3.3 Organisms exchange substances with their environment Flashcards
3.3.1 Surface Area to Volume Ratio
How do you calculate the total surface area of an object?
Sum of surface area of all faces of shape
How do you calculate surface area for squares/rectangles, triangles, circles, spheres, cylinders?
Squares/Rectangles = length x width Triangles = ½ x base x height Circles = π x radius² Spheres = 4 x π x radius² Cylinder = (2 x (2 x π x radius)) + (length x width)
How do you calculate the volume of cubes/cuboids, prisms, spheres?
Cubes/Cuboids = length x width x height Prisms = area of cross-section x length Spheres = 4/3 x π x radiusᶟ
3.3.2 Gas Exchange
Why can’t insects use their body surface to exchange respiratory gases?
An efficient gas exchange surface would also leave them vulnerable to water loss as it would be an efficient water loss surface also
How do insects conserve water?
Rigid Exoskeleton – waterproof cuticle made of chitin
Small Surface Area: Volume – Minimises water loss area
Spiracles – Open and close to prevent water loss
Hairs around spiracles – trap humid air
Air sacs along tracheae – store oxygen if spiracles are closed for long time
How do the tracheae work in insects?
It is an internal network of tubes
Tracheae divide into tracheoles
Tracheoles branch throughout the body tissue of insects
Allows air to be brought directly to respiring tissues
How do spiracles work in insects?
Spiracles are tiny pores at end of tracheae
They allow respiratory gases in and out of insect
Valves control opening/closure of spiracle
When open, water can evaporate out of spiracles
They are closed most of the time to control water loss and only open to allow gas exchange
Whilst spiracles are closed, the level of oxygen in the tracheae decreases. Once level becomes too low, the spiracles open
Why aren’t insects bigger/ limitation of the tracheal system?
- Insects rely on diffusion rather than a transport system such as lungs. For diffusion to be adequate the diffusion distance must be short. This limits the size that insects can grow to
- Bigger insect = more cells = more demand for oxygen. Tracheal system could not meet these demands
- A larger insect = heavier exoskeleton = insect unable to move
How does the diffusion gradient allow gases to move in and out of the tracheal system?
During respiration, oxygen is used
Oxygen concentration at tracheole ends falls which creates a diffusion gradient
Oxygen therefore diffuses from atmosphere along the tracheae and tracheoles to the cells
Carbon Dioxide is produced by respiring cells which creates diffusion gradient in opposite direction
The carbon dioxide then diffuses out of the tracheoles and into the atmosphere
How does muscle contractions/mass transport allow gases to move in and out of tracheal system?
Abdominal pumping means contraction of insect muscles
This causes tracheae to be ‘squeezed’ and reduced in volume
Therefore, some air is expelled from tracheae
This is common in larger insects as it uses energy
How does water filled tracheoles allow gases to move in and out of tracheal system?
Anaerobic respiration produces lactate/lactic acid
Lactate is water soluble so lowers water potential of muscle cells
Water moves into muscle cells from tracheoles meaning the volume of tracheole ends decreases, drawing air in
How do fish exchange gas?
Water containing oxygen enters the fish through its mouth and passes out through the gills
Each gill is made of lots of thin plates called gill filaments, which increase the surface area for more efficient gas exchange
The gill filaments are covered in tiny structures called lamellae, which further increase the surface area
The lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion due to rich blood supply
How does counter-current flow help gas exchange in fish?
Blood flows through the lamellae in one direction and water flows over in the opposite direction
It maintains a large concentration gradient between the water and the blood.
The concentration of oxygen is always higher than that in the blood, so as much oxygen as possible diffuses from the water into the blood
Blood already loaded with oxygen meets water with maximum concentration of oxygen, so oxygen diffuses into the blood
Blood with low oxygen concentration meets water that has had most of its oxygen removed. Diffusion still happens and results in the maintenance of a favourable oxygen gradient across the whole gill which allows maximum oxygen diffusion
What is the equation for photosynthesis?
Carbon dioxide + water -> Glucose + oxygen
6CO2 + 6H2O -> C6H12O6 + 6O2
What is the equation for respiration?
Oxygen + glucose -> Carbon dioxide + water
6O2 + C6H12O6 -> 6CO2 + 6H2O
How are leaves adapted to exchange gas?
Large Surface Area - Greater surface for diffusion Thin - Short diffusion pathway Selectively permeable - Controls what comes in and out Diffusion gradient - Large diffusion gradient = increased rate of diffusion
What structures do leaves have to facilitate efficient exchange?
Stomata
- Small pores which allow gases in and out
- All cells are close to a stomatal pore so there is a short diffusion pathway
Air Spaces
- Interconnected air spaces throughout the mesophyll layer so gases can move around mesophyll cells
Spongy Mesophyll Layer
- Large surface area of mesophyll cells allows for maximum diffusion
What do stomata do?
