3.3 organisms exchange substances with their environment

The primary function of gaseous exchange in animals

To supply oxygen for respiration

efficient gas exchange surfaces have… (gas exchange)

• large surface area

• short diffusion pathway (thin barrier)

• steep concentration gradient

• good blood supply

• ventilation (in larger organisms)

What is the SA to volume ratio in different sized animals

Smaller animals - Large SA to volume ratio

Larger animals - small SA to volume ratio

What is the metabolic activity in different sized animals

Single-celled and smaller organisms - low metabolic activity

Larger multicellular organisms - high metabolic activity

Why do larger organisms need exchange surfaces e.g lungs, small intestine

• SA to volume ratio is too small (SA isn’t big enough) so substances cannot diffuse fast enough to support their cells

• Diffusion distance is too large - becomes insufficient

How do small single-celled organisms absorb substances (nutrients and oxygen)

• directly from their surroundings via outer surfaces

• Due to their large SA to volume ratio

How do larger organisms gain their substances (oxygen, nutrients)

• exchange surfaces e.g lungs, small intestine

What 2 layers of the plant contain chloroplasts (gas exchange in plants)

• The palisade mesophyll

• The spongy mesophyll

What transports water and sugar in a plant

Water - xylem

Food/sugar - phloem

→ phloem and xylem are found within veins of the leaf

Diagram of the structure of a leaf (gas exchange in plants)

How is the leaf adapted to be an efficient exchange surface (gas exchange in plants)

• many stomata - no cell is far from stomata - short diffusion pathway

• Many air spaces throughout mesophyll layer - so gases readily come in contact with mesophyll cells

• Large surface area of mesophyll cells for rapid diffusion

• Thin - short diffusion pathway

How are leaves adapted to limit the amount of water lost by transpiration (gas exchange in plants)

• waxy cuticle - provides waterproof coating

• Ability to close stomata - in the dark the plant can’t photosynthesis so closes more of its stomata to minimise water loss

Which gases are exchanged in plant for which processes (gas exchange in plants)

• carbon dioxide in, oxygen out for photosynthesis

• Oxygen in, CO2 out for respiration

What is transpiration and the transpiration stream (gas exchange in plants)

Transpiration - loss of water in a plant

Transpiration stream - movement of water through a plant

What are xerophytes (gaseous exchange in plants)

• a plant that has adaptations to survive in ana environment with little water (desert)

Common xerophyte adaptations (gaseous exchange in plants)

To reduce water loss:

• rolled leaves - trap humid air inside, eliminates diffusion gradient - less transpiration

• Spines for leaves - reduces surface area - less transpiration

• Thick waxy cuticle - reduces evaporation

• Sunken stomata - traps humid air leaving the leaf, reducing water potential gradient, slows the rate water leaves the leaf

• Hairs on leaves - traps moisture close to leaf surface to decrease diffusion gradient

Efficient water uptake:

• Extensive root systems to absorb water quickly

2 examples of xerophytes and there adaptations (gaseous exchange in plants)

Cacti (desert xerophyte)

• leaves reduced to spines

• Thick waxy cuticle

• Sunken stomata

• Extensive shallow roots

Marram Grass (sand dune xérophyte)

• rolled leaves

• Hairs on inner leaf surface - reduced air movement - reduced transpiration

• Thick waxy cuticle

• Sunken stomata

• Long roots - reach deeper water

Why do insects have a high oxygen demand (gaseous exchange in insects)

• very active

• Very high rate of metabolism

the tracheal system of an insect (gaseous exchange in insects)

what happens when insects are active and respire anaerobically to get additional oxygen (gaseous exchange in insects)

• tracheoles contain tracheal fluid

• when insects are active they respire anaerobically and produce lactic acid in muscle cells

• this lowers the water potential of the muscle cells so the water moves from the tracheoles to the muscle cells

• so air can be drawn in closer to the muscle cells and therefore reduces diffusion distance speeding up diffusion when oxygen is needed most

why do insects not require a circulatory system to transport oxygen (gas exchange)

• oxygen is delivered directly to tissues through tracheoles

how do insects minimise water loss (gaseous exchange in insects)

• exoskeleton made from chitin - coated with a waxy substance - waterproof

• can close their spiracles to prevent water loss

• hairs around the spiracles - trap water - decreases water potential gradient - decreases water loss

adaptation of tracheae in insects (gaseous exchange in insects)

