Answer:
Nitrogen is the most commonly limiting nutrient in plants. Legumes use nitrogen fixing bacteria, specifically symbiotic rhizobia bacteria, within their root nodules to counter the limitation. Rhizobia bacteria convert nitrogen gas (N2) to ammonia (NH3) in a process called nitrogen fixation.
 
        
             
        
        
        
Answer:
Cell will not replicate because of incomplete DNA replication.
Explanation:
DNA replication is crucial for reproduction/replication of any organism as it involves the duplication of genetic material. So if an organism is unable to perform proper DNA replication it would not be able to reproduce.
DNA polymerase is the enzyme that synthesize the new DNA strand in DNA replication. DNA polymerase can synthesize a strand only in 5'→3' direction. Both of the strands of DNA molecules are opposite in direction. So one strand is synthesized continuously called as leading strand while the other strand is synthesized in form of okazaki fragments called as lagging strand.
The okazaki fragments are joined together by the enzyme ligase. So if Ligase enzyme is absent in bacteria it would not be able to synthesize the lagging strand of DNA and thus could not be able to produce a replica of DNA. And if there is No replication of DNA then No replication of cell would occur.
 
        
                    
             
        
        
        
Answer:
Chromosome number variation: B. Down syndrome
Loss-of-function allele  : D. PKU
Physiological trait
: E. Lactose metabolism
Discovery-based science
: A. Human Genome Project
Genetic cross: C. Model organism
Explanation:
Down syndrome is a condition in which there is an extra copy of the chromosome number 21. Hence, it is a chromosome number variation.
Physiological traits refers to any function of a body. Hence, it matches with lactose metabolism.
Human Genome Project was a project under which the whole genome of the humans were sequenced. Hence, it is a discovery based science.
A genetic cross is made between model organisms to test for the offsprings that would be produced from a cross. Hence, genetic cross and model organism math with each other. 
 
        
             
        
        
        
An earthworm removes undigested food by either throwing it up, or getting rid of it from the other end. Hope I helped! ;-)
        
             
        
        
        
Hey can you provide the pictures please.