Exchange

What does the SA:V affect?

How fast substances are exchanged

Do larger or smaller organisms have larger SA:V?

Smaller

How do you work out the surface area?

Length x width x amount of surfaces

How do you work out the volume?

Length x width x height

Why do organisms exchange substances with the environment?

o   Cells need oxygen (aerobic respiration) and nutrients.

o   Cells must excrete waste e.g., CO2 and urea.

o   Heat must be exchanged to keep organisms at roughly same temperature.

Why is diffusion in multicellular organisms slow?

some cells are deep within the body so there is a large distance, and they have a small SA:V making it difficult to exchange substances

What do multicellular organisms need to speed up diffusion?

specialised exchange organs and an efficient system to carry substances to and from their cells – mass transport

What is Ficks law?

rate of diffusion is proportional to: (SA x difference in conc) /            length of diffusion path

What are adaptations for exchange?

1.    Flattened shape brings cells close to surface.

2.    Specialised exchange surfaces with large surface area.

3.    Mass transport systems to carry substances to and from their individual cells.

Why do animals with high SA:V lose more water?

it evaporates from their surface. This is a problem for animals living in hot places

How do some animals overcome the issue of water loss?

Some small mammals have kidney structure adaptations so they produce less urine

How do animals support their metabolic rates?

Eating high energy foods

How do smaller mammals keep warm?

Thick fur and hibernate

How do larger animals adapt to hot conditions?

Elephants have large flat ears and hippos spend a lot of time in the water.

What is the structure of gills?

o   Gills are the gas exchange surfaces in fish.

o   Water is taken in through the mouth and forced over the gills.

o   Composed of gill filaments, stacked.

o   Gill lamellae project at right angles from the filaments and serve to increase the SA of gills for gas exchange.

o   Gill lamellae are a few cells thick and contain blood capillaries which are arranged so the blood flows in the opposite direction to the water.

What is the parallel flow across the lamellae?

conc gradient will level out so diffusion stops when blood is only 50% oxygen (DOESN’T HAPPEN)

What is the counter-current flow across lamellae?

blood flows through lamellae one direction and water flows over them in the other.

This means that water always has a higher oxygen concentration = a steep diffusion gradient maintained along the entire length of the gill structure (DOES HAPPEN).

How do single-celled organisms exchange gases?

o   Unicellular organisms have a large SA:V.

o   Gases are exchanged efficiently across the whole body surface.

o   There is a thin surface membrane and short diffusion pathway enabling oxygen to diffuse into the cell and carbon dioxide to diffuse out the cell.

What are spiracles?

lip-like openings on each segment of the insect that are can close to prevent water loss and opened when more respiration is needed.

What are tracheal tubes?

Connected to each spiracle branch into a series of tracheoles.

What are tracheoles?

fine respiratory tubes of trachea that go into individual body cells so oxygen can directly diffuse

What are tracheal systems?

a highly adapted exchange system where tracheal tubes run from the body surface into the tissues and it transport gases directly between the external environment and body cells.

How are gases exchanged in insects?

1. diffusion gradient

2. ventilation by rhythmic abdominal movements to move air in and out the spiracles

3. the end of the tracheoles are filled with water

How does the diffusion gradient help gas exchange in insects?

o   Oxygen moves down conc gradient from air into body cells.

o   Carbon dioxide moves down a conc gradient from body cells into the air.

How does ventilation help gas exchange in insects?

Further speeds up the exchange of respiratory gases by generating mass movements of air in and out of the tracheal tubes.

How does the end of the tracheole being filled with water help gas exchange in insects?

o   During a lot of activity the muscle cells around the tracheoles respire anaerobically, producing lactate.

o   This lowers the water potential causing water to move into the cels from the tracheoles via osmosis.

o   The water at the end of the tracheoles decreases in volume, causing air to be drawn in.

How do insects control for water loss?

o   If losing too much water, they close spiracles using muscles.

o   They have waxy cuticles and hairs around spiracles to reduce evaporation.

What do plants need CO2 for?

Photosynthesis and produces O2 as waste

What do plants need O2 for?

respiration and produces CO2 as waste

Where are gases exchanged in leaf plants?

Mesophyll cells

How are gases moved through the leaf?

In and out stomata and through air spaces

What are xylem and phloem used for?

Transport systems for water, ions and sucrose

What happens to plants during the day?

CO2 enters and excess O2 and water vapour leave

What happens to plants at night?

O2 enters, CO2 and water vapour leaves (if stomata open)

What are the adaptations of leaf cells for gas exchange?

