Maharashtra Board Class 9 Science Chapter 15 Life Processes in Living Organisms PDF Download

Life Processes In Living Organisms

We have studied how digested food or oxygen inhaled by lungs is transported to every cell of the human body. The farmer also tries to transport the water from wells or dams through a main channel to every plant. The food absorbed by the digestive system is converted into energy. This energy and oxygen are both transported via blood throughout the body.

Transportation

By the process of transportation, a substance either synthesised or absorbed in one part of the body reaches another.

Transportation In Plants

Why do we eat fruits and vegetables? Do the plants also need minerals like we do?

From where do the plants get inorganic substances other than carbon dioxide and oxygen?

Most animals move from place to place but plants do not. There are many dead cells in the plant body. They need less energy as compared to animals. Plants need inorganic substances like nitrogen, phosphorus, magnesium, manganese, sodium, etc. Soil is the nearest and richest source of these substances. Roots of plants absorb these substances from the soil and transport them. There are specific types of tissues to perform this function. The xylem conducts the water whereas the phloem conducts the food. All parts of the plant are connected with these conducting tissues.

Root Pressure

Take a small plant like balsam or tuberose with its roots intact. Wash and clean its roots. As shown in the figure, keep it in the water containing a stain like safranin or eosin. Observe the stem and the veins of the leaves after 2 to 3 hours.

Take a transverse section of the stem of a plant and observe the stained xylem under a compound microscope.

Teacher's Note

You can do this experiment at home with any small plant. When water moves up the plant stem, it carries the coloured stain, and you can see the path of water just like water moves through pipes in your house.

Exam Trick

Remember: Root pressure pushes water up at night when there is no sunlight. Transpiration pulls water up during the day when it is sunny.

Points to Remember

Root pressure happens because root cells absorb water and minerals from soil.
Water moves up through xylem tissue in plants.
Phloem tissue carries food made by leaves to all plant parts.
Guard cells control the opening and closing of stomata on leaves.

Absorption With The Help Of Roots

Root cells are in contact with water and minerals in the soil. Water and minerals enter the cells on the root surface due to differences in concentration. As a result, these cells become turgid. These turgid cells exert pressure on the adjacent cells. This is called 'root pressure'. Under the effect of this pressure, water and minerals reach the xylem of the roots and to reduce this difference in concentration they are continuously pushed forward. As a result of this continuous movement, a water column is formed, which is continuously pushed ahead. This pressure is sufficient to lift the water up in shrubs, small plants and small trees.

Transpiration Pull

Previously you have performed the activity of observing a branch covered in a plastic bag. What did you observe in that activity?

Plants give out water in the form of vapour through the stomata on their leaves. Two cells called guard cells are present around the stomata. These cells control the opening and closing of stomata. Transpiration occurs through these stomata. Water is released into the atmosphere by leaves through the process of evaporation. As a result, water level in the epidermal layer of the leaf decreases. Water is brought up to the leaves through the xylem so as to compensate for the lost water. Transpiration helps in absorption of water and minerals and distribution to all parts of the plant whereas root pressure performs the important role of pushing the water up during the night time.

Teacher's Note

When a plant loses water through its leaves in hot summer, the roots pull water up from the ground to replace it. This is like how your body sweats to cool down on a hot day.

Exam Trick

Remember: Transpiration = T for Trees. Trees release water like we release sweat. Roots pull water up to replace the water lost through leaves.

Points to Remember

Guard cells open and close the stomata on leaves.
Water escapes from leaves as water vapour through stomata.
Xylem brings more water to leaves from the roots.
Root pressure works at night without sunlight.

Transportation Of Food And Other Substances In Plants

The food produced in leaves is transported to each cell in the plant body. Excess food, except amino acids, is stored in roots, fruits and seeds. This process is called 'translocation' of materials. It is carried out in both the upward and the downward directions by the phloem. Translocation of materials is not a simple physical process; it requires energy. This energy is obtained from ATP.

Whenever food material like sucrose is transported towards a part of a plant via the phloem with the help of ATP, the water concentration decreases in that part. As a result, water enters the cell by the process of diffusion. The pressure on the cell wall increases due to the increase in cellular contents. Due to the increased pressure, food is pushed into the neighbouring cells where the pressure is low. This process helps the phloem to transport the materials as per the need of the plant. During flowering season, the sugar stored in roots or stem is transported towards the floral buds to make them open and blossom.

Teacher's Note

Phloem is like the delivery system of a plant. Just as a delivery boy carries food packets to your home, phloem carries food from leaves to all parts of the plant.

Exam Trick

Remember: Xylem goes UP (water). Phloem goes DOWN and UP (food). Xylem has dead cells. Phloem has living cells.

Points to Remember

Phloem transports food up and down the plant.
ATP energy is needed to move food through phloem.
Food is stored in roots, fruits and seeds.
During flowering, stored sugar moves to make flowers open.

Excretion

At least a small quantity of garbage or waste is produced every day in each house. What will happen if you keep this garbage for many days in your house?

Many harmful and waste substances like urea, uric acid, ammonia, etc. are produced in living organisms. If these substances accumulate in the body or are retained in the body for long, it can lead to serious harm or even death. Hence, it is necessary to remove such harmful and waste substances from the body. Different organisms have different methods of doing this. Removal of waste or harmful substances from the body is called excretion. In unicellular organisms, waste materials are directly eliminated across the cell surface whereas the process of excretion in multicellular organisms is complex.

Teacher's Note

Just like you throw garbage out of your house every day, your body throws waste out every day too. If you did not throw garbage, your house would become dirty and sick. If the body does not throw waste, you become sick.

Exam Trick

Remember: Excretion = Exit. Waste must exit the body. Like you exit the classroom when the bell rings, waste must exit your body.

Points to Remember

Excretion means removing waste and harmful substances from the body.
Urea, uric acid and ammonia are waste products made in the body.
If waste stays in the body too long, it causes serious harm.
Different organisms have different ways to excrete waste.

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