Q1) Explain how blood in a vein in the leg is returned to the heart
Q2) Plasma is a solution, cytoplasm is a colloid and blood is a suspension. Explain how the properties of solutions , colloids and suspensions adapt these biological materials to carry out their functions in the body
thankss in advance! 
I think I have answered this before..
Anyway,
Ans 1: When you are in the upright position, the blood in your leg veins must work against gravity to return to your heart. To accomplish this, your leg muscles squeeze the deep veins of your legs and feet. One-way flaps, called valves, in your veins keep blood flowing in the right direction. When your leg muscles contract, the valves inside your veins open. When your legs relax, the valves close. This prevents blood from flowing in reverse, back down the legs. The entire process of sending blood back to the heart is called the venous pump.
The return of blood to the heart is assisted by the action of the skeletal-muscle pump which helps maintain the extremely low blood pressure of the venous system. Fainting can be caused by failure of the skeletal-muscular pump. Long periods of standing can result in blood pooling in the legs, with blood pressure too low to return blood to the heart. Neurogenic and hypovolaemic shock can also cause fainting. In these cases the smooth muscles surrounding the veins become slack and the veins fill with the majority of the blood in the body, keeping blood away from the brain and causing unconsciousness.
I hope that's what you need to know.
Ans 2: A solution is a mixture that has very small particles that cannot be seen.
A colloid are well mixed mixtures with slightly larger particles. Particles are too large to form a solution but do not settle into layers if left standing and cannot be filtered by physical means.
A suspension is a mixture with noticeable different particles, but they are small enough to appear evenly distributed. If left standing, the particles will separate.
In other words, plasma is a solution because it is made up of only one substance, and these cannot be seen or separated by physical means. Blood is a suspension because it is made up of several different components which can be seen and separated by physical means (plasma, cells, etc..) and if left standing, will separate.
Plasma is a solution containing 90% water. it helps to transport hormones, dissolved food substances(glucose,amino acid etc), waste materials(urea, from cells to blood), and blood clotting proteins like fibrinogen and prothrombin.
Cytoplasm is a jelly-like substance that contains most organelles and is where most chemical reaction occurs.
Blood contains plasma and red blood cell. blood helps to transport waste materials, carbon dioxide and oxygen.
I am not sure what your question was about..I am doing CIE A2 Biology and I haven't done such a question till date.
Hope I helped.
