3.3 Organisms exchange substances with their environment Flashcards
What are xerophytes?
-plants living in hot, dry environments, adapted to minimise water loss
-e.g. cacti
Why do xerophytes need to minimise water loss?
hot environment, and low water vapour in the air
-the risk for losing water through transpiration is very high in xerophytes
Adaptations of xerophytes for the opposing needs for efficient gas exchange and the limitation of water loss
Sunken stomata:
➤traps moist air
➤reduces water potential gradient
➤hence lowers water loss in leaves
Less stomata:
➤reduces water loss
➤respond to low water availability by closing stomata to prevent further water loss
Thick waxy cuticle:
➤less water evaporates from leaf surface
Shiny cuticle:
➤reflects sunlight away
➤less heat absorbed
➤prevents water loss through transpiration
Thick stems:
➤stores water
➤less is lost
Large root systems:
➤maximises amount of water taken up from ground
Pointed spines:
➤often instead of leaves
➤less surface area available for water loss
Rolled leaves:
➤traps a layer of humid air
Densely packed mesophyll:
➤reduces surface area for water loss
➤larger surface area for photosynthesis
Trichomes (hairs):
➤fine, so can trap moist air
➤reduces water potential
Why do organisms need to exchange materials with their environment?
- Cells need oxygen and nutrients for metabolism.
- Waste products of metabolism e.g. CO2 and urea need to be excreted from the body.
- To maintain body temperature of animals (exchange of heat between the body and the environment)
Why is exchange easier for single-celled organisms?
Shorter diffusion pathway
Ways to increase SA:V ratio?
-folds in surface of the cell membrane increase surface area
-developing into long, thin, or elongated shaped cells
-presence of large vacuoles inside the cell
╰┈➤ pushes other organelles to the side of the cell
╰┈➤ easier diffusion of materials
2 main factors influencing heat exchange?
- Size
-smaller surface area to volume ratio makes heat loss from the body harder
-but, small organisms have higher surface area to volume ratio
-hence, these organisms need higher metabolic rate to generate more heat for it to stay warm. - Shape
-difference in shape = difference in their surface area
-animals with more compact shape have small surface area
-hence high metabolic rate not needed to minimize heat loss from the body
-but animals with less compact shape have higher surface area
-hence high metabolic rate needed to produce more heat to maintain body temperature
Why can’t Animals/Plants perform exchange via their surface?
-have a small surface area to volume ratio
-multicellular (large diffusion distance and high demand)
-impermeable surface (prevent pathogens entering and reduce water loss)
-therefore, require specialised Exchange & Transport systems
-exchange system = increases rate of diffusion of nutrients in and wastes out
-transport system = deliver nutrients and remove waste from all cells
What does the human gas exchange system consist of?
What is the function of lungs?
Structure of trachea/bronchi?
Structure of alveoli?
Structure of bronchioles?
Lungs are the site of gas exchange in mammals
╰┈➤ oxygen into blood – used in cells for respiration
╰┈➤ carbon dioxide out of the blood – toxic waste product of respiration
Cartilage:
-involved in supporting the trachea and bronchi
-prevents lungs from collapsing in the event of pressure drop during exhalation.
Ciliated epithelium:
-present in bronchi, bronchioles and trachea
-involved in moving mucus along to prevent lung infection by moving it towards the throat where it can be swallowed
Goblet cel:
-cells present in the trachea, bronchi and bronchioles involved in mucus secretion
-traps bacteria and dust
-reduces risk of infection with using lysosomes digest bacteria.
Smooth muscle:
-ability to contract enables them to constrict the airway
-hence controls its diameter and the flow of air to and from the alveoli.
Elastic fibres:
-stretch when we exhale
-recoil when we inhale
-hence controls the flow of air.
Structure of trachea/bronchi:
● The lungs contain a number of parts that facilitate the gas exchange.
╰┈➤Trachea - It functions to funnel the inhaled air into the lungs, while also facilitating the removal of inhaled air out of the lungs.
