Energy P6 PSLE Science

Energy in Food

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Energy in Food

Key Concepts

1. Food as a Form of Chemical Energy

Food contains chemical energy stored in its nutrients (carbohydrates, fats, and proteins)
When we eat food, the body breaks it down to release this stored chemical energy
Different foods store different amounts of energy
- High-energy foods: Rice, bread, butter, oil, meat
- Low-energy foods: Vegetables, fruits (mostly water)

2. The Sun as the Ultimate Source of Energy

The Sun is the main source of energy for most living things on Earth
The Sun provides light energy that plants use to make food
Without the Sun, most life on Earth would not survive
Energy flows from the Sun → plants → animals → decomposers

3. Photosynthesis: How Plants Capture Energy

Plants use photosynthesis to capture light energy from the Sun and convert it into chemical energy stored in food.

The photosynthesis process:

Input: Light energy (from Sun) + Water + Carbon dioxide (from air)
Process: Takes place in the green leaves (contain chlorophyll)
Output: Glucose (sugar/food) + Oxygen

Energy conversion: Light energy → Chemical energy (stored in glucose)

Simple equation: Light + Water + Carbon dioxide → Glucose + Oxygen

3a. How Light Affects Photosynthesis: The Starch Test

Excess glucose produced by photosynthesis is converted and stored as starch in the leaf
Light is essential for photosynthesis — without light, photosynthesis cannot occur
If part of a leaf is deprived of light, that part cannot photosynthesise and no starch is produced there

The iodine test for starch:

Iodine solution is used to detect the presence of starch
Starch present → iodine turns blue-black
Starch absent → iodine remains brown (no colour change)

The black-strip experiment:

A black strip of paper is placed over part of a leaf to block out light
The covered area cannot photosynthesise → no starch is produced
When iodine is applied: covered area stays brown; uncovered area turns blue-black

Full causal chain (must state all links): Black strip blocks out light → cannot photosynthesise → no starch produced → iodine does not turn blue-black (remains brown)

3b. How CO2 Levels Affect Photosynthesis

Plants need carbon dioxide as a raw material for photosynthesis
More CO2 available → faster rate of photosynthesis → more glucose (food) produced → faster plant growth
Animals (including fish) respire and release CO2 into their surroundings
- Fish release dissolved CO2 into the water in a tank
- This increases the CO2 available to aquatic plants, boosting their photosynthesis
This is why a water plant in a tank with fish will grow bigger than one in a tank with no fish

4. How Animals Get Energy: Food Chains

Animals cannot make their own food like plants do, so they must eat other organisms to get energy.

Food chains show how energy is transferred from one organism to another:

Producers: Plants (make their own food using photosynthesis)
Consumers: Animals that eat plants or other animals
- Primary consumers: Herbivores (eat plants)
- Secondary consumers: Carnivores (eat herbivores)
- Tertiary consumers: Top carnivores (eat other carnivores)

Example food chains in Singapore:

Grass → Grasshopper → Frog → Snake
Plant → Caterpillar → Bird → Hawk
Plankton → Fish → Dolphin

5. How Energy is Released from Food: Respiration

Respiration is the process by which living things release energy from food for use in their body.

The respiration process:

Input: Food (glucose) + Oxygen
Process: Takes place in all living cells
Output: Energy (used by the body) + Carbon dioxide + Water

Energy released: Chemical energy (from food) → Usable energy for the body

Simple equation: Food + Oxygen → Energy + Carbon dioxide + Water

Where does respiration happen?

In plants: All cells (roots, stems, leaves)
In animals: All cells throughout the body
In humans: Happens in every living cell (muscles, brain, heart, etc.)

6. Energy Stored in Different Nutrients

Different nutrients provide different amounts of energy and serve different purposes:

Nutrient	Type	Energy Level	Function	Examples
Carbohydrates	Quick energy	Medium	Quick energy for movement and daily activities	Rice, bread, noodles, potato
Fats	Long-term energy	High	Store more energy; keeps us warm	Butter, oil, nuts, fatty meat
Proteins	Structural	Medium	Growth, repair, and building muscles	Meat, fish, eggs, beans

Key points:

Fats store more energy than carbohydrates per gram
Proteins are mainly for growth, not quick energy
Carbohydrates are quickly burned for daily activities

7. Energy Flow in Food Chains

Energy decreases at each level of a food chain because some energy is lost:

What happens to energy at each level?

