Section 3 - Exchange between organisms and their environment

Diffusion equation

diffusion =( SA X difference in conc ) / length of diffusion pathway

gas exchange in single celled organisms

* very large surface area to volume ratio
* therefore gas can be exchanged through diffusion of oxygen through the cell surface membrane
* co2 from respiring can be diffused out of the single celled organism
* there is no cell wall barrier to cross

gas exchange in insects

1. oxygen diffuses into the insect when it has open spiracles and a concentration gradient.
2. the oxygen travel through tubes called tracheae which branch into smaller tubes called tracheoles
3. the tracheae and tracheoles are highly branched and have thin walls to allows for diffusion. they spread throughout the insects body
4. at the end of the tracheoles there is water which the oxygen dissolves into. this makes the diffusion of oxygen easier as the water moves into the cell

gas exchange in active insects

1. when an insect is active, it produces lactate when it respires anaerobically.
2. lactate is soluble so lowers the water potential of cells
3. water therefore moves into the cells through osmosis due to the lower water potential
4. this draws the oxygen further into the tracheoles due to water volume decreasing.
5. final diffusion form is therefore a gas and diffusion can occur much quicker.

gas exchange in insects with abdominal muscle contraction

* when an insect is pumping its muscles, it creates a pressure within the tracheoles which can force out carbon dioxide.

avoiding water loss in insects and their limitations

* insects have spiracles which can be closed to reduce the volume of water that evaporates out.
* limitations include
* system relies mainly on diffusion
* this means the diffusion pathway has to be small and so the insects must also be small

structure of the gills

* gill bar which has gill filaments on
* lamellae are at 90 degrees to gill filaments to increase surface area
* blood capillaries flow in the gill bar

counter current flow system

* blood capillaries in the gill bar have blood flowing in the opposite direction to the water flow
* this maintains a concentration gradient within the water and blood
* ensures that the oxygen is always being diffused from the water into the blood capillaries
* blood capillaries are really thin so short diffusion pathway

gas exchange in plants

* stoma open due to K+ ions moving into guard cells, lowering the WP so water moves into cells making them turgid and bend open.
* CO2 diffuses into the plant and into spongy mesophyll where there are air spaces
* CO2 moves up into the palisade mesophyll where lots of cells are for respiration and photosynthesis
* O2 diffuses out the cell through the stomata

adaptations in plants

* stomata are on the bottom of cells so water doesn’t evaporate and the palisade mesophyll is on the top.
* leaves curl around stoma to allow for humid atmosphere for more water intake
* stomata close at night when there’s no need for water or CO2 so water doesn’t evaporate.
* some plants have thicker epidermis so less water evaporates out
* some plants have longer roots to reach further for water
* have small hairs to trap any water molecules

Structure of mammalian lungs

* trachea made from rings of cartilage to support bending and protect when pressure changes from breathing.
* trachea splits into two bronchi which each go to a lung. covered with cilia to prevent any dust or dirt getting into the lungs
* bronchioles are highly branched and lined with epithelial cells. this controls the flow of air into the alveoli
* alveoli are tiny air sacs (100nanometres to 300nanometres) which have elastic fibres to control stretching and these are the surface for gas exchange

mechanism of breathing

* inspiration
* internal intercostal muscles relax and external intercostal muscles contract
* ribs move upwards and out, diaphragm muscles contract pulling the diaphragm down
* creates low pressure, lower than atm so air is drawn inwards
* expiration
* internal intercostal muscles contract and external intercostal muscles relax
* ribs move inwards and down, diaphragm muscles relax pushing diaphragm upwards.
* the pressure increases, more than the atm so air is forced out the lungs

exchange of gases in the lungs adaptations

1. the walls of the alveoli and capillaries are very thing for a short diffusion pathway
2. the alveoli have a very large surface area
3. red blood cells are slowed down to allow maximum time for gas exchange
4. breathing allows for the constant high conc as to maintain gradient

major areas of digestion

* mouth for physical digestion
* oesophagus to carry food from mouth to stomach
* stomach is a muscular sac which churns food and digests mainly enzymes
* ileum is the small intestine which further digests and absorbs the products
* large intestine absorbs the water
* rectum stores the faeces before is it pooped

digestion of carbohydrates

1. chewing in mouth will break down carbs to larger SA
2. salivary amylase hydrolyses the glyosidic bond between the carbs and breaks them down in maltose
3. in the stomach the salivary amylase is denatured
4. in the ileum pancreatic amylase breaks down any remaining starch into maltose
5. in the ileum there is membrane bound maltase which hydrolyses the maltose bonds into a glucose

digestion of lipids

1. the bile salts from the liver emulsify the lipids into micelles
2. this is to provide a larger SA for enzyme action
3. the enzyme lipase acts on lipids and micelles to hydrolyse the ester bond into fatty acids and monoglycerides

digestion of proteins

* peptidases hydrolyse the peptide bonds in proteins
* endo peptidase hydrolyses the bonds in the middle of the peptide chain
* exopeptidases hydrolyse the terminal peptide bond
* dipeptidases hydrolyse the peptide bond between the dipeptides

absorption of proteins and carbs

* they break down into amino acids and monosaccharides
* these are absorbed by co transportation

absorption of lipids

* micelles are non polar and small so move through the cell membrane of ileum cells
* move into rough endoplasmic reticulum where they’re reformed into triglycerides.
* continue into the Golgi apparatus where they fuse to form a chylomicron.
* these chylomicrons move out of the cell by exocytosis and into the lacteals (inside the villi centre)
* pass through the lacteals through the lymphatic vessel and into the blood system