alevel biology transport

Diffusion (definition + 2 types)

Passive movement of particles from a high concentration to low concentration, down a concentration gradient until an equilibrium is reached.
1. Simple (partially permeable): Particles pass across the membrane, permeable to non-polar, lipid-soluble molecules (exception: water) Hydrophobic tails repel ions
2. Facilitated (selectively permeable): Membrane is a barrier to polar molecules, passive movement of polar molecules via a hydrophilic channel proteins

No. of intrinsic proteins can effect rate of diffusion

Plasma membrane (use of membrane, properties, fluid mosaic model)

phospholipid bilayer - controls movement of substances in/out of the cell. Acts as an impermeable barrier to polar substances, water-soluble; permeable to lipid-soluble, non-polar across membrane. Phospholipid bilayer allows membrane to be flexible, and self-sealing

Fluid mosaic model - mosaic as many molecules embedded within membrane structure. Fluid as phospholipid molecules can move.

Proteins within/ on plasma membrane

Glycoprotein + Glycolipid

Cholestrol

Extrinsinc protein - mechanical support

Intrinsic proteins - channel proteins - hydrophillic channel allowing water-soluble/ polar molecules across membrane. Carrier proteins - active transport

Glycoprotein + Glycolipid - acts as recognition molecule/ receptor for hormones due to branching of carbohydrate, can be used for cell adhesion

Cholestrol - flexibility, stability. Hydrophbic so attracts fatty acids, preventing rigidity, prevents loss of water ions due to repulsion.

Factors effecting diffusion rate

SA:V ^, larger area for substance to diffuse across

Diffusion distance ↓, shorter distance to diffuse across.

Temperature ^, more kinetic energy, so more particles move across quicker + phospholipid molecules vibrate faster, so more permeable. too high tertiary structure denatures, meaning permanent disruption

number of intrinsinc proteins along phospholipid bilayer

Active Transport

Active movement of molecules from a low-high concentration, against a concentration gradient, via a carrier protein, using ATP (from respiration)

1. Molecule binds to specific receptor of carrier protein

2. ATP → ADP + Inorganic Phosphate, phosphate binds to protein, changing shape of protein,

3. Molecule released into cell, ADP + Pi → ATP

Exocytosis - vesicles fuse with cell membrane, molecule is released to outside. ATP required for fusion

Endocytosis - membrane invaginates to make vesicle around material, vesicle pinches off membrane, ATP required.

Osmosis (solutions conditions, water potential, definition)

Isotonic (same),

Hypertonic (Cell has higher water pot) = crenated/plasmolysed,

Hypotonic (Cell has low water pot) = lysed/turgid

Water potential - pressure exerted by a water molecule colliding with a membrane/ container (0 = highest concentration)

Cotransport

Sodium ions actively transported out of cavity in blood, lower concentration in the cavity, so sodium from the ileum diffuses into cavity, glucose transport into cavity via attachment to sodium, then facilitated diffusion into the blood.

Digestion pt1

Mouth: Mechanical digestion. Release of amylase to break starch into disaccharides.
Stomach: Mechanical + Chemical digestion, HCl + protease(endo/exopeptidase) proteins→ dipeptides

Digestion pt2

Duodenum: Bile released (emulsification + neutralisation), amylase + protease + lipase. Pancreatic juices released with enzymes

Ileum: Membrane bound dipeptidases, disaccharides, absorption of molecules'

Large intestine: Reabsorption of water/ molecules

Digestion of Glucose

1. Amylase hydrolyses starch into maltose, carbohydrase/ polysaccharidases hydrolyse polysaccharides into disaccharides

2. Membrane bound disaccharidases hydrolyse disaccharides

   1. Maltase: Maltose → glucose

   2. Sucrase: Sucrose → glucose + fructose

   3. Lactase: Lactose→ glucose + galactose

3. Diffuse into the cell by cotransport membrane

Digestion of Proteins

1. Endo/exopeptidases hydrolyses peptide bonds, polypeptide → dipeptide

2. Membrane-bound dipeptidases hydrolyses dipeptides → amino acids

3. Enters via cotransport/ Diffusion

Digestion of Lipids

1. Bile emulsifies lipid into soluble small lipid

2. Lipase hydrolyses lipid in monoglycerid + 2 fatty acids

3. Bile salts bind and increases SA:V

4. Monoglycerides + Bile Salt + Fatty acid forms a micelle

5. Micelle transports monoglyceride, fatty acids to membrane of epithelial cell, maintaing higher concentration at cell membrane,

   1. Monoglyceride, fatty acids diffuse into cell down concentration gradient

6. Monoglycerid + fatty acid recombine by SER

7. Triglyceride is combined with proteins and cholestrol (SER)

8. Packaged into chylomicrons, leaving cell by exocytosis into lacteal cell

Enzymes in digestion

Water transport (2 pathways, water up the xylem)/ Ion transport

Xylem:

Mineral ions actively transported into, and across root hairs, dissolved in water and pulled up xylem

Water enters via osmosis and move through:

1. Apoplastic pathway:

   Moves through gaps in the cell wall, Then diffuses and moves through cell at caspian wall

2. Symplast pathway:

   Moves through cell cytoplasm and across plasmodemata (slower)

Transpiration causes difference in water potential, causing water from xylem to move into cell by osmosis, due to cohesion causing tension, water column is pulled up

Gas exchange fish

Fish:

1. Floor of mouth lowers (pressure ⬇, vol ⬆) causing pressure difference, water moves into the mouth, passes over the gills, water contains dissolved oxygen.

