Plant System - PSLE Science Study Notes

Key Concepts

Parts of a Plant

Plants have four main parts: roots, stem, leaves, and flowers
Each part has specific structures and functions that help the plant survive
Roots grow underground and anchor the plant
Stem connects the roots to the leaves and flowers
Leaves are usually green and flat
Flowers are the reproductive organs of the plant

Functions of Plant Parts

Roots:

Anchor the plant firmly in the soil
Absorb water and mineral salts from the soil through tiny root hairs
Store food in some plants (e.g., carrots, radishes, sweet potatoes)
Root hairs increase the surface area for absorption

Stem:

Supports the plant and holds up leaves, flowers, and fruits
Transports water and mineral salts from roots to leaves (upward through xylem)
Transports food made in leaves to other parts of the plant (downward through phloem)
Stores food in some plants (e.g., potato, sugarcane)
Some stems are green and can make food through photosynthesis

Leaves:

Main site of photosynthesis - makes food for the plant
Exchanges gases with the environment through tiny pores called stomata
Takes in carbon dioxide for photosynthesis
Releases oxygen as a waste product
Releases water vapour through transpiration
Large, flat surface area to capture maximum sunlight
Contains chlorophyll (green pigment) that traps light energy

Flowers:

Reproduction - produces seeds to grow new plants
Contains male parts (stamens) and/or female parts (carpels/pistils)
Attracts pollinators with bright colours, scent, and nectar
After pollination and fertilization, develops into fruits containing seeds

Transport in Plants

Two transport systems:

Xylem vessels (tubes):
- Transport water and mineral salts
- Move materials upward from roots to stem to leaves
- Made of dead cells forming hollow tubes
- Found closer to the centre of the stem
Phloem vessels (tubes):
- Transport food (sugars made during photosynthesis)
- Move materials up and down to all parts of the plant
- Made of living cells
- Found closer to the outside of the stem

The transport process:

Water enters through root hairs by absorption
Water travels up the xylem due to transpiration pull (water loss from leaves)
Food made in leaves travels through phloem to growing parts and storage organs

Photosynthesis

The process:

Plants make their own food (glucose/sugar) using sunlight energy
Occurs mainly in the leaves, specifically in structures called chloroplasts
Chloroplasts contain chlorophyll (green pigment) which traps light energy

What is needed (Raw materials):

Carbon dioxide - from the air, enters through stomata
Water - from the soil, absorbed by roots and transported via xylem
Light energy - from the sun, trapped by chlorophyll

What is produced:

Glucose (sugar/food) - used for energy, growth, stored as starch
Oxygen - released into the air through stomata as a waste product

Where it happens:

Mainly in leaves (in chloroplasts)
Can occur in green stems

When it happens:

Only in the presence of light (during daytime)
Does not occur in darkness

Important Definitions

Photosynthesis: The process by which green plants make food (glucose) using carbon dioxide, water and light energy. Oxygen is produced as a waste product.

Chlorophyll: The green pigment found in chloroplasts that traps light energy for photosynthesis.

Stomata (singular: stoma): Tiny pores (openings) found mainly on the underside of leaves that allow gases (carbon dioxide in, oxygen and water vapour out) to enter and exit.

Transpiration: The loss of water vapour from the leaves through the stomata.

Xylem: Tube-like structures that transport water and mineral salts upward from the roots to all parts of the plant.

Phloem: Tube-like structures that transport food (sugars) from the leaves to all parts of the plant in both upward and downward directions.

Root hairs: Tiny hair-like structures on roots that increase surface area for absorption of water and mineral salts.

Mineral salts: Nutrients absorbed from the soil that plants need for healthy growth (e.g., nitrogen, phosphorus, potassium).

Chloroplasts: Structures in plant cells (especially in leaf cells) that contain chlorophyll and where photosynthesis takes place.

Diagrams and Structures

Diagram 1: Complete Plant Structure

How to draw:

Draw a plant with roots at the bottom, stem in the middle, leaves and flowers at the top
Below the soil line: Draw branching roots with tiny hair-like projections (root hairs)
Above soil: Draw a vertical stem
Add several leaves attached to the stem (broad, flat, green)
Draw one or two flowers at the top

Labels needed:

Flower (at top)
Leaf (on the side)
Stem (middle vertical part)
Roots (below soil)
Root hairs (tiny projections on roots)
Soil line (to show above/below ground)

Diagram 2: Cross-section of a Stem

How to draw:

Draw a circle (representing a cut through the stem)
In the centre, draw several small circles clustered together (xylem)
Around the outer area, draw small circles in a ring (phloem)
Draw arrows showing direction of transport

Labels needed:

Xylem (centre) - with upward arrow, label “transports water and mineral salts UP”
Phloem (outer area) - with up and down arrows, label “transports food UP and DOWN”

Diagram 3: Structure of a Leaf

How to draw:

Draw a flat, oval leaf shape
Draw a central vein (midrib) running from base to tip
Draw smaller veins branching from the midrib
On the underside (or in a magnified section), draw tiny oval shapes (stomata)

Labels needed:

Leaf blade (flat green part)
Veins (containing xylem and phloem)
Stomata (on underside) - with note “allows gases to enter and exit”

Diagram 4: Photosynthesis Process

How to draw:

Draw a simple leaf shape
Draw the sun above with arrows pointing to the leaf (light energy)
Draw an arrow pointing into the leaf labeled “Carbon dioxide”
Draw an arrow pointing into the leaf from below labeled “Water”
Draw an arrow pointing out labeled “Oxygen”
Inside the leaf write “Glucose (food) made”

Labels needed:

Light energy (from sun)
Carbon dioxide (entering leaf)
Water (from roots via stem)
Oxygen (leaving leaf)
Glucose/Food (produced inside)
Chlorophyll (traps light energy)

Worked Examples

Example 1: Identifying Transport in Plants

Question: A student places a white flower in water containing red dye. After a few hours, red streaks appear in the petals. Explain why this happens.

Step-by-step answer:

Identify what is being transported: The red dye dissolved in water
Identify which transport system: Xylem vessels transport water (and anything dissolved in it)
Describe the direction: Water moves upward from the roots/stem to all parts including the flower
Explain the observation: The red dye travels with the water through the xylem vessels up the stem to the petals
Complete answer:

“The water containing red dye is absorbed and transported upward through the xylem vessels in the stem. The xylem carries the water and dye from the container up to the petals of the flower. This is why red streaks appear in the white petals.”

Key points to include:

Name the transport system (xylem)
State direction (upward)
Mention what is transported (water and dissolved dye)

Example 2: Explaining Photosynthesis

Question: A plant is kept in a dark cupboard for three days. Explain what will happen to the plant and why.

Step-by-step answer:

Identify what process needs light: Photosynthesis requires light energy
State what happens without light: Without light, photosynthesis cannot occur
Explain the consequences: The plant cannot make food (glucose)
Additional effects: The plant will use up stored food and eventually become weak/die
Complete answer:

“The plant will not be able to carry out photosynthesis because there is no light energy. Photosynthesis requires light energy, carbon dioxide and water to make food (glucose). Without light, the plant cannot make food. The plant will use up its stored food and will become weak. The leaves may turn yellow because chlorophyll breaks down without light.”

Key points to include:

Photosynthesis cannot occur without light
Plant cannot make food
Plant will become weak/unhealthy
May mention chlorophyll breakdown

Example 3: Function Analysis

Question: Explain two ways roots are adapted to carry out their function of absorbing water.

Step-by-step answer:

Identify the function: Absorbing water and mineral salts
Identify adaptations:
- Adaptation 1: Root hairs
- Adaptation 2: Branching structure
Explain how each adaptation helps:
Complete answer:

"First adaptation: Roots have many tiny root hairs. These root hairs increase the surface area of the roots in contact with the soil, allowing more water and mineral salts to be absorbed.

Second adaptation: Roots have a branching structure that spreads out in the soil. This increases the volume of soil that the roots can reach, allowing the plant to absorb water and mineral salts from a larger area."

Key points to include:

Name the specific adaptation
Explain how it helps with the function
Use key terms: surface area, absorption

Common Mistakes to Avoid

Mistake 1: Confusing Xylem and Phloem

❌ Wrong: “Phloem transports water up the plant” ✅ Correct: “Xylem transports water and mineral salts upward; Phloem transports food up and down”

Remember: Xylem = Water UP only
Phloem = Food UP and DOWN

Mistake 2: Incomplete Photosynthesis Equations

❌ Wrong: “Plants need light and water to make food” ✅ Correct: “Plants need light energy, carbon dioxide AND water to make food (glucose), and oxygen is released”

Always mention ALL THREE requirements: light energy, carbon dioxide, water
Always mention BOTH products: glucose/food AND oxygen

Mistake 3: Saying Plants Don’t Breathe

❌ Wrong: “Plants don’t need oxygen; they only produce it” ✅ Correct: “Plants produce oxygen during photosynthesis, but they also need oxygen for respiration (to release energy from food) all the time”

Plants respire 24/7 (day and night)
Plants photosynthesize only in light

Mistake 4: Wrong Function of Stomata

❌ Wrong: “Stomata absorb water from the air” ✅ Correct: “Stomata allow carbon dioxide to enter and oxygen and water vapour to exit”

