Properties of Water

Water is a polar substance consisting of positive and negative dipoles and forms hydrogen bonds in between its molecules
Due to its polarity, it is a good solvent and can dissolve ionic substances:
- Cations are attracted towards $\delta ^ -$ oxygen and anions are attracted the $\delta ^ +$ hydrogen
- Can dissolve alcohols as they contain a polar $O H$ / hydroxyl group that forms hydrogen bonds with water
- The $\delta ^ +$ hydrogen is attracted towards the cation, while the $\delta ^ -$ oxygen is attracted towards the cation!
Ice is less dense than liquid water, so it forms an insulating layer on ponds, allowing marine life underneath to thrive
Water is not easily compressed, making it useful in hydraulic mechanisms and by soft-bodied animals.
Cohesive- Can bond to other water molecules
- useful for transport of water in xylem
Adhesive- sticks to other substances
- due to high surface tension
- useful in maintaining transpiration pull streams
Water has High surface tension

Biological molecules: Carbohydrates

Monosaccharides

General formula: $(CH_{2}O)_{n}$ $(C H_{2} O)_{n}$
- n stands for the number of carbon molecules

N	Naming	Uses
3	triose	triose sugars are used in respiration
5	pentose	pentose sugars are used in ribose and deoxyribose in the DNA and RNA molecules
6	hexose	hexose sugars such as glucose and galactose are crucial for energy storage

Isomers of Glucose

Glucose has two isomers: $a - g l u c o s e$ and $\beta-glucose$
$a - g l u c o s e$ is used in polysaccharides
$\beta-glucos e$ is used in cellulose

Diagram source: Cognito, "1.3 - Carbohydrates: Monosaccharides & Disaccharides"

Disaccharides

A disaccharide consists of two monosaccharides joined by a condensation reaction:
- A water molecule is removed, and a glycosidic (covalent) bond is formed
glucose + fructose $\to$ sucrose + water
glucose + galactose $\to$ lactose + water
glucose + glucose $\to$ maltose + water

Polysaccharides

Contain more than two monomers joined with glycosidic bonds
e.g. amylose and amylopectin, starch and glycogen etc.

Property	Amylose	Amylopectin
Base monomer	a- glucose	a-glucose
branching	not branched	highly branched
shape	helical/compact shape	not coiled/straight
bonds	1,4-glycosic bonds	1,4 and 1,6- glycosidic bonds
solubility in water	insoluble	insoluble

properties	Glycogen	Starch
monomers	a- glucose	a-glucose
branching	highly brandhed	less branched than glycogen
usage	used in animals	used in plants
solubility	large and insoluble; no osmotic effect	large and insoluble; no osmotic effect
bonds	1,4 and 1,6 a-glucose bonds	1,4 and 1,6 a- glucose bonds (contains amylose + amylopectin)

Fats

Fats contain carbon, hydrogen and oxygen

Saturated fats

Contain single carbon-carbon bonds only Solid at room temperature Considered "unhealthy animals fats"

Unsaturated fats

Have at least one carbon-carbon double bond
- fats with more than one carbon-carbon double bonds are known as polyunsaturated fats
lower carbon : hydrogen ratio than saturated fats

Image source: My Revision Notes: Edexcel Biology B, Hodder Education, 2015

Esterification

Triglycerides contain three (non-polar) fatty acids, and a (polar) glycerol molecule.
During a condensation reaction, a covalent ester bond is formed between the COOH of fatty acids and OH of glycerol
- a water molecule is removed ![[Pasted image 20250718191509.png]]

Circulation and Mass transport system

Mass transport: The bulk transport of substances to all parts of an organism via specialized transport systems
- i.e. circulatory system in humans
Unicellular organisms have large surface area : volume ratio so gases can diffuse easily; they do not require a mass transport system
Multicellular organisms need a mass transport system to overcome the limits of diffusion
- Have a small surface area : volume ratio
- tend to have long diffusion distances
- tend to have high metabolic rates so require loads of oxygen for respiration
A closed system contains blood within "tubes" i.e. blood vessels
An open system lacks blood vessels. Muscle contractions cause mix-up of oxygenated and de-oxygenated blood.

