Topic 3 (AQA Alevel Biology)

SIZE AND SURFACE AREA

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What do cells exchange?

Intake of oxygen and nutrients

Excrete carbon dioxide and urea

Exchange heat to maintain temperature

Describe the SA:V for a smaller animal

High surface area to volume ratio

How do multicellular organisms exchange with the environment?

Using exchange organs and mass transport systems

Why can't multicellular organisms diffuse directly with the environment?

Some cells are deep within the body

Larger animals have low SA:V - it's difficult to exchange enough substances to supply the larger volume of the animal through the relatively small outer face

What affects heat exchange?

BODY SIZE:

Rate of heat loss depends on surface area

Animals with larger surface area loose heat more easily so have high metabolic rates to generate enough heat to stay warm

Animals with smaller surface area retain heat

SHAPE:

Compact shape Animals also have smaller surface area relative to their volume [Small SA:V] so that minimises heat loss

Animals with less compact shape have larger surface area relative to volume [large SA:V] so that increases heat loss

E.g- less compact=large ears or pointed nose

State some behavioural and psychological adaptations of an animal to assist exchange

Animals with high SA:V tend to lose more water as it evaporates from their surface

Some desert mammals have kidney structure adaptions so they produce less urine to compensate

Small mammals living in cold region eat large amount of high energy food to support their high metabolic rates

smaller mammals can have thicker fur to hibernate during winter

Larger organisms in hotter regions may find it hard to cool down

Elephants have large ears to increase SA so more heat can be lost

Hippos spend much of the day in water to help lose heat

GAS EXCHANGE

Name 2 major adaptations for Gas Exchange Surfaces

Large Surface Area

Thin [often 1 epithelial cell thick] to provide short diffusion path

also requires conc gradient

Describe the gas exchange system in a fish

COUNTER-CURRENT SYSTEM

low conc of oxygen in water than air

Water, containing oxygen, enters fish through mouth and passes out through the gills

Gill made of many thin plates called gill filaments

Gill filaments have large SA for gas exchange

Gill filament covered in smaller lamellae which increases SA further

Lamellae is made of thin surface layer of cells and is close to network of blood capillaries

So increased rate of exchange

Blood flows in opposite direction to water to maintain large conc gradient

Describe the exoskeleton of an insect

Composed of a hard fibrous material called chitin (for protection)

Covered by a lipid rich /waxy layer (to prevent water loss)

No lungs but a tracheal system

Describe the tracheal system of an insect

Consists of series of small holes in the exoskeleton called spiracles

These open to a network of fine tubes called tracheae (lined with rings of chitin)

Tracheae sub-divide into tubes of smaller diameter called tracheoles (unlined)

Tracheoles end at body cells

Name the adaptation of an insect for effective gas exchange

Gaseous exchange is carried out across the walls of the tracheoles by diffusion.

Very large number of fine tracheoles - large surface area

Walls of tracheoles are thin - short diffusion pathway

Use of oxygen and production of carbon dioxide sets up steep diffusion gradients

Walls made of chitin to withstand pressure

Hairs on surface to avoid dehydration on body surface

Name 3 ways an insect exchanges gas

Via a:

Diffusion gradient

Mass transport [abdominal pumping]

Trachioles filling with water during flight

Describe how a insect exchanges gas via a diffusion gradient

OXYGEN

Air moves inwards through spiracles [pores] pn insect's surface

Oxygen travels down a conc gradient towards body cells

Trachae branches into trachioles

Trachioles have thin, permeable walls and go to individual cells

So oxygen diffuses directly to respiring ells

Describe how an insect exchanges gas via mass movement [abdominal pumping]

CARBON DIOXIDE

Abdominal muscles contract to constrict trachiole

increase in pressure = acceleration of carbon dioxide because pressure gradient has steepened from high to low

Describe how an insect exchanges gas when flying

Anaerobic Respiration in insect

Anaerobic respiration produces lactic acid that dissolves in water which alters the water potential of the muscle cell

Lactic acid decreases water potential of muscle cells so water moves inwards via osmosis down the water potential gradient.

