Diversity of Living Things - PSLE Science Study Notes

Key Concepts

What Makes Something “Living”?

All living things share seven characteristics (remember: MRS GREN):

Movement - ability to move parts of the body or the whole body
Respiration - process of releasing energy from food (happens in all living things)
Sensitivity - ability to respond to changes in the environment (light, sound, temperature, touch)
Growth - increase in size and mass
Reproduction - ability to produce offspring (young ones)
Excretion - removal of waste products from the body
Nutrition - taking in food or making food for energy and growth

Classification of Living Things

Scientists group living things based on their similarities and differences
This grouping system is called classification
Classification helps us:
- Organize information about millions of living things
- Identify and study living things more easily
- Understand relationships between different organisms

The Five Main Groups of Living Things

Living things are classified into five kingdoms:

Animals
- Cannot make their own food (need to eat other organisms)
- Can move from place to place
- Examples: humans, dogs, fish, birds, insects, worms
Plants
- Can make their own food through photosynthesis
- Usually stay in one place (fixed to the ground)
- Have parts like roots, stems, leaves
- Examples: trees, grass, ferns, mosses
Fungi (singular: fungus)
- Cannot make their own food
- Feed on dead or decaying matter
- Grow thread-like structures
- Examples: mushrooms, moulds, yeast
Bacteria (singular: bacterium)
- Very tiny single-celled organisms
- Can only be seen under a microscope
- Some are helpful, some cause diseases
- Examples: bacteria in yogurt, bacteria that cause food poisoning
Protists
- Mostly single-celled organisms
- Live in water
- Examples: amoeba, algae
- (Note: This group is less emphasized in PSLE)

Classifying Animals

Animals can be further divided into two main groups:

Vertebrates (animals WITH backbones):

Mammals: have fur/hair, give birth to live young, feed young with milk
- Examples: humans, dogs, whales, bats
Birds: have feathers, wings, lay eggs with hard shells
- Examples: chicken, eagle, penguin
Fish: have scales, fins, gills for breathing in water, lay eggs in water
- Examples: goldfish, shark, stingray
Reptiles: have dry scaly skin, lay eggs with soft leathery shells
- Examples: snake, lizard, crocodile, turtle
Amphibians: have moist skin, live partly on land and partly in water, lay eggs in water
- Examples: frog, toad, salamander

Invertebrates (animals WITHOUT backbones):

Make up about 95% of all animal species
Examples: insects (ant, butterfly), snails, jellyfish, worms, spiders, crabs

Classifying Plants

Plants can be classified into two main groups:

Flowering Plants:

Produce flowers for reproduction
Flowers produce fruits with seeds
Examples: rose, sunflower, mango tree, grass

Non-flowering Plants:

Do not produce flowers
Reproduce using spores (tiny reproductive units)
Examples: ferns, mosses, algae

Fungi in Detail

Fungi are NOT plants even though they don’t move
Cannot make their own food (no photosynthesis)
Feed by breaking down dead organisms or waste matter
This makes them decomposers - very important for recycling nutrients
Grow thread-like structures called hyphae (singular: hypha)
Reproduce using spores
Some fungi are useful:
- Yeast helps bread rise and makes alcoholic drinks
- Some mushrooms can be eaten
- Some fungi produce antibiotics (medicine like penicillin)
Some fungi are harmful:
- Cause food to rot and spoil
- Cause diseases in plants and animals (e.g., athlete’s foot, ringworm)
- Some mushrooms are poisonous

Bacteria in Detail

Microscopic organisms - so tiny you need a microscope to see them
Single-celled organisms
Found everywhere: in air, water, soil, inside our bodies
Different shapes: round (cocci), rod-shaped (bacilli), spiral (spirilla)
Reproduce by binary fission (splitting into two)
Can reproduce very quickly (some divide every 20 minutes!)

