Wednesday, 29 January 2014

Cellular homeostasis

Give 2 examples of root hair cells of plants and cells of villi in the small intestine.
- how does it achieve cellular homeostasis by different transport mechanisms?

Intestinal villi

The villus has microvilli which increase the surface area for absorption of nutrients in the intestine, making the process more efficient. Increased absorptive area allows digested nutrients, such as monosaccharide and amino acids, to pass into the partially permeable membrane of villi through diffusion. These nutrients diffuse down a concentration gradient from a region of high concentration to a region of low concentration.

The villus is specialised for absorption in the small intestine as it has a thin wall, about one cell thick, which enables a shorter diffusion path. The villus also has a rich blood supply to maintain a concentration gradient for diffusion to take place.

Hence, the villus allows digested food to be transported around the body through the bloodstream quickly.

Root hair cells in plants

Root hair cells help to increase water absorption and other minerals. In order for water to be transported via the xylem tube, it moves from root cell to root cell via osmosis.

As water moves into the root hair cell down the concentration gradient, the solution inside the root hair cell becomes more dilute. This means that there is now a concentration gradient between the root hair cell and adjacent root cells, so water moves from the root hair cell and into the adjacent cells, till it reaches the xylem tube for transport, via osmosis.

Fish and Frogs Living Out of Water

What are the differences or similarities in the strategies that they have employed?
Difference: The fish seals itself with mucus to form an impervious body bag while the frog sheds layers of skin to form a waterproof barrier to seal themselves from the drought. 
Similarity: Both of them hibernate in the ground till conditions improve.

From what you understand about Homeostasis so far, how do you think these strategies allow for homeostasis to occur?
Both of the animals hibernate in the ground, where the temperature is lower and kept constant. With thermoregulation, this allows homeostasis to occur as there is a constant internal environment for reactions in the body to occur. 

Friday, 17 January 2014


Temperature regulation: (Thermoregulation)

In relation to OBS, while we were tracking, I noticed that some of our faces turned red and everyone was sweating. This is because homeostasis, specifically thermoregulation, is occurring:

As we trod with heavy backpacks under the hot sun, our body temperature rose. Our blood became warmer and is travelled to the brain. With the brain, there is an area (hypothalamus), which checks the temperature of our body. Sensing that our body temperature is high, it activates heat-loss centre and our skin blood vessels start to dilate (heat loss by radiation) and perspiration occurs. This helps to bring our body back to normal temperature and explains why some of our faces turned red and everyone was sweating.

Water regulation: (Osmoregulation)

Water regulation is the regulation of water potential of blood, controlling the amount of water available for the cells to absorb to ensure that the body maintains water potential of blood.

Whenever too much water is drunk and water content of blood is too high, the brain pituitary releases little ADH, anti-diuretic hormone, which helps the kidney maintain water volume. As such, low volume of water is reabsorbed by the kidney and high volume of dilute urine is passed to the bladder. Thus, low volume of water passes into blood and therefore, water content of blood is normal and vice versa when there is much sweating or salt eaten.