Energy lost as heat: Used for movement, breathing, keeping warm (respiration)
Energy used for growth: Stored in body tissues
Energy not eaten: Parts of the organism that are not consumed

Energy percentage rule:

Only about 10% of energy passes to the next level
90% is lost or used up by the organism

Example:

Grass: 100 units of energy
  ↓ (only 10% transferred)
Grasshopper: 10 units of energy
  ↓ (only 10% transferred)
Frog: 1 unit of energy

Why energy decreases:

Some organisms are not eaten (energy lost)
Some energy is used for movement, breathing, and keeping warm
Some energy is lost as waste (faeces, urine)

8. Why We Need Energy: All Life Processes (MRS GREN)

All living things need energy to carry out life processes. Remember MRS GREN:

M - Movement: Moving muscles, running, walking, swimming
R - Respiration: Releasing energy from food (inside cells)
S - Sensitivity: Responding to surroundings (feeling heat, light, sound)
G - Growth: Building new cells and growing bigger
R - Reproduction: Making babies/offspring; making seeds
E - Excretion: Getting rid of waste products
N - Nutrition: Eating and digesting food

In humans specifically, we need energy for:

Movement (all physical activity)
Growth (childhood and repair of damaged tissue)
Keeping warm (maintaining body temperature)
Thinking and brain function
Maintaining all body functions even when resting

9. Comparing Energy in Different Foods

Foods can be ranked by how much energy they provide:

High-energy foods (a lot of energy):

Rice, bread, pasta (carbohydrates)
Butter, oil, nuts (fats)
Meat, fish, cheese (proteins + fats)

Medium-energy foods:

Eggs, tofu, beans (proteins)
Potatoes, sweet corn (carbohydrates)

Low-energy foods (little energy):

Vegetables: leafy greens, carrots, broccoli
Fruits: apples, oranges, watermelon (mostly water)
Salad (mostly water)

Why the difference?

High-energy foods: Contain more nutrients concentrated in smaller volume
Low-energy foods: Contain more water, less nutrients

Important Definitions

Term	Definition	Example
Chemical energy	Energy stored in food that can be released when food is broken down	The energy in rice
Photosynthesis	Process where plants use light energy to make food from water and carbon dioxide	Happens in green leaves in sunlight
Respiration	Process where living things release energy from food using oxygen	Happens in all living cells all the time
Food chain	A series showing how energy passes from plants to animals	Grass → Goat → Lion
Producer	Organism that makes its own food using photosynthesis	Plants
Consumer	Organism that eats other organisms to get energy	Animals
Herbivore	Animal that eats only plants (primary consumer)	Rabbit, cow, grasshopper
Carnivore	Animal that eats other animals (secondary or tertiary consumer)	Lion, eagle, frog
Nutrient	Substance in food needed by the body	Carbohydrates, fats, proteins, vitamins, minerals
Carbohydrate	Nutrient that provides quick energy; found in rice, bread, pasta	Glucose, starch
Fat	Nutrient that stores long-term energy and keeps us warm	Oil, butter, nuts
Protein	Nutrient mainly needed for growth and repair of body tissues	Meat, eggs, beans
Energy loss	Energy that is not passed to the next level in a food chain	Lost as heat, movement, waste
Starch	A substance in which plants store excess glucose produced by photosynthesis	Found in leaves and seeds
Iodine test	A test using iodine solution to detect starch; iodine turns blue-black if starch is present, remains brown if starch is absent	Used to show whether photosynthesis has occurred in a leaf

Worked Examples (PSLE-Style Questions)

Example 1: Photosynthesis and Energy

Question: Where does a plant get the energy to make its food, and what process is this called?

Answer:

A plant gets energy from sunlight (light energy from the Sun)
The process is called photosynthesis
In photosynthesis, light energy is converted into chemical energy and stored in food (glucose)
This happens in the green leaves which contain chlorophyll

Example 2: Respiration and Energy Release

Question: When we eat food, how is the energy in the food released and used in our body?

Answer:

The energy is released through a process called respiration
During respiration, food (glucose) reacts with oxygen in our cells
This releases usable energy that our body uses for movement, growth, keeping warm, and other activities
Respiration also produces carbon dioxide and water as waste products
Carbon dioxide is breathed out through our lungs

Example 3: Food Chains and Energy

Question: In the food chain: Grass → Locust → Frog → Snake

Which organism is the producer?
Which organism is a primary consumer?
Why is there less energy in the snake than in the grass?

Answer:

Producer: Grass (makes its own food using photosynthesis)
Primary consumer: Locust (eats plants/grass)
Why less energy in snake:
- Energy is lost at each level of the food chain
- Some energy is used by each organism for respiration (movement, keeping warm, growth)
- Some energy is lost as heat
- Not all of the organism is eaten (only about 10% of energy passes to the next level)

Example 4: Nutrients and Energy

Question: Why are some foods called “high-energy foods” while others are “low-energy foods”? Give examples of each.

Answer:

High-energy foods contain more nutrients packed together:
- Examples: Rice, bread, butter, oil, meat
- These contain more carbohydrates and fats
Low-energy foods contain a lot of water and less nutrients:
- Examples: Vegetables (leafy greens, carrots), fruits (apples, oranges), salad
- These have less carbohydrates, fats, and proteins per serving
Why the difference: High-energy foods have nutrients concentrated in a smaller volume, while low-energy foods are mostly water

Example 5: Life Processes and Energy (MRS GREN)

Question: A growing child needs a lot of energy. Name three life processes that require this energy.

