Exchange - Chapter 6 - Mindmap in A Level and IB Biology

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Created on: 21-02-18 18:27

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Exchange
- Fish
  - Structure of gills
    - Made up of gill filaments, stacked in a 'pile' on top of each other
      - At right angles to the filaments are gill lamellae, which increase the SA of the gills.
        Flow of water over the gill lamellae, and the blood within them, are in opposite directions.
        Counter-current flow
        
        Ensures max gas exchange
  - Counter- current exchange principle
    - Blood that is already loaded with oxygen meets water with a higher [O2], and so diffusion of oxygen from water to blood takes place.
    - blood with little oxygen meets the water, which has a relatively same [O2], thus diffusion of oxygen takes place.
    - Diffusion gradient is maintained across the entire width of the gill lamellae.
      - 80% O2 available is absorbed.
      - If blood:water flow was in the same direction, only 50% of O2 would be absorbed
- Leaf of a plant
  - Photo- synthesis and respiration can use each other's "waste" gases
    - Reduces gas exchange with the external air
    - Volumes or types of gas exchange change, depending on the rate of photo-synthesis and respiration.
    - Most CO2 for photo-synthesis is sourced from the external air
      - Similarly, O2 from photo-synthesis is mostly diffused out, instead of being used for respiration
    - During night (or when its dark), oxygen is still taken up, as respiration never stops.
      - Photo-synthesis stops when there is no sunlight.
  - Structure of plant leaf
    - Diffusion takes place in the gaseous phase, therefore more rapid
    - Air spaces within the leaf has a large surface area.
    - Adaptations for gas exchange
      - Small pores, called stomata; no cell is far from a stomata, therefore diffusion pathway is short
      - Numerous inter-connecting air-spaces throughout mesophyll
      - Large SA of mesophyll cells for rapid diffusoin
    - Stomata
      - Minute pores that occur mostly. but not exclusively on leaves, specifically on the underside of the leaf.
      - Surrounded by guard cells
        Open/close stomata pore.
        Control rate of gaseous exchange
        Prevent water loss via evaporation
        Controlled by closing stomata when water loss would be excessive
- Limiting water loss
  - Insects
    - Permeable surface and large surface area are contradictory to conserving water.
    - Adaptations
      - Small surface area to volume ratio (SA:VOL)
      - Waterproof coverings over body surfaces (waterproof cuticle)
      - Spiracles; opening of spiracles happens mostly when insect is resting.
  - Plants
    - Photo-synthesis needs a large surface area to capture sunlight
    - Waterproof coverings (over most of insect), and ability to control stomata.
    - Limit water loss via transpiration (there plants are called xerophytes)
      - Adaptations
        Thick (waxy) cuticle; e.g. holly,
        
        Rolling up of leaves,
        Protects lower epidermis (where stomata are usually found)
        
        Still air build up within rolled up leaf, air becomes saturated with water vapour, increasing its water potential, thus conservation of water.
        
        Example: Marram grass
        
        Hairy Leaves
        Traps still, moist air next to the leaf surface.
        Water potential gradient between inside of leaf and outside is reduced, therefore less water loss.
        Example: Heather Plant
        
        Stomata in pits or grooves
        Trap still, moist air near the leaf and reduces water potential gradient.
        Example: Pine trees.
        
        Reduced SA:VOL of the leaf.
        Leaves that are small and roughly circular in cross-section, rather than broad or flat, rate of water loss can be considerably reduced
        Example: Pine needles
    - Adaptations
      - Thick (waxy) cuticle; e.g. holly,
      - Rolling up of leaves,
        Protects lower epidermis (where stomata are usually found)
        
        Still air build up within rolled up leaf, air becomes saturated with water vapour, increasing its water potential, thus conservation of water.
        
        Example: Marram grass
      - Hairy Leaves
        Traps still, moist air next to the leaf surface.
        Water potential gradient between inside of leaf and outside is reduced, therefore less water loss.
        Example: Heather Plant
      - Stomata in pits or grooves
        Trap still, moist air near the leaf and reduces water potential gradient.
        Example: Pine trees.
      - Reduced SA:VOL of the leaf.
        Leaves that are small and roughly circular in cross-section, rather than broad or flat, rate of water loss can be considerably reduced
        Example: Pine needles
- Human gas-exchange system
  - Structure and function
    - Lungs
      - Series of highly branched tubules, called bronchioles, which end in tiny air sacs called alveoli.
    - Trachea
      - Flexible airway that's supported by cartilage, which prevents trachea from collapsing (as pressure falls within when breathing in).
        Trachea walls made of muscle, lined with ciliated epithelium and goblet cells.
    - Bronchi
      - Two divisions leading to each lung
        Produce mucus to trap dirt particles, have cilia that move dirt-laden mucus to the throat.
      - Larger bronchi are supported by cartilage, although reduced as bronchi get smaller.
    - Bronchioles
      - Series of branching subdivisions of the bronchi
        Walls are made of muscle lined with epithelial cells.
        Muscles allow them to constrict to control flow of air in/out of alveoli.
    - Alveoli
      - Minute air-sacks, at end of bronchioles
        Between alveoli, there are some collagen and elastic fibres.
        
