A keystone species helps define an entire ecosystem. Without its keystone species, the ecosystem would be dramatically different or cease to exist altogether.
Answer:
Rhodopsin is the photopigment in rods.
The indigestible carbohydrates that
are found in plant cell walls are called dietary fibers. Dietary fibers are
group of complex carbohydrates that is found mostly in vegetables, fruits and
legumes. They include beans, whole grains such as wheat, nuts etc. Dietary
fibers cannot be digested in mammals because the body lacks digestive enzyme that
is required to break them down.
Answer:
Mutations of enzymes involved in nucleotide excision repair.
Explanation:
- Xeroderma pigmentosum is a genetic disorder and the person suffering from this disorder is sensitive to ultraviolet light due to the disability of the enzymes involved in nucleotide excision repair which prevents DNA damage caused by ultraviolet light.
- Thus, the individuals are sensitive to the exposure of UV and suffer severe problems when exposed to sunlight.
- The major cause of the disorder is the inability to repair DNA damage caused by exposure to sunlight due to the mutation in an enzyme involved in nucleotide excision repair.
- Nucleotide excision repair is a DNA repair process that can excise out single-stranded DNA that is damaged by UV.
- UV exposure leads to the addition of bulky adducts in the DNA known as thymine dimers. The enzymes of NER are involved in the removal of these adducts by excising out a segment of DNA that contains such lesions.
- However, in the case of XP, the mutations make this repair system non-functional or partially functional and thus, the individual becomes highly sensitive to UV exposure.
