B8 - Exchange and transport in animals

State the factors that effect the rate of diffusion?

• Large SA

• Short diffusion distance

• Concentration gradient

What effect does SA have on diffusion?

The larger the surface area the higher the number of particles that will be able to move in a given time so the faster the rate

What effect does distance have on diffusion?

If the diffusion distance is small, diffusion happens faster because the particles do not have as far to travel

What effect does the concentration gradient have on diffusion?

Diffusion is faster if there is a big difference in the concentration between the area the substance travels from and the area that it is moving to

What adaptation do capillaries have that maximise the diffusion rate?

• There are lots of them in a tissue which increases the SA

• The walls of the capillaries are only 1 cell thick so the diffusion distance is shortened

• There is a constant flow of blood in the capillaries which maintains concentration gradient

What happens to the SA:vol ratio when a cell increases in size?

Decreases the SA:vol ratio

How have alveoli adapted for fast gas exchange

• Thin cell walls of the capillaries and alveolus mean a shorter diffusion distance

• Constant blood flow maintains the concentration gradient between capillary and alveolus, as does ventilation of the lungs

Recall how to calculate the rate of diffusion using Fick’s law

Rate of diffusion ∝ SA x concentration difference/thickness of membrane

Define concentration

The number of particles in a specific volume

Recall how to calculate concentration

Mass of solute / volume of solution (g/cm3)

How does concentration effect the NET movement of particles

The higher the concentration the quicker the movement as there are more particles

What is the relationship between concentration different and the rate of diffusion?

Directly proportional

What is the relationship between the rate of diffusion and surface area?

Directly proportional

How is surface area increased in the lungs/small intestine

Through folds/pockets

What is the relationship between the rate of diffusion and the thickness of a membrane?

Inversely proportional

Recall how to calculate the rate of diffusion in relation to the thickness of a membrane

Rate of diffusion ∝ 1/thickness of membrane

Define an artery

• Carry blood under high pressure away from the heart

Define a vein

• Carry blood under low pressure back to the heart

Give the differences between arteries and veins

Differences	Arteries	Veins
Wall thickness	Thicker	Thinner
Lumen size	Smaller	Bigger
Pressure of blood	High	Low
Direction of blood	Away from heart	Towards heart
Valves	No	Yes

What structures are between arteries and veins

Capillaries

What are the function of valves

They prevent backflow

Name the order of blood flow in the sub structures

Heart —> Arteries —> Arterioles —> Capillaries —> Venules —> Veins

How big are capillaries?

As wide as a red blood cell (10um)

Explain continous blood flow

• The heart contracts (forcing blood out) and then relaxes, however blood flow doesn’t stop

• Arteries are elastic and are stretched by the increased blood pressure due to the contraction of heart muscles

• When the heart relaxes the elastic fibres cause recoil of the arteries causing a pressure wave to pass along the artery and blood to flow, smoothing out blood flow

What causes a pulse

Pressure waves which are caused by successive contractions of the heart

How does having veins inside muscles help with blood return to the heart?

• Muscle contraction squeezes the veins which increases the blood flow/pressure

• This causes the valve at the bottom to close, preventing backflow, but the valve at the top to be forced open and causes blood to flow into the next part of the vein

State the properties of a red blood cell and their function

• Shaped like a biconcave disc - this reduces SA:vol ration for maximum diffusion rate

• Full of the protein haemoglobin - this binds to oxygen in the lungs and releases it in the tissues

• No nucleus - more space for haemoglobin

Explain the colour change in red blood cells

• When oxygen is bound, the colour is a bright red and when oxygen has been released the colour is a darker red

State the function of phagocytes

• Surround and engulf foreign cells and digest them with enzymes

State the function of lymphocytes

• Produce proteins called antibodies which bind to antigens on foreign cells and aids with the destruction of them

State the properties and function of platelets

• They have no nucleus and are disc like cell fragments

• They release chemicals to help clot the blood when a vessel is broken (i.e. after an injury)

• They change shape when activated by contact with a broken blood vessel

What is the function and properties of plasma?

• Straw-coloured

• Carries dissolved substances (e.g. glucose, amino acids, hormones) and cells round in circulation

What order does blood travel through the body?

Lungs —> Veins —> Heart —> Arteries —> Rest of body —> Veins —> Heart —> Arteries —> Lungs

Define double circulation

• Deoxygenated blood is pumped from the heart into the pulmonary arteries to the lungs (for gas exchange) then via the pulmonary veins back to the heart

• Oxygenated blood is pumped from the heart into the aorta to the rest of the body

• Then blood comes back via the veins leading to the vena cava which brings blood back to the heart

What is the heart made from?

Muscle

Why is the left hand side of the heart thicker than the right?

Because the left side has to pump to the rest of the body not just the lungs

Describe the cardiac cycle

1. Heart is at rest - blood flows into the atria and ventricles

2. Atria contract together to push more blood into the ventricles

3. Ventricles contract together to push more blood into the arteries

Define stroke volume

The volume of blood pushed out of a ventricle into an artery

Define cardiac output

The volume of blood pushed into the aorta per minute

State how to calculate the cardiac output

Cardiac output = stroke x heart rate

Why does the heart need its own supply of blood?

• The muscle tissue needs its own supply as it needs to recieve oxygen and glucose and take away carbon dioxide

• These are called coronary arteries

What happens if the coronary arteries become narrowed?

• They become narrowed through fatty deposits in the walls of the arteries

• A heart attack occurs when there is a complete blockage

What is the order for the entire blood circulatory system?

Lungs —> Pulmonary vein —> Left atrium —> Atrioventricular valve —> Left ventricle —> Semi-luna valve —> Aorta —> Body —> Vena Cava —> Right atrium —> Atrioventricular valve —> Right ventricle —> Semi-luna valve —> Pulmonary artery —>Lungs

Define cellular respiration

• A series of chemical reactions that release energy from substances such as glucose

• Some of the released energy escapes as heat

• Therefore it is an exothermic reaction

Why do organisms need energy?

• For movement, from organisms, down active transport

• Keeps organisms warm

• For building and breaking down molecules

Define aerobic respiration

Respiration which requires oxygen

Where does energy releasing occur and what substances are used?

Occurs in the mitochondria, uses oxygen and glucose

State the word equation for respiration

Glucose + Oxygen —> Carbon dioxide + Water

Where is the lowest concentration of oxygen in the cell and why?

Found in the mitochondria because the movement of O2 diffuses in it and is used up

How does the blood facilitate cellular respiration

Good supply of O2 at all times

What increases in the body when exercising

• Breathing rate

• Breathing depth

• Heart rate

• Cardiac output

• Stroke volume

• Concentration of CO2

• Aerobic respiration

Why are factors increased in the body when exercising?

Increased use of glucose in muscles requires more oxygen for respiration, therefore a greater blood supply to tissues is needed

Why does anaerobic respiration occur during strenuous exercise?

Because the oxygen demand is greater than the supply

Where does the reaction for anaerobic respiration occur?

Cytoplasm

Describe anaerobic respiration

Glucose is broken down to lactic acid and releases a very small amount of energy (compared to aerobic)

What does lactic acid cause?

Muscle cramps and fatigue

Define oxygen debt

• When exercise stops the body is at rest, but breathing rate, cardiac output and oxygen consumption doesn’t fall to rest levels immediately

• This left over oxygen replaces the oxygen lost from blood and muscles which releases energy to metabolise the lactic acid in the liver