6. plant water relation

🌿 PLANT WATER RELATION

Recall...🤔🤔

1.Which are the various parts of plant body?

2. What are the functions of various parts of plant body?

3. Which plant tissues are involved in transport of water and minerals?

Plants obtain a variety of substances from their surroundings: Water, Minerals, Nutrients, Gases such as O₂ and CO₂

🤔Why is water so important?

Water is considered the “Elixir of Life”.

The productivity of plants is greatly affected

 by the availability of water. If sufficient water

 is not available, several essential processes

 of the plant are affected mainly photosynthesis.

Water constitutes approximately 90–95% of most plant cells and tissues.

It helps cells to:

maintain their turgidity

maintain their shape

carry out various biochemical activities

 

How does water move from the soil → roots → stem → leaves, even against gravity?

PROPERTIES OF WATER

1. It is in the liquid form at room temperature and is the best solvent for most of the solutes.

2. It is inert inorganic compound with neutral pH when in pure form. Due to this, water is best transporting medium for dissolved minerals and food molecules.

3. It is best aqueous medium for all biochemical reactions occurring in the cells. It is an essential raw material for photosynthesis.

4. Specific Heat: The amount of heat required to raise the temperature of 1 g of a substance by 1°C ⬆️.....(4.18 J/g°C) ( 2260 J/g) ( 334 J/g)

Because water has high specific heat, high heat of vaporization and high heat of fusion, it can help moderate temperature changes.Therefore:

🌡️ Water acts as a THERMAL BUFFER.

PYQ 2023

Give reason - water acts as a thermal buffer ?

The unique properties of water are largely associated with the presence of hydrogen bonds between water molecules.

🤝 ADHESION & COHESION

Water molecules possess strong adhesive and cohesive forces of attraction.

🔵 Cohesion

Cohesion = attraction between water molecules.

💧 ↔ 💧 ↔ 💧 ↔ 💧

🟢 Adhesion

Adhesion = attraction between water molecules and other surfaces/substances.

Together with high surface tension, these properties contribute to the movement of water through very narrow tubes or spaces called capillaries.

PYQ from 2022

Give different properties of water ?

WATER-ABSORBING ORGAN

ROOT — The Main Water-Absorbing Organ

The root is the main organ responsible for the absorption of Water and Minerals.

In terrestrial plants:

Water is absorbed from the soil in the form of liquid water. ( Soil → Root → Plant )

Epiphytic plants

Some plants such as orchids are epiphytic.

Their roots are exposed to the atmosphere and are adapted to absorb water vapour/moisture from the air.

Their epiphytic roots possess a special tissue called VELAMEN

Epiphytic root → Velamen → Absorption of atmospheric moisture

REGIONS OF A TYPICAL ROOT

A typical root can be divided into four different regions.

1. Maturation zone

2. Root hair zone / Zone of absorption

3. Zone of elongation

4. Meristematic region

The root cap is present at the root tip for protection.

ZONE OF ABSORPTION

The zone of absorption is the region where specialised structures called root hairs are present.

The outermost cells of the root are called:

Epidermal cells / Epiblema cells

Some of these epiblema cells develop into long, unicellular, hair-like extensions.

These are called ROOT HAIRS.

Main function

Their large number and elongated shape provide a greater surface area for contact with the surrounding soil, leads to more absorption of water and minerals.

Structure of root hair : 

Root hair is cytoplasmic extension (prolongation) of epiblema cell. 

Size ~ 1mm - 10mm

Tube like, unicellular,  unbranched, ephemeral,thin and delicate.

 It has a large central vacuole surrounded by thin film of cytoplasm, plasma membrane and thin cell wall, which is two layered. 

Outer layer - pectin and inner layer - cellulose. 

Cell wall - permeable but 

plasma membrane - selectively permeable.

PYQ from 2022 

With the help of a neat, labelled diagram describe the structure of root hair.