PLANT FUNCTIONS SCIENCE NOTES
PLANT FUNCTIONS:
Plants germinate from seeds, grow,
develop, mature, reproduce and die. They
perform absorption, photosynthesis, respiration, transportation and
transpiration. Plant physiology deals
with how plants function.
Water is essential for all physiological activities of plants. It plays an important role in physiological activities like photosynthesis, respiration, transpiration and transportation.
The presence of water in the soil is essential for the normal functioning of plants. Soil water contains minerals in the dissolved state.
Plants absorb water and minerals from the soil with the help of root hairs. This process is called absorption.
The three different forces involved in absorption are:
(i) Imbibition
(ii) Diffusion
(iii) Osmosis
i) Imbibition:
Imbibition is the uptake of water by the substances that do not dissolve in water causing swelling of these substances. Eg.wood and seeds. These substances are called imbibants.
In plant cells, the cell wall is the imbibant. It absorbs water and forms a channel for movement of water into the cell by diffusion and osmosis.
Imbibition plays a very important role during germination. Seeds imbibe water through the seed coats. They swell and rupture, allowing the radicle and plumule to emerge.
ii) Diffusion:
Dissolved molecules move from a region of higher concentration to a region of lower concentration until the molecules are evenly distributed throughout the available space. Gases such as oxygen and carbon-dioxide, and nutrients like minerals move into cells by diffusion.
iii) Osmosis:
The movement of water molecule from a region of higher concentration to a region of lower concentration through a semi-permeable membrane is called osmosis.
Demonstration of Osmosis:
A potato is taken and peeled. The base is cut to make it flat. A hollow cavity is made in the centre of the tuber and filled with sugar solution. The initial level of solution is marked with the help of a pin. It is placed in a beaker containing coloured water.
After sometime, it is observed that the sugar solution in the cavity of the potato becomes coloured and its level rises. How has this taken place? This is due to the entry of water from the beaker into the cavity of the potato through the living cells of the potato. Here the living cells of the potato act as a semi-permeable membrane.
When substances move from a region
of higher concentration to a region of
lower concentration, without the use of
metabolic energy, it is said to be passive
transport. Active transport involves the
use of metabolic energy for movement of
molecules. The uptake of mineral ions is
by active transport.Water is essential for all physiological activities of plants. It plays an important role in physiological activities like photosynthesis, respiration, transpiration and transportation.
The presence of water in the soil is essential for the normal functioning of plants. Soil water contains minerals in the dissolved state.
Plants absorb water and minerals from the soil with the help of root hairs. This process is called absorption.
The three different forces involved in absorption are:
(i) Imbibition
(ii) Diffusion
(iii) Osmosis
i) Imbibition:
Imbibition is the uptake of water by the substances that do not dissolve in water causing swelling of these substances. Eg.wood and seeds. These substances are called imbibants.
In plant cells, the cell wall is the imbibant. It absorbs water and forms a channel for movement of water into the cell by diffusion and osmosis.
Imbibition plays a very important role during germination. Seeds imbibe water through the seed coats. They swell and rupture, allowing the radicle and plumule to emerge.
ii) Diffusion:
Dissolved molecules move from a region of higher concentration to a region of lower concentration until the molecules are evenly distributed throughout the available space. Gases such as oxygen and carbon-dioxide, and nutrients like minerals move into cells by diffusion.
iii) Osmosis:
The movement of water molecule from a region of higher concentration to a region of lower concentration through a semi-permeable membrane is called osmosis.
Demonstration of Osmosis:
A potato is taken and peeled. The base is cut to make it flat. A hollow cavity is made in the centre of the tuber and filled with sugar solution. The initial level of solution is marked with the help of a pin. It is placed in a beaker containing coloured water.
After sometime, it is observed that the sugar solution in the cavity of the potato becomes coloured and its level rises. How has this taken place? This is due to the entry of water from the beaker into the cavity of the potato through the living cells of the potato. Here the living cells of the potato act as a semi-permeable membrane.
Ascent of Sap:
Water, along with mineral salts, are absorbed by the root through its root hairs. The absorbed water reaches the xylem vessels and finally reaches the leaves. This movement of water and mineral salts is known as ascent of sap.
Demonstration of Ascent of Sap:
Take an entire balsam plant without damaging the roots. Wash the roots to remove the soil particles. Insert the roots into a bottle containing dilute eosin solution or red ink solution. Leave aside the set-up for sometime. After sometime, red streaks can be observed on the stem and veins of the leaves. If a section of the stem is mounted on a microscope and observed, it will show that only the xylem vessels are coloured, showing that ascent of sap takes place only through the xylem vessels.