Answer:

Growth - Building new cells and growing taller
Movement - Running, playing, physical activity
Respiration - Releasing energy from food in every cell
Keeping warm - Maintaining body temperature
(Or any three from MRS GREN)

Mark-earning phrase: “All these processes require energy from food.”

Example 6: Photosynthesis Equation

Question: Write the word equation for photosynthesis and explain what happens to the energy.

Answer: Equation: Light energy + Water + Carbon dioxide → Glucose + Oxygen

Energy explanation:

Input energy: Light energy from the Sun
Output energy: Chemical energy stored in glucose (food)
The plant converts light energy into chemical energy that is stored in the food
When the plant or an animal eats the plant, this chemical energy is released during respiration

Example 7: Comparing Organisms in a Food Chain

Question: In the food chain: Plant → Grasshopper → Frog Why can there not be a fourth level (like Frog → Hawk → Eagle → Lion) without running out of energy?

Answer:

At each level of the food chain, only about 10% of the energy is passed to the next level
The rest is lost as:
- Heat (from respiration/movement)
- Energy used for movement and breathing
- Energy in parts not eaten
- Energy in waste
After many levels, there is not enough energy left to support the next consumer
Eventually, there is too little energy to feed a large predator

Example 8: Uses of Energy in the Body

Question: List four ways that humans use the chemical energy from food.

Answer:

Movement - Contracting muscles for walking, running, sports
Growth - Building new cells, growing taller, repairing damaged tissue
Keeping warm - Maintaining body temperature in cold environments
Thinking and brain function - Brain uses a lot of energy
Breathing and heartbeat - Maintaining vital functions even at rest
Digestion - Breaking down food

(Any four answers from the list above are acceptable)

Example 9: Fish Tank Experiment (Photosynthesis + Respiration)

Question: Two tanks each contain the same water plant. Tank A also contains fish; Tank B has no fish. After two weeks, the plant in Tank A is bigger. Explain why.

Answer (step-by-step):

Identify the difference: Tank A has fish; Tank B does not.
Link to a biological process: Fish respire and release carbon dioxide into the water.
Chain of effects: The extra dissolved CO2 in Tank A means the water plant has more CO2 available for photosynthesis.
Conclude: With more CO2, the plant in Tank A can photosynthesize faster, produce more food (glucose), and therefore grow bigger than the plant in Tank B.

Key mark-earning phrase: ‘The fish respire and release carbon dioxide into the water, increasing the rate of photosynthesis of the plant.’

Common Mistakes to Avoid

❌ Mistake 1: Thinking animals get energy directly from the Sun

Wrong: “Lions get energy from the Sun”
Correct: Lions get energy from eating meat (which comes from herbivores that eat plants, which capture Sun’s energy)
Key: Only plants can directly capture the Sun’s energy through photosynthesis

❌ Mistake 2: Confusing photosynthesis and respiration

Wrong: “Plants use respiration to make food”
Correct:
- Photosynthesis = Making food using light energy (plants only)
- Respiration = Releasing energy from food (all living things)
Key: Plants do BOTH - they make food through photosynthesis AND release energy through respiration

❌ Mistake 3: Thinking respiration only happens during exercise

Wrong: “We only respire when we run or exercise”
Correct: Respiration happens in every cell, all the time, even when sleeping
Key: Respiration is continuous - it’s how our body releases energy 24/7

❌ Mistake 4: Not understanding energy loss in food chains

Wrong: “A grasshopper stores all the energy from the grass it eats”
Correct: A grasshopper only stores about 10% of the energy; the rest is lost as heat and used for its own activities
Key: Energy decreases at each level - this is why there are usually only 3-4 levels in a food chain

❌ Mistake 5: Thinking all nutrients provide the same amount of energy

Wrong: “Carbohydrates and fats provide the same amount of energy”
Correct: Fats store more energy than carbohydrates per gram
Key: Fats = long-term energy storage; Carbohydrates = quick energy

❌ Mistake 6: Confusing energy loss with waste

Wrong: “Energy is lost because animals produce waste”
Correct: Energy is lost as heat from respiration AND through waste products
Key: Most energy loss is from respiration (movement, keeping warm, growth), not just waste

❌ Mistake 7: Thinking plants don’t need respiration

Wrong: “Plants only photosynthesize; they don’t respire”
Correct: Plants do both - they photosynthesize to make food, and they respire to release energy from that food
Key: Plants respire day and night, but only photosynthesize during the day

❌ Mistake 8: Writing incomplete respiration equations

Wrong: “Food → Energy”
Correct: “Food + Oxygen → Energy + Carbon dioxide + Water”
Key: Don’t forget oxygen, carbon dioxide, and water in the equation

❌ Mistake 9: Saying the black strip ‘covers’ the leaf instead of ‘blocks out light’

Wrong: ‘The black strip covers part of the leaf’
Correct: ‘The black strip blocks out light from that part of the leaf’
Key: The examinable variable is the presence or absence of light, not the physical covering

