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Part V : How Feeding and Breathing are Connected

Topic Chapters Index

 

Crab Spider with prey © Paul Billiet 

Crab spider, on a thistle, with captured prey

 

Cepes © Paul Billiet

Cepes in forest leaf litter

 

HOW FEEDING AND BREATHING ARE CONNECTED

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Feeding and breathing are two of the most important activities carried out by living organisms. This chapter studies the connections between these two activities.

An organism needs food for three main reasons:

 

For growth so that it can increase in size and complexity.
For health since as it grows an organism needs to maintain its body.
For energy to provide fuel for all the living processes, such as movement, sensitivity and reproduction.

 

Energy in Food

Respiration is like combustion. When we burn wood, oil or coal we need oxygen. Burning wood in a fire produces carbon dioxide gas and water vapour as well as heat and light energy. When we 'burn' sugar in our bodies by respiration, the energy that is released is used so that we can move or keep warm.

The carbon dioxide that we produce by respiration must be breathed out through our lungs. We can reuse some of the water which is also made during respiration (our bodies are mostly made of water).

 

Food for Growth

Not all the food that we eat is consumed in respiration. A large amount of the protein in the meat and vegetables that we eat is used for growth. Also the sugars, oils and fats are stored in our bodies for use at some other time.

The food that animals eat can be used in three different ways:

 

Food
Respiration Growth, health and Stored Food Not used
Energy is released to stay alive

Finally excreted as carbon dioxide and water
The food becomes part of the animal's body
= organic matter
This food passes right through the digestive system and is therefore lost

 

Not all animals use their food in the same way. Some animals have diets which are difficult to digest, so a lot of food is wasted. In general herbivores have to eat more food and to digest it for longer than carnivores.

Some small animals may need to keep eating all the time to stay warm. Animals that are very active, such as birds which fly, also need food that has a high energy content.

 

Green plants

Green plants make their own food by photosynthesis.
The herbivores feed upon the leaves, roots and other parts that the plant grows.
The carnivores feed upon the muscles and blood that the herbivore grows.

 

Decomposers

When animals and plants respire they release carbon dioxide into the atmosphere. When they produce wastes or when they die their dead bodies return the minerals to the soil.

The decomposers, such as fungi and bacteria, play an important role in returning these minerals to the soil.

This means that the chemicals in our bodies were once part of a plant. When we die these chemicals will be taken up by the roots of a plant once again. Therefore the chemicals that living things are made of are constantly being recycled.

 

Summary

 

How Feeding and Breathing are Connected: Summary © Shirley Burchill

 

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