• rigid rings in their walls to keep air passages open - similar to rings of cartilage

• lined with chitin for support

what do insects do when active to increase oxygen supply (gaseous exchange in insects)

• contract abdominal muscles - lowers pressure in the tracheal system - more air is drawn in

• tracheal fluid moves to muscles cells to break down lactic acid - decreases diffusion distance - faster rate of diffusion

Adaptations for efficient gaseous exchange in insects (gas exchange in insects)

• spiracles supply oxygen directly to cells - short diffusion distance

• thin walls - short diffusion distance

• Tracheae have rigid rings in walls to keep air passages open

• tracheoles are highly branched - large surface area

Structure of a fish gill and where gaseous exchange takes place (gaseous exchange in fish)

• gill lamellae

Adaptations in fish for efficient gaseous exchange (gas exchange in fish)

• very thin lamellae epithelium

• lamellae covers an extensive network of capillaries - good bloody supply

• many lamellae - a large surface area

• Large concentration gradient - more diffusion

• counter- current flow system

Pathway water travels through a fish (gaseous exchange in fish)

• Water passes through the mouth + over gills

• Oxygen diffuses into blood

• Carbon dioxide diffuses into water

• Water passes out of the Operculum

Explain the counter current system in fish and the importance of it (gaseous exchange in fish)

• Water flows in the opposite direction to blood

• Maintains a diffusion gradient the full length of the capillary

• maximises oxygen uptake - 80% oxygen uptake

The difference between a parallel and counter current system in a fish (gas exchange in a fish)

Parallel - diffusion gradient quickly decrease - diffusion only happens at the start

Counter-current - maintains diffusion gradient - diffusion the full length of capillary

How does the Operculum help ventilation in bony fish (gaseous exchange in fish)

• by maintaining a one-way water flow

What is gaseous exchange (gaseous exchange in mammals)

• diffusion of oxygen into the blood and carbon dioxide into the alveoli

What is breathing and ventilation (gaseous exchange in mammals)

• taking air in and expelling air out

What is respiration (gaseous exchange in mammals)

• chemical reaction that uses oxygen to release energy in the form of ATP

what is the passage of air in the lungs (gas exchange in mammals)

• Nose/mouth

• trachea

• Bronchi (bronchus - single)

• Bronchioles

• Alveoli

Adaptations of the alveoli for efficient gaseous exchange (gas exchange in mammals)

• Capillaries & alveoli - 1 cell thick, constists of squamous epithelial cells (flattened cells) - short diffusion distance

• Large surface area - faster diffusion

• A high concentration gradient - high oxygen in alveoli & low in blood - opposite for CO2 - faster diffusion

• Moist lining - makes the membrane permeable - permeable to oxygen & CO2 - faster diffusion

• Moist lining - lubricant - stops lungs drying out

• surfactant reduces surface tension and prevent collapse

what happens when we inhale (gas exchange in mammals)

• diaphragm contracts and flattens

• thoracic volume increase

• pressure in lungs decreases (lower than the atmospheric air pressure outside)

• external intercostal muscles contract

• internal intercostal muscles relax

• air moves in

what happens when we exhale (gas exchange in mammals)

• diaphragm relaxes and becomes domed

• thoracic volume decreases

• pressure in lungs increases (above atmosphere air pressure)

• external intercostal muscles relax

• internal intercostal muscles contract

• air moves out

structure of the trachea (gas exchange - tissues in the lungs)

• 16-20 rings of hyaline cartilage - provides support, prevent from collapsing

• ring are in C shapes - provides flexibility if food goes down

• elastic fibres and smooth muscle - also provides flexibility

• lined with a ciliated epithelium with goblet cells in-between

→ goblet cells - secrete mucus to trap tiny particles in the air

→ cilia - sweep the mucus to the throat

structure of the bronchi (gas exchange - structure of the lungs)

• similar to trachea but smaller

• small sections of hyaline cartilage - provides support, prevent from collapsing

• ring are in C shapes - provides flexibility if food goes down

• elastic fibres and smooth muscle - also provides flexibility

• lined with a ciliated epithelium with goblet cells in-between

→ goblet cells - secrete mucus to trap tiny particles in the air

→ cilia - sweep the mucus to the throat

structure of bronchioles (gas exhange - tissues in the lungs)

