B3.1 - Gas exchange, B3.2 - Transport, and D2.3 - Water potential

Movement of water

Water moves from a solution with low solute concentration to high solute concentration

Hypotonic solution

Low solute concentration

Hypertonic

High solute concentration

Isotonic

Solute concentration is equal to solvent concentration

Cells in hypotonic solution

Water moves into cell, cell bursts

Cells in hypertonic solution

Water moves out of cell, cell shrinks

Cells in isotonic solution

Water moves both ways, cell volume stays stable (dynamic equilibrium)

Special cases in osmosis

Freshwater unicellular organisms (eg. amoeba proteus): lack cell walls, always take in water by osmosis and use contractile vacuoles to pump excess water and prevent bursting.

Cell wall in isotonic solution

Will be flaccid (turgor pressure)

Cell wall in hypertonic solution

Will undergo plasmolysis (membrane pulls away from cell wall)

Cell walls in hypotonic solution

Will become turgid (swollen)

Why do doctors use isotonic solutions?

Keep cells healthy due to equal movement of water

Why is saline used as the primary isotonic solution?

Consists of 0/9% NaCl, which closely matches the concentration in body fluids

Applications of saline

Iv drip (rehydration), Wound/skin irrigation (clean wounds), Eye drops (safe moisture), Organ preservation before transplants

Water potential

Measures potential energy of water pr unit volume.

Water potential formula

Pressure potential + Solute potential

Direction of water in terms of water potential

Water moves from high water potential to low water potential areas

Values of water potential

Pure water has water potential of 0 Kpa, Cells contain solutes so water potential is negative.

Solute potential

Adding more solutes makes water potential more negative, solutes reduce free water molecules, decreasing potential energy.

Pressure potential

Positive pressure = water potential > 0 (turgor pressure in plant cells)
Negative pressure = Water potential < 0 (tension in xylem vessels pulling water upward)
Pressure potential = 0 at atmospheric pressure

Water potential in hypotonic solutions

Water potential is higher outside, water moves into cells, making cell turgid and pressure builds up

Water potential in hypertonic solutions

Water potential is lower outside cell, water moves out of cell, cell turns plasmolysed and cell shrinks.

For efficient gas exchange to happen, surfaces must:

Have a large surface area, be thin, use a ventilation, be moist, be close to transport system

Thin tissue layer as efficient gas exchange

Should typically be 1 cell thick to minimize diffusion distance

Permeability as efficient gas exchange

Most allow oxygen and carbon dioxide to diffuse freely

Moisture as efficient gas exchange

Gases must dissolve in water

Large surface area as efficient gas exchange

increases amount of gas tha can diffuse at one time

Dense network of blood vessels as maintenance of concentration gradients

quickly carry oxygen away and deliver carbon dioxide from body tissues, ensures blood ear surface is always low in oxygen and high in carbon dioxide.

Continuous blood flow as maintenance of concentration gradients

Prevents buildup of oxygen or slow removal of carbon dioxide

Ventilation as maintenance of concentration gradients

Ensures external side of surface stays high in oxygen and low in carbon dioxide

Adaptations of lungs on gas exchange

Alveoli: Abut 300 million present, providing high surface area
Very thin walls: alveolar and capillary walls are one cell thick
Surfactant production: Type II pneumocytes produce surfactant, fluid that reduces surface tension and prevent alveoli from collapsing
Dense capillary networks
Highly bronchial tree: increases surface area
Ventilation: maintains gradients

Inhalation

1) diaphragm contracts and moves downwards 2) External intercostal moves contracts, ribs move up and out 3) Thoracic cavity volume increases 4) Pressure inside lungs drops below atmospheric pressure 5) Air flows into lungs

Exhalation

1) Diaphragm relaxes and moves upwards 2) External intercostal muscles relaxes, ribs move down and in 3) Thoracic cavity volume decreases 4) Pressure inside lungs increases above atmosphere pressure 5) Air flows out of the lungs

Vital capacity

Tidal volume + Inspiratory reserve + Expiratory reserve

Tidal volume

Air breathed in and out at rest

Inspiratory reserve

Extra air you forcefully inhale

Expiratory reserve

Maximum air exhaled after a full inhalation

Residual volume

Air left in lungs after exhalation

Total lung capacity

Vital capacity + residual volume

Adaptations for gas exchange in leaves

Waxy cuticle: thin, waterproof layer that reduces water loss but allows light to pass through
Spongy mesophyll: Loosely packed cells with air spaces to allow easy gas diffusion
Air spaces: Allows carbon dioxide and oxygen to diffuse quickly
Stomata: Lets carbon dioxide and oxygen enter and exit
Guard cells: Surround each stomata and control opening/closing
Veins: Xylem brings water and phloem carries sugars away