Useful bacteria:

Help make food: yogurt, cheese, pickles
Help digestion in our intestines
Decompose dead matter and recycle nutrients
Used to make medicines and vaccines
Used in sewage treatment to break down waste

Harmful bacteria:

Cause diseases: food poisoning, cholera, tuberculosis, tooth decay
Cause food to spoil
Some produce toxins (poisons)

How to control harmful bacteria:

Cooking food thoroughly (heat kills bacteria)
Refrigeration (cold slows bacterial growth)
Freezing (stops bacterial growth)
Keeping food covered (prevents bacteria from landing on food)
Washing hands before handling food
Sterilization (using very high heat or chemicals)
Preserving food (salting, drying, adding vinegar, adding sugar)

Viruses in Detail

NOT considered fully “living” because they cannot carry out all life processes on their own
Much smaller than bacteria (need electron microscope to see)
Cannot reproduce on their own - need to invade living cells
Cause many diseases: flu, common cold, COVID-19, chickenpox, measles, dengue fever
Cannot be killed by antibiotics (only bacteria can be killed by antibiotics)
Some diseases caused by viruses can be prevented by vaccines

Differences between viruses and bacteria:

Feature	Bacteria	Viruses
Size	Tiny (can see with microscope)	Much tinier (need electron microscope)
Living?	Yes (can reproduce on their own)	Not fully (need host cells to reproduce)
Cell structure	Single-celled	Not made of cells
Treatment	Can be killed by antibiotics	Cannot be killed by antibiotics
Examples	Food poisoning, tuberculosis	Flu, COVID-19, chickenpox

Important Definitions

Living things: Organisms that show all seven life processes (MRS GREN)

Classification: The grouping of living things based on their similarities and differences

Vertebrates: Animals that have a backbone (spine)

Invertebrates: Animals that do not have a backbone

Mammals: Vertebrates that have fur or hair, give birth to live young, and feed their young with milk

Birds: Vertebrates that have feathers, wings, and lay eggs with hard shells

Fish: Vertebrates that have scales, fins, and gills to breathe in water

Reptiles: Vertebrates that have dry scaly skin and lay eggs with soft leathery shells on land

Amphibians: Vertebrates that have moist skin, live partly on land and partly in water, and lay eggs in water

Flowering plants: Plants that reproduce by producing flowers, which develop into fruits containing seeds

Non-flowering plants: Plants that do not produce flowers and reproduce using spores

Spores: Tiny reproductive structures produced by fungi and non-flowering plants

Fungi: Living things that cannot make their own food and feed on dead or decaying matter

Decomposers: Organisms (like fungi and bacteria) that break down dead organisms and waste, returning nutrients to the soil

Bacteria: Microscopic single-celled organisms found everywhere

Viruses: Extremely small particles that can only reproduce inside living cells and cause diseases

Microscopic: Too small to be seen with the naked eye; requires a microscope

Antibiotics: Medicines that can kill bacteria but do not work against viruses

Vaccines: Substances given to help the body build immunity against specific viral diseases

Binary fission: The way bacteria reproduce by splitting into two identical cells

Hyphae: Thread-like structures that make up the body of fungi

Diagrams and Structures

Diagram 1: MRS GREN Memory Aid

Draw a simple stick figure with labels pointing to different parts:

Head (with eyes): SENSITIVITY - "I can sense light and sound"
Mouth: NUTRITION - "I need food"
Chest (with arrows in/out): RESPIRATION - "I release energy from food"
Arms/legs (with motion lines): MOVEMENT - "I can move"
Whole body (with upward arrow): GROWTH - "I grow bigger"
Lower body (with arrow pointing out): EXCRETION - "I remove waste"
Person holding a baby: REPRODUCTION - "I can have offspring"

Diagram 2: Classification of Animals

Draw a branching tree diagram:

                    ANIMALS
                       |
        ________________________________
        |                              |
    VERTEBRATES                  INVERTEBRATES
    (with backbone)              (no backbone)
        |                              |
    ____|_____                   Examples:
    |  |  |  |  |                • Insects
    |  |  |  |  |                • Snails
    M  B  F  R  A                • Worms
    A  I  I  E  M                • Jellyfish
    M  R  S  P  P                • Spiders
    M  D  H  T  H
    A  S     I  I
    L        L  B
    S        E  I
             S  A
                N
                S

Draw 5 simple animals under each vertebrate group with key features:
- Mammal: dog with fur
- Bird: chicken with feathers
- Fish: fish with scales and fins
- Reptile: snake with scales
- Amphibian: frog with moist skin

Diagram 3: Classification of Plants

Draw a branching diagram:

                    PLANTS
                       |
        ________________________________
        |                              |
   FLOWERING PLANTS            NON-FLOWERING PLANTS
        |                              |
  Produce flowers              Reproduce using spores
  Produce fruits                      |
  with seeds                    Examples:
        |                       • Ferns
  Examples:                     • Mosses
  • Rose                        • Algae
  • Sunflower
  • Mango tree

Draw simple sketches:
- A flower with petals, stem, leaves
- A fern with fronds (feather-like leaves)

Diagram 4: Shapes of Bacteria

Draw three types of bacteria:

1. COCCI (round)
   Draw: O O O (small circles in a row)
   Label: "Round-shaped bacteria"

2. BACILLI (rod-shaped)
   Draw: | | | (short rectangular rods)
   Label: "Rod-shaped bacteria"

3. SPIRILLA (spiral)
   Draw: ~~~~ (wavy spiral line)
   Label: "Spiral-shaped bacteria"

Diagram 5: Size Comparison

Draw three circles of different sizes:

Largest circle: "BACTERIA"
                (visible under microscope)
                Draw a small dot

Medium-sized circle: Show a microscope pointing to bacteria

Smallest circle: "VIRUS"
                 (needs electron microscope)
                 Draw a tiny speck with arrow
                 Label: "100x smaller than bacteria"

Worked Examples

Example 1: Identifying Living vs Non-Living Things

Question: A student observes four things in the garden: a rock, a mushroom, a robot toy, and an ant. Which of these are living things? Explain your answer using MRS GREN.

Step-by-step solution:

List MRS GREN characteristics: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition
Examine the rock:
- ✗ Cannot move by itself
- ✗ Does not respire
- ✗ Cannot sense environment
- ✗ Does not grow
- ✗ Cannot reproduce
- ✗ Does not excrete
- ✗ Does not need nutrition
- Conclusion: NON-LIVING (shows no MRS GREN characteristics)
Examine the mushroom (fungus):
- ✓ Parts can move slightly (though not locomotion)
- ✓ Respires to get energy
- ✓ Responds to light and moisture
- ✓ Grows in size
- ✓ Reproduces using spores
- ✓ Excretes waste products
- ✓ Gets nutrition by feeding on dead matter
- Conclusion: LIVING (shows all MRS GREN characteristics)
Examine the robot toy:
- ✗ Can move BUT needs batteries (not its own energy)
- ✗ Does not respire
- ✗ May have sensors BUT does not respond naturally
- ✗ Does not grow
- ✗ Cannot reproduce
- ✗ Does not excrete
- ✗ Does not need food for nutrition
- Conclusion: NON-LIVING (may seem to move but doesn’t show true MRS GREN)
Examine the ant:
- ✓ Moves from place to place
- ✓ Respires to release energy
- ✓ Senses food, danger, light
- ✓ Grows from egg to adult
- ✓ Queen ant reproduces
- ✓ Excretes waste
- ✓ Needs food for nutrition
- Conclusion: LIVING (shows all MRS GREN characteristics)

Final Answer: The mushroom and ant are living things. The rock and robot are non-living.

Example 2: Classifying Animals

Question: Sarah found these animals: dolphin, penguin, snake, frog, and goldfish. Help her classify them into the correct vertebrate groups and give one characteristic that helped you decide.

Step-by-step solution:

Dolphin:
- Has backbone → Vertebrate
- Lives in water but breathes air using lungs
- Gives birth to live young
- Feeds baby with milk
- Has smooth skin (no scales)
- Classification: MAMMAL
- Key characteristic: Feeds young with milk / gives birth to live young
Penguin:
- Has backbone → Vertebrate
- Has feathers covering body
- Has wings (though cannot fly, it can swim)
- Lays eggs with hard shells
- Classification: BIRD
- Key characteristic: Has feathers
Snake:
- Has backbone → Vertebrate
- Has dry scaly skin
- Lays eggs with soft leathery shells on land
- Breathes using lungs
- Classification: REPTILE
- Key characteristic: Has dry scaly skin
Frog:
- Has backbone → Vertebrate
- Has moist, smooth skin (no scales)
- Lives both in water and on land
- Lays eggs in water
- Young (tadpoles) look different from adults
- Classification: AMPHIBIAN
- Key characteristic: Has moist skin / lays eggs in water
Goldfish:
- Has backbone → Vertebrate
- Lives in water
- Has scales and fins
- Breathes using gills
- Lays eggs in water
- Classification: FISH
- Key characteristic: Has gills and scales

