Answer:
one of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome
Explanation:
Pupils dilate and constrict in order to allow an adequate amount of light to pass through the retina. Both great or small amount of light will damage retina and vision. For example, if eyes are exposed to eyes suddenly, and pupils do not constrict, a great amount of light will pass to the retina and the vision will be damaged. Similarly, if there is no enough light and pupil do not dilate, a small amount of light will pass to the retina and, again, the vision will be damaged.
A nucleotide is made up of DNA.
Answer:
A nucleotide is the basic building block of nucleic acids. RNA and DNA are polymers made of long chains of nucleotides. A nucleotide consists of a sugar molecule (either ribose in RNA or deoxyribose in DNA) attached to a phosphate group and a nitrogen-containing base. The bases used in DNA are adenine (A), cytosine (C), guanine (G), and thymine (T). In RNA, the base uracil (U) takes the place of thymine.
Answer:
The body’s first line of defence
•Skin
The skin is the largest organ of your body. It acts as a barrier between invaders (pathogens) and your body. Skin forms a waterproof mechanical barrier. Microorganisms that live all over your skin can’t get through your skin unless it’s broken.
•Tears, mucus and saliva
Your nose, mouth and eyes are obvious entry points for pathogens. However, tears, mucus and saliva contain an enzyme that breaks down the cell wall of many bacteria. Those that are not killed immediately are trapped in mucus and swallowed. Special cells line and protect the nose, throat and other passages within your body. The inner lining of your gut and lungs also produces mucus to trap invading pathogens.
•Cilia
Very fine hairs (cilia) lining your windpipe move mucus and trapped particles away from your lungs. Particles can be bacteria or material such as dust or smoke.
•Stomach acid
Stomach acid kills bacteria and parasites that have been swallowed.
•Urine flow
Your urine flow flushes out pathogens from the bladder area.
