6. LIFE PROCESSES
Organisms show many properties such as movement (growth-related or not). But the
visible movement is not a defining characteristic of life because a plant may not grow
visibly and some animals can breathe without visible movement.
Viruses do not show any molecular movement in them until they infect some cells.
Living organisms are well-organised structures having tissues, cells, cell organelles
etc.Due to the effects of the environment, living structures may be broken down and
dead. So they must be repaired. Since these structures are made up of molecules, they
must always move molecules around.
WHAT ARE LIFE PROCESSES?
• Life processes are all the maintenance processes to prevent damage and break-
down of the body of an organism. E.g. nutrition, respiration, excretion, growth etc.
• For this, energy is needed from the outside. This energy source is called food.
• Since life depends on carbon-based molecules, most of the food sources
are carbon-based.
• Food is broken down or built up in the body. They are finally converted to a
uniform source of energy (for molecular movements) & molecules for growth and
development.
• Oxidising-reducing reactions are some of the most common chemical means to
break down molecules. For this, many organisms use oxygen.
• In cells, various chemical reactions create useless and harmful by-products. These
are removed from the body by a process called excretion.
• In unicellular organisms, the entire surface is in contact with the environment. So,
no specific organs are needed for food intake, gas exchange or removal of wastes.
• In multicellular organisms, all cells are not in contact with the environment. So,
simple diffusion will not meet the requirements of all the cells. That’s why they
have specialised body parts to perform various functions.
• A transportation system is needed to carry food & oxygen to all body parts and
waste products from tissues to excretory system.
NUTRITION
It is the process of transfer of energy source (food) from outside the body to the
inside.
It is needed for body growth, development and synthesis of protein and other
substances.
Even when we are inactive, energy is needed to maintain a state of order in the body.
General requirement for energy & materials is common in all organisms, but it is
fulfilled in different ways.
, • Some organisms use simple food material obtained from inorganic sources such as
CO2 and water. They are called autotrophs. E.g. green plants and some bacteria.
• Some organisms directly or indirectly depend on autotrophs for nutrition. They are
called heterotrophs. E.g. animals and fungi. They utilise complex substances
which are broken down into simpler ones with the help of biocatalysts
called enzymes.
Autotrophic Nutrition
It is a process where an organism prepares its own food from simple inorganic
materials.
Photosynthesis: It is the process by which CO2 & water is converted
into carbohydrates in presence of sunlight & chlorophyll. It occurs in autotrophs
like green plants.
Carbohydrates provide energy to the plant.
The carbohydrates which are not used immediately are stored as starch. It serves as
the internal energy reserve.
In our body, some of the energy derived from food is stored as glycogen.
A cross-section of a leaf under the microscope shows that some cells contain green
dots. They are cell organelles called chloroplasts. It contains chlorophyll.
Events in photosynthesis:
1. Absorption of light energy by chlorophyll.
2. Conversion of light energy to chemical energy and splitting of
water molecules into hydrogen & oxygen.
3. Reduction of CO2 to carbohydrates.
These steps need not occur in sequence immediately. E.g. desert plants take up
CO2 at night and prepare an intermediate. It is acted upon by the energy absorbed by
chlorophyll during the day.
Experiment to show that chlorophyll is essential for photosynthesis:
• Take a potted plant with variegated leaves (e.g. money plant or crotons).
• Keep it in a dark room for 3 days to use up all the starch (destarch).
• Keep the plant in sunlight for about 6 hours.
• Pluck a leaf and mark the green areas in it and trace them on a paper.
• Dip the leaf in boiling water for a few minutes.
Organisms show many properties such as movement (growth-related or not). But the
visible movement is not a defining characteristic of life because a plant may not grow
visibly and some animals can breathe without visible movement.
Viruses do not show any molecular movement in them until they infect some cells.
Living organisms are well-organised structures having tissues, cells, cell organelles
etc.Due to the effects of the environment, living structures may be broken down and
dead. So they must be repaired. Since these structures are made up of molecules, they
must always move molecules around.
WHAT ARE LIFE PROCESSES?
• Life processes are all the maintenance processes to prevent damage and break-
down of the body of an organism. E.g. nutrition, respiration, excretion, growth etc.
• For this, energy is needed from the outside. This energy source is called food.
• Since life depends on carbon-based molecules, most of the food sources
are carbon-based.
• Food is broken down or built up in the body. They are finally converted to a
uniform source of energy (for molecular movements) & molecules for growth and
development.
• Oxidising-reducing reactions are some of the most common chemical means to
break down molecules. For this, many organisms use oxygen.
• In cells, various chemical reactions create useless and harmful by-products. These
are removed from the body by a process called excretion.
• In unicellular organisms, the entire surface is in contact with the environment. So,
no specific organs are needed for food intake, gas exchange or removal of wastes.
• In multicellular organisms, all cells are not in contact with the environment. So,
simple diffusion will not meet the requirements of all the cells. That’s why they
have specialised body parts to perform various functions.
• A transportation system is needed to carry food & oxygen to all body parts and
waste products from tissues to excretory system.
NUTRITION
It is the process of transfer of energy source (food) from outside the body to the
inside.
It is needed for body growth, development and synthesis of protein and other
substances.
Even when we are inactive, energy is needed to maintain a state of order in the body.
General requirement for energy & materials is common in all organisms, but it is
fulfilled in different ways.
, • Some organisms use simple food material obtained from inorganic sources such as
CO2 and water. They are called autotrophs. E.g. green plants and some bacteria.
• Some organisms directly or indirectly depend on autotrophs for nutrition. They are
called heterotrophs. E.g. animals and fungi. They utilise complex substances
which are broken down into simpler ones with the help of biocatalysts
called enzymes.
Autotrophic Nutrition
It is a process where an organism prepares its own food from simple inorganic
materials.
Photosynthesis: It is the process by which CO2 & water is converted
into carbohydrates in presence of sunlight & chlorophyll. It occurs in autotrophs
like green plants.
Carbohydrates provide energy to the plant.
The carbohydrates which are not used immediately are stored as starch. It serves as
the internal energy reserve.
In our body, some of the energy derived from food is stored as glycogen.
A cross-section of a leaf under the microscope shows that some cells contain green
dots. They are cell organelles called chloroplasts. It contains chlorophyll.
Events in photosynthesis:
1. Absorption of light energy by chlorophyll.
2. Conversion of light energy to chemical energy and splitting of
water molecules into hydrogen & oxygen.
3. Reduction of CO2 to carbohydrates.
These steps need not occur in sequence immediately. E.g. desert plants take up
CO2 at night and prepare an intermediate. It is acted upon by the energy absorbed by
chlorophyll during the day.
Experiment to show that chlorophyll is essential for photosynthesis:
• Take a potted plant with variegated leaves (e.g. money plant or crotons).
• Keep it in a dark room for 3 days to use up all the starch (destarch).
• Keep the plant in sunlight for about 6 hours.
• Pluck a leaf and mark the green areas in it and trace them on a paper.
• Dip the leaf in boiling water for a few minutes.