• do not have hyaline cartilage (only large bronchioles)

• only have elastic fibres and muscle - to they can contract and expand easily

• still has ciliated epithelium with goblet cells

explain how the bronchioles constrict and relax and why (gas exchange - tissues in the lungs)

• contains smooth muscle

• smooth muscle contract - bronchioles constrict as elastic fibres deform (close)

→ less harmful substances in gases reaching alveoli

• smooth muscle relaxes - bronchioles dilate as elastic fibres recoil to original size and shape (open)

compare the structure of bronchioles and trachea (gas exhange - tissues in the lungs)

structure of the alveoli and features of the structures (gas exchange - tissues in the lungs)

• elastic fibres

→ become deformed when we breathe in so the alveoli can stretch without bursting

→ recoil when we breathe out forcing the air out

• squamous epithelial cells

→ flattens cells - reduces diffusion distance

→ permeable - allows diffusion of gases

compare the difference in structure between the trachea, bronchi, bronchioles and alveoli (gas exchange - tissues in the lungs)

what does gas exchange efficiency depend on (gas exchange)

• SA

• thickness

• concentration gradient

What is tidal volume (gas exchange - measurements of lung capacity)

• the volume of air inspired or expired per breath when at rest

What is vital capacity (gas exchange - measurements of lung capacity)

• the largest volume of air that can be inspired or expired in one breath

What is residual volume (gas exchange - measurements of lung capacity)

• the volume of air that always remains in the lungs

What is dead space (gas exchange - measurements of lung capacity)

• the air in the bronchioles, bronchi and trachea - no gaseous exchange between this air and the blood

What is inspiratory reserve volume and expiratory reserve volume (gas exchange - measurements of lung capacity)

• Inspiratory - how much more air can be breathed in above normal tidal volume when taking in a deep breath

• Expiratory - how much more air can be breathed out above normal tidal volume

How to work out total lung capacity (gas exchange - measurements of lung capacity)

• vital capacity + residual volume

Diagram of the measurements of lung capacity from a spirometer (gas exchange)

How does a spirometer work (gas exchange - measurements of lung capacity)

• a chamber filled with medical grade oxygen

• when a person breathes in - oxygen leaves the chamber and sinks down (volume decreases)

• breathe out - fills the chamber - floats upwards and volume increases

• picked up by a kymograoh to produce a trace

• soda lime absorbs carbon dioxide exhaled

• volume in spirometer decreases over time as oxygen is used in respiration

spirometer health and safety (gas exchange- measurements of lung capacity)

• disposable mouth piece

• soda lime to absorb CO2

• medical grade oxygen

what is pulmonary ventilation and the calculation (gas exchange - measurements of lung capacity)

• the total volume of air that moves in or out lungs per minute

• pulmonary ventilation rate = tidal volume x breathing rate

what is a risk factor (gas exchange - lung disease)

• any factor that is linked with with an increased chance of suffering from a particular condition or disease

what is the incidence of disease (gas exchange - lung disease)

• the number of cases that occur within a particular group of people within a given time

e.g the number of smokers that develop cancer in a year

what is correlation (gas exchange - lung disease)

• an association between two variable

• a positivite correlation doesn’t equal causation

lung disease risk factors (gas exchange - lung disease)

• smoking

• air pollution

• genetic makeup

• infections - frequent chest infections increase incidence

• occupation - dust, chemical exposure

general symptoms of lung diseases + why (gas exchange - lung disease)

• shortness of breath - loss of elasticity - reduced oxygen levels

• wheezing - air passing through constricted bronchi and bronchioles

• pain and discomfort in chest - tissue causing pressure on the lungs

• fatigue - reduced intake of oxygen - less energy from respiration

what is prospective and retrospective study (gas exchange - lung disease)

• prospective - collecting data as it becomes available

• retrospective- collecting data from the past

difficulties when collecting data on health risks (gas exchange - lung disease)

• it’s hard to find enough people with similar lifestyles for the control group

• data from asking people about their past is often unreliable

• studies with multiples follow ups cost time and money

what to consider when looking at the results of a health risk study (gas exchange - lung disease)

