Life Processes | Revision Notes

Life Processes | Revision Notes

Revision Notes

Life Processes

Life processes 
The processes performed by living organisms in order to maintain and continue life are called as life processes.  Life processes include nutrition, respiration, circulation or transport, excretion, and reproduction.



It is the process by which organisms can assimilate and utilise food for their basic needs. Nutrition is of two different types, namely, autotrophic and heterotrophic.

Autotrophic Nutrition

It is the mode of nutrition in which organisms synthesise their own food from simple inorganic substances such as water and carbon dioxide.Green plants are autotrophs.

They synthesise food by the process of photosynthesis.Photosynthesis is a physiological process by which plant cells containing chlorophyll produce food in the form  of  carbohydrates by  using  carbon  dioxide,  water  and  light  energy.  

Oxygen  is  released  as  a by-product.

Chlorophyll –The Vital Plant Pigment

Chlorophyll  is  the  green  pigment  found  in  green  plants.  It  is  a  complex  substance  made  of  carbon, hydrogen, oxygen, nitrogen and magnesium. Although there are nine types of chlorophyll, two types—chlorophyll a and chlorophyll b—are best known and abundant.


Chloroplast is a membrane-bound oval cell organelle.It is enclosed by a double membrane. Its interior contains closely packed flattened sacs called thylakoids. Chlorophyll is present in thylakoids.Thylakoids are arranged in piles called grana lying in a colourless ground substance called stroma.

Section of Leaf

Cells present in the spongy mesophyll layer and the palisade layer contain chloroplasts;therefore,they are the site of photosynthesis.


Stomata are minute openings present in the epidermal layers of leaves.They are responsible for gas exchange during photosynthesis.

Process of Photosynthesis


Basic raw materials for photosynthesis
Photosynthesis requires carbon dioxide, sunlight, water and chlorophyll as its basic raw materials.







  • The biological process involved in the removal of harmful metabolic wastes from the body is called excretion.
  • Many unicellular organisms remove these wastes by simple diffusion from the body surface into the surrounding water
  • Complex multi-cellular organisms use specialised organs for excretion.

Excretion in Human Beings

  • The excretory system of human beings includes a pair of kidneys, a pair of ureters, a urinary bladder and a urethra.
  • Kidneys are located in the abdomen, one on either side of the backbone.
  • Urine produced in the kidneys 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 basic filtration unit in the kidneys is a cluster of very thin-walled blood capillaries.
  • Each capillary cluster in the kidney is associated with the cup-shaped end of a tube that collects the filtered urine.
  • Each kidney has large numbers of these filtration units called nephrons packed close together.
  • Some substances in the initial filtrate, such as glucose, amino acids, salts and a major amount of water, are selectively re-absorbed as the urine flows along the tube.
  • The amount of water reabsorbed depends on how much excess water there is in the body, and on how much of dissolved waste there is to be excreted.
  • The urine forming in each kidney eventually enters a long tube, the ureter, which connects the kidneys with the urinary bladder.
  • Urine is stored in the urinary bladder until the pressure of the expanded bladder leads to the urge to pass it out through the urethra.
  • The bladder is muscular, so it is under nervous control and, we can usually control the urge to urinate.

Excretion in Plants

  • They can get rid of excess water by transpiration.
  • For other wastes, plants use the fact that many of their tissues consist of dead cells, and that they can even lose some parts such as leaves.
  • Many plant waste products are stored in cellular vacuoles.
  • Waste products may be stored in leaves that fall off.
  • Other waste products are stored as resins and gums, especially in old xylem.
  • Plants also excrete some waste substances into the soil around them.