╰┈➤Bronchi - These are smaller passages where air enters the lungs from the trachea
╰┈➤Bronchioles - The bronchi further divide into smaller, and smaller passages called bronchioles.
Alveoli
-contain thin-walled cells that are directly connected to capillaries
-oxygen transferred down a concentration gradient from the alveoli into blood cells
-at the same time, carbon dioxide is transferred from the blood cells to the alveoli
-wall made of c-shaped cartilage
-cartilage is strong so trachea/bronchi do not collapse
-cartilage is c-shaped to give flexibility
-lining made of goblet cells and ciliated epithelial cells
-goblet cells make mucus, which traps pathogens/particles
-ciliated epithelial cells have cilia, which pushes mucus up and out of lungs
Structure of bronchioles?
-wall made of smooth muscle
-smooth muscle contracts, lumen narrows, bronchiole constricts
-occurs when surrounded by noxious gases – reduces amount reaching alveoli
-lining made of goblet cells and ciliated epithelial cells
The essential features of the alveolar epithelium as a surface over which gas exchange takes place
-millions of tiny alveoli that are folded (large surface area)
-thin wall/one cell thick/squamous epithelial cells (short diffusion distance)
-elastic tissue in wall (stretches when breathing in to increase surface area, recoils when breathing out to push the air out)
-ventilation maintains concentration gradient (high oxygen, low carbon dioxide)
How O2 moves from the alveoli to the capillaries? by simple diffusion passes through the alveolar epithelium and capillary epithelium
How CO2 moves from capillaries to the alveoli?
-by simple diffusion
-passes through the capillary epithelium and alveoli epithelium
Describe the process of ventilation
State the formula for pulmonary ventilation
Breathing In/Inhalation:
-internal intercostalmuscles relax
-external intercostal muscles contract
-rib cage moves up and out
-diaphragm contracts (flattens)
-increase in volume in thoracic cavity
-decrease in pressure
-so air moves in
Breathing Out/Exhalation
-internal intercostal musclescontract
-external intercostal muscles relax
-rib cage moves down and in
-diaphragm relaxes (back to dome shape)
-decrease in volume in thoracic cavity
-increase in pressure
-so air pushed out (aided by elastic recoil in the alveoli)
Formula for Pulmonary Ventilation
PV = tidal volume x ventilation rate
tidal volume = volume of air breathed in/out in one breath
ventilation rate = number of breaths per minute
Why can microorganisms exchange substances via their surface
-have a large surface area to volume ratio
-have a short diffusion distance
-have low demand
How is a single-celled organism adapted for gaseous exchange across its body surface
Thin cell membrane:
-shorter diffusion distance
-hence faster rate of O2 in and CO2 out
Larger surface area to volume ratio:
-faster rate of diffusion due to more space for the exchange of materials
How is the tracheal system of an insect adapted for gaseous exchange across its body surface
- Air move into trachea through pores on surface called spiracles
- oxygen travels down the concentration gradient towards the respiring cells
- the tracheae branch off into smaller tracheoles
╰┈➤have a thin, permeable wall
╰┈➤ go to individual cells
╰┈➤means that oxygen diffuses directly into the respiring cells - CO2 diffuses from the cells
╰┈➤ moving down its conc gradient into tracheal tubes towards spiracles and released into the atmosphere. - insects use rhythmic abdominal movements to move air in and out of spiracles
Structure of tracheal system:
-starts with openings on body surface called spiracles
-spiracles contain valves, open = gas exchange, closed = prevent water loss
-spiracles connect to trachea
-trachea connect to tracheoles
-tracheoles connect directly to respiring cells (delivering oxygen, removing carbon dioxide)
Why insects need a tracheal system:
-multicellular organism so has a small surface area to volume ratio, large diffusion distance, high demand & body surface made of exoskeleton (impermeable barrier to reduce water loss)
-therefore, cannot perform gas exchange (O2 in/CO2 out) via their surface, they require a tracheal system
at rest = down a concentration gradient, oxygen moves in & carbon dioxide moves out by simple diffusion