Single circulatory system:

Blood passes through the heart only once in a complete circuit
Oxygenated and deoxygenated blood are mixed

Double circulatory system:

Blood passes the heart twice in one complete circuit
Systemic system: carries oxygenated blood from heart to body
Pulmonary system: carries deoxygenated blood from heart to lungs
Oxygenated and de-oxygenated blood do not mix

Structure of blood vessels

Arteries:

carry blood away from heart
only aortic and pulmonary arteries have valves
they contain thick, smooth muscle for controlling blood pressure and vasodilation
contain elastic tissue with loads of elastic fibers for recoil
Have loads of collagen for high tensile strength
Small lumen for high blood pressure
All carry oxygenated blood except pulmonary artery and umbilical artery

Capillaries

link arterioles and venules together
are one cell think and branch in between cells
- provides a short diffusion distance
have a large surface area
- allow for quick diffusion
are one blood cell wide

Veins

carry blood back to heart
most of them carry deoxygenated blood except:
- pulmonary veins
- umbilical vein
have valves
- valves prevent backflow
- act as a reservoir for blood when closed
- muscle contraction and high blood pressure opens them
- have tendonous chords to prevent valves from turning inside out
- papillary muscles pull on tendons controlling the valves
have a large lumen to decrease resistance to blood flow
have thin muscular walls to maintain low blood pressure

Image source: My Revision Notes: Edexcel Biology B, Hodder Education, 2015

Blood speed

Blood speed reduces as it travels further away from heart due to resistance and friction against the blood vessels. The amount of oxygen in the blood decreases as well, as cells use the oxygen for respiration

The Cardiac Cycle

Blood comes from the superior and inferior vena cava right into the right atrium
The muscles of the right atrium contract. Tricuspid valves open and blood fills the right ventricle
The valve closes and the right ventricle contracts.
Semi-lunar valve opens and blood travels to pulmonary artery. It then goes to the lungs via the pulmonary vein back to the heart
Blood then goes intro the right atrium, it contracts and the bicuspid valve opens.
The blood rushes into the left ventricle. When the left ventricle contracts, the semi-lunar valve opens and the blood goes to the aorta and then to the rest of the body.

Image source: Science Direct, Heart Sound; In subject area: Agricultural and Biological Sciences

Atrial systole

A.V. = Atrioventricular valves

Atrial walls contract
Pressure increase opens the A.V. valves
Ventricle muscle relaxes as the ventricle fills with blood
A.V. valve closes is open to allow blood flow into the ventricles and stay open long enough for ventricle to be full.

Ventricular systole

Right ventricle contracts
Blood pressure increases
A.V. valves close
Semi-lunar valve opens & blood pushed into pulmonary artery
Atria remain relaxed and begin to fill with blood again.

Cardiac diastole

Atria relax – blood flows into them & pressure increases enough to open atrioventricular valves
Ventricles relax – back pressure of blood in arteries closes semi-lunar valves. Blood neither leaves nor enters ventricles till pressure in atria higher than ventricles

1- Atrial Systole 2- Ventricular Systole 3- Diastole Image source: My Revision Notes: Edexcel Biology B, Hodder Education, 2015

Haemoglobin

Red blood cells contain haemoglobin, which is a globular protein. It contains:
- hydrophobic interactions in the middle
- a haem group (Fe containing prosthetic group), which binds with O₂
- hydrophilic edges
- hydrogen bonds
- α & β chains (folded to make quaternary structure)
- four polypeptide chains/sub-units
Each haemoglobin can bind to four O₂ $H b + 4 O_{2} ⇌ H b .4 O_{2} Hb + 4O₂ ⇌ Hb.4O₂$
oxyhaemoglobin = $Hb.4O_{2}$
Oxygen binds with the haem-group as haemoglobin has an affinity (attraction towards) O₂

Haemoglobin dissociation curve and cooperative binding

*Image source: My Revision Notes: Edexcel Biology B, Hodder Education, 2015*

The haemoglobin dissociation curve is a sigmoid shaped curve, due to a phenomenon known as "cooperative binding"
Cooperative binding happens when the tertiary structure of haemoglobin shifts after an oxygen molecule binds to it, which makes it easier for the next oxygen molecule to attach.
- The first O₂ is really hard to bind to,
- After binding, the tertiary structure of haemoglobin changes.
- Cooperative binding continues.
- The affinity for the next O₂ molecule increases, and binding becomes easier (this process repeats until haemoglobin holds four O₂ molecules).
- The partial pressure of free O₂ in the cytoplasm of red blood cells stays the same.