❌ Mistake 10: Giving an incomplete causal chain for the iodine test

Wrong: ‘No light means no starch, so iodine stays brown’
Correct: ‘No light → cannot photosynthesise → no starch produced → iodine will not turn blue-black’
Key: Every link in the chain must be stated; skipping ‘cannot photosynthesise’ loses a mark

❌ Mistake 11: Naming the black strip as the factor being tested

Wrong: ‘The factor being tested is the black strip’
Correct: ‘The factor being tested is the presence or absence of light’
Key: Always name the scientific variable, not the equipment used to manipulate it

❌ Mistake 12: Saying ‘more CO2’ without naming the process that produced it

Wrong: ‘The plant grows bigger because there is more carbon dioxide in Tank A.’
Correct: ‘The fish respire and release carbon dioxide into the water. This increases the CO2 available, so the plant photosynthesizes faster and grows bigger.’
Key: You must name the process (respiration) and the organism performing it. Stating ‘more CO2’ alone is incomplete and will lose marks.

❌ Mistake 13: Omitting the keyword ‘respire’ in experiment answers

Wrong: ‘Fish release CO2 into the water.’
Correct: ‘Fish respire and release carbon dioxide into the water.’
Key: Examiners look for the word ‘respire’ — it shows you understand the biological mechanism, not just the outcome.

Exam Tips with Mark-Earning Phrases

Tip 1: Use “Chemical Energy” Precisely

Instead of: “Food has energy”
Say: “Food contains chemical energy that is stored in nutrients”
Mark gain: +1 mark for using correct terminology

Tip 2: Explain the Source of Energy

Instead of: “We need energy”
Say: “We need energy from food which ultimately comes from the Sun through photosynthesis”
Mark gain: Connects all concepts; shows deeper understanding

Tip 3: Use “Converted” or “Transformed” When Discussing Energy Changes

Instead of: “Light energy becomes food”
Say: “Light energy is converted into chemical energy and stored in food”
Mark gain: Shows understanding of energy conservation

Tip 4: Name the Specific Processes

Instead of: “Plants make food”
Say: “Through photosynthesis, plants use light energy to make food”
Mark gain: Correct process terminology = automatic mark

Tip 5: Explain BOTH Directions for Food Chains

When answering food chain questions:

Name the producers: “Plants are producers because they make their own food”
Name the consumers: “Herbivores are primary consumers because they eat plants”
Explain energy transfer: “Only about 10% of energy is transferred to the next level”
Mark gain: Comprehensive answer = full marks

Tip 6: Use “Respiration” vs “Breathing”

Wrong: “Breathing releases energy from food”
Right: “Respiration releases energy from food; breathing is just one part of respiration”
Mark gain: Shows precise scientific knowledge

Tip 7: Name MRS GREN Processes Correctly

When asked why we need energy:

Say: “We need energy for movement, respiration, sensitivity, growth, reproduction, excretion, and nutrition”
Or pick specific relevant ones: “For growth and movement in humans”
Mark gain: Naming specific processes shows detailed knowledge

Tip 8: Complete Equations Fully

Instead of: “Glucose + O₂ → Energy”
Say: “Glucose + Oxygen → Energy + Carbon dioxide + Water”
Mark gain: Complete equations get full marks

Tip 9: Compare High and Low Energy Foods Correctly

Instead of: “Rice has more energy than lettuce”
Say: “Rice is a high-energy food containing carbohydrates and fats, while lettuce is a low-energy food mostly containing water”
Mark gain: Shows understanding of nutrient composition

Tip 10: Explain Why Not All Energy Transfers

Instead of: “Energy is lost”
Say: “Energy is lost as heat during respiration, used for movement and growth, and in parts of organisms not eaten”
Mark gain: Specific explanation = more marks

Tip 11: Use the 3-Step Approach for Experiment Questions

Identify the purpose — what is the experiment trying to show?
Consider the variable — how does the manipulated factor (e.g. light) affect the relevant process (photosynthesis)?
Link to the result — connect the process change to the observable outcome (iodine colour)

Tip 12: State the Full Causal Chain (Never Skip Steps)

Model answer: ‘The black strip blocks out light, so the covered part cannot photosynthesise, therefore no starch is produced, so the iodine will not turn blue-black’
Each bold phrase is a potential mark-earning keyword

Tip 13: Key Scoring Keywords for Photosynthesis/Starch Questions

‘blocks out light’
‘cannot photosynthesise’
‘starch is not produced’
‘iodine will not detect starch’ / ‘iodine remains brown’

Tip 14: Name the Variable as ‘Presence/Absence of Light’

Instead of: ‘The black strip is the variable’
Say: ‘The variable is the presence or absence of light’
Mark gain: Naming the correct scientific variable earns marks; naming the apparatus does not

Tip 15: Use a 4-step structure for experiment-comparison questions

When asked to compare two setups (e.g., tank with fish vs. tank without fish):

State the difference: ‘Tank A has fish; Tank B does not.’
Name the biological process: ‘The fish respire…’
Trace the chain of effects: ‘…releasing carbon dioxide into the water, which increases the CO2 available to the plant, so the plant photosynthesizes at a faster rate…’
Conclude with the outcome: ‘…therefore the plant in Tank A produces more food and grows bigger.’

