Transporting materials against a concentration gradient is called active transport and it requires an energy source of the work done.
Active transport can only take place in living cells that contain an energy source called ATP.
ATP is found inside cells, acting rather like a rechargeable battery, releasing energy when it is required and recharged from the energy released by the mitochondria of the cell.
In some physiological circumstances, molecules may need to be moved very rapidly and accurate transport can be sussed here.
Factors affecting the rate of active transport involve:
- The difference in the concentration gradients
- Surface areas to be covered
- The quantity of energy available to carry out the task
During respiratory difficulties, the rate of active transport slows.
Contents of the cell include proteins and other large molecules were as the fluid bathing cells contain much less therefore, one of the main ways in which water passes through the cell membrane is by osmosis.
The ‘extra’ water that passes through the membrane exerts a pressure called osmosis pressure and osmosis potential is the power of a solution to gain or lose water molecules through a membrane.
Cells that are surrounded by tissue fluid of the correct strength are said to be isotonic with their surroundings.
When the potato tissue was bathed in the hypotonic solution the cell swelled up and nearly burst.
When the potato tissue was put into the hypertonic solution the water left the cell and the cell shrunk.
Cells that more bathed by more dilute fluid are in a hypotonic environment and those in more concentrated medium are in a hypertonic environment.
Hypertonic and hypotonic environments will disturb the metabolism of cells and can even cause their deaths. Water, glucose and salts affect the tonicity of fluids.
Osmoregulation
Osmoregulation refers to the regulation of the water content of the body. The total body water is either contained inside the living cells or external cells. Twice as much water is inside cells than outside.
Receptors are necessary to detect the change in water balance. These are known as osmoreceptors and lie in the hypothalamus of the brain close to blood vessels. They are modified neurones that make anti – duretic hormone that is actually secreted by the posterior pituitary gland.
ADH causes parts of the renal nephrons to become more permeable to water that can then be reabsorbed into the tributaries of the renal vein and thus returned to the extra – cellular body water. A lack of ADH causes these parts to become ‘waterproofed’. Water is not reabsorbed and passes through the kidneys to the bladder and beyond.
The Renal System
The renal system consists of two kidneys and the tubes leading from them to the bladder are called the ureters. The only difference between males and females is that the urethra in the male is longer and also serves as part of the reproductive system as it is used to convey semen during copulation.
Sexual Reproduction
The cells of the human body contain nuclei with 46 or 23 pairs of chromosomes that contain units of heredity or genes.
The number of chromosomes is very important in a species because any deviation from this number produces abnormalities in human life.
When humans reproduce they do so, sexually.
A female cell nucleus unites with a male cell nucleus. The male and female cells are known as, gametes.
Male gametes are spermatozoa.
Female gametes or ova are usually produced singly every four weeks by the ovary.
The ovum enters the oviducts and travels slowly towards the uterus or womb. It may not become fertilized during this journey, depending on whether insemination or sexual intercourse occurs at the right time.
When fertilization has taken place the resulting cell known as a zygote undergoes many cell divisions to form an embryo.