The end of the tracheoles decrease in volume as water travels from tracheole to muscle cells.

Decrease in volume draws air inwards down a pressure gradient

final diffusion pathway is gas rather than liquid

How do plants control water loss?

Plants's stomata surrounded by guard cells

if plant is dehydrates, guard cells lose water and become placid which closes pore

What is a xerophyte?

a plant adapted to reduce water loss (reduce transpiration) for life in a warm, dry or windy habitat

Describe the adaptation of a Xerophyte

Stomata in sunken pits-trap still moist air

Hairs-"

Curled leaves with stomata inside-protects stomata from windy conditions that increase rate of diffusion and evaporation

Reduced no. stomata-fewer places for water to escape

waxy cuticles-reduce evaporation

What is a halophyte?

salt-tolerant plant

GAS EXCHANGE IN HUMANS

Describe the path of oxygen from the air

Mouth+Nose > trachea > 2 bronchi > 1 bronchus > bronchioles > alveoli

What is ventilation?

movement of air in and out of the lungs

Consists of inspiration [breathing in] and expiration [breathing out]

What components control ventilation action?

Diaphragm

Internal and external intercostal muscles

Rib cage

Describe the process of inspiration

External intercostal muscles contract

Diaphragm contracts

Rib cage moves up and out

Diaphragm flattens, so volume of thoracic cavity increases

As volume of thoracic cavity increases, lung pressure decreases [to below atmospheric pressure]

Air flows down a pressure gradient

From high atmospheric pressure to low internal pressure inside thoracic cavity

So air flows inwards

ACTIVE PROCESS as it requires energy

Describe the process of expiration

External intercostal and diaphragm muscles relax

Rib cage moves downwards and inwards

Diaphragm curves

Volume of thoracic cavity decreases causing air pressure to increase [above atmospheric pressure]

Air flows out down the pressure gradient and out of the lungs

PASSIVE PROCESS as does not require energy

State the difference between forced expiration and normal expiration

Forced = ACTIVE

Normal = PASSIVE

Describe the process of forced expiration

External intercostal muscles relax AND internal intercostal muscles constrict [antagonistic intercostal muscle moemtn]

Rib cage pulled further down and in

Where does gas exchange happen in humans?

alveoli

State the adaptation of the alveoli

Large SA because there's a huge number of alveoli in the lungs

Surrounded by network of capillaries

Thin exchange surface- alveolar epithelium is 1 cell thick sos short diffusion path

Describe the path of oxygen in alveoli

Oxygen diffuses out of the alveoli

Across alveolar epithelium

Across capillary endothelium [type of epithelium]

Oxygen associates to haemoglobin in the blood

What is an endothelium?

A type of epithelium

THE EFFECTS OF LUNG DISEASE

What is tidal volume?

Volume of air in each breath

What is ventilation rate?

Number of breath per minutes

What is FEV1?

Forced expiatory volume is the maximum volume of air that can be breathed out in 1 second

What is FVC?

Forced vital capacity is the maximum volume of air it is possible to breathe forcefully out of the lungs after a really deep breath in

What is residual air?

Leftover air in lungs

Cant be expelled

How is a lung function test presented and how is the data colected?

A graph produced by spirometer

Name 4 diseases that affect the lungs

TB --> Pulmonary Tuberculosis

Fibrosis

Asthma

Emphesyma

Describe how TB affects the lungs

TB Bacteria triggers immune réponse

Immune system builds wall around bacteria on the region of lung that its situated on--> forms small, hard lump called TUBERCLES

Infected tissue within tubercle dies

so gaseous exchange surface is damaged and limited so the tidal volume decrease

Reduced tidal volume = less air inhaled with each breath so person breathes faster to compensate lack of oxygen

Ventilation rate increases

Symptoms: persistent cough

TB can cause fibrosis

Describe how fibrosis affects the lungs

Fibrosis is the formation of scar tissue

Scar tissue may be formed in response to an infection or the exposure to asbestos or dust

