Definition of ch 6 in science
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Introduction
All living organisms have certain common characteristics such as breathing, growing, requiring nutrition, producing offspring, responding to stimuli, etc. that distinguish them from non-living things. There are certain vital processes that maintain homeostasis and proper functioning of the body, they are called life processes. These processes continue to occur even when we are sleeping or not performing any action. These processes are essential for all living organisms including plants and animals. These life processes are nutrition, photosynthesis, transportation, metabolism, respiration, reproduction and excretion.
In this chapter, we will learn about the details of these processes occurring in plants, animals and human beings in particular.
Life
Earth happens to be the only known planet having a life. There are beings who live, die and become part of nature again. The living organism can be differentiated from the inanimate entities on various parameters of life processes.
Living and Non living Things - Characteristics And Difference
Life Process
The maintenance of living organisms is essential even if they are moving, resting or even sleeping.
The processes which together perform the function of maintenance of ‘life’ are called as life processes.
Nutrition, respiration, circulation, and excretion are examples of essential life processes.
In unicellular organisms, all these processes are carried out by a single cell.
In multicellular organisms, well-developed systems are present to carry out the processes.
Nutrition
The process of acquiring food that is needed for nourishment and sustenance of the organism is called nutrition.
There are two main modes of nutrition, autotrophic and heterotrophic.
Autotrophic nutrition is present in plants, algae and some bacteria. Organisms produce their own food using light energy or chemical energy by photosynthesis or chemosynthesis, respectively.
Heterotrophic nutrition is present in bacteria, fungi and animals. They derive energy from organic compounds. Such as animals eating plants or other animals for food.
Heterotrophic nutrition has subtypes such as holozoic, saprophytic and parasitic nutrition.
Autotrophic Nutrition
If an organism can nourish itself by making its own food using sunlight or chemicals such mode of nutrition is called as autotrophic nutrition.
Plants photosynthesize (use light energy) and are called photoautotrophs.
Few bacteria use chemicals to derive energy and are called chemoautotrophs.
Photosynthesis
Photosynthesis is an important process by which food is formed.
The plants make food using sunlight and water, which provides nourishment to other organism and themselves.
Chlorophyll present in the green parts absorbs light energy.
This light energy is used to split water into hydrogen and oxygen.
Hydrogen is then used to reduce carbon dioxide into carbohydrates, typically glucose.
Chlorophyll is essential for photosynthesis and stomata to facilitate intake of carbon dioxide.
The overall reaction occurring in photosynthesis is as follows:
6CO2 + 6H2O → C6H12O6 + 6O2
Stomata
Stomata are pores on the leaves that help in the exchange of gases.
They are mostly found on the underside of the leaf.
Each stoma is guarded by guard cells, which control the opening and closing of the pore.
The water content of the guard cells is responsible for their function.Saprophytic Nutrition
Some organisms feed on dead and decaying organic matter. This mode of nutrition is called saprophytic nutrition.
The food is partially digested outside the body and then it is absorbed.
E.g. Fungi are saprophytes.
Parasitic Nutrition
Some organisms feed at the expense of another organism and in turn cause harm. This is called the parasitic mode of nutrition.
These parasites live on the body or in the body of a host organism and derive the nutrients directly from the body of the host.
E.g. Leech is an ectoparasite while Ascaris is an endoparasite. Cuscuta is a parasitic plant.Amoeba feeds by holozoic mode of nutrition.
It engulfs the food particle using pseudopodia, the process is called phagocytosis.
The engulfed food gets enclosed in a food vacuole.
As the food vacuole passes through the cytoplasm, digestion, absorption and assimilation take place.
When the food vacuole opens to outside, the egestion of undigested food takes place.Nutrition in Paramoecium
Paramoecium also exhibits holozoic nutrition.
However, they have cilia that help them to engulf the food through the oral groove.
A food vacuole is created enclosing the food.
It moves through the cytoplasm, the process is called cyclosis.
Food digested in the food vacuole is absorbed by the cytoplasm.
Undigested food is given out to a tiny pore called anal pore or cytopyge.