when active = by ventilation, air inhaled for mass flow of O2 in & air exhaled for mass flow of CO2 out
How are the gills of a fish adapted for gaseous exchange across its body surface
–multicellular organism so has a small surface area to volume ratio, large diffusion distance, high demand & body surface impermeable
-also, as fish live underwater, it is harder to obtain oxygen from the environment due to lower oxygen concentration in water than in air
-therefore, cannot perform gas exchange (O2 in/CO2 out) via their surface, they require gills
-gills
-made up of thin plates called gill filaments
-provides large surface area for gaseous exchange
-lamellae
-tiny structures with lots of blood capillaries and thin surface layer of cells
-speeds up diffusion, as shorter diffusion distance
- covers gill filaments which increases the surface area further
-countercurrent flow
-blood and water flow opposite
-ventilation brings in pure water (high oxygen, low carbon dioxide)
- circulation brings in deoxygenated blood (low oxygen, high carbon dioxide)
-diffusion gradient for oxygen uptake is maintained across entire width of gill lamellae
- equilibrium is never reached, hence transfer of oxygen is more efficient
-majority of oxygen available in the water is absorbed into the blood
How are the leaves of dicotyledonous plants adapted for gaseous exchange across its body surface
-stomata open to allow gas exchange and close if the plant is losing too much water
-guard cells control the opening and closing of stomata.
Mesophyll cells are differentiated into palisade and spongy mesophyll:
-Palisade Mesophyll: Elongated cells beneath the upper epidermis, densely packed with chloroplasts for optimal light absorption.
-Spongy Mesophyll: Loosely arranged cells with intercellular spaces beneath the palisade layer, facilitating gas movement and exchange.
Outline some lung diseases and risk factors/symptoms associated with it
General causes for lung diseases:
-genetic makeup
-occupation
-air pollution
-tobacco from smoking
(remember GOAT)
Pulmonary fibrosis:
-epithelial tissue in lungs become irreversibly thicker and less elastic
-thicker = longer diffusion distance
-less elastic = cannot recoil or force air out of alveoli
-hence results in shortness of breath and chest pain
Lung cancer:
-if malignant, it can split and spread into capillaries and organs
-caused by uncontrollable dividing of cells via mitosis
Chronic Obstructive Pulmonary Disease (COPD):
-includes emphysema and chronic bronchitis:
-emphysema = smoking destroys alveoli (either elastin is broken down or alveoli fuses together, reducing surface area to volume ratio)
-chronic bronchitis = more mucus produced due to destroyed cilia, and the irritation leads to scar tissue
What is the importance of digestion?
Function of intestines?
Large biological molecules must be hydrolysed to smaller molecules so they can be absorbed across cell membranes
Site of exchange of digested nutrients in mammals
Small intestine absorbs small soluble nutrients, e.g. glucose, amino acids
Large intestine absorbs water
Outline the digestion and absorption of carbohydrates, including any enzymes
Enzymes:
Starch/glycogen —> maltose:
-salivary amylase in mouth
-pancreatic amylase in small intestine
Maltose —> glucose:
-maltase on lining of small Intestine
Lactose —> glucose and galactose:
-lactase on lining of small intestine
Sucrose —> glucose and fructose:
-sucrase on lining of small intestine
Digestion:
-in the mouth, starch is digested into shorter polysaccharides by salivary amylase (partial digestion as some maltose appears)
-food travels to stomach via oesophagus
-no digestion in stomach due to lack of necessary enzymes
-salivary amylase that comes to stomach with food is unable to work due to stomach pH being too low (due to HCl)
-in the duodenum, complete digestion of starch to maltose occurs with pancreatic amylase
-disaccharidase in lining of ileum digests all carbohydrates to monosaccharides
Absorption of glucose in small intestine
-occurs via co-transport mechanism
-sodium ions are actively transported from the cells lining the ileum into the blood
-ATP hydrolysed to ADP and Pi
-energy released allows ions to be moved against concentration gradient
-lowers the sodium ion concentration in the cell