Transpiration

loss of water vapor from surface of leaves, mainly through stomata

Factors affecting transpiration

Light intensity: More light, stomata opens wider, more water loss
Temp: Warmer air holds more water vapor, increases evaporation rate
Humidity: High humidity, reduced water potential, slows transpiration
Wind/Air movement: Wind removes humid air near stomata, maintains steep gradient
Soil water availability: Dry soil limits water uptake, reduces transpiration

Cooperative binding

When first oxygen binds to haemoglobin, it causes a conformational change, making it easier for the next 3 oxygens to bind, leading to sigmoidal oxygen dissociation curve

Fetal haemoglobin

HIgh oxygen affinity as it takes oxygen from maternal blood, shifts curve left

Adult haemoglobin

Lower oxygen affinity due to high exposure of oxygen, shifts curve right slightly

Left shift is caused by

increases affnity of oxygen, decreased temp. and higher pH

right shift is caused by

decrease in affinity of oxygen, increased temp and lower pH

Bohr effect

Carbon dioxide binds to haemoglobin allosterically, changing haemoglobins shape and reduces oxygen affinity

Bohr shift

1) cells respire and release carbon dioxide 2) Carbon dioxide dissolves and reacts with water to form carbonic acid 3) Carbonic acid releases hydrogen ions and lowers blood pH 4) Hydrogen ions bind to haemoglobin, changing its shape 5) Reduces Haemoglobin’s affinity for Oxygen, oxygen is reduced more easily

Benefits of bohr shift

Supports high respiration rate, helps maintain homeostasis, efficient oxygen under stress

Reason for sigmoidal curve

As first oxygen binds, the affinity for oxygen is low, so curve starts to shallow, at 2nd and 3rd oxygen, affinity increases and curve steepens, and at last oxygen affinity decreases and curve flattens.

Capillaries

Smallest blood vessels in body, exchange substances such as oxygen, carbon dioxide, and nutrients

Adaptations of capillaries

Large surface area: Dense capillary networks around tissues, allowing for more diffusion
Narrow lumen: Only one RBC at a time, slowing flow which allows more time for exchange
Thin walls: Made of single layer epithelial cells, which allows for a very short diffusion distance
Fenestrations: In kidneys, intestines, and endocrine glands, allowing for passage of material rapidly

Arteries

Carry blood away from the heart

Veins

Carry blood into the heart

Components of arteries

Small lumen: maintains high pressure
Thick smooth muscle: Contracts to push blood
Thich elastic tissue
Collagen: Prevents rupture
No valves: Blood flows in one direction

Components of veins

Large lumen: Holds more blood
Thin smooth muscle: Less need to push blood
Thin elastic tissue
Valves: Prevents backflow
Flexible wall: Works with skeletal muscles to move blood

Adaptations for arteries for transporting blood

Smooth muscle layer: Helps control blood flow by vasoconstriction and vasodilation
Elastic fibres in middle layer: Allows artery to stretch and recoil with each heartbeat
Narrow lumen: increases resistance to help maintain high pressure
Smooth endothelium: Reduces friction to help maintain high pressure
No valves: High pressure prevents backflow

Adaptations of veins for returning blood to heart

Valves: Prevents backflow
Thin, flexible walls: Allows veins to be easily compressed by surrounding skeletal muscles during movement
Wide lumen: Reduces resistance
Located near muscles: Muscle contractions squeeze veins, pushing blood upward
Low elasticity: Not needed as veins don’t need to stretch and recoil

Occlusion

Blockage/closing of a blood vessel. In coronary arteries (supply oxygen and nutrients), this is caused by build up of fatty deposits in artery walls

Causes of cornoary artery occlusion

Atherosclerosis, High LDL, High blood pressure, smoking, diabetes, lack of exercise, diet high in saturated fats, genetics, age and gender

Consequences of occlusion

Angina, heart attack, arrhythmias, sudden cardiac death

How water moves through plant

Water evaporates from moist cell walls of mesophyll cells into air spaces in the leaf, then diffuses through stomata which causes a drop in water potential, water is drawn out of xylem vessels in the leaf to replace lost water, created tension pulls water upward from the roots through the stem. Due to cohesion, water molecules stick together and form an unbroken column from roots to leaves.