Mark gain: Each step in the chain earns a mark — a complete chain answer scores full marks.

Tip 16: Always write ‘respire’ not just ‘release CO2’

Instead of: ‘Fish release carbon dioxide into the water’
Say: ‘Fish respire and release carbon dioxide into the water’
Mark gain: The word ‘respire’ explicitly demonstrates understanding of the cellular process and is required for full credit in experiment-type questions.

Quick Summary

The Big Picture

Sun → Plants → Animals → Energy Used → Heat Lost
The Sun provides light energy
Plants convert light → chemical energy (photosynthesis)
Animals eat plants/animals to get chemical energy
All living things release energy from food (respiration)
Energy decreases through each level of a food chain

Key Equations

Photosynthesis: Light + H₂O + CO₂ → Food + O₂
Respiration: Food + O₂ → Energy + CO₂ + H₂O

Energy Facts

Only ~10% of energy transfers between food chain levels
Fats store more energy than carbohydrates
The Sun is the ultimate source of energy for life
Energy is needed for all life processes (MRS GREN)
Respiration happens in all cells all the time

Food Chain Terminology

Producers: Plants (make food)
Primary Consumers: Herbivores (eat plants)
Secondary Consumers: Carnivores (eat herbivores)
Tertiary Consumers: Top predators (eat other carnivores)

Energy Flow Path

SUN (light energy)
  ↓
PLANTS (photosynthesis: light → chemical energy)
  ↓
HERBIVORES (eat plants: gain ~10% of plant energy)
  ↓
CARNIVORES (eat herbivores: gain ~10% of herbivore energy)

Remember for Exams

Use proper terminology: “chemical energy,” “photosynthesis,” “respiration”
Explain energy conversions, not just energy flow
Complete all equations with all products
Name specific MRS GREN processes when asked about life processes
Explain WHY energy decreases at each level, not just that it does
Connect the Sun → Food → Living Things → Energy Used

Good luck with your PSLE Science exam, Jamie! Master this topic and you’ll ace the energy section.

✏️ 29 practice questions available

30 questions from school exam papers

Which of the following human body system(s) work together to provide energy for daily activities?

Four human body diagrams labeled A, B, C, and D showing different organ systems. A shows the circulatory/nervous system (blood vessels and nerves throughout the body). B shows the respiratory system (lungs highlighted). C shows the digestive system (stomach and intestines highlighted). D shows the skeletal system (bones highlighted).

📊 Diagram: Four human body diagrams labeled A, B, C, and D showing different organ systems. A shows the circulatory/nervous system (blood vessels and nerves throughout the body). B shows the respiratory system (lungs highlighted). C shows the digestive system (stomach and intestines highlighted). D shows the skeletal system (bones highlighted).

A. D only

B. B and C only

C. A and D only

D. A, B and C only

P6_Science_SA2_2018_-_Anglo_Chinese 2018

Put a tick (✓) in the box(es) below to indicate which plant was unable to carry out photosynthesis when placed in the boxes made of material B.

A table with two columns: 'Thickness of box (cm)' and 'Tick (✓)'. The thickness values listed are: 1, 2, 3, 4, 5. The tick column is empty for students to fill in.

📊 Diagram: A table with two columns: 'Thickness of box (cm)' and 'Tick (✓)'. The thickness values listed are: 1, 2, 3, 4, 5. The tick column is empty for students to fill in.

1 mark

P6_Science_SA2_2018_-_Catholic_High 2018

When the plant is exposed to light, what substances will it produce?

1 mark

P6_Science_SA2_2018_-_Catholic_High 2018

Raju conducted an experiment to investigate the effect of different coloured lights on a process taking place in green plants. He recorded his findings in the graph shown below. Based on the information given above, which of the following statements are correct?

A graph showing the effect of different coloured lights on light absorption and oxygen release by plants. The x-axis shows colour of light from blue to red (blue, green, yellow, orange, red). The y-axis shows amount of light absorbed and oxygen released. Two curves are plotted: X (solid line) represents absorption of light by the leaves, and Y (dashed line) represents release of oxygen by plants. The X curve shows peaks at blue and red wavelengths with a dip in the green-yellow region. The Y curve shows a similar pattern to X, with peaks corresponding to blue and red light.

📊 Diagram: A graph showing the effect of different coloured lights on light absorption and oxygen release by plants. The x-axis shows colour of light from blue to red (blue, green, yellow, orange, red). The y-axis shows amount of light absorbed and oxygen released. Two curves are plotted: X (solid line) represents absorption of light by the leaves, and Y (dashed line) represents release of oxygen by plants. The X curve shows peaks at blue and red wavelengths with a dip in the green-yellow region. The Y curve shows a similar pattern to X, with peaks corresponding to blue and red light.

