Home / IB MYP Biology – Circulation – Study Notes

IB MYP Biology – Circulation – Study Notes

IB myp 4-5 Biology – Study notes- All Topics

Topic :Metabolism-Circulation

Topic :Metabolism– Weightage : 21 % 

All Questions for Topic : Nutrition,Digestion,Biochemistry and enzymes,Movement and transport,Diffusion,Osmosis,Gas exchange,Circulation,Transpiration and Translocation,Homeostasis

Human Circulatory System

What Is the Circulatory System?

The human circulatory system is the body’s internal transport network. It delivers oxygen, nutrients, and hormones to all body cells and carries away wastes like carbon dioxide and urea.

It Includes:

  • Heart – the pumping station
  • Blood vessels – the pipelines
  • Blood – the transport fluid

Main Functions:

  • Transport of oxygen and nutrients to body cells
  • Removal of carbon dioxide and waste products
  • Circulation of hormones from glands to target organs
  • Helps regulate body temperature
  • Supports the immune system

Double Circulation in Humans

Humans have two circulation loops:

1. Pulmonary Circulation

  • Carries deoxygenated blood from the heart to the lungs
  • Returns oxygenated blood to the heart

2. Systemic Circulation

  • Sends oxygenated blood to the body
  • Returns deoxygenated blood to the heart

Structure and Function of the Heart

FeatureDescription
Chambers4 – two atria (top), two ventricles (bottom)
ValvesPrevent backflow (tricuspid, bicuspid, semilunar)
Right SidePumps deoxygenated blood to the lungs
Left SidePumps oxygenated blood to the rest of the body
Pacemaker (SA node)Controls heartbeat rhythm
HeartbeatCaused by muscle contraction, creates pulse

Blood Flow Path:

  1. Body → Right Atrium (via vena cava)
  2. Right Atrium → Right Ventricle
  3. Right Ventricle → Lungs (via pulmonary artery)
  4. Lungs → Left Atrium (via pulmonary veins)
  5. Left Atrium → Left Ventricle
  6. Left Ventricle → Body (via aorta)

Types of Blood Vessels

TypeFunctionStructure
ArteriesCarry blood away from the heartThick muscular walls, small lumen, no valves
VeinsCarry blood to the heartThin walls, large lumen, valves to prevent backflow
CapillariesAllow exchange between blood and tissuesVery thin (1 cell thick), tiny and branched

Blood Components & Their Roles

ComponentFunction
Red Blood Cells (RBCs)Carry oxygen using hemoglobin
White Blood Cells (WBCs)Defend against infections
PlateletsHelp in blood clotting
PlasmaTransports nutrients, hormones, CO₂, and wastes

Oxygen Transport & High Altitude

Role of RBCs and Hemoglobin:

  • Hemoglobin binds to oxygen in the lungs and releases it in body tissues
  • More RBCs = better oxygen delivery

Effect of High Altitude:

  • Less oxygen in the air
  • Body responds by:
    • Increasing heart rate
    • Producing more hemoglobin
    • Reducing oxygen saturation

Cardiovascular Diseases

  • Atherosclerosis: Fatty deposits narrow the arteries
  • High cholesterol: Increases blockage risk
  • Smoking, high blood pressure, lack of exercise

Treatments

InterventionDescription
AngioplastyBalloon used to open blocked arteries
StentsMesh tube keeps arteries open
StatinsDrugs that lower cholesterol levels

Lifestyle & Heart Health

  • Eat a balanced diet (low in saturated fats)
  • Do regular exercise
  • Avoid smoking
  • Manage stress and check blood pressure

Public Responsibility:

  • Health campaigns (anti-smoking ads)
  • Health education
  • Regular checkups

Key Features of the Circulatory System

  • Closed system: Blood flows only in vessels
  • Double circulation: Blood goes through heart twice
  • Efficient: Delivers oxygen quickly
  • Responsive: Adjusts to exercise and stress

Xylem and Phloem Transport in Plants

What Are Xylem and Phloem?

Plants have a transport system made up of two main tissues:

  • Xylem – moves water and minerals from roots to leaves
  • Phloem – moves sugars (food) made during photosynthesis from leaves to other parts of the plant

These two tissues work like highways inside the plant, helping it survive, grow, and stay healthy.

Xylem – Transport of Water and Minerals

Function:

Carries water and dissolved minerals from the roots to the stem and leaves

Key Features:

  • Made up of dead, hollow cells joined end to end
  • Forms long tubes with no end walls, allowing water to flow easily
  • Lignin in the walls makes them strong and waterproof
  • Transport is one-way only – from roots upwards

How It Works:

  • Water enters the roots by osmosis
  • Water moves up due to:
    • Root pressure = pushing from below
    • Capillary action = narrow tubes draw water up
    • Transpiration pull = the main upward force

Phloem – Transport of Sugars (Translocation)

Function:

Carries glucose and other sugars from the leaves (where they are made) to the rest of the plant

Key Features:

  • Made of living cells called sieve tube elements
  • Sieve tubes have sieve plates at their ends
  • Companion cells provide energy for transport
  • Transport is two-way – up and down the plant

Process Name:

This movement of sugars is called translocation

Why Is Phloem Important?