-hence sodium ions move from the lumen of ileum into the cell
-this pulls in glucose via a co-transporter protein
-hence glucose builds up in the cell and moves into the blood by facilitated diffusion
Outline the digestion and absorption of lipids, including any enzymes
Digestion:
-bile breaks down triglycerides before lipase (by emulsification)
-smaller droplets of lipid produced have larger surface area for enzyme action
-hence faster hydrolysis
-bile salt has two parts
-hydrophobic part attaches to broken triglyceride
-hydrophilic part sticks to outside to prevent broken lipids from rejoining
-ester bonds are broken by lipase (found in pancreas)
-inside lumen of duodenum
-triglyceride (in micelle form) hydrolysed to glycerol, fatty acid and monoglyceride
Absorption:
-micelles bring products to ileum from duodenum
-products are still attached to bile salt
-micelles release products on microvilli on the surface of lining cell
-as they are non-polar/hydrophobic, can pass through phospholipids of membrane by simple diffusion
-glycerol, fatty acid, monoglyceride enter smooth endoplasmic reticulum by simple diffusion
-in SER, they undergo re-esterification and form triglyceride again
-triglyceride moves from SER to Golgi apparatus
-protein added to triglyceride to form lipoprotein
-lipoprotein released from lining cell into lymph vessel by exocytosis
-lining cell of blood capillary produces lipase which hydrolyses lipoprotein into fatty acid/glycerol
-lymph vessel opens into bloodstream
-products diffuses into body cells
Outline the digestion of proteins, including any enzymes
-endopeptidase: breaks polypeptide from middle of chain
-two types of endopeptidase = pepsin (found in stomach) and trypsin (found in pancreas)
-exopeptidase: breaks polypeptide from a terminal (found in pancreas)
-two types of exopeptidase = aminopeptidase/carboxypeptidase
-endopeptidase produces shorter polypeptide chains
-exopeptidase produces amino acids
-dipeptidase (found in lining cell of ileum alongside disaccharidase) hydrolyses peptide bond in dipeptides
Digestion:
-pepsin hydrolyses proteins to smaller polypeptides in stomach
-partially digested protein enters duodenum, which receives pancreatic juice
-pancreatic juice contains trypsin, which further reacts on partially digested protein
-sodium hydrogencarbonate in pancreatic juice and bile (hence pH is around 7-8)
-from pancreatic juice, exopeptidase produces a mixture of amino acids and some dipeptides
-when products are absorbed into ileum, dipeptides are further digested into amino acids by dipeptidase in the membrane of lining cell
Absorption:
-absorbed similarly to glucose: by co-transport of Na+ ions
-sodium ions are actively transported from the cells lining the ileum into the blood
-lowers the sodium ion concentration in the cell
-hence sodium ions move from the lumen of ileum into the cell
-this pulls in amino acids via a co-transporter protein
-hence amino acids builds up in the cell and moves into the blood by facilitated diffusion
-amino acids are then absorbed into blood
Adaptations of ileum for digestion/absorption?
-folded villi to increase surface area of wall of ileum
-lining cells have microvilli (folded membranes) to further increase surface area
-increased folding also means larger amounts of disaccharidase and dipeptidase can be stored in membrane of lining cell of ileum
-allows faster rate of hydrolysis, as more enzymes available to form E-S complexes
-many mitochondria in lining cells, as co-transport is active process
-hence energy is required for absorption of glucose/amino acids
Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels. (5 marks)
- Micelles contain bile salts and fatty acids/monoglycerides;
Ignore other correct components of micelles - Make fatty acids/monoglycerides (more) soluble (in water)
OR
Bring/release/carry fatty acids/monoglycerides to cell/lining (of the iluem)
OR
Maintain high(er) concentration of fatty acids/monoglycerides to cell/lining (of the ileum);
Accept lipid/fat for fatty acid/ monoglyceride - Fatty acids/monoglycerides absorbed by diffusion;
Reject if absorbed by facilitated diffusion
Ignore if micelles themselves are being absorbed - Triglycerides (re)formed (in cells);
Accept chylomicrons form - Vesicles move to cell membrane;
Accept exocytosis for ‘vesicles move’