A Photosynthesis takes place most actively in blue and red light.

B The plant releases more oxygen in the presence of orange light than in yellow light.

C The colour of the light does not affect the amount of light absorbed by the plant.

(1) A and B only

(2) A and C only

(3) B and C only

(4) A, B and C

P6_Science_SA2_2018_-_Henry_park 2018

Tom wanted to investigate the effect of the intensity of different coloured lights on the rate of photosynthesis. The experiment was set up as shown below. He measured the number of bubbles given out at different distances. He repeated the experiment using blue and red light. The results are shown in the graph below. (a) Explain why the number of bubbles decreased as distance d increased.

Experimental setup showing: a beaker containing water and pond weed, with oxygen bubbles being released from the weed. A lamp is positioned at distance d from the beaker, giving out white light. Below this is a line graph with "Number of bubbles" on the y-axis and "Distance d (cm)" on the x-axis. Three curves are shown in the legend: solid line for white light, dashed line for blue light, and dash-dot line for red light. All three curves show a decreasing trend as distance increases, with white light producing the most bubbles at any given distance, followed by blue light, then red light.

📊 Diagram: Experimental setup showing: a beaker containing water and pond weed, with oxygen bubbles being released from the weed. A lamp is positioned at distance d from the beaker, giving out white light. Below this is a line graph with "Number of bubbles" on the y-axis and "Distance d (cm)" on the x-axis. Three curves are shown in the legend: solid line for white light, dashed line for blue light, and dash-dot line for red light. All three curves show a decreasing trend as distance increases, with white light producing the most bubbles at any given distance, followed by blue light, then red light.

1 mark

P6_Science_SA2_2018_-_Maha_Bodhi 2018

Tom had some fishes and pond weeds in his aquarium at home. Based on the results, which coloured light was most suitable for the survival of the fishes? Explain your answer.

1 mark

P6_Science_SA2_2018_-_Maha_Bodhi 2018

Which species of plants best match the dispersal patterns respectively?

Three diagrams showing plant fruits: Species X has a feathery structure; Species Y has a stiff hair structure; Species Z has seeds. Below are three dispersal patterns (A, B, C) shown as 1 km × 1 km grids. Pattern A shows seedlings scattered around a parent plant (marked with arrow for wind direction). Pattern B shows seedlings more densely clustered around a parent plant with wind direction indicated. Pattern C shows seedlings scattered with some distance from the parent plant and wind direction indicated. Key shows: filled circle = parent plant, star symbol = seedlings, arrow = direction of wind.

📊 Diagram: Three diagrams showing plant fruits: Species X has a feathery structure; Species Y has a stiff hair structure; Species Z has seeds. Below are three dispersal patterns (A, B, C) shown as 1 km × 1 km grids. Pattern A shows seedlings scattered around a parent plant (marked with arrow for wind direction). Pattern B shows seedlings more densely clustered around a parent plant with wind direction indicated. Pattern C shows seedlings scattered with some distance from the parent plant and wind direction indicated. Key shows: filled circle = parent plant, star symbol = seedlings, arrow = direction of wind.

A. Species X: B, Species Y: A, Species Z: C

B. Species X: C, Species Y: B, Species Z: A

C. Species X: A, Species Y: B, Species Z: C

D. Species X: B, Species Y: C, Species Z: A

P6_Science_SA2_2018_-_Methodist_Girls 2018

Suresh prepared the set-up below and left it under the sun for 8 hours. Then he tested the leaf for the presence of starch using iodine solution. What would Suresh observe about the colour of iodine when he added it to parts P, Q and R of the leaf after 8 hours?

Experimental set-up showing a plant leaf exposed to sun with three parts labeled P, Q, and R. Part P is covered with black tape on the left side of the leaf. Parts Q and R are on the right side of the leaf exposed to sunlight. The setup includes a plastic bag at the base with pellets to absorb carbon dioxide. The diagram shows the leaf before testing (left) and after testing for starch (right).

📊 Diagram: Experimental set-up showing a plant leaf exposed to sun with three parts labeled P, Q, and R. Part P is covered with black tape on the left side of the leaf. Parts Q and R are on the right side of the leaf exposed to sunlight. The setup includes a plastic bag at the base with pellets to absorb carbon dioxide. The diagram shows the leaf before testing (left) and after testing for starch (right).

P6_Science_SA2_2018_-_Methodist_Girls 2018

The plants given the liquid from the composter will grow healthier than the plants given tap water. Explain why.

1 mark

P6_Science_SA2_2018_-_Nan_Hua 2018

Q10

Other than part (b), name one other environmental benefit of composting. Explain your answer.

1 mark

P6_Science_SA2_2018_-_Nan_Hua 2018

Q11

He noticed that the seeds in both setups could germinate. Explain why they were able to germinate.