1.    Diffusion distance – spongy mesophyll has air spaces so no cell is far from air spaces. There are so many stomata so no cell is far from stomata.

2.    Surface area – large surface of mesophyll cells in contact with air spaces.

What is transpiration?

What are the factors that reduce water loss and how do they effect water loss?

1.    High humidity – reduces conc gradient for water loss as there is water vapour in the air.

2.    Low temperatures – less evaporation so less water drawn up and water particles move slower.

3.    Out of wind – reduces the removal of water so reduces conc gradient.

4.    Closing the stomata - water cannot enter or leave.

How do plants control for water loss?

o   When guard cells are turgid, they bulge and the stomata opens. If the guard cells start to dehydrate, they lose water and shrink which closes the stomata.

o   Waxy cuticle on leaf is impermeable to water.

o   Most stomata found on underside of leaf as its cooler.

o   Thick leaves = reduces water loss.

o   Spines/ hairs increase boundary layer.

As you breathe in, where does air enter?

Trachea

What does the trachea split into?

Two bronchi that each lead to a lung

What does each bronchus branch into?

Bronchioles which end in alveoli

What is the trachea?

Main passageway where air passes from the upper respiratory tract to the lungs.

What is the C shaped cartilage?

Allows flexibility and prevents the trachea from collapsing during respiration, they are rings stacked on top of each other.

What is the ribcage?

Protect the vital organs in the chest and assist in breathing by expanding and contracting.

What do the bronchus and bronchioles do?

Conducts air to the lungs. The bronchi cleans the air and distributes it into the gas exchanging zone. Bronchioles deliver air to diffuse to the alveoli.

What does the alveolus do?

Move oxygen and carbon dioxide molecules into and out of the bloodstream.

What does the pleural cavity do?

Allows optimal expansions and contraction of the lungs.

What does the diaphragm do?

Muscle that forms a dome shape at base of chest to help you breathe as it contracts. Separates the abdomen from the chest

What does the intercostal muscles do?

Found between the ribs, made of two layers: internal and external intercostal muscles. Creates and moves the chest wall and the muscles help elevate the ribs.

What processes does ventilation consist of?

inspiration/inhalation and expiration/exhalation

What type of intercostal muscles are used in inhalation?

External, they contract along with diaphragm muscles

What does this muscle contraction cause?

rib cage to move upwards and outwards and diaphragm to flatten which increases the volume of the thoracic cavity (space where lungs are).

As the volume of thoracic cavity increases, what happens?

the lung pressure decreases to below atmospheric pressure.

Air will always flow from higher pressure to lower pressure so air flows down the trachea into the lungs.

Active process and requires energy.

What type of intercostal muscles are used in normal exhalation?

External, they along with diaphragm muscles relax

What does the muscles relaxing cause?

Ribcage moves downwards and inwards and the diaphragm curves upwards to become dome shaped.

Volume of thoracic cavity decreases, causing the air pressure to increase to above atmospheric pressure so air is forced down the gradient and out the lungs.

What is forced exhalation?

Forcing the air out your lungs

What type of intercostal muscles are used in forced exhalation?

External relax and internal contract to pull the ribcage further down and in

Why does the alveoli have large SA:V?

Millions of alveoli.

Larger surface to exchange over.

Why do the alveoli have a short diffusion pathway?

Walls of the alveoli are very thin.

Less distance for the diffusion to travel = more efficient.

Why are the alveoli partially permeable?

Allow gases to pass through easily but not larger molecules.

How does air flowing in and out the lungs help with gas exchange?

Breathing ensures a continuous flow of fresh air to the alveoli ensuring there is always a higher conc of oxygen in the alveoli than the blood.

How does the blood flowing through capillaries help with gas exchange in lungs?

Blood circulation ensures deoxygenated blood with a higher conc of CO2 reaches the capillaries around the alveoli, ensuring there is always a higher conc of CO2 in the blood than the alveoli.

How does oxygen move through the body?

down the trachea, bronchi and bronchioles into the alveoli. This happens down a pressure gradient.

Oxygen diffuses out the alveoli, across the alveolar epithelium and capillary endothelium into haemoglobin in the blood where it can be transported round the body down diffusion gradient.

How does co2 move through the body?

Carbon dioxide moves down its own diffusion and pressure gradient in opposite direction to oxygen so it can be breathed out. CO2 diffuses into the alveoli from the blood.

What is the tidal volume?

Volume of air in each breath (usually between 0.4 dm³ and 0.5 dm³)

What is the ventilation rate?

number of breaths per minute (healthy – 15 breaths)

What is the forced expiratory rate?

 max volume of air that can be breathed out in 1 second.

