Module 3

• Organsims need to exchange substances with their environment.
  • Cells need to take in substances - oxygen & glucose for aerobic respiration & other metabolic reactions.
  • Cells need to excrete waste products from these reaxtions - CO2 & urea.
  • In multicellular organsims cells are surrounded by tissue fluid - they get all the substances from it & secrete their waste products to it.
• Single-celled organisms: organisms can diffuse directly into/ out of the cell across the cell surface membrane.
  • Diffusion rate is quick - substances have to travel small distances.
• Multicellular organisms: diffusion across outer membrane is too slow
  • Some cells are deep within the body - big distance between them & the outer environment.
  • Larger animal has low surface area to volume ratio - difficult to exchange enough substances to supply a large volume of animal through a small outer surface.
  • Have a higher metabolic rate than single-cells organisms - use up oxygen & glucose faster.
  • Need specialised exchange surfaces.
• Surface area : volume ratio:
  • To exchange enough substances - exchange surface must be big enough compared to the volume.
  • Smaller animals have higher surface area to volume ratios.

Exchange surfaces have a large surface area:

Example: root hair cells

• Cells on plant roots grow into long hairs sticking out into the soil - covers branches of roots.
• Gives roots a large surface are - helps increase rate of absorption of water (osmosis) & mineral ions (active transport) from the soil.

Exchange surfaces are thin:

Example: alveoli

• Are the gas exchange surface in the lungs.
• Alveolus made from single layer of alveolar epithelium (thin flat cells).
• O2 diffuses out of the alveolar space into the blood.
• CO2 diffuses out of the blood into the alveolar space.
• Alveolar epithelium helps decrease the distance of diffusion of O2/CO2 - increasing rate of diffusion.

Exchange surfaces have a good blood supply and/or ventilation:

Example: alveoli

• Surrounded by large capillar network - each alveolus has its own blood supply.
• Blood constantly takes O2 away from alveoli & brings more CO2.
• Lungs are ventilated - air in each alveolus constantly replaced.
• Help maintain concentration gradients of O2/CO2.

Example: fish gills

• Gills - gas exchange surface in fish.
• O2 &CO2 exchanged between fish's blood & the surrounding water.
• Gills contain large network of capillaries - good supply of blood.
• Well-ventilated - fresh water constantly passes over them.
• Help maintain concentration gradient of O2 - increasing rate of O2 diffusing into the blood.

• Exchange Organs - lungs in mammals.
  • Air enters the body through the mouth or nose.
  • Air enters the trachea (windpipe).
  • Trachea splits into 2 bronchi - 1 bronchus leading to each lung.
  • Bronchi branch into smaller tubes - bronchioles.
  • Bronchioles end in small air sacs - alveoli where gases are exchanged.
  • Ribcage, intercostal muscles & diaphragm work together to move air in & out.
• Trachea:
  • Cartilage - large C shaped pieces. Smooth muscle. Elastic fibres. Goblet cells. Ciliated epithelium.
• Bronchi:
  • Cartilage - smaller pieces. Smooth muscle. Elastic fibres. Goblet cells. Ciliated epithelium.
• Larger bronchiole:
  
  • Smooth muscle. Elastic fibres. Goblet cells. Ciliated epithelium.
• Smaller bronchiole:Smallest bronchiole: Elastic fibres.
  • Smooth muscle. Elastic fibres. Ciliated epithelium.
• Alveoli: Elastic fibres.

• Goblet cells: lining the airways, secrete mucus.
  • Mucus - traps microorganisms & dust particles in the inhaled air preventing them from reaching the alveoli.
• Cilia: on the surface of cells lining the airways, beat the mucus.
  • Moves the mucus upwards away from alveoli, towards the throat where it's swallowed.
  • Preventts lung infections.
• Elastic fibres: in the walls of trachea, bronchi, bronchioles, alveoli - help the process of breathing out.
  • Breathing in - lungs inflate & the elastic fibres are stretched.
  • The fibres then recoil to help push the air out when exhailing.
• Smooth muscle: in walls of trachea, bronchi, bronchioles - allows their diameter to be controlled.
  • During exercise smooth muscle relaxes - making tubes wider.
  • Less resistance to airflow - air moves in/out the lungs more easily.
• Carilage rings: in walss of trachea & bronchi - provide support.
  • Stong but flexible - stops trachea & bronchi from collapsing when you breathe in & the pressure drops.

