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1-1-Cell-Cycle

1.1: Characteristics of Living Organisms

Learning Objectives

  • Describe movement as an action causing a change of position or place.
  • Describe respiration as chemical reactions releasing energy for metabolism.
  • Describe sensitivity as detecting and responding to internal or external changes.
  • Describe growth as a permanent increase in size and dry mass.
  • Describe reproduction as processes making more of the same kind.
  • Describe excretion as removing metabolic wastes and excess substances.
  • Describe nutrition as taking in materials for energy, growth and development.

Core vs Extended Guide

  • 📌 Core students study only the unlabeled sections.
  • 📌 Extended students must study everything, including 🚀 Extended points.
  • 📌 Extended = Core + Supplement.

Movement

Living things show movement as an action by an organism or part of an organism causing a change of position or place, which distinguishes them from non-living objects. Movement involves actions that result in displacement. It may involve the whole organism or a specific part. The key outcome is a measurable change of position or place. Internal activity that does not alter position is not counted as movement. Because the definition centres on displacement, wording about “action” and “change of position” must both appear.

⚠ Misconception

Movement is not the same as internal transport or temporary shape change without displacement. The definition requires an action that changes position or place. If nothing ends up in a new position, it is not movement. Exam cue: include the words “change of position or place”.

Exam-style questions

  1. State the definition of movement in organisms.
    Answer: Movement is an action by an organism or part causing a change of position or place.

  2. Decide if a 3 cm bend of a body part counts as movement.
    Answer: Yes. It changes the position of a part, so it is movement by definition.

The cheetah’s rapid sprint illustrates movement — a change in position over time. Cheetah

Respiration

Living things carry out respiration as the chemical reactions in cells that break down nutrient molecules and release energy for metabolism, which supplies energy for life processes. In respiration, reactions occur inside cells. These reactions break down nutrient molecules [small usable molecules taken in or stored] and release energy for metabolism [all the chemical processes that keep an organism alive]. Because energy is released, other essential processes can proceed.

🧠 Examiner Insight

Write the full definition: chemical reactions in cells, breaking down nutrient molecules, releasing energy for metabolism. Shortened phrases lose required elements. Exam cue: include “chemical reactions in cells” and “release energy for metabolism”.

Exam-style questions

  1. Define respiration in cells.
    Answer: Respiration is chemical reactions in cells that break down nutrient molecules and release energy for metabolism.

  2. Explain if reactions releasing energy for 60 seconds in one cell are respiration.
    Answer: Yes. They are chemical reactions in a cell that break down nutrient molecules and release energy for metabolism.

Sensitivity

Living things show sensitivity as the ability to detect and respond to changes in the internal or external environment, enabling coordinated reactions. Sensitivity includes detection and response; both elements are required. A stimulus [a detectable change] can come from inside the body or from surroundings. Responses follow detection and help the organism deal with the change. The definition focuses on the sequence: detect, then respond.

Exam-style questions

  1. State what sensitivity means in organisms.
    Answer: Sensitivity is the ability to detect and respond to changes in the internal or external environment.

  2. Decide if detecting a change of 1 unit in an internal condition shows sensitivity.
    Answer: Yes. Detecting and then responding to an internal change meets the definition of sensitivity.

Growth

Living things undergo growth as a permanent increase in size and dry mass, which results from adding new material. Dry mass [mass excluding water] rises when new substances are made. Growth must be permanent; temporary swelling does not qualify. Because the definition specifies permanence and dry mass, reversible size changes are excluded. The focus is on lasting increase, not short-term variation.

Exam-style questions

  1. Define growth in organisms.
    Answer: Growth is a permanent increase in size and dry mass.

  2. Decide if a size increase that reverses after 1 hour is growth.
    Answer: No. It is not permanent, so it does not meet the definition of growth.

Reproduction

Living things perform reproduction as the processes that make more of the same kind of organism, ensuring continuity. The emphasis is on producing new individuals of the same kind. These processes allow populations to persist through time. Without reproduction, the kind would not continue. The definition covers making more of the same kind; precise mechanisms are not required here.

Exam-style questions

  1. State what reproduction means in biology.
    Answer: Reproduction is the processes that make more of the same kind of organism.

  2. Explain why reproduction keeps a kind of organism existing over time.
    Answer: By making more of the same kind, new individuals replace older ones, so the kind persists.

Excretion

Living things carry out excretion as the removal of the waste products of metabolism and substances in excess of requirements, maintaining suitable internal conditions. Waste products of metabolism [by-products from chemical reactions] must be removed. Substances that are present beyond what is needed also require removal. Both parts of the definition are essential. Excretion focuses on removal, not mere movement, of unwanted materials.

Exam-style questions

  1. Define excretion in organisms.
    Answer: Excretion is the removal of the waste products of metabolism and substances in excess of requirements.

  2. Decide if removing a compound 5 units above requirement counts as excretion.
    Answer: Yes. It removes a substance in excess of requirements, so it is excretion.

Nutrition

Living things require nutrition as the taking in of materials for energy, growth and development, supplying inputs for life. Materials [substances required by cells] provide energy for processes and matter for building. Taking in materials supports growth and development as well as energy needs. The definition links intake directly to what the organism uses and builds. Without intake, processes and structures could not be maintained.

Exam-style questions

  1. State the meaning of nutrition.
    Answer: Nutrition is the taking in of materials for energy, growth and development.

  2. Explain if taking in materials used mainly for building is nutrition.
    Answer: Yes. The definition includes materials for growth and development, not just immediate energy.

Summary

Living organisms are defined by seven shared characteristics that specify what they do and why these actions matter. Movement requires an action that produces a change of position or place. Respiration consists of chemical reactions in cells that break down nutrient molecules and release energy for metabolism, allowing other processes to run. Sensitivity demands both detecting and responding to changes in the internal or external environment, linking perception to action. Growth is a permanent increase in size and dry mass, so reversible swelling does not qualify.

These characteristics connect logically. Nutrition supplies materials for energy, growth and development, which feed into respiration and the making of new structures. Energy released by respiration supports movement, sensitivity, and the synthesis required for growth. Excretion removes substances that are waste products of metabolism and those present in excess of requirements, helping to keep internal conditions suitable for ongoing processes. Reproduction ensures more individuals of the same kind are made, so the kind continues through time. Together, the seven definitions provide a precise, syllabus-aligned framework for recognising living organisms.

Quick Recap

  • Movement: action causing change of position or place.
  • Respiration: chemical reactions in cells releasing energy for metabolism.
  • Sensitivity: detect and respond to internal or external changes.
  • Growth: permanent increase in size and dry mass.
  • Reproduction: processes making more of the same kind.
  • Excretion: remove metabolic wastes and excess substances.
  • Nutrition: take in materials for energy, growth, development.
  • Movement needs displacement, not just internal activity.
  • Respiration definition must include “in cells”.
  • Sensitivity links detection with response.
  • Growth excludes reversible swelling.
  • Excretion includes wastes and excess substances.
  • Nutrition links intake to energy and building.
  • Reproduction maintains the kind over time.

Can I…? Progress Check

  • Define each characteristic accurately in one complete sentence.
  • Decide if a described scenario fits a definition using key phrases.
  • Identify which definition requires “in cells” and which requires “dry mass”.
  • Compare movement with internal activity that lacks positional change.
  • Explain why removing excess substances belongs under excretion.