- IB DP Biology 2025 SL- IB Style Practice Questions with Answer-Topic Wise-Paper 1
- IB DP Biology 2025 HL- IB Style Practice Questions with Answer-Topic Wise-Paper 1
- IB DP Biology 2025 SL- IB Style Practice Questions with Answer-Topic Wise-Paper 2
- IB DP Biology 2025 HL- IB Style Practice Questions with Answer-Topic Wise-Paper 2
B3.2-1 Transport in animals: The circulatory system
Heart and Circulation in Animals
All organism respire
Cell respiration releases energy , needed for cell activities
movement, beating of heart and breathing movements
Oxygen + Glucose needed to release energy
Respiration that needs oxygen = aerobic respiration
Gas exchange :
- Getting oxygen from the environment
- Releasing CO2 to environment
Gas exchanges occur by diffusion across cell membrane
Gas exchange surface = Surface of the organism dedicated to gas exchanges
All organisms respire, grow, respond, reproduce…
These activities need energy, amino acids, hormones…
Nutrients and hormones needed to perform these activities
Transport/ Circulation = distributing molecules/ions where needed
-Needed all over the body
-Need for a circulatory system to all over the body
Circulatory system = system of organs to transport and distribute molecules and ions
Why is the need for a transport system inside large organisms ?
If cell size increases,
The distance from the centre of cell to its exterior increases
– Exchanges with environment become more challenging
Small organisms have a large SA/V ratio
– Cells directly in contact with environment
– Can exchange material easily with environment
Bigger organisms have a small SA/V ratio
– Cells mostly very far from environment
– Cannot exchange material easily with environment
– To reach cells inside the body, Need to transport substances to these cells (Oxygen, nutrients…) from these cells (Waste)
– Need a transportation system
The circulatory system
Heart, blood, arteries, veins…
Heart = PUMP
Gives blood pressure to
1. Exit the heart through arteries,
2. Reach tissues and lungs,
3. Re-enter the heart through veins
Blood pressure is highest when exits heart
Then decreases
Low when reaches capillaries
Very low in veins
Lowest when enters heart again
Arteries carry blood away from the heart
Veins carry blood into the heart
- Blood pressure is highest when exits heart
Then decreases - Low when reaches capillaries
- Very low in veins
- Lowest when enters heart again
Arteries, veins and capillaries are adapted to different blood pressures.
Structures and functions of blood vessels
- Arteries: Carry blood away from the heart
- Capillaries: Link arteries to veins
Exchange of materials between blood and cells (lungs, tissues) , Lungs: +O2 – CO2 , Tissues: -O2 + CO2 - Veins: Carry blood into the heart
- Arteries
Withstand and maintain high blood pressure from the heart
- Small lumen
Keep higher pressure from heart - Thick smooth muscle layer
Helps the flow of blood by contracting - Thick elastic layer
Elastic recoil after contraction - Outer coat contains collagen
Prevents from bursting - No valves
- Veins
- Large lumen
Keeps blood pressure until the heart - Thin smooth muscle layer
Keeps the flow of blood by contracting - Thin elastic layer
elastic recoil after contraction - Valves
Flexible wall facilitates return of blood to the heart
- Capillaries
- Very small lumen
- No muscle
- No elastic layer
- No valves
- One cell-thick wall
Thin wall – one-cell thick – short diffusion distance
Numerous and highly branched – large Surface Area for diffusion
Narrow diameter – keep all cells close by
Narrow lumen – bring RBC close to the cells = short diffusion distance
Size of lumen just more than enough for RBC
Fenestration = Spaces between cells – allow fast exchanges and WBC to escape
- Identify an artery, a vein and a capillary on the micrograph
Ans.
