Characteristics of Living Organisms

The Role of Nutrition: All living things require nutrition to obtain the chemical energy and building blocks necessary for growth, repair, and the maintenance of life processes. This energy is typically transferred within cells through the production of ATP.

Autotrophic Nutrition: Plants are autotrophs that produce their own organic food via photosynthesis. By combining sunlight, carbon dioxide ($CO_2$), and water ($H_2O$), they synthesize glucose and release oxygen as a byproduct.

Heterotrophic Nutrition: Animals and fungi are heterotrophs that must consume other living organisms to survive. They utilize digestion to break down large, complex molecules into simpler units that can be absorbed and transported through the bloodstream to individual cells.

Cellular Respiration: This is a chemical process occurring in all living cells to release energy from glucose. Aerobic respiration uses oxygen to maximize energy yield, while anaerobic respiration occurs without it; both processes result in byproducts like carbon dioxide ($CO_2$) and water ($H_2O$).

The Process of Excretion: Excretion is the active removal of metabolic waste products that are produced by chemical reactions within cells. These substances, such as urea in animals or excess gases in plants, can become toxic if they accumulate in the body.

Plant vs. Animal Excretion: Animals primarily excrete urea, carbon dioxide, and water. Plants excrete oxygen as a byproduct of photosynthesis during the day and carbon dioxide as a byproduct of respiration at night, utilizing their leaf structures for gas exchange.

Locomotion and Orientation: Movement is a change in position or place. While animals typically engage in locomotion (moving the whole body), plants move by changing their orientation, such as leaves turning to face the sun throughout the day.

Reproductive Strategies: Reproduction leads to the production of new individuals, ensuring the survival of the population. Sexual reproduction involves the fusion of male and female gametes to create genetic variety, whereas asexual reproduction involves a single parent producing identical clones.

Permanent Growth: Growth is the permanent increase in the size or dry mass of an organism. Animals usually grow significantly during their early stages of life, while many plants continue to grow and add new structures like branches and leaves throughout their entire lifespan.

Acronym Application: When asked to explain why an organism is 'living', always start with the MRS C GREN acronym. Mentioning at least three specific processes with their definitions often secures the most marks.

Avoid Mismatched Terms: Never use 'breathing' when you mean 'respiration'. Examiners look for the specific term 'chemical process' to define respiration within the cell.

Plant Movements: Remember that 'non-motile' does not mean 'non-moving'. Always cite phototropism or sun-tracking as evidence that plants fulfill the 'Movement' criteria of life.

Homeostasis Identification: If a question mentions temperature control, water balance, or internal stability, always categorize this under Control. This process is what keeps cellular enzymes at their optimum working conditions.