        Lined with epithelium.
        
        Elastic fibres allow alveoli to stretch when they fill with air.
        Spring back during breathing out in order to expel the carbon dioxide-rich air.
        Alveoli membrane is the gas-exchange surface.
  - Mechanism of breathing
    - Breathing is also known as ventilation
    - When pressure of atmosphere is greater than in the lungs, air is forced into the lungs.
      - Called inspiration (inhalation)
        Step - by - step process:
        1) External intercostal muscles contract, internal intercostal muscles relax.
        2) Ribs are pulled upwards and outwards, increasing volume of thorax.
        3) Diaphragm muscles contract, causing it to flatten, which also increases volume of thorax.
        4) Increased volume of thorax results in reduction of pressure in the lungs.
        5) Atmospheric pressure greater than pulmonary pressure, so air is forced into the lungs.
        
        Untitled
    - When air pressure in lungs is greater than the atmosphere, air is forced out.
      - Called expiration (exhalation)
        Step - by - step process:
        1) internal intercostal muscles contract, wile the external intercostal muscles relax.
        2) Ribs move downwards and inwards, decreasing the volume of the thorax.
        3) Diaphragm muscles relax, pushed up again by contents of abdomen. Volume of thorax therefore decreases.
        4) Decreased volume of the thorax increases the pressure in the lungs.
        5) Pulmonary pressure is now greater than that of the atmosphere, air is forced out of the lungs.
        
        Passive process
    - Pressure changes brought about by three sets of muscles
      - Diaphragm
      - Internal intercostal muscles - contraction = expiration
      - External intercostal muscles - contraction = inspiration
    - During normal breathing, the recoil of the elastic tissue in lungs us the main cause of air being force out.
      - Only under strenuous conditions such as exercise do various muscles play a vital part.
  - Exchange of gases in lungs
    - Efficient transfer, surfaces must be thin, partially permeable and have a large surface area.
    - Role of alveoli in gas exchange
      - 300 million alveoli in each human lung
      - Each alveolus is lined with epithelial cells.
        Around each alveolus is a network of pulmonary capillaries.
        Red blood cells are flattened against the thin capillary walls.
      - Capillaries have walls consisting of one cell thickness.
    - Diffusion of gasses is rapid because:
      - Red blood cells are slowed as they pass through the pulmonary capillaries, allowing more time for diffusion.
        Distance between alveolar air and red blood cells is reduced as the red blood cells are flattened against the capillary walls
        Walls of alveoli and capillaries are very thin, therefore distance of diffusion pathway is very short.
        Alveoli and pulmonary capillaries have very large total surface area.
        Breathing movements constantly ventilate the lungs, action of the heart constantly circulates blood around the alveoli.
        These ensure that a steep concentration gradient of the gases to be exchanged is maintained.
        Blood flow through pulmonary capillaries maintains a concentration gradient.
- Enzyme and digestion
  - Digestive system
    - Oesophagus
      - Carries food from mouth to stomach
    - Stomach
      - Muscular sac, with inner layer that produces enzymes
        Mainly digest protein, has glands that produce enzymes to help digest proteins
    - Ileum
      - Long muscular tube
      - Food further digested by enzymes produced by its walls and the glands that pour their secretions into it
        Inner walls folded into villi.
        Gives them a large surface area
        Surface areas of the villi is further increased by millions of tiny projections, called microvilli.
        Helps (adaptation) absorb products of digestion into the bloodstream.
        
        Surface areas of the villi is further increased by millions of tiny projections, called microvilli.
        Helps (adaptation) absorb products of digestion into the bloodstream.
    - Large intestine
      - Absorbs water
        Most water absorbed is from the secretions of the many digestive glands.
    - Rectum
      - Final section of intestine
        Faeces are stored here
        Removed via egestion.
    - Salivary glands
      - Located near the mouth
        Pass secretions via a duct into the mouth
        Secretion contain amylase, which hydrolyses starch into maltose.
    - Pancreas
      - Large gland located behind the stomach.
        Produces secretion known as pancreatic juice.
        Contains protrases to hydrolyse proteins
        Lipase to hydrolyse lipids
        Amylase to hydrolyse starch.
  - Stages of digestion
    - Physcial breakdown
      - Carried out by structures such as teeth
        Provides a larger surface area for Chemical digestion.
    - Chemical digestions
      - Hydrolyses large, insoluble molecules into smaller, soluble ones.
        Carried out by enzymes.
      - One enzyme hydrolyses a large molecule into smaller sections
        Additional enzymes then hydrolyse the molecule even more,
  - Types of digestion (2)
    - Carbohydrate digestion
      - Many enzymes involved in breaking down large molecules into their monomers
        Usually produced in different parts of the digestive system.
      - Amylase is produced in the mouth and pancreas
        Hydrolyses the alternate glycosidic bonds of the starch molecule to produce the dissacharide maltose.
        Hydrolysed into the mono-saccharide alpha-glucose by a second enzyme.
        Second enzyme is the disaccheride maltase
        Produced by lining of the ileum.
      - Process takes place as follows:
        1) Saliva enters the mouth through the salivary glands and is thoroughly mixed with the food chewing.
        2) Saliva contains salivary amylase; starts hydrolysing any starch.
        Also contains mineral salts that help to maintain the pH at around neutral (optimum pH)
        