  • Supplies growing parts like buds and fruits
  • Sends sugars to roots for storage
  • Helps repair damaged parts of the plant

Differences Between Xylem and Phloem

FeatureXylemPhloem
Type of transportWater and mineralsSugars and other nutrients
DirectionOne-way (roots to leaves)Two-way (depends on need)
Cell typeDead cellsLiving cells
Cell structureHollow tubes with thick wallsSieve tubes with sieve plates
Energy requiredPassive (no energy used)Active (needs energy)

Why Is This Transport System Important?

  • Helps plants grow taller and reach sunlight
  • Keeps leaves firm by maintaining water pressure
  • Supplies all plant parts with the substances they need
  • Supports photosynthesis, growth, storage, and repair

Real-Life Example

If you cut a celery stalk and place it in colored water, the color moves up through the xylem. This shows how water travels inside the plant.

If the leaves are removed or damaged, less translocation happens – affecting growth in roots and fruits.

Transpiration Stream

What is Transpiration?

Transpiration is the loss of water vapor from plant leaves, mainly through tiny pores called stomata. It’s a natural process that:

  • Helps pull water upward from roots
  • Cools the plant
  • Transports minerals
  • Supports photosynthesis

Role of Stomata:

  • Stomata are small openings on the underside of leaves.
  • They allow carbon dioxide in and water vapor out.
  • Guard cells control stomatal opening and closing.
  • When open, water evaporates = transpiration happens!

What is the Transpiration Stream?

The transpiration stream is the continuous flow of water from roots → stem → leaves, driven by water loss from the leaves.

Step-by-Step Flow:

  1. Water uptake by roots (osmosis)
  2. Transport upward through xylem vessels
  3. Evaporation from leaf surface via stomata
  4. Transpirational pull creates upward suction

🌡️ Factors That Affect Transpiration

FactorWhat It DoesEffect on Transpiration
LightOpens stomata for photosynthesis⬆ Increases
WindRemoves humid air from leaf surface⬆ Increases
TemperatureSpeeds up evaporation⬆ Increases
HumidityAdds moisture to surrounding air⬇ Decreases

How Do We Measure Transpiration?

We use a tool called a potometer – it measures the rate of water loss in plants.

Types of Potometers:

  • Bubble Potometer: Tracks movement of air bubble to measure rate (e.g. cm/h)
  • Mass Potometer: Measures weight loss – more accurate in sealed systems

Investigating Transpiration

Try These Experiments:

  • Use a fan to vary wind speed
  • Compare leaves of different surface areas
  • Use sealed beakers to track water loss
  • Change light intensity or temperature and record results

Hypothesis Example:

“If fan speed increases, the rate of transpiration will increase because wind removes water vapor faster from the leaf surface.”

Graph Interpretation Skills

  • Plot transpiration rate vs. environmental factor
  • Spot patterns (e.g., higher temp = faster loss)
  • Compare control vs. test groups
  • Suggest improvements (e.g., repeat trials, keep light constant)

Transpiration and Forest Ecosystems

Biotic Pump Hypothesis:

  • Forests transpire large amounts of water
  • Water vapor rises, cools, and forms clouds
  • This pulls in moist air from oceans → causes rainfall

Case Study: Atlantic Forest

  • Deforestation reduces transpiration
  • Less water vapor = fewer clouds
  • Rainfall drops, increasing risk of drought

Water Cycle in Forests:

  • Water evaporates from leaves
  • Rises and cools → forms clouds
  • Clouds rain → repeats the cycle

Scientific Thinking Skills

SkillExample Task
Designing a methodSet up a potometer with fan and thermometer
Building a hypothesisPredict how temperature affects bubble speed
Interpreting graphsDescribe trends and reasons for results
Evaluating methodsSuggest control variables and improvements
Explaining forest impactLink transpiration with rainfall patterns

Key Points to Remember

  • Transpiration: Water loss from leaves via stomata
  • Transpiration Stream: Continuous water flow from root to leaf
  • Xylem: Transports water upwards
  • Potometers: Used to measure transpiration rate
  • Environmental factors: Light, wind, humidity, and temperature affect transpiration
  • Forests: Vital for rainfall due to transpiration
  • Scientific skills: Design, predict, measure, evaluate, and explain
Scroll to Top