Coronary heart disease
- CHD and heart attacks
A part of thrombus breaks away
= Embolus
Carried away by blood flow
Single or double circulation (HL only)
In bony fish:
Blood flows ONCE through the heart
Single Circulation
Heart = “single pump”
1. Deoxygenated blood pumped by heart
2. Gets oxygenated in the gills
3. Oxygenated blood gives oxygen to tissues
4. Deoxygenated blood back to heart
Between 1 and 2, blood pressure decreases Blood flow slows down in 3
Delivery of \(O_2\) to cells is limited
Mammals need much more \(O_2\) than fish (higher metabolism, maintenance of body temperature)
Mammals cannot use single circulation
In mammals:
Blood flows TWICE through the heart
Double Circulation
Heart = “double pump”
1. Deoxygenated blood pumped by heart
2. Gets oxygenated in the lungs
3. Oxygenated blood back to heart
4. Oxygenated blood pumped by heart
5. Oxygenated blood gives oxygen to the tissues
6. Deoxygenated blood back to heart
Structure of the mammalian heart (HL only)
- Heart’s position in thorax
- Internal view of the heart
Cardiac Cycle (HL only)
The septum separates the left and right sides of the heart
The vena cava carry deoxygenated blood from the body to the right atrium
The right atrium collects deoxygenated blood and pumps it to the right ventricle
The right ventricle pumps deoxygenated blood into the pulmonary artery
The pulmonary arteries carry deoxygenated blood from the right ventricle to the lungs
In the lungs
\(CO_2\) diffuses from the blood into the alveoli
Oxygen diffuses from the alveoli into the blood
Deoxygenated blood becomes oxygenated blood
The pulmonary veins carry oxygenated blood from the lungs to the left atrium
The left atrium collects the oxygenated blood and pumps it to the left ventricle
The left ventricle pumps oxygenated blood to the body via the aorta
The artery named aorta carries oxygenated blood from the left ventricle to the rest of the body
In the rest of the body
\(O_2\) diffuses from the blood into the cells
\(CO_2\) diffuses from the cells into the blood
Oxygenated blood becomes deoxygenated blood
Atrio-ventricular valves prevent backflow of blood into the atria when ventricles contract
Semi-lunar valves prevent backflow of blood from arteries into the ventricles when ventricles relax
Thickness of walls of ventricles
Pulmonary circulation way shorter than systemic circulation
Systemic circulation needs higher pressure than pulmonary circulation
Muscles around left ventricle way thicker than those around right ventricle
Origin and control of the heart rate
- Muscles around four chambers of the heart contract rhythmically
- All muscles except the cardiac muscles require external stimulation to contract
- External stimulation via action potential reaching the muscles
- Cardiac muscles contract in response to stimulation within the heart
- Heart beat is myogenic = generated by the muscles themselves
- Origin of stimulation = sino-atrial node = SAN = natural pacemaker
- Cluster of cells inside top left part of muscles around of right atrium
- SAN generates nerve impulse
- Impulse radiates through muscles fibers of both atria
Atria contract = atrial systole
To ensure the right one-way flow of blood through the heart, atria have to contract before ventricles do:
- Impulse generated by SAN should NOT reach ventricles directly
If it did, ventricles would contract at the same time as atria
Speed of nerve impulse = 100 m/s - Tissue between atria and ventricles prevent impulse from SAN to reach ventricles
- Nerve impulse from SAN reaches another node = AVN = atrio-ventricular node
AVN at the bottom right part of right atrium
1. AVN picks up nerve impulse from SAN
2. AVN sends nerve impulse between ventricles along Bundle of His
Bundle of His = muscle fibres modified to transmit nerve impulse
Bundle of His passes nerve impulse to Purkinje fibres
Purkinje fibres = muscle fibres modified to transmit nerve impulse
Purkinje fibres – contract: ventricle systole
– transmit nerve impulse to next Purkinje fibres
Contraction of ventricles starts at the bottom of the heart
Propagates up the ventricles
Ensures flow of blood towards arteries
Pressure is everything
Two phenomena
Diastole = relaxation
Systole = contraction
For the 2 atria and the 2 ventricles
Three stages
1. Diastole of both Atria and Ventricles
2. Atrial systole + Ventricular diastole
3.Ventricular systole + Atrial diastole
- Measuring systolic and diastolic blood pressure with a sphygmomanometer (a.k.a. pressure cuff)
- The cuff is inflated and blood flow is monitored in the arm (brachial) artery at the elbow, using the stethoscope. Inflation is continued until there is no sound (that is, no flow of blood, because the cuff has completely occluded the artery).
- Air is now allowed to escape from the cuff slowly, until blood can just be heard sputting through the constriction point in the artery. This pressure at the cuff is recorded, for it is equal to the maximum pressure created by the heart(systolic pressure).
- Pressure in the cuff is allowed to drop until the blood can be heard flowing constantly. This is the lowest pressure the blood falls to between beats (diastolic pressure).
