Answer:
Because of the chemical and structural nature of the phospholipid lipid by layer the lipid soluble molecule can just pass the lipid membrane and some small molecules can also pass freely.
Explanation:
as we know that the homeostasis is an important process for a  living cell to maintain it self so for the the exchange of materials between the external and internal environment is must so for that it exchange material with the outside environment of the cell.as the cell membrane is semipermeable(mean allow some molecule to pass(lipid soluble) and not others(lipid non soluble) to pass through the membrane.the cell membrane is selectively permeable due to its nature and chemical composition the chemical composition is lipid and  phosphate and glycerol(head) with fatty acid that may b saturated or unsaturated(tail).so finally all those molecule which are polar can not pass through the membrane and  non polar can pass the membrane.The size of the molecule is also a factor on which the permeability depends.
 
        
             
        
        
        
C) Renal pelvis is the part of the kidney that acts as a funnel to pass the urine that is produced in several nephrons to the ureters. 
        
                    
             
        
        
        
Human exploitation of fragile ecosystems can lead to the droughts and arid conditions characteristic of desertification. Effects include land degradation, soil erosion and sterility, and a loss of biodiversity, with huge economic costs for nations where deserts are growing.
        
             
        
        
        
Answer:
Q2->They all form acids when combined with hydrogen. They are all fairly toxic. They readily combine with metals to form salts.
Q3->Because their outermost orbit is complete.  In Mendeleev's original periodic table there was no place reserved for noble gas.  They were discovered in end of 19th century.  So Mendeleev created zero group without disturbing original periodic table.
Explanation: