Topic 1: Lifestyle, Health, and Risk

What do cells need to survive?

* Constant supply of reactants

How do single- celled organisms get the supply of reactants?

* Gain O2 and glucose directly from surroundings
* Molecules can diffuse to all parts of the cell quickly due to short diffusion distances

Why can large organisms not operate in the same way?

* Made up of many layer of cells so time taken for substances such s glucose and oxygen is too long
* Diffusion distance too great
* High energy requirements so delivery of reactants needs to happen quickly

How do large organisms get their supply of reactants?

* The exchange surfaces are connected to a mass transport system
* eg. lungs connected to circulatory system

What is mass transport?

* The bulk movement of gases or liquids in one direction, usually via a system of vessels and tubes
* The circulatory system is a mass transport system

What do mass transport substances help to do?

* Bring substances quickly from one exchange site to another
* Maintain diffusion gradients at exchange sites and between cells and their fluid surroundings
* Ensure effective cell acctivit by supplying reactants and removing waste products

What does water do in terms of transport?

* The medium in which all metabolic reactions take place in cells and in which all substances are transported around the body

What is water composed of?

* One Oxygen atom covalently bonded (sharing e-) with two Hydrogen atoms

Dipolar nature of water

* Uneven sharing of electrons
* O attracts the electrons more strongly than the H atoms
* Weak -ve charge on the O atom
* Weak +ve charge on the H atoms
* Therefore H2O is a polar molecule

Result of the dipolar nature of water

* Hydrogen bonds form between the +ve and -ve Q regions of molecules as a result of the polar nature of water
* Hydrogen bonds are weak when few in number so constantly breaking and reforming
* Molecules flow past each other in a liquid state

What prooperties of water (due to its polar nature) make it good for transporting substances?

* It isCohesive
* It is a solvent

What is cohesion?

* The attraction of water molecules to each other
* This is due to the H bonds
* Water molecules pull other water molecules along due to adhesion

What is adhesion?

* Water can hydrogen bond to other molecules
* Water adheres to the sides of a vessel due to adhesion

How do adhesion and cohesion help transport?

* Water molecules pull other water molecules along due to cohesion
* Water adheres to the sides of a vessel due to adhesion
* This means that water flows easily

What makes water a solvent?

* It is a polar molecule meaning many ions dissolve in it

How do ions dissolve in water?

* +ve part of water (H) attracted to the -ve charged patticles
* -ve part of water (O) attracted to the +ve charged particles
* This causes the surrounding molecules to break aprt (dissvolve)

What is the purpose of dissolving ions?

* Allows chemical reactions to occur within cells as the dissolved solutes are more chemicaly reactive when they are free to move about
* Metavolites can be transported efficiently in a dissolved state

What is a circulatory system?

* A system which transports fluids containing materials needed by the organism as well as waste materials that need to be removed

What happens in a closed circulatory system?

* Blood is pumped around the body and is always contained within a network of blood vessels

What happens in an open circulatory sytem?

* The blood, or blood equivalent, is inside the body cavity and bathes the organs

What is a double circulatory system?

* They have two loops
* One to the lungs and one to the body

What is a single circulatory system?

* They have one loop that includes the lungs and the body

What type of circulatory systems do humans have?

* Closed, double circulatory system
* Right side of the heart pumps deoxygenated blood to the lungs for gas exchange (pulmonary circulatory system)
* Blood returns to the left side of the heart so oxygenated blood can be pumped at high pressure around the body (systemic circulatory system)

Structure of the heart

* Divided into four chamber
* Top 2 chambers are the atria
* The bottom 2 chambers are ventricles
* Left and right sides of the heart are separated by a wall of muscular tissue called the septum
* Protected in the chest cavity by the pericardium, a tough and fibrous sac

What is the role of the septum?

* Ensures blood doesn’t mix between the left and right sides of the heart

What are the roles of valves in the heart?

* Keep blood flowing forward in the right direction and for maintaining the correct pressure in the chambers of the heart

What separates the right atrium and right ventricle

* An AV valve called the tricuspid valve

What separates the left atrium from left vetricle

* An AV valve called the bicuspid valve

What separates the right vantricle from the pulmonary artery

* Semilunar valve called the pulmonary valve

What separates the left ventricle and the aorta

* Semilunar valve called the aortic valve

When do valves open?

* Open when pressure of the blood behind them is greater than the pressure in front

When do valves shut?

* Shut when the pressure in front of them is greater than the pressure behind them
* Preventing the backflow of blood

How are the valvesattached to the walls of the heart

* By valve tendons (cords)
* Prevent the valves from flipping inside out under high pressure

How have the ventricles adapted to their function?

* Thicker walls than atria to pump blood out of the heart
* Atria only pump blood into ventricles and are assisted by gravity ig

Left vs right ventricle

* Left ventricle:Thicker muscle than right ventricle for strong contraction to pump blood all the way around the body
* Right ventricle only has to pump blood to the nearby lungs

Function of AV valves

* Prevent backflow of blood from ventricles into atria

Function of the SL valves

* Prevent backflow of blood from the aorta or pulmonary artery into the ventricles

Function of the vena cava

* Brings deoxygenated blood from the body into the heart

Function of the pulmonary vein

* Bring oxygenated blood from the lungs into the heart

Function of the pulmonary artery

* Takes deoxygenated blood to the lungs

Function of the aorta

* Takes oxygenated blood into the body

What is the function of the coronary arteries?

* Run across the surface of the heart
* supplies blood to the heart muscle

Function of the arteries

* Transport blood away from the heart, usually at high pressure, to the tissues

What are arterioles?

* Arteries branch into narrower blood vessels called arterioles which transport blood into capillaries

What do veins do?

* Transport blood to the heart, usually at low pressure

What do venules do?

* These narrower blood vessels transport blood from the capillaries to the veins

What do capillaries do?

* Microscopic blood vessels that carry blood to the cells

What is the lumen?

* The central cavity of an intestine or blood vessel through which the blood flows
* Arteries have a narrow lumen and veins have a wider lumen

Properties of the artieries?

* Tunica intima
* Endothelium
* Tunica media
* Smooth muscle
* Elastic tissue
* Tunica externa
* Contains collagen
* Narrow lumen to maintainn high bloof pressure
* Pulse present so they stretch to accomodate increased volume of blood with every heartbeat

Features of the endothelium (tunica intima)

* One cell thick and lines the lumen of all blood cells
* Smooth to reduce friction for blood flow
* Endothelium highly folded, so it can expand under high pressure

Features of the tunica media

* Thick layer of smooth muscle and elastic tissue
* Muscle strengthens the artieris so they can withstand high pressure
* Muscle can contract to constrict and narrow the lumen to reduce blood flow
* Elastic tissue maintains blood pressure as it stretches and recoils to even out fluctuations in pressure

Features of the tunica externa

* Contains structural protein collagen
* Strong so protects blood vessels from damage by over-stretching

Function of the veins

* Recieve blood that has passed through capillary networks and send it to the heart

Propoerties of veins

* Smooth muscle and elastic layer
* Lumen
* valves
* noo pulse due to increased distance from the heart

Smooth muscle and elastic tissue in veins?

* Much thinner as veins don’t need to withstand the high pressure

Lumen in the veins

* Wider in the veins than in the artery
* Ensures blood returns to the heart at adequate speed
* Reduces friction between the blood and endothelium of the vein

How does the larger lumen in the veins affect speed of blood flow?

* The rate of blood flow slower in veins but in a larger lumen the volume of blood delivered per unit of time is equal to that of the arteries

What is the purpose of valves in the veins?

* Prevents backflow of blood, helping blood return to the heart

Properties of the capillaries?

* thin walls which are permeable
* narrow lumen
* Wall is a single layer of endothelial cells

What is a capillary bed?

* Exchange surfacea
* Large number of capillaries that branch between cells
* Showrt diffusion distance so substances dffuse quicker

Why is the lumen narrow in a capillary?

* Red blood cells travel in a single file line
* Forces blood to travel slower which provides more time for diffusion to occur

Feature of the capillary cell wall?

* One cell thick which Reduces diffusion distance for O2 and CO2
* Single layer of endothelial cells
* They have pores which allow blood plasma to leak out and form tissue fluid
* White blood cells can squeeze through these pores to combat infection

Steps of the cardiac cycle

* Atrial systole
* Ventricular systole
* Atrial and ventricular diastole

Atrial systole

* Walls of atria contract
* Volume decreases
* Pressure decreases causes AV valve to open
* Blood forced into ventricles
* Ventricles relaxed

Ventricular systole

* Walls of ventricle contract
* Ventricular volume decrease
* Ventricular pressure increases
* Pressure in ventricles greater than in atria so AV valve close, prevent backflow of blood
* Pressurein ventricles greater than in the veins so SL valves open
* Blood forced into arteries
* Arial diastole

Cardiac Diastole

* Ventricles and atria both relaxed
* SL valves close as pressure in veins greater than in ventricles
* Atria fill with blood
* AV valves open
* Blood flows passively into ventricles

Cardiac Cycle Graph

* The lines of the graph = pressure of left ventricle atrium and aorta

Whta stage of the cardiac cycle does point A represent?

* End of diastole
* Atrium has just filled with blood
* Higher pressure in the atrium so AV valve open

What stage of the cardiac cycle is between point A and B?

* Arial systole
* Atrium contracts
* Ventricle pressure increases as it fills with blood
* AV valve remains open

What stage of the cardiac cycle occurs at point B?