Bohr’s Effect and $CO_{2}$ transport

CO₂ Diffusion and Reactions:

Waste CO₂ diffuses out of cells into the blood, reacting with H₂O to form carbonic acid (H₂CO₃).
Further combination with hemoglobin forms carbaminohemoglobin (CO₂ is also transported as hydrogen carbonate ions, HCO₃⁻).
- Note: Not all CO₂ molecules bind to hemoglobin.

Role of Carbonic Anhydrase

This enzyme controls the reaction rate and CO₂ binding.
It catalyzes the reverse reaction in the lungs, allowing CO₂ to diffuse out for exhalation.

High CO₂ and O₂ Affinity

High CO₂ levels (e.g., in respiring tissues) reduce hemoglobin’s affinity for O₂.
Partial pressure of CO₂ is higher in respiring tissues.
- The Bohr effect occurs, shifting the O₂ dissociation curve right.
- O₂ is more likely to be released from hemoglobin (affinity reduced).

Fetal Haemoglobin

A fetus depends on the mother for O₂ supply.
Oxygenated blood flows close to the placenta.
Fetal hemoglobin has a higher affinity for O₂ than adult hemoglobin, meaning:
- It can remove O₂ from maternal blood even at low O₂ levels.
- The O₂ concentration difference between mother and fetus is maintained.
- It can bind O₂ even at lower partial pressures.

Myoglobin

Myoglobin is a respiratory pigment found in the muscles and has a stronger affinity for oxygen than haemoglobin. It can release oxygen at lower partial pressures than haemoglobin.

Atherosclerosis

Happens when the endothelial cell lining of the vessel is damaged
- This triggers an immune response, which leads to white blood cells arriving
  - cholesterol + lipoproteins accumulate at the site of the damage
- An atheroma forms
- Fibrous tissues & calcium gathers around plaque, hardening it
  - The hardening of the plaque is known as atherosclerosis
- Area becomes less elastic and the lumen grows narrow
- Blood has to be pumped with a higher pressure, damaging other parts of the vessel

High blood pressure can lead to damaging kidney vessels, eyes, & bleeding from capillaries into brain, causing a stroke

Terminology

• Aneurysm:

Bursting of an artery, resulting in internal bleeding •Angina:
The slow plaque buildup in the heart, often resulting in chest pains • Thrombus:
- A thrombus is a clot within a vessel
- An embolus is a dislodged thrombus • Myocardial infarction:
Heart attack
- Blockage of coronary artery
- Heart muscle doesn’t receive O₂ & dies • A Stroke:
Caused by interruption in blood flow
Hemorrhagic stroke: weakened arteriole in brain bursts

Why is clotting necessary?

An Open wound means that there is a risk of pathogens entering, increasing chance of infection and other diseases.

Can also lead to an excess loss of blood, resulting in death

Clotting Cascade

*Image source: My Revision Notes: Edexcel Biology B, Hodder Education, 2015* ## Main components

Thrombokinase:

Enzyme
Insoluble in plasma
Active

Prothrombin:

Inactive
Soluble plasma protein

Thrombin:

Active
Enzyme
Soluble

Factors contributing to Cardiovascular disease

Factor	Explanation
Genetics	Major Non-modifiable risk - Some people are more susceptible to CVD than others
Alcohol	Increases risk of developing CVD as it affects High-density lipoproteins & Low-density lipoproteins. - Alcohol damages the liver - Can increase blood pressure
Diet	- A high salt diet increases blood pressure - A diet high in LDLs means more cholesterol is being carried in the bloodstream, so there is a higher chance of plaque formation - A diet that is high in saturated fats/cholesterol increases chances of plaque formation
Age	As age increases, risk of developing CVD increases due to loss of elasticity in blood vessels
Gender	Men are more likely to get CVD than women
High Blood Pressure	A high blood pressure damages the endothelium
Inactivity	Leads to a fat buildup in the arteries
Diabetes	High blood sugar can damage vessels, leading to plaque buildup
Obesity	Leads to cholesterol buildup on arteries - If a person eats a sugar/fat-rich diet, then their energy balance is imbalanced - They are taking in more energy than required/used; excess is stored as fat
Dietary Antioxidants	Antioxidants protect cells from damage - During chemical reactions, unstable free radicals form which damage arterial lining & the bases in DNA. This can lead to plaque build up, resulting in increased blood pressure - Antioxidants reduce the number of free radicals
Smoking	Smoking decreases the amount of antioxidants. Damages blood vessels, increasing the risk of plaque formation Increases Low density lipoprotein levels in the blood, increasing risk of CVD

