Almost all the ques in the bio tys don't have ans except for mcqs so can anyone help me out with some ques? thanks..
Explain what is meant by the terms:
(i)allele
(ii)mutation
(iii)dominant
Mutation - the sudden or spontaneous change in gene structure or a chromosome, or even the chromosome number, and may be inheritable.
Allele - Different forms of a gene which occupy the same relative positions on a pair of homologous chromosomes.
Dominant - a form of a gene that expresses itself and gives the same phenotype in both the homozygous and heterozygous conditions.
Originally posted by Vendettus:Mutation - the sudden or spontaneous change in gene structure or a chromosome, or even the chromosome number, and may be inheritable.
Allele - Different forms of a gene which occupy the same relative positions on a pair of homologous chromosomes.
Dominant - a form of a gene that expresses itself and gives the same phenotype in both the homozygous and heterozygous conditions.
thanks.. but what is homologous?
The blood system circulates through arteries, capillaries and veins.
(i) veins have valves, but arteries do not. explain why.
(ii)describe how the structure of capillaries helps their function.
Originally posted by crucifiedx:The blood system circulates through arteries, capillaries and veins.
(i) veins have valves, but arteries do not. explain why.
(ii)describe how the structure of capillaries helps their function.
(i) Veins have valves to prevent the backflow of blood. Arteries do not have valves as they carry blood away from the heart and valves would only hinder the flow of blood from the heart to other parts of the body.
(ii) Capillaries have walls made up of only a single layer of cells called the endothelium, which is partially permeable to enable substances to diffuse quickly through capillary walls. Capillaries have many branches, providing a large surface area for the exchange of substances between blood and tissue cells.
standard professional answer. esp the first one.
(i) Veins have valves to prevent the backflow of blood. Arteries do not have valves as they carry blood away from the heart and valves would only hinder the flow of blood from the heart to other parts of the body.
Arteries --> no valves --> blood flows in spurts, high pressure, very fast --> blood unlikely to backflow --> valves unneccessary
Arteries --> thick elastic muscular walls --> strong stretching and recoiling --> pushes blood forward at high pressure --> blood unlikely to backflow --> valves unneccessary
Veins --> low blood pressure, slow --> blood likely to backflow --> valves needed
Veins --> thin walls; blood unable to move forward on its own --> dependant on skeletal muscles for blood movement --> blood likely to backflow --> valves needed
(ii) Capillaries have walls made up of only a single layer of cells called the endothelium, which is partially permeable to enable substances to diffuse quickly through capillary walls. Capillaries have many branches, providing a large surface area for faster/efficient/rapid exchange of substances between blood and tissue cells.
Homologous - chromosomes which have the same genes, shape and length.