Two experimental set-ups shown side by side. Set-up A contains a seed on moist cotton wool in a container. Set-up B contains a seed covered with bird droppings on moist cotton wool in a container. Both setups appear identical except for the presence or absence of bird droppings on the seed.

📊 Diagram: Two experimental set-ups shown side by side. Set-up A contains a seed on moist cotton wool in a container. Set-up B contains a seed covered with bird droppings on moist cotton wool in a container. Both setups appear identical except for the presence or absence of bird droppings on the seed.

1 mark

P6_Science_SA2_2018_-_Nanyang 2018

Q12

Draw the bar graphs to show the amount of oxygen and carbon dioxide in the paper bag after two minutes, based on the key provided. The results for nitrogen has been drawn for you.

A partially completed bar graph with amount (unit) on the y-axis and three gas components on the x-axis: nitrogen, oxygen, and carbon dioxide. The graph shows a key indicating 'before running' (white/empty bars) and 'after running' (hatched/diagonal line bars). The nitrogen bars are already drawn showing: before running approximately 4 units (white bar) and after running approximately 4.5 units (hatched bar). The oxygen and carbon dioxide bars need to be completed by the student.

📊 Diagram: A partially completed bar graph with amount (unit) on the y-axis and three gas components on the x-axis: nitrogen, oxygen, and carbon dioxide. The graph shows a key indicating 'before running' (white/empty bars) and 'after running' (hatched/diagonal line bars). The nitrogen bars are already drawn showing: before running approximately 4 units (white bar) and after running approximately 4.5 units (hatched bar). The oxygen and carbon dioxide bars need to be completed by the student.

1 mark

P6_Science_SA2_2018_-_Nanyang 2018

Q13

Which of the following two activities contribute to an increase in the amount of carbon dioxide in the air?

A: Using a bicycle to get around

B: Using reusable bags when shopping

C: Clearing forest area to make factories

D: Burning trash instead of dumping them into landfills

(1) A and B

(2) A and C

(3) B and D

(4) C and D

P6_Science_2019_Prelims_SA2_-_Anglo_Chinese 2019

Q14

The diagram below shows the cross-section of a deep pond. There are more aquatic plants found at the top part of the deep pond. What is the main reason for such an observation?

Cross-section diagram of a deep pond showing top part with aquatic plants, aquatic animals, and bottom part with sediment. Dashed line separates top and bottom sections.

📊 Diagram: Cross-section diagram of a deep pond showing top part with aquatic plants, aquatic animals, and bottom part with sediment. Dashed line separates top and bottom sections.

A. The aquatic plants can get sufficient nutrients to grow well.

B. The aquatic plants can absorb more sunlight for photosynthesis.

C. The aquatic plants can take in oxygen from the air above the water.

D. The aquatic plants can provide shade and shelter for the aquatic animals living in the pond.

P6_Science_2019_Prelims_SA2_-_CHIJ 2019

Q15

Deforestation can also lead to global warming. Explain why.

1 mark

P6_Science_2019_Prelims_SA2_-_CHIJ 2019

Q16

Based on the experiment, what is the effect of the amount of chemical X on the rate of photosynthesis?

1 mark

P6_Science_2019_Prelims_SA2_-_Catholic_High 2019

Q17

Give a reason why Meili filled the test tube completely with water at the start of the experiment.

1 mark

P6_Science_2019_Prelims_SA2_-_Catholic_High 2019

Q18

Suggest a control set-up to show that the increase in the number of bubbles was caused by chemical X.

1 mark

P6_Science_2019_Prelims_SA2_-_Catholic_High 2019

Q19

Which of the following activities help to keep the environment clean and green?

A: drive to a nearby destination

B: turn unwanted vegetable parts into fertiliser

C: bring your own bag during shopping

D: turn on the air-conditioners all the time

(1) B and C only

(2) A, B and D only

(3) B, C and D only

(4) A, B, C and D

P6_Science_2019_Prelims_SA2_-_Henry_Park 2019

Q20

Based on Graphs 1 and 2, what is the relationship between carbon dioxide levels and temperature in the environment?

Graph 2 shows a line graph with 'Temperature' on the y-axis and 'Year' on the x-axis, spanning from 1998 to 2018. The line shows a general upward trend with fluctuations, starting around 1998 and increasing progressively to 2018, showing a similar pattern to Graph 1.

📊 Diagram: Graph 2 shows a line graph with 'Temperature' on the y-axis and 'Year' on the x-axis, spanning from 1998 to 2018. The line shows a general upward trend with fluctuations, starting around 1998 and increasing progressively to 2018, showing a similar pattern to Graph 1.

1 mark

P6_Science_2019_Prelims_SA2_-_Henry_Park 2019

Q21

Which of the following shows the incorrect way in which organisms obtain energy?

