- Cellular respiration is the metabolic process through which glucose is broken down in the cells to produce energy in the form of ATP. Anaerobic respiration or glycolysis is the anaerobic breakdown of glucose into ATP, which requires no oxygen. This process involves removal of hydrogen and electrons from glucose to generate NADH, pyruvate and energy equivalent to two molecules of ATP. In the absence of oxygen pyruvate undergoes fermentation, whereas in the presence of oxygen, pyruvate is siphoned into the mitochondria and is completely broken down. The citric acid cycle occurs in the matrix of the mitochondria and completes the metabolic breakdown of glucose, with the release of carbon dioxide and additional two molecules of ATP per glucose molecule. NADH carries hydrogen and electrons away from glycolysis and citric acid cycle, which get syphoned into the electron transport chain. The electron transport chain involves the aerobic respiration, in which the high-energy electrons from NADH are passed through a series of carriers and finally accepted by oxygen to form water.
- Both the eukaryotic and the prokaryotic cells contain an outer membrane called as the plasma membrane and a semifluid liquid called cytoplasm which contains different organelles. The primary organelle of a eukaryotic cell is the membrane bound nucleus, which is absent in a prokaryotic cell. The prokaryotic as well as the eukaryotic cell contain DNA. However, it is centrally suspended in the cytoplasm in the prokaryotic cell, unlike in the eukaryotic cell, where it is enclosed in the nucleus. The eukaryotic cell may have evolved from archaea, which were resistant to extreme environments which resemble the primitive environments on the earth. Prokaryotic cells such as bacteria have environmental and commercial implications. For instance, antibiotics against many diseases are derived from bacteria and human intestine contains beneficial bacteria.
- Animal cells contain a nucleus, whereas bacterial cells lack a nucleus and the DNA is centrally suspended in their cytoplasm. Animal cells contain mitochondria wherein cellular respiration occurs, whereas bacterial cells lack these organelles. Both animal and bacterial cells contain ribosomes, where protein synthesis occurs. Ribosomes in bacterial cells are small and scattered in the cytoplasm, whereas in the animal cells, these occur in organelles called the endoplasmic reticulum (ER).
- The nucleus contains DNA which encodes for proteins. Endoplasmic reticulum (ER) is divided into two types; rough ER (RER), which contains ribosomes and is involved in protein biosynthesis and smooth ER (SER), which lacks the ribosomes and functions in lipid biosynthesis. Mitochondria are the powerhouse organelles of the cell and are involved in the generation of ATP or energy from the chemical energy stored in the form of glucose. An enzyme is a protein that speeds up a chemical reaction in the cell and is a critical component in metabolic pathways. The specific substrate for an enzyme binds to an active site on the enzyme and the chemical reaction is accelerated by decreasing the rate of reaction.
- A tissue is an organization of specialized cells that perform a specific function in the body. Connective tissue is divided into fibrous, supportive and fluid connective tissue types. The most rigid type of connective tissue is bone, containing a hard matrix of calcium salts. Epithelial tissue is classified as simple, psuedostratified columnar epithelium, transitional, stratified and glandular epithelium.
- Homeostasis is the process through which the body regulates the internal physiological conditions, by adjusting to the external environment and maintains stability. The nervous and endocrine systems, along with other organs work in concert to preserve homeostasis. Positive and negative feedback mechanisms work towards establishing homeostasis. A positive feedback loop occurs when the physiological changes are driven in one direction. Negative feedback mechanism maintains homeostasis by keeping one variable constant. A sensor recognizes a change in the internal environment and the control center reverts the variable back to its normal condition.
- The molecules that are large enough to traverse the plasma membrane and hence need to be broken down into their subunits are called macromolecules. Carbohydrates (e.g. Starch), fats (e.g. Oil) and proteins (e.g. Collagen) are the types of macromolecules.
Mader, S. Human Biology. NY: McGraw-Hill, 2010, 11th Edition.