Scar tissue thicker and less elastic than normal lung tissue

Lungs ability to expand s reduced

Lungs cant hold as much air —> Tidal volume is reduced

—> FVC is also reduced

Reduction is rate of gaseous exchange as diffusion is slower across a thicker membrane

Faster ventilation rate to get enough air into lungs to oxygenate their blood

Symptoms: Shortness of breath, a dry cough, chest pain, fatigue and weakness

Describe how asthma affects the lungs

Airways become inflamed and irritated due to allergic reaction

Smooth muscle lining the bronchioles contracts and large mass of mucus is produced

Airways become constricted so breathing becomes difficult

Air flows in and out is reduced so less oxygen enters the alveoli to oxygenate blood

Reduced air flow = reduced FEV1

Symptoms: wheezing, tight chest, shortness of breath

DIGESTION AND ABSORPTION

Whta is digestion?

The breaking down of large biological molecules into smaller molecules to be able to move across membranes and be easy absorbed

What is amylase used for?

Break down of starch[polysaccharide] to maltose[disaccharide]

Involves hydrolysis of glycosidic bonds

Where is amylase produced?

salivary glands and pancreas

Where does amylase act?

mouth and small intestine

What enzymes hydrolyse disaccharides?

Membrane bound disaccharidases attached to the cell membrane of epithelial cells lining the ileum [final part of small intestine]

Breaks disaccharides into monosaccharides

Glucose + Glucose --> Maltose

Glucose + Fructose --> Sucrose

Glucose +. Galactose --> Lactose

Describe how lipids are broken down

Lipase made in pancreas to work in small intestine

HAEMAGLOBIN

What are haemoglobins?

A group of chemically similar molecules found in many different organisms that all complete the same function

What is haemoglobin composed of?

Protein with a quaternary structure-it's made of four polypeptide chains

What does each polypeptide chain in haemoglobin contain?

A haem group which contains an iron ion and gives the haemoglobin it's red colour

What is the role of haemoglobin?

To carry oxygen around the body

What is oxyhaemoglobin?

haemoglobin bound to oxygen

How many molecules of oxygen can each molecule of human haemoglobin carry?

4

Where does oxygen join and leave haemoglobin/oxyhaemoglobin?

Oxygen joins haemoglobin, in red blood cells, in the lungs

Oxygen leaves oxyhaemoglobin near the body cells

What is association/loading?

When an oxygen molecule joins to haemoglobin

What is dissociation/unloading?

When oxygen leaves oxyhaemoglobin

What does having an affinity for oxygen mean?

The tendency a molecule has to bind with oxygen

What does Haemoglobin's affinity for oxygen depend on?

The partial pressure of oxygen (pO2)

What is partial pressure of oxygen?

A measure of oxygen concentration

What is the relationship between haemoglobins affinity for oxygen and partial pressure of oxygen?

High pO2= Oxygen loads onto haemoglobin to form oxyhaemoglobin

Lower pO2= Oxyhaemoglobin unloads its oxygen

What happens to oxygen loading and unloading in the alveoli?

>HIGH oxygen concentration

>High pO2

>HIGH affinity

>Oxygen ASSOCIATES/LOADS

What happens to oxygen loading and unloading in the respiring tissue?

>LOW oxygen concentration

>LOW pO2

>LOW affinity

>Oxygen DISASSOCIATES/UNLOADS

What does a dissociation curve show?

how saturated the haemoglobin is with oxygen at any given partial pressure

Why is the oxyhaemoglobin dissociation curve S shaped?

When haemoglobin combines to its first O2 molecule it changes shape to make it easier for more O2 to join, creating the steep part.

Once the haemoglobin gets more saturated it's hard for more oxygen to bin, creating the shallow part at the end

What is the partial pressure of carbon dioxide (pCO2)?

measure of concentration of CO2 in a cell

How does pCO2 effect the rate of unloading of O2 in respiration?

What is this called?

