Why diffusion process is not suitable for transportation in multicellular organisms ?

Multicellular organism body makeup is complex than that of unicellular organisms. Unicellular organisms have only one cell, so are in direct contact with the environment. Here the mode of transportation needed is also simple like the diffusion process can meet all the demands of the unicellular organisms. But in multicellular organisms, diffusion cannot do all the transportation because body cells are not in direct contact with the environment. They cannot rely on diffusion for the transportation of food and oxygen to all cells. They need a specialised system for this.

What are modified as tusks, in elephants ?

In elephants, the incisors of the upper jaw grow into huge tusks that project out of the mouth. A tooth consists of 3 regions: crown, neck and root. The Crown is the exposed part. The neck is surrounded by a soft, fleshy skin called the gum. The root is embedded in the socket of the jaw bone.

What type of dentition is seen in mammals?

Mammals can be thecodont, diphyodonts, monophyodonts or heterodonts. Teeth embedded in pits, the pockets or alveoli of the jawbones named maxillae and mandible. Such teeth are described as the thecodont. The number of teeth is fixed, and they are produced in two sets- milk and permanent teeth. Milk teeth are shed after some age and are replaced by permanent teeth between 6 and 12 years of age. The teeth that appear in two sets are described as diphyodonts. We, humans, have different types of teeth, so we are heterodonts and two sets of teeth are produced in the whole life, so we are also diphyodonts. Different types of teeth we have are incisors, canines, premolars and molars. But Whales are monophyodont as they have a single set of teeth.

Arrange the organs of the human excretory system in the correct order, based on the passage of urine. ureter, urethra, kidney, urinary bladder

Organs of the human excretory system in the correct order:- Kidney, Ureter, Urinary Bladder, Urethra Fig: Excretory System Urine produced from the kidney passes through the ureter to the urinary bladder, where it is stored for a while and then got excreted out through the urethra. Renal vein and renal artery shown in the figure carries deoxygenated but clean and oxygenated but dirty blood respectively.