Summary Table:

Animal	Group	Key Feature
Dolphin	Mammal	Feeds young with milk
Penguin	Bird	Has feathers
Snake	Reptile	Dry scaly skin
Frog	Amphibian	Moist skin, lays eggs in water
Goldfish	Fish	Has gills and scales

Example 3: Fungi vs Bacteria vs Viruses

Question: Explain the differences between fungi, bacteria, and viruses. Include: (a) whether they are living things, (b) how they can affect humans, and © one way to control harmful ones.

Step-by-step solution:

Part (a): Are they living things?

Fungi: YES, fully living
- Show all MRS GREN characteristics
- Can grow, reproduce (using spores), respire, etc.
- Can survive on their own by feeding on dead matter
Bacteria: YES, fully living
- Show all MRS GREN characteristics
- Can grow, reproduce (by binary fission), respire, etc.
- Can survive and reproduce on their own
Viruses: NOT considered fully living
- Cannot reproduce on their own
- Must invade living cells to make copies of themselves
- Cannot carry out most life processes independently

Part (b): How they affect humans

Fungi:
- Helpful: Yeast makes bread rise; mushrooms for food; produce medicines like penicillin
- Harmful: Cause athlete’s foot, ringworm; some mushrooms are poisonous; spoil food
Bacteria:
- Helpful: Make yogurt, cheese; help digest food in intestines; decompose waste
- Harmful: Cause food poisoning, tooth decay, tuberculosis; spoil food
Viruses:
- Mostly harmful: Cause flu, common cold, COVID-19, chickenpox, measles, dengue fever
- Note: Very few viruses are helpful to humans

Part ©: How to control harmful ones

Fungi:
- Keep areas clean and dry (fungi grow in damp places)
- Store food properly
- Use anti-fungal creams for skin infections
Bacteria:
- Cooking food thoroughly (heat kills bacteria)
- Refrigeration (cold slows bacterial growth)
- Washing hands before eating
- Use antibiotics (medicines that kill bacteria)
- Keep wounds clean and covered
Viruses:
- Vaccines to prevent viral diseases
- Rest and drink fluids to help body fight infection
- Good hygiene (wash hands, cover mouth when coughing)
- Note: Antibiotics do NOT work on viruses!

Complete Answer Summary: Fungi and bacteria are fully living things that can be helpful or harmful. Viruses are not considered fully living and are mostly harmful. We control harmful fungi by keeping clean and dry, harmful bacteria by cooking food and using antibiotics, and viruses by using vaccines and good hygiene. Remember: antibiotics work on bacteria but NOT on viruses.

Common Mistakes to Avoid

Mistake 1: Confusing viruses with bacteria

Wrong: “Viruses are tiny bacteria”
Wrong: “We can kill viruses with antibiotics”
Correct: Viruses are NOT bacteria; they are much smaller and cannot be killed by antibiotics
Remember: Antibiotics work ONLY on bacteria, NOT on viruses

Mistake 2: Thinking fungi are plants

Wrong: “Mushrooms are plants because they don’t move”
Wrong: “Fungi can make their own food like plants”
Correct: Fungi are NOT plants; they cannot make their own food and must feed on dead or decaying matter
Remember: Plants can photosynthesize; fungi cannot

Mistake 3: Forgetting that ALL living things respire

Wrong: “Only animals respire, plants don’t”
Wrong: “Plants only photosynthesize, they don’t respire”
Correct: ALL living things respire (release energy from food) - animals, plants, fungi, bacteria
Remember: Respiration happens 24/7; photosynthesis only happens in plants during daytime

Mistake 4: Confusing vertebrate groups

Wrong: “Dolphins are fish because they live in water”
Wrong: “Penguins are not birds because they can’t fly”
Wrong: “Turtles are amphibians because they live in water and on land”
Correct:
- Dolphins are mammals (give birth, feed milk, breathe air with lungs)
- Penguins are birds (have feathers)
- Turtles are reptiles (dry scaly skin, lay eggs on land)
Remember: Where an animal lives doesn’t determine its group; its characteristics do