* Begining of ventricular systol
* Ventricle contracts
* Atrium pressure drops
* Pressure in ventricle> than in atrium so AV valve closes

What stage of the cardiac cycle is at point c

* Ventricular systole
* Ventricle continues to contract
* Aortic valves opens as pressure in ventricle> pressure in aorta
* Blood forced into aorta

What stage of the cardiac cycle is at point D?

* The begining of diastole
* Ventricles relax
* Aortic valve closes as pressure> pressure in ventricle

What stage of the cardiac cycle is at point D-E?

* Ventricle remains relax and ventricular pressure still decreases
* Blood flows into the relaxed atrium form pulmonary veins

What stage of the cardiac cycle is at point E?

* AV valve opens as pressure in atrium> pressure in ventricle

What happens in cardiac cycle after point E

* Late diastole
* here is a short period of time during which the **left ventricle expands** due to relaxing muscles
* This increases the internal volume of the left ventricle and **decreases the ventricular pressure**
* At the same time, blood is flowing slowly through the newly opened AV valve into the left ventricle, causing a **brief decrease in pressure** in the left atrium


* The pressure in both the atrium and ventricle then **increases slowly** as they continue to fill with blood

Core practical 1: Investigating heart rate

What factors can influence heart rate?

* Drugs
* Caffeine
* Alcohol
* Sex i.e. male or female
* Weight
* Height
* Temperature
* Diet
* Dehydration

Core practical 1: Investigating heart rate

What are daphnia?

* Small aquatic vertebrates

Core practical 1: Investigating heart rate

Why are daphnia suitable for this expriment?

* Transparent bodies so their internal organs can be observd using a light microscope

Core practical 1: Investigating heart rate

Apparatus

* Light microscope
* Cavity slide
* Culture of *Daphnia*
* Pipette 
* Caffeine solutions at a range of concentrations
* Distilled water
* Stop watch

Core practical 1: Investigating heart rate

Method

1. Prepare five different concentrations of caffeine solution and a control solution of distilled water
* The serial dilution technique could be used here
2. Add some pond water into the well of a cavity slide and add three drops of distilled water 
3. Select a large *Daphnia* and use a pipette to carefully transfer it to the cavity slide
* You can also use a Petri dish if you do not have access to a cavity slide
4. Place the cavity slide onto the stage of a microscope and observe the animal under low power
* The beating heart is located on the dorsal side just above the gut and in front of the brood pouch
5. Use a stopwatch to time 20 seconds, and count the number of heart beats
* The heart beat of *Daphnia* is very rapid, so you can count the beats by making dots on a piece of paper
6. Count the dots and express heart rate as number of beats per minute
* Multiply by three to convert beats per 20 seconds into beats per 60 seconds
7. Return the *Daphnia* to the stock culture
8. Repeat steps 3-7 with at least 5 other *Daphnia* individuals
9. Repeat steps 3-8 with different caffeine concentration solutions

Core practical 1: Investigating heart rate

Variations

* You can also investigate the effect of
* Temperature 
* Other chemicals such as alcohol (1% ethanol solution)

Core practical 1: Investigating heart rate

Results

* To analyse your results it is best to draw a graph
* Take an average of the heart rate repeats for each caffeine concentration
* Plot average heart rate (y axis) against caffeine concentration (x axis)
* The graph should show a positive correlation; as caffeine concentration increases, heart rate increases

Core practical 1: Investigating heart rate

Ethical considerations

* Less sophisticated nervous system so don’t feel paint the same way
* Cannot give consent
* Cannot express pain

Core practical 1: Investigating heart rate

How to miniimise poential harm of the daphniia

* Handle gently
* Examination preiods should e kept as short as possible
* Animals should be returned promptly to the holding tank
* Extreme ranges of variables tested should be avoided

What is atherosclerosis?

* Narrowing of the lumen in the arteries due to a build up of plaque
* Hardening of the arteries
* Progressive disease

What is a progressive disease?

* A disease that gets worse over time

Steps of atherosclerosis

* Damage to the endothelium (due to high blood pressure), cholesterol accumulates and oxidises causing an inflammatory response
* Lipids and cholesterol accumulate in the damaged area
* White blood cells (macrophages) enter the endothlium, attempt to digest cholesterol and turn into foam cells
* Foam cells degenerate and form the atheroma t on the endothelium wall
* Plaque ruptures and platelets accumulate and form a plaque called an atheroma
* Atheroma narrows lumen of the artery, raising lood pressure and reducing blood flow
* Plaque hardens over time further reducing easticity of artery wall

What is the pupose of blood clotting?

* Prevents excess blood loss and prevents entry of pathogens
* Provides a barrier (scab) so healing can occur

What causes the formation of a blood clot?