Grace

During today's youth group, the leader— whom I'll refer as L.— talked about grace, the unmerited love that God gives to everyone. He explained how every part of us, including our bodies, is given to us by God; how everything we have is grace. God has not only created us, but has also bore our sins for us, despite the fact that we rejected him. He could easily have destroyed the human race when we did all the horrible things to him, but instead he chose to bore all the sins for us and to suffer for us. Not because we did anything deserving, but simply because he loved us.

Since everything we have is grace— we are all sinners and we don't actually deserve anything that we have  —there is no reason for us to be proud. That is, because we couldn't have accomplished anything without the gifts of God, nothing we do is great in God's eyes. This also means that we should never expect things from God just because we have done "good" deeds— to God, these things are like "polluted garments" and they are nowhere close to God's holiness and perfection.

At the end, L. said that when one truly understands what grace is, there should be a radical change in one's thoughts and behaviours. One would become humble, and one's actions would be spurred by one's love of god, not by an urge to please god and be saved.

Unfortunately, I can't remember exactly what L. has taught us during youth group; even the things above are formed from my fragmented memory (and this is probably why many things seem vague). However, when he was talking, I felt a stirring within my heart. I don't know why, but for the first time in my life, I felt God's presence, I believed in the existence of God!

Actually, to think of it now, I didn't really believe in the existence God at the moment. Instead, I simply started to accept the possibility that God exists. Still, it was a big moment for me, because it had always been difficult to accept this possibility— it had been too abstract to me.

Of course, the concept of God is still very abstract to me. But now a brand-new perspective is open to me, and I am confident that I have experienced some spiritual gains, however little it might be. At the same time, I am ready to adopt a different mindset, and change the way I think and act.

Tomorrow I will go to church as well. Hopefully I will get to understand God more.

Monopolistic Competition

What is a monopolistic competition?
A monopolistic competition is an imperfect competition in which many firms sell a product that has product differentiation. An example would be the hamburger market, where there are many stores selling hamburgers, but the taste and quality of the burgers from each store are slightly different. The firms in a monopolistic competition are not price-takers, but they face a very elastic demand due to the availability of substitutes.

Also, there's an ease of entry and exit for a monopolistic competition

Advertising
In order to differentiate their products, firms in a monopolistic often rely on advertisements to create brand names, to increase market share.

In the short Run
In the short run, the graph of a firm in monopolistic competition is very similar to that of a monopoly. The marginal cost curve is different from the average revenue curve, the firm produces at a point where MR=MC, and it can earn economic profit by charging the consumers at where the quantity intersects with the demand curve..

The only difference is that the demand is more elastic, and therefore the demand and MC curves look more "flat".

The Human Respiratory System

As mentioned in the post named Respiration, humans cannot rely on simple diffusion for gas exchange. Instead, we have to rely on a specialized respiratory system to do so.

In this post, I will be describing how the human respiratory system works.   

Nose

The nose (nasal cavity) is where the air comes into our body. The nostrils contain tiny hair that clean the air, and the epithelium lining have capillaries that warm the blood. Also, the turbinate bones are lined with a thin membrane that secrets mucus, which moistens the air.

(turbinate bones: thin bones in the nose that increase surface area, and warm and moisten the air)

Larynx

• The larynx house the vocal cords

Trachea 

• have mucous cells and cilia.
• mucous cells trap foreign particles, and cilia brush them away
• maintains its rigidity because of the cartilage rings

Bronchi

• like the trachea, they are also reinforced with cartilage
• lead to bronchiole, and then alveoli

Alveoli

• Spherical hollow cavities (grape-like structures) that are lined up with capillaries
• where gas exchange occurs

Lung surfactant: a complex substance that reduces the surface tension throughout the lung

Lungs

• The right lung has three lobes, while the left lung has only two lobes (to accommodate for the heart) 
• protected by a flexible membrane called pleura, which allows the lung to expand and contract

Types of respiration:

• Breathing: the act of drawing air into and then out of the lungs
• External respiration: gas exchange between the air and the blood
• Internal respiration: gas exchange between the blood and other cells
• Cellular respiration: the process in which cells convert oxygen and glucose into useful energy, creating carbon dioxide in the process.

Respiration

Cellular respiration: Almost every organism needs cellular respiration, as it allows cells to convert glucose and oxygen into useful energy.

Gas Exchange: As oxygen is a key component in cellular respiration, a cell needs to constantly bring in oxygen so that it can go through cellular respiration. Also, each cell needs to eliminate its carbon dioxide, a waste product of cellular respiration. Therefore, gas exchange— the process by which oxygen enters a cell and carbon dioxide leaves it— is necessary.