Stomata are for GAS EXCHANGE, not water absorption
Water is absorbed by ROOTS, not leaves

Mistake 5: Forgetting Where Photosynthesis Occurs

❌ Wrong: “Photosynthesis occurs in the whole plant” ✅ Correct: “Photosynthesis occurs mainly in the leaves, specifically in the chloroplasts which contain chlorophyll”

Be specific: leaves (and some green stems)
Mention chloroplasts and chlorophyll when asked for detail

Mistake 6: Incomplete Function Descriptions

❌ Wrong: “Roots absorb water” ✅ Correct: “Roots absorb water AND mineral salts, anchor the plant, and may store food”

Give complete functions when asked
Remember roots absorb both water AND mineral salts (not just water)

Mistake 7: Confusing Transport Direction

❌ Wrong: “Food travels down from the leaves in the xylem” ✅ Correct: “Food travels from the leaves to other parts in the phloem (both upward and downward)”

Check which transport system you’re discussing
Check the direction of movement

Mistake 8: Not Understanding “Made” vs “Used”

❌ Wrong: “Plants use carbon dioxide, water and light to grow” ✅ Correct: “Plants use carbon dioxide, water and light energy to make food (glucose). The food is then used for growth and energy”

Light energy is used to MAKE food
Food (glucose) is then used for growth, energy, storage

Exam Tips

For Definition Questions:

Use the exact keywords from your definition
For photosynthesis, always include:
- “Process by which”
- “green plants”
- “make food/glucose”
- “using carbon dioxide, water and light energy”
- “oxygen is released/produced”

For Function Questions:

List ALL main functions, not just one
Use action verbs: absorbs, transports, makes, supports, stores, anchors
Be specific: don’t just say “for the plant” - say HOW it helps

For Diagram Questions:

Draw neat, labeled lines with a ruler
Label lines should not cross each other
Write labels horizontally (not at angles)
Use pencil for drawing, pen for labels
Make diagrams large enough to show detail

For Transport Questions:

Always specify WHICH transport system (xylem or phloem)
Always specify WHAT is being transported
Always specify DIRECTION (upward/downward/both)
Example: “Water and mineral salts are transported UPWARD through the XYLEM from roots to leaves”

For Photosynthesis Questions:

Magic formula - always write all parts:

Raw materials needed: carbon dioxide + water + light energy
Where: leaves (chloroplasts)
What’s needed in leaves: chlorophyll
Products: glucose/food + oxygen
When: in the presence of light only

Keywords That Earn Marks:

“Surface area” (when discussing root hairs or leaf structure)
“Absorb” or “absorption” (for roots and water/mineral salts)
“Transport” (not just “carry” or “move”)
“Upward” and “downward” (for direction)
“Chlorophyll” (for photosynthesis)
“Stomata” (for gas exchange)
“Anchor” (for root function)

For “Explain” Questions:

State WHAT happens
Explain WHY it happens
Link to the function or process

Example: “Root hairs increase the surface area (WHAT). This allows more water and mineral salts to be absorbed (WHY/LINK TO FUNCTION).”

For Comparison Questions:

Use a clear structure:

“Xylem transports… while phloem transports…”
“Xylem moves materials upward only, whereas phloem moves materials both upward and downward”
Make the contrast clear with comparison words: while, whereas, but, however

Quick Summary

Essential points to remember for exam:

✓ Four main parts of a plant: roots, stem, leaves, flowers - each with specific functions

✓ Roots: Absorb water and mineral salts, anchor plant, may store food; root hairs increase surface area

✓ Stem: Supports plant, transports materials, may store food; contains xylem and phloem

✓ Leaves: Main site of photosynthesis, gas exchange through stomata, large flat surface to trap light

✓ Flowers: Reproduction - produce seeds to grow new plants

✓ Xylem: Transports water and mineral salts UPWARD ONLY from roots to all parts

✓ Phloem: Transports food (sugars) UP AND DOWN from leaves to all parts

✓ Photosynthesis equation: Carbon dioxide + Water + Light energy → Glucose (food) + Oxygen

✓ Photosynthesis location: Mainly in leaves, in chloroplasts containing chlorophyll

✓ Photosynthesis timing: Only occurs in the presence of light (not in darkness)

✓ Stomata function: Allow carbon dioxide to enter, oxygen and water vapour to exit (gas exchange)

✓ Complete functions: When listing functions, give ALL main functions, not just one; be specific and use correct terminology

Remember: In exams, read questions carefully for how many points to give, use scientific terms correctly, and always explain your answers fully with the “what” and “why”!