Organismal Biology

• Almost all organisms depend on the Sun's radiant energy for food
• Autotrophs, such as plants and other photosynthetic organisms, convert water and carbon dioxide, with the Sun’s energy, into organic sugar which they can use for growth and development.
• Heterotrophs are organisms that cannot make their own food, such as animals.
• Humans largely depend on autotrophs for harnessing light energy from the Sun through photosynthesis.
• In autotrophic nutrition, light energy is used to convert simple substances to complex organic compounds.
• In Chemoautotrophic nutrition, the oxidation of inorganic compounds is used as an energy source for the conversion of simple inorganic compounds to complex organic compounds.
• Plants use a special organelle called chloroplast to carry out the process of photosynthesis.
• Light-dependent reaction, the photosynthetic pigment called chlorophyll a harvests solar energy, producing the energy rich molecules, adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH). This reaction transforms radiant energy to chemical energy in a structure called thylakoid.
• Light-independent reaction, which is also called Calvin cycle, ATP and NADPH produced in the light-dependent reaction, are used to convert CO2 into sugar. This reaction happens in the stroma.
• Heterotrophs depend on other organisms for their food which is why they are called the consumers in the ecosystem.
• Heterotrophs may be characterized as parasitic, saprophytic or holozoic, depending on the mode of food intake of the organisms.
• Parasitic organisms or parasites live on or inside other living organisms called hosts and obtain their food from them. The host does not benefit from the parasite.
• Saprophytic organisms or saprophytes obtain their food from dead organisms. They secrete enzymes that are released on the food material outside their body. These enzymes break complex food into simple forms.
• Holozoic organisms ingest food that is mechanically broken down and is subsequently digested by enzymes produced within the organism. Digested food is absorbed into the body and the undigested product is egested (expelled). This kind of nutrition is found in non-parasitic animals from the simple ones like Amoeba to the complex ones like human beings.
• Holozoic nutrition in humans is called digestion, the breaking down of food into parts that can be utilized by the body.
• The basic stages of the digestive process include ingestion, digestion, absorption, and elimination.
• Ingestion is the process of eating or taking in food.
• Bulk feeders, which include most animals including humans, eat large pieces of food.
• Mechanical digestion of food refers to the breaking down of food into small pieces as when food is chewed and ground by the teeth. This type of digestion does not alter the chemical compositions of food. It simply increases the surface area upon which chemicals of digestion can act.
• Chemical digestion usually involves enzymes in breaking down food into simpler molecules like glucose and amino acids that can be absorbed or stored by the cells. Amylase in the saliva and other enzymes in the gastric (stomach) juice are some of the important enzymes in digestion. This type of digestion alters the chemical composition of food.
• The small intestine has finger-like projections called villi which in turn have microscopic projections called microvilli.
• Excess water is absorbed in the walls of the large intestine, while undigested materials undergo elimination as feces.
• To obtain energy from sugar, including the sugar from the photosynthesis of plants, organisms process sugar through cellular respiration, three-step metabolic pathway that converts sugar to an energy molecule called adenosine triphosphate (ATP), which cells use for all their processes.
• The three metabolic pathways of cellular respiration are glycolysis, citric acid cycle also known as Krebs cycle, and oxidative phosphorylation.
• Glycolysis is the first step in cellular respiration where sugar, usually in the form of glucose, enters a series of steps to form two molecules of pyruvate.
• Glycolysis process takes place in the cytoplasm of the cell.
• The pyruvate from glycolysis will be further “digested” or broken down during the citric acid cycle in the mitochondrial matrix.
• Oxidative phosphorylation includes the electron transport chain and chemiosmosis.
• All organisms eventually die. Nevertheless, reproduction ensures the perpetuity of life.
• Asexual reproduction results in new organisms formed by mitotic cell division producing offspring that are genetically similar to their parents.
• Sexual reproduction involves the fusion of gametes or sex cells from two parent organisms which are produced through meiosis. Sexual reproduction results genetically unique offspring.
• The daughter cells of meiosis are called germ cells, which develop into gametes or sex cells.
• The egg is usually large and nonmotile whereas, the sperm is

  generally much smaller and motile.
• External fertilization usually occurs in aquatic animals where the gametes are released from both the male and female animals, and the fusion takes place outside the body.
• Internal fertilization, usually observed among terrestrial animals, is a strategy used to prevent dehydration of the gametes on land. Internal fertilization also enhances the fertilization of eggs by a specific male. Even though fewer offspring are produced through this method, the survival rate of individuals is higher external fertilization.
• Plant needs plenty of water to manufacture their own food and grow. Roots take up water and minerals from the soil which are transported throughout the body of plants by a special conduction tissue called xylem.
• Transpiration is the process through which water evaporates from the stomata or the pores on the surface of leaves.
• Sugars and other food molecules synthesized in the leaves are transported to other parts of the plant through a specialized tissue called phloem.
• The movement of food materials from leaves to other parts of the plant is called translocation.
• Humans have distinct organ systems that transport different materials, such as nutrients, wastes, end gases. We have a respiratory system for the exchange and transport of gases, a digestive system to process and transport nutrients, and an excretory system that transports wastes to organs of excretion, which move them out of the body and into the environment.