Key forces involved in transpiration

Transpiration pull: Negative pressure created by water loss pulls water upwards through xylem
Cohesion: Water molecules sticking to itself through hydrogen bonds
Adhesion: Water sticks to walls of xylem helps resist gravity
Capillary action: helps draw water through tiny spaces in cell walls

Adaptations of xylem

No cell contents: Open tube for water flow
Absent/incomplete walls: Allows uninterrupted vertical flow of water
Lignified walls: Prevents collapse under tension during transpiration
Narrow diameter: Helps with capillary action and cohesion
Bordered pits: allows sideways movement of water between vessels or into surrounding cells
Tubes arranged vertically: Supports efficient upward flow of water

Tissue fluid

Watery fluid that surrounds body cells, delivers oxygen and nutrients to cells, and removes waste products, formed from blood plasma

Formation of tissue fluid in arterial end of capillaries

1) Blood enters capillaries from arterioles under high hydrostatic pressure (pumping action of heart)
2) Pressure forces plasma out of the capillaries through gaps (pressure filtration)
3) Large proteins and blood cells stay in blood (too big)
4) Filtered fluid is tissue fluid (allows exchange of substances)

Reabsorption of tissue fluid at venous end

1) Hydrostatic pressure drops (blood pressure decreases)
2) Oncotic pressure remains (plasma proteins create a pulling force that draws water back in)
3) Net inward flow (tissue fluid returns to capillaries by osmosis)

differences between plasma and tissue fluid

tissue fluid doesn’t contain plasma proteins, red blood cells, rarely white blood cells, and platelets

Lymphatic system

Network of vessels, ducts, and nodes that help drain excess fluid, transports white blood cells, and support the immune system

Single circulation in bony fish

Blood flows through heart once per complete body circuit. Heart - gills - body - heart

components of single circulation in bony fish

2 chambered heart, blood is oxygenated at gills, after gills blood goes to the rest of the body, slower flow due to drop in pressure after gills

Double circulation in mammals

Pulmonary circuit: heart - lungs - heart
System circuit: Heart - body - heart

components of double circulation

4 chambered heart, maintains high pressure in systemic circuit, faster and more efficient oxygen delivery

Process of lymphatic drainage

1) Tissue fluid builds up in spaces between cells
2) Enters lymph capillaries via tiny gaps in their thin walls
3) Travels through vessels which have thin walls with gaps and contain valves to prevent backflow
4) Lymph is returned to blood stream after getting filtered

Cardiac muscle

specialized self contracting muscle, strong and thick walls in ventricles. Allows forceful contraction to pump blood under high pressure

Sinoatrial node

Located in right atrium wall. Initiates electrical impulse that causes rhythmic contractions, controls heart rate and coordinated pumping.

Atria

Push blood into ventricles at low pressure

Ventricles

Thicker muscular walls than atria, allows pumping of blood into aorta under high pressure

Atrioventricular valves

Prevent backflow into atria when ventricles contract

Semilunar valves

At exits of ventricles, prevent backflow from arteries into ventricles

Septum

Muscular wall that separates left and right, prevents mixing of oxygenated and deoxygenated blood.

Coronary vessels

Supply oxgen and glucose to heart, essential for maintaining continuous contraction.

Cardiac cycle stages

1) Atrial systole: SA node fires, sending electrical impulse. Left atrium contracts, blood pushed into left ventricle through bicuspid valve
2) Ventricular systole: Impulse reaches AV node. Left ventricle contracts, blood pushed into aorta through aortic valve. Bicuspid valve closes to prevent backflow.
3) Both atrium and ventricle relax, aortic valve closes to prevent backflow, blood starts to fill atrium again from pulmonary vein.

High systolic

May indicate strain on arteries

Low diastolic

Poor blood flow/dehydration

Root pressure

Positive pressure that helps push water upward through xylem vessels

Process of root pressure

1) Active transport of mineral ions from root cells to xylem
2) Increases solute concentration 
3) Creates water potential gradient
4) Water moves into xylem by osmosis from surrounding root cells
5) Incoming water creates positive hydrostatic pressure
6) Root pressure helps push water up the stem

Translocation

Active transport of sap through phloem from source (where sugars are made) and sink (where sugars are used)

Phloem

Sieve tube elements, companion cells, parenchyma and fibers

Adaptations of sieve tubes

Sieve plates: Allow easy flow of sap between cells
Reduced cytoplasm: More space from sap flow
No nucleus or ribosomes: No obstruction to flow
Long tube like cells: Form a continuous transport system

Adaptations of companion cells

Many mitochondria: Provide ATP for active loading
Nucleus and full organelles: Control metabolism of both themselves and sieve tubes
Allow exchange substances between companion cells and sieve tubes

Process of Translocation

Companion cells use ATP to pump sucrose into sieve tubes → decreases water potential → water enters by osmosis → generates pressure

Adaptations (no nucleus, sieve plates) reduce resistance → sap flows by pressure

Sugars actively or passively removed → water follows by osmosis → pressure drops → keeps flow going