Organising animal and plant cells

• adaptations of red blood cell

  -biconcave - increased surface area to volume ratio for diffusion

  -haemoglobin - binds to oxygen

  -no nucleus - more space for haemoglobin
• Substances plasma transports around the body

  -waste carbon dioxide

  -urea formed in your liver from breakdown of excess proteins

  -small, soluble products of digestion pass into plasma from small intestine
• ways white blood cell protects against microorganisms

  phagocytes - engulfs and digests invading bacteria and viruses

  lymphocytes - forms antibodies against microorganisms

  form antitoxins against poisons made by microoorganisms
• white blood cell structure compared to red blood cell

  -bigger

  -have a nucleus

  -fewer of them
• structure and function of platelets

  -no nucleus

  -small fragments of cells

  -help blood clot at site of wound
• how do platelets work in blood clotting

  -converts fibrinogen into fibrin

  -produces network of lots of protein fibres that captures lots of red blood cells and more platelets to form a jelly-like clot that stops you bleeding out

  -clot dries and hardens to form a scab

  -scab protects new skin as it grows and stops bacteria entering the body through the wound
• functions of the blood

  -transport of blood cells

  -transport of dissolved gases

  -transport of food

  -transport of hormones

  -transport of waste products

  -defence against infection

  -preventing blood loss through clotting
• functions of blood plasma

  transports waste products to kidneys as urea,

  transports soluble products of digestion to cells,

  transports waste carbon dioxide to lungs,

  transports oxygen around body in red blood cells
• structure and function of arteries

  -small lumen, thick walls, thick layer of muscle and elastic fibres

  -carry oxygenated blood away from heart to organs of your body
• structure and function of veins

  -large lumen, thin walls, often have valves

  -carries deoxygenated blood to heart
• structure and function of capillaries

  -walls a cell thick, tiny vessel with narrow lumen

  -huge network of tiny vessels linking artery and veins

  -enables substances such as oxygen and glucose to diffuse easily out of blood and into your cells
• what is a double circulatory system

  -one transport system carries blood from heart to lungs and back again, allows oxygen and carbon dioxide to be exchanged with air in lungs

  -other transport system carries blood from heart to all other organs of the body and back again
• why is muscle wall of left ventricle thicker than the right

  -allows left ventricle to develop pressure needed to force the blood through the arterial system all over the body

  -right ventricle only has to send blood to the lungs (where high pressure would be damaging
• what is a stent

  metal mesh placed in artery and opened up by inflation of tiny balloon to hold narrowed blood vessel open so blood can flow freely
• advantages and disadvantages of stent

  Advantages: Stent: no anaesthetic required, relatively cheap, effective Bypass surgery: very effective against severe blockages Disadvantages: Stent: ineffective against severely blocked or narrowed arteries Bypass surgery: general anaesthetic required, expensive
• where is natural pacemaker found

  right atria
• how does an artificial pacemaker work

  electrical device implanted into chest producing regular electrical signals to stimulate heart to contract and beat, often inactive if heart beating normally and activated by change in heart rhythm may measure additional demands increase heart rate during exercise
• how can a leaky valve cause health issues

  Valves prevent backflow of blood in heart. Leaky valve can allow blood to flow backwards, which means full amount of blood does not leave heart and blood coming into heart chamber mixes with blood that hasn’t left, making heart less efficient.
• advantage and disadvantage of mechanical replacement heart valve

  advantage: lasts a long time disadvantage: lifetime medication required to prevent clotting
• disadvantage and advantage of biological replacement heart valve

  advantage: no medication

  needed disadvantage: limited lifespan (12–15 years)
• arguments for and against development of artificial heart

  Can be used to keep patient alive until suitable heart for transplant becomes available. Can be used in some cases to rest patient’s own heart and allow it to recover. May be used to replace the natural heart in the long term. Very expensive, not effective over long periods, could be overtaken by organs grown from stem cells.
• breathing in on the diaphragm

  increased volume means lower pressure in the chest, atmospheric air at higher pressure than chest, so air is drawn into the lungs
• breathing out on the diaphragm

  pressure in chest higher than outside so air is forced out of lungs

  -diaphragm moves up, volume of chest gets smaller
• how steep concentration gradient is maintained

  breathing in, oxygen moves into lung, so alveoli has more oxygen than red blood cell for steep diffusion concentration gradient

  -breathing out removes carbon dioxide from lungs so RBC has more carbon dioxide for steep concentration gradient for diffusion
• how does air move in and out of lungs

  Intercostal muscles between ribs and diaphragm contract and relax, changing chest volume and pressure and forcing air in or out
• adaptation of human gas exchange system

  ventilation and rich blood supply for steep concentration gradient, clusters of alveoli/spherical alveolus shape for large surface area,

  thin alveolus walls to minimise diffusion distances
• epidermal tissue


  covers surfaces and protects them by secreting a waxy substance that waterproofs surface of leaf

  
• how is palisade mesophyll adapted for photosynthesis

  contains lots of chloroplasts for photosynthesis
• spongy mesophyll

  some chloroplasts for photosynthesis

  big air spaces

  large surface area to make diffusion of gases easier
• how tissues in leaf are arranged to form effective organ for photosynthesis

  Tightly packed palisade mesophyll cells at top of leaf contain many chloroplasts for photosynthesis and are protected by epidermis. Spongy mesophyll cells also photosynthesise and have large air spaces and surface area to maximise gas exchange.

  Xylem supply water for photosynthesis,

  phloem transport food from photosynthesis around plant.

  Stomata can be opened or closed by guard cells to let gases in and out
• translocation

  movement of dissolved sugars from leaves to rest of plant
• where is xylem and phloem found

  xylem is found in vascular bundles, whereas phloem is outside
• why might it be a good idea to protect trunk of young trees

  -phloem found in trees in a ring just underneath bark and xylem found in roots, which may be vulnerable to animals

  -if ring of bark eaten, transport systems would be cut off
• transpiration

  -stomata is open, plant loses water vapour.

  -water vapour evaporates from cells lining the air spaces then passes out of leaf through stomata by diffusion

  -loss of water vapour is transpiration
• transpiration stream

  constant movement of water through xylem from roots to the leaves
• role of stomata

  Stomata open to allow air into the leaves to provide carbon dioxide for photosynthesis, and close to control loss of water.
• why are most stomata found on underside of leaves

  protects them from direct light and energy of the sun
• what may plants do when water loss is faster than the uptake of water

  -wilt, reduces surface area available for water loss by evaporation

  -stomata close, risks overheating and stops photosynthesis
• Factors that affect rate of transpiration:

  -temperature

  -humidity

  -air movement

  -light intensity
• parts of leaf that helps plant reduce water loss

  guard cell

  waxy cuticle