What living things are and how they stay alive

Understand the idea

The earth holds living and non-living things. Living things have life: they are made of cells, use energy, respond, grow, reproduce, and finally die. A tree does not walk away when you touch it, but it is still alive because those life processes run inside it.

A cell is the basic unit of life. It has protoplasm inside a plasma membrane. Plant cells also have a cell wall, a large central vacuole, and chloroplasts. Animals are motile heterotrophs without a cell wall. Plants are non-motile autotrophs with a cell wall. Bacteria are prokaryotes: they have no nucleus.

Energy comes from photosynthesis or from breaking food in respiration to make ATP. Anabolism builds complex molecules. Catabolism breaks them. Together they are metabolism. Autotrophs make food; heterotrophs eat plants or animals. Living things also remove wastes by excretion.

What to remember

• Life signs: organisation, energy, metabolism, growth, response, reproduction, death.
• Anabolism builds; catabolism breaks; metabolism is both.
• Autotrophs make food; herbivores, carnivores, and omnivores consume it.

Recap

Living things are cellular, use energy, metabolise, grow, respond, reproduce, and die. Know plant versus animal cells, autotroph versus heterotroph, and the difference between photosynthesis and respiration.