Q: What does IP Combined Science Notes (Lower Sec, Year 1-2): 06) Transport Systems in Humans & Plants cover? A: Track nutrient and gas transport in humans and plants, including circulation, transpiration, and phloem flow calculations.
Transport systems move substances efficiently over distances too large for diffusion alone. Understand structure-function relationships to explain oxygen delivery, sugar transport, and water movement.
These notes align with MOE's Lower Secondary Science syllabus themes commonly taught in IP Sec 1-2, and act as a bridge into upper-secondary Physics, Chemistry, and Biology.
Status: MOE Lower Secondary Science syllabus (current release) checked 2025-11-30 - scope unchanged; remains the reference for these combined science notes.
The core idea is simple: Transport systems move substances too far for diffusion alone.
Use it as a working check: In humans, track blood through heart, lungs, and body. In plants, separate xylem water transport from phloem sugar transport.
Then go one layer deeper: Example: exercise raises heart rate and stroke volume, so cardiac output rises and more oxygen reaches working muscles each minute.
Learning targets
Describe the structure of the human circulatory system and pathway of blood flow.
Use cardiac output formulas to solve numerical problems and compare fitness levels.
Explain the roles of xylem and phloem, including adaptations for their functions.
Analyse factors affecting transpiration rate and interpret potometer data.
Exchange gases, nutrients, and wastes with tissues.
Capillary exchange checkpoint
When explaining capillaries, connect structure to exchange direction. Do not stop at "thin walls"; say what moves, where it moves from, and why the short distance matters.
blood in capillary
-> oxygen and glucose diffuse to body cells
-> carbon dioxide and other wastes diffuse into blood
-> one-cell-thick wall keeps the diffusion distance short
Substance
Main direction at body tissues
Reason to write
Common trap
Oxygen
From blood to body cells
Cells use oxygen for aerobic respiration.
Saying oxygen leaves the body at every capillary.
Glucose
From blood to body cells
Cells need glucose as a respiratory substrate.
Treating glucose like a waste product.
Carbon dioxide
From body cells to blood
Cells produce carbon dioxide during respiration.
Saying carbon dioxide moves into cells for respiration.
Urea and other wastes
From body cells to blood
Blood carries wastes to organs that remove them.
Forgetting that exchange includes wastes, not only gases.
Worked check: after exercise, muscle cells use more oxygen and glucose and produce more carbon dioxide. Capillaries allow these substances to move between blood and muscle cells quickly because the wall is only one cell thick.
Misconception check: capillaries do not "pump" substances into cells. The heart moves blood; diffusion moves many small substances across the capillary wall.
Blood pathway (systemic circuit)
Left ventricle→Aorta→Body→Vena cava→Right atrium.
Pulmonary circuit mirrors this with lungs as the gas-exchange site.
Blood route map
Use this map to avoid mixing up the two circuits:
body cells
give carbon dioxide to blood
|
v
right side of heart
sends blood to lungs
|
v
lungs
carbon dioxide leaves, oxygen enters
|
v
left side of heart
sends oxygenated blood to body cells
Common trap: arteries are named by direction, not by oxygen content. An artery carries blood away from the heart, so the pulmonary artery carries deoxygenated blood from the heart to the lungs.
Cardiac output calculation
Cardiac output=Stroke volume×Heart rate.
Cardiac output unit checkpoint
Before multiplying, make sure stroke volume and heart rate describe the same time scale.
Given information
First check
Calculation move
Common trap
Stroke volume in mL⋅beat−1, heart rate in beats⋅min−1
Units already cancel beats.
Multiply to get mL⋅min−1.
Dropping "per minute" from the final answer.
Stroke volume in mL, heartbeats counted in 30s
Convert the count to beats per minute.
Double the 30-second count before multiplying.
Multiplying by the 30-second count and calling it mL⋅min−1
Final answer requested in L⋅min−1
Convert millilitres to litres.
Divide mL⋅min−1
Worked check: If stroke volume is 70mL⋅beat−1 and a pulse count is 36 beats in 30s, heart rate is 72beats⋅min−1. Cardiac output is 70×72=5040mL⋅min−1=5.04L⋅min−1.
Misconception check: cardiac output is a rate. A larger number of beats only means more blood per minute after the time interval has been converted correctly.
