiration

• High light intensity causes stomata to open to allow photosynthesis which allows transpiration to occur

Translocation

- movement of sucrose and amino acids in phloem;

- from regions of production to regionsof storage OR to regions of utilisation in respiration or growth

The leaf and water loss

- Water is lost by evaporation and diffusion from the leaf surface

- Stomata need to open so that the leaf can take in carbon dioxide

• https://www.twig-world.com/film/plants-in-extreme-environments-1184/

Adaptation of plants to reduce water loss

• Cacti– Green stem carries out

photosynthesis– Leaves reduced to spines to reduce

surface area for water loss– Stomata are sunk in grooves to

avoid drying winds– Swollen stem stores water

• Aquatic plants– Leaves with little lignin in

the xylem, since the leaf is supported by the water

– A very thin cuticule– Stomata on the upper

surface

• Wilting – Leaves collapse ane stomata close to reduce heat absorbtion and

evaporation

• Leaf fall– In very severe conditions plants allow the leaves to fall of so that

no water loss can occur

• https://www.youtube.com/watch?v=xGCnuXxbZGk