>When cells respire they produce CO2 raising pCO2 and increasing the rate of oxygen unloading because HIGHER pCO2= quicker unloading of O2

>The Bohr effect

How does high pCO2 affect the dissociation curve?

It shifts it right

What does it mean when the dissociation curve is more to the left or right?

Left= higher affinity for oxygen

Right= lower affinity for oxygen

What is a Lugworm's affinity for oxygen like?

>Lives in burrows beneath sand

>LOW oxygen concentration in environment

>HIGH affinity for oxygen

What is a Hawk's affinity for oxygen like?

>HIGH respiratory rate

>HIGH oxygen concentration in environment

>LOW affinity for oxygen

What is a Rat's affinity for oxygen like?

>High surface area to volume ratio

>So greater oxygen demmand

>LOW affinity for oxygen

What is Foetal haemoglobin's affinity for oxygen like?

>HIGH affinity for oxygen

>This means maternal haemoglobin will dissociate itself in the placenta and the foetal haemoglobin will load with oxygen.

What is Myoglobin's affinity for oxygen like?

>Red pigment in mammalian muscles.

>Higher affinity for O2 than Hb only releasing it at low partial pressure

THE CIRCULATORY SYSTEM

What is the mammalian circulatory system?

A mass transport system that carries raw materials and waste products around the body

What are the types of blood vessels?

Arteries, arterioles, veins, venules and capillaries

The pulmonary artery carries blood from..... and carries blood to..... ?

From= heart

To=Lungs

The pulmonary vein carries blood from..... and carries blood to..... ?

From= lungs

To= heart

The aorta carries blood from..... and carries blood to..... ?

From= heart

To= body

The vena cava carries blood from..... and carries blood to..... ?

From= body

To= heart

The renal artery carries blood from..... and carries blood to..... ?

From= body

To= kidneys

The renal vein carries blood from..... and carries blood to..... ?

From= kidneys

To= vena cava

What does blood transport?

Respiratory gases, products of digestion, metabolic wastes and hormones

How are the two circuits of the circulatory system different?

One takes blood from the heart to the lungs and back to the heart, and the other takes blood around the rest of the body. Meaning blood goes through the heart twice to complete one full circuit

Structure and function of arteries?

Carries oxygenated blood away from the heart (apart from pulmonary)

-Thick, muscular wall with elastic layer

>Able to withstand high pressure bursts of blood from the heart

-Medium sized lumen

>Encourages fast movement of blood around the body

Structure and function of arterioles?

Arteries divide into smaller vessels called arterioles which direct blood to areas that need it

-Contract to restrict blood flow and relax to allow full blood flow

>Gets blood to the areas that need it

-Circular muscle

>Directs blood to areas that need it

Structure and function of veins?

Carries deoxygenated blood back to the heart

-Thin, muscular wall

>Low pressure

-Valves

>Prevent backflow

-Large lumen

>Allows movement of large volumes of blood to the heart at normal pressure

Structure and function of capillaries?

Arterioles branch into capillaries which form networks called capillary beds

-Always close to cells in exchange tissues decreasing diffusion pathway

-Walls are one cell thick to decrease diffusion pathway

-Large number to increase surface area

>Exchange substances between capillaries and cells

What are venules?

Capillaries connect arterioles and venules at the capillary beds; venules are small blood vessels that connect to veins

What is tissue fluid?

The fluid that surrounds cells in tissues

What is tissue fluid made from?

Small molecules that leave the blood plasma, e.g. Oxygen, water, and nutrients

What does tissue fluid lack that blood contains?

It doesn't have red blood cells are big proteins as they're too large to be pushed out through the capillary walls

What do cells exchange with tissue fluid?

Cells take in oxygen and nutrients from tissue fluid and release metabolic waste into it

What is pressure filtration?

In capillary beds, small molecules are filtered out of the capillary under hydrostatic pressure forming tissue fluid

Why is fluid pushed out of the capillaries?

There is a greater hydrostatic pressure at the start of the capillary bed (nearest the arteries) than in the tissue fluid.