Key Points

The essential processes required to maintain life in an organism are nutrition, respiration, transportation, and excretion. These processes work together to repair and maintain the body's structures.

Autotrophs (e.g., plants) produce their own food from simple inorganic sources like $CO_2$ and $H_2O$. Heterotrophs (e.g., animals) obtain complex organic food from other organisms.

Photosynthesis is the process where autotrophs convert light energy into chemical energy. The overall equation is $6CO_2 + 12H_2O \xrightarrow[\text{Sunlight}]{\text{Chlorophyll}} C_6H_{12}O_6 + 6O_2 + 6H_2O$.

Stomata are tiny pores on the surface of leaves that are essential for gaseous exchange (intake of $CO_2$ and release of $O_2$). They also play a major role in transpiration, the loss of water vapor.

Key enzymes break down complex food into simpler molecules. Salivary amylase digests starch, pepsin digests proteins in the stomach, and trypsin and lipase digest proteins and fats respectively in the small intestine.

The stomach secretes hydrochloric acid (HCl), which creates an acidic medium to facilitate the action of the enzyme pepsin. It also helps to kill harmful bacteria that may enter with food.

The small intestine has numerous finger-like projections called villi, which vastly increase the surface area for the absorption of digested food into the bloodstream.

Cellular respiration is the process of breaking down glucose to release energy. This energy is immediately stored in molecules of ATP (Adenosine Triphosphate), the energy currency of the cell.

Glucose is first broken down into pyruvate in the cytoplasm. In the presence of oxygen (aerobic), it breaks into $CO_2$, water, and energy in mitochondria. In the absence of oxygen (anaerobic), it forms ethanol in yeast or lactic acid in human muscles.

Aerobic respiration occurs in the presence of oxygen and releases a large amount of energy. Anaerobic respiration occurs in the absence of oxygen and releases significantly less energy.

The lungs contain millions of tiny air sacs called alveoli, which provide a large surface area for efficient gas exchange. Haemoglobin in red blood cells binds with oxygen and transports it throughout the body.

In humans, blood passes through the heart twice for each complete circuit of the body. This system separates oxygenated and deoxygenated blood, allowing for a highly efficient supply of oxygen to the body's cells.

Plants have two main transport tissues. Xylem transports water and minerals from the roots upwards, driven by transpiration. Phloem transports food (sucrose) from the leaves to other parts of the plant through a process called translocation, which requires energy.

The nephron is the basic structural and functional unit of the kidney. Its primary function is to filter nitrogenous waste products like urea from the blood and form urine.

Urine is formed in two main steps. First, blood is filtered under high pressure in the Bowman's capsule (glomerular filtration). Second, useful substances like glucose, amino acids, salts, and water are reabsorbed back into the blood in the tubule.

Plants get rid of waste products in various ways. They release gaseous waste ($O_2$) through stomata, remove excess water via transpiration, store wastes in falling leaves or as gums and resins, and excrete some substances into the soil.