Why plants need transport system

• By using the CO2 energy ( food ) is produced in the leaves

• The soil is the nearest & richest source of raw materials like nitrogen, phophorous & other minerals

• The absorption of these substances occurs through the part in contact with the soil, called roots if these distances between soil containing regions & chlorophyll containing regions are small energy & raw materials can easily diffuse to all parts of the plant body

• If these distances are large the diffusion pressure will not be sufficient to provide raw materials in leaves & energy in roots

Why plants have low energy needs

• 1. Plants do not move • 2.Plant bodies have large proportion of

dead cells in many tissues As a result plants have low energy

needs & use low transport system

Plant transport systems

• There are two transport systems • 1. One transport system moves water &

minerals from roots to leaves through the xylem

• 1. Another transport system moves energy stores ( food ) from leaves to body parts

•

TRANSPORT OF WATER• It takes place through the Xylem• Vessels & Tracheids are the water

conducting cells in the xylem• In xylem tissue vessels & trachieds of

the roots , stem, leaves are interconnected to form a continuous system of a water conducting channels reaching all parts of the plant

Mechanism of water conduction

• It is explaind by many theories. Important theories among these are

• 1. Root pressure theory• 2. transpiration pull theory

Root pressure theory• At the roots cells in contact wit the soil

actively take up the mineral ions • This creates a difference in the

concentration of these ions between the roots & the soil

• Therefore water moves from the soil into the cells to eliminate this difference

• So there is a steady movement of water into root xylem, creating a column of water that is steadily pushed upwards this is due to the creation of pressure in the xylem vessels of the root

Demerits of root pressure theory

• This pressure is not sufficient to push the water to the great heights

Transpiration pull theory• Plants lose water in the form of water vapour

through the stomata of the leaf• This water loss is replaced by the by the

xylem vessels in the leaf• Evaporation of water from the cells of the

leaf creates a suction which pulls water from the xylem vessels of the root

• It makes the root to absorb water from the soil

• The root pressure is the major driving force during the night time

• During the day when the stomata are open , the transpiration pull is the major driving force

Transpiration

• The loss of water in the form of water vapour from the aerial parts of the plant is called transpiration

Functions of transpiration• 1. It helps in temperature regulation• 2. It helps in absorption& upward

movement of the water minerals dissolved in it from roots to the leaves

Transport of food & other substances

• The transport of soluble products of photosynthesis from leaves to all parts of the plant is called translocation

• Phloem transports the food • Besides the products of photosynthesis the

phloem also transports amino acids & other substances

• These substances are moved to the storage organs of the roots, fruits, seeds & to growing regions

In phloem the food conducting cells are the sieve tubes

The translocation of food & other substances takes place in the sieve tubes with the help of adjacent companion cells both in upward & downward direction

Mechanism of translocation• Translocation utilizes the energy• Sucrose is transferred into phloem

using energy from ATP• This increases the osmotic pressure of

the phloem causing water to move from xylem to phloem

• This pressure moves the materials in the phloem to tissues which have less pressure

• This allows the phloem to move the materials according to the plant needs

• Ex- in the spring sugar stored in roots or stem transported to the buds which need energy to grow

• Translocation takes place both in upward & down ward directions

Differences between conduction of water & conduction of food

Conduction of water conduction of food1. It occurs through the It occurs through the xylem phloem 2. It does not utilize It utilizes energy energy.3. It is in upward It is both in upward direction downward direction