Are tiny pores on the underside of leaves
Each stoma is surrounded by guard cells which control the opening and closing of stomata
Control the diffusion of gas and water vapour
In daytime: Photosynthesis occurring so needs lots of CO2 so stomata usually open
In night-time/dark: No photosynthesis so no need for CO2 so stomata closed
How can adaptations be detrimental to a plant?
Large SA of a leaf allows it to exchange gases and absorb sunlight
These features also promote desiccation (drying out)
What are xerophytes and how are they adapted to limit water loss?
Xerophytes are plants adapted to living in areas with short supply of water Thick cuticle - Barrier to evaporation - Shiny surface reflects heat so lowers temperature Sunken stomata - Moist air trapped so lengthens diffusion pathway and reduces evaporation rate Reduced SA:Vol ratio - Less efficient diffusion Hairs on leaves - Traps heat Rolled up leaves - Traps heat and moisture
Features of human gas exchange system
Lungs
- Lobed structures made up of a series of highly branched tubules (bronchioles) which end in tiny air sacs called alveoli
Trachea
- Flexible airway supported by cartilage rings
- The cartilage prevents the trachea collapsing as air pressure inside falls when breathing in
- Muscular walls lined with ciliated epithelium and goblet cells
Bronchi
- Trachea splits into 2 bronchi
- Larger bronchi are supported by cartilage rings
- Lined with ciliated epithelial and goblet cells
- Produce mucus to trap dirt particles and have cilia that move the dirt-laden mucus towards throat
Bronchioles
- Subdivisions of bronchi
- Muscular walls lined with epithelial cells allowing them to constrict to control airflow in and out of alveoli
Alveoli
- Minute air sacs at the end of bronchioles
- Collagen and elastic fibres between alveoli
- Lined with epithelium
- Elastic fibres allow alveoli to stretch as fill with air when breathing in. They then spring back during breathing out to expel CO2 rich air
- Alveolar membrane is the gas exchange surface
Why does gas exchange need to happen?
All aerobic organisms need a constant supply of O2 to release energy in the form of ATP during respiration
The CO2 produced needs to be removed as its build up could be harmful to the body
Why is the volume of O2 absorbed and volume of CO2 removed large in mammals?
They are relatively large organisms with a large volume of living cells
They maintain a high body temperature which is related to them having high metabolic and respiratory rates
Why is the site of gas exchange in mammals (lungs) located inside the body?
Air is not dense enough to support and protect these delicate structures
The body as a whole would otherwise lose a great deal of water and dry out
What is inspiration?
When air pressure of atmosphere is greater than air pressure inside the lungs, and air is forced into the lungs
Is an active process so requires energy
What is expiration?
When air pressure in lungs is greater than air pressure of atmosphere, and air is forced out of lungs
Is a largely passive process so does not require much energy
What three sets of muscles movement cause pressure changes in the lungs?
Diaphragm
- A sheet of muscle that separates the thorax from the abdomen
Internal Intercostal Muscles
- Lie between the ribs whose contractions lead to expiration
External Intercostal Muscles
- Lie between the ribs whose contractions lead to inspiration
How do you calculate the pulmonary ventilation rate?
Pulmonary ventilation rate (dm3min-1) =
Tidal volume (dm3) x Breathing rate (min-1)
Describe the process of inspiration
External intercostal muscles contract, while internal intercostal muscles relax
Ribs are pulled upwards and outwards, increasing the volume of the thorax
The diaphragm muscles contract, causing it to flatten, which also increases the volume of the thorax
The increased volume of thorax results in reduction of pressure in the lungs
Atmospheric pressure is now greater than pulmonary pressure, and so air is forced into lungs
Describe the process of expiration
Internal intercostal muscles contract while external intercostal muscles relax
Ribs move downwards and inwards decreasing volume of the thorax
Diaphragm muscles relax and so it is pushed up again by contents of abdomen that were compressed during inspiration. Volume of the thorax is therefore further decreased
Decreased volume of thorax increases pressure in lungs
Pulmonary pressure now greater than atmospheric pressure, and so air is forced out of lungs
Where is the site of gas exchange in mammals?
The epithelium of the alveoli
What does there need to be to maintain a diffusion gradient?
Movement of both the environmental medium (e.g. air) and internal medium (e.g. blood)
Describe features of alveoli
300 million alveoli in each human lung
Total surface area around 70m2
Each alveolus lined with epithelial cells
Around each alveolus is a network of pulmonary capillaries, so narrow that red blood cells are flattened against the thin capillary walls order to fit through
These capillaries have walls that are only a single layer of cells thick
Why is the diffusion of gases between alveoli and blood very rapid?