Electrocardiogram = ECG
Measures electrical signals through the heart
“P” wave : atrial depolarisation and contraction
“QRS” waves complex: depolarisation and contraction of the ventricles
QRS much larger than “P” wave (ventricles’ muscles are much larger than the atria’s muscles)
“T” wave : repolarization and relaxation of the ventricles
Repolarisation of the atria is masked by the “QRS” complex
Tissue fluid, capillaries and lymph ducts (HL only)
Tissue fluid bathes cells of tissues aka interstitial fluid
Arterioles: Tissue fluid production from blood
Veinules: Reuptake from tissue fluid into blood
- Blood pressure is highest when exits heart
Then decrease - Low when reaches capillaries
- Very low in veins
- Lowest when enters heart again
Arteries, veins and capillaries are adapted to different blood pressures
Pressure filtration
= production of tissue fluid through fenestrations
Reuptake
= drain back of tissue fluid through fenestrations
Water and Waste products exit cells
Re- uptaken from tissue fluid into veinules
Water, Nutrients, oxygen, hormones
from arterioles to tissue fluid
by pressure filtration
then diffuse into cells
Plasma and tissue fluid
• The yellowish liquid part of blood
• 90% is water
• Transports dissolved substances :
• Glucose
• CO2
• Hormones
• Mineral salts
• Nitrogenous waste
Lymph
Lymphatic system
Production of white blood cells Protection against pathogens
Absorb lipids from food
Osmoregulation
Remove cell waste
- Excess tissue fluid enters lymph ducts
Pressure in lymph ducts - Movement of lymph in ducts
Valves in duct ensure one-way lymph transport - Lymph returned to blood circulation
- Excess tissue fluid enters lymph ducts
Pressure in lymph ducts - Movement of lymph in ducts
Valves in duct ensure one-way lymph transport - Lymph returned to blood circulation
B3.2-2 Transport in plants: Xylem and Phloem
Transport of water from roots to leaves
- Importance of Water to Plants
Reasons why plants need appropriate amounts of water:
1. 80% of a plant cell is water
2. Water = environment of all chemical reactions
3. Support of plants depends on turgidity
4. Gas exchanges only possible when stomata are opened
Stomata are opened only when turgid
5. To avoid wilting, water evaporating from inner moist surfaces must be replaced
Stomata on lower leaf epidermis
Transpiration = water loss through stomata of leaves
Stomata only open in daylight
Opened stomata
– Gas exchanges possible
– Photosynthesis: \(CO_2\) in \(O_2\) out \(O_2\) used for respiration
– Water vapour diffuses out
Light provides energy for
– photosynthesis (photolysis of water)
and for
– evaporation of water into water
vapour in air spaces in mesophyll
Evaporation cools down
leaf cells
Plants transport water from roots up to leaves through xylem vessels
Water in xylem
Pulled up by transpiration
Pulled down by gravity
Two opposite forces
– Tension in water in xylem
– Water drawn up
Adaptations of xylem vessels for transport of water
Xylem vessels
- Dead cells, all cell components gone
- Cells on top of each other
- End cell walls broken down
Continuous narrow tubes (Flow upwards unimpeded ) - Water and minerals transported
without barrier from roots to top - Strengthened by lignin(Withstand tension)
- Holes in lignin = pits
Water moves between vessels
Xylem and phloem vessels
Anatomy of stems in dicotyledonous plants
Flowering Plants: Monocots or Eudicots
Anatomy of roots in dicotyledonous plants
Generation of root pressure in xylem vessels (HL only)
Mineral ions are actively transported from soil to Xylem
- Mineral ions enter the root hair cells by
Diffusion/Facilitated diffusion or Active transport
Depending on concentration gradient soil to root hair cells - Most mineral ions are more concentrated in soil
Mostly active transport: \(K^{+} Cl^{-} Ca^{2+} Mg^{2+} Na^{+} NO^{-}_{3}\)
Many mitochondria in root hair cells - Selective absorption
Depending on the plant’s needs - Ways of transport: dissolved in water
Up the xylem towards transpiring leaves
Water follows by osmosis from soil to Xylem
Usefulness of root pressure
Adaptations of phloem sieve tubes and companion cells for
translocation of sap (HL only)
Mass/Pressure-flow hypothesis/theory
• Explains how sap moves in a plant from source to sink:
– Sucrose from source is actively pumped into phloem sieve tube cells
– Osmosis moves water into the cells and raises pressure.
– Pressure moves the sap
Pressure flow 1
• In leaves
• Photosynthesis
• Produces Glucose and Fructose
• Combined to make sucrose
Pressure flow 2
• Active transport is used to load sucrose into phloem SET against a diffusion gradient.
Phloem loading
Pressure flow 3
• High concentration of sucrose in the sieve tube cells
• Water moves from xylem to STE by osmosis,
• Pressure raises in STE
• Sap moves from high pressure to low pressure
Pressure flow4
• A developing fruit is one example of a sink
Sucrose actively
– transported out of phloem into the fruit cells.
• In a root, sucrose is converted into starch,
Keeps sugar moving in by diffusion.
Pressure flow 5
• Sugar concentration drops in the sieve tube cells
• Osmosis moves water out of the tube into fruit
Pressure flow 6
• As water moves out by osmosis,
Pressure in the sieve tube cells drops.
The pressure difference along the column of sieve tube cells keeps the sap flowing.
Review
Sieve tube elements and companion cells
STE:
– Live cells
– No nucleus
– SER
– Elongated and widened
– Thick primary cell wall
– Between two STE: sieve plate
– Callose
– Center cytoplasm: no organelles
– No tonoplast
– Slimy sap + protein strands
– Transports sap
Companion cells:
– Live cells
– Large nucleus
– Many mitochondria
Cellular functions of STE are performed by CC
Exchange of materials: cytoplasms are connected via plasmodesmata