Worked example
An athlete has stroke volume 75mL at rest and heart rate 58beats⋅min−1.
CO=75×58=4350mL⋅min−1=4.35L⋅min−1.
During exercise, heart rate rises to 150beats⋅min−1 with stroke volume 120mL:
CO=120×150=18000mL⋅min−1=18.0L⋅min−1.
2 Blood components
Red blood cells: transport OX2 via haemoglobin.
White blood cells: immune defence (phagocytosis, antibody production).
Platelets: clot formation.
Plasma: transports nutrients, hormones, COX2, and waste products.
3 Plant transport
Tissue
Structure
Function
Xylem
Dead, hollow vessels; lignified walls.
Carries water and mineral salts mainly upward from roots to leaves; lignin also supports the plant.
Phloem
Living sieve tube elements with companion cells.
Carries sugars from sources such as leaves to sinks such as growing tissues, roots, fruits, or storage organs.
Plant transport route map
Keep xylem and phloem separate in explanations:
xylem route
roots absorb water and mineral salts
|
v
xylem carries them upward
|
v
leaves use water in photosynthesis and lose water vapour by transpiration
phloem route
leaves make sugars by photosynthesis
|
v
phloem carries sugars to sinks
|
v
growing tips, roots, fruits, and storage tissues use or store the sugars
Common trap: xylem is about water and mineral salts, while phloem is about sugars. Do not say that transpiration directly moves food; transpiration pull mainly helps move water through xylem.
Phloem source-sink checkpoint
For phloem questions, decide where sugars are being made and where they are being used or stored before choosing a direction. The same plant can move sugars in different directions at different times.
Plant situation
Source to name
Sink to name
Direction to explain
Common trap
Sunny mature leaf feeding a growing shoot
Leaf making sugars by photosynthesis
Growing shoot tip
From leaf to shoot
Saying phloem always moves upward.
Leaf sending sugars to roots for storage
Leaf making sugars by photosynthesis
Root storage tissue
From leaf to roots
Treating roots as only water-absorbing organs.
Germinating seedling before many leaves open
Stored food in seed or storage organ
Young growing shoot and root
From store to growing regions
Saying leaves must always be the source.
Worked check: if a question says a plant is storing sugars in a root, the leaf is the source and the root is the sink, so sugar moves down through phloem. If the stored food is later used by a new shoot, the storage organ becomes the source and the shoot becomes the sink.
Misconception check: xylem has one main upward water route, but phloem direction depends on source and sink. Do not answer phloem questions with "up" or "down" until you have identified both.
Transpiration factors
Factor
Effect on rate
Light intensity
Increases (stomata open for photosynthesis).
Temperature
Increases (higher kinetic energy and evaporation).
Humidity
Decreases (reduced concentration gradient).
Wind speed
Increases (removes saturated air).
Transpiration direction checkpoint
When a question changes one condition, write the answer in three steps: condition change, gradient or stomata change, then rate change.
Question wording
First change to state
Why the rate changes
Common trap
Higher temperature
Faster evaporation from leaf surfaces
More water vapour leaves the air spaces in the leaf
Saying only "particles move faster" without linking to evaporation.
Higher humidity
Smaller water-vapour gradient
Water vapour diffuses out of the leaf more slowly
Saying humid air makes the plant lose more water because there is more water in the air.
Stronger wind
Moist air is removed from around the leaf
A steep diffusion gradient is maintained
Saying wind directly pulls water up the xylem.
Lower light intensity
Stomata may close more
Less water vapour escapes through stomata
Treating light as heat only and ignoring stomatal opening.
Misconception check: do not memorise every factor as "more means faster". Higher humidity slows transpiration because the outside air is already more water-rich.
Potometer question
Water level in a capillary tube drops 12mm in 5min. Tube radius 0.50mm.
Discuss how ensuring airtight seals and cutting the stem underwater improves accuracy.
Try it yourself
Compare artery and vein structures in terms of elasticity, muscle thickness, and presence of valves.
Describe how guard cells regulate stomatal opening in response to light and water status.
A student records that a plant loses 0.75g of mass overnight due to transpiration. Assuming density of water =1g⋅cm−3, calculate the average volume of water lost per hour and suggest two methods to reduce further loss.