Red blood cells are slowed as they pass through pulmonary capillaries, allowing more time for diffusion
The distance between alveolar air and red blood cells is reduced as the red blood cells are flattened against capillary walls
The walls of both alveoli and capillaries are very thin and therefore the distance over which diffusion takes place is short
Alveoli and pulmonary capillaries have a large total surface area
Breathing movements constantly ventilate the lungs, and the action of the heart constantly circulates blood around the alveoli. Together, these ensure that a steep concentration gradient of the gases to be exchanged is maintained
Blood flow through the pulmonary capillaries maintains a concentration gradient
What is a correlation?
Occurs when a change in one of two variables is reflected by a change in the other variable
A correlation does not mean that there is a causal link
What are the risk factors for lung disease?
Smoking Air pollution Genetic make-up Infections Occupation
What is emphysema?
A loss of elasticity preventing expansion and contraction
Common in smokers
Healthy lungs contain elastic tissue made from elastin (protein), so lungs stretch when we inhale and spring back when we exhale
In emphysemous lungs the elastin has been permanently stretched so lungs no longer able to expel all air from alveoli
SA of alveoli reduced as some alveoli burst so little gas exchange occurs
3.3.3 Digestion and absorption
What is the role of the oesophagus?
Carries food from the mouth to the stomach
What is the role of the stomach?
A muscular sac with an inner layer that produces enzymes
Its role is to store and digest food, especially proteins
It has glands that produce enzymes which digest protein
What is the role of the ileum?
A long muscular tube
Food is further digested in the ileum by enzymes that are produced by its walls and by glands that pour their secretions into it
The inner walls of the ileum are folded into villi, giving them a large SA
The surface area of the villi is further increased by millions of tiny projections called microvilli on epithelial cells of each villus
This adapts the ileum for its purpose of absorbing the products of digestion into the bloodstream
What is the role of the large intestine?
Absorbs water
Most of the water that is absorbed is water from the secretions of the may digestive glands
What is the role of the rectum?
The final section of the intestines
The faeces are stored here before periodically being removed via the anus in a process called egestion
What is the role of the salivary glands?
Situated near the mouth
They pass their secretions via a duct into the mouth
These secretions contain the enzyme amylase, which hydrolyses starch into maltose
What is the role of the pancreas?
A large gland situated below the stomach
It produces a secretion called pancreatic juice
This secretion contains proteases to hydrolyse proteins, lipase to hydrolyse lipids and amylase to hydrolyse starch
What is digestion?
The process in which large molecules are hydrolysed by enzymes into small molecules, which can be absorbed and assimilated
What are the two stages of human digestion?
Physical breakdown
Chemical digestion
What is physical breakdown?
If the food is large, it is broken down into smaller pieces by means of structures such as teeth
This makes it possible to ingest the food and also provides a large SA for chemical digestion
Food is churned by the muscles in stomach wall and this also physically breaks it up
What is chemical digestion?
Chemical digestion hydrolyses large, insoluble molecules into smaller, soluble ones
It is carried out by enzymes
All digestive enzymes function by hydrolysis which is the splitting up of molecules by adding water to chemical bonds that hold them together
Enzymes are specific so more than one enzyme is needed to hydrolyse large molecules
Name the three most important digestive enzymes and their roles
Carbohydrases – hydrolyse carbohydrates to monosaccharides
Lipases – hydrolyse lipids (fats and oils) into glycerol and fatty acids
Proteases – hydrolyse proteins to amino acids
Describe the process of carbohydrate digestion
The enzyme amylase is produced in the mouth and pancreas.
Amylase hydrolyses the alternate glycosidic bonds of the starch molecule to produce the disaccharide maltose
The maltose is then hydrolysed into the monosaccharide alpha glucose by the enzyme maltase
Maltase is produced in lining of ileum
What is the process of carbohydrate digestion (especially maltose) in humans?
Saliva enters mouth from salivary glands and is mixed with food during chewing
Saliva contains salivary amylase which starts to hydrolyse any starch in the food to maltose. Also contains mineral salts that maintain pH at neutral which is optimum pH for salivary amylase to work
Food is swallowed and enters stomach, where conditions are acidic. Acid denatures amylase and prevents further hydrolysis of the starch
Food is passed to small intestine, where it mixes with secretion from pancreas called pancreatic juice
Pancreatic juice contains pancreatic amylase. This continues hydrolysis of remaining starch to maltose. Alkaline salts are produced by both pancreas and intestinal wall to maintain pH at neutral so amylase can function
Muscles in intestine wall push food along ileum. Its epithelial lining produces disaccharide maltase. Maltase is not released into lumen of ileum but is part of cell-surface membranes of epithelial cells. So is referred to as membrane-bound disaccharidase
Maltase hydrolyses maltose from starch break down into alpha glucose
