The processes which perform the maintenance functions in an organism are called life processes. These processes require energy which comes from outside the body of the individual. This energy comes from the food that the organism consumes which provided nutrition.
The process to transfer a source of energy from outside the body of the organism to the inside is called nutrition. The different modes of nutrition are:
1. Autotrophic nutrition
- Autotrophs take in substances from the outside and convert them into energy.
- Photosynthesis is the process from which autotrophs obtain food. The following events occur during photosynthesis:
- Absorption of light energy by chlorophyll
- Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen
- Reduction of carbon dioxide to carbohydrates
2. Heterotrophic nutrition
- The organisms that obtain their nutrition from other plants and animals are called heterotrophs.
NUTRITION IN HUMANS
Humans are heterotrophs. Food is first crushed with the teeth to break it down into small pieces. From the mouth, the food is taken to the stomach through the food pipe. The stomach is a large organ which expands when food enters it. The stomach has muscular walls which help in mixing the food thoroughly with digestive juices.
The exit of the food from the stomach is regulated by a sphincter muscle which releases it in small amounts into the small intestine. The small intestine is excessively coiled. It is the site of the complete digestion of carbohydrates, protein and fats with the help of secretions it receives from the liver and pancreas. The digested food is taken by the walls of the intestine. The inner lining of the small intestine has numerous finger-like projections called villi in order to increase the surface area for absorption.
The unabsorbed food is sent into the large intestine where more villi absorb water from this material. The rest of the material is removed from the body via the anus.
The food material taken in during the process of nutrition is used in cells to provide energy for various life processes. Breaking down glucose into a three carbon molecule called pyruvate. This pyruvate can be further broken down. If this occurs in the presence of air, it is called aerobic respiration and in the absence of air, it is called anaerobic respiration.
Human respiratory system
Air is taken into the body through the nostrils. The air passing through the nostrils is filtered by fine hairs that line the passage. The air then passes through the throat and into the lungs. Within the lungs the passage divides into smaller and smaller tubes which finally terminate in balloon like structures called alveoli. The respiratory pigments take up oxygen from the air in the lungs and carry it into the tissues which are deficient in oxygen.
In human beings, the transport of materials such as oxygen, carbon dioxide, food and excretory products is the function of the circulatory system. The circulatory system consists of the heart, blood and the blood vessels.
In plants, transport of water, minerals, food and other materials is a function of the vascular tissue which consists of xylem and phloem.
The excretory system of human beings includes a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra. The urine produced in the kidney’s passes through the ureters into the urinary bladder where it is stored until it is released through the urethra. Nitrogenous waste such as urea or uric acid are removed from blood in the kidneys
The excretory system of plants is completely different from that of the animals. They get rid of excess water by transpiration. Waste products can also be stored in leaves that fall off. Other waste products can be stored as resins and gums, especially in old xylem. Plants can also excrete some waste into the soil around them.