Requirements for gas exhange:

• large surface area: so that it can occur at a fast-enough speed
• moist environment

Diffusion

• Diffusion is a natural process in which molecules travel from areas of high concentration to low concentration
• It is only effective if an organism is only a few cells think
• Therefore, only uni-cellular organisms and very thin multi-cellular organisms (such as planarian) rely on diffusion

Specialized Respiratory Systems

• As organisms become larger, diffusion becomes inefficient.
• Also, many cells become specialized for other functions (e.g., reproduction)
• Therefore, a respiratory system is needed — a system that consists of respiratory surfaces, and muscles and tubes that allow air to contact the surface.
• Different types:
• Skin Respiration: The skin is lined with capillaries so that air can diffuse from the skin into the blood. The blood then transfers the oxygen to rest of the organism. Since diffusion must occur in a moist environment, organisms that rely on skin respiration must live in moist/damp environments. Examples: annelids (including earthworms, leeches)
• Gills: gills are organs that have high surface area and a lot of capillaries. They allow diffusion and gas exchange to occur efficiently for aquatic animals. 
• Tracheal Respiratory System: This is for insects. Many insects have spiracles (external pores) that allow the air to go into their trachea, which come in close contact to all the living cells.
• Lungs: organs that forcibly bring in air so that gas exchange can occur at the capillaries located on the lung surface. The blood then transports the oxygen to other parts of the body.

Oligopoly

What is an oligopoly?
An oligopoly market is one that is dominated by a few large firms. Firms in an oligopoly selling similar but branded products, and thus advertising plays an important role in the market. Also, there are high barriers to entry, and thus the small number of firms in the market.

Interdependence of Oligopoly
Since there are only a few firms in the market, the decisions of one firm can significantly affect all the other firms. Thus, the firms are interdependent on each other, and in many cases they might want to collude.

Kinked Demand Theory (Non-collusive behavior)
If the firms do not collude, then for each individual firm, we will see a kinked demand curve. That is, at the current market price, the demand becomes elastic as price increases, and inelastic as price decreases.

Why? If a firm raises its price, then consumers are simply going to switch to the other firms. Thus, quantity will decrease drastically and the demand will be elastic. On the other hand, if a firm lowers its price, then all the other firms are going to follow suit. This, in the end, will mean that the firm doesn't get that much more quantity, and that the demand becomes sinelastic.

Digestive Tract #2

This is a continuation of Digestive Tract #1.


Small Intestines:

After turning into chyme, the food enters the small intestines, which are comprised of three parts:

• Duodenum: receives secretions from the gall bladder and the pancreas (pancreatic juice). It is where the majority of chemical digestion takes place
• Jejunum: absorption of carbohydrates and proteins takes place
• Ileum: absorption takes place, especially vitamin B-12 and bile salts

Large Intestines:
The large intestines absorb water, and they also contain bacteria that produce vitamin K and vitamin B-12. In addition, they pass waste material to the anus.

Anus:
The anus expels the wastes.

Pancreas:
The pancreas secretes bicarbonate ions, which neutralize the stomach acid and inactivates pepsin. The pancreas also secretes pancreatic juice, which is comprised of pancreatic amylase (breaks down starch), lipase and trypsin.

Gall Bladder:
The gall bladder stores bile, which emulsifies fat and allows a greater surface area for fat to be broken down .

Liver:
The liver produces bile and cholesterol. It also converts excess glucose to glycogen, detoxifies poisons, and stores fat-soluble vitamins.

Digestive Tract #1

The digestive tract (also called the alimentary canal or the gastrointestineal tract) consists of: mouth→ pharynx→ epiglottis→ esophagus→ stomach→ small intestine→ large intestine→ anus

This entire post will be used to describe each part of the digestive tract, as well as other organs in the digestive system, such as livers and gallbladders.

Mouth:
The mouth (oral cavity) is where the food enters our body, and in it, both physical and chemical digestion take place.

The teeth physically break down the food, with different types of teeth breaking the food down different ways:

The saliva contains mucus and enzymes, such as amylase (breaks down polysaccharides) and maltase. Saliva is produced by the salivary glands, which are the parotid gland, the sublingual gland, and the submandibular gland:

The tongue moves the food when the person is chewing. In addition, it has taste buds, which are receptors that send messages to our brain: 

In the mouth, with the chewing and the mixing with the saliva, the food becomes a food bolus, and it now travels to the pharynx.

Esophagus: 

The food bolus then goes through the pharynx and into the esophagus, and long muscular tube made up circular and longitudinal muscles. In the esophagus, food is moved along with peristalsis.

Stomach:
At the end of the esophagus, there's the cardiac sphincter, which controls the movement of the food from the esophagus to the stomach. The stomach is a J-shaped organ with a volume of 1.5L, and it has thick layers of smooth muscle (rugae) that allows it to stretch. The stomach uses its longitudinal, circular, and oblique muscles to churn the food, and it also secretes gastric juices to chemically digest the food.

With both physical and chemical digestion, the food bolus is turned into a thick liquid called chyme.

Some components of the gastric juice:

• Hydrochloric acid: destroys invading microbes, breaks down food bolus, and turns pepsinogen into pepsin
• Pepsinogen: In acidic environments, it turns into pepsin, which breaks polypeptides into dipeptides
• Lipases: enzymes that break down lipids
• Mucus: secreted by the rugae, it forms a protective coating for the stomach that prevents the hydrochloric acid from burning through