        3) Food enters stomach, where the conditions are acidic; this denatures the amylase.
        4) After, food has passed through the small intestine, where it mixes with the secretion from the pancrease
        5) Contains pancreatic amylase; continues to hydrolyse any remaining starch to maltose.
        Alkaline salts are produced by pancreas and intestinal wall to maintain H around neutral.
        
        6) Muscles in intestine push the food along the ileum; epithelial lining produces maltase.
        Not released into lumen of the ileum, but is part of the cell-surface membranes of epithelial cells.
        
        7) Maltose hydrolyses the maltose from the starch breakdown into the alpha- glucose.
      - Sucrose/ Sucrase
        Hydrolyses single glycosidic bond in the sucrose molecule.
        
        Produces two mono-saccharides glucose and fructose.
      - Lactose/ Lactose
        Hydrolyses single glycosidic bond in the lactose molecule.
        
        Hydrolysis produces the two mono-saccharides glucose and galactose.
    - Protein digestion
      - Endo-peptidases
        Hydrolyse peptide bonds between amino acids in the central region of the protein molecule
      - Exo-peptidases
        Hydrolyses peptide bonds on the terminal amino acids of the peptide molecules formed by endo-peptidases
      - Dipeptidases
        hydrolyses bonds between two amino acids of a dipeptide
        Dipeptides are membrane -bound, being part of the cell-surface membrane of the epithelial cells lining the ileum.
  - Types of digestion (1)
    - Lipases
      - Produced by the pancreas
      - Hydrolyses lipids.
        Hydrolyse the ester bond found in triglycerides to form fatty acid molecule attached.
        
        Split up into tiny droplets called micelles by bile salts (produced by the liver).
        Process is called emulsification
        Increases the surface area of the lipids so that the action of lipases is sped up
  - Absorption of products of digestion
    - Structure of ileum
      - Wall of ileum is folded and possesses finger-like projections called villi
        Think walls, line with epithelial cells on the other side of which is a rich network of blood capillaries.
        They increase surface area, therefore accelerate the rate of absorption.
      - Villi are situated at the interface between the lumen and the other tissues inside the body.
        Increase the efficiency of absorption in the following ways:
        Increase surface area for diffusion
        
        Very thin walled, reducing the distance over which diffusion takes place.
        
        Contain muscle and so are able to move; helps to maintain diffusion gradients because their environment mixes the contents of the ileum.
        
        Ensures product of digestion is absorbed by the villi.
        
        They're well supplied with blood vessels so that blood can carry away absorbed molecules and hence maintain a diffusion gradient.
        
        Epithelial cells lining the villi possess microvilli.
        Finger-like projections of the cell-surface membrane that further increase the surface area for absorption
  - Absorbing different molecules
    - Amino acids and mono-saccherides
      - Method of absorption is mainly diffusion and co-transport
    - Triglycerides
      - Mono-saccherides and fatty acids remain associated with the bile salts that initially emulsified the lipid droplets
        Called micelles
        
        Through the movement of other material, Micelles come into contact with the epithelial cells lining the villi of the ileum.
      - Through the movement of other material, Micelles come into contact with the epithelial cells lining the villi of the ileum.
      - Micelles break-down, releasing mono-glycerides and fatty acids.
        Non-polar, so normally diffuse across cell-membrane into the epithelial cell.
      - Transported to the endoplasmic reticulum where they recombined to form triglycerides.
        Starting at the ER and continuing to the Golgi apparatus, the triglycerides associate with cholesterol and lipoproteins
        Forms structures called chylomicrons
        Special particles adapted for the transport of lipids.
        
        Move out of epithelial cells by exocytosis.
        Enter lymphatic capillaries called lacateals
        Found at the centre of each villus.
        
        Pass via lymphatic vessels, into the blood stream.
        Triglycerides in the chylomicrons are hydrolysed by an enzyme in the endothelial cells of blood capillaries
        From here they diffuse into cells

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Exchange - Chapter 6

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