b2

• diffusion


  the net movement of molecules from a higher concentration to a lower concentration down their concentration gradient
• how does temperature affect diffusion?

  • as the temperature increases, the rate of diffusion increases
  • because the particles have more kinetic energy and move faster
• how does the concentration gradient affect diffusion?

  the greater the concentration gradient (the difference between the two areas), the faster the rate of diffusion
• how does surface area of the membrane affect diffusion?

  • if the surface area increases, the rate of diffusion increases
  • because there is more space for the particles to move through
• osmosis

  the net movement of water particles from a higher water potential to a lower water potential down their concentration gradient across a partially permeable membrane
• active transport


  the movement of molecules from a lower concentration to a higher concentration against their concentration gradient using energy
• describe mitotsis (including the cell cycle)

  1. the chromosomes are replicated
  2. the chromosomes line up in the middle
  3. the chromosomes are pulled apart
  4. membranes form around the chromosomes and the cytoplasm divides
  5. the two cells then continue growing
• cell differentiation


  where cells become specialised for a particular function
• how are sperm cells specialised for their function?

  • large tail for movement
  • acrosome (containing enzymes) to digest the egg membrane
  • lots of mitochrondria for energy
  • haploid nucleus
• how are nerve cells specialised to carry impluses?

  • they have long axon to transport the impulse long distances
  • contain extensions to connect to other nerve cells and contain neurotransmitters to transmit the impulse
• how are root hairs specialised to take up minerals?

  • they have lots of mitochondria to generate energy
  • they have a large surface area for faster diffusion
• what are stem cells?

  undifferentiated cells that can develop into various types of cells in the body
• where are animal stem cells found?

  • embryos
  • bone marrow
• what is the difference between adult and embryonic stem cells?

  embryonic stem cells can differentiate into any type of cell whereas adult stem cells can only differentiate into cell types from the tissue the stem cells are in
• where are plant stem cells found?


  meristematic tissue
• what are stem cells used for?

  • naturally used for growth and repair
  • can also be used for treatments in Parkinson's disease and burns
• why do large multicellular organisms need transport systems?

  they have a small surface area to volume ratio and so the rate of diffusion alone would not be fast enough to transport substances around
• give four examples of substances transported in organisms

  • oxygen - in for respiration
  • CO2 - out for respiration
  • dissolved food molecules from digestion
  • urea and waste products
• why do mammals need a double circulatory system?

  • double circulatory systems have blood at a higher pressure
  • allowing it to flow faster
  • and move substances quickly around the body
• describe the double circulatory system in mammals

  1. the heart pumps blood to the lungs
  2. the oxygenated blood returns to the heart
  3. and is then pumped around the body
• what is the difference in function between veins, arteries and capillaries?

  • veins carry blood towards the heart
  • arteries carry blood away from the heart
  • capillaries flow close to tissues for exchange
• structure of arteries

  • thick walls made of muscle and elastic tissue
  • a small lumen to transport blood under high pressure
• structure of capillaries

  • thin walls about one cell thick to allow for the easy exchange of substances at the tissues
• structure of veins

  • have less muscle and elastic tissue than arteries
  • have a larger lumen as the blood is at lower pressure
  • have valves to prevent backflow
• structure of lungs

  • trachea branches into two bronchi
  • bronchi branch into bronchioles
  • bronchioles end in alveoli which are lined with capillaries for exchange
• describe the blood flow through the right side of the heart

  • deoxygenated blood flows into the right atrium from the vena cava
  • this blood passes through the right AV valve into the right ventricle
  • the blood is then pumped out of the heart to the lungs through the right SL valve and into the pulmonary artery
• describe the blood flow through the left side of the heart

  • blood enters into the left atrium from the pulmonary vein
  • the blood is then pumped through the left AV valve and into the left ventricle
  • the blood is then pumped out through the left SL valve and into the aorta
• what is the name of the wall that separates the right and left sides of the heart?

  septum
• what is the name of the artery that supplies the heart tissue with blood?

  coronary artery
• what type of muscle is the heart made of?

  cardiac muscle
• why is the wall of the left ventricle thicker than the wall of the right ventricle?

  the left ventricle has to pump blood a further distance around the whole body so the blood needs to be under a higher pressure
• how is plasma adapted as a transport medium?

  plasma is the liquid part of the blood and most molecules transported in blood need to be dissolved in water
• give three adaptions of red blood cells to their function

  • have a biconcave shape which gives them a large surface area
  • have no nucleus so there is more space for haemoglobin
  • very flexible so they can fit through capillaries
• how are root hair cells adapted to their function?

  • long root hair extension to increase surface area for uptake
  • thin membranes to decrease diffusion distance
• what does the xylem transport?

  water and minerals
• three benefits of transpiration

  • stream of water cools the plant
  • water helps to support the plant by creating turgor pressure
  • constant water supply for photosynthesis
• how is xylem adapted to transport water?

  • waterproofed using a substance called lignin
  • xylem cells are dead and have no organelles so there is more space for water
• structure of leaf tissue

  A) waxy cuticle

  B) upper epidermis

  C) palisade mesophyll

  D) spongy mesophyll

  E) lower epidermis

  F) guard cells

  
• process of transpiration

  • water lost through the stomata
  • more water is drawn up to replace the lost water
• transpiration stream


  flow of water through a plant