Analysing Data

Risk: the probability of an event happening.
Perceived risk ≠ actual risk.
People overestimate risk if:
- It is involuntary.
- It is unlikely to occur.
- It is unnatural.
- It is unfamiliar
- It is very small.
Overestimation usually occurs for sudden dangers
Underestimation occurs when the risk has a long-term effect.

Correlation

If one variable changes, a change in the other is seen as well.
However, correlation does not imply causation.
- For example, there is a correlation between the age of participants and the number of heart attacks. However, this doesn't mean that age is the only/main cause. It can be due to a number of combined factors discussed above.

Designing Studies

The bigger the study, the more meaningful the results.
Only one independent factor should be tested.
The study should have a clear aim or hypothesis.
Use a representative sample and avoid selection bias.
The method should produce valid and reliable results.
- Validity: is the experimental design appropriate for measuring what it intends to measure?
- Precise: measurements show little difference between repeated trials.
- Reliability: Consistent of the data generated (between measurements)
  - The investigation can be repeated by others and should produce the same result.

Commenting on Studies

When commenting on study designs, consider:

Sample size.
Variables.
Data collection method.
Repeats.
Conflicts of interest.

Type of study	Explanation
Meta-data analysis	Secondary research Data from all available studies in a particular area are analysed together
Longitudnal study	Follows the same group of individuals over many years. Usually expensive and time-consuming.
Case Controlled study	Compares people with a disease to those without it.

Indiciators

BMI

BMI is a measure of obesity/healthy weight
Formula:
$BMI = \frac{mass (kg) }{height² ~(m²)}$
BMI ≥ 30 → obese
BMI < 18.5 → underweight
A person is considered obese when energy input > energy output.

Waist to Hip Ratio

Formula:
$\large \frac{waist ~measurment}{ hip ~measurement}$
Waist: measured at the smallest part of the waist.
Hip: measured at the largest part of the hips.
A ratio of > 1 indicates obesity.

Treatment of CHD/CVD

Treatment	Explanation	Advantages	Disadvantages
Anti-hypertensives	Used to control high blood pressure (hypertension). 1- Diuretics: Increase volume of urine. Less blood volume results in a decrease in blood pressure. 2-Beta-Blockers: Prevent stimulating signals from the nervous system from being sent (e.g. constricting arteries, raising blood pressure). Dilate arteries and lower blood pressure.	Lowers blood pressure. Lowers risk of cardiovascular disease (CVD). Reduces risk of damage to kidneys and eyes.	Blood pressure may get too low or cause nausea. Side effects include swelling, fatigue, impotence. May cause an abnormal heart rhythm.
Statins	Lower cholesterol in the blood. - Block the enzyme that makes cholesterol and produces LDLs.	Lower cholesterol. Improve HDL to LDL balance. Reduce arterial inflammation. Few side effects.	Muscle and joint aches. Risk of degenerative diseases (e.g. dementia); more research needs to be done regarding this Risk of relying on statins over adopting healthy lifestyle choices.
Plant Sterols and Stanols	Reduce amount of cholesterol absorbed in the gut and help metabolise cholesterol and reduce LDL levels.	Not classed as drugs. Effective when taken at recommended amounts. Can lower LDL levels by as much as 28% when taken correctly.	Only data from meta-analysis is available to support claims. Strict recommended amounts needed. More analysis and research needed.
Anticoagulants	Interferes with platelet production in the body, so clotting of blood is more difficult. E.g. Aspirin	Reduced risk of clot formation, decreasing risk of artery blockage	Can lead to excessive bleeding if an injury happens Can result in rashes forming, liver dysfunction and lining damage in extreme cases combining more than one type of anticoagulants and platelet inhibitors increases risk of harmful side effects

Any harmful effects discourage the use of medicine, increasing the risk of CVD redeveloping

StudyHaven

WBI11 Unit 1 - Topic 1 Molecules, Transport and Health