Transport in plants

Transport systems

There are two transport systems in a plant;

One that transports water and minerals from root to all other parts.

These vessels are called xylem vessels

Another vessels transport sugars (sucrose) and amino acids made in leaves to all other plant parts.

These are called phloem vessels.

Positions of xylem and phloem in dicotyledonousroots, stems and leaves.

Xylem vessels

Are long , hollow, continuous tubes that carry water and dissolved minerals from the root up to all parts of the plant.

Contain a tough substance called lignin that lines the walls to provide support.

Phloem vessels

Phloem tubes are living cells with end tubes with pores (sieve plate).

All cell contents have disappeared except the cytoplasm

The phloem cells have companion cells near them.

Phloem cells transport sucrose and amino acids from where they are made to where they are used or stored.

Dicotyledonous stem Dicotyledonous root

Structure of Dicotyledonous Stem & Root

Stem structure

Root structure

Root hair cells as seen under the light microscope

Root hairs’ function is uptake of water & mineral ions

How are root hairs adapted to their functions? long and thin to provide large

surface area for absorption cell membranes with carrier

proteins for ion uptake by active transport

partially permeable membrane for absorption of water by osmosis

thin cell wall thus a short diffusion distance

cell sap with a high concentration of solutes hence creating a low water potential for absorption of water by osmosis

How water moves into the plant.

Pathway taken by water through the plant

water move from the soil to root hair, cortex of root, xylem in root, xylem in stem, xylem in leaf, leave mesophyll, air space and eventually through the stoma to the atmosphere

atmosphere has low water potential

there is a water potential gradient from xylem in root to the atmosphere

evaporation of water from mesophyll causes water molecules to be pulled up the xylem i.e. transpiration pull

cohesion between water molecules, adhesion between water molecules and wall of xylem vessel maintain a continuous column of water

Transpiration

It is the loss of water vapour out of leaves (and stems) through stomata by diffusion.

Experiments

1. measure water uptake by plant shoots.

2. Show that transpiration takes place in shoots.

3. Show there are more stomata on the lower side of a leaf.

Potometer

A potometer measures the rate of water uptake.

The distance moved by the air bubble can be measured every minute to show the rate of water uptake.

The air bubble can be moved back to the start position by…………………….

Water is not only lost by transpiration in the leaves it is also used by the leaves during ………….….

Put your thinking caps on!

Predict what would happen to the rate of water uptake if the temperature increases.

When the wind speed increases?When light intensity increases?When humidity increases?

Transpiration is affected by

Weather condition Rate of transpiration Why?

Windy Speeds up transpiration

Moist air around the

leaf is blown away

Humid Slows down transpiration

Air around the leaf is

already full of moisture

Warm Speeds up transpiration

Evaporation occurs faster

Light Speeds up transpiration The stomata opens

Translocation

Translocation; the movement of food such as sucrose and amino acids from the source to sinks through the phloem vessels.

Source; place where a substance starts its journey in plant transport tissue e.g. leaf, root

Sinks; place where a substance ends its journey in plant transport tissue e.g. developing flowers, fruits, seeds, stem or roots

Revision Questions

(a) Explain with details how the transpiration rate of a plant is affected by;

(i) decreasing the humidity of the surrounding air

(ii) increasing the temperature of the surrounding air. [7]

(b) Suggest how transpiration is of value to a plant. [3]

(c) Explain how xylem is suited to its functions in a plant. [7]

(d) Suggest why some insects that are parasitic on plants obtain their food from the phloem, rather than from the xylem. [3]

(e) Explain how root hair cells are suited to the functions they perform. [4]

(f) Explain the significance of leaf structure in the process of transpiration. [6]

The end of Topic 5.1

Read your textbook pages 88 to 93 & page 96 to 97 and answer the questions on page 98 and 99