Needs & Characteristics of Living Things

Brainstorming & Guiding Questions

• "What characteristics make something alive? What makes me alive?"
  • Use these as personal reflection prompts before studying the list of universal needs & traits.

Defining “Organism”

• Organism = any living thing.
  • Includes plants, animals, fungi, protists, bacteria, archaeans, etc.
• Common misconception check:
  • Plants are organisms → True (confirmed twice in slides).

UNIVERSAL NEEDS OF ALL ORGANISMS

• Summary list (to be memorised): Water, Nutrients, Space, Air ( $\text{CO}<em>2$ or $\text{O}</em>2$ ).
• Some extremophiles can live without sunlight, but none can live without the other three.

1. Water

• Critical roles inside every cell:
  • DNA replication, cell division, protein synthesis.
  • Hydrolysis of food molecules.
  • Transport medium for nutrients & wastes.
• Human survival trivia (under ideal conditions):
  • Average person survives ≈ $3$–$7$ days without water
  • Multiple-choice in slide listed options $3$, $7$, $14$, $30$ days. The best‐supported answer in biology texts = about $3$ days; some reports stretch to $7$.
• TEDEd video reference: “What would happen if you didn’t drink water?” → illustrates dehydration cascade (dry mouth → reduced blood volume → organ failure).

2. Nutrients

• Provide the building blocks for growth & repair.
• Organisms grouped by how they obtain them:
  • Autotrophs (Producers) – make organic food from inorganic sources.
  • Examples: green plants, cyanobacteria.
  • Heterotrophs (Consumers) – obtain ready-made organics.
  • Carnivores eat animals; Herbivores eat plants; Omnivores eat both.
• Quiz clarification:
  • Statement: “Plants make their own food through photosynthesis, so they do NOT need nutrients from other sources.” → False.
  • Reason: Photosynthesis supplies energy (sugars) but not minerals such as $\text{P}$, $\text{N}$, $\text{K}$, $\text{Mg}^{2+}$, etc. These minerals are absorbed from soil/water to build DNA, ATP, membranes, etc.
• Special focus on Phosphorus:
  • Incorporated into ATP, nucleic acids, phospholipids.
  • Promotes strong roots, flowers, and overall cell health.

3. Space to Live (Habitat)

• Provides integrated access to food, water, shelter, mates.
• Scarcity of suitable habitat → competition among organisms.
• Quiz examples:
  • Bear’s optimal habitat = Forest (provides berries, prey, cover, dens).
  • Best explanation for competition → “Space limits access to resources like food, water, and shelter.”

4. Air ( $\text{CO}<em>2$ & $\text{O}</em>2$ )

• Plants use $\text{CO}<em>2$ during photosynthesis to fix carbon and release $\text{O}</em>2$.
• Both plants and animals use $\text{O}_2$ in cellular respiration to make energy as ATP.
• Quiz correction: “Cellular respiration only occurs in animal cells.” → False (plant, fungal, protist & most bacterial cells respire too).

8 UNIVERSAL CHARACTERISTICS OF LIFE

(Easy mnemonic: “Cool Hippos Eat Really Tasty Green Red Cherries.”)

1. Cells – composed of one (unicellular) or many (multicellular).
2. Homeostasis – maintain internal balance.
3. Energy – obtain & use (metabolism → ATP).
4. Reproduce – sexual or asexual.
5. Traits – hereditary information (DNA) passed to offspring.
6. Grow – increase in cell number or size.
7. Respond – detect & react to stimuli.
8. Change/Evolve – populations adapt over generations.

Characteristic 1 – Made of Cells

• Unicellular (e.g., bacteria): simple organisation; single cell performs all life functions.
• Multicellular (e.g., humans, oak trees): division of labour among specialised cells, tissues, organs.

Characteristic 2 – Maintain Homeostasis

• Definition: keeping internal conditions within narrow limits despite external change.
• Human examples:
  • Hot → sweat (evaporative cooling).
  • Cold → shiver (muscle contraction generates heat).
• Ectotherm scenario (quiz): In hot weather, a lizard will find shade or burrow to cool down (external behavioural adjustment).

Characteristic 3 – Obtain & Use Energy

• Primary cellular “cash” = ATP (adenosine triphosphate).
  • Structure: adenine + ribose + $3$ phosphate groups.
  • Hydrolysing the terminal phosphate releases ≈ $7.3$ kcal/mol.
• Fuels movement, active transport, biosynthesis, repair.

Characteristic 4 – Reproduce

• Sexual reproduction: two parents → genetically diverse offspring.
  • Increases variation → raw material for evolution.
• Asexual reproduction: one parent → clone (e.g., binary fission in bacteria, budding in hydra).

Characteristic 5 – Pass Traits to Offspring

• Units of inheritance = genes located on DNA (Deoxyribonucleic acid).
• Works in both sexual & asexual modes.

Characteristic 6 – Grow

• Achieved by:
  • Cell enlargement (increase in cytoplasm & organelles).
  • Cell division (mitosis for body cells; binary fission for prokaryotes).
• Quiz correction: “Bacteria are unicellular therefore they cannot grow.” → False (they elongate, then split).

Characteristic 7 – Respond to Environment

• Stimulus → detectable change; Response → action taken.
• Internal stimuli examples: hunger, thirst, fatigue.
• External stimuli examples: light, sound, temperature.
• Quiz: “You feel tired and decide to nap.” = internal stimulus response.

Characteristic 8 – Change Over Time (Evolution)

• Occurs at the population level via natural selection.
  • Individuals with advantageous traits survive & reproduce → traits become common.
• Clarification quiz: First human born with a tail has a mutation, but one individual ≠ evolution; population would need several generations for trait frequency increase.

Recap Checklist (merge Needs & Characteristics)

• Needs → W.N.S.A. (Water, Nutrients, Space, Air).
• Characteristics → C.H.E.R.T.G.R.C. (mnemonic above).
• Use flashcards (minimum $6$ required; extra credit if entire unit covered) via Knowt.com as per activity slide.

Connections & Big-Picture Relevance

• Cellular respiration & photosynthesis form a biochemical cycle exchanging $\text{CO}<em>2$ and $\text{O}</em>2$ between organisms and atmosphere (to be detailed in next lesson).
• Homeostasis principles underpin human medicine (fever, diabetes, blood pH regulation).
• Evolution explains biodiversity & guides conservation strategies.
• Understanding nutrient cycles (phosphorus, nitrogen) is critical for agriculture and ecosystem health.

Ethical / Practical Implications

• Water scarcity & access affect organism survival → ties to global humanitarian issues.
• Habitat competition highlights impact of deforestation & urbanisation on wildlife.
• Genetic inheritance knowledge raises discussions on gene editing (CRISPR) and biodiversity preservation.

Study Tips

• Memorise acronyms; associate each letter with a personal example.
• Practise quiz questions aloud; justify why each incorrect option is wrong.
• Sketch a concept map linking “needs” to “characteristics” (e.g., Energy need ⇄ Obtain & use energy characteristic).
• Create flashcards on Knowt.com as encouraged; include visuals for plant vs. animal processes.