2. counter current, water flows in the opposite direction that blood flows, ensuring gas exchange happens across entire gill, ensuring a concentration gradient is maintained.

Plant gas exchange, (Adaptations of normal+desert plants)

Plants

1. Guard cells control the opening/closing of stomata, evaporated water can diffuse out.

   Many stomata to increase rate of diffusion

   Large SA:V ratio

   Many air spaces in spongy mesophyll, reducing diffusion distance to palisade mesophyll

   Desert plants have less stomata (none on upper epidermis), more closed stomata, (all to reduce water evaporation)

   no leaves or rolled + hairy leaves (reduced sa:v for water to evaporate, or traps moisture, creating a diffusion gradient where water does not leave the leaf)

Human gas exchange (Inspiration + expiration)

1. Diaphragm contracts, diaphragm moves down, external intercostal muscle contracts (internal relaxes), ribs move up and out, pressure ⬇ volume ⬆, pressure difference causes air to enter lungs (lungs expand)

2. Air moves through trachea, through bronchi, and bronchioles into alveoli

3. Concentration gradient between red blood cells and alveoli, so oxygen diffuses across epithelium of alveoli, and endothelium of capillary, then into red blood cell.

Expiration:

1. Concentration gradient (of CO2) between red blood cells and alveoli, so CO2 diffuses across endothelium of capillary, and epithelium of alveoli

2. Diaphragm relaxes, external intercostal muscle relaxes (internal contracts), ribs move down and in, volume ⬇ pressure ⬆, pressure difference causes air to be forced out of lungs, lungs are elastic so recoil to further force air out

Lung adaptations

One cell thick, shorter diffusion area, and flattens + slows down red blood cells, allowing for more time for diffusion

Many capillaries to maintain diffusion rate

Moist - easier diffusion

Alveoli - increased sa:v

Goblet cells - produce and secrete mucuous to protect the lungs and prevent bacteria moving into blood stream

Haemoglobin (structure, bohr effect, affinity of oxygen in certain conditions/ animals

4 alpha helices associated with haem groups

affinity of oxygen increases as pressure of oxygen increases (conc ⬆)

so oxygen more readily associates to haem/ CO2 more readily dissociates
bohr effect: CO2 increase in pressure causes more ready dissociation of oxygen from haemoglobin

Association of first oxygen is the hardest, once bound causes haemoglobin to change shape, which makes oxygen able to associate more easily

Different animals/ organisms have differen affinities, fetal haemoglobin has higher affinity as oxygen pressure has already decreased when reaching the baby.

Cardiac cycle

Sequence of events which occur within a heart beat

Atrial systole: Atrial muscle contracts, pressure ⬆, volume ⬇, higher pressure in atria than ventricle, so atrioventricular valve opens. Ventricular diastole occurs at same time (muscle relax, pressure ⬇)

Ventricular systole: Ventricle muscle contracts, pressure ⬆ volume ⬇, higher pressure in ventricle than aorta and atria, causing av valve to close, and aortic valve (semilunar valve) to open.

High pressure in aorta causes aortic valve to close

Blood vessels + blood content

Vein: towards heart, thinner muscle and elastic tissue, less pressure, contains valves to prevent backflow

Artery: Away from heart, thick muscle tissue to contract, thick elastic layer allow recoil (maintaining blood pressure), narrow lumen to maintain blood pressure

Arteriole: Muscle Contracts to narrow/ widen lumen to control movement of blood into the capillary.

Capillary: allow substances to reach tissue, thin wall allows quicker diffusion, porous to allow blood plasma out, branched between cells + one cell thick - shorter diff dist

increased blood content causes blood to thicken, which will cause clots to more likely form.

Tissue fluid

Hydrostatic pressure of blood created by heart contractions,

arterial end of capillary:

higher hydrostatic pressure than tissue, plasma moves out,

lower water potential (larger solutes cannot pass through pores) water moves in by osmosis, Greater hydrostatic pressure than osmotic pressure so tissue fluid moves out of capillary

Venous end:

Hydrostatic pressure decreases, lower pressure, plasma moves in, osmotic pressure remains same (lower water potential water moves in by osmosis) Greater osmotic pressure than hydrostatic pressure, so net movement into capillary

Excess tissue fluid moves into lymphatic capillary

Insect respiration

Insects:

1. Respiring tissue use up oxygen, creating a concentration gradient

2. Valve periodically opens allowing air to move into the trachea down a conc gradient

3. Moves through trachea, and tracheoles into the respiring tissue

During movement, water from ends of tracheoles moves into respiring tissue, creating air space, and allowing oxygen to diffuse more efficiently from air into the tissue

Plant transport sugars (Loading, Mass transport theory)

Phloem - translocation (movement of assimilates from source to sink)

Loading:

1. Hydrogen ions are actively pumped out of cytoplasm into cell walls by proton pump using ATP, creating a conc gradient of H⁺

2. Hydrogen ions diffuse down a concentration gradient into sieve tubes and cotransports sucrose across a cotransport protein against sucrose conc gradient

Unloading:

Same

Mass flow:

1. Sucrose is actively transported into the sieve tube by companion cells,

2. sucrose in phloem creates a water potential difference, so water from xylem moves into the phloem by osmosis

3. Pressure increases, forming pressure difference between source and sink, causing sucrose to move to sink

4. At sink the sucrose is converted to glucose for respiration to release energy

Ringing (cutting part of stem), Tracing (radioactive carbon-13) experiments