Plant transport

M.Iqbal Khan SS Biology GHSS Mochh Mianwali 03135448175

Plant Transport1- Reason for transport system2- Transport system in plants3- Adaptations of xylem tissues4- Adaptations of phloem tissues

5- Absorption of root hair cells6- Water movement processes7- Transpiration pull8- Rate of transpiration


1. Reason for transport system Unicellular organisms

They can transport materials like oxygen and urea in and out of their bodies by diffusion or osmosis easily.

Multicellular organisms Most of the cells inside the organisms are too far from the

surface of their bodies and diffusion and osmosis are too slow to be relied on.

A transportation system is required for food and oxygen to be brought efficiently from one place to another.

Diffusion and osmosis would take place between the transport system and the cells.


2. Transport system in plants Xylem and Phloem tissues

Xylems transport water and minerals salts (nitrates) from roots to leaves in a unidirectional motion

Phloems transport organic products (sucrose) from the leaves to all parts of the plant in a bidirectional motion

Vascular bundles Xylem and Phloem tissues are arranged in vascular

bundles. A cambium separates the xylems and phloems. The cambium undergoes division to produce new xylems

and phloems.


How are plants supported? 1. Support in young plants or non-woody

parts of plants is contributed mainly by turgidity of the thin-walled cells in the cortex and pith.

Contents


Turgidity of cellsTurgidity of cellsInside stem of herbaceous plants-(non-woody)

water potential of living cells

water potential of

xylem >

water move from xylem to living cells in stems

Cells become turgid

Turgid cells press against each other to give support to the plant

If adequate water supply,


Turgidity of cellsTurgidity of cellsInside stem of herbaceous plants

water potential of living cells

water potential of

xylem <

Cells become flaccid

Flaccid cells cannot provide support to the plantThe plant wilts

If inadequate water supply,


The hardness of thick-walled cellsThe hardness of thick-walled cells

Plants are also supported by thick-walled cells

mostly xylem cells which contain lignin

As plant grows, older xylem tissues in stems are pushed inwards and become wood.


2. Diagrams of the system

Sites of xylem and

phloem tissues


3. Functions of Xylem tissues Support

Consists of lignin to provide the plant with support Transport of water and nitrates

Conducts water and dissolved mineral salts from the roots to all other parts of the plant


3. Formation of Xylem tubes The xylem cells die when they mature. The cross

walls and cell contents will break down. A hollow lumen will be left. There is no obstruction

to the flow of water. The walls of the cells are thickened with lignin. It

causes the walls to be rigid, supporting the plant.


3. Adaptations of Xylem tissues Absence cross walls

Maintains a continuous lumen

Protoplasm disintegrate Allows water to move

efficiently

Dead empty tube Maintains a continuous

lumen Lignified walls

Walls are rigid Xylem will not collapse Supports the plant


4. Adaptations of Phloem tissues Bi-directional sucrose

flow Food can be transported

to all parts of the plant Cross walls perforated

by sieve tubes Single row of thin

elongated walls with minute pores

Living cells to conduct the food in the tube

Companion cell present Consists of protoplasm

and mitochondria Assists sieve tubes in

transport of food Provides energy

required for active transport

When dead, sieve elements will die off


5. Root hair cells Plants absorb water and minerals from the soil

through the root hairs. Root hair cells absorb water and nitrates from the

soil efficiently. They help to hold the plant more firmly to the

ground.


5. Adaptations of root hairs Finger-like extensions

Increases surface area to volume ratio

To absorb water and mineral salts at a faster rate

Lower water potential Allow osmosis and

diffusion of nitrates to take place

Large vacuole To absorb as much

water as it can hold Is a living cell

Carries out respiration This provides energy for

active transport to take place when water potential is lower in the soil


5. Osmosis in the Root cells The soil particles have a higher water potential than the vacuole

of the root hair cell. Water and nitrates diffuse from the soil particles to the root

hair cell. The root hair cell becomes more dilute than the surrounding

cortex cells. Water and nitrates diffuse from the root hair cell to the cortex cells by osmosis.

Water diffuses from one cell to another until water eventually enters the xylem tubes

Intake of water in the roots, the root hair cells become turgid. A pressure is thus generated. This pressure is called root pressure. This forces water up the xylem tissues.


6. Forces causing water movement Root pressure

Produced by the continuous movement of water through the root hair cells

Pushes water up the xylem Transpiration pull

Produced by the evaporation of water from the leaves Pulls water up the xylem

Capillary action Produced by the conduction of water by the xylem

through its continuous lumen Pushes water up narrow xylem vessels


7. Transpiration in the stomata In the stem xylem, water is pulled up the stem by

transpiration pull. Osmosis continues through the leaf cells and water is

eventually drawn in from the xylem vessels in the stem. As the water evaporates, the water potential of cell sap

decreases. It draws water from the lower cells by osmosis. Water evaporates from the surfaces of leaf cells into air

spaces. Water vapour from the air spaces diffuses through the stoma

and into the atmosphere.


7. Transpiration pull of plants Plants absorb a large amount of water, but make use of only a

small portion of the water. A large portion of water is lost by evaporation of water

through the stomata of the leaves. This process is called transpiration.

Transpiration is the loss of water vapour mainly from the stomata of the leaves.

As water evaporates from the leaves, more is drawn up through the plant to replace it due to cohesion forces between water molecules in the xylem tissues.

A pulling force called the transpiration pull is formed.


7. Importance of Transpiration pull Transpiration pull is the transport of water and

mineral salts or nitrate ions from the soil to the leaves.

Ensures a constant flow of water to be taken from the soil to the leaves.

Enables photosynthesis to occur.


8. Rate of transpiration increase Humidity of air

Low Dryness of air

High

Temperature of air High

Speed of wind High

Light intensity High


8. Light intensity Presence of light

Photosynthesis occurs. Cell sap in guard cells has higher concentration of glucose. Water enters the guard cells by osmosis causing guard

cells to become turgid. Stomata opens and transpiration increases.

Absence of light No photosynthesis occurs. Plant loses water, guard cells flaccid. Stomata closes and transpiration decreases.

Education

Plant transport