Why is diffusion insufficient to meet the oxygen requirements of multi-cellular organisms like humans?

Multicellular organisms such as humans possess complex body designs. They have specialised cells and tissues for performing various necessary functions of the body such as intake of food and oxygen. Unlike unicellular organisms, multicellular cells are not in direct contact with the outside environment. Therefore, diffusion cannot meet their oxygen requirements.

Related Questions Life Processes

(a) The process in plants that links light energy with chemical energy
 Ans. Photosynthesis
(b) Organisms that can prepare their own food
 Ans. Autotrophs
(c) The cell organelle where photosynthesis occurs
 Ans. Chloroplast
(d) Cells that surround a stomatal pore
 Ans. Guard cells
(e) Organisms that cannot prepare their own food
 Ans. Heterotrophs
(f) An enzyme secreted from gastric glands in stomach that acts on proteins.
 Ans. Pepsin 

Match the words of Column (A) with that of Column (B)

Column (A)  

Column (B)
(a) Phloem (i) Excretion
(b) Nephron (ii) Translocation of food
(c) Veins (iii) Clotting of blood
(d) Platelets (iv) Deoxygenated blood

Ans. (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)

Nephrons are the basic filtering units of kidneys. Each kidney possesses large number of nephrons, approximately 1-1.5 million. The main components of the nephron are glomerulus, Bowman's capsule, and a long renal tubule.

Structure of a nephron

Functioning of a Nephron:

The blood enters the kidney through the renal artery, which branches into many capillaries associated with glomerulus.

The water and solute are transferred to the nephron at Bowman's capsule.

In the proximal tubule, some substances such as amino acids, glucose, and salts are selectively reabsorbed and unwanted molecules are added in the urine.

The filtrate then moves down into the loop of Henle, where more water is absorbed.

From here, the filtrate moves upwards into the distal tubule and finally to the collecting duct. Collecting duct collects urine from many nephrons.

The urine formed in each kidney enters a long tube called ureter. From ureter, it gets transported to the urinary bladder and then into the urethra.

The following raw materials are required for photosynthesis:

 The raw material CO2 enters from the atmosphere through stomata.

 Water is absorbed from the soil by the plant roots.

 Sunlight, an important component to manufacture food, is absorbed by the chlorophyll and other green parts of the plants.

The kidneys in human beings are a part of the system for
(a) nutrition.

(b) respiration.

(c) excretion.

(d) transportation.

Ans: (c) excretion.