Mistake 5: Thinking movement means locomotion only

Wrong: “Plants don’t show movement, so they’re not living”
Correct: Movement includes any change in position of body parts (leaves turning toward light, roots growing downward, flowers opening)
Remember: Movement doesn’t always mean moving from place to place

Mistake 6: Saying bacteria and viruses are not living at all

Wrong: “Bacteria and viruses are both non-living”
Correct: Bacteria ARE fully living; viruses are NOT considered fully living
Remember: Bacteria can reproduce on their own; viruses need host cells

Mistake 7: Forgetting that invertebrates have no backbone

Wrong: “Crabs are vertebrates because they have a hard shell”
Wrong: “Insects have backbones”
Correct: Invertebrates have NO backbone (spine); they may have other hard parts (shells, exoskeletons) but no backbone
Remember: VERTEBRATE = BACKBONE; no backbone = invertebrate (even if hard outside)

Mistake 8: Thinking refrigeration kills bacteria

Wrong: “Freezing kills all bacteria”
Correct: Cold temperatures SLOW DOWN or STOP bacterial growth; they don’t always kill bacteria. Cooking (heat) kills bacteria.
Remember:
- Hot = kills bacteria
- Cold = slows/stops bacterial growth

Mistake 9: Listing only 6 characteristics instead of 7 (MRS GREN)

Wrong: Forgetting one characteristic when asked to list all
Correct: Always remember all seven: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition
Tip: Use the acronym MRS GREN and practice writing all seven

Mistake 10: Not giving specific examples when asked

Wrong: “Some animals are vertebrates” (too vague)
Correct: “Examples of vertebrates include humans, fish, and birds”
Remember: Always give specific, concrete examples to earn marks

Exam Tips

General Answering Strategies

When asked about characteristics of living things:
- Use the acronym MRS GREN to remember all seven
- Write the full words, not just the letters (Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition)
- If asked for examples, give specific ones (e.g., “A plant grows taller and develops more leaves”)
When classifying animals:
- First identify: vertebrate or invertebrate?
- If vertebrate, identify the group using key features:
  - Mammals: fur/hair, live birth, milk
  - Birds: feathers, hard-shelled eggs
  - Fish: scales, fins, gills
  - Reptiles: dry scales, soft-shelled eggs on land
  - Amphibians: moist skin, eggs in water
- Always give at least one characteristic to support your answer
When asked about fungi, bacteria, or viruses:
- State whether they are living or not
- Mention size (bacteria = microscopic; viruses = much smaller)
- Give specific examples of helpful or harmful ones
- For control methods, be specific (e.g., “Cook food at high temperature to kill bacteria”)

Keywords That Earn Marks

For MRS GREN:

“All living things show these seven characteristics…”
“Movement includes movement of body parts, not just locomotion”
“Respiration releases energy from food”
“Sensitivity means responding to changes in the environment”

For vertebrates:

“Has a backbone/spine”
“Gives birth to live young” (mammals)
“Feeds young with milk” (mammals)
“Has feathers” (birds)
“Has gills” (fish)
“Has dry scaly skin” (reptiles)
“Has moist skin” (amphibians)

For invertebrates:

“Does not have a backbone”
“Has an exoskeleton” (insects)
“Has a soft body” (worms)

For plants:

“Flowering plants produce flowers and fruits with seeds”
“Non-flowering plants reproduce using spores”
“Can make their own food through photosynthesis”

For fungi:

“Feeds on dead or decaying matter”
“Cannot make its own food”
“Decomposes dead organisms”
“Reproduces using spores”
“NOT a plant” (if comparing)

For bacteria:

“Microscopic” or “Can only be seen under microscope”
“Single-celled organisms”
“Reproduces by binary fission”
“Can be killed by antibiotics”
“Can be controlled by cooking/heating”

For viruses:

“Not considered fully living”
“Much smaller than bacteria”
“Needs to invade living cells to reproduce”
“Cannot be killed by antibiotics”
“Can be prevented by vaccines”

How to Answer Common Question Types

Type 1: “State the characteristics of living things”

List all seven MRS GREN characteristics
Write in full sentences or bullet points
Don’t just write the acronym letters

Type 2: “Classify the following animals…”

Create a table with columns: Animal | Group | Key Characteristic
Be specific about the group (don’t just write “vertebrate”)
Give at least one observable feature

Type 3: “Explain the difference between [X] and [Y]”

Use a comparison format
Include at least 2-3 differences
Give specific examples for each
Example structure:
- “[X] is…, while [Y] is…”
- “[X] has…, but [Y] has…”
- “Example of [X] includes…, whereas [Y] includes…”

Type 4: “How can we prevent/control [harmful organisms]?”

