1.0 Characteristics of Living Organisms

• Living things (alive), non-living (were never alive), dead (previously alive/part of something that was alive)

• Necessary features of living things (MRS GREN)

  • Movement

  • Respiration

  • Sensitivity

  • Growth

  • Reproduction

  • Excretion

  • Nutrition

• Seven characteristics of living things (MR H GREN)

  • Metabolism

    • Living things use energy and consume nutrients to carry out chemical reactions that sustain life.

    • The total of all biochemical reactions occurring in a living organism is called metabolism.

    • Anabolism; Organisms form complex molecules from simple molecules - consumes energy.

    • Catabolism; Organisms break down complex molecules into simple molecules - releases energy.

  • Reproduction

    • Organisms reproduce themselves to make new organisms

    • Asexual; single parent

    • Sexual: two parents

      • Parents produce sperm and egg cells, each with half the genetic information that the child will receive.

      • Sperm and egg cells fuse to form a child with combined genetic set.

    • Single-celled organisms can reproduce by splitting in two (cells > mitosis)

  • Homeostasis

    • Regulation of internal environment to maintain conditions required for all cell processes to function, despite constantly changing external environment.

      • e.g human body temperature needs to be 37 degrees Celsius.

  • Growth

    • Increase in size and biomass of an organism, representing development over time.

    • Associated with mitosis - cell division

    • Associated with differentiation of cells that allow cells to perform specific functions

    • Growth depends on anabolic (^ metabolism) pathways that form complex molecules e.g protein and DNA.

  • Response

    • Response to stimuli in the external environment.

      • Light, heat, sound, chemical and mechanical contact.

      • Organisms have means of receiving information (eyes, ears, skin, tastebuds)

  • Excretion

    • All living organisms produce waste that needs to be removed.

      • Urine, dead cells, carbon dioxide (for humans)

    • Therefore, all organisms have means of removing waste.

    • Excretion represents removal of waste products from an organism.

  • Nutrition

    • Survival of organisms requires food for energy and nutrients.

    • Can be obtained by eating other organisms or from the environment (e.g plants photosynthesise)

1.1 Cell Theory

• Cell theory, proposed by Theodor Schwann in 1839, states the following:

  • All living things are composed of cells.

  • The cell is the smallest unit of life.

  • Cells only arise from pre-existing cells (life begets life begets life begets life…)

• Cells are the smallest structural and functional units of all organisms, and are usually only visible through microscopes.

  • Whether unicellular or multicellular, all organisms contain specialised cell structures (organelles) which obtain nutrients, make proteins, produce energy…

• Some organisms are unicellular (composed of one cell):

  • The single cell must be able to carry out all life functions

  • Unicellular organisms are more abundant than multicellular ones and have existed for a bonus 2 billion years longer.

• Others are multicellular (more than one cell, even trillions)

  • Cells differentiate and have different purposes early on (skin, muscle, blood, nerve cells etc)

  • Cells group together to form tissues which group together to form organs which group together to form organ systems, which work together so that the organism can survive.

• All cells need to be able to respond to stimuli, gain energy from food and reproduce.

summary

Living organisms are classified as living when they fulfil the characteristics of living organisms; that they metabolise, they reproduce, they undergo homeostasis, they grow, respond to stimuli, excrete waste, and require nutrition for survival. They are comprised of cells, according to Schwann’s cell theory. Whether unicellular (one cell) or multicellular (more than one cell), specialised cell structures (organelles) help keep the organism functioning by allowing it to respond to stimuli, turn food into energy, and reproduce.