A. sun → plant

B. sun → plant-eater

C. plant-eater → plant and animal eater

D. animal-eater → plant and animal eater

P6_Science_2019_Prelims_SA2_-_Maha_Bodhi 2019

Q22

Fill in the boxes to list the requirements and products of photosynthesis

A diagram showing photosynthesis process with two columns: 'requirements' (left) and 'products' (right). The center box states 'photosynthesis in the presence of light and chlorophyll'. On the left are two empty boxes labeled (i) and (ii) for requirements. On the right are two empty boxes labeled (iii) and (iv) for products. Arrows connect the requirements and products to the central process box.

📊 Diagram: A diagram showing photosynthesis process with two columns: 'requirements' (left) and 'products' (right). The center box states 'photosynthesis in the presence of light and chlorophyll'. On the left are two empty boxes labeled (i) and (ii) for requirements. On the right are two empty boxes labeled (iii) and (iv) for products. Arrows connect the requirements and products to the central process box.

1 mark

P6_Science_2019_Prelims_SA2_-_Maha_Bodhi 2019

Q23

A tank containing some aquatic plants and fish is placed in the garden on a sunny day. Which of the following factor(s) will affect the amount of oxygen in the water?

A rectangular tank with aquatic plants inside and fish. The tank is in sunlight (sun symbol shown above). Labels indicate 'aquatic plants' and 'fish' within the tank. The question refers to three factors: A (the number of fish in the tank), B (the material used to make the tank), and C (the amount of aquatic plants in the tank).

📊 Diagram: A rectangular tank with aquatic plants inside and fish. The tank is in sunlight (sun symbol shown above). Labels indicate 'aquatic plants' and 'fish' within the tank. The question refers to three factors: A (the number of fish in the tank), B (the material used to make the tank), and C (the amount of aquatic plants in the tank).

A. B only

B. C only

C. A and C only

D. A, B and C

P6_Science_2019_Prelims_SA2_-_Maris_Stella 2019

Q24

Based on Muthu's results, what is the relationship between the distance of lamp from the water plant and the rate of photosynthesis? Explain your answer.

Experimental set-up showing a light source positioned at various distances from a container with a water plant submerged in water. Gas P is collected in a tube labeled 'Gas P' at the top. Bubbles are produced by the plant during photosynthesis. A data table shows: Distance of lamp from set-up (cm): 25, 20, 15, 10, 5 and corresponding Number of bubbles per minute: 10, 15, 20, 25, 25.

📊 Diagram: Experimental set-up showing a light source positioned at various distances from a container with a water plant submerged in water. Gas P is collected in a tube labeled 'Gas P' at the top. Bubbles are produced by the plant during photosynthesis. A data table shows: Distance of lamp from set-up (cm): 25, 20, 15, 10, 5 and corresponding Number of bubbles per minute: 10, 15, 20, 25, 25.

2 marks

P6_Science_2019_Prelims_SA2_-_Methodist_Girls 2019

Q25

Muthu prepared another set-up as above without the light source. Explain the purpose of the set-up.

1 mark

P6_Science_2019_Prelims_SA2_-_Methodist_Girls 2019

Q26

What is the relationship between the number of plants grown and the height of the plants?

A graph showing Height of plants (cm) on the y-axis and Number of plants on the x-axis. The x-axis shows values at 10 and 20. The curve shows that plant height decreases from around 10 plants (reaching a minimum), then increases as the number of plants increases beyond 10, with the height continuing to rise towards 20 plants.

📊 Diagram: A graph showing Height of plants (cm) on the y-axis and Number of plants on the x-axis. The x-axis shows values at 10 and 20. The curve shows that plant height decreases from around 10 plants (reaching a minimum), then increases as the number of plants increases beyond 10, with the height continuing to rise towards 20 plants.

2 marks

P6_Science_2019_Prelims_SA2_-_Nanyang 2019

Q27

Draw a diagram using arrows to show how energy from the Sun is passed on to Joel.

📊 Diagram: Empty rectangular box provided for drawing the energy transfer diagram

1 mark

P6_Science_2019_Prelims_SA2_-_Pei_Hwa 2019

Q28

Give a reason why Joel does not get all the energy that the plant obtained from the Sun.

1 mark

P6_Science_2019_Prelims_SA2_-_Pei_Hwa 2019

Q29

Which one of the following graphs correctly shows how carbon dioxide affects the rate of photosynthesis?

📊 Diagram: Four graphs labeled (1) through (4), each showing the relationship between 'Amount of carbon dioxide' (x-axis) and 'Rate of photosynthesis' (y-axis). Graph (1): Shows a curved line starting from origin, rising steeply initially then leveling off asymptotically (saturation curve). Graph (2): Shows a curve starting high and decreasing as carbon dioxide increases (inverse/negative relationship). Graph (3): Shows a horizontal straight line, indicating no change in photosynthesis rate regardless of carbon dioxide amount. Graph (4): Shows a vertical line, indicating instantaneous change at a specific carbon dioxide level.

Graph (1)

Graph (2)

Graph (3)

Graph (4)

P6_Science_2019_Prelims_SA2_-_Raffles_Girls 2019

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