Be specific about the method
Explain why it works (e.g., “Cooking at high temperature kills bacteria”)
Give 2-3 different methods if possible

Type 5: “Is [organism] living or non-living? Explain.”

State your answer clearly first
Give at least 2-3 MRS GREN characteristics as evidence
Use “because” or “as” to link answer to evidence
Example: “The mushroom is a living thing because it grows in size, reproduces using spores, and respires to release energy.”

Mark-Earning Phrases

When describing living things:

“Shows all seven characteristics of living things”
“Can reproduce to produce offspring”
“Responds to changes in its environment”

When describing classification:

“Based on similarities and differences”
“Helps scientists organize and identify living things”

When describing control methods:

“High temperature kills bacteria”
“Low temperature slows down bacterial growth”
“Antibiotics kill bacteria but do not work on viruses”
“Vaccines help the body build immunity against viruses”

When comparing:

“Unlike [X], [Y] is…”
“Both [X] and [Y] can…, but only [X] can…”
“[X] is similar to [Y] in that they both…, but [X] differs because…”

Watch Out For These Question Tricks

“Give an example of a mammal that lives in water”
- Answer: Dolphin or whale (NOT fish!)
- Trick: They want you to know that habitat doesn’t determine classification
“Can antibiotics cure the flu?”
- Answer: No, because flu is caused by a virus, and antibiotics only work on bacteria
- Trick: Testing whether you know viruses ≠ bacteria
“Why is a mushroom not a plant?”
- Answer: It cannot make its own food / cannot photosynthesize / feeds on dead matter
- Trick: Testing whether you know fungi are a separate group
“All living things need food. True or false?”
- Careful! Plants don’t “eat” food; they make their own food
- Better to say: “All living things need nutrition”

Quick Summary

Essential Points to Remember for PSLE:

✓ MRS GREN: All living things show 7 characteristics - Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition

✓ Five kingdoms: Animals, Plants, Fungi, Bacteria, Protists (focus on first four)

✓ Vertebrates (with backbone): Mammals, Birds, Fish, Reptiles, Amphibians

Mammals: fur/hair, live birth, milk
Birds: feathers, hard-shelled eggs
Fish: scales, fins, gills
Reptiles: dry scales, soft-shelled eggs on land
Amphibians: moist skin, eggs in water

✓ Invertebrates: No backbone (insects, worms, snails, jellyfish, spiders)

✓ Plants: Flowering (seeds in fruits) vs Non-flowering (reproduce using spores)

✓ Fungi:

NOT plants; cannot make own food
Feed on dead/decaying matter (decomposers)
Reproduce using spores
Can be helpful (yeast, edible mushrooms) or harmful (cause diseases, spoil food)

✓ Bacteria:

Microscopic, single-celled, fully living
Reproduce by binary fission
Can be helpful (yogurt, digestion) or harmful (diseases, food poisoning)
Killed by cooking/heating
Killed by antibiotics

✓ Viruses:

NOT fully living; much smaller than bacteria
Need host cells to reproduce
Cause diseases (flu, COVID-19, chickenpox)
NOT killed by antibiotics
Prevented by vaccines

✓ Key differences: Antibiotics work on bacteria but NOT viruses

✓ Control methods:

Bacteria: cooking (heat), refrigeration (cold), antibiotics, hygiene
Viruses: vaccines, good hygiene, rest
Fungi: keep clean and dry, anti-fungal treatments

✓ Common mistakes to avoid:

Dolphins are mammals, NOT fish
Fungi are NOT plants
Cold slows bacteria but doesn’t kill them
All living things respire (not just animals)

Final Exam Tip: When in doubt, go back to MRS GREN and use specific examples. Always read the question carefully to see how many marks are given - this tells you how many points to write!