• Ventilation - movement of air in & out of the lungs.
  • Controlled by the movements of the diaphragm, internal/ external intercostal muscles & ribcage.
• Insspiration: breathing in - active process requiring energy.
  • External intercostal muscles contract (internal intercostal muscles relax).
  • Pulls the ribcage upwards & outwards.
  • Diaphragm muscles also contract - causes diaphragm to flatten increasing the volume of the thorax (space where the lungs are).
  • Lung pressure decreases (to below atmospheric pressure) as thorax volume increases.
  • Causes air to flow into the lungs.
• Expiration: breathing out
  • External intercostal muscles relax (internal intercostal muscles contract).
  • Causes ribs to move inwards & downwards.
  • Diaphragm muscles also relax - causing diaphram to become curved again.
  • Thorax volume decreases causing air pressure to increase (to above atmospheric pressure).
  • Air is forced out of the lungs.
  • Normal expiration is passive - doesn't require energy.
  • Expiration can be forced - internal intercostal muscles contract pulling ribcage down & in.

• Tidal volume - the volume of air breathed in & out.
• Vital capacity - the maximum volume of air that can be breathed out.
• Expiratory reserve volume - the maximum volume of air that can be expelled from the lungs after normal expiration.
• Inspiratory reserve volume - the maximum volume of air that can be breathed in after normal inspiration.
• Breathing rate - how many breaths are taken per minute.
• Oxygen consumption - the rate at which an organsims uses up oxygen.
• Spirometers: used to investigate breathing
• Has an oxygen-filled chamber with a movable lid.
• Person breathes through a tube connected to the oxygen chamber.
• The lid of the chamber moves up and down as person breathes in & out.
• Movements recorded with a pen attached to the lid - writes on a rotating drum creating a spirometer trace.
• Or spirometer can be hooked to a motion sensor producing electronic signals picked up by a data logger.
• Soda lime in theh tube absorbs CO2.
• Total volume of gas in the cahmber decreases over time - air breathed out is a mixture of O2 & CO2.
• CO2 gets absorbed by the soda lime - only O2 in the chamber which gets inhaled.
• Total volume decreases as O2 gets used up by respiration.

Insects use tracheae to exchange gases.

Tracheae (1=trachea) - microscopic air-filled pipes used for gas exchange.

• Air moves into the tracheae through spiracles (pores) on the insect's surface.
• O2 travels down the concentration gradient towards the cells.
• CO2 from cells move down its concentration gradient towards the spiracles - released into the atmosphere.
• Tracheae branch off into smaller tracheoles - have thin permeable walls (singel layer of cells) & go to individual cells.
• Contain fluid - oxygen dissolves in.
• Insect is active - respires more & concentration of sulutes in cells increases.
• Fluid in the tracheoles drawn into the respiring cells by osmosis - leaving tracheoles filled with O2 gas.
• O2 diffuses directly into the respiring cells - insect's circulatory system doesn't transport O2.
• Insects use rhythmic abdominal movements to change volume of their bodies & move air in/out of spiracles.
• Larger insects flying - use their wing movements to pump their thoraxes.

Fish use a counter-current system for gas exchange.

Lower concentration of O2 in water than in air.

• Water containing O2 enters the fish throught its mouth & passes out through the gills.
• Each gill made of lots of thin branches - gill filaments/ primary lamellae, giving it a big surface area for exchange of gases.
• Gill filaments covered in lots of gill plates/ secondary lamellae - increasing surface area even more.
• Each gills supported by a gill arch.
• Gill plates have blood capillaries & a thin surface layer of cells - speed up diffusion.
• Blood flows through the gill plates in one direction - water flows over in the opposite direction (counter-current sytem).
• Mainains a large concentraion gradient between water and blood.
• Concentration of O2 in water is always higher than that in the blood - maximum amount of O2 diffuses into the blood.

Ventilation of fish gills in bony fish:

The fish opens its mouth lowering the floor of the buccal cavity (space inside the mouth).

Volume of buccal cavity increases - decreasing the pressure inside the cavity.

Water gets sucked in to the cavity.

Fish closes its mouth raising the floor of the buccal cavity.

The volume inside the buccal cavity decreases - increasing the pressure.

Water is forced out of the cavity across the gill filaments.

Each gill covered by a bony flap - operculum - which protects the gill.

Increase in pressure forces the operculum on each side of the head to open - allowing water to leave the gills.

Multicellular organisms need transport systems.

Mammals - circulatory system uses blood to carry O2/ glucose/ hormones/ antibodies/ waste around the body.

• Single circulatory system - blood only passes through the heart once for each complete circuit of the body.
• Double circulatory system - blood passes through the heart twice for each complete circuit of the body.
• Fish: single circulatory system
  • The heart pumps blood to the gills (pick up O2) & then on through the rest of the body (to deliver O2) in a single circuit.
• Mammals: double circulatory system
  • Right side of the heart pumps blood to the lungs (to pick up O2).
  • From the lungs it travels to the left side of the heart which pumps it to the rest of the body.
  • When blood returns to the heart it enters the right side again.
  • Right & left sides are reversed in diagrams.
• Pulmonary system - sends blood to the lungs.
• Systemic system - sends blood to the rest of the body.
• Advantage - heart can give the blood an extra push between the lungs & the rest of the body.
  • Makes blood travel faster - O2 delivered to tissues more quickly.

