BIOLOGY 2

• Photosynthesis


  The process by which plants use energy from sunlight to convert carbon dioxide and water into glucose and oxygen
• Plants are Able to Make Their Own Food by Photosynthesis
• Photosynthesis


  1. Photosynthetic organisms, such as green plants and algae, use energy from the Sun to make glucose

  2. Some of the glucose is used to make larger, complex molecules that the plants or algae need to grow

  3. The energy stored in the organisms' biomass then works its way through the food chain as animals eat them and each other

  4. Photosynthesis happens inside chloroplasts-they contain chlorophyll which absorbs light
• Photosynthesis equation


  carbon dioxide + water -> glucose + oxygen
• Photosynthesis is an endothermic reaction-energy is taken in during the reaction
• Factors affecting rate of photosynthesis

  • Light intensity
  • Concentration of CO2
  • Temperature
• Any of the three factors (light, CO2, temperature) can become the limiting factor, meaning it's stopping photosynthesis from happening any faster
• Investigating effect of light intensity on rate of photosynthesis

  1. Set up apparatus with Canadian pondweed and gas syringe

  2. Place light source at specific distance from pondweed

  3. Measure volume of oxygen produced over time

  4. Repeat with light source at different distances

  5. Control variables like temperature and CO2 concentration
• Light intensity increases


  Rate of photosynthesis increases (up to a point)
• CO2 concentration increases


  Rate of photosynthesis increases (up to a point)
• Temperature increases


  Rate of photosynthesis increases (up to a point)
• Temperature gets too high (around 45°C)


  Enzymes needed for photosynthesis become denatured, decreasing rate
• Transpiration


  The loss of water from a plant, mainly through the leaves
• Transpiration stream


  Water enters through the roots, moves up through the xylem vessels, and evaporates from the leaves
• Stomata


  • Tiny pores on the leaf surface that allow gas exchange and transpiration
  • Surrounded by guard cells that control the size of the pore
• Environmental factors


  Affect the rate of transpiration (light intensity, temperature, air flow)
• Using a potometer to estimate transpiration rate

  1. Set up apparatus with plant cutting and air bubble

  2. Measure distance moved by air bubble over time to estimate transpiration rate

  3. Can investigate effect of light, temperature, air flow
• Hormones are chemical messengers sent in the blood
• Key endocrine glands


  • Pituitary gland
  • Ovaries
  • Testes
  • Thyroid gland
  • Adrenal glands
  • Pancreas
• Differences between hormones and neurones

  Hormones have slower action, act for longer, and act in a more general way, while neurones have very fast, short-lived, and precise effects
• Hormones


  Regulate body conditions
• Pituitary gland


  Sometimes called the 'master gland' because these hormones act on other glands, directing them to release hormones that bring about change
• Ovaries


  • Females only
  • Produce oestrogen, which is involved in the menstrual cycle
• Testes


  • Males only
  • Produce testosterone, which controls puberty and sperm production in males
• Thyroid gland


  • Produces thyroxine, which is involved in regulating functions like the rate of metabolism, heart rate and temperature
• Adrenal glands


  • Produce adrenaline, which is used to prepare the body for a 'fight or flight' response
• Pancreas


  • Produces insulin, which is used to regulate the blood glucose level
• Hormones


  Slower action, act for a long time, act in a more general way
• Adrenaline


  Hormone released by the adrenal glands that prepares the body for 'fight or flight'
• Adrenaline release


  1. Brain detects a stressful situation

  2. Sends nervous impulses to the adrenal glands

  3. Adrenal glands secrete adrenaline

  4. Gets the body ready for action
• Thyroxine


  Hormone released by the thyroid gland that plays an important role in regulating metabolic rate
• Thyroxine regulation


  1. Blood thyroxine level lower than normal

  2. Hypothalamus releases TRH

  3. Pituitary gland releases TSH

  4. Thyroid gland releases thyroxine

  5. Blood thyroxine level rises back to normal

  6. Blood thyroxine level higher than normal

  7. Release of TRH and TSH inhibited

  8. Blood thyroxine level falls
• Stages of the menstrual cycle

  • Menstruation
  • Uterus lining repair
  • Egg development and release
  • Uterus lining maintenance
• Menstrual cycle hormones


  • FSH (follicle-stimulating hormone)
  • Oestrogen
  • LH (luteinising hormone)
  • Progesterone
• Menstrual cycle hormone regulation

  1. FSH causes follicle maturation and oestrogen production

  2. Oestrogen stimulates LH surge

  3. LH surge causes ovulation

  4. Corpus luteum produces progesterone

  5. Progesterone maintains uterus lining
• If a fertilised egg implants, progesterone level stays high to maintain uterus lining during pregnancy
• Clomifene therapy


  Drug that causes more FSH and LH to be released, stimulating egg maturation and ovulation
• IVF


  Collecting eggs, fertilising them in a lab, and transferring embryos to the uterus
• Hormonal contraceptives


  Oestrogen and/or progesterone prevent ovulation and thicken cervical mucus
• Contraceptive methods


  • Hormonal (pill, patch, injection)
  • Barrier (condoms, diaphragms)