Answer:
Living things use structural strategies and behavioral strategies that increase their chances of reproduction.
Living things do so to reach the reproduction goal that is to pass genes on to offspring. For example: the pouch of a kangaroo, a frog croaking a mating call,  and colorful petals of flower etcetera helps in increasing mating chances so that their genes can be followed to the generation.
 
        
             
        
        
        
Answer:
Marine ecosystem have biotic organisms like phytoplankton and photosynthetic algae that do photosynthesis and converts the atmospheric carbon dioxide into organic matter most of the carbon dioxide is released when other organisms eat phytoplankton and release the carbon dioxide through respiration.
But some of the algae and phytoplanktons die naturally get down to the bottom of the ocean where they make carbon sink. Some organisms accumulate CO₂ in their exoskeleton that is made up of calcium carbonate.  
Therefore this use of carbon by living organisms in oceans brings carbon dioxide from the atmosphere to oceans. This is why the ocean plays a critical role in the carbon cycle and called carbon sink.
 
        
             
        
        
        
Answer:
Due to presence at early days of the planet.
Explanation:
We only find the remains of single celled organisms in the oldest fossils because the single celled organisms are the organisms that were present in the early days of this planet. These single celled microbes were present about 3.7 billion years ago while on the other hand, the oldest rocks are only a little older i. e. 3.8 billion years so these single celled organisms are considered as oldest fossils on this planet.
 
        
             
        
        
        
 
The ER functions as a manufacturing and packaging system. #markasbrainliest