biology revision

 Recently, my biology teacher assigned us a practice paper as homework ( •̀ ω •́ )✧

Unfortunately, I made many careless mistakes when answering. For example, I forgot to mention light intensity in an experiment investigating the effect of light intensity on the rate of photosynthesis. I also forgot some key terms when talking about kidney nephrons and anti-diuretic hormone (ADH). Mistaking the glomerulus for the Bowman’s capsule was one thing, but forgetting about the thin partially-permeable membrane along the glomerulus is pushing it (and then all of a sudden, my grades are on the floor!).

Also, I had assumed that the pituitary gland both detected blood water potential and secreted ADH, but every organ is specialised and rarely do they multitask. The truth is that the hypothalamus detects changes in blood water potential and instructs the pituitary gland to secrete more or less ADH, depending on the data obtained about the current blood water potential. If the blood water potential is too high, the hypothalamus will command the pituitary gland to secrete more ADH, which circulates in the bloodstream before eventually reaching the kidneys, specifically the cells in the walls of the collecting duct. ADH makes these cells less permeable to water, allowing less water to be reabsorbed into the bloodstream. Thus, more water flows down the collecting duct and into the bladder as urine. Tada! More water being excreted via urine reduces the blood water potential, bringing it back to normal. The opposite happens when blood water potential is too low, like after a run on a hot day.

Enough about urine and hormones! Let’s talk mountain climbing and heart rate. While climbing a mountain, your muscles need energy to contract and propel you forward, against gravity. This energy is obtained via cellular respiration, which requires oxygen.

C6H12O6 + 6O2 --> 6CO2 + 6H2O + energy

As such, your breathing rate increases to supply this oxygen and remove the carbon dioxide byproduct that is created, while your heart rate increases to transport this oxygen to your muscles faster. When you climb quickly, or continuously for a long period of time, your breathing rate is at its maximum, but the oxygen supply cannot meet the oxygen demand. As such, your muscles desperately search for an alternative energy source: anaerobic respiration.

C6H12O6 --> 2C3H6O3 + less energy

Less energy is better than no energy, so your muscles utilise anaerobic respiration when aerobic respiration just isn’t enough. However, this golden trick to release more energy has a cost. Over time, lactic acid builds up in your muscles, and an oxygen debt is incurred. This is because oxygen is needed to convert lactic acid back into glucose. Lactic acid is converted back to glucose after exercise primarily through a metabolic process called gluconeogenesis, which occurs mainly in the liver.

Why does lactic acid need to be converted back into glucose? When lactic acid builds up, the muscles get tired and may not be able to contract as effectively. Some people may also notice a burning sensation in the muscles during exercise. Source: https://orthosportsmed.com/lactic-acid-build-up-what-it-means-and-how-to-get-rid-of-it/

After climbing the mountain, even when you’re at rest, your heart rate and breathing rate remain high for a while. This is because a high breathing rate allows higher intake of oxygen to repay the oxygen debt, and a high heart rate allows oxygen to reach the liver faster so that lactic acid can be converted back into glucose. Furthermore, a high heart rate also allows lactic acid that is still in the muscles to be transported to the liver, where it can be converted back into glucose.

All in all, it was a good study period and I can't wait for more learning! (*^▽^*)