All vertebrates (fish/mammals) have closed circulatory systems - blood enclosed inside blood vessels.

• Heart pumps blood into arteries - branch out into capillaries.
• Substances diffuse from blood in capillaries into body cells - blood stays inside blood vessles as it circulates.
• Veins take blood back to the heart.

Invertebrates (insects) have open circulatory systems - blood isn't enclosed in blood vessels all the time.

• Flows freely throug the body cavity.
• The heart is segmented.
• It contracts in a wave starting from the back - pumping blood into a single main artery.
• Artery opens up into the body cavity.
• Blood flows around the insect's organs.
• Starts making its way back into the heart segments through series of valves.
• Circulatory system supplies cells with nutrients/ transports hormones around the body.
• Doesn't supply cells with oxygen - done by system of tubes, tracheal system.

• Transport substances round the body.
• Arteries: carry blood from heart to rest of the body.
• Walls are thick/muscular & havae elastic tissue to strech/recoil as heart beats - help maintain high pressure.
• Inner lining (endothelium) folded allowing artery to expand - helps maintain high pressure.
• Carry oxygenated blood - pulmonary arteries carry deoxygenated blood to lungs.
• Arteries branch into arterioles: smaller than arteries.
• Layer of smooth muscle - allows arteriole to expand/contract, controlling amount of blood flowing to tissues.
• Arterioles branch into capillaries: smallest of blood vessels.
• Substances exchanged between cells & capillaries.
• Adapted for efficient diffusion - wall only one cell thick.
• Capillaries connect to venules: join together to form veins - very thin walls containing muscle cells.
• Veins: take blood back to the heart under low pressure.
• Wider lumen - little elastic & muscle tissue.
• Contain valves - prevent backflow of blood.
• Blood flow helped by contraction of surrounding body muscles.
• Carry deoxygentated blood (O2 used up by body cells) - pulmonary veins carry oxygenated blood to the heart from the lungs.

• Tissue fluid is formed from blood.
• Tissue fluid - fluid that surrounds cells in tissues.
• Made from substacnes that leave the blood plasma - water/ O2/ nutrients.
• Cells take in O2/nutrients from tissue fluid releasing metabolic wawste into it.
• Pressure filtration: substances move out of capillaries into tissue fluid.
  • Start of capillary bed (nearest the arteries) - hydrostatic pressure inside capillaries greater than hydrostatic pressure in tissue fluid.
  • Difference in pressure forces fluid out of capillaries into spaces around the cells forming tissue fluid.
  • As fluid leaves - hydrostatic pressure reduces in capillaries.
  • Hydrostatic pressure much lower at end of capillary bed (nearest to the venules).
  • Oncotic pressure - generated by plasma proteins present in capillaries lowering water potential.
  • End of capillary bed - water potential in capillaries lower than in the tissue fluid due to fluid loss from capillaries & high oncotic pressure.
  • Some water re-enters capillaries from tissue fluid at end of capillary bed by osmosis.

• Excess tissue fluid drains into the lymph vessels.
• Excesss tissue fluid gets returbed to the blood through the lymphatic system - drainage system made of lymph vessels.
• Lymph capillaries - smallest lymph vessels.
• Excess tissue fluid passes into lymph vessels - now called lymph.
• Valvess in lymph vessels prevent backflow of lymph.
• Lymph gradually moves towards main lymph vessels in the thorax (main chest cavity) - returns to blood near the heart.

• Red blood cells: Blood (too big to get through capillary walls into tissue fluid).
• White blood cells: Blood. Tissue fluid - very little. Lymph (mostly in lymph system - only enter tissue fluid when there's an infection).
• Platelets: Blood (Only present in tissue fluid if capillaries are damaged).
• Proteins: Blood. Tissue fluid - very few. Lymph - only antibodies. (Most too big to get through capillary walls).
• Water: Blood. Tissue fluid. Lymph. (Tissue fluid/ lymph have higher water potential than blood).
• Dissolved solutes: Blood. Tisisue fluid. Lymph. (Solutes can move freely betweenn the three).

Heart consists of 2 muscular pumps.

Right side pumps deoxygenated blood to the lungs.

Left side pumps oxygenated blood to the rest of the body.

Valves in the heart prevent blood flowing the wrong way.

Atrioventricular valves link the atria to the ventricles.

Semi-lunar valves link the ventricles to the pulmonary artery & aorta.

Valves open one way only.

Whether they're open/closed depends on the relative pressure of the heart chambers.

Higher pressure behind a valve - forced open.

Higher pressure in front of the valve - forced shut.