• sample size - larger sample is more reliable

• control group - did it match close enough

• levels of exposure - pay attention to the different levels of exposure to the risk factor in the study e.g how many cigarettes smoked a day

What is the alimentary canal (digestion and absorption)

The passage from the mouth to the anas

• Mouth

• oesophagus

• stomach

• small intestine

• large intestine

• Rectum

• Anus

What is digestion (digestion and absorption)

• the hydrolysis of large insoluble biological molecules into smaller soluble molecules that can be absorbed across cell membranes and used in the body

What are lacteals (digestion and absorption)

• lymphatic vessels found at the centre of the villi

What is the lumen (digestion and absorption)

The hollow part of a structure

What are micelles (digestion and absorption)

Emulsified fat droplets

What are chylomicrons (digestion and absorption)

• the product of triglycerides associating with cholesterol and lipoproteins

What is the Ileum and Colon (digestion and absorption)

Ileum - small intestine

Colon - large intestine

What is assimilate (digestion and absorption)

• nutrients in food are taken into the cells of the body

What is emulsification (digestion and absorption)

• breakdown of fat into smaller molecules

• To provide a large surface area

The two stages of digestion (digestion and absorption)

physical breakdown

• teeth and muscles (churning)

Chemical breakdown

• enzymes hydrolyse large insoluble molecules into smaller ones

Where are the three main enzymes produced, what does the reaction catalyse and where does the reaction occur (digestion and absorption)

How are carbohydrates digested (digestion and absorption)

• saliva (contains salivary amylase - SA) is mixed with food

• Starch → maltose

• in stomach, acid denatures SA to prevent further breakdown of starch

• In small intestine, mixes with pancreatic juices contains pancreatic amylase - remaining starch is hydrolysed into maltose

• Small intestine muscles pushes food along - maltase a ‘membrane-bound disaccharide’ hydrolyses maltose into alpha glucose

How are sucrose and lactose broken down - carbohydrates (digestion and absorption)

• sucrose + sucrase → glucose + fructose

• Lactose + lactase → glucose + galactose

Adaptations of the Ileum (small intestine) (digestion and absorption)

• thin

• Villi give it a large surface area

• Steep concentration gradient as dense capillary network

What do the three digesting proteins do (digestion and absorption)

endopeptidases

• hydrolyse peptide bonds in the middle of the protein molecule to produce polypeptides

exopeptidases

• hydrolyse end amino acids of polypeptide to release dipeptides

Dipeptidases

• hydrolyse bonds between two amino acids of a dipeptide to release single amino acids

• These are membrane bound, part of the epithelial cell lining of the Ileum

How are proteins digested (digestion and absorption)

Stomach:

• Stomach acid conditions start to denature proteins for enzymes to work better

• Endopeptidases are released into stomach lining e.g pepsin

small intestine:

• endopeptidases from the pancreas continue breaking down polypeptides e.g trypsin

• Exopeptidases then release dipeptides

• Dipeptidases in the epithelial membrane hydrolyse peptides into single amino acids - absorbed into the bloodstream

How are lipids digested (digestion and absorption)

in the small intestine:

• emulsification - bile salts split lipids into micelles (emulsified fat droplets)

• This increases surface area to ensure lipases work more effectively

• Lipase (produced in the pancreas) hydrolyses the ester bonds in triglycerides to produce monoglycerides and fatty acids

How are lipids absorbed (digestion and absorption)

• fatty acids + monoglycerides (micelles) re associate with bile salts - so they don’t clump together and can move through Ileum

• Micelles break down when they come in contact with epithelial cells -release monoglycerides and fatty acids and enter epithelial cells by diffusion

• Link to form triglycerides

• Combine with proteins at Golgi apparatus to form chylomircons

• Move out by exocytosis and enter lymphatic capillaries - transported away from Ileum

How are amino acids and monosaccharides e.g glucose absorbed (digestion and absorption)

Facilitated diffusion - when there is a high concentration of glucose in the lumen

Or

Co-transport:

• Active transport of sodium ions out of the cell + into the blood to lower concentration in the epithelial cells

• So sodium ions can move from the Ileum down the concentration gradient with glucose (co-transport) by facilitated diffusion

• Constant diffusion of glucose from cells to blood as blood is moved around body so conc in always lower in the blood