The answer is A. Commensalism
refers to relationships between organism where one benefits while the other
is unaffected. The relationship is also not
obligatory. In this case, the hippo is unaffected
while the catfish benefit from its feces. The other choices involve mutualism.
Tissues refer to a group of similar cells that perform a particular function. In vertebrates, the tissues are orgainzed into four types called the epithelial tissues, muscle tissue, connective tissue and the nervous tissue.
Epithelial tissue refers to the tightly packed group of cells covering the body outside, lining the body cavities and glands. Based on the shape, it is classified into squamous (flat), cuboidal and columnar. It can be single layered (simple) or stratified (multilayered). It protects the body, helps in the absorption of nutrients and elimination of wastes.
Muscle tissue is made up of the muscle cells that coordinate and bring movement and locomotion. It is made up of muscle fibres and the proteins called the actin and myosin. Muscle tissue is of three types-
(a) Skeletal muscle tissue is a striated tissue which is under the voluntary control.
(b) Smooth muscle tissue found in the walls of the blood vessels, digestive tracts and other parts of the body and are involuntary in nature.
(c) Cardiac tissue is an involuntary, straited tissue found in the walls of the heart.
Connective tissue contain cells present in an extracellular matrix connecting tissues, giving shape to the organs and holding them in place. It can be classified into loose connective tissue found throughout the body, dense connective tissue found in the bones and the ligaments and fluid connective tissue of the blood.
Nevous tissue is the tissue involved in control and coordination of the body. It helps in transmission of messages in the form of nerve impulse with the help of the structural and functional unit of the nervous system called the neurons.
Failur of repair by ligase and codon errors
