bio paper 2

• Photosynthesis is the method by which green plants make their own food
• Word equation for photosynthesis

  Carbon dioxide + water → glucose + oxygen
• Balanced equation for photosynthesis

  6CO2 + 6H2O → C6H12O6 + 6O2
• Limiting factors for photosynthesis


  • Carbon dioxide
  • Light intensity
  • Temperature
• In the morning (low temperature, low light)


  Low temperature and low light intensity limit the rate of photosynthesis
• At midday (high temperature, high light)


  Carbon dioxide levels are the most likely limiting factor for photosynthesis
• Uses of glucose produced in photosynthesis


  • Making fats and proteins
  • Storing as starch
  • Making cellulose for cell walls
• Xylem


  • Hollow structure to transport water
  • Cell walls made of lignin to provide strength
• Phloem


  • Transports sugars around the plant
  • Has sieve plates to allow easy movement of food
  • Coupled with companion cells that provide energy
• Palisade mesophyll cells


  • Contain lots of chloroplasts to carry out photosynthesis
  • Located at the top of the leaf to capture sunlight
• Root hair cells


  • Have a large surface area to absorb water and minerals
  • Have a large permanent vacuole to aid water movement
• Transpiration


  Evaporation of water from the leaf surface
• Factors affecting transpiration rate


  • Humidity
  • Wind
  • Sunlight
  • Temperature
• Potometer


  Device used to measure the rate of transpiration
• Potometer setup


  • Cut shoot underwater to prevent air locks
  • Use angled cut and Vaseline to seal joints
  • Use capillary tubing to magnify water uptake
• Xylem and phloem in root

  • Xylem in the centre, phloem surrounding it
• Xylem and phloem in stem


  • Phloem in the outer layer, xylem in the inner layer
• Leaf structure


  • Waxy cuticle to prevent water loss
  • Upper epidermis transparent to allow light entry
  • Palisade mesophyll packed with chloroplasts
  • Spongy mesophyll with air spaces for gas exchange
  • Lower epidermis with stomata to allow gas exchange
• Gas exchange in plants


  • Carbon dioxide diffuses into the leaf, oxygen diffuses out
  • At night, oxygen diffuses into the leaf as plants respire
• Adaptations of deciduous plants


  • Lose leaves in winter to conserve water
• Adaptations of conifers


  • Needle-shaped leaves to reduce water loss
  • Stomata hidden in pits to trap water vapour
• Adaptations of cacti


  • Leaves reduced to spines to reduce surface area
  • Stomata in pits to trap water vapour
• Needle-shaped leaves


  • Smaller surface area, catch the wind less, less likely to get blown over
• Stomata hidden in pits

  • Helps trap water vapour around the leaf, decreases transpiration
• Cactus-type plants


  • Leaves become spines to reduce water loss
  • Tiny hairs trap water vapour around the plant
  • Stomata in pits to increase humidity and decrease transpiration
  • Thick cuticle and stem stores water to prevent water loss
• Stimulus


  Change in the environment
• Phototropism


  Plant's response to light
• Geotropism


  Plant's response to gravity
• Phototropism in plant stems


  • Positive phototropism, grow towards the light
• Phototropism in plant roots


  • Negative phototropism, grow away from the light
• Geotropism in plant roots


  • Positive geotropic response, grow down in the direction of gravity
• Geotropism in plant stems


  • Negative geotropic response, grow away from gravity
• Auxins


  Plant hormones that regulate growth responses to stimuli like light and gravity
• How plant stems bend towards light


  1. Auxins concentrate on the side farthest from the light source

  2. This causes cell elongation on that side

  3. The plant stem bends towards the light
• Coleoptiles are cereal seedlings used to investigate tropisms
• Clinostat


  Device used to remove stimulus like gravity or light to study plant responses
• Adrenaline


  Fight or flight hormone released under stress
• Effects of adrenaline


  • Hairs stand on end to appear scarier
  • Pupils dilate to see more clearly
  • Heart rate increases to deliver blood faster
  • Breathing rate increases for more oxygen
  • Blood diverted from digestive system to active muscles
• Female reproductive system


  • Ovaries
  • Fallopian tubes
  • Uterus
  • Cervix
  • Vagina
• Menstrual cycle


  Cyclical process that happens every 28 days on average