What is the forced vital capacity?

max volume of air possible to breathe forcefully out of the lungs after a deep breath in.

What causes emphysema?

Air pollution or smoking

What happens during emphysema?

Smoking/air pollution causes inflammation that attracts phagocytes to produce an enzyme to break down elastin

What is elastin?

protein found in walls of alveoli that helps alveoli return to normal shape after inhalation/exhalation

What does the loss of elastin lead to?

alveoli can’t recoil to expel air. 

Leads to destruction of alveoli walls = reduced surface area = decreased rate of gas exchange. 

What are the symptoms of emphysema?

shortness of breath, wheezing, increased ventilation rate as they try to increase air getting to lungs.

What causes tuberculosis?

Bacteria

What happens during tuberculosis?

Immune system cells build a wall around the bacteria in lungs.

This forms small, hard lumps – tubercles.

Infected tissue within the tubercles dies and gas exchange surface is damaged.

During TB, does tidal volume increase?

No, it decreases which means less air can be inhaled, to take up enough oxygen they have to breathe faster

What are the symptoms of TB?

persistent cough, coughing up blood, chest pains, shortness of breath and fatigue

What is fibrosis?

Formation of scar tissue in the lungs as a result of an infection or exposure to substances like dust

Why is having scar tissue bad?

Scar tissue is thicker and less elastic than normal lung tissue = lungs less able to expand so cant hold as much air = decreased tidal volume.

During fibrosis, does ventilation rate increase?

Yes, to get enough air into their lungs to oxygenate blood

What are the symptoms of fibrosis?

shortness of breath, dry cough, chest pain, fatigue and weakness

What is asthma?

Respiratory condition where airways become inflamed and irritated

What causes asthma?

Allergic reaction

What happens during an asthma attack?

During an asthma attack, smooth muscle lining the bronchioles contracts and lots of mucus produced

Causes constriction of airways, making it difficult to breathe properly = air flow in/out lungs reduced.

During asthma, does forced expiratory rate increase?

No, it reduces

What are the symptoms if asthma?

wheezing, tight chest, shortness of breath

How do drugs relieve asthma symptoms?

Symptoms can be relieved with drugs (inhalers) which can cause the muscle in bronchioles to relax = opens airways

What are risk factors?

factors that increase a persons chance of getting a disease

What is a correlation?

link between two factors, doesn’t always mean one causes another

What happens during digestion?

digestion breaks down those large insoluble molecules into smaller soluble ones through hydrolysis so they can cross the cell membrane.

Why do large insoluble molecules need to be broken?

They are too big to cross the cell membranes

What is chemical digestion?

using enzymes to catalyse hydrolysis reactions

What is physical digestion?

using teeth or churning in the stomach to break down large molecules into smaller ones with a larger surface area for enzymes to work on

What is amylase?

o   Digestive enzyme that catalyses breakdown/hydrolysis of starch into maltose by breaking glycosidic bonds.

o   Produced in salivary glands and pancreas which releases amylase into small intestine.

o   Starch + water = maltose + glucose

What are membrane bound disaccharides?

o   Enzymes that are attached to the cell membranes of epithelial cells lining the ileum (microvilli).

o   Help breakdown/hydrolysis disaccharides into monosaccharides for absorption.

o   For example, lactose is broken down into glucose and galactose by breaking the glycosidic bonds.

What are endopeptidases?

o   Enzyme that cleave (cut) peptide bonds within the interior of a polypeptide chain producing shorter fragments.

o   Trypsin and pepsin operate in small intestine and stomach.

o   Polypeptide + water = polypeptide fragments.

What are exopeptidases?

o   Catalyse the hydrolysis of peptide bonds at the end of protein molecules.

o   Dipeptidases work specifically on dipeptides, they act to separate the 2 amino acids that make up dipeptides by hydrolysing the peptide bond between them

o   Dipeptidases are often found on the cell-surface membrane of the epithelial cells in the small intestine.

What is lipase?

o   Catalyse the breakdown of lipids into monoglycerides and fatty acids by hydrolysing the ester bonds in lipids.

o   Made in pancreas then secreted into the small intestine.

o   Triglyceride + water = fatty acid + monoglyceride.

What is bile?

o   Emulsifies fat globules into smaller droplets.

o   This increases the surface area for lipase to work more efficiently.

o   Produced by the liver and stored in the gallbladder.

o   They are not enzymes, but they are important in lipid digestion.

What is the ileum?

Found after the duodenum and jejunum and its function is to absorb vitamin B12 and anything not absorbed by the jejunum.